伊犁地块北缘别珍套山中泥盆统汗吉尕组物源特征及其地质意义

Provenance Characteristics and Geological Significance of the Middle Devonian Hanjiga Formation in Biezhentao Mountain,the Northern Margin of Yili Block,China

天山造山带位于中亚造山带西南缘,是探索中亚造山带增生造山过程的重要窗口。西北天山是伊犁地块与准噶尔地块的结合部位,保存了两者之间构造演化的重要地质信息。出露于伊犁地块北缘别珍套山的泥盆系是记录西北天山晚古生代早期构造演化过程的重要载体。基于此,对中泥盆统汗吉尕组砂岩进行岩相学和LA-ICP-MS碎屑锆石U-Pb定年与微量元素研究。结果表明:碎屑锆石U-Pb年龄介于500~370 Ma,并可以分为两期,主峰年龄为386 Ma,次峰年龄为490 Ma,结合岩相学和锆石微量元素特征,汗吉尕组砂岩的物源主要为晚古生代早期中酸性岩浆岩和早古生代早—中期中基性岩浆岩。综合分析认为,汗吉尕组于中泥盆世晚期沉积于弧前盆地沉积构造环境,物源主要为伊犁地块北缘的古生代岩浆弧,暗示伊犁地块北缘在晚古生代早期受准噶尔洋向南俯冲作用影响,为活动大陆边缘。

Tianshan orogen,which is located in the southwestern part of the Central Asian orogenic belt(CAOB),is a window to explore the accretionary orogenic process of the CAOB.The northwest Tianshan orogen,which is the joint of Yili block and Junggar block,preserves the important geological information of the evolution between them.Especially,the Devonian exposed in Biezhentao Mountain on the northern margin of Yili block is an important carrier for recording the evolution of the northwest Tianshan in the early Late Paleozoic.Detrital zircon LA-ICP-MS U-Pb dating of sandstone from Hanjiga Formation shows that the ages of detrital zircons range from 500 Ma to 370 Ma,and can be divided into two periods:the main period peak value is 386 Ma,followed by 490 Ma.According to the petrographic characteristics,ages and trace elements of zircon,the provenance of sandstone is mainly intermediateacid magmatic rock of the early Late Paleozoic and intermediate-basic magmatic rock of the early-middle Early Paleozoic.It is inferred that the sedimentary age of Hanjiga Formation is late Middle Devonian and formed in the forearc basin environment.It is also indicated that the detrital materials of the studied sandstone are mainly derived from the Paleozoic magmatic arc in the northern margin of Yili block,which belongs to the near-source sediments.Meanwhile,it is suggested that the northern margin of Yili block is an active continental margin due to the southward subduction of Junggar ocean in the early Late Paleozoic.