Petrogenesis Of Aillikites In The Tarim Large Igneous Province,NW China:Implications For Deep-earth Carbon Cycle

As typical deep-mantle derived rocks,alkaline ultramafic lamprophyre can provide important clues to metasomatism of mantle by recycled crustal materials and deep-Earth carbon-water-sulfur cycle.To provide new insights into the petrogenesis of aillikites and their mantle source as well as,more broadly,the genetic link between intraplate magmatism and deep carbon cycle in continental interiors,we examined aillikites in the Tarim Large Igneous Province.New mineral and rock geochemistry,along with Sr-Nd-Pb isotope data were obtained.The Wajilitag aillikites are slightly differentiated（Mg^#=69-73）,silica-undersaturated（Si O₂=28.7-31.2%）,alkaline in nature（Na₂O+K₂O=1.12-2.18%）,and show enrichment in Fe₂O₃T（13.6-15.3%）、Ti O₂（1.89-2.11%）and compatible elements（i.e.,Ni and Cr）.They are also characterized by enrichment of incompatible elements,including light rare earth elements（LREEs）,and depletions of high field strength elements（HFSEs）,and possess negative spikes of varying magnitudes at K、P、Ti、Nb-Ta、Zr-Hf.Bulk-rock(⁸⁷Sr/⁸⁶Sr)_i（0.70377-0.70391）,ε_Nd（t）（+4.48-+4.75）and(²⁰⁶Pb/²⁰⁴Pb)_i（18.456-18.753）of the Wajilitag aillikites,signify derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB.The trace elements and isotope compositions therefore indicate the aillikites may be the result of the combination of metasomatic enriched lithospheric mantle and mantle plume.Additionally,high Mn/Zn（11.1-16.4）and 100Mn/Fe（1.02-3.29）in primitive olivine phenocrysts（Fo>85）,coupled with their high Ni,low Ca、Li contents are indicative for the presence of recycled oceanic crust in a mantle peridotite source,which are possibly present in the form of peridotite source containing carbonated phlogopite-rich pyroxenite metasomatic veins.Our results also provide solid evidence for the deep carbon cycle in continental interiors.