Petrogeochemical Characteristics Comparison And Implications For Magmatic Processes Of The MORBs Between SAR And SWIR

In this study, we comparatively analyzed the petrological, geochemical and mineralogical characteristics of typical MORBs from SAR and SWIR. SAR is typical representation of slow spreading ridge, and SWIR is typical representation of ultraslow spreading ridge.This research is helpful to reveal the petrogeochemistry and magmatic processes defferences between slow and ultraslow spreading ridge, and reveal the restrictive role of spreading rate on magmatic processes. With this research, we can make five conclusions:(1) The MORBs of SAR and SWIR all belong to tholeiite series.The phenocrysts are mainly plagioclase, and less olivine, Clinopyroxene is absent.In SAR, the phenocrysts of plagioclase are belonging to bytownite and labradorite chiefly, in SWIR, the phenocrysts of plagioclase are belonging to labradorite chiefly and andesine. The MORBs of SAR are N-MORB,and the MORBs of SWIR is composed of both N-MORB and T-MORB.(2) The MORBs of SAR have positive anomaly of Ba and negative anomaly of Th, Nb, the MORBs of SWIR have positive anomaly of Ba?U, and negative anomaly of Th, Nb, The MORBs show light REE depleted patterns in chondrite-normalized REE diagram, slight Eu.(3) Spinel peridotite zone is the origin of the basaltic magmas of SAR and SWIR, but the originated depth and melting temperature of SWIR is higher than that of SAR. The degree ofpartial melting ofSAR(19.46%) is bigger than SWIR(18.22%)?(4) The fractional crystallization of clinopyroxene and plagioclase have happened during the segregation and aggregation process of basaltic magmas, but the most of clinopyroxene phenocrysts have corroded before reached to the surface. The magmas mainly experienced low pressure fractional crystallization of olivine and plagioclase in the magma chamber.(5) The spreading rate can influence the degree of partial melting and magma supply of SAR and SWIR. The degree of partial melting and magma supply will increase with the spreading rate, but the magmatic processes are not strictly controlled by the spreading rate. The Ascension hotspot and Crozet hotspot are also critical influences.