大别-苏鲁造山带橄榄岩:进展和问题

Orogenic peridotites in the Dabie-Sulu orogenic belt are commonly subdivided into 'crustal' type and 'mantle' type. They exhibit distinct mineral textures, metamorphic evolution, and whole-rock and mineral compositions. Most 'mantle' type peridotites originated from the subcontinental lithospheric mantle (SCLM) of the North China Craton and thus provide direct evidence of crust-mantle interactions in the continental subduction channel. In garnet peridotites, both garnet and Cr-spinel can be equilibrated at peak pressure conditions. Their stabilities are mainly controlled by the refertilized degree of whole-rock; therefore, spinel composition cannot be used to discriminate the partial melting degree of orogenic peridotites. Refractory mantle-derived dunites contain the textures of low Mg and high Ca olivine veins that crosscut orthopyroxene porphyroblasts, which is considered as evidence for silica-undersaturated melt-rock reactions. Such reactions occurring before subduction may potentially affect Re-Os isotopic compositions. Rutile, Ti-clinohumite and zircon in mantle-derived peridotites or pyroxenites provide direct mineralogical evidence for the transport of high field strength elements (HFSEs) from the subducted crust into the mantle wedge. Based on detailed in situ element and isotope analyses, we can constrain the source of metasomatic agents, the metasomatic time and the process of mass transfer. The mantle wedge above continental subduction zones has a wide range of oxygen fugacity values (FMQ=-5.50-1.75), showing a roughly negative correlation with the subducted depths. However, the calculated results of oxygen fugacity are significantly affected by mineral assemblages, P-T conditions and dehydrogenation-oxidation of nominally anhydrous mantle olivine during exhumation. Although significant progress has been made in the study of orogenic peridotites in the Dabie-Sulu orogenic belt, many critical questions remain. With new approaches and advanced technologic applications, additional knowledge of the phase relation in the peridotite-pyroxenite complex system, the mantle geodynamic process before continental subduction, the effects of crustal metasomatism on chemical composition, the oxygen fugacity, and the physical properties of the mantle wedge is anticipated.