科研之友
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摘要
Late Neoarchean granitoid gneisses are widespread in the Jiapigou-Jingyu area of the Southern Jilin Province (SJP) of the North China Craton (NCC). These rocks are composed of tonalitic-trondhjemitic-g ranodioritic-dioritic (TTGD) gneisses and preserve important information on the geodynamic evolution and Archean crustal growth along the northeastern margin of the NCC. Here we present LA-ICP-MS zircon U-Pb isotopic ages which reveal that the magmatic precursors of the tonalitic-trondhjemitic gneisses were emplaced at similar to 2578-2574 Ma, and the granodioritic-quartz dioritic magmas crystallized at similar to 2546-2524 Ma. The rocks were subjected to regional amphibolite facies metamorphism at similar to 2510-2490 Ma. @@@ Geochemically, the tonalitic-trondhjemitic gneisses can be subdivided into two subgroups. The magmas of high-Yb subgroup were derived by partial melting of dominantly ancient basaltic materials at the crustal level in the stable field of amphibole, clinopyroxene and significant amounts of garnet, and subsequently subjected to varying degrees of fractionation. Magmas of the low-Yb subgroup were generated by partial melting of dominantly juvenile basaltic materials with minor greywackes at the lower crustal level in the stability field of garnet and rutile, with a possible eclogitic residue. The magmatic precursors of granodioritic gneisses were produced by partial melting of subducted oceanic slabs and minor sediments, with the melts contaminated by the mantle wedge materials during their ascent. The parental magmas for the quartz dioritic gneisses were possibly generated by partial melting of a depleted mantle source that was significantly metasomatized by slab-derived fluids or melts. @@@ Combined with their petrogenesis, similar to 2578-2574 Ma tonalitic-trondhjemitic gneisses display positive zircon epsilon(Hf)(t(2)) values (+0.4 to +6.2) with T-DM(Hf) ages of 2856-2643 Ma, suggesting a crustal reworking process. On the other hand, similar to 2546-2524Ma granodioritic to quartz dioritic gneisses have highly depleted zircon epsilon(Hf)(t(2)) values (+4.5 to +7.7) and T-DM(Hf) ages of 2682-2550 Ma that are close to their magmatic crystallization ages, indicating a significant crustal growth. Integrated with our recent studies on similar to 2683-2654Ma metavolcanic rocks in Helong granite-greenstone belt and voluminous similar to 2588-2536 Ma metavolcanics in Jiapigou granite-greenstone belt, we infer that the Southern Jilin Province experienced Neoarchean subduction-related evolution history, with an Andean-type active continental margin along the northern margin of the NCC, and witnessed two major episodes of subduction-related crustal growth at similar to 2.7 Ga and similar to 2.6-2.5 Ga, with the latter period coupled with reworking of old crustal materials.
- 出版日期2017-12
- 单位北京大学; 中国地质大学（北京）
