Composition and tectonic significance of Jitang metamorphic core complex in eastern Xizang
The Jitang metamorphic core complex is a key window for studying the tectonic evolution of the northern Lancangjiang zone.In this paper,through the study of structural lithology mapping,structural analysis,and zircon U-Pb dating,the Jitang metamorphic core complex is dissected from top to bottom into the upper unit(low-grade metamorphic or unmetamorphic sedimentary sequence),the middle unit(schists and phyllites),and the lower unit(gneiss core).The lower unit(gneiss core)and the middle unit are connected by a ductile detachment shear zone,with the shear sense of the ductile shear zones indicating southeastern shearing of the upper plate.The zircon U-Pb age of syn-tectonic granitic mylonite in the Jitang metamorphic core complex ranges from(33.0±1.2)Ma to(28.4±0.6)Ma,and that of the post-tectonic vein is(18.35±1.2)Ma.It is speculated that the Cenozoic uplift process of the Jitang metamorphic core complex is as follows:strong strike-slip fault activity leads to the formation of a pull-apart basin,whose extensional environment leads to crustal thinning and a large amount of magma upwelling.Finally,this process resulted in the uplift of the Jitang metamorphic core complex during the Oligocene-Miocene.It is concluded that the Jitang metamorphic core complex is the product of a regional post-orogenic extension and a large-scale south-east trending escape tectonic event caused by the Oligocene-Miocene large-scale strike-slip faulting.
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