Exploring the potential of hydrothermal-fissure monazite geochronology for constraining retrograde orogenic evolution: Examples from Urals, Himalaya, Dinarides, and Araçuaí

Hydrothermal monazite from fissures and cleft mineralizations can provide temporal constraints on retrograde metamorphic and fluid-assisted processes that operate during the late stages of orogenic evolution, potentially extending beyond the effective closure of many conventional geochronometers. While fissure-hosted hydrothermal monazite dating has been extensively developed and calibrated in the European Alps, its broader applicability in other orogens with limited structural documentation, sparse sampling, and restricted exposure remains insufficiently tested. Here, we evaluate the method using four reconnaissance-scale case studies characterized by limited structural control, sparse sampling, and restricted exposure. The analyzed samples originate from four distinct orogens: the central Araçuaí orogen (Brazil), the central Subpolar Urals (Russia), the westernmost Lesser Himalaya (Pakistan), and the Inner Dinarides Mid-Bosnian Schist Mountains (Bosnia and Herzegovina). In the Araçuaí orogen, fissure monazite yields weighted mean ages of 460.0 ±6.9 Ma and 462.0 ±6.9 Ma, overlapping with or postdating late magmatic and metamorphic activity and consistent with prolonged regional cooling. Monazite ages from the Subpolar Urals span 245 ±7 Ma to 187 ±5 Ma and fall within the time frame of Triassic to Jurassic tectonic reorganization. In the western Lesser Himalaya, monazite crystallization ages averaging 31.90 ±0.48 Ma tentatively point to Cenozoic fluid-assisted processes affecting fissure formation. In the Mid-Bosnian Schist Mountains, monazite ages between 32.47 ±0.87 Ma and 24.55 ±1.30 Ma indicate sustained hydrothermal activity during exhumation of metamorphic units. Across all regions, hydrothermal fissure monazite yields geologically plausible age information that can be placed in a consistent temporal framework despite limited independent geochronological constraints. These results demonstrate that fissure-hosted hydrothermal monazite can provide meaningful timing constraints on late-stage fluid-assisted processes in diverse orogenic settings, even where structural context and sampling density are inherently restricted.