The Yingmailai granite, located along the southern margin of the South Tianshan Orogen, provides an important record of Permian magmatism associated with the tectonic reorganization of the southern Central Asian Orogenic Belt. Previous studies have established the basic lithological and whole-rock geochemical characteristics of the intrusion, but the nature of its magma source and the relationship between magma differentiation and regional tectonic evolution remain insufficiently constrained. Here, we integrate petrography, whole-rock major- and trace-element geochemistry, zircon UPb geochronology, zircon trace-element compositions, and LuHf isotopes to investigate the petrogenesis and tectonic significance of the Yingmailai granite. The granite is characterized by high SiO₂ and alkali contents, low Ba, Sr, Eu, Ti, and P, and enrichment in Rb and other incompatible elements, indicating extensive magmatic differentiation. Zircon UPb dating constrains the emplacement of the Yingmailai granite to 258.1 ± 4.7 Ma. Zircon εHf(t) values range from −7.9 to +1.0, indicating a predominantly evolved crustal source with a contribution from juvenile components. The absence of pronounced HREE depletion in whole-rock compositions suggests that garnet was not a major residual phase during magma generation. Integrating geochemical data with regional geological constraints, we interpret the Yingmailai granite as a hybrid S-type granite derived from the melting of old crustal materials with a contribution from juvenile crustal components, followed by fractional crystallization during Late Permian tectonic reorganization in the South Tianshan region. Its association with regional fault-controlled polymetallic geochemical anomalies indicates a potentially favorable regional metallogenic setting.
The use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for mapping analysis can provide geochemical and geochronological data in conjunction with crucial spatial information. The combination of these datasets is important for understanding the mineral paragenesis within a rock sample. However, several issues may arise during analysis that can cause increased dispersion and therefore minimise accuracy and/or precision. These issues include analytical and data reduction artefacts caused by incomplete screening of secondary phases, the discrepancy between laser repetition rate and the total sweep cycle time, biasing towards different isotopes during the sequential cycling of the quadrupole, and random single isotope spikes/noise. This is further compounded when outlier pixel data are grouped into pseudo-analytical points based on proxies for their radiogenic isotopic ratio (e.g., 207Pb/235U, 238U/208Pb), a popular approach for ensuring the best possible spread of data on an isochron diagram. We propose alternative approaches for processing data from LA-ICP-MS mapping analysis in order to minimise the impact of outlier pixels. The first option is to use robust regression in order to assign weighting to pixels which has been shown to be effective against outliers. A second option is a Bayesian estimation to calculate a probability density surface for estimating the maximum likelihood of a sample's age and initial 207Pb/206Pb composition. The robust regression and Bayesian estimation methods were tested against the traditional grouping technique using in-situ U–Pb geochronology data of natural carbonate samples from the Proterozoic to the Palaeocene across four analytical LA-ICP-MS mapping sessions.
We describe an ultrarefractory Ca,Al-rich inclusion (UR CAI) CC072–1 in the ordinary H3 chondrite Chug Chug 072 (CC 072), which is a polymict microbrecia containing carbonaceous chondrite clasts. CC072–1 consists of several mineralogically-zoned nodules. The cores of nodules, composed of perovskite, warkite, and kangite, are surrounded by mantles of Sc-rich davisite and spinel. The texture and mineralogical zoning of CC072–1 suggest it formed by gas-solid condensation in a cooling nebular gas. Most primary minerals of CC072–1 are enriched in FeO, indicative of metasomatic alteration and thermal metamorphism in an asteroidal setting. The CAI is isotopically heterogeneous: spinel is 16O-rich (Δ17O ~ −23 ‰, where Δ17O = δ17O – 0.52 × δ18O), whereas warkite, perovskite, and davisite are 16O-depleted to various degrees (Δ17O ranges from ~ −18 to −3 ‰). We concluded that CC072–1 likely originated in a 16O-rich gas of approximately solar composition, and subsequently experienced post-crystallization O-isotope exchange with an aqueous fluid. Since Δ17O of aqueous fluid in type 3 ordinary chondrites inferred from Δ17O of secondary magnetite and fayalite is ~ +5 ‰, significantly higher than the Δ17O of 16O-depleted minerals in CC072–1, the oxygen-isotope exchange experienced by CC072–1 could have occurred prior to its incorporation into the CC072 parent asteroid, possibly in a CM-like chondrite parent body. Following the migration, accretion and low-velocity impact event the UR CAI was incorporated in the H3 chondrite during brecciation.
The Mekongga and Pompangeo complexes of the Sulawesi Metamorphic Belt in the Kolaka area are associated with the East Sulawesi Ophiolite and contain metasedimentary schists and gneisses derived mainly from greywacke and pelite protoliths. The present study aims to characterize lithium (Li) distribution in these metasedimentary rocks and to constrain the provenance, compositional maturity, and tectonic setting of their protoliths. To address these objectives, an integrated approach combining petrographic investigation, mineral chemistry, and whole-rock geochemistry was applied. Of 50 field samples, 20 were examined petrographically and eight geochemically. The mineral assemblages indicate greenschist-facies retrogression and suggest a possible earlier upper-greenschist- to amphibolite-facies metamorphism. Calculated chemical index of alteration values of 54.43-73.56 (mean 67.76), excluding the carbonate-rich BNL1 and the anomalous KIL1, show weak to moderate weathering. Compositional variability index values of 0.72-1.19 in these samples, five of which are below 1, indicate heterogeneous compositional maturity. For six samples, light rare earth element (LREE)-enriched patterns, negative Eu anomalies (Eu/Eu* = 0.58-0.63), and immobile trace-element ratios (Th/Sc = 0.98-1.68, La/Sc = 2.30-4.75, Th/Co = 1.88-3.46, and Cr/Th = 1.98-2.56) are consistent with predominantly felsic to intermediate continental sources, whereas the single sample KIL1 is compatible with localized mafic-ultramafic input. Tectonic discrimination diagrams, interpreted with the provenance data, show compositions consistent with a provisional model of deposition along an active continental margin. Li concentrations range from 18 to 106 ppm (mean 41.75 ppm, n = 8; mean 32.6 ppm without the anomalous sample KIL1), representing a modest occurrence rather than evidence of economic mineralization and providing a first whole-rock Li baseline from the Kolaka area. Li shows positive whole-rock rank correlations with Fe2O3(t), TiO2, Al2O3, and Cr that persist when KIL1 is excluded, whereas the apparent associations with MgO, Co, and Ni collapse or reverse in sign without KIL1. These associations are compatible with the aluminous-ferruginous pelitic component of the protolith but do not identify a specific Li host. Phyllosilicates such as biotite, muscovite, and chlorite are therefore considered possible, rather than confirmed, hosts, and contributions from albite and clinopyroxene cannot be excluded. Broader sampling and mineral-scale Li analyses are needed to resolve Li inheritance versus redistribution and test regional applicability.
Deccan volcanism was a consequence of drifting of the Indian plate over the R & eacute;union hotspot. The basalt lavas in the Main Deccan Plateau are tholeiitic in composition. A similar to 1200 m thick basalt lava was recovered from the scientific drilling of a deep bore-hole KBH-8 in the Koyna-Warna region of south-west Deccan Traps. The thick sequence yielded fifteen Eruptive Phases (EPs) of variable thickness consisting of distinct rare earth element and high field strength element characteristics. In this contribution, we present highly siderophile element (HSE) geochemistry of sixty-one basalt lava samples representing the fifteen EPs from the well-core KBH-8, and three samples from the Deccan Trap extrusion in the eastern Dharwar Craton, which is identical to the Eruptive Phase EP3. This essentially indicates reactivation of deep-seated faults/fractures during the end Cretaceous in the Dharwar Craton. Apparently, the HSE systematics in combination with trace elements, REE, SrNd isotopes and available delta O-18 isotopic compositions in the literature do not reconcile with contamination by the felsic upper crust. Instead, mild assimilation of the subcontinental lithosphere is envisaged. The trace element attributes and HSE systematics of the Deccan Traps resemble the Ni-Cu-HSE undepleted tholeiites of the Siberian Traps. By analogy, the Deccan basalts evolved from extensive fractionation of an olivine-rich high-Mg magma under S-undersaturated conditions. Unlike the coeval subvolcanic intrusions in the Noril'sk region of the Siberian Traps, neither the lava flows nor the coeval subvolcanic intrusions in the Deccan Traps yield any known occurrence of Ni-Cu-HSE mineralization. Importantly, Ti-Nb-Zr systematics in the R & eacute;union lavas recovered during scientific ocean drilling program Leg 115 from the sites 706, 707, 713 and 715 are comparable to EP4 and EP14 in the Main Deccan Plateau. Thus, linking Deccan volcanism over the last 66 m.y. via hotspot trail to the R & eacute;union Island.
