华南地块中三叠统巴东组红层磁倾角浅化效应  

Paleomagnetic Inclination Shallowing in Badong Formation Red Beds,Middle Triassic of South China Block

作　　者：韩露 黄宝春[1] 赵千 薛艺 李能韬 Umar Farooq Jadoon HAN Lu;HUANG Baochun;ZHAO Qian;XUE Yi;LI Nengtao;Umar Farooq Jadoon(Key Laboratory of Orogenic Belts and Crustal Evolution(MOE),School of Earth and Space Sciences,Peking University,Beijing 100871)

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《北京大学学报（自然科学版）》2022年第3期469-480,共12页Acta Scientiarum Naturalium Universitatis Pekinensis

基　　金：国家自然科学基金(41774074,92055025)资助。

摘　　要：对华南地块中三叠统巴东组红层样品进行系统的岩石磁学和古地磁学研究,采用高场等温剩磁各向异性(hf-AIR)方法,识别出巴东组红层的磁倾角浅化因子f=0.63。岩石磁学研究结果显示,巴东组红层的主要载磁矿物为赤铁矿和少量磁铁矿;磁化率和高场等温剩磁各向异性组构均指示其具有典型沉积组构特征,表明未遭受后期构造应力改造。高温特征剩磁分量为碎屑赤铁矿所携带,具有单一负极性,并在95%置信水平上通过褶皱检验,与前人在同一剖面不同位置获得的以正极性为主的古地磁方向一致。该特征剩磁方向在地层校正后的平均方向为Ds=222.1°,I_(s)=−27.2°(α95=8.7°),对应古地磁极为48.1°N,215.5°E(A_(95)=8.4°)。对包括本文数据在内的华南中三叠世红层高质量古地磁极数据(Q≥5)用f=0.63进行统一校正后,获得平均古地磁极为48.5°N,207.6°E(A_(95)=10.7°)。对比华北地块同样经hf-AIR方法浅化校正后的早三叠世古地磁极,两者在其东部参考点上的古纬度完全一致,验证了前人提出的华南华北中生代剪刀式旋转拼合模型。Paleomagnetic and rock magnetic studies are conducted on Middle Triassic Badong Formation red beds from the South China Block(SCB).The anisotropy of high-field isothermal remanent magnetization(hf-AIR)method indicates that the characteristic remanent magnetization(ChRM)is significantly affected by inclination shallowing with a flattening factor f=0.63.Rock magnetic analysis indicates that hematite is the main magnetic carrier with a subordinate contribution from magnetite.Anisotropy of magnetic susceptibility(AMS)and hf-AIR results both show a typical depositional fabrics without significant distortion from tectonic stress.The ChRM,carried by detrital hematite,has a unique negative polarity and passes the fold test at the 95%confidence level.The ChRM yields a common mean direction with that previously reported from the same section.The ChRM yields a tilt-corrected mean direction of D_(s)=222.1°,I_(s)=−27.2°(α95=8.7°)and a corresponding paleomagnetic pole at 48.1°N,215.5°E(A_(95)=8.4°).Combined with high quality published data(Q≥5)for the Middle Triassic,the mean paleomagnetic pole for the SCB is corrected to 48.5°N,207.6°E with A_(95)=10.7°by using a flattening factor f=0.63.Comparing this inclination shallowing-corrected mean paleomagnetic pole with Early Triassic pole for the North China Block,which has also inclination shallowing-corrected by the hf-AIR method,it shows that paleolatitudes of these two blocks at their eastern reference points are exactly compatible.This further confirms that the South and North China blocks experienced a scissors-like rotational collision during the Mesozoic times,as proposed by previous researches.

关 键 词：华南地块 巴东组红层 磁倾角浅化校正 高场等温剩磁各向异性 古纬度 

分 类 号：P318.4[天文地球—固体地球物理学]