Continental crust melting induced by subduction initiation of the South Tianshan Ocean: Insight from the Latest Devonian granitic magmatism in the southern Yili Block, NW China. (March 2018)

• Record Type: Journal Article
• Authors: Bao, Zihe; Cai, Keda; Sun, Min; Xiao, Wenjiao; Wan, Bo; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping
• Is Part Of: Journal of Asian earth sciences. Volume 153(2018)
• Page Start: 100
• Page End: 117
• Publication Date: 2018-03
• Subjects: Yili Block -- CAOB -- South Tianshan Ocean -- Subduction initiation -- Kazakhstan orocline; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2017.04.026
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: The Wusun Mountain granitic intrusions were emplaced at 362–360 Ma. They are I-type granites and were likely generated by partial melting of continental crust mixing with mantle-derived magmas. Underplating of the mantle-derived magmas was in an extensional setting. The extensional setting may be associated with the subduction initiation of the South Tianshan Ocean. A late Paleozoic nascent arc- back-arc system was inferred in the southern margin of the Yili Block. Abstract: The Tianshan belt of the southwestern Central Asian Orogenic Belt was generated by Paleozoic multi-stage subduction and final closure of several extinct oceans, including the South Tianshan Ocean between the Kazakhstan-Yili and Tarim blocks. However, the subduction initiation and polarity of the South Tianshan Ocean remain issues of highly debated. This study presents new zircon U-Pb ages, geochemical compositions and Sr-Nd isotopes, as well as zircon Hf isotopic data of the Latest Devonian to Early Carboniferous granitic rocks in the Wusun Mountain of the Yili Paleozoic convergent margin, which, together with the spatial-temporal distributions of regional magmatic rocks, are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the South Tianshan Ocean. Our zircon U-Pb dating results reveal that these granites were emplaced at the time interval of 362.0 ± 1.2–360.3 ± 1.9 Ma, suggesting a marked partial melting event of the continental crust in the Latest Devonian to Early Carboniferous. These granites, based on their mineral compositions and textures, can be categorized as monzogranites and K-feldspar granites. Geochemically, both monzogranites and K-feldspar granites have characters of I-type granites with high K2 O contents (4.64–4.83 wt.%), and the K-feldspar granites are highly fractionated I-type granites, while the monzogranites have features of unfractionated I-type granites. Whole-rock Sr-Nd isotopic modeling results suggest that ca. 20–40% mantle-derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites. The mantle-derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting, which is evidenced by the high zircon saturation temperatures (713–727 °C and 760–782 °C) of the studied granites. The Latest Devonian to Early Carboniferous extensional setting in the Wusun Mountain region of the Yili Paleozoic convergent margin is addressed by the subduction initiation of the South Tianshan Ocean and constituted a late Paleozoic nascent arc- back-arc system in the southwestern CAOB.