西秦岭白垩纪车拉盆地的磁性地层学及古地磁学研究

发布时间：2018-02-09 02:08

  本文关键词： 磁性地层学 古地磁学 白垩纪 车拉盆地 西秦岭　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：自晚三叠世秦岭造山带完成其主体拼合过程以来,西秦岭发育了众多的陆相山间沉积盆地,其中,晚中生代山间盆地记录秦岭造山带陆内演化阶段浅部地壳调整的详细信息,其盆地性质及构造—沉积演化过程日渐成为中外学者关注的热点。本文对陇南宕昌地区白垩纪车拉盆地进行了高精度的磁性地层学、岩石磁学和构造古地磁研究。车拉—寺麻剖面(N:34°5.5",E:104028.3M)位于车拉盆地北部,厚约1450m,代表性样品的岩石磁学实验(饱和等温剩磁和磁化率随温度变化曲线)结果表明:车拉—寺麻剖面主要的磁性矿物为磁铁矿和赤铁矿。通过系统地逐步热退磁技术进行剩磁测试,633块磁性地层定向样品产生稳定的特征剩磁,部分样品可分离出双分量特征,其低温分量方向在地理坐标系下十分接近现今地磁场偶极子场方向,可能由现今地磁场方向的粘滞剩磁产生;大部分样品具有单分量特征,与双分量样品的高温分量的地磁场方向基本一致。结合该剖面的磁极性序列与沉积速率变化特征,车拉—寺麻剖面的沉积时代可追溯到145～76Ma。通过该剖面19个构造古地磁采点,231块定向样品的热剩磁测试分析,能够产生稳定特征剩磁的182块定向样品的古地磁研究表明:以白垩纪欧亚板块的古地磁极为参考极,车拉盆地存在约18°的顺时针旋转,且早白垩世其旋转速率约为0.69°/Ma,略小于晚白垩世的0.89°/Ma。白垩纪车拉盆地的旋转可能是块体沿盆地西南缘岷县—宕昌左行走滑断裂东向旋转挤出引起的,或叠加白垩纪羌塘—昌都地块和拉萨地块汇聚碰撞背景下中国西部的区域走滑作用。
[Abstract]:Since the late Triassic Qinling orogenic belt completed its main assembly process, many continental intermountain sedimentary basins have been developed in the West Qinling Mountains. Among them, the late Mesozoic intermountain basin records the detailed information of the shallow crustal adjustment in the evolution stage of the Qinling orogenic belt. The nature of the basin and the process of tectonic-sedimentary evolution have become the focus of attention of Chinese and foreign scholars. In this paper, the Cretaceous Cretaceous Cretaceous Chela Basin in Longnan is studied in this paper. Petromagnetism and tectonic paleomagnetism. The Chela-Simma section N: 34 掳5.5 "E: 104028.3M) is located in the northern part of the Chela basin. The results of rock magnetic experiments (saturation isothermal remanence and magnetic susceptibility curves with temperature) show that the main magnetic minerals in Chela-Sima section are magnetite and hematite. Demagnetization Technology for remanence testing: 633 directional samples of magnetic strata produce stable characteristic remanence. Some samples can be separated with two-component characteristics, and the direction of low-temperature component is very close to the direction of the dipole field of the present geomagnetic field in geographical coordinate system, which may be produced by the viscous remanent magnetic field in the direction of the present geomagnetic field, and most of the samples have the characteristics of single component. The direction of geomagnetic field of the high-temperature component of the two-component sample is basically the same. The sedimentary epoch of the Chela Sima section can be traced back to 145U 76 Ma.The thermal remanence test and analysis of 231 directional samples from 19 tectonic paleomagnetic mining sites in this section were carried out. Paleomagnetic studies of 182 directional samples capable of producing stable characteristic remanence show that the paleomagnetic pole of the Cretaceous Eurasian plate is used as the reference pole, and that there is a clockwise rotation of about 18 掳in the Cretaceous Eurasian plate. The rotation rate in early Cretaceous is about 0.69 掳/ Ma, which is slightly smaller than that in late Cretaceous 0.89 掳/ Ma.The rotation of Cretaceous Cretaceous Cretaceous Chela basin may be caused by the rotating extrusion of the block along the eastward direction of Minxian-Dangchang left strike-slip fault in the southwestern margin of the basin. Or stacking the Cretaceous Qiangtang-Changdu block and Lhasa block converging in the background of the regional strike slip in western China.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P539.3;P318.44
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本文编号：1496822