EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia

Hai Zhou1,2, Guochun Zhao2,3, and Donghai Zhang2
Hai Zhou et al.
  • 1School of Earth Science and Resources, Chang’an University, Xi’an, 710054, China (
  • 2State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an, 710069, China
  • 3Department of Earth Sciences, University of Hong Kong, Hong Kong, China

Oceanic subduction and its last underthrusted part can both triggers arc-like magmatism. As the existence of multi-subduction zones in the Central Asian Orogenic Belt, controversy still surrounds on when and especially how the subduction of the (Paleo-Asian Ocean) PAO terminated. We present geochronological, geochemical, and Lu-Hf isotopic data for a suite of basalt-andesites, dacite-rhyolites and later trachyandesite-mugearitic dykes from the Khan-Bogd area in the Gobi Tianshan Zone (GTZ) of the southern Mongolia. U-Pb dating of zircons indicate the basalt-andesites and dacite-rhyolites were formed at ~334-338 Ma, and the dykes at ~300 Ma. These Early Carboniferous volcanic rocks display high U/Th, Ba/Th, low La/Sm and variable Zr/Nb ratios, implying the involvement of subduction fluids or sediment melt. They display arc geochemical features such as calc-alkaline and metaluminous nature and positive Ba and U and negative Nb, Ta and Ti anomalies. Moreover, their continental geochemical signals (e.g. positive Pb, K anomalies) and some old captured zircons implying a continental arc setting. Comparatively, the ~300 Ma dykes are characterized by high alkaline contents, which are common for coeval (~320-290 Ma) and widespread post-subductional granites there. Given a mainly crust-derived magma source for those granites, these dykes likely reflect a mantle disturbance due to: (1) their relative low SiO2 (51.71-55.85 wt. %) and high Mg# (40.3-67.3) values, and (2) positive zircon ƐHf(t) (most > 12). Considering a slab rollback model during the Carboniferous and Triassic, the mantle disturbance was possibly induced by the oceanic slab breakoff. Combined with previous work, this ~320-290 Ma slab breakoff-induced extension marks the closure of a wide secondary ocean (North Tianshan-Hegenshan ocean) north of the main ocean basin of the PAO. This research was financially supported by NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).

How to cite: Zhou, H., Zhao, G., and Zhang, D.: Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16411,, 2021.

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