阿拉善地块二叠纪古地磁研究

The AlashanTerrane (ALT) that bridged the Central Asian Orogenic Belt, the Tarim, the Qaidam, and North China Block (NCB), is considered as the key region in understanding the tectonic evolution of Northern China. However, there are ongoing debates on multiple academic questions, such as whether the ALT belongs to NCB, and when the ALT and NCB unified to the whole one. The great stratigraphic hiatus in the NCB from the Upper Ordovician to the Lower Carboniferous has caused the lack of paleomagnetic data during that period，making the difficulty to compare the mid-Palaeozoic paleomagetic connections between NCB and ALT in details. And the key to resolve the above controversies is to re-carry out detailed paleomagnetic study on Post-Permian strata in the ALT. However, the paleomagnetic data of the Permian for ALT need to be improved. So, Paleomagnetic study of Permian units in the ALT will be focused on in the project to obtain reliable paleomagnetic poles, and to perfect apparent polar wander paths (APWP) and the variation curve of paleolatitudes. And combined with previous researches, the tectonic relationship and collision-related kinematic processes between the ALT and NCB will be explored.

阿拉善地块位于中亚造山带、塔里木板块、柴达木板块和华北板块的枢纽地带，是了解中国北方各板块构造演化的关键。但是，阿拉善地块是否属于华北板块、二者何时拼合为统一的整体等多个学术问题仍然存在争议。华北板块因上奥陶系至下石炭系地层普遍缺失造成该期间的古地磁数据缺乏，导致无法对比华北板块与阿拉善地块古生代中期的古地磁亲缘性。因而，对比二者二叠纪以来的视极移曲线则是解决这些问题的关键。但是目前阿拉善地块二叠纪古地磁数据仍需完善，因此本项目拟重点对阿拉善地块二叠纪地层开展全面的古地磁学研究，获得该时代可靠古地磁极，完善阿拉善地块的视极移曲线，对比华北板块同时期古地磁数据，探讨阿拉善地块与华北板块之间的构造亲缘性。

阿拉善地块位于中亚造山带、塔里木板块、柴达木板块和华北板块的枢纽地带，是了解中国北方各板块构造演化的关键。但是，阿拉善地块是否属于华北板块、二者何时拼合为统一的整体等多个学术问题仍然存在争议。华北板块因上奥陶系至下石炭系地层普遍缺失造成该期间的古地磁数据缺乏，导致无法对比华北板块与阿拉善地块古生代中期的古地磁亲缘性。因而，对比二者二叠纪以来的视极移曲线则是解决这些问题的关键。但是目前阿拉善地块二叠纪古地磁数据仍需完善，因此本项目拟重点对阿拉善地块二叠纪地层开展全面的古地磁学研究，获得该时代可靠古地磁极，完善阿拉善地块的视极移曲线，对比华北板块同时期古地磁数据，探讨阿拉善地块与华北板块之间的构造亲缘性。本项目通过对阿拉善地块东部二叠纪典型剖面的古地磁研究，得到该地区晚二叠世古地磁极位置为：λ=29.2°N，Ф=14.4°E (dp=4.7°，dm=8.4°)，当时古纬度是16.6±6.2°N。该古地磁极与Yuan et al., 2015在贺兰山、中卫、景泰得到的晚二叠世古地磁极为λ=26.2°N，Ф=18.0°E(dp=7.5°，dm=13.3°)，在误差范围内一致。这几个剖面分布范围包含了宁夏贺兰山地区和甘肃河西走廊，通过区域一致性检验。结合前人研究成果，本项目最终建立了阿拉善地块从早石炭世到中三叠世视极移曲线。阿拉善二叠纪相对于华北同时代古地磁极(λ=50.3°N，Ф=355.1°E，A95=5.7°，N=11，Yang et al.,2001 )存在30.5±5.7°差异，如果将阿拉善东部的二叠纪-三叠纪视极移曲线绕欧拉极(44°N，84°E)做逆时针旋转31°后与华北地块同时代古地磁视极移曲线重合。表明在二叠纪时，阿拉善与华北板块并非同属一个块体，二者完成拼合应该是发生在三叠纪以后。