Geologic Characteristics And Petrogenesis Of The Mafic Dykes In The Wajilitag,Tarim Large Igneous Province

This study presents an integrated study of whole-rock major and trace elements and Sr-Nd,Mg-Zn isotopes on the diabase and diabasic porphyrite exposed in the Wajilitag area located in the Tarim Large igneous province.Based on the study,we constrained the petrogenesis and the deep geological processes of the Tarim Large igneous province.The Wajilitag diabase and diabasic porphyrite have low Mg^#,and their Ti O₂,Fe₂O₃^T and Al₂O₃ show good geochemical trends with Mg O in the Harker diagrams.These features suggest obvious fractional crystallization(eg.pyroxene and iron-titanium oxides)in the evolution process of the magma.The study of Mg-Zn isotopes shows that the Wajilitag diabase and diabasic porphyrite have normal?²⁶Mg(-0.23±0.02‰?-0.34±0.06‰)and heavy?⁶⁶Zn values(+0.28±0.00‰?+0.46±0.01‰).The influence of the crustal contamination or fractional crystallization may not produce such Mg-Zn isotopic characteristics,and we suggest these features imply the involvement of the oceanic ferromanganese nodules and the carbonate minerals(calcite)in the source of the diabase and diabasic porphyrite.The samples show rich Fe and Ti values,suggesting the presence of eclogite components in the source.In addition,the characteristics of the high alkali values may be due to the low degree partial melting and the influence of the carbonated mantle.Combined with the Sr-Nd isotopic features((⁸⁷Sr/⁸⁶Sr)_i=0.70629?0.70368,?_Nd(t)=-4.64?-0.25),we concluded that the primary magma of the diabase and diabasic porphyrite may be produced by the low degree partial melting of the mixed asthenosphere and enriched lithospheric mantle in the presence of eclogite,oceanic ferromanganese nodules and carbonate(calcite).According to this study,we proposed a plate-plume-lithosphere model of Tarim Large igneous province.In the early-middle Paleozoic,the south Tianshan oceanic plate subducted southward beneath the Tarim craton,and the carbonatic melts/fluids released from the subduction plate would metasomatize the overlying lithospheric mantle and form the carbonated peridotite.The continuous subduction of the subduction plate caused the melting of the eclogite and produced the high-Si melts.The high-Si melts would react with the overlying lithospheric mantle and generate the iron-rich domain.In addition,some oceanic ferromanganese nodules and carbonate fall into the deep mantle with the subducted slabs.In the ca.280Ma or later,the submerged slabs with ferromanganese nodules may be caught by the upwelling plume,and then interact with the lithosphere mantle.The primary magma of the diabase and diabasic porphyrite were produced by the low degree partial melting of the mixed mantle source,and then undergo fractional crystallization in the magma chamber before emplacement into the former plutons.