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Late Paleoproterozoic Collision between the Eastern and Western Blocks of the North China Craton

Author: WangJing
Tutor: WuYuanBao
School: China University of Geosciences
Course: Geochemistry
Keywords: North China Craton North China Orogen Zircon geochronology Zircon trace elements Paleoproterozoic Plate flattener
CLC: P542
Type: Master's thesis
Year: 2010
Downloads: 82
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Abstract


North China Orogen is a land - continent collision orogenic belt, east and west by the North China land mass formed in the Paleoproterozoic collision, and put together to form the North China Craton old basement along the North China Orogen. So far, however, the North East, West China block flattened era still did not get the precise limits. We therefore the vian areas in the northern section of the North China Orogen, select six representative rock samples zircon U-Pb age and zircon trace element analysis, including five samples of high-grade metamorphic rocks and a Wei crystal dykes sample. TTG gneiss samples and high-pressure mafic granulite samples of Zhongyuan magma zircon core analysis points given 207Pb/206Pb age of 2503 ± 17 and 1964 ± 38 Ma, representing the TTG gneiss and high-pressure The mafic granulite protolith age. The analysis points given two metasedimentary samples magma inherited zircon nuclear age of 2683 ± 22 to 1964 ± 13 Ma, indicating metasedimentary protolith substances except a small portion from the Archean continental crust of the North China Craton rock, mostly from North China Orogen. TTG gneiss samples and two metasedimentary rocks of metamorphic zircon samples HREE loss differentiation smaller chondrite-normalized diagrams presented from which the rare earth to the heavy rare earth REE patterns seen significant negative Eu anomalies that such zircon formed in symbiosis with garnet and feldspar granulite facies metamorphic stage. High pressure mafic granulite samples and the TTG gneiss pale body samples, the metamorphic zircon heavy rare earth content is relatively low, from earth to the heavy rare earth no obvious differentiation, indicating that these zircons formed at granulite facies conditions under, but their negative Eu anomaly is weak or no negative Eu anomalies, may be related to host rock protolith composition. Zircon Ti thermometer display all these metamorphic zircon formation temperature of between 702 to 749 ℃, with high-pressure granulites peak metamorphic temperature similar region. Zircon U-Pb ages are consistent within the error range of approximately 1845 Ma, this age group should represent the the vian rocks in granulite facies peak metamorphism era best estimate. This result further confirmed the eastern part of North China, the western two predecessors raised land mass the Paleoproterozoic along North China Orogen collided model. In addition, the TTG gneisses pale body samples, the metamorphic zircon cathodoluminescence image display come forward shaped to fan-zoning feature, U and Th contents and Th / U ratios and high REE contents in chondrites standardized diagrams presented from which the rare earth to heavy rare earth progressively enriched clear trend that these zircon may be formed in the foldback process stage there are a large number of garnet exploded and partial melting occurs, such zircon given weighted average age results 1819 ± 13 Ma, which may represent the era of retrograde metamorphism occurred in the region. Combined predecessors have been published in high-grade metamorphic rocks of the North China Orogen metamorphic zircon age data analysis, and visible three different age peak, were 1876 ± 6,1849 ± 2, and 1814 ± 4 Ma, this The findings suggest that there may be a long-term multi-stage metamorphic event in the North China Orogen, or the existence of at least three different metamorphism. In addition, interspersed with high pressure mafic granulite foliation pegmatite samples the magmatic zircon analysis point given age of 1806 ± 15 Ma, this age represents the age of emplacement of the pegmatite veins, that in the bosom security area, north eastern, western two continental blocks collided has ended.

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