超高温变质作用：以华北内蒙古土贵乌拉地区为例

超高温麻粒岩(富Mg-Al)是指温度高于900℃、压力为0.7~1.3GPa条件下形成的麻粒岩相变质岩,它记录了下地壳超高温极端变质作用的地质信息。富Mg-Al典型超高温矿物组合有:假蓝宝石+石英,尖晶石+石英,大隅石+石榴石,斜方辉石+夕线石+石英,高氟黑云母和钙镁闪石,刚玉+石英。目前世界上发现的超高温麻粒岩带(块)地区有非洲阿尔及利亚、南非、东南极、巴西中部、澳大利亚中部、印度南部和东南部等地。我们在华北克拉通北部内蒙古中南部地区孔兹岩区中发现了超高温麻粒岩,岩性主要为灰黑色条带状夕线石榴黑云片麻岩,其中含有尖晶石+石英、假蓝宝石+石英、斜方辉石+夕线石+石英以及刚玉+尖晶石+石榴石等超高温矿物组合,指示温度达1000℃,压力超过1.0GPa的变质作用。独居石定年获得了(1927±11)Ma以及(1819±11)Ma两个峰期年龄,代表变质年龄。华北克拉通北部超高温麻粒岩的发现对研究华北克拉通与哥伦比亚超大陆的演化关系有重要意义。

Review of ultrahigh-temperature (UHT) metamorphism study: a case from North China Craton

Ultrahigh-temperature granulites are rocks that underwent extreme metamorphism at temperatures exceeding 900 ℃ and at pressures that can reach 0.7-1.3 Gpa. This extreme metamorphism left imprints on the rocks with UHT mineral assemblages, such as Spr+Qtz, Spl+Qtz, Osm+Grt, Opx+Sil+Qtz, high-F biotite and pargasite, and Crn+Qtz. Up to now, typical UHT granulites in the world have been found in Algeria, South Africa, Eastern Antarctica, Central Brazil, Central Australia, Southern and Southeastern India. Similar to normal granulites, UHT granulites usually produce two types of p-T paths: isothermal decompression (ITD) and isobaric cooling (IBC). In recent years, UHT granulites were found in khondalite belts in Inner Mongolia, North China Craton, which has typical UHT mineral assemblages, including Spl+ Qtz, Spr+Qtz, Opx+Sil+Qtz and Crn+Spl+Grt. These assemblages suggest T>1 000 ℃ and p>1.0 Gpa metamorphism. Monazites give the age of metamorphism at (1 927±11) Ma and (1 819±11) Ma. The discovery of UHT rocks of North China Craton provides useful insights in the study of relationship between the North China Craton and the supercontinent Columbia.