Wetting of olivine by sulfide liquid: an example from the Central Asian Orogenic belt in NW China

Experimental studies have demonstrated that olivine can be wetted by sulfide liquid under specific conditions. In this study, we investigate elongated sulfide-olivine patches in lherzolite from the Dahuangshan mafic–ultramafic complex (Central Asian Orogenic Belt, NW China), which display textural evidence indicative of this phenomenon. Two-dimensional (2D) microbeam X-ray fluorescence (micro-XRF) mapping and three-dimensional (3D) high-resolution X-ray computed tomography (HRXCT) scanning reveal that the sulfide-olivine patches are 1.0‒4.8 cm long, 0.3‒2.3 cm wide and 0.2‒2.0 cm thick, and have sharp boundaries in the lherzolite matrix. These patches consist entirely of olivine (Fo_7–81.9) embedded within interstitial sulfides. The sulfides dominantly comprise pyrrhotite (>94 vol%), minor pentlandite (< 6 vol%) and trace chalcopyrite, and contain a total of 1.1‒1.9 wt.% (Ni + Cu + Co). Low olivine-olivine-sulfide dihedral angles (averaging 44.9°) indicate that olivine was wetted by the sulfide liquid in these patches. The crystal size distributions (CSDs) of the olivine grains in the sulfide-olivine patches are different from those of the olivine in the lherzolite matrix. These observations can be explained by the entrainment of pre-existing sulfide-olivine cumulates into flowing magma. The elongated shape and parallel distribution of the sulfide-olivine patches indicate that the magma flow was laminar. These findings support the hypothesis that sulfide liquid can wet olivine and under the right conditions can be transported and deposited as sulfide-olivine aggregates within magma conduits.