贵州镇远地区钾镁煌斑岩产出控制因素浅析

Controlling Factors of Lamprophyre’s Occurrence in the Zhenyuan Area of Guizhou Province

贵州镇远马坪钾镁煌斑岩为我国发现的第一个含原生金刚石的钾镁煌斑岩,其时代为加里东中期。根据区内当时沉积建造的特点,结合钾镁煌斑岩常包含早期捕虏体的情况,尤其是区内钾镁煌斑岩主要产于加里东期北东向背斜构造翼部拐点范围的事实,认为区内钾镁煌斑岩的侵位应发生在加里东期沉积建造结束褶皱构造开始时刻。加里东构造运动先是沉积建造的塑性变形褶皱造山,岩层能干化后才开始发育大量断裂构造。纵弯褶皱在挤压作用背景下,因褶皱拐点存在拉伸和剪切的应力而构成透入性构造软弱部位,被深部岩浆热力所突破而成为上涌侵位及喷发通道。区域上,四堡期东西向基底断裂构造控制区内钾镁煌斑岩东西向带状分布,而加里东期褶皱及其拐点控制钾镁煌斑岩体(群)的产出,因此金刚石的找矿勘查应主要在有金刚石找矿信息的褶皱构造拐点范围开展。

The Maping lamprophyre in the Zhenyuan area of Guizhou Province is the first one containing primary diamonds discovered in China, which was formed in the middle Caledonian period. In light of features of sedimentary formations, the fact that lamprophyre often contains early xenoliths and that this rock occurs at bending points of flanks of the NE-trending anticlines of the Caledonian period, this work suggests that this rock intruded in the Caledonian when sedimentary formations have ended folding. In the early Caledonian tectonic movement, sedimentary formations firstly underwent plastic transformation to form folds and mountains, and then a large number of fracture structures developed. With compressive and shear stresses, fold inflections of vertical bending folds formed penetrative weak-strueture portions, which can serve as migration conduits for magma due to deep magmatic thermal up- welling. The EW-trending basement faults in the Sibao stage controlled the distribution of the EW-trending lamprophyre, and the Caledonian folds and their bends exerted a key control on lamprophyre bodies. It is thus considered that the diamond survey in this region should be conducted around the fold bends with diamond prospecting information.