Petrogenesis of Aillikites in the Tarim Large Igneous Province,Northwest China:Implications for the Deep Carbon Cycle in the Continental Interior
As typical deep-mantle-derived melts,alkaline ultramafic lamprophyre provide important clues to mantle metasomatism by recycled crustal materials and the deep-earth carbon-water-sulfur cycle. To provide new insights into the petrogenesis of aillikites as well as their mantle source,more broadly,the genetic link between intraplate magmatism and the deep carbon cycle in continental interiors,we examined the Wajilitag aillikites in the Tarim Large Igneous Province. New mineral and bulk-rock geochemistry along with Sr-Nd-Pb isotope results were obtained. The Wajilitag aillikites are nearly primitive (Mg#=69-73),silica-undersaturated (SiO2=28.67％-31.20％),alkaline in nature (Na2O+K2O=1.12％-2.18％),and enriched in FeOT (13.57％-15.32％),TiO2 (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 element (LREE),and depletion of high field strength elements (HFSE),and possess negative K,P,Ti,Nb-Ta,and Zr-Hf anomalies,similar to those of volcanic arc basalts. Bulk-rock (87Sr/86Sr)i (0.703765-0.703914),εNd(t) (4.48-4.75),and (206Pb/204Pb)i (18.4563-18.7527) of the Wajilitag aillikites indicate derivations from slightly depleted mantle sources similar to those of FOZO-type mantle. The trace element and isotopic compositions therefore indicate that the aillikites are integrated results of metasomatic enriched lithospheric mantle and mantle plume. In addition,high 100×Mn/Fe (1.02-3.29) and 10000×Zn/Fe ratios (10.6-23.0) in phenocrystic olivines from the Wajilitag aillikites,coupled with their Mn/Zn ratios of 11.1-16.4,are indicative of a source containing pyroxenite rather than a homogeneous peridotite source. These phenocrystic olivines also show a positive correlation between Sc and Ni as well as no obvious correlation between Co and Ni,further indicating that the addition of recycled oceanic crust to the mantle peridotite produced pyroxenite components in the source of the Wajilitag aillikites. The coupled enrichment of Ca and Ti in the phenocrystic olivines and the occurrence of carbonate minerals in the aillikites point to a carbonate metasomatized mantle source. Hence,it can be inferred that low-degree partial melting of the metasomatized lithospheric mantle containing PIC-type veins under the impact of a carbonated mantle plume produced the aillikitic magmas. Our results provide solid evidence of the deep carbon cycle in the continental interior.
aillikitesTarim large igneous provinceolivinemantle plumepyroxenite
万方数据
维普
