内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义  

Zircon U-Pb-Hf Isotopic Characteristics from Felsic Volcanic Rocks of Baoligaomiao Formation, the Middle Segment of Inner Mongolia: Implications for Geological Evolution

作　　者：贺淑赛 李秋根[1,2] 王宗起[3] 徐学义[4] 刘树文[1] 陈隽璐[4] 李智佩[4] 胡兆初[5] 

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871 [2]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [3]中国地质科学院矿产资源研究所,北京100037 [4]西安地质矿产研究所,西安710054 [5]地质过程与矿产资源国家重点实验室,中国地质大学地球科学学院,武汉430074

出　　处：《北京大学学报（自然科学版）》2015年第1期50-64,共15页Acta Scientiarum Naturalium Universitatis Pekinensis

基　　金：中国地质调查局项目(1212011085475);国家重点基础研究发展计划(2013CB429800)资助

摘　　要：锆石SHRIMP U-Pb定年结果显示:内蒙古中部白音乌拉地区原宝力高庙组的流纹岩形成时代为300.0±2.9 Ma,属晚石炭世;青格勒宝拉格地区原宝力高庙组的凝灰岩结晶年龄为159.6±1.4 Ma,并获得3颗捕获锆石的年龄分别为291.8±3.4,304.0±3.3和734.7±9.2 Ma,应属于晚侏罗世满克头鄂博组。锆石LA-MCICP-MS Hf同位素分析显示:流纹岩锆石εHf(t)值为+10.5^+12.9,TDMC值为493~645 Ma;凝灰岩岩浆锆石εHf(t)值为+10.1^+13.1,TDMC值为369~563 Ma。研究结果表明,流纹岩源于晚古生代新生地壳的重熔并混入少量老地壳物质,凝灰岩源于晚古生代地壳的熔融。Hf同位素特征显示晚古生代流纹岩和中生代凝灰岩源于相似的源区,揭示了晚古生代的一次重要的增生事件,并且在约160 Ma时期发生过地壳的再造。结合前人的研究成果表明,兴蒙造山带在约300 Ma时处于古亚洲洋演化过程中岛弧向碰撞后伸展环境的转换时期,在约160 Ma受到蒙古鄂霍茨克构造域的影响。Zircon SHRIMP U-Pb ages and LA-MC-ICP-MS Lu-Hf isotopic compositions of a rhyolite sample and a tuff sample of Baoligaomiao Formation from Baiyinwula region and Qinggelebaolage region respectively in the middle Inner Mongolia were determined. Zircon U-Pb dating gives the eruption age of rhyolite from the Baiyinwula region as 300.0±2.9 Ma, indicating that the volcanic member of Baoligaomiao Formation formed during the Late Carboniferous. The Qinggelebaolage tuff, which was considered as a part of Baoligaomiao Formation, has a zircon SHRIMP U-Pb age of 159.6±1.4 Ma, belonging to Late Jurassic Manketouebo Formation, with three ages of captured zircons（291.8±3.4, 304.0±3.3 and 734.7±9.2 Ma, respectively）. In-situ zircon LA-MC-ICP-MS Hf analyses show that magmatic zircons from Baiyinwula rhyolite and Qinggelebaolage tuff have εHf（t） values of ＋10.5-＋12.9 and ＋10.1-＋13.1, with TDM^C of 493-645 Ma and 369-563 Ma, respectively. Thus, the Baiyinwula rhyolite should be derived from partial melting of Late Paleozoic juvenile crust with involvement of ancient crustal materials whereas the Qinggelebaolage tuff should be generated by partial melting of Late Paleozoic crust. Integrating previous studies, the results review that the Mesozoic and Paleozoic volcanic rocks in the Uliastai continental margin might be derived from similar sources, revealing that there was an important crustal accretion event in Late Paleozoic. Moreover, two Paleozoic captured zircon grains in Qinggelebaolage tuff, which have U-Pb ages of ca. 300 Ma, are similar in Hf isotopic features to the magmatic zircons from both the Baiyinwula rhyolite and the Qinggelebaolage tuff, signifying significant crust reworking during formation of the Late Jurassic Qinggelebaolage tuff. These results, together with previous data from the literature, indicate that in the Inner Mongolia Orogenic Belt, a transition from island arc to post-collision extension related to evolution of Paleo-Asian Ocean occurred at ca. 300 Ma, whereas the influence of th

关 键 词：内蒙古 宝力高庙组 火山岩和火山碎屑岩 SHRIMP锆石U-PB定年 HF同位素 地壳演化 

分 类 号：P588.14[天文地球—岩石学] P597[天文地球—地质学]