内蒙古苏尼特左旗地区岩脉群的地球动力学意义

发布时间：2018-11-07 20:53

【摘要】：苏尼特左旗地区位于内蒙古中北部,属于中亚造山带东段的兴蒙造山带,研究区构造上位于二连-贺根山弧增生带上。该二连-贺根山弧增生带呈北东东向伸展,南北边界分别为二连-贺根山断裂带和查干敖包-阿荣旗断裂带。区内发育密集的岩脉群,侵位于泥盆系泥鳅河组的砂岩和砾岩和石炭系宝力高庙组火山岩、石炭纪花岗闪长岩、二长花岗岩等晚古生代岩浆岩中。岩脉群整体呈平行分布,走向为北东东向,与区域构造线走向一致。在地貌上,岩脉大多数呈“S”型弯曲,部分岩脉被北北东向断裂错断。由于岩脉具有强抗风化能力,与围岩存在明显风化差异而形成山脊,在遥感影像中显示为密集的条带状凸起。相邻脉体间隔主要集中在70-100米,密集区最小间隔约10-20m,单条岩脉出露长度可达数公里,宽度主要在20-30m之间,走向在75°-90°之间,近于直立。岩脉种类主要为酸性的花岗斑岩脉和流纹岩脉,另外还有少量的闪长玢岩脉,由于其数量很少,没有太多的实际研究意义,将不在本文的研究范围之内。花岗斑岩脉和流纹岩脉均为斑状结构,花岗斑岩脉斑晶主要为钾长石和石英及部分斜长石,流纹岩脉斑晶为石英和少量长石,并且流纹岩脉发育特征的流纹构造和球粒构造。通过LA-ICP-MS法测得花岗斑岩的锆石U-Pb谐和年龄为289.2±2.8Ma,流纹岩的锆石U-Pb谐和年龄为282.4±7.4Ma,由此可确定本区岩脉群的侵位时代为早二叠世。在岩石地球化学方面,花岗斑岩脉与流纹岩脉特征相似,主量元素上表现为富硅、富碱、富铝和贫钙的特征;微量元素上具有轻稀土元素较富集以及重稀土元素平坦的分布特征,铕显示弱的负异常。另外,岩石富集Rb、Ba、Th、U、K及Pb,而Nb、Ta、Ti、P呈明显的负异常。这些地球化学特征显示该岩脉群是由岛弧岩浆岩地壳部分熔融形成的。西伯利亚板块南缘发育的巨型A型花岗岩带(年龄为276Ma-286Ma)及双峰式火山岩线(年龄为270Ma-281Ma)均代表着伸展构造环境,与之相比,本研究区岩脉群更能代表区域伸展构造环境,并且比上述的A型花岗岩带和双峰式火山岩线的年龄略早,提高了西伯利亚板块南缘伸展构造环境的年龄上限。综上所述,本文认为研究区岩脉群为早二叠世的伸展构造背景下岛弧岩浆岩地壳局部熔融的产物。
[Abstract]:The Sunita Zuo Banner area is located in the central and northern part of Inner Mongolia and belongs to the Xingmeng orogenic belt in the eastern part of the Central Asian orogenic belt. The arc-accretive zone of Erlian-Hegenshan extends in the north and west direction, and the north and south boundary is the Erlian-Hegenshan fault zone and the Chagan Aobo-Aronqi fault zone. There are dense vein groups in the area, which are located in late Paleozoic magmatic rocks, such as sandstone and conglomerate of the Loach River formation of Devonian, volcanic rock of Baoligaomiao formation of Carboniferous, granodiorite of Carboniferous, monzogranite and other late Paleozoic magmatic rocks. The whole vein group is distributed in parallel with the strike of east-west direction, which is consistent with the regional tectonic line. In geomorphology, most of the veins are "S" curved, and some of them are faulted in NNE direction. Because of the strong weathering resistance of the vein and the obvious difference between the rock and the surrounding rock, the ridge is formed, which is shown to be a dense banded protuberance in remote sensing images. The distance between adjacent veins is mainly 70-100 m, the minimum interval in dense area is about 10-20 m, the length of single vein is several kilometers, the width is mainly between 20-30 m, and the strike is between 75 掳-90 掳, which is nearly vertical. The main types of veins are acidic granitic porphyry veins and rhyolite veins, and a small amount of diorite-porphyrite veins, due to the small number of diorite-porphyrite veins, there is not much practical significance, so it will not be within the scope of this study. The granitic porphyry vein and the rhyolite vein are both porphyry structure. The porphyry crystals of the granitic porphyry vein are mainly potash feldspar, quartz and some plagioclase, while the rhyolite vein porphyry is quartz and a little feldspar. The zircon U-Pb harmonic age of granitic porphyry is 289.2 卤2.8 Ma. and the zircon U-Pb harmonic age of rhyolite is 282.4 卤7.4 Ma.Therefore, the emplacement age of the vein group in this area is determined to be early Permian. In the aspect of rock geochemistry, the characteristics of granitic porphyry vein and rhyolite vein are similar, and the main elements are silicon-rich, alkali-rich, aluminum-rich and calcium-poor. The trace elements are relatively rich in light rare earth elements and flat in the distribution of heavy rare earth elements. Europium shows weak negative anomalies. In addition, the rocks are enriched in Rb,Ba,Th,U,K and Pb, but Nb,Ta,Ti,P is obviously negative abnormal. These geochemical characteristics indicate that the vein group was formed by the partial melting of the crust of island arc magmatic rocks. The giant A-type granite belt (age 276Ma-286Ma) and the bimodal volcanic rock line (age 270Ma-281Ma) developed on the southern edge of the Siberian plate represent the extensional tectonic environment. In this study area, the vein group is more representative of the regional extensional tectonic environment, and the age limit of the extensional tectonic environment in the southern edge of the Siberian plate is raised slightly earlier than that of the A-type granite belt and the bimodal volcanic line mentioned above. To sum up, the study area is considered as the product of local melting of island arc magmatic rock crust in the early Permian extensional tectonic setting.
【学位授予单位】：石家庄经济学院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P597.3;P583

【参考文献】