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.