Mantle source of tephritic porphyry in the Tarim Large Igneous Province constrained from Mg, Zn, Sr, and Nd isotope systematics: Implications for deep carbon cycling

The nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn−Mg−Sr−Nd isotopes of a rare tephritic rock suite. The Sr−Nd isotopes [(87Sr/86Sr)i = 0.70368−0.70629; εNd(t) = −0.25−4.64] and δ26Mg values (−0.23‰ to −0.34‰) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28‰ to +0.46‰ and +0.30‰ to +0.39‰, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06‰) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05‰). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs.

Volcanic spherules condensed from supercritical fluids in the Payenia volcanic province, Argentina

Spherules can be formed by high-temperature processes during volcanic eruptions, lightning strikes and meteorite impacts. Here we report four different types of spherules and spheroidal particles associated with tephra deposits from two separate volcanic fields in the southern Payenia province of Argentina. These silicate and carbonate spherules represent <0.01% of the sampled material, with individual spherules <200 µm in size. Thirty particles were imaged. Only the transparent spherules are smooth, perfect spheres; other morphologies include ellipsoids and aggregated dumbbells. The spheroids are either hollow or solid. Major element analyses show that the spherules and spheroids have silica-rich, Fe-rich, carbonate and basaltic compositions. Chemical analysis of the carbonate spheroids shows some variability in the trace element content between the cores and rims, suggesting element mobility and loss towards the margins. All the analysed carbonate spheroids have elevated Sr/Y, La/Y and La/Ce ratios outside the range for sedimentary carbonates. All four spherule types are considered to be volcanic in origin, with the excess CO2 required for the formation of the carbonate spherules potentially sourced from the basement lithologies. Based on the major and trace element analyses, we conclude that the silica-rich and carbonate spherules formed by instantaneous condensation from supercritical CO2-rich hydrous fluids saturated with dissolved silicates.Supplementary material: Appendix A, containing the full analytical dataset collected by electron probe microanalysis and secondary ion mass spectrometry, is available at https://doi.org/10.6084/m9.figshare.c.5108689

Strontium isotopic composition in waters of mud volcanoes of Azerbaijan

The isotopic composition of strontium was studied in the waters of 22 Azerbaijan mud volcanoes, in which the isotope composition of oxygen and hydrogen, as well as the concentration of macro and micro elements, was previously [Lavrushin et al., 2015] determined. 87Sr/86Sr ratios in the waters of Azerbaijan mud volcanoes are within 0.70670.7083. The minimum ratio was established in Neftechala Yuzhnaya volcano, located in the south of the territory ‒ in the Kura region, which is characterized by the lowest average values of 87Sr/86Sr = 0.70700.0003 and 18O = 2.01.8 compared to volcanoes situated northern ‒ in Shemakha ‒ Gobustan, Absheron and Caspian regions (87Sr/86Sr average = 0.70760.0005, 18O average = 4.82.5). The relation between the strontium isotopic composition and the isotopic composition of oxygen suggests that the formation of the isotopic characteristics of the mud volcanic waters of Azerbaijan involves two main sources, one of which is predominantly associated with sedimentary carbonates of Cretaceous-Paleogene age, and the second, prevailing in the Kura region, has traces of isotopic exchange with volcanic rocks. The role of strontium dissolved in the sea water, as well as strontium, which could be extracted from modern terrigenous sediments of the Caspian Sea and terrigenous clay rocks of the Maikop series in the mud volcanic waters of Azerbaijan is insignificant.