Geochemical Characteristics and Geological Significance of the Shangzhuang Carbonate Complex,Qinghai
The Shangzhuang complex in Qinghai is a mineralized rock body of phosphorus,iron and rare earth,and phosphorus ore is an important material for phosphate fertilizer production.The Shangzhuang complex consists of ultramafic rocks,alkaline syenites and carbonatites.The carbonatites are mainly calcite carbonatites,others are dolomite carbonatite.The predecessors have studied the pyroxenite in detail.However,the petrogenesis and mineralization mechanism of the pyroxenite syenite carbonatite as a whole are still unclear.In this paper,petrography,major and trace elements of the whole rock,and C-O-Sr-Nd isotopes have been studied.Petrographic study shows that the sequence of rock formation is pyroxenite-syenite-carbonatite.The Sr and Ba contents of calcite carbonatite are 10 928.13 ppm and 14 293.18 ppm respec-tively,The δ13C value is-4.72‰,indicating that it is igneous carbonate rock.The pyroxenite syenite car-bonatite complex is rich in light rare earth elements(LREE)and large ion lithophile elements(LILE)Rb,Sr,Ba,and depleted in high field strength elements(HFSE)Nb,Ta,Zr,Hf.Similar trace element distri-bution patterns and Sr Nd isotope characteristics indicate that the complex has a common mantle source area,which was enriched by subduction materials.The study shows that the Shangzhuang subalkaline py-roxenite alkali syenite carbonatite complex was formed in the tectonic system of subduction to extension.The mantle derived subalkaline carbonatite basic magma formed Fe-P-REE enriched clinopyroxenite due to the crystallization of mafic minerals and apatite.The composition of the residual melt differentiated towards felsic end elements,forming syenite.Subsequently,the carbonatite melt may be produced by immiscibil-ity,forming carbonatite,The metasomatism of syenite by the exsolution fluid of carbonatite may be the rea-son why the metasomatic syenite has high REE content.
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维普
