内蒙古阿尔山地区奥陶纪火山岩地球化学特征及其构造意义

发布时间：2018-04-30 16:12

本文选题：阿尔山 + 奥陶纪火山岩　；参考：《吉林大学》2015年硕士论文

【摘要】：头道桥-新林-塔原断裂带位于额尔古纳地块与兴安地块之间，沿断裂带出露有新林蛇绿岩、环宇蛇绿岩和头道桥蓝片岩，近年来的研究认为它是两大地块的缝合带，然而额尔古纳和兴安地块的碰撞时代和模式一直存在争议。多宝山奥陶纪岛弧位于头道桥-新林-塔原蛇绿岩带的东南侧，它的成因及性质可以为区域构造演化提供较好的约束。由于缺少对该岛弧西南延伸区奥陶纪火山岩的系统的年代学和地球化学研究，致使多宝山奥陶纪岛弧的成因及性质一直不明。因此，论文对多宝山岛弧南段阿尔山地区的代表性的奥陶纪火山岩进行了系统的岩石学、年代学和地球化学研究，旨在为区域构造演化提供依据。阿尔山地区多宝山组火山岩由变玄武岩、变玄武安山岩和变英安岩组成，变玄武安山岩和变英安岩的锆石U-Pb年龄分别为469±6Ma和475±4Ma。岩石富集Th、U、Zr、Hf等高场强元素，Nb、Ta弱亏损，显示出弧火山岩向OIB过渡的地球化学特征。阿尔山地区佳疙疸组变玄武岩的锆石U-Pb年龄为464±7Ma，变玄武岩按地球化学特征可以分为两类，第一类高钛玄武岩富集Rb、Ba、Th、U、K等强不相容元素，Nb、Ta正异常，具有与OIB型玄武岩一致的地球化学特征；第二类低钛玄武岩则与本区多宝山组火山岩具有相似的地球化学特征，也体现出弧火山岩向OIB过渡的特征。综合分析认为多宝山组和佳疙疸组低钛玄武岩的源区具有OIB深部上涌地幔和俯冲洋壳释放的流体组分的双重贡献，但佳疙疸组高钛玄武岩的岩浆源区则以OIB地幔性质为主。结合阿尔山地区构造位置，本文认为阿尔山地区奥陶纪火山岩产生于弧后盆地的早期阶段。综上所述，头道桥-新林-塔原蛇绿岩带早古生代构造演化特征如下：寒武纪末额尔古纳地块与洋内岛弧或是兴安地块拼贴形成头道桥蓝片岩，，早中奥陶世古亚洲洋向北俯冲，形成多宝山火山弧，在弧后伸展盆地形成区内的奥陶纪过渡型+OIB的火山岩组合，典型的弧火山岩应该位于阿尔山地区的东南侧。
[Abstract]:The Toutaoqiao-Xinlin-Tarim fault zone is located between the Erguna block and the Xingan block. Along the fault zone, there are Xinlin ophiolite, Huanyu ophiolite and Toutaoqiao blue schist, which have been considered to be suture zones of the two major landmasses in recent years. However, the era and model of collision between Erguna and Xingan landmasses have been controversial. The Ordovician island arc in Dobaoshan is located on the southeast side of the Tudaoqiao-Xinlin-Tarim ophiolite belt. Its genesis and properties can provide a good constraint for the regional tectonic evolution. Due to the lack of systematic geochronology and geochemistry of Ordovician volcanic rocks in the southwestern extension of the island arc, the origin and nature of the Ordovician island arc in Dobaoshan have been unknown. Therefore, the representative Ordovician volcanic rocks in the Arshan area in the southern segment of the island arc of Dobaoshan are systematically studied in petrology, geochronology and geochemistry in order to provide the basis for the regional tectonic evolution. The volcanic rocks of the Dobaoshan formation in the Alshan area are composed of metamorphic basalt, altered Black Tortoise andesite and metamorphic andesite. The zircon U-Pb ages of altered Black Tortoise andesite and metamorphic andesite are 469 卤6Ma and 475 卤4Marespectively. The low depletion of high field strength elements such as Th _ (U) U _ (Zr) ~ (H _ f) _ f shows the geochemical characteristics of the transition from arc volcanic rocks to OIB. The zircon U-Pb age of the metabalts of Jiakujing formation in Alshan area is 464 卤7 Ma.The metabalts can be divided into two types according to their geochemical characteristics. The second type of low titanium basalt has similar geochemical characteristics to that of Dobaoshan formation volcanic rocks in this area, which also shows the transition of arc volcanic rocks to OIB. It is considered that the source regions of the low titanium basalts of the Dobaoshan and Jiakuji formations have dual contributions from the deep upwelling mantle of OIB and the fluid released from the subduction oceanic crust, but the magmatic source of the high-titanium basalts of the Jiakuji formation is dominated by the OIB mantle. Based on the tectonic location of the Alshan area, it is believed that the Ordovician volcanic rocks in the Alshan area originated in the early stage of the back-arc basin. To sum up, the early Paleozoic tectonic evolution characteristics of the Tudaoqiao-Xinlin-Tarim ophiolite belt are as follows: the late Cambrian Erguna block and the intraoceanic island arc or Xingan block collage together to form the Toutaoqiao blue schist, and the early middle Ordovician ancient Asian ocean subducts north. The formation of the Dobaoshan volcanic arc and the formation of the Ordovician transitional OIB volcanic rock assemblage in the back-arc extensional basin, the typical arc volcanic rocks should be located on the southeast side of the Alshan area.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.14

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