Petrology and geochemistry of mantle/crust xenoliths and the host basalts from southeastern China.

摘要

Cenozoic basaltic rocks from SE China can be grouped into three different series: tholeiites, alkali basalts, and picritic-nephelinitic basalts. Each basaltic series has distinctive geochemical features and is not derived from a common source rock by different degrees of partial melting or from a common parental magma by fractional crystallization. The petrography and major- and trace-element geochemistry of the tholeiites from SE China are similar to Hawaiian tholeiites, implying that the mantle source for these Chinese continental tholeiites is similar to that of the oceanic island basalts--an asthenospheric mantle. The alkali basalts and picritic-nephelinitic basalts are enriched in incompatible trace elements and are the products of low degree partial melting of an enriched lithospheric mantle.;Geochemical data on mantle peridotite xenoliths from SE China demonstrate that the lithospheric mantle under this region is heterogeneous. The depleted signatures of Sr and Nd isotopic compositions and major-element contents (low CaO and Al;A rare variety of Fe-Al-rich xenolith, tridymite-hercynite rock, was entrained in the Cenozoic tholeiite from Niutoushan, southeastern China. Based upon the available mineralogical and geochemical data, this type of rock is not the product of an extreme tholeiitic fractionation or the Fe-rich and Si-poor portion of silicate-immiscible liquids from an extremely fractionated residual tholeiite magma, but is the product of metamorphism, including partial to complete melting, of a sedimentary protolith. An Fe-Al-rich shale (quartz 5%, kaolinite 75%, hematite 20%) has the approximate composition of the tridymite-hercynite rock.