东准噶尔卡拉麦里松喀尔苏岩体花岗岩年代学、地球化学特征及其构造意义

东准噶尔地区岩浆活动丰富,侵入岩发育广泛。松喀尔苏岩体位于准噶尔东缘,卡拉麦里构造带南侧,岩体规模较小,主要由二长花岗岩和正长花岗岩组成。锆石U-Pb定年结果表明其形成年龄为(410.2±2.2)Ma(MSWD=0.30),是卡拉麦里构造带南缘首次报道的早泥盆世花岗质岩石年龄。从岩石地球化学成分上看,岩体主要为碱性花岗岩,具高硅、低钛、高铝、富碱和贫钙特征,弱过铝质,属A2型花岗岩;相对于原始地幔,不相容元素Rb、Th、U、K富集,具Sr、P、Ti明显负异常。结合区域地质资料综合分析认为,松喀尔苏岩体形成于卡拉麦里洋盆打开后不断扩张生长的阶段,该地区在早泥盆世时期处于伸展构造背景。

Geochronology,Geochemistry and Tectonic Significance of Songkarsu Granites in Karamali,Eastern Junggar

The Eastern Junggar region was magmatic active and intrusive rocks were extensively developed.The Songkarsu pluton is located in the eastern margin of Junggar and the southern side of the Karamaili tectonic belt. The small pluton is composed mainly of monzogranite and syenite granite. Zircon U-Pb dating yielded a formation age of (410.2±2.2) Ma(MSWD=0.30),representing the first Early Devonian granite reported in the southern margin of the Karamaili belt. The rocks are alkaline granitic,and are featured by high Si,low Ti,high Al,alkali-rich,Ca-poor,and weakly peraluminous. The granites belong to A2-type,and are (primitive mantle-normalized) enriched in large ion lithophile elements (LILEs, e.g., Rb,Th,U, and K) with obvious negative Sr,P and Ti anomalies. Based on regional geological data analysis, we considered that the Songkarsu pluton was formed under continuous expansion and growth after the initial opening of the Karamaili ocean basin.The Karamaili area was under extensional tectonic regime during the Early Devonian.