2021 Vol. 12, No. 2

Research Paper
Geochemistry of core sediments from the southeastern Bay of Bengal: Inferences on weathering and early diagenetic changes
A. Prajith, Abhishek Tyagi, P. John Kurian
2021, 12(2): 495-504. doi: 10.1016/j.gsf.2020.08.011
A sediment core (ABP24/05), collected at a water depth of 3520 m from the southeastern Bay of Bengal was studied to determine the change in chemical weathering during the last glacial to deglacial periods and the factors of sedimentary environment which controlled earliest diagenetic changes in the sediment after its deposition. High ratios of K/Rb, Ti/Al and Zr/Rb during ~45 to ~18 cal kyr B.P. in the core sediments may be attributed to the stronger physical erosion and turbidity currents activity during this period. This might have brought a higher quantity of unaltered minerals to the study area. Low ratios of K/Rb, Zr/Rb, and Ti/Al and increase of SiO2/TiO2, Rb/Al and Cs/Al from ~18 cal kyr B.P. to present may be indicating an increase in the rate of chemical weathering during this period. The time of increased chemical weathering in the study area is consistent with deglaciation warming in the tropical Indian Ocean and strengthening of river runoff into the Andaman Sea. Climate change during the interglacial period by increased solar insolation thereby strengthened the summer monsoon which might have led to intensified chemical weathering in the source region since ~18 cal kyr B.P. The low organic carbon (OC), high Mn/Al, Fe/Al and the Mn-oxides minerals precipitation indicate prevailing of oxic conditions during ~11 cal kyr B.P. in the core sediments, which is contradictory to suboxic conditions developed in the deep ocean sediments in the western Bay of Bengal and the equatorial Indian Ocean. The low terrigenous influx and export of less OC to the bottom sediments might have created a favorable condition for the formation of Mn-oxides in the study area during Holocene.
Evaluation of deep learning algorithms for national scale landslide susceptibility mapping of Iran
Phuong Thao Thi Ngo, Mahdi Panahi, Khabat Khosravi, Omid Ghorbanzadeh, Narges Kariminejad, Artemi Cerda, Saro Lee
2021, 12(2): 505-519. doi: 10.1016/j.gsf.2020.06.013
The identification of landslide-prone areas is an essential step in landslide hazard assessment and mitigation of landslide-related losses. In this study, we applied two novel deep learning algorithms, the recurrent neural network (RNN) and convolutional neural network (CNN), for national-scale landslide susceptibility mapping of Iran. We prepared a dataset comprising 4069 historical landslide locations and 11 conditioning factors (altitude, slope degree, profile curvature, distance to river, aspect, plan curvature, distance to road, distance to fault, rainfall, geology and land-sue) to construct a geospatial database and divided the data into the training and the testing dataset. We then developed RNN and CNN algorithms to generate landslide susceptibility maps of Iran using the training dataset. We calculated the receiver operating characteristic (ROC) curve and used the area under the curve (AUC) for the quantitative evaluation of the landslide susceptibility maps using the testing dataset. Better performance in both the training and testing phases was provided by the RNN algorithm (AUC=0.88) than by the CNN algorithm (AUC=0.85). Finally, we calculated areas of susceptibility for each province and found that 6% and 14% of the land area of Iran is very highly and highly susceptible to future landslide events, respectively, with the highest susceptibility in Chaharmahal and Bakhtiari Province (33.8%). About 31% of cities of Iran are located in areas with high and very high landslide susceptibility. The results of the present study will be useful for the development of landslide hazard mitigation strategies.
Carbon cycle variability in tropical Atlantic across two Early Eocene hyperthermals
Shijun Jiang, Ying Cui, Yasu Wang
2021, 12(2): 521-530. doi: 10.1016/j.gsf.2020.07.014
Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth's ecosystem due to massive additions of isotopically light carbon to the ocean-atmosphere system. They serve as ancient analogs for understanding how the oceanic carbonate system and surface-ocean ecosystem would respond to ongoing and future climate change. Here, we present a continuous carbonate record across the Eocene Thermal Maximum 2 (ETM2 or H1, ca. 54.1 Ma) and H2 (ca. 54 Ma) events from an expanded section at Ocean Drilling Program Site 1258 in tropical Atlantic. The abundant calcareous nannofossils and moderate carbonate content throughout the studied interval suggest this record was deposited above the calcite compensation depth (CCD), but below the lysocline and under the influence of terrestrial dilution. An Earth system model cGENIE is used to simulate the carbon cycle dynamics across the ETM2 and H2 to offer insights on the mechanism of the rapid warming and subsequent recovery in climate and ecosystem. The model suggests moderate changes in ocean pH (0.1-0.2 unit) for the two scenarios, biogenic methane from a rechargeable methane capacitor and organic matter oxidation from thawing of the permafrost. These pH changes are consistent with a recent independent pH estimate across the ETM2 using boron isotopes. The carbon emission flux during the ETM2 is at least an order of magnitude smaller than that during the Paleocene-Eocene Thermal Maximum (PETM) (0.015-0.05 Pg C yr-1 vs. 0.3-1.7 Pg C yr-1). The comparable pre- and post-event carbonate contents suggest the lysocline did not over deepen following the ETM2 at this tropical Atlantic site, indicating spatial heterogeneity in the carbonate system due to strong dilution influence from terrestrial weathering and riverine discharge at Site 1258.
Paleozoic convergence processes in the southwestern Central Asian Orogenic Belt: Insights from U-Pb dating of detrital zircons from West Junggar, northwestern China
Pan Zhang, Guocan Wang, Tianyi Shen, Ali Polat, Chengyu Zhu
2021, 12(2): 531-548. doi: 10.1016/j.gsf.2020.07.015
The West Junggar orogen, located in the southwestern Central Asian Orogenic Belt (CAOB), preserves an abundant record of tectonic processes associated with the evolution of the Junggar Ocean. In this study, we use detrital zircon U-Pb age data from Ordovician to Carboniferous sandstones in the southern and central West Junggar domains, complemented by literature data, to better constrain the tectonic evolution of the southwestern CAOB. The Kekeshayi, Qiargaye, and Laba formations in the southern West Junggar domain were deposited during the Darriwilian-Sandbian, Katian-Aeronian, and Homerian-Emsian, respectively. Detrital zircon provenances of these formations display a marked shift from the southern West Junggar domain to the Paleo-Kazakhstan Continent (PKC). This suggests that the southern West Junggar intra-oceanic arc might have gradually accreted to the northern margin of the PKC prior to the Emsian, which has significantly contributed to the lateral growth of the PKC. The Carboniferous strata, Xibeikulasi, Baogutu, and Tailegula formations, in the central West Junggar domain represent a coherent sequence of volcaniclastic turbidites and were deposited in a progressively shrinking remnant oceanic basin during the Visean to Moscovian. They contain unimodal detrital zircon distributions and are derived from the local and coeval magmatic rocks in the central West Junggar domain. We propose that the final closure of the Junggar Ocean likely occurred in the end of the Late Carboniferous in response to regional amalgamation events in the southwestern CAOB, which marks the final assembly of the Kazakhstan Orocline. The central and southern West Junggar domains underwent individual evolution in the Paleozoic, and were recombined by the significant intra-continental reworking along the large-scale strike-slip faults.
Depositional age and tectonic environment of the Gouap banded iron formations from the Nyong group, SW Cameroon: Insights from isotopic, geochemical and geochronological studies of drillcore samples
Landry Soh Tamehe, Chongtao Wei, Sylvestre Ganno, Carlos Alberto Rosi ere, Jean Paul Nzenti, Chesther Gatse Ebotehouna, Guanwen Lu
2021, 12(2): 549-572. doi: 10.1016/j.gsf.2020.07.009
The discovery of the Gouap banded iron formations (BIFs)-hosted iron mineralization in the northwestern of the Nyong Group (Ntem Complex) in southwestern Cameroon provides unique insights into the geology of this region. In this contribution, we firstly report detailed study of geochemistry, isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond drillcores. The Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe2O3 + SiO2 contents and variable contents of CaO, MgO and SO3, consistent with the presence of amphibole, chlorite, epidote and pyrite, formed during amphibolite facies metamorphism and overprinted hydrothermal event. The amphibole-pyrite BIFs are typically enriched in trace and rare earth elements (REE) compared to the amphibole BIFs, suggesting the influence of detrital materials as well as secondary hydrothermal alteration. The Post Archean Australian Shale (PAAS)-normalized REE-Y profiles of the Gouap BIFs display positive La, Eu anomalies, weak negative Ce anomalies, indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.
We present here the first isotopic data of BIFs within the Ntem Complex. The δ30SiNBS28 values of the quartz from the Gouap BIFs vary from -1.5‰ to -0.3‰ and from -0.8‰ to -0.9‰ for the amphibole BIFs and amphibole-pyrite BIFs, respectively. The quartz has δ18OV-SMOW values of 6.8‰-9.5‰ (amphibole BIFs) and 9.2‰-10.6‰ (amphibole-pyrite BIFs). The magnetite from the Gouap BIFs shows δ18O values ranging from -3.5‰ to -1.8‰ and from -3‰ to -1.7‰ for the amphibole BIFs and amphibole-pyrite BIFs, respectively. Moreover, the pyrite grains in the amphibole-pyrite BIFs display δ34S values of 1.1‰-1.8‰. All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity. According to their geochemical and isotopic characteristics, we propose that the Gouap BIFs belong to the Superior type.
In situ U-Pb zircon dating of BIFs was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section. The Gouap BIFs were probably deposited at 2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the Cauê Formation of the Minas Supergroup, Brazil. The studied BIFs have experienced regional hydrothermal activity and metamorphism at 2089±8.3 Ma during the Eburnean-Transamazonian orogeny. These findings suggest a physical continuity between the protocratonic masses of both São Francisco and Congo continents in the Rhyacian Period.
Integration of zircon and apatite U-Pb geochronology and geochemical mapping of the Wude basalts (Emeishan large igneous province): A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP
Jia-Nan Fu, Franco Pirajno, Fan Yang, Espine Shivute, Yi-Zhan Sun, Ning Ai, Kun-Feng Qiu
2021, 12(2): 573-585. doi: 10.1016/j.gsf.2020.08.004
Radiogenic isotopic dating and Lu-Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) of the Wude basalt in Yunnan province from the Emeishan large igneous province (ELIP) yielded timing of formation and post-eruption tectonothermal event. Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP. A zircon U-Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP. Such zircons had εHf(t) values ranging from -7.3 to +2.2, identical to those of magmatic zircons from the intrusive rocks of the ELIP, suggesting that crust-mantle interaction occurred during magmatic emplacement, or crust-mantle mixing existed in the deep source region prior to deep melting. The apatite U-Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event, corresponding to the Indian-Eurasian plate collision. Negative Nb, Ta, Ti and P anomalies of the Emeishan basalt may reflect crustal contamination. The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin. Therefore, the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian-Eurasian plate collision during early Eocene.
Multistage mineralization in the Haoyaoerhudong gold deposit, Central Asian Orogenic Belt: Constraints from the sedimentary-diagenetic and hydrothermal sulfides and gold
Hai-Dong Zhang, Jian-Chao Liu, Mostafa Fayek
2021, 12(2): 587-604. doi: 10.1016/j.gsf.2020.08.003
The Central Asian Orogenic Belt, as one of world-class gold economic belts, preserves a number of giant, large black shale-hosted gold deposits, while it is still debated for origin of sulfides and gold mainly due to lack of identification for multiple stages of sulfides. The Haoyaoerhudong gold deposit is hosted in a sequence of Mesoproterozoic carbonaceous and pyritic slate, phyllite, and schist that form a tight syncline along the north margin of the North China Craton. Detailed petrography of the host rocks and mineralization have defined five stages of pyrites. The earliest form of pyrite (Py1) occurs as fine-grained dispersed pyrite in black carbonaceous slate and medium- to coarse-grained disseminated pyrite in pyrite-rich layers, contains relative low gold and high arsenic content, indicating a syn-sedimentary or diagenetic in origin. Stage Ⅱ pyrite (Py2) occurs with garnet and quartz inclusions and Py3 occurs as pyrite veins, contains higher gold and lower As content, and are interpreted to have formed from the dissolution-reprecipitation of Py1 during the peak metamorphism or post-peak metamorphism. Stage IV pyrite (Py4) from the pyrite-quartz veins crosscut the metamorphic garnet, contains the highest gold concentrations and other trace elements, and is considered to have formed post-peak metamorphism. Abundant native gold, electrum, and maldonite occur as inclusions within Py4 and monazite and in fractures that crosscut garnet. While, Py5 with typical remobilized feature is thought to be a product of melting of former pyrites (Py1 to Py4) triggered by the large-scale Hercynian magmatism. The sedimentary/diagenetic Py1 have δ34S values that range from +12.4‰ to +16.2‰. Later generations of sulfides, including Py2 to Py5, and Ccp2 to Ccp3, have δ34S values from +9.5‰ to +12.7‰. Monazite with maldonite inclusions from quartz-pyrite veins yielded an intercept age of 341.3±6.6 Ma, while coarse grained monazite associated biotite along fractures in the reefs yielded an intercept age of 254.6±8.2 Ma.
The paragenetic, textural, chemical, and isotopic data suggest three distinct gold producing episodes at Haoyaoerhudong gold deposit. Gold and arsenic were clearly initially concentrated in organic muds, and enriched along the structures of diagenetic arsenic-rich pyrite. Subsequently, accompanying metamorphism and deformation, gold was liberated from the dissolution of diagenetic pyrites to form the pyrite veins. Finally, accompanying transformation of pyrite into pyrrhotite, gold was released into the metamorphic fluids to become concentrated as native gold, electrum, and maldonite in pyrite-quart veins. Monazite with age of 341 Ma from quartz-pyrite veins suggests that the third major gold mineralizing event in Haoyaoerhudong occurred before the Hercynian magmatism, suggesting that the Haoyaoerhudong deposit is a typical orogenic gold deposit rather than intrusion-related deposit.
Gold and antimony metallogenic relations and ore-forming process of Qinglong Sb(Au) deposit in Youjiang basin, SW China: Sulfide trace elements and sulfur isotopes
Jun Chen, Zhi-Long Huang, Rui-Dong Yang, Li-Juan Du, Ming-Yang Liao
2021, 12(2): 605-623. doi: 10.1016/j.gsf.2020.08.010
In the northwestern margin of the Youjiang basin (NWYB) in SW China, many Carlin-like gold deposits are highly antimony (Sb)-rich, and many vein-type Sb deposits contain much Au. These deposits have similar ages, host rocks, ore-forming temperatures, ore-related alterations and ore mineral assemblages, but the Au and Sb metallogenic relations and their ore-forming process remain enigmatic. Here we investigate the large Qinglong Sb deposit in the NWYB, which has extensive sub-economic Au mineralization, and present a new metallogenic model based on in-situ trace elements (EPMA and LA-ICP-MS) and sulfur isotopes (NanoSIMS and fs-LA-MC-ICP-MS) of the ore sulfides. At Qinglong, economic Sb ores contain coarse-grained stibnite, jasperoid quartz and fluorite, whilst the sub-economic Au-Sb ores comprise dominantly veined quartz, arsenian pyrite and fine-grained stibnite. Three generations of ore-related pyrite (Py1, Py2 and Py3) and two generations of stibnite (Stb1 and Stb2) are identified based on their texture, chemistry, and sulfur isotopes. The pre-ore Py1 is characterized by the lower ore element (Au, As, Sb, Cu and Ag) contents (mostly below the LA-ICP-MS detection limit) and Co/Ni ratios (average 0.31) than the ore-stage pyrites (Py2 and Py3), implying a sedimentary/diagenetic origin. The Py2 and Py3 have elevated ore element abundance (maximum As=6500 ppm, Au=22 ppm, Sb=6300 ppm, Cu=951 ppm, Ag=77 ppm) and Co/Ni ratios (average 1.84), and have positive As vs. Au-Sb-Cu-Ag correlations. Early-ore Stb1 has lower As (0.12-0.30 wt.%) than late-ore Stb2 (0.91-1.20 wt.%). These features show that the progressive As enrichment in ore sulfides is accompanied by increasing Au, Sb, Cu and Ag with the hydrothermal evolution, thereby making As a good proxy for Au. As-rich, As-poor and As-free zones are identified via NanoSIMS mapping of the Au-bearing pyrite. The As-rich zones in the Qinglong Au-bearing pyrites (Py2 and Py3) and ore stibnites (Stb1 and Stb2) have narrow δSH2S ranges (-8.9‰ to +4.1‰, average -3.1‰) and -2.9‰ to +6.9‰, average + 1.3‰), respectively, indicating that the Au-rich and Sb-rich fluids may have had the same sulfur source. Published in-situ sulfur isotopic data of pyrite As-rich zones from other Carlin-like Au deposits (Shuiyindong, Taipingdong, Nayang, Getang and Lianhuashan) in the NWYB have similar ore-fluid δSH2S values (-4.5‰ to +6.7‰, average -0.6‰) to those of Qinglong. Therefore, we infer that the sulfur of both Au and Sb mineralization was derived from the same magmatic-related source (0±5‰) in the NWYB.
Moreover, the core of pyrites (Py1) has variable S isotope fractionation (-18.9‰ to +18.1‰, mostly +3‰ to +12‰), suggesting that the higher-34S H2S was produced by bacterial sulfate reduction (BSR). The hydrothermal pyrite (Py2 and Py3) δ34S values gradually decrease with increasing As concentrations, and ultimately, within the restricted range (-5‰ to +5‰) in As-rich zones. This variation implies that the As-rich pyrite was formed through ongoing interactions of the magmatic-hydrothermal fluid with pre-existing sedimentary pyrites, causing the progressive decreasing δ34S values with As content increase, Hence, the fluid/mineral interaction may have generated the observed variation in δ34S and As contents. Overall, comparing the Au and Sb deposits in the NWYB, we favor a magmatic-related source for the Au-Sb-As-rich fluids, but the Au- and Sb-ore fluids were likely evolved at separate stages in the ore-forming system.
Spatial landslide susceptibility assessment using machine learning techniques assisted by additional data created with generative adversarial networks
Husam A. H. Al-Najjar, Biswajeet Pradhan
2021, 12(2): 625-637. doi: 10.1016/j.gsf.2020.09.002
In recent years, landslide susceptibility mapping has substantially improved with advances in machine learning. However, there are still challenges remain in landslide mapping due to the availability of limited inventory data. In this paper, a novel method that improves the performance of machine learning techniques is presented. The proposed method creates synthetic inventory data using Generative Adversarial Networks (GANs) for improving the prediction of landslides. In this research, landslide inventory data of 156 landslide locations were identified in Cameron Highlands, Malaysia, taken from previous projects the authors worked on. Elevation, slope, aspect, plan curvature, profile curvature, total curvature, lithology, land use and land cover (LULC), distance to the road, distance to the river, stream power index (SPI), sediment transport index (STI), terrain roughness index (TRI), topographic wetness index (TWI) and vegetation density are geo-environmental factors considered in this study based on suggestions from previous works on Cameron Highlands. To show the capability of GANs in improving landslide prediction models, this study tests the proposed GAN model with benchmark models namely Artificial Neural Network (ANN), Support Vector Machine (SVM), Decision Trees (DT), Random Forest (RF) and Bagging ensemble models with ANN and SVM models. These models were validated using the area under the receiver operating characteristic curve (AUROC). The DT, RF, SVM, ANN and Bagging ensemble could achieve the AUROC values of (0.90, 0.94, 0.86, 0.69 and 0.82) for the training; and the AUROC of (0.76, 0.81, 0.85, 0.72 and 0.75) for the test, subsequently. When using additional samples, the same models achieved the AUROC values of (0.92, 0.94, 0.88, 0.75 and 0.84) for the training and (0.78, 0.82, 0.82, 0.78 and 0.80) for the test, respectively. Using the additional samples improved the test accuracy of all the models except SVM. As a result, in data-scarce environments, this research showed that utilizing GANs to generate supplementary samples is promising because it can improve the predictive capability of common landslide prediction models.
Landslide susceptibility mapping using machine learning algorithms and comparison of their performance at Abha Basin, Asir Region, Saudi Arabia
Ahmed Mohamed Youssef, Hamid Reza Pourghasemi
2021, 12(2): 639-655. doi: 10.1016/j.gsf.2020.05.010
The current study aimed at evaluating the capabilities of seven advanced machine learning techniques (MLTs), including, Support Vector Machine (SVM), Random Forest (RF), Multivariate Adaptive Regression Spline (MARS), Artificial Neural Network (ANN), Quadratic Discriminant Analysis (QDA), Linear Discriminant Analysis (LDA), and Naive Bayes (NB), for landslide susceptibility modeling and comparison of their performances. Coupling machine learning algorithms with spatial data types for landslide susceptibility mapping is a vitally important issue. This study was carried out using GIS and R open source software at Abha Basin, Asir Region, Saudi Arabia. First, a total of 243 landslide locations were identified at Abha Basin to prepare the landslide inventory map using different data sources. All the landslide areas were randomly separated into two groups with a ratio of 70% for training and 30% for validating purposes. Twelve landslide-variables were generated for landslide susceptibility modeling, which include altitude, lithology, distance to faults, normalized difference vegetation index (NDVI), landuse/landcover (LULC), distance to roads, slope angle, distance to streams, profile curvature, plan curvature, slope length (LS), and slope-aspect. The area under curve (AUC-ROC) approach has been applied to evaluate, validate, and compare the MLTs performance. The results indicated that AUC values for seven MLTs range from 89.0% for QDA to 95.1% for RF. Our findings showed that the RF (AUC=95.1%) and LDA (AUC=941.7%) have produced the best performances in comparison to other MLTs. The outcome of this study and the landslide susceptibility maps would be useful for environmental protection.
Constraining the links between the Himalayan belt and the Central Myanmar Basins during the Cenozoic: An integrated multi-proxy detrital geochronology and trace-element geochemistry study
F. Arboit, M. Min, D. Chew, A. Mitchell, K. Drost, E. Badenszki, J. S. Daly
2021, 12(2): 657-676. doi: 10.1016/j.gsf.2020.05.024
Geological and tectonic analysis of the Eastern Himalayan basins has given rise to a decade-long debate on the geodynamic evolution of the Burmese terrane and on the extent of reorganization of the main SE Asia drainage systems. However, the influence of the Himalayan belt on the Central Myanmar Basin (CMB) system remains poorly documented, although it is key to providing more accurate models for the evolution of the Himalayan-Burmese orogen. In this contribution, we present geochronological, isotopic and geochemical analysis from 2500 zircon, 1700 titanite, 700 rutile and 850 apatite detrital grains from fifteen Cenozoic siliciclastic samples and one Cretaceous igneous rock. The samples were collected within the fore- and back-arc basins of the Central Myanmar Basin domain (CMB) to constrain the provenance, maximum depositional ages, and depositional environments of the west Burma terrane. Nine key lithological units, the Sadwingyi, Ketpanda, Wabo Chaung, Gwegon, Minwun, Padaung, Okmintaung and Irrawaddy formations have detrital age spectra spanning from the Miocene to Paleoarchean. The entire data set has common age peaks at ca. 20, 40, 60, 90, 100 Ma, with about 80% of the U-Pb ages younger than ca. 140 Ma and only ca. 1% of the grains predating ca. 3.0 Ga.
Our results shed light on the current ambiguities on the transport pathways of Himalayan detritus in the CMB. They show that the fore-arc basin was open to the trench and fed by the unroofing of both the Wuntho Popa volcanic arc to the east and possibly from the Burmese basement and/or from Himalayan-derived Bengal Fan detritus to the west during the Eocene, from at least ca. 44 Ma to before ca. 39 Ma. We show that the west Burma Terrane was partitioned into pull-apart basins such as the Minwun Basin, which during the Oligocene recorded the first evidence of a new source contribution into the CMB at ca. 27 Ma. This new source is characterized by detritus highly compatible with the SE Asia basement rocks, which we suggest corresponds to the initiation of the palaeo-Irrawaddy River. This geodynamic evolution does not require any Yarlung Tsangpo-Irrawaddy-Brahmaputra paleodrainage reorganization, since from the Oligocene to the Early Miocene, the Irrawaddy River fed an internally drained basin, and from the Late Miocene onwards, the Yarlung drained into the Brahmaputra in the Bengal Basin.
Structural and tectonothermal evolution of the ultrahigh-temperature Bakhuis Granulite Belt, Guiana Shield, Surinam: Palaeoproterozoic to recent
Frank F. Beunk, Emond W. F. de Roever, Keewook Yi, Fraukje M. Brouwer
2021, 12(2): 677-692. doi: 10.1016/j.gsf.2020.05.021
We constrain the multistage tectonic evolution of the Palaeoproterozoic UHT metamorphic (P=0.9-1.0 GPa, T >1000 ℃, t=2088-2031 Ma) Bakhuis Granulite Belt (BGB) in Surinam on the Guiana Shield, using large- to small-scale structures, Al-in-hornblende thermobarometry and published fluid inclusion and zircon geochronological data. The BGB forms a narrow, NE-SW striking belt between two formerly connected, ~E-W oriented granite-greenstone belts, formed between converging Amazonian and West African continental masses prior to collision and Transamazonian orogeny. Inherited detrital zircon in BGB metasediments conforms agewise to Birimian zircon of West Africa and suggests derivation from the subsequently subducted African passive margin. Ultrahigh-temperature metamorphism may have followed slab break-off and asthenospheric heat advection. Peak metamorphic structures result from layer-parallel shearing and folding, reflecting initial transtensional exhumation of the subducted African margin after slab break-off. A second HT event involves intrusion, at ca. 0.49 GPa, of charnockites and metagabbros at 1993-1984 Ma and a layered anorthosite at 1980 Ma, after the BGB had already cooled to <400 ℃. The event is related to northward subduction under the greenstone belts, along a new active margin to their south. A pronounced syntaxial bend in the new margin points northward towards the BGB and is likely the result of indentation by an anticlinorial flexural bulge of the subducting plate. Tearing of the subducting oceanic plate along this bulge explains why the charnockites are restricted to the BGB. The BGB subsequently experienced doming under an extensional detachment exposed in its southwestern border zone. Exhumation was focused in the BGB as a result of the flexural bulge in the subducting plate and localised heating of the overriding plate by charnockite magmatism. The present, straight NE-SW long-side boundaries of the BGB are superimposed mylonite zones, overprinted by pseudotachylites, previously dated at ca. 1200 Ma and 950 Ma, respectively. The 1200 Ma mylonites reflect transpressional popping-up of the BGB, caused by EW-directed intraplate principal compressive stresses from Grenvillian collision preserved under the eastern Andes. Further exhumation of the BGB involved the 950 Ma pseudotachylite decorated faulting, and Phanerozoic faulting along reactivated Meso- and Neoproterozoic lineaments.
A unified model for the formation and distribution of both conventional and unconventional hydrocarbon reservoirs
Xiongqi Pang, Chengzao Jia, Junqing Chen, Maowen Li, Wenyang Wang, Qinhong Hu, Yingchun Guo, Zhangxin Chen, Junwen Peng, Keyu Liu, Keliu Wu
2021, 12(2): 695-711. doi: 10.1016/j.gsf.2020.06.009
The discovery and large-scale exploration of unconventional oil/gas resources since 1980s have been considered as the most important advancement in the history of petroleum geology; that has not only changed the balance of supply and demand in the global energy market, but also improved our understanding of the formation mechanisms and distribution characteristics of oil/gas reservoirs. However, what is the difference of conventional and unconventional resources and why they always related to each other in petroliferous basins is not clear. As the differences and correlations between unconventional and conventional resources are complex challenging issues and very critical for resources assessment and hydrocarbon exploration, this paper focused on studying the relationship of formations and distributions among different oil/gas reservoirs. Drilling results of 12,237 exploratory wells in 6 representative petroliferous basins of China and distribution characteristics for 52,926 oil/gas accumulations over the world were applied to clarify the formation conditions and genetic relations of different oil/gas reservoirs in a petroliferous basin, and then to establish a unified model to address the differences and correlations of conventional and unconventional reservoirs. In this model, conventional reservoirs formed in free hydrocarbon dynamic field with high porosity and permeability located above the boundary of hydrocarbon buoyancy-driven accumulation depth limit. Unconventional tight reservoirs formed in confined hydrocarbon dynamic field with low porosity and permeability located between hydrocarbon buoyancy-driven accumulation depth limit and hydrocarbon accumulation depth limit. Shale oil/gas reservoirs formed in the bound hydrocarbon dynamic field with low porosity and ultra-low permeability within the source rock layers. More than 75% of proved reserves around the world are discovered in the free hydrocarbon dynamic field, which is estimated to contain only 10% of originally generated hydrocarbons. Most of undiscovered resources distributed in the confined hydrocarbon dynamic field and the bound hydrocarbon dynamic field, which contains 90% of original generated hydrocarbons, implying a reasonable and promising area for future hydrocarbon explorations. The buried depths of hydrocarbon dynamic fields become shallow with the increase of heat flow, and the remaining oil/gas resources mainly exist in the deep area of “cold basin” with low geothermal gradient. Lithology changing in the hydrocarbon dynamic field causes local anomalies in the oil/gas dynamic mechanism, leading to the local formation of unconventional hydrocarbon reservoirs in the free hydrocarbon dynamic field or the occurrence of oil/gas enrichment sweet points with high porosity and permeability in the confined hydrocarbon dynamic field. The tectonic movements destroy the medium conditions and oil/gas components, which leads to the transformation of conventional oil/gas reservoirs formed in free hydrocarbon dynamic field to unconventional ones or unconventional ones formed in confined and bound hydrocarbon dynamic fields to conventional ones.
Inclusive Multiple Models (IMM) for predicting groundwater levels and treating heterogeneity
Rahman Khatibi, Ata Allah Nadiri
2021, 12(2): 713-724. doi: 10.1016/j.gsf.2020.07.011
An explicit model management framework is introduced for predictive Groundwater Levels (GWL), particularly suitable to Observation Wells (OWs) with sparse and possibly heterogeneous data. The framework implements Multiple Models (MM) under the architecture of organising them at levels, as follows: (i) Level 0: treat heterogeneity in the data, e.g. Self-Organised Mapping (SOM) to classify the OWs; and decide on model structure, e.g. formulate a grey box model to predict GWLs. (ii) Level 1: construct MMs, e.g. two Fuzzy Logic (FL) and one Neurofuzzy (NF) models. (iii) Level 2: formulate strategies to combine the MM at Level 1, for which the paper uses Artificial Neural Networks (Strategy 1) and simple averaging (Strategy 2). Whilst the above model management strategy is novel, a critical view is presented, according to which modelling practices are: Inclusive Multiple Modelling (IMM) practices contrasted with existing practices, branded by the paper as Exclusionary Multiple Modelling (EMM). Scientific thinking over IMMs is captured as a framework with four dimensions: Model Reuse (MR), Hierarchical Recursion (HR), Elastic Learning Environment (ELE) and Goal Orientation (GO) and these together make the acronym of RHEO. Therefore, IMM-RHEO is piloted in the aquifer of Tabriz Plain with sparse and possibly heterogeneous data. The results provide some evidence that (i) IMM at two levels improves on the accuracy of individual models; and (ii) model combinations in IMM practices bring ‘model-learning’ into fashion for learning with the goal to explain baseline conditions and impacts of subsequent management changes.
Diversified roles of mineral transformation in controlling hydrocarbon generation process, mechanism, and pattern
Jiazong Du, Jingong Cai, Tianzhu Lei, Yingli Li
2021, 12(2): 725-736. doi: 10.1016/j.gsf.2020.08.009
Organic matter (OM) is intimately associated with minerals in clay-rich mudstones, leading to widespread organic-mineral interaction during hydrocarbon generation in argillaceous source rocks. What we are concerned is the effects of the different mineral properties on hydrocarbon generation process and mechanism during mineral transformation. In this way, pyrolysis experiments with smectite-octadecanoic acid complexes (Sm-OA and Ex-Sm-OA) were conducted to analyze correlation of mineralogy and pyrolysis behaviors. Based on organic-mineral interaction, hydrocarbon generation process was divided into three phases. At 200-300 ℃, collapse of smectite led to desorption of OM, resulting in high yield of resin and slight increase in saturates. Subsequently, enhanced smectite illitization at 350-450 ℃ was accompanied with large amounts of saturates and a mere gaseous hydrocarbon. Featured by neoformed plagioclase, ankerite, and illite, 500 ℃ saw plenty of asphaltene and methane-rich gaseous hydrocarbons, revealing cracking reactions of OM. Noteworthy is that saturated and gaseous hydrocarbons in Ex-Sm-OA were considerably more than that in Sm-OA during second and third phases. Quantitative calculation of hydrogen revealed organic hydrogen provided by cross-linking of OM could not balance hydrogen consumed by cracking reactions, but supply of inorganic hydrogen ensured cracking could readily occur and consequently greatly promoted hydrocarbon generation. Further investigating characteristics of mineralogy and pyrolytic products, as well as effects of solid acidity on hydrocarbon generation, we concluded desorption of OM and decarboxylation promoted by Lewis acid were dominated at 200-300 ℃, resulting in low-degree hydrocarbon generation. While high yield of saturated and gaseous hydrocarbons in second and third phases, together with occurrence of ankerite, indicated predominance of decarboxylation and hydrogenation promoted by Lewis and Brønsted acid, respectively. Variations in organic-mineral interactions indicated (1) the controls of mineral transformation on hydrocarbon generation process and mechanism include desorption, decarboxylation, and hydrogenation reactions; (2) clay minerals acted as reactants evolving together with OM rather than catalysts. These findings are profoundly significant for understanding the hydrocarbon generation mechanisms, organic-inorganic interactions, and carbon cycle.
Unusual dinosaur trackway preservation as clues to paleo-landscape and behavior from the Lower Cretaceous Luohe Formation, Shaanxi Province, China
Lida Xing, Martin G. Lockley, Yongzhong Tang, Hendrik Klein, W. Scott Persons IV, Miaoyan Wang, Xingwen Li, Hao Wu
2021, 12(2): 737-745. doi: 10.1016/j.gsf.2020.09.014
Poorly preserved tracks have limited ichnotaxonomic or biotaxon utility, but may reveal useful information about the paleoenvironment, behavior and track taphonomy. Eight mostly parallel to sub parallel trackway segments (T1-T8) were registered on a truncation surface in the Lower Cretaceous Luohe Formation of Shaanxi Province. These attest to the passage of several bipeds, probably all theropods, in a paleo-contour-parallel, south-north direction in an arid setting. Quality of preservation in these trackways is poor, but notably superior in two additional trackways (T9-T10) on a foreset surface. Trackway T9 indicates a didactyl trackmaker, probably a deinonychosaurian, heading north to south. This is the 13th report of deinonychosaurian tracks from the Lower Cretaceous of China. If any or all the eight south-north oriented trackway segments represent continuations of other segments in the same trackways, the total number of individual trackmakers heading in this direction may have been as low as three. Although the trackway pattern and sedimentological evidence could indicate a physically controlled pathway influencing the direction taken by these trackmakers, the possibility that the trackways also represented small social or gregarious group cannot be ruled out.
Volcanic emissions and atmospheric pollution: A study of nanoparticles
Erika M. Trejos, Luis F. O. Silva, James C. Hower, Eriko M. M. Flores, Carlos Mario González, Jorge E. Pachón, Beatriz H. Aristizábal
2021, 12(2): 746-755. doi: 10.1016/j.gsf.2020.08.013
The influence of emissions of an active volcano on the composition of nanoparticles and ultrafine road dust was identified in an urban area of the Andes. Although many cities are close to active volcanoes, few studies have evaluated their influence in road dust composition. Air quality in urban areas is significantly affected by non-exhaust emissions (e.g. road dust, brake wear, tire wear), however, natural sources such as volcanoes also impact the chemical composition of the particles. In this study, elements from volcanic emissions such as Si > Al > Fe > Ca > K > Mg, and Sisingle bondAl with K were identified as complex hydrates. Similarly, As, Hg, Cd, Pb, As, H, Cd, Pb, V, and salammoniac were observed in nanoparticles and ultrafine material. Mineral composition was detected in the order of quartz > mullite > calcite > kaolinite > illite > goethite > magnetite > zircon > monazite, in addition to salammoniac, a tracer of volcanic sources. The foregoing analysis reflects the importance of carrying out more studies relating the influence of volcanic emissions in road dust in order to protect human health. The road dust load (RD10) ranged between 0.8 and 26.8 mg m-2 in the city.
A GIS tool for infinite slope stability analysis (GIS-TISSA)
Rüdiger Escobar-Wolf, Jonathon D. Sanders, C. L. Vishnu, Thomas Oommen, K. S. Sajinkumar
2021, 12(2): 756-768. doi: 10.1016/j.gsf.2020.09.008
Landslides are one of the most common and a destructive natural hazard in mountainous terrain and thus evaluating their potential locations and the conditions under which they may occur is crucial for their hazard assessment. Shallow landslide occurrence in soil and regolith covered slopes are often modeled using the infinite slope model, which characterizes the slope stability in terms of a factor of safety (FS) value. Different approaches have been followed to also assess and propagate uncertainty through such models. Haneberg (2004) introduced the use of the First Order Second Moment (FOSM) method to propagate input uncertainty through the infinite slope model, further developing the model and implementing it in the PISA-m software package (Haneberg, 2007). Here we present an ArcPy implementation of PISA-m algorithms, which can be run from ESRI ArcMap in an entirely consistent georeferenced framework, and which we call “GIS Tool for Infinite Slope Stability Analysis” (GIS-TISSA). Users can select between different input options, e.g., following a similar input style as for PISA-m, i.e., using an ASCⅡ.csv parameters input file, or providing each input parameter as a raster or constant value, through the program graphic user interface. Analysis outputs can include FS mean and standard deviation estimates, the probability of failure (FS < 1), and a reliability index (RI) calculation for FS. Following the same seismic analysis approach as in PISA-m, the Newmark acceleration can also be done, for which raster files of the mean, standard deviation, probability of exceedance, and RI are also generated. Verification of the code is done by replicating the results obtained with the PISA-m code for different input options, within a 10-5 relative error. Monte Carlo modeling is also applied to validate GIS-TISSA outputs, showing a good overall correspondence. A case study was performed for Kannur district, Kerala, India, where an extensive landslide database for the year 2018 was available. 81.19% of the actual landslides fell in zones identified by the model as unstable. GIS-TISSA provides a user-friendly interface, particularly for those users familiar with ESRI ArcMap, that is fully embedded in a GIS framework and which can then be used for further analysis without having to change software platforms and do data conversions. The ArcPy toolbox is provided as a.pyt file as an appendix as well as hosted at the weblink: https://pages.mtu.edu/~toommen/GeoHazard.html.
Reconstructing seafloor age distributions in lost ocean basins
Simon Williams, Nicky M. Wright, John Cannon, Nicolas Flament, R. Dietmar Müller
2021, 12(2): 769-780. doi: 10.1016/j.gsf.2020.06.004
Reconstructions of past seafloor age make it possible to quantify how plate tectonic forces, surface heat flow, ocean basin volume and global sea level have varied through geological time. However, past ocean basins that have now been subducted cannot be uniquely reconstructed, and a significant challenge is how to explore a wide range of possible reconstructions. Here, we investigate possible distributions of seafloor ages from the late Paleozoic to present using published full-plate reconstructions and a new, efficient seafloor age reconstruction workflow, all developed using the open-source software GPlates. We test alternative reconstruction models and examine the influence of assumed spreading rates within the Panthalassa Ocean on the reconstructed history of mean seafloor age, oceanic heat flow, and the contribution of ocean basin volume to global sea level. The reconstructions suggest variations in mean seafloor age of ~15 Myr during the late Paleozoic, similar to the amplitude of variations previously proposed for the Cretaceous to present. Our reconstructed oceanic age-area distributions are broadly compatible with a scenario in which the long-period fluctuations in global sea level since the late Paleozoic are largely driven by changes in mean seafloor age. Previous suggestions of a constant rate of seafloor production through time can be modelled using our workflow, but require that oceanic plates in the Paleozoic move slower than continents based on current reconstructions of continental motion, which is difficult to reconcile with geodynamic studies.
Hydrogeochemical characterization and quality assessment of groundwater using self-organizing maps in the Hangjinqi gasfield area, Ordos Basin, NW China
Chu Wu, Chen Fang, Xiong Wu, Ge Zhu, Yuzhe Zhang
2021, 12(2): 781-790. doi: 10.1016/j.gsf.2020.09.012
Water resources are scarce in arid or semiarid areas, which not only limits economic development, but also threatens the survival of mankind. The local communities around the Hangjinqi gasfield depend on groundwater sources for water supply. A clear understanding of the groundwater hydrogeochemical characteristics and the groundwater quality and its seasonal cycle is invaluable and indispensable for groundwater protection and management. In this study, self-organizing maps were used in combination with the quantization and topographic errors and K-means clustering method to investigate groundwater chemistry datasets. The Piper and Gibbs diagrams and saturation index were systematically applied to investigate the hydrogeochemical characteristics of groundwater from both rainy and dry seasons. Further, the entropy-weighted theory was used to characterize groundwater quality and assess its seasonal variability and suitability for drinking purposes. Our hydrochemical groundwater dataset, consisting of 10 parameters measured during both dry and rainy seasons, was classified into 6 clusters, and the Piper diagram revealed three hydrochemical facies: Cl-Na type (clusters 1, 2 and 3), mixed type (clusters 4 and 5), and HCO3-Ca type (cluster 6). The Gibbs diagram and saturation index suggested that weathering of rock-forming minerals were the primary process controlling groundwater chemical composition and validated the credibility and practicality of the clustering results. Two-thirds of 45 groundwater samples were categorized as excellent-or good-quality and were suitable as drinking water. Cluster changes within the same and different clusters from the dry season to the rainy season were detected in approximately 78% of the collected samples. The main factors affecting the groundwater quality were hydrogeochemical characteristics, and dry season groundwater quality was better than rainy season groundwater quality. Based on this work, such results can be used to investigate the seasonal variation of hydrogeochemical characteristics and assess water quality accurately in the others similar area.
Calculation of groundwater head distribution with a close barrier during excavation dewatering in confined aquifer
Hai-Min Lyu, Shui-Long Shen, Yong-Xia Wu, An-Nan Zhou
2021, 12(2): 791-803. doi: 10.1016/j.gsf.2020.08.002
When pumping is conducted in confined aquifer inside excavation pit (waterproof curtain), the direction of the groundwater seepage outside the excavation changes from horizontal to vertical owing to the existence of the curtain barrier. There is no analytical calculation method for the groundwater head distribution induced by dewatering inside excavation. This paper first analyses the mechanism of the blocking effects from a close barrier in confined aquifer. Then, a simple equation based on analytical solution is proposed to calculate groundwater heads inside and outside of the excavation pit with waterproof curtain (hereafter refer to close barrier) in a confined aquifer. The distribution of groundwater head is derived according to two conditions: (i) pumping with a constant water head, and (ii) pumping with a constant flow rate. The proposed calculation equation is verified by both numerical simulation and experimental results. The comparisons demonstrate that the proposed model can be applied in engineering practice of excavation.
Avalonia, get bent!-Paleomagnetism from SW Iberia confirms the Greater Cantabrian Orocline
Bruno Daniel Leite Mendes, Daniel Pastor-Gal an, Mark J. Dekkers, Wout Krijgsman
2021, 12(2): 805-825. doi: 10.1016/j.gsf.2020.07.013
The amalgamation of Pangea formed the contorted Variscan-Alleghanian orogen, suturing Gondwana and Laurussia during the Carboniferous. From all swirls of this orogen, a double curve in Iberia stands out, the coupled Cantabrian Orocline and Central Iberian curve. The Cantabrian Orocline formed at ca. 315-290 Ma subsequent to the Variscan orogeny. The formation mechanism of the Cantabrian Orocline is disputed, the most commonly proposed mechanisms include either (1) that south-westernmost Iberia would be an Avalonian (Laurussian) indenter or (2) that the stress field changed, buckling the orogen. In contrast, the geometry and kinematics of the Central Iberian curve are largely unknown. Whereas some authors defend both curvatures are genetically linked, others support they are distinct and formed at different times. Such uncertainty adds an extra layer of complexity to our understanding of the final stages of Pangea's amalgamation. To solve these issues, we study the late Carboniferous-early Permian vertical-axis rotations of SW Iberia with paleomagnetism. Our results show up to 70° counterclockwise vertical-axis rotations during late Carboniferous times, concurring with the anticipated kinematics if SW Iberia was part of the southern limb of the Cantabrian Orocline. Our results do not allow the necessary penecontemporaneous clockwise rotations in Central Iberia to support a concomitant formation of both Cantabrian and Central Iberian curvature. The coherent rotation of both Gondwanan and Avalonian pieces of SW Iberia discards the Laurussian indenter hypothesis as a formation mechanism of the Cantabrian Orocline and confirms the Greater Cantabrian Orocline hypothesis. The Greater Cantabrian Orocline likely formed as a consequence of a change in the stress field during the late Carboniferous and extended beyond the Rheic Ocean suture affecting the margins of both Laurussia and Gondwana.
Transformation of PGM in supra subduction zones: Geochemical and mineralogical constraints from the Veria (Greece) podiform chromitites
George Tsoupas, Maria Economou-Eliopoulos
2021, 12(2): 827-842. doi: 10.1016/j.gsf.2020.08.005
Extremely abundant PGE-minerals (PGM) hosted in chromitites from the Veria ophiolite complex in Macedonia (N. Greece) may be unique among ophiolite complexes. This study focuses on differences between the low- and high-PGE chromitites. New textural, mineralogical and geochemical constraints from those ores are presented, aiming to define factors controlling the PGE enrichment in a supra subduction environment, in the light of post-magmatic processes. The whole ore analyses for mmajor and trace elements indicated an unusually high-IPGE content (up to 25 ppm) and higher Fe, Ca, Mn, Zn and V contents in high-PGE compared to low-PGE in massive chromitites. The wide compositional variation of chromite, even in the same polished section, the occurrence of very fine PGM (less than 20 μm) as inclusions within chromite and extremely large (>1000 μm), angular or fine-grained PGM aggregates ones within a matrix of highly fragmented chromite-Cr-garnet matrix, may indicate crystallization/recrystallization of chromite from more than one precursor phases. Laurite (RuS2) is very limited, occurring as remnants surrounding by Ru-Os-Ir oxides/hydroxides, of a wide compositional variation. Irarsite occurs as euhedral crystals up to 200 μm, surrounding by chromite, as anhedral exsolutions 1-200 μm within laurite, or creating segregates with platarsite and relics of (Ru, Pt, Rh, Os) sulfarsenides. Platinum-Ru-Rh-Pd-minerals occur commonly as relatively fine-grained assemblages, up to 50 μm, along with irarsite and other relics of (Ru, Pt, Rh, Os) sulfarsenides. Pt-alloys show a variation ranging from tetraferroplatinum to Pt-Ir-Fe-Ni alloys. The presence of laurite relics in large IPGM, awaruite, heazlewoodite, and carbon-bearing material reflecting a super-reducing environment, and the transformation of primary PGM into Os-Ir-Ru-alloys and oxides/hydroxides in association with Fe-chromite and Fe3+-bearing garnet (andradite-uvarovite solid-solution series) may reflect changes of the redox conditions from reducing to oxidizing. The relatively high Na content in hydrous mineral inclusions within high-PGE chromitites suggest a hydrous mantle source and provide the possibility for estimation of the P (average 3.0 kbar) and T (average 874 ℃), indicating formation at a shallow mantle environment.
Maximum depositional age estimation revisited
Pieter Vermeesch
2021, 12(2): 843-850. doi: 10.1016/j.gsf.2020.08.008
In a recent review published in this journal, Coutts et al. (2019) compared nine different ways to estimate the maximum depositional age (MDA) of siliclastic rocks by means of detrital geochronology. Their results show that among these methods three are positively and six negatively biased. This paper investigates the cause of these biases and proposes a solution to it. A simple toy example shows that it is theoretically impossible for the reviewed methods to find the correct depositional age in even a best case scenario: the MDA estimates drift to ever smaller values with increasing sample size. The issue can be solved using a maximum likelihood model that was originally developed for fission track thermochronology by Galbraith and Laslett (1993). This approach parameterises the MDA estimation problem with a binary mixture of discrete and continuous distributions. The ‘Maximum Likelihood Age’ (MLA) algorithm converges to a unique MDA value, unlike the ad hoc methods reviewed by Coutts et al. (2019). It successfully recovers the depositional age for the toy example, and produces sensible results for realistic distributions. This is illustrated with an application to a published dataset of 13 sandstone samples that were analysed by both LA-ICPMS and CA-TIMS U-Pb geochronology. The ad hoc algorithms produce unrealistic MDA estimates that are systematically younger for the LA-ICPMS data than for the CA-TIMS data. The MLA algorithm does not suffer from this negative bias. The MLA method is a purely statistical approach to MDA estimation. Like the ad hoc methods, it does not readily accommodate geological complications such as post-depositional Pb-loss, or analytical issues causing erroneously young outliers. The best approach in such complex cases is to re-analyse the youngest grains using more accurate dating techniques. The results of the MLA method are best visualised on radial plots. Both the model and the plots have applications outside detrital geochronology, for example to determine volcanic eruption ages.
Pristine atmospheric condition over the Third Pole: An insight from levoglucosan records
Chao Xu, Chao You
2021, 12(2): 851-856. doi: 10.1016/j.gsf.2020.09.003
Expanding urbanization and agricultural intensification across neighboring South Asia and East Asia have substantially threatened atmospheric condition over the Third Pole (TP) during the past few decades. Whether the atmospheric condition over the TP is still as clean as a representative of the regional background draws great concern. In this work, great differences in levoglucosan concentration within/above the atmospheric boundary layer height are revealed. Levoglucosan results support the hypothesis that atmospheric pollutants in the mid-troposphere over the TP are mainly affected by long-range transport, although there are some local biomass burning emissions in residential areas. In addition, levoglucosan concentration in the mid-troposphere over the TP is at the same magnitude as marine and polar regions, but about 2-3 magnitudes lower than neighboring densely-populated Asian regions. With insights of levoglucosan records, this work therefore proves that the high-altitude TP still has largely pristine atmospheric conditions, and is one of the cleanest remote regions on the Earth.
GIS-based landslide susceptibility modeling: A comparison between fuzzy multi-criteria and machine learning algorithms
Sk Ajim Ali, Farhana Parvin, Jana Vojteková, Romulus Costache, Nguyen Thi Thuy Linh, Quoc Bao Pham, Matej Vojtek, Ljubomir Gigović, Ateeque Ahmad, Mohammad Ali Ghorbani
2021, 12(2): 857-876. doi: 10.1016/j.gsf.2020.09.004
Hazards and disasters have always negative impacts on the way of life. Landslide is an overwhelming natural as well as man-made disaster that causes loss of natural resources and human properties throughout the world. The present study aimed to assess and compare the prediction efficiency of different models in landslide susceptibility in the Kysuca river basin, Slovakia. In this regard, the fuzzy decision-making trial and evaluation laboratory combining with the analytic network process (FDEMATEL-ANP), Naïve Bayes (NB) classifier, and random forest (RF) classifier were considered. Initially, a landslide inventory map was produced with 2000 landslide and non-landslide points by randomly divided with a ratio of 70%:30% for training and testing, respectively. The geospatial database for assessing the landslide susceptibility was generated with the help of 16 landslide conditioning factors by allowing for topographical, hydrological, lithological, and land cover factors. The ReliefF method was considered for determining the significance of selected conditioning factors and inclusion in the model building. Consequently, the landslide susceptibility maps (LSMs) were generated using the FDEMATEL-ANP, Naïve Bayes (NB) classifier, and random forest (RF) classifier models. Finally, the area under curve (AUC) and different arithmetic evaluation were used for validating and comparing the results and models. The results revealed that random forest (RF) classifier is a promising and optimum model for landslide susceptibility in the study area with a very high value of area under curve (AUC=0.954), lower value of mean absolute error (MAE=0.1238) and root mean square error (RMSE=0.2555), and higher value of Kappa index (K=0.8435) and overall accuracy (OAC=92.2%).
Application of grouped detrital zircon analyses to determine provenance and closely approximate true depositional age: Early Cretaceous McMurray-Clearwater succession, Canada
L. Rinke-Hardekopf, S. E. Dashtgard, C. Huang, H. D. Gibson
2021, 12(2): 877-892. doi: 10.1016/j.gsf.2020.11.016
In the Lower Cretaceous McMurray-Clearwater succession of the intracontinental Alberta Foreland Basin, Canada, detrital zircon U-Pb geochronology samples (referred to herein as DZ samples) have been used to interpret the strata as representing a paleo-continental-scale drainage system. However, the majority of DZ samples are relatively small (n≈90-100), and syndepositional DZ (i.e., crystallization age <5 Ma older than depositional age) are rare. This has forced a reliance on dinocysts with long stratigraphic ranges to chronostratigraphically subdivide the McMurray-Clearwater succession rather than employing maximum depositional ages (MDAs) derived from DZ samples. Herein, 43 DZ samples (taken from 20 subsurface cores) are assigned to 1 of 5 stratigraphic intervals, and in each stratigraphic interval all associated DZ samples are combined to produce a grouped DZ sample. Analysis and comparison of individual and grouped DZ samples are used to (1) assess variability in provenance through time and space, and (2) assess the accuracy of chronostratigraphically subdividing the succession using MDAs.
Along the main paleo-drainage axis, a comparison of dissimilarity between DZ samples from the same stratigraphic interval, as well as between stratigraphic intervals, reveals increasing average dissimilarity between individual DZ samples and their respective grouped DZ sample with increasing spatial separation of samples. These data indicate that in the McMurray Depocenter some sediment is sourced from local tributaries, leading to geographical provenance variability.
Calculated MDAs for all 43 DZ samples and grouped MDAs (gMDAs) for the 5 grouped DZ samples are compared to an ash-derived absolute age and existing biostratigraphy. In the McMurray Formation, comparison of MDAs to gMDAs shows that in basins with rare syndepositional DZ, the gMDA method improved depositional age estimates by transforming low-confidence MDAs (e.g., youngest single grains) into high-confidence (multi-grain) gMDAs. In the Clearwater Formation where syndepositional DZ are plentiful (i.e., >5% of the total DZ population), calculating maximum likelihood ages from grouped DZ samples avoids negatively biased (i.e., too young) MDAs. We suggest grouped DZ samples and the gMDA method be used in systems with multiple DZ samples from a well-defined stratigraphic interval as a means of assessing variability in provenance within a depositional system and for improving estimates of depositional ages using DZ.
Special Issue: High Pressure Geochemistry
Dehydration melting of amphibolite at 1.5 GPa and 800-950 ℃: Implications for the Mesozoic potassium-rich adakite in the eastern North China Craton
Zhilin Ye, Fang Wan, Neng Jiang, Jingui Xu, Yuanyun Wen, Dawei Fan, Wenge Zhou
2021, 12(2): 896-906. doi: 10.1016/j.gsf.2020.03.008
Mesozoic intermediate-felsic magmatic rocks in the eastern North China Craton commonly show geochemical similarity to adakites. However, the lack of direct constraints from partial melting experiments at high pressures and temperatures fuels a debate over the origin of these rocks. In this work, we performed partial melting experiments at 1.5 GPa and 800-950 ℃ on amphibolite samples collected from the vicinity of the Mesozoic potassium-rich adakitic rocks in the Zhangjiakou area, northern margin of the North China Craton. The experimental melts range from granitic to granodioritic compositions, with SiO2=56.4-72.6 wt.%, Al2O3=16.1-19.3 wt.%, FeO*=2.4-9.6 wt.%, MgO=0.3-2.0 wt.%, CaO=0.6-3.8 wt.%, Na2O=4.7-5.3 wt.%, and K2O=2.6-3.9 wt.%, which are in the ranges of the surrounding Mesozoic potassium-rich adakitic rocks, except for the higher Al2O3 contents and the data point at 1.5 GPa and 800 ℃. Trace element compositions of the melts measured by LA-ICP-MS are rich in Sr (849-1067 ppm) and light rare earth elements (LREEs) and poor in Y (<10.4 ppm) and Yb (<0.88 ppm), and have high Sr/Y (102-221) and (La/Yb)n (27-41) ratios and strongly fractionated rare earth element (REE) patterns, whereas no obvious negative Eu anomalies are observed. The geochemical characteristics show overall similarity to the Mesozoic potassium-rich adakitic rocks in the area, especially adakites with low Mg#, again except for the data point at 1.5 GPa and 800 ℃. The results suggest that partial melting of amphibolite can produce potassium-rich adakitic rocks with low Mg# in the eastern North China Craton under the experimental conditions of 1.5 GPa and 850-950 ℃. The experimental restites consist of hornblende (Hbl) + plagioclase (Pl) + garnet (Grt)±clinopyroxene (Cpx), a mineral assemblage significantly different from that of the nearby Hannuoba mafic granulite xenoliths which consist of Cpx + orthopyroxene (Opx) + Pl±Grt. Chemically, the experimental restites contain higher Al2O3 but lower MgO and CaO than the Hannuoba mafic granulite xenoliths. We therefore argue that the Hannuoba mafic granulite xenoliths cannot represent the direct products of partial melting of the experimental amphibolite.
Reaction between basaltic melt and orthopyroxene at 3.0-4.5 GPa: Implications for the evolution of ocean island basalts in the mantle
Chunjuan Zang, Mingliang Wang, Hongfeng Tang, Hanqi He
2021, 12(2): 907-919. doi: 10.1016/j.gsf.2020.05.023
Interactions between basaltic melt and orthopyroxenite (Opx) were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts (OIBs) within the mantle. The experiments were conducted using a DS-3600 six-anvil apparatus at 3.0-4.5 GPa and 1300-1450 ℃. The basaltic melt and Opx coexisted at local equilibrium at these pressures and temperatures; the initial melts dissolved Opx, which modified their chemical composition, and clinopyroxene (Cpx) precipitated with or without garnet (Grt). The trace-element contents of Grt, Cpx, and melt were measured and the mineral-melt distribution coefficients (D) of Cpx-melt and Grt-melt were calculated, which can be used to assess the distribution of trace elements between basalt and minerals in the mantle. Two types of reaction rim were found in the experimental products, Cpx, and Cpx + Grt; this result indicates that residual rocks within the mantle should be pyroxenite or garnet pyroxenite. Both rock types are found in mantle xenoliths from Hawaii, and the rare-earth-element (REE) pattern of Cpx in these mantle pyroxenites matches those of Cpx in the experimental reaction rims. Furthermore, residual melts in the experimental products plot in similar positions to Hawaiian high-SiO2 OIBs on major-element Harker diagrams, and their trace-element patterns show the signature of residual Grt, particularly in runs at ≤1350 ℃ and 4.0-4.5 GPa. Trace-element concentrations of the experimental residual melts plot in similar positions to the Hawaiian OIBs on commonly used discrimination diagrams (Ti vs. Zr, Cr vs. Y, Cr vs. V, Zr/Y vs. Zr, and Ti/Y vs. Nb/Y). These results indicate that reaction between basaltic melt and pyroxenite might contribute to the generation of Hawaiian high-SiO2 OIBs and account for their chemical variability.
Thermoelasticity and stability of natural epidote at high pressure and high temperature: Implications for water transport during cold slab subduction
Bo Li, Jingui Xu, Dongzhou Zhang, Zhilin Ye, Shijie Huang, Dawei Fan, Wenge Zhou, Hongsen Xie
2021, 12(2): 921-928. doi: 10.1016/j.gsf.2020.05.022
Epidote is a typical hydrous mineral in subduction zones. Here, we report a synchrotron-based single-crystal X-ray diffraction (XRD) study of natural epidote [Ca1.97Al2.15Fe0.84(SiO4)(Si2O7)O(OH)] under simultaneously high pressure-temperature (high P-T) conditions to ~17.7 GPa and 700 K. No phase transition occurs over this P-T range. Using the third-order Birch-Murnaghan equation of state (EoS), we fitted the pressure-volume-temperature (P-V-T) data and obtained the zero-pressure bulk modulus K0=138(2) GPa, its pressure derivative K0'=3.0(3), the temperature derivative of the bulk modulus ((∂K/∂T)P=-0.004(1) GPa/K), and the thermal expansion coefficient at 300 K (α0=3.8(5) ×10-5 K-1), as the zero-pressure unit-cell volume V0 was fixed at 465.2(2) Å3 (obtained by a single-crystal XRD experiment at ambient conditions). This study reveals that the bulk moduli of epidote show nonlinear compositional dependence. By discussing the stabilization of epidote and comparing its density with those of other hydrous minerals, we find that epidote, as a significant water transporter in subduction zones, may maintain a metastable state to ~14 GPa along the coldest subducting slab geotherm and promote slab subduction into the upper mantle while favoring slab stagnation above the 410 km discontinuity. Furthermore, the water released from epidote near 410 km may potentially affect the properties of the 410 km seismic discontinuity.
Aluminum solubility in bridgmanite up to 3000 K at the top lower mantle
Zhaodong Liu, Ran Liu, Yucheng Shang, Fangren Shen, Luyao Chen, Xuyuan Hou, Mingguang Yao, Tian Cui, Bingbing Liu, Tomoo Katsura
2021, 12(2): 929-935. doi: 10.1016/j.gsf.2020.04.009
The temperature dependence of the Al2O3 solubility in bridgmanite has been determined in the system MgSiO3-Al2O3 at temperatures of 2750-3000 K under a constant pressure of 27 GPa using a multi-anvil apparatus. Bridgmanite becomes more aluminous with increasing temperatures. A LiNbO3-type phase with a pyrope composition (Mg3Al2Si3O12) forms at 2850 K, which is regarded as to be transformed from bridgmanite upon decompression. This phase contains 30 mol% Al2O3 at 3000 K. The MgSiO3 solubility in corundum also increases with temperatures, reaching 52 mol% at 3000 K. Molar volumes of the hypothetical Al2O3 bridgmanite and MgSiO3 corundum are constrained to be 25.95±0.05 and 26.24±0.06 cm3/mol, respectively, and interaction parameters of non-ideality for these two phases are 5.6±0.5 and 2.2±0.5 KJ/mol, respectively. The increases in Al2O3 and MgSiO3 contents, respectively, in bridgmanite and corundum are caused by a larger entropy of Al2O3 bridgmanite plus MgSiO3 corundum than that of MgSiO3 bridgmanite plus Al2O3 corundum with temperature, in addition to the configuration entropy. Our study may help explain dynamics of the top lower mantle and constrain pressure and temperature conditions of shocked meteorites.
The effect of iron on the sound velocities of δ-AlOOH up to 135 Gpa
Xiaowan Su, Chaoshuai Zhao, Chaojia Lv, Yukai Zhuang, Nilesh Salke, Liangxu Xu, Hu Tang, Huiyang Gou, Xiaohui Yu, Qiang Sun, Jin Liu
2021, 12(2): 937-946. doi: 10.1016/j.gsf.2020.08.012
δ-(Al,Fe)OOH is considered to be one of the most important hydrous phases on Earth, remaining stable under the extreme conditions throughout the mantle. The behavior of δ-(Al,Fe)OOH at high pressure is essential to understanding the deep water cycle. δ-(Al0.956Fe0.044)OOH crystals synthesized at 21 GPa and 1473 K were investigated by high-pressure Brillouin light scattering spectroscopy and synchrotron X-ray diffraction up to 135.4 GPa in diamond anvil cells. The incorporation of 5 mol% FeOOH increases the unit-cell volume of δ-AlOOH by ~1% and decreases the shear-wave velocity (VS) by ~5% at 20-135 GPa. In particular, the compressional (VP) and shear (VS) wave velocities of δ-(Al0.956Fe0.044)OOH are 7%-16% and 10%-24% greater than all the major minerals in the mantle transition zone including wadsleyite, ringwoodite, and majorite. The distinctly high sound velocities of δ-(Al0.956Fe0.044)OOH at 20-25 GPa may contribute to the seismic anomalies observed at ~560-680 km depths in the cold and stagnant slab beneath Izu-Bonin and/or Korea. Furthermore, the VS of δ-(Al0.956Fe0.044)OOH is about 10% and 4%-12% lower than iron-bearing bridgmanite Mg0.96Fe0.05Si0.99O3 and ferropericlase (Mg0.92Fe0.08)O, respectively, under the lowermost mantle conditions, which might partially contribute to the large low-shear-velocity provinces and ultralow velocity zones at the bottom of the lower mantle.
Thermal properties of harzburgite and dunite at 0.8-3 GPa and 300-823 K and implications for the thermal evolution of Tibet
Jianhua Ge, Baohua Zhang, Zili Xiong, Lanfang He, Heping Li
2021, 12(2): 947-956. doi: 10.1016/j.gsf.2020.01.008
Thermal diffusivity (D) and thermal conductivity (κ) of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus. The results show that the values of D and κ of both samples systematically decrease with increasing temperature and increase with increasing pressure. By combination of the thermal physical data of rocks and minerals and geophysical constraints, we performed numerical simulation on the thermal evolution of Tibet vary over depth, distance and geologic ages. The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.
Stability and band gap engineering of silica-confined lead halide perovskite nanocrystals under high pressure
Ruijing Fu, Yaping Chen, Lingrui Wang, Zhiwei Ma, Pengfei Lv, Ying Song, Songrui Yang, Guanjun Xiao, Bo Zou
2021, 12(2): 957-963. doi: 10.1016/j.gsf.2020.07.004
SiO2 is the major mineral substance in the upper mantle of the earth. Therefore, studies of the silica-coated materials under high-pressure are essential to explore the physical and chemical properties of the upper mantle. The silica-confined CsPbBr3 nanocrystals (NCs) have recently attracted much attention because of the improved photoluminescence (PL) quantum yield, owing to the protection of silica shell. However, it remains considerable interest to further explore the relationship between optical properties and the structure of CsPbBr3@SiO2 NCs. We systemically studied the structural and optical properties of the CsPbBr3@SiO2NCs under high pressure by using diamond anvil cell (DAC). The discontinuous changes of PL and absorption spectra occurred at ∼1.40 GPa. Synchrotron X-ray diffraction (XRD) studies of CsPbBr3@SiO2 NCs under high pressure indicated an isostructural phase transformation at about 1.36 GPa, owing to the pressure-induced tilting of the Pb-Br octahedra. The isothermal bulk moduli for two phases are estimated about 60.0 GPa and 19.2 GPa by fitting the equation of state. Besides, the transition pressure point of CsPbBr3@SiO2 NCs is slightly higher than that of pristine CsPbBr3 NCs, which attributed to the buffer effect of coating silica shell. The results indicate that silica shell is able to enhance the stabilization without changing the relationship between optical properties and structure of CsPbBr3 NCs. Our results were fascinated to model the rock metasomatism in the upper mantle and provided a new ‘lithoprobe’ for detecting the upper mantle.
High-pressure phase transformation of carbonate malachite Cu2(CO3)(OH)2 driven by [CuO6] regularization and [CO3] rotation
Jing Gao, Xueyin Yuan, Bin Chen, Zhenxian Liu, Wen Su
2021, 12(2): 965-973. doi: 10.1016/j.gsf.2020.07.006
High-pressure synchrotron X-ray diffraction and infrared absorption spectroscopy have been employed to study the crystal chemistry and phase transitions in an [OH]-bearing carbonate, malachite Cu2(CO3)(OH)2, to determine the effect of [OH] on the stability of carbonate. We found that the crystal structure of malachite is stabilized by a high degree of [CuO6]-octahedron distortion, as is manifested by large variations in Cu-O bond lengths resulting from oxygen atoms that connect to hydrogen at crystallographically different sites. External pressure offsets the effect of hydrogen bond, promotes [CuO6] compression and regularization and accordingly [CO3] rotation. Rotation of [CO3]-triangles, in turn, assists in a conversion in the crystal orientation of the [CuO6] structural unit. During compression to above ~6 GPa, malachite begins to turn into the rosasite lattice, accompanied with a jump in density of 3.3%. Rosasite is characterized with a hardened lattice and preserves to the maximum pressure (18.2 GPa) of the present study. Phase transformation mechanism of malachite to rosasite is different from that of carbonates, with the latter being driven by an almost uniform compression of [MO6]-octahedron (M=Ca, Cd, Mn, Fe, Zn, Mg, etc.) and rotation/translation of [CO3]-triangle under pressure.
Deep mantle hydrogen in the pyrite-type FeO2-FeO2H system
Qingyang Hu, Jin Liu
2021, 12(2): 975-981. doi: 10.1016/j.gsf.2020.04.006
The pyrite-type FeO2 and FeO2H were synthesized at the pressure-temperature conditions relevant to Earth's deep lower mantle. Through the water-iron reaction, the pyrite-phase is a good candidate to explain the chemical heterogeneities and seismological anomalies at the bottom of the mantle. The solid solution of pyrite-type FeO2 and FeO2H, namely the FeO2Hx (0 ≤ x ≤ 1), is particularly interesting and introduces puzzling chemical states for both the O and H atoms in the deep mantle. While the role of H in the FeO2-FeO2H system has been primarily investigated, discrepancies remain. In this work, we summarize recent progress on the pyrite-phase, including FeO2, FeO2H, and FeO2Hx, which is critical for understanding the water cycling, redox equilibria, and compositional heterogenicities in the deep lower mantle.
The effect of nitrogen on the compressibility and conductivity of iron at high pressure
Yukai Zhuang, Xiaowan Su, Nilesh P. Salke, Zhongxun Cui, Qingyang Hu, Dongzhou Zhang, Jin Liu
2021, 12(2): 983-989. doi: 10.1016/j.gsf.2020.04.012
Although nitrogen in the Earth's interior has attracted significant attention recently, it remains the most enigmatic of the light elements in the Earth's core. In this work, synchrotron X-ray diffraction (XRD) and electrical conductivity experiments were conducted on iron nitrides (Fe2N and Fe4N) in diamond anvil cells (DACs) up to about 70 GPa at ambient temperature. These results show that iron nitrides are stable up to at least 70 GPa. From the equation of state (EOS) parameters, iron nitrides are more compressible than iron carbides. Moreover, using the van der Pauw method and Wiedemann-Franz law, the electrical and thermal conductivity of samples were determined to be much lower than that of iron carbides. The conductivities of Fe2N and Fe4N were similar at 20-70 GPa, suggesting no evident effects by varying the N stoichiometries in iron nitrides. Iron nitrides are less dense and conductive but more compressible than carbides at 0-70 GPa. This study indicates that less nitrogen than carbon can explain geophysical phenomena in the deep Earth, such as the density deficit.
Adsorption behavior of CO2 in magnesite micro-pores at high temperature and pressure
Longxing Yang, Lei Liu, Hong Liu, Li Yi, Xiaoyu Gu, Haibo Liu, Hanyu Wang
2021, 12(2): 991-999. doi: 10.1016/j.gsf.2020.06.001
The fluid inclusions in mantle rocks and melt indicated that a large amount of CO2 fluid exists in the deep earth, which is of great significance for understanding the deep carbon cycle and the composition of mantle. However, it was also suggested that carbonate minerals were likely to be the main host of mantle carbon. At the same time, the distribution and behavior of carbon in the mantle still remain a puzzle. In this paper, the adsorption behavior and occurrence characteristics of supercritical CO2 in magnesite (MgCO3) pores were studied by the Grand Canonical Monte Carlo method (GCMC) under the different conditions of CO2 pressures (0-100 MPa), temperatures (350-1500 K) and the pore sizes (7.5-30 Å). The simulated results showed that the adsorption of CO2 in magnesite was a physical adsorption, which was mainly controlled by the intermolecular force. The gas adsorption became more stable when the adsorption site shifted from the high energy site to the low energy site with increasing pressure (P) and decreasing temperature (T) and pore size. At the same time, the variations of excess adsorption amounts of CO2 in the pores of magnesite (Nexcess) under the different conditions were quantitatively calculated. It was found that the Nexcess decreased with increasing T, but increased with increasing P and pore size. The results favor understanding the CO2 migration, seismic precursor observations, and heat transfer process in the deep earth.
A first-principles study of helium diffusion in quartz and coesite under high pressure up to 12GPa
Hong Liu, Lingling Wang, Shuchen Li, Yaochun Yang, Hua Tian, Fengxia Sun, Chaowen Xu, Lei Liu, Yi Li, Yueju Cui, Ying Li, Jijun Zhao
2021, 12(2): 1001-1009. doi: 10.1016/j.gsf.2020.09.009
Helium diffusion in mantle minerals is crucial for understanding mantle structure and the dynamic processes of Earth's degassing. In this paper, we report helium incorporation and the mechanism of its diffusion in perfect crystals of quartz and coesite. The diffusion pathways, activation energies (Ea), and frequency factors of helium under ambient and high pressure conditions were calculated using Density Functional Theory (DFT) and the climbing image nudged elastic band (CI-NEB) method. The calculated diffusive coefficients of He in the quartz in different orientations are:
D[100]=1.24×10-6 exp. (-26.83 kJ / mol / RT) m2 /s
D[010]=1.11×10-6 exp. (-31.60 kJ / mol / RT) m2 /s
and in the coesite:
D[100]=3.00×10-7 exp. (-33.79 kJ / mol / RT) m2 /s
D[001]=2.21×10-6 exp. (-18.33 kJ / mol / RT) m2 /s
The calculated results indicate that diffusivity of helium is anisotropic in both quartz and coesite and that the degree of anisotropy is much more pronounced in coesite.
Helium diffusion behavior in coesite under high pressures was investigated. The activation energies increased with pressure: Ea[100] increased from 33.79 kJ/mol to 58.36 kJ/mol, and Ea[001] increased from 18.33 kJ/mol to 48.87 kJ/mol as pressure increased from 0 GPa to 12 GPa. Our calculations showed that helium is not be quantitatively retained in silica at typical surface temperatures on Earth, which is consistent with the findings from previous studies. These results have implications for discussion of the Earth's mantle evolution and for recognition thermal histories of ultra-high pressure (UHP) metamorphic terranes.
Chemical transformations of n-hexane and cyclohexane under the upper mantle conditions
Xin Yan, Yapei L, Yajie Wan, Haiyan Zheng, Kuo L, Ho-kwang Ma
2021, 12(2): 1010-1017. doi: 10.1016/j.gsf.2020.06.006
Alkanes are an important part of petroleum, the stability of alkanes under extreme conditions is of great significance to explore the origin of petroleum and the carbon cycle in the deep Earth. Here, we performed Raman and infrared (IR) spectroscopy studies of n-hexane and cyclohexane under high pressure up to ~42 GPa at room temperature (RT) and high temperature (HT). n-Hexane and cyclohexane undergo several phase transitions at RT around 1.8, 8.5, 18 GPa and 1.1, 2.1, 4.6, 13, 30 GPa, respectively, without any chemical reaction. By using resistive heating combined with diamond anvil cell at pressure up to 20 GPa and temperature up to 1000 K, both n-hexane and cyclohexane decompose to hydrogenated graphitic carbon and n-hexane exhibits higher stability than cyclohexane. Our results indicate that hydrocarbons tend to dehydrogenate in the upper mantle, and the extension of carbon chains may lead to the formation of some unsaturated compounds and eventually transfer into graphitic products.
Raman and infrared spectroscopic quantification of the carbonate concentration in K2CO3 aqueous solutions with water as an internal standard
Yunlu Ma, Wei Yan, Qiang Sun, Xi Liu
2021, 12(2): 1018-1030. doi: 10.1016/j.gsf.2020.03.002
Carbonate-bearing fluids widely exist in different geological settings, and play important roles in transporting some elements such as the rare earth elements. They may be trapped as large or small fluid inclusions (with the size down to <1 μm sometimes), and record critical physical-chemical signals for the formations of their host minerals. Spectroscopic methods like Raman spectroscopy and infrared spectroscopy have been proposed as effective methods to quantify the carbonate concentrations of these fluid inclusions. Although they have some great technical advantages over the conventional microthermometry method, there are still some technical difficulties to overcome before they can be routinely used to solve relevant geological problems. The typical limitations include their interlaboratory difference and poor performance on micro fluid inclusions. This study prepared standard ion-distilled water and K2CO3 aqueous solutions at different molarities (from 0.5 to 5.5 mol/L), measured densities, collected Raman and infrared spectra, and explored correlations between the K2CO3 molarity and the spectroscopic features at ambient P-T conditions. The result confirms that the Raman O-H stretching mode can be used as an internal standard to determine the carbonate concentrations despite some significant differences among the correlations, established in different laboratories, between the relative Raman intensity of the C-O symmetric stretching mode and that of the O-H stretching mode. It further reveals that the interlaboratory difference can be readily removed by performing one high-quality calibration experiment, provided that later quantifying analyses are conducted using the same Raman spectrometer with the same analytical conditions. Our infrared absorption data were collected from thin fluid films (thickness less than ~2 μm) formed by pressing the prepared solutions in a Microcompression Cell with two diamond-Ⅱ plates. The data show that both the O-H stretching mode and the O-H bending mode can be used as internal standards to determine the carbonate concentrations. Since the IR signals of the C-O antisymmetric stretching vibration of the CO32- ion, and the O-H stretching and bending vibrations from our thin films are very strong, their relative IR absorbance intensity, if well calibrated, can be used to investigate the micron-sized carbonate-bearing aqueous fluid inclusions. This study establishes the first calibration of this kind, which may have some applications. Additionally, our spectroscopic data suggest that as the K2CO3 concentration increases the aqueous solution forms more large water molecule clusters via more intense hydrogen-bonding. This process may significantly alter the physical and chemical behavior of the fluids.
High-pressure investigations on the isostructural phase transition and metallization in realgar with diamond anvil cells
Linfei Yang, Lidong Dai, Heping Li, Haiying Hu, Meiling Hong, Xinyu Zhang, Pengfei Liu
2021, 12(2): 1031-1037. doi: 10.1016/j.gsf.2020.05.017
The high-pressure structural, vibrational and electrical properties for realgar were investigated by in-situ Raman scattering and electrical conductivity experiments combined with first-principle calculations up to ~30.8 GPa. It was verified that realgar underwent an isostructural phase transition at ~6.3 GPa and a metallization at a higher pressure of ~23.5 GPa. The isostructural phase transition was well evidenced by the obvious variations of Raman peaks, electrical conductivity, crystal parameters and the As-S bond length. The phase transition of metallization was in closely associated with the closure of bandgap rather than caused by the structural phase transition. And furthermore, the metallic realgar exhibited a relatively low compressibility with the unit cell volume V0=718.1.4 Å3 and bulk modulus B0=36.1 GPa.
Can HHe+ exist at high pressure: Exploration of high pressure induced HF-He compounds
Zifan Wang, Haixu Cui, Jingyu Hou, Xiao Dong
2021, 12(2): 1039-1043. doi: 10.1016/j.gsf.2020.03.010
HHe+ is considered as the strongest acid and most powerful proton donor known to human. Whether HHe+ exists at planetary high pressure environment is a quite important problem in physics, chemistry and planetary sciences. Here, using the ab initio evolutionary algorithm USPEX package, we searched HF-He system, which was reported as the most possible candidate to contain HHe+. The calculation proved HHe+ cannot form at pressure <1000 GPa, due to a conflict between the covalent component in symmetric hydrogen bond and ionic HHe+. Although He atoms have no chemical bonding with other elements, they can supply a chemical pressure, leading to two new phases He2(HF)4 and He(HF). With coplanar (HF)4 rings, He2(HF)4 have an aromaticity-like electronic behavior while He(HF) has a new type of chiral HF chain. The formation of He2(HF)4 and He(HF) prove that the chemical pressure from He, on par with external pressure, have ability to control the structural and electronic configuration and induce some new familiars of compounds include H and He elements which are fundamental planetary materials in giant planets.