Preservation of Re‐Os isotope signatures in pyrite throughout low‐T, high‐P eclogite facies metamorphism

Abstract

Pyrite in LT–HP eclogites from the western Tianshan orogenic belt yields a Re‐Os age of 378.1 ± 8.9 Ma, which is 30–70 Ma older than ages previously obtained for the same rocks using the Rb–Sr, Sm–Nd, Ar–Ar, U–Pb, and Lu–Hf isotope systems. The Tianshan LT–HP eclogite experienced temperatures of up to ~570 °C combined with pressures of up to 2.1 GPa during metamorphism. These conditions are below the transition of pyrite to pyrrhotite, which defines both pyrite stability and possibly its closure temperature for Re‐Os. Pyrite can preserve Re‐Os signatures through eclogite facies peak metamorphic conditions, and thus allow determination of the formation age of pyrite in the protolith.

Understanding Re–Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation

“…McCandless et al, 1993;Suzuki et al, 1993;Stein et al, 1998Stein et al, , 2001Selby et al, 2009;Ootes et al, 2010;van Acken et al, 2014) we recommend caution when interpreting Re-Os data from metamorphosed ultramafic rocks. As a result, neither whole-rock ultramafic samples nor single chromite grains provide a robust Re-Os record of age information in the Ujaragssuit nunât layered body, due to its complex metamorphic history.…”

“…Such work has been crucial in establishing the Re-Os evolution of the PUM and enabling the calculation of Re-Os model ages for more ancient samples. Numerous studies of crustal rocks have demonstrated that phases such as molybdenite (McCandless et al, 1993;Suzuki et al, 1993;Stein et al, 1998Stein et al, , 2001Ootes et al, 2010), bornite (Selby et al, 2009), chalcopyrite (Selby et al, 2009) and pyrite (Selby et al, 2009;van Acken et al, 2014), which have high Re/Os, can retain pristine Re-Os systematics despite experiencing metamorphic grades as intense as eclogite facies (van Acken et al, 2014). Zhao et al, 2001;Rollinson et al, 2002).…”

Contemporaneous east–west extension and north–south compression at 43 Ma in the Himalayan orogen

“…43.3 Ma (n = 9) could be taken as the Re-Os dating result for all the sulfide samples. The slightly large MSWD of our plotted data is possibly due to variation in the initial 187 Os/ 188 Os ratio or differential diffusion of Os between samples, however, the Re-Os age is nevertheless considered useful (Stein and Hannah, 2014;van Acken et al, 2014). In fact, Re-Os isochron ages with large MSWD (4-17) for pyrite, chalcopyrite and sphalerite have been previously reported (e.g.…”

“…It is difficult to directly obtain evidence of the exact timing of movement on a fault. In some sulfide minerals, the Re-Os isotopic system has a relatively high closure temperature, and remains stable during thermal metamorphism and deformation events; accordingly, it can be applied to place timing constraints on sulfide-bearing faults and ore deposits (Stein et al, 1998;van Acken et al, 2014)…”

U-Th-He Geochronology of Pyrite from the Uzelga VMS Deposit (South Urals)—New Perspectives for Direct Dating of the Ore-Forming Processes

“…Pyrite is relatively fast oxidized under atmospheric or aquatic conditions [76]. However, under anoxic conditions pyrite has been shown to remain robust for billions of years even through post-mineralization thermal and metamorphic disturbances [77][78][79].…”