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SiO_(2)含量为66.46%74.08%,Al_(2)O_(3)含量为13.71%19.07%,K 2O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^(-6)50.29×10^(-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;10^(4)×Ga/Al值变化于2.474.35;CaO/Na_(2)O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)。
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 SiO_(2) is 66.46%74.08%,Al_(2)O_(3) content is 13.71%19.07%,K_(2)O 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).ΣREE 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(δCE=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;10^(4)×Ga/Al values vary from 2.47 to 4.35;CaO/Na_(2)O 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 A_(2))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).
作者
戴元
刘亮
吕丰强
陈红波
补祥誉
黄承权
DAI Yuan;LIU Liang;LV Feng-qiang;CHEN Hong-bo;BU Xiang-yu;HUANG Cheng-quan(Pingwu Natural Resources Bureau,Pingwu 622550,Sichuan,China;Baise City Natural Resources Bureau,Baise,533000,Guangxi,China;Northwest Sichuan Geological Team,Sichuan Bureau of Geology and Mineral Exploration and Development,Mianyang 621010,Sichuan,China)
出处
《贵州地质》
2022年第3期251-261,共11页
Guizhou Geology
基金
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)。
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
Songpan-Ganzi Orogenic Belt
Pegmatite Vein
A-type Granite
Potassic Basalt
Tectonic environment
