华北克拉通北缘孔兹岩带两期深熔石榴花岗岩地球化学特征及其地质意义  

Geochemistry and Geological Significance of the Two Episodes of Anatectic Garnet Granites in the Khondalite Belt,Northern Margin of the North China Craton

作　　者：石强 李晨[1] 周煜欣 高鑫 李蕙萱 马人文 许严 赵忠海 徐仲元 Shi Qiang;Li Chen;Zhou Yuxin;Gao Xin;Li Huixuan;Ma Renwen;Xu Yan;Zhao Zhonghai;Xu Zhongyuan(College of Mining Engineering,Liaoning Technical University,Fuxin 123000,Liaoning,China;Department of Geology,Northwest University,Xi’an 710000,China;College of Earth Science,Jilin University,Changchun 130026,China)

机构地区：[1]辽宁工程技术大学矿业学院,辽宁阜新123000 [2]西北大学地质系,西安710000 [3]吉林大学地球科学学院,长春130026

出　　处：《吉林大学学报（地球科学版）》2023年第4期1090-1116,共27页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项(41872194);辽宁省教育厅基本科研项目(LJKMZ20220689);辽宁工程技术大学学科创新团队项目(LNTU20TD-14);大学生创新创业训练项目(X202210147061)。

摘　　要：华北克拉通北缘孔兹岩带大青山地区和集宁—凉城地区石榴花岗岩与深熔源岩(泥质片麻岩)在野外空间上渐变过渡、密切共生。石榴花岗岩中含有大量的源岩包体、残留体、残留矿物相/转熔矿物相,深熔源岩中也存在大量的石榴花岗岩团块,这些混合岩的岩性在宏观上具有不均一性。岩相学研究表明,石榴花岗岩与泥质片麻岩矿物组成相近,二者具有特征十分相似的石榴石,主要为残留矿物相/转熔矿物相。地球化学研究表明,石榴花岗岩与泥质片麻岩拟合程度较好,均具有高TFeO/MgO值和Al_(2)O_(3)质量分数,K_(2)O/Na_(2)O值和CaO质量分数存在较大变化,相对富集轻稀土元素和大离子亲石元素,相对亏损Ta、Nb、Ti和P等元素。与世界上典型的S型花岗岩成分偏离,大青山地区和集宁—凉城地区石榴花岗岩具有低SiO_(2)质量分数(50.30%~73.10%)和高MgO+TFeO质量分数(1.6%~14.8%)。研究认为偏离正常S型花岗岩的成分范围与石榴石残留体带入和幔源物质添加有关。结合前人资料,认为大青山地区和集宁—凉城地区石榴花岗岩由2.45~2.37 Ga和1.95~1.90 Ga两期深熔事件形成,与区域上幔源岩浆底侵时代相近,指示大青山地区和集宁—凉城地区石榴花岗岩是幔源基性岩浆侵入麻粒岩相变质沉积岩中引起变沉积岩发生大规模部分熔融的产物。Garnet granites and anatectic source rocks(pelitic gneiss)in Daqingshan and Jining-Liangcheng areas at the northern margin of the North China craton gradually transition and closely coexist in the field.The garnet granites contain many source rock enclaves,residual bodies and residual mineral phases/peritectic minerals.There are also a large number of garnet granite blocks in anatectic source rock.All these migmatites have heterogeneity macroscopically.Petrographic studies show that the mineral composition of garnet granites and the anatectic source rocks are similar and both contain garnet with similar characteristics.This can be considered a residual mineral/peritectic minerals facies type.Geochemical studies indicate that garnet granites are relatively well integrated with their anatectic source rocks,both have high Al_(2)O_(3) values and TFeO/MgO ratio,with a large variation in CaO values and K_(2)O/Na 2 O ratio.They are relatively enriched in light REE and large ion lithophile elements,and relatively depleted in Ta,Nb,Ti and P.Deviating from the composition range of typical S-type granites in the world,garnet granites have lower SiO 2(50.30%-73.10%)and greater MgO+TFeO(1.6%-14.8%).It is believed that this deviation from the normal S-type granite compositon is related to the introduction of residual garnet and the addition of mantle-derived materials.The garnet granites in the Daqingshan and the Jining-Liangcheng areas were formed by two episodes of anatexis at the 2.45-2.37 Ga and 1.95-1.90 Ga respectively,consistent with the regional mantle-derived magma underplating in this area.This indicates that garnet granites are the products of large-scale partial melting of metasedimentary rocks caused by mantle-derived basic magma intruding into granulite facies metasedimentary rocks.

关 键 词：孔兹岩带 大青山地区 集宁—凉城地区 石榴花岗岩 地球化学 华北克拉通 

分 类 号：P588.121[天文地球—岩石学]