龙门山构造带早三叠世古地磁新结果及其对四川盆地构造旋转的制约  

New paleomagnetic result of Early Triassic rocks from the Longmenshan belt and its tectonic implications

作　　者：叶小舟[1] 孙知明[1] 李海兵[2] 曹勇[1,3] 张蕾[1,4] 王雷振[5] 赵越[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国地质科学院地质研究所,北京100037 [3]中国地质大学(北京),北京100083 [4]中国地质大学(武汉),湖北武汉430074 [5]中国建筑材料工业地质勘查中心江苏总队,江苏南京211135

出　　处：《地质通报》2016年第6期971-978,共8页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41330211);中国地质调查局项目(编号:12120115026901)

摘　　要：选择龙门山构造带剑阁县竹园镇马鹿乡地区早三叠世飞仙关组,开展了详细的古地磁研究。通过对飞仙关组9个采样点灰岩、泥质灰岩样品系统的古地磁测试,热退磁结果分离了一组高温特征剩磁分量。样品的高温剩磁分量具有正、反双极性,且通过了倒转检验,表明它们很可能代表了岩石形成时的原生剩磁。构造校正后的特征剩磁方向为:偏角D_s=42.3°,倾角I_s=12.6°,α_(95)=9.4°;相应的极位置为:经度φ_p=219.3°E,纬度λ_p=42.9°N,d_p/d_m=4.9°/9.6°,古纬度plat=6.4°。对比稳定的四川盆地早三叠世的古地磁结果,获得龙门山构造带相对于稳定四川盆地发生了1.2°±4.4°的顺时针旋转运动,为此从构造古地磁角度,提出龙门山构造带和四川盆地自早三叠世以来,在动力学上已是统一的构造单元,并没有发生明显的构造旋转作用。This paper reports new Early Triassic paleomagnetic results from Jiange County （32.2° N, 105.3° E） in the Longmenshan belt. Based on the stepwise thermal demagnetization of limestone and argillaceous limestone specimens from 9 sampling sites, the authors revealed a characteristic remanent magnetism （ChRM）. Both normal and reversal polarities were observed in the study section, and the high temperature components pass reversal tests at the 95%confidence level. This indicates that the ChRM may represent the primary remanent magnetism of the Early Triassic limestone. The tilt-corrected mean direction for the Early Triassic is Ds/Is=42.3°/12.6° withα95=9.4° and N=9 sites, corresponding to a paleopole at 42.9°N, 219.3°E, dp/dm=4.9°/9.6°. A comparison with the Early Triassic poles from the Sichuan basin shows that insignificant post-Early Triassic motion may have occurred between the Longmen shan belt and the Sichuan basin. It is thus considered that the Sichuan basin has not experienced whole-scale vertical axis rotation since the Early Triassic.

关 键 词：龙门山构造带 早三叠世 古地磁学 四川盆地 构造旋转 

分 类 号：P534.51[天文地球—古生物学与地层学]