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Accreted seamounts in North Tianshan, NW China: implications for the evolution of the Central Asian Orogenic Belt

Yang, Gaoxue, Li, Yongjun, Kerr, Andrew and Tong, Lili 2018. Accreted seamounts in North Tianshan, NW China: implications for the evolution of the Central Asian Orogenic Belt. Journal of Asian Earth Sciences 153 , pp. 223-237. 10.1016/j.jseaes.2017.05.010

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Abstract

The Carboniferous Bayingou ophiolitic mélange is exposed in North Tianshan accretionary complex in the southwestern part of the Central Asian Orogenic Belt (CAOB). The mélange is mainly composed of serpentinised ultramafic rocks (including harzburgite, lherzolite, pyroxenite, dunite and peridotite), pillowed and massive basalts, layered gabbros, radiolarian cherts, pelagic limestones, breccias and tuffs, and displays block-in-matrix structures. The blocks of ultramafic rocks, gabbros, basalts, cherts, and limestones are set in a matrix of serpentinised ultramafic rocks, massive basalts and tuffs. The basaltic rocks in the mélange show significant geochemical heterogeneity, and two compositional groups, one ocean island basalt-like, and the other mid-ocean ridge-like, can be distinguished on the basis of their isotopic compositions and immobile trace element contents (such as light rare earth element enrichment in the former, but depletion in the latter). The more-enriched basaltic rocks are interpreted as remnants/fragments of seamounts, derived from a deep mantle reservoir with low degrees (2–3%) of garnet lherzolite mantle melting. The depleted basalts most likely formed by melting of a shallower spinel lherzolite mantle source with ∼15% partial melting. It is probable that both groups owe their origin to melting of a mixture between plume and depleted MORB mantle. The results from this study, when integrated with previous work, indicate that the Junggar Ocean crust (comprising a significant number of seamounts) was likely to have been subducted southward beneath the Yili-Central Tianshan block in Late Devonian-Early Carboniferous. The seamounts were scraped-off and accreted along with the oceanic crust in an accretionary wedge to form the Bayingou ophiolitic mélange. We present a model for the tectonomagmatic evolution of this portion of the CAOB involving prolonged intra-oceanic subduction with seamount accretion.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Uncontrolled Keywords: geochemistry; tectonics; Bayingou ophiolitic mélange; seamount; CAOB
Publisher: Elsevier
ISSN: 1367-9120
Date of First Compliant Deposit: 7 July 2017
Date of Acceptance: 7 May 2017
Last Modified: 28 Apr 2018 13:54
URI: http://orca.cf.ac.uk/id/eprint/102199

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