大别山造山带作为三叠纪华北与扬子大陆碰撞成因并形成超高压变质岩石已经没有异议。然而,对侏罗纪的变形性质和大地构造背景的认识还未取得一致意见。通过前陆早侏罗世地层褶皱,前陆深部反射地震探测,造山带内 SE 角闪岩相线理变形以及...大别山造山带作为三叠纪华北与扬子大陆碰撞成因并形成超高压变质岩石已经没有异议。然而,对侏罗纪的变形性质和大地构造背景的认识还未取得一致意见。通过前陆早侏罗世地层褶皱,前陆深部反射地震探测,造山带内 SE 角闪岩相线理变形以及160～120Ma 岩浆岩记录和同位素年代学研究等新的研究成果,证实中侏罗世大别山曾发生强烈的造山运动。这次造山运动相当于“燕山运动”,由于扬子与华北陆块在三叠纪已经拼合成一个大陆,所以侏罗纪变形属于陆内造山性质。将侏罗纪变形事件从大别山碰撞造山过程中分离出来可以合理地解释大别山超高压岩石第二次折返(从壳幔边界到地壳浅部)机理,150Ma 的混合岩化作用和广泛的130～120Ma 花岗岩-火山岩成因,以及大别山前陆 MOHO 错断等现象。展开更多
If the protolith of coesite-bearing eclogite was gabbro, it could undergo ultrahigh-pressure metamorphism under dry condition. In this case, the Hocking temperatures of those minerals could be higher, so that Nd isoto...If the protolith of coesite-bearing eclogite was gabbro, it could undergo ultrahigh-pressure metamorphism under dry condition. In this case, the Hocking temperatures of those minerals could be higher, so that Nd isotope disequilibrium between minerals could be observed. If the protolith of coesite-bearing edogite was metabasalt, amphiboles in the metabasalt were decomposed during ultrahigh-pressure metamorphism and released water. Thus Nd isotope compositions between the minerals were in equilibrium because the blocking temperatures of those minerals could he lower. The secondary alteration and fluid-rock interaction in high-pressure are major problems for Sm-Nd dating of eclogite. The reliable Sm-Nd isotopic ages of coesite-bearing eclogite from the Dabie Mountains and Su-Lu terrane range from 221 to 232 Ma. They are slightly lower, but very close to the peak metamorphic ages of the eclogites. The cold eclogite from the Sujiahe complex could be oceanic subduction origin in the Paleozoic.展开更多
基金Project supported by the National Natural Science Foundation of China and the Max-Planck-Institut fur Chemie.
文摘If the protolith of coesite-bearing eclogite was gabbro, it could undergo ultrahigh-pressure metamorphism under dry condition. In this case, the Hocking temperatures of those minerals could be higher, so that Nd isotope disequilibrium between minerals could be observed. If the protolith of coesite-bearing edogite was metabasalt, amphiboles in the metabasalt were decomposed during ultrahigh-pressure metamorphism and released water. Thus Nd isotope compositions between the minerals were in equilibrium because the blocking temperatures of those minerals could he lower. The secondary alteration and fluid-rock interaction in high-pressure are major problems for Sm-Nd dating of eclogite. The reliable Sm-Nd isotopic ages of coesite-bearing eclogite from the Dabie Mountains and Su-Lu terrane range from 221 to 232 Ma. They are slightly lower, but very close to the peak metamorphic ages of the eclogites. The cold eclogite from the Sujiahe complex could be oceanic subduction origin in the Paleozoic.
