摘要
胶北莱西古元古代的高压基性麻粒岩和钙硅酸盐岩的基本矿物组合分别为以铁铝榴石为主的石榴石-普通辉石-铁紫苏辉石和钙铝榴石-黝帘石-葡萄石-钠长石。矿物岩石学研究表明钙硅酸盐岩是由含石榴石高压基性麻粒岩经退变质和钙质交代作用形成。南山口高压基性麻粒岩记录了麻粒岩相变质作用前、麻粒岩相变质作用、退变质和钙硅酸盐岩化共同作用以及完全钙硅酸盐岩化的四个阶段的地质作用,其矿物组合分别为Cpx+Pl+Qtz(M1),Grt+Cpx+Rt+Qtz(M2),Cpx+Pl+Opx+Ilm+Mgt+Ep(M3)和Grs+Zo+Prh+Ab+Cal(M4)。微量元素研究表明,高压基性麻粒岩中大离子亲石元素Ba、Rb、K、Rb、Th富集,而高场强元素Nb、Zr、Ti、Y亏损,具有轻稀土富集的右倾型稀土配分曲线。稀土元素和微量元素配分图解显示了岛弧拉斑玄武岩的特征。主元素、微量元素的构造判别图解进一步分析表明高压基性麻粒岩及其钙硅酸盐岩的原岩形成于大陆边缘的岛弧环境。综合高压基性麻粒岩岩石学、元素地球化学特征认为,莱西高压基性麻粒岩的原岩是拉斑玄武岩质岩石,可能是形成于弧后扩张背景下基性的侵入岩或喷出岩。岩石形成以后,在胶-辽-吉带碰撞闭合过程中,经历了麻粒岩相变质作用,又在后来的抬升过程中经历退变质和钙硅酸盐岩化作用。
The Paleoproterozoic HP mafic granulite and calc-silicate were found from Laixi,Jiaobei terrane,consisting of almandine dominated garnet-augite-ferrohypersthene and grossular-zoisite-prehnite-albite respectively.Mineralogical and petrological studies show that the calc-silicate formed after the HP mafic granulite by processes combined retrogressive metamorphism with Ca alteration.The HP mafic granulites records four stage geological processes,including pre-granulite facies,peak granulite facies,retrogressive combined with Ca alteration and complete Ca alteration processes with mineral assemblages as Cpx ＋ Pl ＋ Qtz （M 1）,Grt ＋ Cpx ＋ Rt ＋ Qtz （M 2）,Cpx ＋ Pl ＋ Opx ＋ Ilm ＋ Mgt ＋ Ep （M 3） and Grs ＋ Zo ＋ Prh ＋ Ab ＋ Cal （M 4）.The HP mafic granulite is rich in LIL elements Ba,Rb,K,Rb,Th and depleted in HFS elements Nb,Zr,Ti and Y,having LREE rich right-inclined REE pattern and showing island-arc basaltic characteristics.Further studies by using discrimination diagrams,the HP mafic granulite presents island-arc tholeiitic characteristics,probably formed in the back-arc extension tectonic setting.After formation of the mafic rock,it experienced granulitic facies metamorphism during collisional convergence of the Jiao-Liao-Ji orogenic belt and afterwards experienced retrogressive and Ca alteration processes during the lift of the belt.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2013年第7期2340-2352,共13页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41272072)
国家基础研究发展计划"973项目"(2012CB416606)联合资助
