The Petrogenesis Of Baima And Taihe Mafic Layered Intrusions In Elip,Western China

Plume-related magmatism has formed a series of ultra-large layered intrusions and Fe-Ti-V oxide ore-bearing deposits in the Emeishan large igneous province?ELIP?,Southwest China.The Baima and Taihe mafic layered intrusions host the world class Fe-Ti-V oxide deposits.The type of the confirmed crustal contaminations and information of mantle plume in the intrusions require evidences from carbon and noble gas isotopic compositions.In the present study,we have measured the carbon and noble gas isotopic compositions of volatiles from magmatic minerals in the Baima and Taihe mafic layered intrusions.These data have been measured to reveal the origin of magmatic volatiles,the mixing of mechanism of the crustal materials and petrogenesis.The most important conclusions from this study are summarized as following:?1?The?¹³C_CO2?-28.9‰^-3.9‰?and?¹³C_CH4H4 values?-52.4‰^-8.6‰?in the Baima and Taihe intrusions are plotted into the ranges of mantle and crust.The carbon isotopic composition of methane homologues show normal or partial reversal distribution patterns.?2?The ³He/⁴He?0.47¹.85Ra?and ⁴⁰Ar/³⁶Ar values?293.3⁹92.2?in the Baima intrusion is lower than the Taihe intrusion?0.89¹.96Ra and 366.1⁴347.1?.The²⁰Ne/²²Ne and ²¹Ne/²²Ne are plotted around the mass fractionation line and mid-ocean ridge basalts.The noble gases exhibit a negative correlation between ³He/⁴He and ⁴He in the Baima intrusion,and a positive correlation between ⁴⁰Ar/³⁶Ar and ⁴⁰Ar in the Taihe intrusion.?3?The magmatic volatiles in the Baima and Taihe intrusions were charactered by the mixing of the deep mantle,crust and atmosphere:The ³He/⁴He and ⁴⁰Ar/³⁶Ar values are plotted between the atmosphere,crust and mantle plume.The ²⁰Ne/²²Ne and²¹Ne/²²Ne values indicated a large proportion of air,mantle plume and upper mantle origins.The?¹³C of CO₂ and CH₄ suggested that the magmatic volatiles of the mantle mixed with the volatiles of crustal origins.?4?The type and contaminated mechanism of crust materials in the Baima and Taihe intrusions were discussed:The characteristics of carbon isotope show normal or partial reversal distribution patterns could be interpreted as recycled oceanic plate in the magma source or sedimentary organic materials from country rocks additions.The subduction of the oceanic plate can transport crust materials and atmosphere into the mantle.The ³He/⁴He and?¹³C_CO2O2 indicated that the parent magma mixed with altered oceanic fluid components or sedimentary.The lower ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios may be related to addition of recycled oceanic crust material in the magma source.?5?The mantle plume could be contributed to the formation of the Baima and Taihe mafic layered intrusions:the ages of the formation of mafic intrusions in the Baima and Taihe are similar to the ELIP basalts.Noble gas isotopes indicated that the Baima and Taihe magma could be originated from the mantle plume and lithospheric mantle that was modified by subducted fluid.The Baima intrusion was contaminated by more crustal fluid.