LA-ICP-MS Zircon U-Pb Dating and Its Geological Implications of Post Collision Granite in the Sawuer Mountain
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摘要: 新疆西准噶尔北部萨吾尔山塔斯特岩体出露在吉木乃县托斯特乡西南,岩性主要为花岗闪长岩、二长花岗岩等,对其中的花岗闪长岩进行LA-ICP-MS锆石U-Pb定年,206Pb/238U加权平均年龄为(332±1.9)Ma,表明该岩体形成于早石炭世晚期。岩石SiO2(64.03%~66.44%),Na2O/K2O(1.887 8~2.488 5)、A/CNK(1.766 7~1.920 4)显示I型花岗岩特征。岩石富集大离子亲石元素(Rb、K),亏损高场强元素(Nb、Ti)。ΣREE(54.68×10-6~57.56×10-6)、δEu(1.03~1.09)、(La/Sm)N(3.173~3.54)表现出后碰撞花岗岩特点。指示早石炭世中期萨吾尔山地区乃至整个西准噶尔地区已处在后碰撞构造环境,早石炭世后碰撞花岗闪长岩的确定为西准噶尔晚古生代构造格局演化提供了新的证据。Abstract: The Tasite pluton is located in the Sawuer Mountain of West Junggar, Jimunai County, Xinjiang.The pluton consists of granodiorite, monzonite granite, etc. According to U-Pb age analysis, the formation age of the granodiorite from the Tasite pluton is (332±1.9)Ma(the middle stage of Early Carboniferous).The geochemical studies indicate that the SiO2 contents vary from 64.03% to 66.44%, Na2O/K2O ratios change from 1.887 8 to 2.488 5, A/CNK ratios range from 1.7667 to 1.9204, which belongs to the I type granite. This pluton is enriched in LILE, such as Rb and K, and depleted in HFSE, such as Nb and Ti. The pluton has low ΣREE contents (54.68×10-6~57.56×10-6) and no Eu anomalies, with δEu values of 1.03~1.09and the (La/Sm)Nratiosvarying from 3.173 to 3.54. All of the geochemical features above show that the Sawuer Mountain in the middle stage of Early Carboniferous or the West Junggar are in post-collisional environment. The confirmation of post-collisional I type granites in the middle stage of Early Carboniferous provides new tectonic evolution evidence for the West Junggar region.
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