松潘—甘孜造山带南部龙溪沟伟晶岩脉地球化学特征及地质意义

戴元; 刘亮; 吕丰强; 陈红波; 补祥誉; 黄承权

戴元,刘亮,吕丰强,陈红波,补祥誉,黄承权.松潘—甘孜造山带南部龙溪沟伟晶岩脉地球化学特征及地质意义[J].贵州地质,2022,39(3):251-261

松潘—甘孜造山带南部龙溪沟伟晶岩脉地球化学特征及地质意义

Geochemical Characteristics and Geological Significance of Longxigou Pegmatite Dikt in the Southern Songpan-Ganzi Orogenic Belt

投稿时间：2022-02-03

DOI：

中文关键词: 松潘—甘孜造山带伟晶岩脉 A型花岗岩钾玄岩构造环境

英文关键词:Songpan-Ganzi Orogenic Belt Pegmatite Vein A-type Granite Potassic Basalt Tectonic environment

基金项目:中国地质调查局基金项目四川九龙乌拉溪1∶5万4幅区域地质矿产调查(12120113048600)。

作者	单位
戴元	平武县自然资源局，四川平武622550
刘亮	百色市自然资源局，广西百色533000 四川省地质矿产勘查开发局川西北地质队，四川绵阳621010
吕丰强	四川省地质矿产勘查开发局川西北地质队，四川绵阳621010
陈红波	百色市自然资源局，广西百色533000
补祥誉	百色市自然资源局，广西百色533000
黄承权	百色市自然资源局，广西百色533000

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中文摘要:

龙溪沟伟晶岩位于松潘—甘孜造山带南部，岩脉侵位于褶皱的三叠系地层中，岩石类型为花岗岩。为探讨龙溪沟伟晶岩脉源区、构造背景、成因机制等，对其地球化学特征进行了研究；其SiO₂含量为6646%7408%，Al2O3含量为1371%1907%，K2O 含量376%716%，富铝高钾，过碱指数[NK/A] 068083，里特曼指数(σ)185375，铝饱和指数(A/CNK)值109136，为过铝质富钾钙碱性A型花岗岩系列(钾玄岩系列)。∑REE为706×10-65029×10-6，所有样品具有相似的平坦右倾海鸥型稀土元素配分模式(A型)，LREE/HREE为221643，(La/Yb)N=10351240，具负Eu(024137，平均068)、负Ce异常(δCe=073095)，显示同源岩浆演化特征。富集大离子亲石元素K、Rb，具明显的Ta、Nb负异常，Ba、Nb、Sr、P和Ti亏损；104×Ga/Al值变化于247435；CaO/Na2O值01028，均＜03，表明伟晶岩岩脉源区物质应主要为贫长石、富粘土的泥质岩。在构造环境判别图解中，样品多落入碰撞后(板内)环境，属A型花岗岩中的PA(或A2)型花岗岩，岩浆起源于后碰撞岩石圈拆沉、软流圈上涌所携带的热量诱发中下地壳发生部分熔融，造成岩浆上侵就位，从而形成以地壳岩浆为主体，伴有地幔物质加入的龙溪沟伟晶岩岩脉(壳幔混合型)。

英文摘要:

Longxigou pegmatite is located in the south of Songpan Ganzi orogenic belt，the dyke intrudes into the fold Triassic strata and the rock type is graniteThe geochemical characteristics of longxigou pegmatite vein are studied in order to discuss its source area，tectonic background and genetic mechanismThe content of SiO₂ is 66.46%74.08%，Al2O3 content is 13.71%19.07%，K2O content is 3.76%7.16%It is rich in aluminum，high in potassium and alkali index [NK / A]0.68%0.83，Richman index (σ)1.85%3.75，and aluminum saturation index (A/CNK)1.09%1.36 are peraluminous K-rich calc alkaline A-type granite series (k-basanite Series).Σ REE is 7.06-50.29 × 10-6，and all samples have a similar flat right dipping seagull REE distribution pattern (type A)，LREE/HREE is 2.21%6.43，(La/Yb)N = 10.35%12.40，with negative Eu (0.24%1.37，average 0.68)，negative Ce anomaly (δ CE = 0.73%0.95)，showing the evolution characteristics of the same source magmaK and Rb are rich in large ion lithophile elements，with obvious TA and Nb negative anomalies，and Ba，Nb，Sr，P and Ti are deficient；104×Ga/Al values vary from 2.47 to 4.35；CaO/Na2O values range from 0.1 to 0.28，all of which are less than 0.3，indicating that the materials in pegmatite vein source area are mainly feldspar poor and clay rich argillaceous rocksIn the diagram of tectonic environment discrimination，most of the samples fall into post collisional (intraplate) environment，belonging to PA (or A2) type granite in A-type graniteThe magma originates from the heat brought by post collisional lithosphere delamination and asthenosphere upwelling，which induces partial melting of the middle and lower crust，resulting in magma upwelling and emplacement，thus forming longxigouwei，which is dominated by crustal magma with the addition of mantle material Crystalline vein (crust mantle mixed type).

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