Reduced mineral assemblages of superficial origin in west-central Jordan

Mineral assemblages formed at low oxygen fugacity are commonly confined to the lithologies of extraterrestrial or deep Earth origin. The occurrences of reduced mineral phases in upper crustal rocks [formed under oxygen fugacity conditions below the iron-wüstite (IW) buffer] are rare. However, they are important for understanding the chemical drivers of natural redox processes. Here, we present detailed studies of reduced mineral assemblages, which were found in situ in superficial combustion metamorphic (CM) rocks of west-central Jordan and compare them to reduced mineral assemblages found in situ in the CM rocks of south-central Israel. The studied assemblages contain a suite of exotic phases more typical of meteorites: native iron, phosphides (schreibersite, Fe₃P; allabogdanite, Fe₂P; transjordanite, Ni₂P; murashkoite, FeP; halamishite, Ni₅P₄; zuktamrurite, FeP₂; polekhovskyite, MoNiP₂), and sulphides (daubréelite, FeCr₂S₄; oldhamite, CaS; troilite, FeS), part of which (native iron, allabogdanite, halamishite, polekhovskyite, daubréelite) have not previously been discovered in the CM rocks of west-central Jordan. The mineralogical diversity of terrestrial phosphides and the occurrence of Ni- / Mo-rich phases can be explained by (1) high P, Ni, and Mo content in the sedimentary protolith, (2) transformations of primary Fe₃P / Fe₂P, (3) extreme disequilibrium of the processes, and (4) crystal-chemical control of Ni- / Mo- speciation.