江南造山带中段古地磁特征与构造意义

地体构造是当代地球科学研究的前沿,而古地磁学则是查明地体构造存在和活动演化的最有效方法之一。本文以江南造山带中段赣北地区为例,进行了地体构造的古地磁研究。工作表明,赣北前震旦纪构造区可划分为两个各具特色的地体构造,即怀玉地体和九岭地体。它们在碰撞拼贴前古纬度不同,彼此远离,视极移路径各异,为相互独立的地质体。到震旦纪,经长距离迁移运动和碰撞拼合,两个地体已实现统一,古纬度、古磁极位置基本一致。磁偏角研究揭示,两个地体在碰撞拼贴中发生过一次显著的逆时针旋转运动,反映一个斜向碰撞——左旋走滑剪切或人坞式的碰撞缝合动力学过程。

PALEOMAGNETISM FEATURES AND ITS TECTONIC SIGNIFICANCE IN THE MIDDLE PART OF THE JIANGNAN BALT,SOUTH CHINA

The paper studies the paleomagnetism features of the Proterozoic rocks in the middle part of the Jiangnan Belt. Our researches indicate that two distinct terranes, the Huaiyu Terrane and the Jiuling Terrane, can be distinguished on the basis of the analysis of the stratigraphic geology, the tectonics and the paleomagnetism. Paleomagnetic results reveal that before the late Proterozoic collision and amalgamation, the two terranes had different paleolatitudes and different curves of apparent polar wandering. During the early Sinian, the two terranes had finished their collision and amalgamation, and the middle part of the Jiangnan Belt became a composite terrane tectonics. The research of the declination indicates that a counterclock rotation movement between the Huaiyu and the Jiuling had ever occurred from the late Proterozoic to the early Sinian, implicating a suturing geodynamic process from the collision in an oblique direction to sinistral strike-slip type,or "docking" type.