大别山北部榴辉岩的大地构造属性及冷却史

Tectonic Setting and Cooling History of Eclogites from Northern Dabie Mountains

岩石地球化学及同位素年代学研究表明 ,大别山北部榴辉岩的大部分属印支期扬子俯冲陆壳 (下地壳 )的一部分 ;大致沿磨子潭 -晓天断裂附近分布的含榴辉岩、大理岩和变质橄榄岩的镁铁 -超镁铁质岩带可能代表扬子与华北 2个大陆板块之间的变质构造混杂岩带 ,它应接近于扬子与华北 2个大陆板块之间的缝合线 (镁铁 -超镁铁质岩带以北 ) ,而五河 -水吼剪切带则可能代表扬子俯冲陆壳内部的 1条拆离带或滑脱带 .冷却史研究表明 ,大别山北部榴辉岩峰期变质后初期 (2 30～ 2 10Ma)仅抬升到下地壳水平 ,因而未经历降温过程并具有比大别山南部榴辉岩较低的抬升速率 ,峰期变质后较慢的抬升速率及相应的近于等温或局部升温阶段也许是造成大别山北部榴辉岩与南部超高压带中榴辉岩差异的重要原因之一 ;同时 。

The petrologic geochemistry and isotopic chronology of the eclogites imply most of the eclogites in the northern Dabie Mountains produced from the Triassic Yangtze subducted continental crust (lower crust formed during the deep subduction) and the metamorphosed mafic untramafic belt with eclogite, marble and meta peridotite blocks around the Mozitan Xiaotian fault zone may represent the meta tectonic melange produced during the active subduction of an ancient oceanic slab and subsequent collision between the Yangtze and North China continental plates. The cooling history of the eclogites from about 900 ℃ to 300 ℃ can be subdivided into three stages: one isothermal stage and two rapid cooling stages. The initial stage during (230±6) Ma and ca 210 Ma was a near isothermal or temperature rise process corresponding to the retrograded metamorphism of granulite facies with a rapid uplift of about 4 mm/a, then two fast cooling stages occurred with cooling rate of about 10 ℃/Ma (210 Ma to (172±3) Ma) and about 4 ℃/Ma ((172±3) Ma to 130 Ma). After the ultra high pressure metamorphism of eclogite facies, relatively slower uplift rate and cooling rate and high T overprinting of granulite facies metamorphism is the major difference of the eclogites in northern Dabie Mountains from those in southern Dabie Mountains.