4 years ago

Age and geochemistry of the intrusive rocks from the Shaquanzi-Hongyuan Pb–Zn mineral district: Implications for the Late Carboniferous tectonic setting and Pb–Zn mineralization in the Eastern Tianshan, NW China

The Central Tianshan Terrane (CTT) in the Eastern Tianshan (Xinjiang, NW China) is an important Pb–Zn metallogenic belt and played a pivotal role in crustal evolution and collisional tectonics of the southern Central Asian Orogenic Belt. The Shaquanzi gabbro and Hongyuan granodiorite are located in the northern margin of the CTT and associated with Pb–Zn mineralization. Zircon U–Pb dating yielded weighted mean ages of 307.2±1.5Ma and 301.2±1.5Ma for the Shaquanzi gabbro and the Hongyuan granodiorite, respectively. These rocks are medium-K calc-alkaline series and enriched in large ion lithophile elements (LILEs; e.g., K, Rb, Ba) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), displaying typical arc affinities. The Shaquanzi gabbro shows low Nb/Ta (11.0–14.2), a high Mg# range (56–59), positive zircon ε Hf(t) (+3.30+7.26) and whole rock ε Nd(t) (+0.70+1.38) values, and low I Sr ratios (0.704858–0.705137), which indicate that the protolith was probably derived from the sub-continental lithospheric mantle that had been metasomatized by subduction-related fluids. The Hongyuan granodiorite contains hornblende but lack of Al-rich minerals and has low I Sr ratios (0.704769–0.706211<0.707), suggesting an I-type origin. Moreover, the Hongyuan granodiorite has positive ε Hf(t) (+1.12+5.57) and ε Nd(t) (+0.38+1.86) values, with high Mg# (52), variable Nb/Ta ratios (12.6–12.9), low contents of Ni, Cr and Co and Pb isotopes (206Pb/204Pb=17.461–18.299, 207Pb/204Pb=15.541–15.581, 208Pb/204Pb=37.456–38.129), suggesting the Hongyuan granodiorite was generated by partial melting of juvenile crust sources mixed with some mantle-derived materials. Combined published works with our new geochronological, geological, geochemical and isotopic data, we propose that the CTT may have evolved from a continental arc to a syn-collisional setting during the period of ca. 307–301Ma. The continuing southward subduction of the Junggar oceanic slab beneath the CTT in the Late Carboniferous resulted in extensive arc-related volcanic rocks emplacement that had indirect links to the Pb–Zn mineralization (e.g., reworked/upgraded).

Publisher URL: www.sciencedirect.com/science

DOI: S0024493717303523

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