内蒙古中南部古元古代高温型双变质带及其构造意义  

Paleoproterozoic High Temperature Paired Metamorphic Belt in Central Parto f Southern Inner Mongolia and Its Tectonic Implication

作　　者：刘守偈[1] 李江海[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室(北京大学),北京大学地球与空间科学学院,北京100871

出　　处：《高校地质学报》2009年第1期48-56,共9页Geological Journal of China Universities

基　　金：国家自然科学基金资助项目(40472097)

摘　　要：内蒙古中南部集宁—丰镇—土贵乌拉地区发育了一条超高温变质岩带。通过对土贵乌拉地区超高温变质岩的矿物组合研究,发现其中包含了尖晶石+石英、假蓝宝石+石英、斜方辉石+夕线石+石英的超高温标型矿物组合,并且在超高温变质作用区域内,经历了初始近等压冷却,随后近等温降压的逆时针退变质过程。已有的年代学数据表明,超高温变质作用峰期变质时代为1920Ma左右,降压退变质时代为1850Ma左右。在超高温变质岩带的东南地区,包括怀安—宣化一带,还出露了高压麻粒岩带。高压麻粒岩经历了近等温降压的顺时针退变质过程。年龄数据表明高压麻粒岩峰期变质时代为～1900Ma,退变质时代为1850Ma左右。内蒙古中南部超高温变质岩带和高压麻粒岩带相邻分布、产状相似且变质时代接近,共同构成了类似都城秋穗提出的双变质带;由于其温度偏高,故称为高温型双变质带,为世界上最古老的双变质带之一。该高温型双变质带可能反映了内蒙古中南部不同层次地壳物质在早前寒武纪碰撞作用中经历了P-T演化截然不同的变质作用,两条变质带在经历了各自的峰期变质作用后,作为一个共同的地体抬升。对内蒙古中南部古元古代高温型双变质带开展进一步研究,为认识华北克拉通早期构造背景、地壳热演化,特别是板块构造、不同地壳层次的构造作用提供了难得的科学机遇。An ultra-high temperature （UHT） metamorphic rock belt occurs in Jining-Fengzhen-Tuguiwula, central part of southern Inner Mongolia. Detailed study on the mineral assemblages shows UHT indicators such as Spl＋Qtz, Spr＋Qtz and Opx＋Sil＋Qtz. UHT rocks underwent initial isobaric cooling followed by isothermal decompression in the field of UHT metamorphism. Available age data suggest peak metamorphism at 1 920 Ma followed by retrogressive metamorphism at 1 850 Ma of the UHT rocks. To the southeast, including Huai＇an-Xuanhua area, outcropped a high pressure granulite, which has a isothermal decompression retrograde metamorphic history along a clockwise P-T path. Most of the ages show a peak metamorphism at -1 900 Ma followed by a ca. 1 850 Ma retrograde metamorphism. Both the UHT rocks and high pressure granulite have a foliation striking NEE and dipping to NNW at ca. 70°. UHT rock belt and high pressure granulite formed a paired metamorphic belt due to the coincidence of distribution, altitude and metamorphic age. Since the metamorphic temperature is relatively higher than the traditional paired metamorphic belt, it could be defined as high temperature paired metamorphic belt, which is one of the oldest paired metamorphic belts. This high temperature paired metamorphic belt indicates that the crustal material at different levels in mid-southern Inner Mongolia underwent metamorphisms with entirely different P-T paths during a collision event at ca. 1 900 Ma, then the UHT rocks and high pressure granulite were uplifted as a whole block. Further research on the high temperature paired metamorphic belt provides a chance to study the early structural framework and crustal thermal evolution of North China Craton, especially the plate tectonics and structural process at different crustal levels.

关 键 词：华北克拉通 超高温变质作用 高压麻粒岩 双变质带 

分 类 号：P588.34[天文地球—岩石学]