大别山北部超高压变质大理岩及其地质意义

岩石学研究表明 ,大别山北部镁铁 超镁铁质岩带中白云质大理岩至少经历过三期变质阶段 :(1)榴辉岩相峰期变质阶段 ,矿物组合主要为方解石 +白云石 +金红石 +镁橄榄石 +钛 斜硅镁石 +富镁的钛铁矿±文石±石榴子石 ;(2 )麻粒岩相退变质阶段 ,矿物组合主要为方解石 +白云石 +金云母 +镁橄榄石 +透辉石 +钛铁矿 +尖晶石±斜方辉石等 ;(3)角闪岩相退变质阶段 ,主要矿物组合为方解石 +白云石 +磷灰石 +磁铁矿+榍石等。它的峰期变质矿物组合 ,类似于苏 鲁超高压大理岩 ,形成压力至少大于 2 .5GPa。这进一步证明 ,大别山北部大多数高级变质岩 (包括大理岩等 )都曾经过超高压变质作用 ,应属于印支期扬子俯冲陆壳的一部分。

Ultra-High-Pressure Marble in the Northern Dabie Mountains and Its Geological Significance

At least three metamorphic stages of dolomitic marble associated with a few retrograded eclogite lenses can be distinguished from the mafic-ultramafic belt in the northern Dabie Mountains: ①the peak metamorphic stage of eclogite facies with calcite＋dolomite＋forsterite＋Ti-clinohumite＋rutile＋Mg-rich ilmenite±aragonite±garnet mineral assemblage；②the granulite facies retrograded stage with calcite＋dolomite＋diopside＋ilmenite＋phlogopite＋spinel±orthopyroxene；③the amphibolite facies vetrograded stage with calcite＋dolomite＋apatite＋titanite＋magnetite. Its peak metamorphic minerals are similar to ultra-high-pressure marble in the Su-Lu UHP terrane. This confirmed that the marbles suffered the UHP metamorphism with the least pressure of 2.5 GPa and provided some new indicators for UHP metamorphism of crust rocks. In the meantime, it implies that most of the high-grade metamorphic rocks including marble from northern Dabie Mountains belong to a part of Triassic Yangtze subducted continental crust.