Genesis of late carboniferous granitoid intrusions in the Dayinsu area, West Junggar, Northwest China: evidence of an arc setting for the western CAOB

The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO₂ contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K₂O + Na₂O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.

大印苏（Dayinsu）地区位于西准噶尔北部中哈边境附近，是中亚造山带（Central Asian Orogenic Belt, CAOB）的重要组成部分。该区域的泥盆纪-石炭纪火山沉积地层中发育大量花岗质岩体。西侧为时代较老的老大印苏岩体与库北岩体（形成时代为345~330 Ma），东侧则分布时代较新的巴依木扎岩体与前锋岩体（形成时代为330~325 Ma）。四个花岗质岩体的全岩二氧化硅（SiO₂）含量介于52.22~68.42 wt.%，总碱含量（K₂O + Na₂O）介于4.94~9.16 wt.%。该类花岗岩富集大离子亲石元素与轻稀土元素，相对亏损铌（Nb）、钽（Ta）、铈（Ce）、镨（Pr）、磷（P）与钛（Ti）。此类岩体为准铝质，具有I型花岗岩特征。侵入岩的地球化学特征表明其形成于俯冲带构造环境，侵位过程中经历了分离结晶作用，且东部岩体的分离结晶程度高于西部。大印苏地区花岗质岩体的年代学与地球化学特征与其西侧的塔北（Tabei）地区岩体具有相似性，表明二者均属于石炭纪塔尔巴哈台山侵入事件的组成部分。塔尔巴哈台山早石炭世（345~324 Ma）花岗质侵入体，可能形成于中亚造山带演化过程中的岛弧俯冲构造环境。