A novel model for silicon recycling in the lithosphere: Evidence from the Central Asian Orogenic Belt

Zhang, Chen and Jiang, Shu and Liu, Dong Dong and Chakrabarti, Ramananda and Zeng, Jian Hui and Santosh, M and Luo, Qun and Spencer, Christopher J and Ma, Chao and Liu, Luo Fu and Kong, Xiang Ye (2019) A novel model for silicon recycling in the lithosphere: Evidence from the Central Asian Orogenic Belt. In: GONDWANA RESEARCH, 76 . pp. 115-122.

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Abstract

Global-scale cycling of silicon through the biosphere, atmosphere, and hydrosphere has received much attention although, silicon cycling in the Earth's lithosphere remains poorly understood. As the products of internal heat and material exchange, igneous rocks preserve significant information of silicon migration through the lithosphere. Here we report silicon isotopic compositions of nine peraluminous granites from the Chinese Altai, which forms part of the Central Asian Orogenic Belt. These rocks are characterized by the heaviest delta Si-30 values (-0.13 +/- 0.03 parts per thousand to +0.78 +/- 0.05 parts per thousand) compared to global granites, with a linear variation in the silicon isotopic values against silica content, with high silica-rich granites displaying more depleted isotopic compositions. In conjunction with the whole rock weakly negative epsilon Nd(t) and uniform delta Mg-26 values, as well as high delta O-18 values, we suggest that the delta Si-30 values of these granites were mainly inherited from the magma source, rather than produced by magmatic fractionation. In addition, the wide range of initial Sr-87/ Sr-86 ratios and high Ba content of the samples suggest the role of aqueous fluids. The Chinese Altai is considered to have formed through accretion of volcanic arcs associated with subduction of the Paleo-Asian oceanic lithosphere. The magma derived through partial melting of metasomatic mantle scavenges the heavy Si-30 isotopes derived through fluids released from oceanic sediments and transfers to the upper crust where partial melting of crustal sedimentary rocks occur. Mixing of these two melts generated the peraluminous granites. Our study offers a novel insight into a potentially important mechanism of silicon cycling in the lithosphere.

Item Type:	Journal Article
Publication:	GONDWANA RESEARCH
Publisher:	ELSEVIER
Additional Information:	Copyright of this article belongs to ELSEVIER
Keywords:	Silicon isotopes: subduction tectonics; Oceanic lithosphere; Peraluminous granites; Central Asian Orogenic Belt
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	16 Dec 2019 05:56
Last Modified:	16 Dec 2019 05:56
URI:	http://eprints.iisc.ac.in/id/eprint/63916

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