Voluminous literature has resulted from studies of the geology and tectonic environments of the eastern Tianshan Mountains in Hercynian. However, whether the Indosinian tectonic evolution is a continuing episode of Hercynian orogeny or has been significantly influenced by other tectonic regimes remains to be understood. Integrated petrographic, geochemical and isotopic studies of the Indosinian magmatism are critical to understand the tectonic evolution of the eastern Tianshan Mountains in Triassic. The Weiya quartz diorite, situated in eastern segment of the Middle Tianshan Mountains, was formed in early-middle Indosinian. The rock is mainly composed of quartz (5~10 %), plagioclase (An 35-40, 55~60 %), K-feldspar (1~10 %), biotite (10~15 %) and hornblende (5~10 %). Geochemically, SiO2 contents of this rock vary from 62.40 % to 65.25 %. The rock is higher in Al2O3 (16.06~16.90 %) and lower in TiO2 (0.70~0.88 %), with high ratios of Na2O/K2O (1.26~1.75). the Weiya quartz diorite is metaluminous with aluminium saturation indices (ASI) of 0.91~0.93 and can be defined as high K calc-alkaline rocks. It is enriched in large ion lithopile elements (LILE) such as Cs, Rb, Ba, K and Pb and high field strength elements (HSFE) such as U, Th and Zr , depleted in HFSE such as Nb. All samples display similar chondrite-normalized REE patterns with enrichment in LREE, depletion in HREE and significant fractionation (LaCN/YbCN=12.07~17.29) between LREE and HREE. Isotopically, the Weiya quartz diorite exhibits O isotope values ranging from 8.64 ‰ to 8.73 ‰. It has initial Sr values ranging from 0.70672 to 0.70879 and initial Nd values varying from 0.512413 to 0.512441, respectively. In terms of Nd isotope ratios, the rock is characterized by positiveNd(t) values (1.64~2.16) and young Nd model ages (TDM ) of 0.79~0.80 Ga. The Weiya quartz diorite is derived from neither direct fractionation of mantle-derived magmas nor deep hybrid sources between mantle-derived magmas and crustal felsic melts. Rather, it could have been generated from partial melting of juvenile lower crust rocks (middle-high K metabasaltic rocks) at 1000~1100℃ and 16~18 kbar conditions. Such high temperature and pressure conditions met with petrogenesis of the Weiya quartz diorite are attributed to intra-continental subduction, which was likely triggered by northward subduction of the Paleo-Thethys ocean plate from the late Permian to Triassic period. It is supposed that Indosinian system is not a continuing episode of the Hercynian orogeny in eastern Tianshan Mountains, but yet it has been significantly influenced by Paleo-Tethys tectonic regime.