Petrogenesis And Deep Dynamic Processes Of Early Permian Alkaline Lamprophyres In The Tarim Large Igneous Province,NW China

The Tarim Large Igneous Province is characterized by long duration,complex rock types and wide distribution of iron-rich alkaline basalts,although the source and petrogenesis of magmatism associated with it remain disputed.Here we chose the Wajilitag alkaline lamprophyres in the northwestern margin of the Tarim Large Igneous Province to precisely determine their emplacement ages,constrain its petrogenesis and discuss the deep dynamic processes involved in the formation of the Tarim Large Igneous Province using LA-ICP-MS zircon U-Pb dating,mineral and whole-rock geochemistry.Zircon U-Pb geochronology indicates that the Wajilitag alkaline lamprophyres formed at 279±1 Ma,belonging to the second pulse of Tarim Large Igneous Province magmatism.The lamprophyre is characterized by a panidiomorphic-porphyritic texture imparted by olivine,clinopyroxene,amphibole and biotite set in a groundmass of plagioclase,clinopyroxene,amphibole,biotite and titanomagnetite microcrysts.These rocks have low Si O2（42.9-49.4%）,high Fe₂O₃t（9.32-15.5%）,Ti O₂（2.28-5.61%）,Mg^#numbers of 43.6-60and are enriched in mantle compatible elements（Ni,Cr）.Meanwhile,they also show high Na2O（2.58-5.50%）and low K2O/Na2O ratios（0.31-0.78）,highlighting their sodic characters.Fractionated chondrite normalized REE patterns indicates involvement of an enriched mantle source from within the garnet stability field whereas slightly negative K,Sr,Ti,Zr-Hf anomalies displayed on the primitive mantle normalized multi-element spidergram highlight involvement of a subducted component in the mantle source.Bulk-rock(⁸⁷Sr/⁸⁶Sr)_i（0.70436-0.70534）,ε_Nd（t）（-1.88-+1.10）and(²⁰⁶Pb/²⁰⁴Pb)_i（17.19-17.89）of the Wajilitag alkaline lamprophyres signify derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB.Notably,theδ²⁶Mg values of the Wajilitag alkaline lamprophyres are typically lighter than the normal mantle source.The primitive magmas of the Wajilitag alkaline lamprophyres are likely derived from low degrees melting of carbonated eclogite bearing mantle plume,and possibly affected by the plume-lithosphere interaction.Ultimately,our study suggest that plume-subducted altered oceanic slab interaction could make important contributions to the genesis of the Tarim Large Igneous Province.