Petrogenesis and Deep Dynamic Processes of Early Permian Alkaline Lamprophyres in Tarim Large Igneous Province, NW China

The Tarim Large Igneous Province is characterized by long duration of magmatism, 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 phase 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 SiO2 (43.5%-49.4%), high Fe2O3t (9.32%-15.50%), high TiO2 (2.28%-4.58%), and Mg# numbers of 43.6-52.9, and 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 and 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 (0.704 36-0.705 34), εNd(t) (-1.88-+1.10) and (206Pb/204Pb)i (17.19-17.89) of the Wajilitag alkaline lamprophyres indicate derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB. Notably, the δ 26Mg values of the Wajilitag alkaline lamprophyres are typically lighter than those of 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 suggests that plume-subducted altered oceanic slab interaction could make important contributions to the genesis of the Tarim Large Igneous Province. © 2024 China University of Geosciences. All rights reserved.