Episodic Triassic magmatism in the western South Qinling Orogen, central China, and its implications

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    Abstract

    © 2014 John Wiley & Sons, Ltd. The Qinling Orogen is located between the North China and South China cratons. The Mianlue Suture is the key boundary between the orogen and the South China Craton marking where the South China Craton subducted northward beneath the North China Craton during the late Triassic. Another older suture, the Shangdan Suture, divides the orogen into the North Qinling and South Qinling terranes. Our new geochronological data on eight granite plutons in the South Qinling Terrane indicate that the major phase of the Zhongchuan Granite is 219.5±2.1Ma, Luchuba is 217.1±1.0Ma, Baijiazhuang is 215.9±3.0Ma, Jiaochangba is 213.9±1.7Ma, Lvjing is 214.5±2.1Ma, Xiba is 215.6±1.8Ma, Wenquan is 217.3±2.1Ma and Fengxian is 240.9±1.0Ma. Compiled results reveal widespread magmatism began in the northwestern part of the South Qinling Terrane at ~240-250Ma and episodically progressed to the southeast in the North Qinling Terrane. Magmatism was then widespread throughout the South Qinling Terrane during the Late Triassic. A new division of Triassic intrusions has been proposed across the Qinling Orogen based on critical geochemical and geochronological differences. First, the western part of the South Qinling Terrane, (western South Qinling suite), is significantly enriched in large ion lithophile elements, including Cs, Rb, U, Th and K, whereas the eastern part of the South Qinling Terrane, (eastern South Qinling suite), has moderate enrichment in these elements. Second, there is an obvious transition from calcium to potassium enrichment in the Late Triassic western-South-Qinling suite, whereas the Late Triassic eastern South Qinling suite appears to follow a curved trajectory starting from high Na through K to high Ca. Third, the Ba and Sr concentrations of the western South Qinling suite have marked troughs, whereas the eastern South Qinling suites have relative enrichment of the two elements. The source of the Triassic magma becomes increasingly juvenile towards the east-southeast in the Qinling Orogen. Geochemical and isotopic data indicate that there are differences in the granites across the Chengxian-Huixian-Fengxian Fault within the western South Qinling Orogen, which highlight the tectonic significance of this northeast-trending fault that is now recognized as a significant boundary within the orogen. The identification of such a large-scale structure should attract some exploration attention, since this fundamental lineation is likely to be associated with some large mineral systems.
    Original languageEnglish
    Pages (from-to)402-423
    JournalGeological Journal
    Volume49
    Issue number4-5
    Early online date2 Jun 2014
    DOIs
    Publication statusPublished - Jul 2014

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