青藏高原古近纪沱沱河盆地磁性地层及其古环境演变

发布时间：2018-05-20 01:07

本文选题：沱沱河盆地 + 磁性地层　；参考：《中国科学院研究生院(地球环境研究所)》2015年硕士论文

【摘要】：印度板块与亚欧板块的碰撞形成了面积超过250万平方公里,平均海拔在5000m以上的青藏高原。由于青藏高原具有如此大的面积和海拔高度,它的隆升不仅对我国的气候产生重大影响,而且造成全球气候格局的改变。同时青藏高原是印度板块与欧亚板块碰撞的结果且这种碰撞作用仍然在继续,所以青藏高原也是研究碰撞造山带、大陆变形以及地球动力学的天然场所。到目前为止,对于印度板块与欧亚板块碰撞的时间、高原隆升的过程、机制都存在较大的争议。沉积盆地是研究构造隆升的重要场所,目前青藏高原周边的盆地都得到了较高程度的研究,而高原中部的盆地研究相对滞后。沱沱河盆地属于可可西里盆地的一部分,位于可可西里盆地的南边,北边是金沙江缝合带,南边是唐古拉山逆冲断裂带。沱沱河盆地包含有完整的一套从晚白垩到中新世的地层,即风火山群、沱沱河组、雅西措组、五道梁组。这套地层有可能记录了印度板块俯冲以及与欧亚板块碰撞所产生的构造响应,对于理解青藏高原的隆升过程研究具有明显的帮助,同时还有助于解决风火山群的年代问题。本文通过岩石磁学、磁性地层学、沉积相、生物地层学以及磁化率各向异性等研究了沱沱河盆地的主要磁性矿物、高原隆升可能的时间节点、主要的古气候变化事件等。本文得到以下结论:1.通过磁化率随温度变化曲线(K-T)、等温剩磁(IRM)获得曲线以及等温剩磁的CLG模型分析,沱沱河盆地剖面的主要磁性矿物是赤铁矿和磁铁矿。同时在热退磁的过程中,有些样品在120℃左右磁化强度显著的降低到原磁化强度的15%左右,说明存在一定量的针铁矿。2.沱沱河盆地剖面自下而上(由老到新)可以划分为沱沱河组、雅西措组。磁性地层及其生物地层研究表明沱沱河组的地质年代为59.8-52.6Ma,雅西措的地质年代为51.8-24.1Ma。如果风火山群和沱沱河组是同一套地层,那么风火山群的年龄至少要老于52.6Ma,如果沱沱河组不整合于风火山群之上,那么风火山群的年龄至少在59.8Ma之前。3.沉积相表明沱沱河盆地存在5次明显的沉积相变化,分别是:第一次明显变化开始的时间为52.6Ma,在此之前气候干旱,从52.6Ma开始,气候变得湿润。通过孢粉、化石的分析以及与区域性的孢粉、化石对比,再结合全球温度的变化,52.6Ma之前的干旱主要是受控于副热带高气压带以及全球气温降低的双重控制。之后气候变得湿润主要是受到早始新世气候适宜期的影响。结合降水的变率以及这个时期气候湿润期的分布范围,此时季风有可能已经发育。考虑到沱沱河盆地位于青藏高原的中部,不排除青藏高原的构造隆升对盆地的气候会产生影响。第二次明显变化开始的时间为43.2Ma,地层中出现了白色的顺层石膏。第三次开始的时间为41Ma,出现了厚层的石膏。这两次时期的干旱化原因有可能是特提斯海的退却、青藏高原的构造隆升、全球气候的变冷共同导致的。但是特提斯海的退却很大程度上是受控于全球气候变化,同时,磁组构和磁学相关指标分析表明,在41Ma左右青藏高原发生了一次构造运动,而且磁学指标表明高原的隆升对区域的干旱化作用开始变得明显,因此青藏高原的隆升开始超过全球气温及特提斯海对区域的影响。第四次变化开始的时间为34.5Ma,地层中出现了厚层的石膏。这个时期的干旱同样可以由特提斯海的退却、青藏高原的隆升、全球气候变冷导致形成,特提斯海的退却还是受控于全球气候变化,另外后面的磁学指标从这个时候开始都整体下降,而全球的温度变化幅度较大,磁学指标与之变化的趋势逐渐不一致,说明全球因素对沱沱河盆地的影响逐渐减小,而青藏高原的影响因素加大,占据主导。第五次变化也是出现了非常厚层的石膏,开始的时间为26.9Ma。磁学指标暗示青藏高原对区域的干旱化作用更明显。4.磁化率各向异性表明沱沱河盆地受到了构造应力的作用,从老到新可以划分出四次构造应力期,分别是:T1段:地质年代为59.8-52.6Ma,构造应力方向为南西,印度板块与欧亚板块在这个时间段之前已经发生碰撞。T3段:地质年代为46.8-44Ma,构造应力的方向为南西。这段的构造应力作用比较明显,具有区域性。根据沉积相的变化,C段以后出现了石膏,推测此时沱沱河盆地南部已经存在可以阻挡水汽深入北进的地貌,促进了沱沱河盆地的干旱。T5段:地质年代为41.1-34.3Ma,磁偏角的平均值,在41.1Ma发生了明显的偏转,应力的来源不仅来自南西,还来自南东。41.1Ma出现的南东方向构造应力,表明此时印度板块在东部与欧亚板块之间开始碰撞。此时青藏高原的平均海拔加大,对水汽的阻挡更加显著。T7段:地质年代为26.2-24.1Ma,应力方向为南西方向和南东,通过磁学指标分析,暗示着此时高原的构造运动更加强烈。5.沱沱河盆地磁化率与频率磁化率、百分比频率磁化率之间的反位相关系表明超顺磁颗粒组分对剖面的磁化率几乎没有贡献。另外磁学指标在51.8-41Ma与41-32Ma整体都趋于下降,与全球这个时间段温度的下降以及沱沱河盆地逐渐变干的趋势相符合,说明全球的气候在51.8-41Ma与41-32Ma范围内对区域气候有影响。但是在41-32Ma,各个指标整体都高于51.8-41Ma、32-24.1Ma,分析表明约41Ma开始,青藏高原发生了一次构造运动(磁化率各向异性结果也支持这个结论),此时青藏高原的构造隆升对沱沱河盆地干旱的影响是叠加在全球的降温趋势上,但是高原对区域的影响开始占主导。在32-24.1Ma,指标都整体下降,此时全球的温度却变化幅度较大,磁学指标与之变化的趋势逐渐不一致,说明全球因素对沱沱河盆地的影响逐渐减小,而青藏高原的影响因素加大,占据绝对主导地位。
[Abstract]:The collision between the India plate and the Eurasian plate has formed the Qinghai Tibet Plateau with an area of more than 2 million 500 thousand square kilometers and above 5000m above sea level. Because of such a large area and altitude of the Qinghai Tibet Plateau, its uplift not only has a significant impact on the climate of our country, but also causes a change in the global climate pattern. At the same time, the Qinghai Tibet Plateau is a India plateau. The collision between the plate and the Eurasian plate and the collision are still continuing, so the Qinghai Tibet Plateau is also a natural place to study the collision orogenic belt, continental deformation and geodynamics. So far, there are considerable disputes over the time of the collision between the India plate and the Eurasian plate, the process of Plateau uplift, and the sedimentary basin. It is an important place to study the tectonic uplift. At present, the basins around the Qinghai Tibet Plateau have been studied in a high degree, while the basin research in the middle of the plateau is relatively lagging. The Tuo Tuo basin belongs to a part of the cocoa Xili basin, located on the southern side of the cocoa West Basin, the northern side of the Jinsha River suture zone and the Tanggula Mountain Thrust Belt on the south. The Tuotuo basin contains a complete set of strata from the late Cretaceous to the Miocene, that is, the wind volcano group, the Tuotuo River formation, the Iasi measure and the five road formation. This set of strata may record the subduction of the India plate and the tectonic response to the collision with the Eurasian plate, which is of great help to the understanding of the uplift process of the Qinghai Tibet Plateau. In this paper, the main magnetic minerals of the Tuotuo basin, the possible time nodes of the uplift of the plateau and the major paleoclimate change events are studied through rock magnetism, magnetic stratigraphy, sedimentary facies, biostratigraphy and the anisotropy of magnetic susceptibility. The following conclusions are obtained: 1. the following conclusions are obtained by magnetization With the temperature change curve (K-T), the isothermal remanence (IRM) obtained curve and the CLG model of isothermal remanence, the main magnetic minerals in the Tuo Tuo basin section are hematite and magnetite. In the process of thermal demagnetization, the magnetization of some samples is significantly reduced to about 15% of the original magnetization at about 120 degrees C, indicating that there is a certain degree of magnetization. The.2. Tuo Tuo basin section from the Tuo Tuo River Basin (from the old to the new) can be divided into Tuo Tuo formation and Iasi measures. The study of magnetic strata and its biostratigraphy shows that the geological age of the Tuo Tuo formation is 59.8-52.6Ma, and the geological age of the Tuo Tuo group is 51.8-24.1Ma. if the wind volcano group and Tuo Tuo River group are the same set of strata, then the wind volcano group. The age of the Tuo Tuo River group is at least 52.6Ma. If the Tuo Tuo formation is not integrated with the wind volcano, the.3. sedimentary facies of the Tuo Fire Mountain Group at least before 59.8Ma indicates that there are 5 obvious sedimentary facies changes in the Tuo Tuo basin, respectively: the first obvious change began to be 52.6Ma. Before this, the climate was drought, from 52.6Ma to the climate. It becomes humid. Through the analysis of sporopollen, fossils, and regional sporopollen, fossils, and global temperature changes, the drought before 52.6Ma is mainly controlled by the double control of the subtropical high pressure zone and the global temperature reduction. Then the climate becomes wetted mainly by the early Eocene climatic suitability period. When the Tuotuo basin is located in the middle of the Qinghai Xizang Plateau, the tectonic uplift of the Qinghai Xizang Plateau affects the climate of the basin. The second obvious change begins at 43.2Ma, and the white Paris stone appears in the formation. The third time began with a thick layer of gypsum. The reasons for the two periods of droughts may be the retreat of the Tethys Sea, the tectonic uplift of the Qinghai Tibet Plateau, and the cooling of the global climate. But the retreat of the Tethys Sea is largely controlled by global climate change, at the same time, magnetic fabric and magnetism are related. The index analysis showed that a tectonic movement occurred on the Qinghai Tibet Plateau around 41Ma, and the magnetic indexes indicated that the uplift of the plateau began to become obvious to the region. Therefore, the uplift of the Qinghai Tibet Plateau began to exceed the global temperature and the effect of the Tethys on the region. The fourth change began as 34.5Ma. The droughts of this period can also be retreated by the Tethys Sea, the uplift of the Qinghai Tibet Plateau, the cooling of the global climate and the global climate change in the Tethys Sea. In addition, the following magnetic indicators have fallen from this time, and the global temperature changes are larger, magnetic indexes are larger. The trend of the change is gradually disagreement, indicating that the influence of the global factors on the Tuo Tuo basin is gradually decreasing, while the influence factors of the Qinghai Tibet Plateau are increasing and dominant. The fifth change is also a very thick layer of gypsum. The beginning time of the 26.9Ma. magnetic index suggests that the Qinghai Tibet Plateau has more obvious.4. magnetization to the region. The rate anisotropy indicates that the Tuo Tuo basin has been subjected to tectonic stress, and four tectonic stress periods can be divided from the old to the new. The T1 section is: the geological age is 59.8-52.6Ma, the tectonic stress is South West, the India plate and the Eurasian plate have collided.T3 segments before this time period: the geological age is 46.8-44Ma and the structure should be constructed. The direction of the force is Nancy. The tectonic stress of this section is obvious and regional. According to the change of the sedimentary facies, the gypsum has appeared after the C section. It is presumed that in the south of the Tuo Tuo basin there is a geomorphology that can block the deep water vapor entering into the North of the Tuo Tuo basin, which promotes the arid.T5 segment of the Tuo Tuo basin: the geological age is 41.1-34.3Ma, the average magnetic deflection angle is the average. There is a significant deflection in 41.1Ma. The source of the stress is not only from the South West, but also from the South East.41.1Ma tectonic stress, which indicates that the India plate began to collide between the East and the Eurasian plate at this time. The average elevation of the Qinghai Tibet Plateau increased, and the water vapor was blocked more.T7 segment: the geological age was 26.2-24.1Ma, The direction of stress is South West and South East. Through the analysis of magnetic index, it is suggested that the tectonic movement of the plateau is more intense at this time, and the magnetic susceptibility and frequency susceptibility of.5. Tuo Tuo basin and the reverse phase relation between the percentage frequency magnetization of the Tuo Tuo basin show that the superparamagnetic particle composition has little contribution to the magnetic susceptibility of the section. In addition, the magnetic index is in the 51.8-41. Both the Ma and the 41-32Ma tend to decline, in accordance with the global temperature decline and the trend of the Tuo Tuo basin gradually drying up, indicating that the global climate has an impact on the regional climate in the range of 51.8-41Ma and 41-32Ma. But in 41-32Ma, each index is higher than 51.8-41Ma, 32-24.1Ma. Analysis shows that 41Ma began, Qinghai Xizang There is a tectonic movement in the plateau (the results of the anisotropy of magnetic susceptibility also support this conclusion). At this time, the influence of the tectonic uplift of the Qinghai Tibet Plateau on the Tuo Tuo basin drought is superimposed on the global cooling trend, but the influence of the plateau on the region begins to dominate. In 32-24.1Ma, the indices are all decreased, and the global temperature changes at this time. The amplitude of the magnetic index is not consistent with the change trend, which indicates that the influence of the global factors on the Tuo Tuo basin is gradually reduced, while the influence factors of the Qinghai Tibet Plateau are increasing, which occupies an absolute dominant position.
【学位授予单位】：中国科学院研究生院(地球环境研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P318.4;P534.6

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