Discovery of ∼4.0 Ga detrital zircons in the Aermantai ophiolitic mélange, East Junggar, northwest ChinaReport as inadecuate




Discovery of ∼4.0 Ga detrital zircons in the Aermantai ophiolitic mélange, East Junggar, northwest China - Download this document for free, or read online. Document in PDF available to download.

Chinese Science Bulletin

, Volume 58, Issue 30, pp 3645–3663

First Online: 06 May 2013Received: 16 November 2012Accepted: 22 March 2013DOI: 10.1007-s11434-013-5842-y

Cite this article as: Huang, G., Niu, G., Zhang, Z. et al. Chin. Sci. Bull. 2013 58: 3645. doi:10.1007-s11434-013-5842-y

Abstract

The East Junggar is an important part of the Central Asian Orogenic Belt CAOB. Using in situ zircon dating and Hf isotopic analysis by LA-ICP-MS and MC-ICP-MS, respectively, a detrital zircon of ∼4040 Ma age was found in sedimentary sequences from the Aermantai ophiolitic mélange, East Junggar. This is the oldest age record in the East Junggar terrane, and also marks the first zircon locality in the CAOB with an age older than 4.0 Ga, which is attributed to the Hadean crust. The ∼4040 Ma detrital zircon has an ɛHft value of −5.2 and a two-stage Hf modal age of 4474 Ma, suggesting the presence of very old Hadean crustal material in the source area. Beside peak ages of 446 Ma, we found four age groups of 3.6-3.1 Ga, 2.53–2.37 Ga, 1.14–0.89 Ga and 0.47–0.42 Ga from 141 effective measuring points. The age of 426±4 Ma for the five youngest detrital zircons defines the lower limit of the deposition time of sedimentary sequencess in the Aermantai ophiolitic mélange. The 0.47–0.42 Ga zircons exhibit Hf-Hf ratios of 0.282156 to 0.282850, corresponding to variable ɛHft values from −9.3 to 12.0 and Hf model ages from 2011 to 646 Ma. These characteristics are similar to those of the early Paleozoic igneous and gneissic zircons from the Altai, but significantly different from those of the East Junggar. Based on the material structures of felspathic greywacke, the morphology, internal texture and age distributions of dated detrital zircons, in combination with a study of the regional geological data, it is suggested that the sedimentary sequences in the Aermantai ophiolitic mélange was deposited in the Late Silurian, with the main provenance from the Altai Orogen in the north. This indicates that the early Paleozoic ocean represented by the Aermantai ophiolitic mélange was readily closed during the Late Silurian, and the northern edge of the East Junggar terrane was accreted to the Altai Orogen. The joint of them then served as a marginal orogen in the southern edge of the Siberia Paleocontinent.

KeywordsEast Junggar Aermantai ophiolitic mélange Hadean detrital zircon zircon U-Pb dating Hf isotopes This article is published with open access at Springerlink.com

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Author: Gang Huang - GuangZhi Niu - ZhanWu Zhang - XinLu Wang - XueYi Xu - Jun Guo - Feng Yu

Source: https://link.springer.com/







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