南非林波波带中央带Sand River地区高压麻粒岩变质作用  

Metamorphism of High-pressure Granulites in Sand River Area of the Central Zone of Limpopo Belt,South Africa

作　　者：张慧明[1] 郑常青[1] 徐学纯[1] 徐久磊[1] 韩晓萌[1] 周晓萍[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《地球科学与环境学报》2016年第5期612-622,共11页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41472164);国土资源部公益性行业科研专项经费项目(201011083)

摘　　要：南非林波波带中央带Sand River地区存在高压基性麻粒岩,其峰期矿物组合为石榴石＋单斜辉石＋石英＋钛铁矿＋磁铁矿。岩石学研究表明,该高压麻粒岩经历了两期退变质作用,早期退变质阶段以斜方辉石和斜长石的出现为特征,晚期退变质阶段以角闪石的出现为特征。传统温压计计算表明：高压麻粒岩峰期变质温度为820℃~900℃,压力为13.5~15.4kbar;早期退变质的形成温压为800℃~890℃和8.8~11.2kbar;晚期退变质条件为540℃~650℃和2.7~4.4kbar。其退变质作用P-T轨迹为顺时针型近等温降压到降温降压的过程。高压麻粒岩经历的这种顺时针P-T轨迹通常发育在大陆碰撞环境,指示其形成可能与津巴布韦克拉通、卡普瓦尔克拉通在碰撞后地壳快速剥露事件有关,这对探讨林波波带中央带的构造演化具有重要意义。High-pressure mafic granulite with a peak mineral assemblage of garnet＋clinopyroxene＋quartz＋ilmenite＋magnetite was found in Sand River area of the central zone of Limpopo Belt,South Africa.The high-pressure granulite experiences two stages of retrograde metamorphism.Early retrograde metamorphic stage is characterized by the appearance of orthopyroxene and plagioclase;late retrograde metamorphic stage is characterized by the appearance of amphibole.P-T estimates suggests that the peak metamorphic conditions are 820 ℃-900 ℃ and 13.5-15.4kbar,which retrogress from the post-peak phase at 800 ℃-890 ℃and 8.8-11.2kbar to the amphibolite facies at 540 ℃-650 ℃and 2.7-4.4kbar.The three stages define a clockwise P-T path with near-isothermal decompression and cooling following the peak high-pressure metamorphism.The granulites experience this clockwise P-T paths,and usually develop in the continental collision setting.It means that the formation of high-pressure granulite relates to the crust fast stripping event after the collision of Zimbabwe craton and Kaapvaal craton.It is important for exploring the tectonic evolution in the central zone of Limpopo Belt.

关 键 词：变质作用 高压麻粒岩 P-T轨迹 林波波带 大陆碰撞 SAND River地区 南非 

分 类 号：P588.3[天文地球—岩石学]