俯冲陆壳和洋壳对华北克拉通中生代岩石圈地幔改造的氧同位素记录  

The modification of the lithospheric mantle beneath the North China Craton by subducted continental and oceanic crust:Oxygen isotopic records of olivine

作　　者：郭锋[1] 

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640

出　　处：《岩石矿物学杂志》2013年第5期593-603,共11页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(90914009,41121002)

摘　　要：来自华北克拉通山东省中生代镁铁质岩石及地幔包体的橄榄石氧同位素组成显示,早白垩世岩石圈地幔主要受到了来自俯冲的华南陆壳不同组分的改造作用,包括镁铁质下地壳和长英质上地壳组分以及少量的海相沉积碳酸盐岩,而晚白垩世的岩石圈地幔则受到了来自俯冲的太平洋板块的改造。早白垩世受俯冲陆壳改造的岩石圈地幔橄榄石相对正常地幔高D18O(610j^712j),而晚白垩世被俯冲洋壳改造的局部地幔则相对正常地幔低D18O(411j^513j)。板块俯冲作用是导致华北克拉通岩石圈地幔破坏的重要深部机制,三叠纪华南陆壳深俯冲导致了华北克拉通地幔强烈富集相容组分而转变为易熔的岩石圈,早白垩世大规模幔源岩浆的侵位很可能与俯冲大陆板片的整体断离或拆离作用相关;晚中生代以来的太平洋俯冲作用则引发了岩石圈地幔的置换和增生作用,形成了目前新、老地幔共存的格局。Oxygen isotopic records from olivine crystals in Mesozoic mafic rocks and xenoliths in Shandong Province indicate an important contribution of both subducted continental crust and oceanic crust to the modifica- tion of the lithospheric mantle beneath the North China Craton （NCC）. The early Cretaceous lithospheric man- tle that has higher 3180 （6.0‰- 7.2‰） than normal mantle was mainly metasomatized by melts/fluids derived from the subducted Yangtze crustal rocks, which included the lower mafic and upper felsic components with sub- ordinate marine carbonates. In contrast, some low-MgO peridotite xenoliths in the late Cretaceous lithospheric mantle that has lower 3180 （4.1‰--5.3‰） than normal mantle were ascribed to the modification of subducted oceanic crust that had been hydrothermally altered prior to the subduction. The incorporation of recycling crustal rocks into the lithospheric mantle through plate subduction was an important mechanism for the modification and destruction of the lithospheric mantle beneath the NCC, e.g. , the introduction of the fertile continental crustal components led to the refertilization of the lithospheric mantle that made it more fusible in response to thermal perturbation. The large-scale early Cretaceous mafic magmatism in NCC resulted probably from the breakoff or detachment of the entire subducted continental slab. The subduction of the paleo-Pacific Ocean since late Me^zoic has exerted a significant impact on the mantle replacement and accretion, resulting in the coexistence of ＂old＂ and ＂newly aeereted＂ mantle domain beneath the NCC.

关 键 词：地幔改造作用 氧同位素 橄榄石 中生代 华北克拉通 

分 类 号：P597.2[天文地球—地球化学]