Stratigraphic Evidence of the Exhumation and Uplift of Ultrahigh-Pressure Metamorphic Rocks in the Dabie Orogenic Belt: Enlightenment from Eclogite Gravels in the Maotanchang Formation

Mesozoic-Cenozoic clastic rocks of ten thousands metres thick, on the northern flank of the Dabie Mountains recorded the evolution of the Dabie orogenic belt since the Jurassic. Gravels composed of eclogites were founded in the Late Jurassic Maotanchang Formation in the Lu'an region, Anhui Province. The gravels are hard and without weathering, and thus belong to the first cycle. The eclogites are composed of garnet, phengite, epidote, quartz, rutile, etc. , which marked retrogressive process and developed symplectites composed of albite and amphibole, etc. , and symplectites around garnet crystals. The garnets consist mainly of almandine and grossularite, and belong to C-type eclogite. Petrologic features suggest that the eclogites came from ultrahigh-pressure metamorphic rocks developed in the South and North of Dabie Mountains. The Stratigraphic age of the Maotanchang Formation is certain and mainly belongs to the Late Jurassic based on fossils and isotopic ages. The discovery indicates that eclogites at the base of the Dabie orogenic belt emerged on the earth's surface in the Late Jurassic and became the provenance of the Maotanchang Formation. So, it is in the Late Jurassic that the ultrahigh-pressure metamorphic rocks in the Dabie orogenic belt exhumed, uplifted to the surface, and were subject to violent denudation.