安哥拉地块北部Dondo地区古元古代花岗岩岩石成因:Columbia超大陆聚合的响应  

Petrogenesis of Paleoproterozoic granites in the Dondo area,northern Angola block:Geological response to the assembly of Columbia Supercontinent

作　　者：刘伟 张洪瑞 罗迪柯 贾鹏飞 靳立杰 周永刚 梁云汉 王子圣 李春稼 LIU Wei;ZHANG Hongrui;LUO Dike;JIA Pengfei;JIN Lijie;ZHOU Yonggang;LIANG Yunhan;WANG Zisheng;LI Chunjia(No.1 Geological Team of Shandong Provincial Bereau of Geology and Mineral Resources,Jinan 250014,China;Shandong Engineering Research Center of High-grade Iron Deposits Exploration and Exploitation,Jinan 250014,China;Citic Construction Co.,Ltd.,Beijing 100027,China)

机构地区：[1]山东省第一地质矿产勘查院,山东济南250014 [2]富铁矿勘查开发技术山东省工程研究中心,山东济南250014 [3]中信建设有限责任公司,北京100027

出　　处：《地学前缘》2024年第4期237-257,共21页Earth Science Frontiers

基　　金：安哥拉国家地质调查计划项目(PLANAGEO)。

摘　　要：安哥拉西部地区广泛发育古元古代Eburnean造山期花岗岩,是研究安哥拉地块构造岩浆作用特征的理想场所。本文对安哥拉地块北部Dondo地区大面积出露的花岗岩开展系统的岩相学、岩石地球化学和锆石U-Pb年代学研究。结果显示:Dondo地区斑状黑云母二长花岗岩与黑云母二长花岗岩的侵位年龄分别为(1983.3±7.7)Ma和(1956.6±7.5)Ma,均为古元古代中期岩浆活动的产物。全岩样品具有高SiO_(2)含量、富碱、高10~4Ga/Al值、高FeO^(T)/(FeO^(T)+MgO)值和Zr+Nb+Ce+Y含量,低MgO、TiO_(2)、CaO和P_(2)O_(5)含量的特征;微量元素富集Rb、K、Th、U、Zr和Hf,亏损Sr、Nb、Ta、P和Ti;稀土元素总量较高,轻稀土富集,重稀土亏损,整体不具有显著的负Eu异常;锆饱和温度计算所有花岗岩的结晶温度为757~889℃;以上这些岩石地球化学特征与A2型花岗岩一致。岩相学及地球化学的数据表明,两种花岗岩可能由来源于下地壳物质与地幔来源基性岩浆混合所形成。两种花岗岩具有相似的形成时代、矿物组成和连续的主微量元素变化趋势,这些特征表明它们的原始岩浆来自同一岩浆房,而二者之间特征的差别是由岩浆房内的晶体-熔体分异所主导。据此,本文认为:产生钾长石斑晶的岩浆曾经在地壳深部作过长时间滞留,导致钾长石稳定结晶,增加了岩浆的黏度和密度,使岩浆处于冻结状态;随后在幔源岩浆注入带来的热扰动和富集挥发分的作用下,冻结岩浆房迅速活化,从而发生晶体-熔体的分离,抽离的熔体形成了黑云母二长花岗岩,而混有先存晶体的岩浆则形成了斑状黑云母二长花岗岩。综合区域和全球构造演化历史,本次研究认为Dondo地区花岗岩形成于巴西Sao Francisco克拉通和Congo克拉通后碰撞的构造环境,该期岩浆活动可能是Columbia超大陆的碰撞造山事件在安哥拉地块的响应。The Paleoproterozoic Eburnean orogenic granites are widely exposed in the western part of Angola,offering an ideal setting to study the magmatism and tectonic evolution of the Angola Block.This paper presents systematic studies of petrology,petrogeochemistry,and zircon U-Pb geochronology on the exposed granites in the Dondo area,northern Angola Block.The results indicate that the emplacement ages of porphyritic biotite monzonite granite and biotite monzonite granite in the Dondo area are 1983.3±7.7 Ma and 1956.6±7.5 Ma,respectively,both products of middle Paleoproterozoic magmatic activity.The whole-rock samples are characterized by high SiO_(2),ALK,10000Ga/Al,FeO^(T)/(FeO^(T)+MgO),and Zr+Y+Nb+Ce,and low MgO,TiO_(2),CaO,and P_(2)O_(5).Trace elements are enriched in Rb,K,Th,U,Zr,and Hf,and depleted in Sr,Nb,Ta,P,and Ti.All samples are enriched in LREE and depleted in HREE,with no significant negative Eu anomaly.The crystallization temperature,calculated using zircon saturation thermometry,ranges from 757 to 889℃.Based on these geochemical characteristics,the granites in the Dondo area are classified as A2-type granite.Mineralogical and geochemical features suggest that the porphyritic biotite monzonite granite and biotite monzonite granite were generated by the mixing of crustderived melts and mantle-derived mafic magma.The similar formation ages within analytical error,identical mineral assemblages,and consistent variations in major and trace elemental compositions indicate that their parental magma originated from a common magma chamber,with lithological differences resulting from melt extraction processes.It is proposed that the magma producing the potassium feldspar porphyry resided in the deep crust for an extended period,leading to stable crystallization of potassium feldspar,increased viscosity and density,and a frozen state of the magma.Subsequent thermal disturbance and volatile enrichment from mantle-derived magma injection rapidly reactivated the frozen magma chamber,resulting in crystal-melt separa

关 键 词：安哥拉地块 古元古代 岩石成因 A型花岗岩 冻结岩浆房活化 Columbia超大陆 

分 类 号：P581.121[天文地球—岩石学] P597.3[天文地球—地质学]