Gao, Qiang, Yan, Mao-Qiang, Huizenga, Jan Marten, Lai, Lian-Xin, Li, Bin, Zeng, Hong-Hong, Moritz, Robert, and Wei, Jun-Hao (2024) Late Paleozoic slab rollback events in the southeastern part of the Central Asian orogenic belt: Implications for Paleo-Asian Ocean subduction and continental crust growth. Geological Society of America Bulletin. (In Press)

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Abstract

The Central Asian orogenic belt is considered to be the largest Phanerozoic accretive orogenic belt on Earth. The late Paleozoic magmatic rocks in central Inner Mongolia are crucial for understanding continental crust growth and the tectonic evolution of the southeastern part of the Central Asian orogenic belt. We present comprehensive geochemical, isotopic, and geochronological data from three late Paleozoic magmatic units in the Mandula area, west of the Solonker suture zone. Zircon U-Pb dating indicates that these rocks formed during the late Carboniferous (316–304 Ma). The Mandula high-Mg diorites exhibit high MgO (3.9–6.5 wt%), high Mg# (61–69), and depleted Nd-Hf isotopic compositions, generated through interaction between a metasomatized mantle and slab melts with the overlying sediments. The Mandula granodiorites display adakite geochemical characteristics with high Sr/Y mass ratios (29–52), high MgO (1.7–2.2 wt%), and high Mg# (52–54), formed by partial melting of the oceanic slab with the addition of overlying sediment. Mafic microgranular enclaves have consistent ages, Sr-Nd-Hf isotope compositions, and hornblende temperature-pressure conditions with their host granodiorite, formed from a cognate magma associated with the host granodiorites through cumulate. We propose that two phases of slab rollback took place during the late Paleozoic southward subduction-accretion of the Paleo-Asian Ocean. The first phase corresponded to the transformation of low to medium-angle slab subduction, while the second phase led to subduction-related extension. Considering the tectonic-magmatic evolution, crustal maturity, and thickness variations in the late Paleozoic southeastern part of the Central Asian orogenic belt, we propose that prolonged subduction and slab rollback promoted continental crust growth. The Central Asian orogenic belt coincides temporally and spatially with the Phanerozoic Pangea cycle, suggesting that continuous subduction and supercontinent amalgamation significantly contributed to continental crust growth.

Item ID:	83889
Item Type:	Article (Research - C1)
ISSN:	1943-2674
Copyright Information:	© 2024 Geological Society of America
Date Deposited:	28 Oct 2024 23:17
FoR Codes:	37 EARTH SCIENCES > 3703 Geochemistry > 370302 Inorganic geochemistry @ 50% 37 EARTH SCIENCES > 3705 Geology > 370511 Structural geology and tectonics @ 50%
SEO Codes:	28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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