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Consolidation and mantle evolution of the Sinokorean Craton in Early Precambrian time

University of British Columbia

The oldest nuclei of the Sinokorean Craton are the 3.5 Ga amphibolites and grey gneisses of the Qianxi Complex and the ≥3.0 Ga Qingyuan Complex that may extend to the Anshan area to include the ≥3.O Ga Tiejiashan and Lishan granites. Other highgrade metamorphic complexes of the Sinokorean Craton are mostly between 2.7 and 2.8 Ga in age - the Anshan, Longgang, Jianping, Taishan, Jiaodong, and Taihua complexes. The high-grade Fuping Complex formed about 2.6 Ga ago in an environment like a modern island arc: it is not one of the earliest nuclei. The medium— grade Wutai Complex formed by 2.5 Ga ago, mostly in a tectonic setting similar to that of Fuping Complex, with the exception that one volcanic cycle formed in an environment like a modern MOR and one unit formed in an environment transitional between modern within-plate and plate margin settings. There is no evidence for continental crust older than 2.6 Ga in the Wutaishan and Taihangshan regions. The Sm-Nd systems for metabasaltic rocks in the Wutaishan and Taihangshan region, are all significantly disturbed, in contrast with the undisturbed Sm-Nd system reported for rocks older than 2.6 Ga in the Sinokorean Craton. High-grade rocks of the Sanggan and Dengfeng complexes, and some granulites in the Qianxi Complex are ≥2.5 Ga in age. Available Nd isotopic data show that rocks older than 2.5 Ga in the Sinokorean Craton are derived from a mantle source more depleted than that defined by DePaolo’s depleted mantle evolution curve. Granitic magmatism peaked 2.5 Ga ago in the Sinokorean Craton, affecting all the previously formed rocks. Nd isotopic data show significant crustal involvement in formation of some ~2.5 Ga granites in the Sinokorean Craton. Early Proterozoic mafic volcanic rocks of the 2.3 to 2.4 Ga Kuandian Complex in Liaoning Province and the Hutuo Complex in Shanxi Province, formed in a intra—continental environment. Kuandian granites have an anorogenic granite character. The early Proterozoic mantle magma source in the eastern Liaoning Province is less depleted than the mantle of DePaolo’s (1981) average mantle evolution curve. This can be explained by contamination of Archean basement or derivation from a different mantle source.

Thesis/Dissertation

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2008-12-17

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http://hdl.handle.net/2429/3049

Geological Sciences

University of British Columbia

UBCV

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