摘要
岩浆混合作用是花岗岩成岩的重要方式,一直是地质学研究的热点。东昆仑造山带东段的哈拉炸南石英黑云母闪长岩和哈拉炸北花岗闪长岩内含有丰富的暗色微粒包体,为研究岩浆混合提供了理想样本。这些包体多呈椭圆状,少量呈条带状,其中哈拉炸南部分椭圆状包体具一定拖尾。哈拉炸南石英黑云母闪长岩中,角闪石具有较高的结晶温度和压力,并且变化范围不大;斜长石的An值变化范围较小,呈振荡变化;而其岩石中暗色微粒包体的捕虏晶斜长石和寄主岩中的斑晶斜长石较为干净,捕虏晶角闪石和斑晶角闪石包裹有大量斜长石、黑云母和副矿物。哈拉炸北花岗闪长岩中,角闪石结晶温度和压力较低,斜长石的An值变化范围较大,斑晶角闪石和斑晶斜长石较为干净,其中捕虏晶斜长石和捕虏晶角闪石含有大量包裹矿物;捕虏晶斜长石边部的包裹矿物呈针柱状,在核部和边部中间有窄的筛孔状构造。暗色微粒包体中捕虏晶角闪石和基质角闪石的形成温度和压力明显高于寄主岩角闪石。这些特征表明,哈拉炸南石英黑云母闪长岩结晶于较深的环境,暗色微粒包体的形成是镁铁质岩浆与寄主岩浆混合的结果。镁铁质岩浆注入寄主岩浆后,岩浆在塑性状态下的局部流动导致成岩后岩体具有一定的定向构造,也使暗色微粒包体呈条带状。哈拉炸北花岗闪长岩的原生岩浆在地壳深部形成,然后在地壳浅部侵位,结晶环境变化较大,而镁铁质岩浆在注入岩浆房之前,在地壳深部已与其他长英质岩浆经历过一次岩浆混合。哈拉炸北花岗闪长岩岩浆房和镁铁质岩浆可能都经历了较长时间的演化,结晶程度都较高,致使寄主岩矿物较少进入暗色微粒包体。上述情况表明,岩浆混合具有多期次性。在同一次岩浆混合作用中,镁铁质岩浆和长英质岩浆的物理属性对岩浆混合具有重要影响。
Crust-mantle magma mixing is one of the most critical processes in granite formation and has been a subject of extensive research.Mafic microgranular enclaves(MMEs)are widespread in the south(SHLZ)and north Halazha plutons(NHLZ)in the East Kunlun,making them ideal targets for studying magma mixing processes.Most of MMEs in the SHLZ and NHLZ are elliptical in shape,while some MMEs in the SHLZ are tailed and elongated.Hornblendes in the SHLZ have a high and steady crystallization temperature and pressure,and the An value of plagioclase varies in a narrow range.Plagioclase xenocrysts in MMEs and plagioclase phenocrysts in host rocks of the SHLZ are relatively“clean”,with few inclusions,but the hornblende xenocrysts and hornblende phenocrysts are“dirty”,with a large number of plagioclase,biotite,and accessory minerals.Hornblendes and plagioclases in the host rock of NHLZ are relatively“clean”,the crystallization temperature and pressure of hornblendes are low,and the An value of plagioclase varies widely.Plagioclase and hornblende xenocrysts in MMEs of the NHLZ contain many mineral inclusions.The inclusion minerals at the rims of plagioclase xenocrysts are needle-like,and there is a narrow sieve-like texture between the core and the rim.The crystallization temperatures and pressures of hornblende xenocrysts and matrix hornblendes in MMEs are higher than those of host rocks.These results show that the SHLZ crystallized in a deeper and more stable environment.The MMEs of the SHLZ result from the mixing of mafic magma into the host rock magma.When mafic magma is injected into the host rock,the local flow of the magma in a plastic state can cause the rock mass to have a directed structure and cause the MMEs to be elongated.After the formation of the magma in the deep part of the crust,the magma of the NHLZ explosion intruded into the shallow part of the crust,which made the environment of mineral crystallization more variable due to its long transport distance.Before the mafic magma was injected into the NHLZ magma chamber,it had undergone a magmatic mixing process with other felsic magma chambers in the deep crust.Both the NHLZ and mafic magma chambers may have evolved over a long period with a high degree of crystallization,resulting in fewer host rock minerals entering the MMEs.The above shows that magma mixing is multi-phase.The physical properties of mafic and felsic magmas significantly influence their mixing.
作者
陈国超
裴先治
李瑞保
李佐臣
裴磊
陈有炘
刘成军
李小兵
CHEN Guochao;PEI Xianzhi;LI Ruibao;LI Zuochen;PEI Lei;CHEN Youxin;LIU Chengjun;LI Xiaobing(Nanyang Institute of Technology,Nanyang 473000,Henan,China;Key Laboratory of Western China’s Mineral Resources and Geological Engineering,Ministry of Education,Chang’an University,Xi’an 710054,Shaanxi,China;Shanxi Normal University,Linfen 041004,Shanxi,China)
出处
《大地构造与成矿学》
北大核心
2025年第2期367-385,I0003-I0008,共25页
Geotectonica et Metallogenia
基金
国家自然科学基金项目(42172236、41872233、41872235)
河南省重点研发与推广专项项目(212102310030)
资源与生态环境地质湖北省重点实验室开放基金项目(HBREGKFJJ-202304)
南阳理工学院交叉科学研究项目(24NGJY014)联合资助。
关键词
东昆仑造山带
岩浆混合
岩浆演化
暗色微粒包体
捕虏晶
East Kunlun orogenic belt
magma mixing
magma evolution
mafic microgranular enclave
xenocryst
