摘要
岩石学及同位素地质学研究均表明，含榴辉岩的胶南地块在高温高压变质后经历过快速降压过程，这一过程在构造上表现为隆升－伸展构造。这种构造在胶南地块有两种形式：其一为地块内部的垂向缩短、水平向伸展构造，以浅色脉体的变形为特征，并反映出从深层次向浅层次的转化；另一为地块边部的正滑型构造带，可分为早期塑性变形和叠加于其上的且分布于地块外侧的晚期脆性－半脆性变形。反映运动矢量的拉伸线理走向呈放射状：北段走向近南北，中西段近东西。这是地块北西侧的变形特点，东南侧情况不明。北部正滑型剪切带中白云母40Ar／39Ar坪年龄表明，伸展构造的时代为146Ma±。这次构造运动可能由俯冲至上地幔的大洋板块与地壳拆离造成的重力均衡所引起，其结果不仅使得大陆地壳上隆，而且还使榴辉岩从下地壳上升至地表。
Studies of petrology and isotope geology have shown that the eclogite-bearing Jiaonan block has experienced a rapid decompression after its high-temperature and pressure metamorphic process, as reflected by a uplift-extension structure. This uplift-extension structure takes two forms in the Jiaonan block. One is vertical shortening and horizontal extension structure in the internal block and characterized by the deformation of light veins,reflecting the inversion from deep level to shallow level as well' Another is a normal slip structure on the margin of the block which consists of the plastic deformation in the early period and the superimposed brittle-semi-brittle deformation distributed in the outer zone of the block in the late period. The strikes of stretch lineations which reflect the movement vectors show a radiation pattern: they are in NS direction nearly in the north part and nearly EW direction in the central and west parts. This is the deformational characteristic in the north-west part of the block. As to the south-east f the situation is nuclear. According to the 40Ar/39Ar plateau age of muscovite taken from the normal-slip shear zone in the north,the age of the stretching structure is 146Ma±.This tectonic movement may be caused by the gravitational isostasy which has been resulted from the detatchment of the oceanic plate subducted into the upper mantle from the crust. This has resulted not only the uplift of the continental crust,but also the rise of eclogites from the lower crust to the surface.
出处
《山东地质》
1997年第1期67-76,共10页
Geology of Shandong
