关于大陆地壳消亡与再生循环过程的新认识——大别山新的区域地质资料和榴辉岩专题研究成果提出的启示

A new view on consumption and regeneration of the continental crust:enlightenment from the new regional geological researching on the UHP rocks in the Dabie mountains,

越来越多的区域地质资料显示,大别山 UHP 榴辉岩相变质的大陆岩石以及在片麻岩中发现的含有柯石英包裹体的锆石和含有绿辉石包裹体的石榴子石等重矿物可能却是一个已经熔融了的榴辉岩相大陆岩片遗留下来的残留体,它们被包裹在由变形、变质深成侵入体构成的正片麻岩之中。这些深成侵入体底辟在扬子陆决北缘新元古代低-中级变质的火山一沉积地层之下。依据上述区域地质事实,本文认为,大别山含有榴辉岩残留体的高级片麻岩不是一个“UHP 变质地体”或“含有榴辉岩外来构造块体的混杂岩”,其原岩应该是一套由榴辉岩化大陆岩片熔融形成的深成岩浆底辟体。由此本文提出一个新的理论假说和构造模型,即深俯冲到地幔软流圈之中的大陆边缘在不同的深度发生了相应的 HP-UHP 榴辉岩相变质作用,随着与俯冲洋壳的断离,其在浮力的作用下快速底垫在仰冲大陆边缘之下并发生部分熔融,熔融体底辟并置换了造山带原有的根,后经过同结晶过程的变形和变质作用形成一套含有榴辉岩相残留体的,高级片麻岩本文称之为再生地壳。

In the Dabie Mountains, more and more regional geological data show that the UHP continental rocks and the coesitebearing zircons,omphicite-bearing garnets, etc. which have extensively been discovered within gneiss country rock were relics from a melted eclogitized continental slice and kept within the high-grade gneiss country rock which is composed of a suite of metamorphic and ductile deformed plutons intruded under Newprotozoic low to mid-grade metamorphic volcanic-sedimentary strata on the Yangtze northern margin. Based on these facts, we suggest that the eclogite-bearing gneiss is not an “UHP terrance” or “m lange” included eclogite fragments and its protolith should be a suite of magmatic diapirite produced by an eclogitized continental slice melting, and advance a new hypothesis for continental crust consumption and regeneration and model of the Dabie collision zone evolutiona, that is after deep-subducted continental margin underwent the HP to UHP eclogite-facies metamorphism at different depth in anthenosphere, whit the subducted oceanic crust and continental mantle broken-off, the continental crust rapidly underplated under the obducted margin by buoyancy and took place part melt as rapidly decompression and mantle-heat input, and the melted mass replaced “former root” of the margin and diaper penetrated under the metamorphic strata, and at the same time of crystallizing, it experienced coordinating metamorphism and deformation with its depth to produce a high-grade orthrgneiss, that is “ regenerated crust”.