A newly defined latest Carboniferous-Permian ridge subduction in the southern Altaids: Insights from adakitic, S-type, and I-type granitoids in the northern East Junggar (NW China)

ABSTRACT

Late Palaeozoic evolution of the Chinese Altai-East Junggar orogenic collage is vital for a better understanding of the accretionary evolution in the southern Altaids. This paper reports new geochronological, geochemical, and isotopic data for the magmatic rocks collected from the northern part of the Dulate arc. The ~304.6 Ma tonalite samples present typical adakitic features of high Sr (396–714 ppm), low Y (1.42–2.60 ppm), Yb (0.11–0.24 ppm), and high Sr/Y (177.25–440.23) ratios. Combining high Mg# (55.35–57.21) and depleted isotopic composition (ε_Hf(t): +9.89 to +13.37 and ε_Nd(t): +5.36 to +6.06), we suggest that they were derived from the partial melting of a subducted oceanic slab. The ~299.4 Ma monzogranite samples have high A/CNK values (1.08 to 1.25), CIPW normative corundum contents (1.28–3.25 wt.%), and positive ε_Hf(t) (+5.14 to +8.63) and ε_Nd(t) (+1.08) values, which are similar to S-type granite that may be generated by the melting of greywackes. The monzogranite (~286.9 Ma) and rhyolitic porphyry (~283.9 Ma) are high-K calc-alkaline and similar to the highly fractionated I-type granites with depleted isotopic features (ε_Hf(t): +11.68 to +14.99 and +0.75 to +7.18, ε_Nd(t): +5.91 and +6.18). The monzogranite and rhyolitic porphyry could have been derived from a depleted mantle source, but the rhyolitic porphyry probably suffered partial assimilation of the overlying crust materials. Combining regional rock associations of mafic-ultramafic complexes, adakitic rocks, high-Mg diorites, and A-type granites with close spatial-temporal relationship, we conclude that a mid-oceanic ridge of the Ob-Zaisan Ocean subducted southward beneath the Dulate arc during the latest Carboniferous to Permian. With the opening of the slab window, the upwelling asthenosphere provided high heat flux and triggered various magmatism in the upper plate. We propose that ridge subduction is one of the most effective mechanisms of continental growth in the southern Altaids.

KEYWORDS:

• East Junggar
• Ob-Zaisan Ocean
• adakitic rocks
• ridge subduction
• slab window

Acknowledgement

We are very grateful to Editor Robert J. Stern and two anonymous reviewers for the constructive revision advice about this paper. We thank Yichao Chen, Rubin Yan and Dzhovid Yogibekov for field work assistance. This work was jointly supported by the National Natural Science Foundation of China (41888101, 41822204), the Third Xinjiang Scientific Expedition Program (2022xjkk1301), the Science and Technology Major Project of Xinjiang Uygur Autonomous Region, China (2021A03001-1&4, 2022A03010-1), One Hundred Talent Program of the Chinese Academy of Sciences (E2250403), and Youth Innovation Promotion Association Chinese Academy of sciences (2022446). This is a contribution to IGCP 662.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2246072

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China (41888101, 41822204), the Third Xinjiang Scientific Expedition Program (2022×jkk1301), the Science and Technology Major Project of Xinjiang Uygur Autonomous Region, China (2021A03001-1&4, 2022A03010-1), One Hundred Talent Program of the Chinese Academy of Sciences (E2250403), and Youth Innovation Promotion Association Chinese Academy of sciences (2022446). This is a contribution to IGCP 662.