华北克拉通东北缘改造:来自吉林辉南地区构造热事件的古地磁记录

Reconstruction of the northeastern margin of the North China Craton:Paleomagnetic records from tectonic thermal events in Huinan of Jilin Province

华北克拉通东北缘处于构造运动活跃地区,古地磁研究可为构造演化和岩浆热事件提供依据。笔者在吉林辉南地区中寒武统32个采点共采集246块样品进行了岩石学、岩石磁学及系统热退磁实验。古地磁实验表明,徐庄组砂质泥岩主要磁性矿物是赤铁矿和磁铁矿,张夏组灰岩主要磁性矿物是颗粒较小的磁铁矿和黄铁矿,且均发生了重磁化,并记录了稳定的中温分量,前者中温分量地理坐标平均方向为D/I=10.9°/50.8°,α_(95)=11.7°,对应的极位置为76°N,264.6°E,A_(95)=13°,与早白垩世岩浆活动记录的古地磁极位置一致;后者中温分量地理坐标平均方向为D/I=29.1°/59.0°,α_(95)=6.5°,对应的极位置为68°N,213.7°E,A_(95)=8.4°,与第四纪火山岩记录的古地磁极位置一致。综合区域地质背景分析,早白垩世—第四纪,吉林辉南及邻区古地磁记录的2次较为强烈的构造热事件,以及因敦化-密山断裂带左旋走滑运动造成的北向运移形成的古纬度差,一定程度上对华北克拉通东北缘起到双重改造作用。

The northeastern margin of North China Craton is located in an active area of tectonic movement.Paleomagnetic study can provide a basis record for tectonic evolution and magmatic thermal events.246 samples were collected from 32 mining sites of the Middle Cambrian in Huinan area,Jilin Province,for petrology,rock magnetism and systematic thermal demagnetization experiments.Rock magnetic study implies that the main magnetic minerals of the Xuzhuang Formation sandy mudstone are hematite and magnetite.The main magnetic minerals of the Zhangxia Formation limestone are magnetite with smaller particles and a small amount of pyrite.Stepwise thermal demagnetization succeeded in isolating the middle-temperature characteristic directions of the samples.The average direction of the Xuzhuang Formation(D/I=10.9°/50.8°,α_(95)=11.7°,corresponding pole position is 76°N,264.6°E,A_(95)=13°),indicates that magmatic activity in the Early Cretaceous affected it.The average direction of the Zhangxia Formation(D/I=29.1°/59.0°,α_(95)=6.5°,corresponding pole position is 68°N,213.7°E,A_(95)=8.4°)were remagnetized which is related to Quaternary volcanic activity.Based on the analysis of regional geological background,at least two strong tectonic thermal events may have occurred from the Early Cretaceous to Quaternary respectively in Huinan area of Jilin Province,which also moved toward north large distance affected by Dunhua-Minshan sinistral slip fault during that time.These magnetic minerals were all remagnetizd and recorded a stable middle-temperature characteristic direction.