Geochronological and geochemical characteristics of the deformed diorite from the North Altyn brittle-ductile shear zone and its constraint on the Early Paleozoic tectonic evolution of the North Altyn Tagh

The North Altun brittle-ductile shear zone as an important tectonic boundary in the North Altyn Tagh is important to be investigated. In particular, detailed studies on its deformation timing is significant to improve understandings on the tectonic evolution history of the North Altyn Tagh. According to the current study, a set of deformed diorites involved in the brittle-ductile shear zone in the Kaladawan area were found, focusing on which comprehensive studies consisting of field investigation, microstructure observation, major and trace element geochemical analysis and LA-ICP-MS zircon U-Pb dating were performed. Field observations noticed that the deformed diorite have weak SE-trending stretching lineation, with plunge of 25° ∼43°, and well-developd foliation with attitudes from ca. 98° to 120° and the SE-diping with an angle of 60° ∼75°, which are parallel to the extension of the brittle-ductile shear zone. By microstructure observation, dislocation amphibole porphyroclasts, S-C fabrics and mica-fish textures developed in the deformed diorite indicate the dextral strike-slip shearing. The geochemical analysis results show that the deformed diorite is characterized by relatively high contents of MgO (3. 10% ∼4. 04%) and Mg# values (49. 9 -51. 2), with the SiO2 content ranges from 57. 59% to 62. 39%, ALK (Na2O + K2O) content ranges from 4. 79% to 5. 29% and aluminium saturation index (A/NCK) =0.81-0.89, belonging to metaluminous and calc-alkaline I-type granites. In addition, The diorite plutons exhibit enrichment of large-ion lithophile elements (LILEs, e. g., Rb, Ba, K), light rare-earth elements (LREEs) and more mobile incompatible elements (e. g., Th, U), as well as depletion of high field strength elements (HFSEs, e. g., Nb, Ta, Zr, Hf, Ti) and heavy rare earth elements (HREEs), and weakly negative Eu anomalies (