北大别超高压榴辉岩的快速折返与缓慢冷却过程

岩石学研究表明,北大别超高压榴辉岩经过了超高压和高压榴辉岩相变质作用以及麻粒岩相叠加和角闪岩相退变质作用.其中,高压麻粒岩相和角闪岩相变质阶段形成的后成合晶以及石榴子石和单斜辉石等矿物中成分分带的存在,证明该区榴辉岩经历了一个快速折返过程;而不同变质阶段的温度、压力和形成时代,却反映该区榴辉岩在峰期超高压变质作用之后又经历了一个缓慢冷却过程.超高压岩石折返期间的缓慢冷却过程也许正是北大别长期难以发现柯石英和有关超高压证据的重要原因.因此,本文为大别山不同超高压岩片的差异折返模型的建立提供了新的证据.

Rapid exhumation and slow cooling of ultrahigh-pressure eclogite in the North Dabie complex zone, central China

Metamorphic petrology of ultrahigh-pressure (UHP) eclogites was studied in the North Dabie complex zone (NDZ), central China. The results suggest that the eclogites underwent UHP and HP eclogite-facies metamorphism, and subsequent HP granulite-facies overprinting and amphibolite-facies retrogression. The symplectites formed by HP granulite- and amphibolite-facies metamorphism and the occurrence of compositionally zoned minerals such as garnet and clinopyroxene show a rapid exhumation of UHP eclogites in the region, whereas their metamorphic temperature and pressure conditions at various stages and ages indicate they experienced a relatively slow cooling process after peak UHP metamorphism. This may be one of major reasons to be rarely preserved coesite and related evidences for UHP metamorphism in the rocks from the NDZ. In addition, these provide further evidence on a multi-slice successive exhumation model that the detachment and decoupling occurred at variable depths within subducted continental crust and multi-slices of the UHP rocks were successively exhumed during the continental collision between the South China and North China blocks.