罗迪尼亚超大陆聚合在华南陆块北缘的镁铁质岩浆岩记录

Mafic Magmatic Records of Rodinia Amalgamation in the Northern Margin of the South China Block

超大陆的聚合必然伴随着从大洋俯冲、弧陆碰撞到陆陆碰撞等一系列板块汇聚和造山过程,这些不同阶段的俯冲和汇聚过程会产生不同特征的岩浆岩记录.华南陆块是新元古代罗迪尼亚超大陆的重要组成部分,在这个超大陆聚合过程中有格林维尔期洋壳俯冲及其伴随的壳幔相互作用.总结了华南陆块北缘记录的罗迪尼亚超大陆聚合不同阶段发生的岩浆活动,比较了其产物的地球化学特征,探讨了它们对应的构造环境.华南陆块北缘900~950 Ma的岩浆活动产物以镁铁质岩浆岩为主,伴随有少量斜长花岗岩,为洋壳俯冲作用的产物.当洋壳俯冲到大陆边缘之下形成安第斯型俯冲带,古老陆源沉积物也被携带进入俯冲带,由此部分熔融产生的含水熔体交代上覆地幔楔形成极度富集的造山带岩石圈地幔,其在新元古代中期发生部分熔融形成具有极负锆石εHf(t)值的镁铁质岩浆岩.因此,在罗迪尼亚超大陆聚合过程中地幔楔被交代形成镁铁质-超镁铁质交代岩,其中一部分在俯冲阶段就发生部分熔融形成大洋弧或大陆弧镁铁质岩浆岩,另一部分在俯冲之后由于大陆裂断引起造山带岩石圈拉张使其与上覆地壳一起部分熔融形成双峰式岩浆岩.

The amalgamation of supercontinents is associated with a series of orogenic processes during plate convergence from oceanic subduction,arc-continent collision and continent-continent collision.These processes are recorded in different types of magmatic rocks.The South China block is one of the most important continents in supercontinent Rodinia,whose amalgamation is caused by Grenvillian subduction of oceanic slabs with considerable crust-mantle interaction.This paper presents a summary of magmatic records in the northern margin of the South China block during the Rodinia amalgamation.The 900-950 Ma magmatic rocks are mainly of mafic to intermediate compositions with a few plagiogranites,and they are the products of intraoceanic subduction.As the subduction style evolved into Andean type,ancient terrigenous sediments were carried into subduction zones to undergo dehydration melting,giving rise to hydrous felsic melts which would react with the overlying mantle wedge.This results in the formation of highly enriched mantle sources,whose partial melting in the Middle Neoproterozoic to produced mafic magmatic rocks with very negative zirconεHf(t)values.In this regard,mafic to ultramafic rocks were generated in the mantle wedge through crustal metasomatism by subducting oceanic crust-derived fluids during the Rodinia amalgamation.Some of these rocks were partially melted in the subduction stage to form mafic arc volcanics along convergent plate boundaries,and the other parts were partially melted together with the overlying crust during lithospheric extension by continental rifting at a later time for bimodal magmatism.