岩墙群圆柱状节理的发现和成因机制探讨

在鲁西地区前寒武纪基性岩墙群内发育一种罕见的原生圆柱状节理，由同轴圆柱状节理和放射状节理组成，垂直于岩墙走向，沿岩墙走向排列，是一种指示岩浆水平侵位的流动构造。岩墙发育圆柱状节理表明出露的是岩墙的顶部，反映基性岩墙群侵位时岩浆具有黏滞性剪切作用的流变学特征。柱状节理长轴的倾伏向垂直岩墙的两壁，可以反映岩墙的产状。岩墙圆柱状节理的倾伏角反映了岩墙所在地块的掀斜程度。岩墙发育圆柱状节理表明岩墙侵位时地块已经处于上地壳脆性构造环境，中元古代鲁西地区是一个脆性伸展的大地构造环境。

The Discovery and Origin of the Round Columnar Joints in the Basic Dyke Swarms

A rare kind of primary round columnar joints is developed in the basic dyke swarms in the western Shandong,which is made of the radial joints and the round columnar joints with same axis vertical to the strike of the dyke, arranged one by one along the strike of the dyke. The round columnar joints are one of the flow structures showing the horozontal emplacement of basic dyke swarms. The round columnar joints show that the basic dyke has rheological behaviour of the viscous shearing in magma emplacement.Usually the dip of the axis of round columnar joints vertical to the dyke boundary shows the dip of the dyke and the tilting of the block with the dyke. The round columnar joints show that the dyke swarms are in upper crust brittle tectonic setting, and the western Shandong block is brittle extensional in the Mesoproterozoic time.