摘要
磁倾角是古纬度的记录者,对许多构造活动有着很好的揭示作用。但在青藏高原,沉积物的磁倾角往往要比火山岩或欧亚极预测的值要小,这很大程度上制约了对该地区构造演化历史的了解。本文应用E/I统计分析法对青藏高原东北部几个典型山间盆地的已有古地磁数据进行分析,发现该地区沉积物中普遍存在的10°～20°磁倾角浅化可以通过该法矫正,揭示出该地区的磁倾角浅化可能是由于沉积物在沉积过程中或沉积后的压实作用造成;同时也表明该地区在晚新生代以来南北向缩短量并不是十分显著,至少是在古地磁研究的误差范围以内。
The north East Tibetan Plateau is the young outgrowth part of the Tibetan Plateau. Recent paleomagnetic data obtained from sedimentary rocks of the region appear to show a pronounced bias towards too-shallow inclinations, with respect to Eurasia reference apparent polar wander paths or same age volcanic rocks, where the causes of such bias are still under debate. The Linxia,Jiuquan and Qaidam Basins are three typical intramountain basins of the north East Tibetan Plateau. Magnetostratigraphy studies in the three basins have provided large paleomagnetic data set. The work of this paper is to utilize the existing large paleomagnetic data set to perform the recently published Tauxe and Kent＇s ＂Elongation/Inclination＂ statistic analyses for the three basins, and combined with other studies, to discuss the possible causes of the bias inclination in the region. The analyses of the large paleomagnetic data set of the three basin indicate that, the Linxia Basin has a mean paleomagnetic direction of D = 7.8°, I--44. 1°, 0%5 = 2. 1°during ca. 29.0 -1.8Ma,where the Jiuquan Basin has a mean of D =0.4°, I=45.4° ,a95 = 2.4° during the last 13Ma,and the Qaidam Basin has a mean of D=7.4°,I=40.9°,0%5 = 1.7° during ca. 15.0 - 1.8Ma. The expected inclination for the three basins is 56.4~,59. 5~and 57. 7° at 3.1Ma, or 58.0° ,60. 9°and 59. 1 °at 11.9Ma for the Linxia,Jiuquan and Qaidam Basins,respectively. These obtained mean inclinations are 10° -20° shallower than those expected from the Eurasia reference apparent polar wander paths. By utilizing the E/I method, those biased inclinations have been corrected and match well with those expected from the Eurasia reference apparent polar wander paths. Combined with other studies in the region, we believe that shallow inclinations of the sedimentary rocks are a common phenomenon of the north East Tibetan Plateau,and the most likely cause of the inclination bias was due to syn-/or post-depositional compaction of the sedimentary rocks. In addition, as these obtained shallow inclinations can be corrected by the E/I method,and the corrected inclinations match well with the expected inclinations from the Eurasia reference apparent polar wander paths, we believe that the north-southward shortening in the north East Tibetan Plateau was insignificant since Neogene time, at least the amount of shortening is within the paleomagnetic study error range.
出处
《第四纪研究》
CAS
CSCD
北大核心
2012年第4期588-596,共9页
Quaternary Sciences
基金
中国科学院"百人计划"国外杰出引进人才计划择优支持项目
国家重点基础研究发展规划项目(973项目)(批准号:2011CB403006)
国家自然科学基金委创新研究群体科学基金项目(批准号:41021001)共同资助
关键词
青藏高原东北部
磁倾角浅化
E/I法
同-后沉积压实
northeast Tibetan Plateau, inclination bias, E/I correction, syn-/or post-depositionalcompaction
