滇西卓潘碱性杂岩体成因及其成矿意义

发布时间：2018-04-17 00:28

  本文选题：卓潘碱性杂岩体 + 电子探针　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：卓潘碱性杂岩体位于澜沧江断裂带东部,是金沙江-哀牢山新生代富碱侵入岩带的重要组成部分,侵位于兰坪走滑拉分盆地西部,本文主要从岩石学、矿物学与地球化学角度对该碱性杂岩体进行系统研究,进而探讨了该杂岩体的成因和就位机制。卓潘杂岩体主要由辉长岩、辉石岩及正长岩组成,主要含有钙质的辉石、碱性长石、镁质的黑云母等矿物,辉石岩、正长岩风化均较为严重,辉石岩、正长岩在野外多呈疏松状。岩体具有富碱、高钾低TiO2、高Al2O3的特征,岩石中赋存的辉石为透辉石,属钙质辉石,钙质辉石出现与该岩体含有高含量的Ca、K有关;辉石的结晶温度范围介于1070-1490℃之间。黑云母高TiO2,结构式中低AlⅥ,反映卓潘杂岩体岩浆体系具有富铁、高氧逸度的特征。角闪石为韭闪石,具有较高含量的硅、钙和镁、低碱性的化学特征,卓潘杂岩体中的黑云母和辉石均为非碱性暗色矿物。稀土元素地球化学表明,各类样品稀土配分模式均为明显的右倾轻稀土元素富集模式,轻稀土元素总量高于重稀土元素总量,且轻稀土元素相比于重稀土元素分异明显,无明显铕异常。微量元素地球化学特征显示该岩体相比于原始地幔富集K、Rb、Sr、Ba等大离子亲石元素,相比于原始地幔较为亏损高场强元素(Nb、Ta、Ti),表现出该岩体具有壳源的特征,即大离子亲石元素更为富集,说明该杂岩体在形成过程中可能受到地壳物质的混染。本文通过锆石U-Pb年龄获得卓潘杂岩体的成岩年龄应在34.88-35.50Ma之间,该成岩年龄与区域上其他碱性岩体成岩时间一致,均形成于新生代,属喜山期构造阶段。Sr-Nd-Pb同位素比值:87Sr/86Sr介于0.708011-0.709619之间、143Nd/144Nd介于0.512209-0.512297之间、206Pb/204Pb介于18.7248-19.2883之间,207Pb/204Pb介于15.6749-15.7202之间,208Pb/204Pb介于39.0759-40.8077之间。分析表明,卓潘碱性杂岩体的岩浆源区是EMⅡ型富集地幔,其岩浆源区可能是经历过壳幔相互作用的富集地幔。利用与黑云母成分相关的构造环境判别图解,并结合地球化学特征,认为卓潘碱性杂岩体应形成于后碰撞的挤压向伸展环境转换的构造背景。卓潘岩体位于金沙江-哀牢山走滑断裂带中段,拉伸强度大、断裂深度大,导致岩浆的起源深度大,进而导致该岩体具有与区域上其他岩体不同的地质特征。
[Abstract]:The Zhuopan alkaline complex is located in the eastern part of the Lancang River fault zone. It is an important part of the Cenozoic alkali-rich intrusive rock belt from Jinshajiang to Ailaoshan. It is located in the western part of the Lanping strike-slip pull-apart basin.The mineralogy and geochemistry of the alkaline complex are systematically studied, and the genesis and emplacement mechanism of the complex are discussed.The Zhuopan complex is mainly composed of gabbro, pyroxenite and syenite, mainly containing calcareous pyroxene, alkaline feldspar, magnesia biotite and other minerals, pyroxenite and syenite weathering more seriously.Syenite is loose in the wild.The rock mass is characterized by rich alkali, high potassium and low TIO _ 2, and high Al2O3. The pyroxene in the rock is diopside, which belongs to calcareous pyroxene. The occurrence of calcareous pyroxene is related to the high content of CaOK in the rock mass, and the crystallization temperature range of pyroxene is between 1070-1490 鈩，

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