Mid-ocean Ridge Basalt Near East Paciifc Rise13°N

In this paper, we analyzed mineral components, major elements and traceelements of mid-ocean ridge basalt, major elements and trace elements in meltinclusions hosted in olivine in mid-ocean ridge basalt （MORB） near East Pacific Rise13°N, and silicon and oxygen isotopes in igneous rocks. We discuss thecharacteristics of MORB and the formation process of MORB in our study area.Through modeling the crystallization paths of MORB, we trace the way of magmaticevolution. This study would be useful in understanding the origin and derivation ofMORB in fast spreading ridge, and be helpful in understanding the characteristics ofactivity of basaltic magma.Through the analyses of major and trace elements of MORB, some E-MORBsare involved in MORBs in our study area. The major elements of MORB displaythese basalts derive from areas with different depths, and experience melting indifferent degrees. It also shows there are olivine and plagioclase co-existing in thesebasalts. The trace elements of MORB display there are enriched components involvedin parental magma of MORB.Combining with the major elements of MORB and melt inclusions, we can seethat olivine, plagioclase and clinopyroxene co-exist in basaltic magma near EPR13°N,while only olivine and plagioclase co-exist in MORB that erupted out of the surface.It means the theory of “pyroxene paradox” is also right in the basalts near EPR13°N.Meanwhile, through using the thermodynamics of crystallization software–COMAGMAT to model the crystallization paths of minerals in MORB and meltinclusion, and the studying of trace elements in melt inclusion, we conclude theseE-MORBs appear near EPR13°N are the productions of two different processes. Firstis low pressure melting （1±1kbar） of enriched component, and the second is highpressure mixing （4±2kbar） of enriched component and normal magma.The mean values of δ³⁰Si and δ18O of MORB near EPR13°N are different fromδ³⁰Si and δ18O values of normal MORB, we suppose it is caused by the enrichedcomponent in basalts near EPR13°N. As the contrast area, the igneous rocks fromManus Basin with relative high δ³⁰Si and δ18O display they may have been affectedby the hydrothermal fluid in Manus Basin. In the series of basalt–andesit–dacite, δ³⁰Si and δ18O increase as the increasing of silica content. We suppose that during theevolution of magma, the fractionation of silicon and oxygen isotopes have beenaffected by the silica content.