甘肃金塔县碱凹井岩体岩石地球化学特征及构造环境分析  

Tectonic Setting and Geochemical Characteristics of the Jianaojing Pluton in Jinta County,Gansu

作　　者：蒲万峰 严镜[1] 汪宏涛[1] 王舒恒 刘景显[1] 

机构地区：[1]甘肃省地矿局第三地质矿产勘查院,甘肃兰州730050

出　　处：《新疆地质》2015年第2期263-269,共7页Xinjiang Geology

基　　金：甘肃省金塔县石板泉一带矿产远景调查(甘财建(2010)254号)资助

摘　　要：甘肃金塔县东北的张家疙瘩一带发育大量侵入岩体，碱凹井岩体出露规模较大，侵入蓟县系平头山组，北东局部侵入石炭系干泉组，岩性主要为二长花岗岩和正长花岗岩。岩石组合类型和岩石地球化学研究表明，碱凹井岩体SiO2含量71.59%-75.86%，平均74.06%，Na2O含量3.73%-4.10%，K2O含量4.55%-4.76%，铝饱和指数A/CNK=1.04-1.20，稀土元素总量为79.95×l0^-6-201.65×l0^-6，（La/Yb）N=1.05-2.24，球粒陨石标准化分布模式图总体呈略微右倾的V字型，具相对平缓的富集轻稀土元素稀土分布模式。重稀土元素分馏不明显且相对亏损，Eu具明显负异常，δEu=0.07-0.36。在微量元素原始地幔标准化蛛网图上，亏损Ba，Nb，Sr，Ti，富集Rb，Th，K。结合区域地质背景认为，该岩体形成于后碰撞伸展作用阶段，可能源于幔源岩浆底侵，导致上覆年轻地壳（可能为洋壳和岛弧建造组成）部分熔融，并发生了较强的结晶分异作用。A large lump intrusive rocks develop in Zhangjiageda area of northeast of Jinta County, Gansu Province. Among them, Jianaojing pluton is the biggest one in the region. The pluton, intruding into Jixian Period Pingtoushan For-mation in the west and south, and Carboniferous Period Ganquan Formation in the northeast, is mainly composed of sye-nogranite and monzonitic granite. Based on detailed field survey, the rock assemblage and geochemistry shows that the SiO2 content in the pluton is 71.59%-75.86%, the average is 74.06%, Na2O content is 3.73%-4.10%, K2O content is 4.55%-4.76%, aluminum saturation index A/CNK=1.04-1.20, and the total rare earth element （REE） between 79.95×l0^-6 and 201.65 ＆#215; l0-6, （La/Yb）N=4.95-28.95. The Chondrite-normalized REE pattern was slightly rightist Figure V-shaped, with a relatively flat LREE enriched REE patterns. Besides, heavy REE fractionation is not obvious and relatively at loss. Moreover, Eu has obvious negative anomaly, withδEu=0.07-0.36. In the trace element spider diagram, loss is marked as Ba, Nb, Sr, Ti and the enrichment as Rb, Th, K. Combined with regional geological background, it is inferred that the pluton emplaced in post-collision setting. It may be resulted from partial melting of the overlying young crust （possibly be constructed by oceanic crust and island arc） caused by bottom invasion of mantle-derived magmas and a strong crystallization and differentiation occurred.

关 键 词：北山 碱凹井 富碱高钾花岗岩 岩石地球化学 构造环境 

分 类 号：P588.12[天文地球—岩石学]