滇东南建水官厅地区中晚二叠世基性–超基性岩墙群的发现意义

The Significance of Discovery on the Basic-Ultrabasic Dike Swarms of Mid-Late Permian in Jianshui Guanting Area, Southeast Yunnan

摘要: 笔者在滇东南建水官厅地区中晚泥盆世–二叠纪(D-P)深灰色薄层状泥晶灰岩夹硅质岩、硅质条带灰岩、基性火山岩的地层中首次发现了基性–超基性岩墙群。现有资料表明：官厅地区经历了中晚泥盆世–二叠纪长期的区域性伸展作用，在晚二叠世达到了颠峰状态，爆发了大范围、大规模的基性、(局部)酸性火山喷发活动，喷发堆积了巨厚的火山岩(他痴组)，并伴随着同期异相的基性–超基性岩墙群的顺层侵入。在岩浆演化过程中不存在地壳物质混染，Ni、Cr含量较高，均显示具有原始地幔岩浆的特点。因此，一方面强烈的伸展作用导致官厅地区在中–晚二叠世时期的地壳厚度大大减薄，地幔源区的基性岩浆在上升侵位过程中没有受到地壳物质的混染；另一方面强烈的伸展作用使官厅地区在中–晚二叠世时期发生了巨烈的沉降、裂陷，甚至出现了初始洋盆或裂谷中心地带，由此奠定了个旧裂谷盆地的形成。个旧裂谷盆地经个旧–普者哨–丘北–者太延伸至贵州省境内的册亨地区，完成了与区域上右江裂谷型盆地的全面接轨。官厅地区晚中–晚二叠世基性–超基性岩墙群的发现为深入研究区域上右江裂谷盆地的形成及发展、演化提供了全新的岩石学信息。

Abstract: In this paper, the basic-ultrabasic dike swarms were first discovered in the middle-late devo-nian-Permian charcoal grey flaggy micrite limestone with siliceous, siliceous banded limestones, basic volcanic rock in the Jianshui Guanting area. The existing data showed that Guanting area ex-perienced D-P long-term regional extensional regime. The extensional regime was attained peak form in the late Permian. Accurred large range, large scale, local acid volcanic eruption activities had happened and very thick volcanic rocks (Tachi Formation) had accumulated in this period, along with the intrusion of the basic-ultrabasic dike swarms of synchrono-heteropic facies. Three basic-ultrabasic dike swarms samples respectively fall into mid-oceanic ridge tholeiite area，ocean ridge area and ocean floor area on the FeO*-MgO-Al₂O₃ graph, FeO/MgO-TiO₂ graph. The δEu in the rocks closed to 1, Nb* > 1. There was no hybridization of crust materials during the progress of magma evolution. The high content of Ni and Cr has the characteristics of the primary mantle magma. This text thinks that strong extensional regime made the Guanting area violently settled and split-depressed, even the initial ocean basin and the rift heartland have appeared in the Mid-late Permian. Thus, the formation of Gejiu rift basin was established. Gejiu rift basin by Ge-jiu-Puzheshao-Qiubei-Zhetai extend to Ceheng of Guizhou province, completed with Youjiang rift basin connection on regional range. The discovery of the Mid-late Permian basic-ultrabasic dike swarms provided a new lithology information for deeply study the formation, development and evolution of Youjiang rift basin on regional range.