塔里木盆地二叠纪大火山岩省古地磁学研究

The Early Permian period represents a momentous turning point in the evolution history of the Tarim plate, for the tectonics transformed to a new global regime from the ancient system. In this time , The Tarim underwent strong magmatism, form a very important tectonic thermal events in the evolution history of the basin, showed a large eruption of basalt - acidic tuff and massive mafic dyke swarms invade , and has become a large igneous megaprovince related to mantle plume activity like the Emeishan large igneous province. The Tarim Permian large igneous province which contains abundant geodynamic information and good oil and gas and the prospect of the development of mineral resources, has important scientific significance.In order to obtain a high quality paleomagnetic data of the Tarim large igneous province formed stage (20 myer) with accurate age control, this project intends to carry out a refined paleomagnetic studies on the permian volcanic rocks in four areas of Tarim block. This application plan on the basis of predecessors' research results, select several volcanic rocks section to carry out the careful study of paleomagnetism, associates research techniques of paleomagnetism, magnetostratigraphy, volcanic chronology, rock magnetism and magnetic fabric analysis, in the hope of using fine quality paleomagnetic study to cooperate the important research progress of the Tarim Permian large igneous province in recent years. This study will provide reliable data support to reveal the large igneous province's major tectonic significance , plate kinematics characterize spatial and temporal changes in detail and paleogeographic reconstruction, for the quantitative study of the Tarim block Paleozoic geography, history of ocean-continent conversion , marine hydrocarbon raw rock distribution and accumulation environment, provide a reliable basis for the distribution of the reservoir environment , the formation and evolution of ancient Paleo-Tethys Ocean and Asia , as well as the formation and development of China and Asia as a whole structure.

塔里木二叠纪大火山岩省是我国继峨眉山之后又一个被认为可能与地幔柱活动有关的大火成岩省，蕴含着丰富的地球动力学信息和良好的油气及矿产资源信息，具有十分重要的科学意义。本申请拟将传统古地磁学研究手段与火山岩同位素年代学、磁性地层学及精细岩石磁学分析、岩石磁组构分析等有机结合，在塔里木地块柯坪、塔西南、南天山及盆地中南部选择数条地层连续完整、同位素年龄准确的二叠纪火山岩剖面开展精细古地磁学、岩石磁学等研究，获得塔里木大火山岩省形成阶段（20Myer）的精细古地磁数据。以期利用精细的、高质量的古地磁研究来配合塔里木地块二叠纪大火山岩省近年来的重要研究进展，为揭示其重大构造意义、刻画板块运动学时空变化细节和古地理重建提供可靠的数据支撑，为定量研究塔里木地块古生代古地理环境、洋陆演化变迁过程、海相烃原岩的分布与成藏环境，古亚洲洋和古特提斯洋的形成演化，以及中国乃至亚洲整体构造的形成和发展提供可靠基础。

石炭—二叠纪时期被认为是塔里木地块由古全球构造运动机制向新全球构造运动机制转化的重要时期。在这一转折期，板块内部经历了大规模的岩浆活动，构成了中国境内的又一个大火成岩省。本文对塔里木二叠纪大火成岩省进行了系统的岩石磁学、古地磁场方向与强度研究，获得了早-中二叠世库普库兹曼组与开派兹雷克组5个喷发旋回玄武岩及其沉积岩夹层的古地磁方向结果；同时于开派兹雷克组第五层玄武岩中获得了通过国际公认筛选标准的古强度数据，为国际大火成岩省古强度数据库增添可靠的基础数据。目前，部分研究成果已经公开发表或者是正在发表过程中。我们的研究结果结合前人发表数据表明, （1）塔里木地块、哈萨克斯坦地块与西伯利亚地块在早二叠世已完成了碰撞拼合，古亚洲洋的闭合时间上限应在早二叠世；现今位于塔里木地块东南缘的柴达木地块于晚二叠世与塔里木地块完成碰撞拼合，成为了欧亚大陆的一部分；塔里木地块与羌北地块在早二叠世时期还相距甚远，说明这一时期两地块间的古特提斯洋还具有很大的规模；早二叠世开始，古特提斯洋盆开始俯冲消减，直至晚三叠世塔里木地块与羌北地块完成碰撞拼合，两地块间的古特提斯洋盆也于该时期完成闭合。（2）在齐亚曼反极性期的开始与结束阶段，地球磁偶极子场均处于低能量的状态，但在超静磁期内，地球磁偶极子场的低能量状态并不是一直保持不变的，地球磁场强度在齐亚曼反极性期内很有可能是波动的；本项目获得的中二叠世末的地磁场强度异常高值，可能指示了一次重要的地球动力学过程。这个古强度新数据与峨眉山大火山岩省及全球其他类似地幔柱的对比，具有十分重要的地球动力学意义。