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 Fe₂O₃ᵗ, 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 Réunion hotspot. The basalt lavas in the Main Deccan Plateau are tholeiitic in composition. A ∼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 δ18O 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 Réunion 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 Réunion Island.
The petrogenesis of I-type granites yields critical insights into crust–mantle interactions and geodynamic transitions. The Late Permian (ca. 256–254 Ma) I-type Moonbi Suite, intruding the southern New England Orogen (NEO) of eastern Australia, preserves a key record of the tectonic reorganization following the terminal Hunter-Bowen contractional event. To constrain its melt sources and magmatic evolution, we present an integrated study of mineral chemistry, whole-rock geochemistry, Sr–Nd–Pb–Hf isotopes, and zircon U–Pb–Hf isotopes from the monzogranites. Mineralogical features, including oscillatory-zoned plagioclase and compositional variations in hornblende and biotite, provide compelling evidence for magma mixing. Geochemically, the suite exhibits adakitic signatures (e.g., elevated Sr/Y) and isotopic compositions (whole-rock εNd(t) = +1.0 to +2.4 and εHf(t) = +1.4 to +7.2, and zircon εHf(t) = +5.2 to +8.0), indicative of a hybrid source. Trace element modeling demonstrates that mixing between mantle-derived melts and crustal melts derived from a garnet-bearing mafic lower crust was the dominant process, whereas fractional crystallization played a subordinate role. We propose that a Late Permian to Early Triassic transtensional regime (ca. 255–245 Ma), herein referred to as the post-Hunter-Bowen extension, potentially driven by lithospheric delamination or slab breakoff, facilitated the upwelling of enriched mantle melts. These melts supplied both heat to induce anatexis of the overthickened lower crust and mafic material for mixing, thereby generating voluminous I-type magmatism. Consequently, the Moonbi Suite exemplifies syn-extensional magmatism in a collapsing orogen, highlighting the essential role of mantle input in the genesis of post-orogenic granites.
Feldspar dissolution and/or precipitation is the most significant process controlling the chemical composition of volcanic rocks (including alkali and plagioclase), which, in turn, affects hydrothermal alteration. Compositional changes in Na2O, CaO, and K2O result from feldspar destruction as fluid pH decreases and temperature increasesc. The major elemental oxides (Na2O, K2O, CaO, and Na2O + CaO) and their ratios (Al2O3/Na2O, Al2O3/K2O, K2O/Al2O3, Na2O/Al2O3, Na2O/K2O, and K2O/Na2O) are some of the methods that have been successfully applied in soil sciences, locating ore deposits, and mineral exploration. However, applying these oxides and their ratios to identify zones of hydrothermal alteration in a geothermal area is not well established. Several inferences have been made based on compositional changes (increases or decreases) in rocks resulting from hydrothermal alteration. Some of these inferences are: (1) The lower the Na2O and K2O content, the more intense the rock's hydrothermal alteration; (2) A gradual decrease in CaO and K2O and an increase in Na2O concentrations in volcanic rocks result from alteration of calcic and potassic feldspar to albite; (3) Na2O < 2 wt% in a rock suggests that it is altered; (4) decrease in the molar ratios of Na2O/Al2O3 and K2O/Al2O3 was observed with increasing alteration; (5) low Al2O3/Na2O and K2O/Na2O ratios indicate that the rocks are fresh; (6) High K2O/Al2O3 ratios in the rocks indicate that they have undergone hydrothermal alteration; (7) K2O/Na2O and Al2O3/Na2O are both good indicators of the alteration degree, indicating lower values for less alteration and higher values for more altered rocks, among others.These methods have been successfully applied to the surface rocks of the Acoculco Geothermal Field (AGF), where petrographic and mineralogical methods have already identified alteration status. The studied major element oxides and their ratios appear to be relatively easy, quick, and cost-effective tools for detecting altered volcanic rocks during the initial stages of geothermal exploration.
Post-collisional to within-plate granites, mostly coarse-grained monzogranite, form a prominent pluton with sharp intrusive contacts against the older rocks at the Wadi Rahjan area in western Saudi Arabia. The monzogranite bears considerable amount of accessory minerals (~5–10%), which are non-radioactive and represent a potential reservoir of rare-earth elements (REEs). Feldspars, biotite and amphibole compositions suggest alkaline affinity of possible calc-alkaline magma, and confirm the post-collisional emplacement during the late Neoproterozoic as a highly fractionated felsic pluton. Chemistry of amphibole (ferro-calcic to sodic-calcic) indicates low-pressure (3.1–4.8 kbar) and low fO2. Accessory minerals are coarse (allanite, bastnäsite, fluorite, Fe-Ti oxides), fine (zircon, fluoroapatite) and extremely fine (yettro-columbite, xenotime-Y). Allanite dominates the accessory minerals (˃90%), remarkably coarse, euhedral and occasionally zoned. It is Y-free ferriallanite-(Ce) with remarkable enrichment of LREEs+Y (R2O3 = 22.73–30.19 wt%). Zircon is U-, Th-, and REEs-free. This zircon is characterized by low Hf content (nil-1.14 wt%), which is abnormally low for magmatic zircon. In addition to LREEs, yettro-columbite and xenotime-(Y) as magmatic minerals are F-bearing (up to 7.7 wt%) and contain high Y2O3 (16.25–22.73 wt% and ~36 wt%, respectively).Textural evidence indicate slight to extensive bastnäsitization of the magmatic ferriallanite-(Ce). Hydrothermal solutions bearing F− and CO2 facilitate the formation of bastnäsite with doubled LREEs (R2O3 = 49.71–70.72 wt%) compared with the allanite precursor. La2O3, Ce2O3 and Nd2O3 are the most common in bastnäsite reaching up to Σ59.98 wt%, together with noticeable F content (up to 7.8 wt%). It is concluded ferriallanite-(Ce) is exclusively magmatic, the major reservoir for REEs, together with F-bearing phases (apatite, fluorite, yettrocolumbite, xenotime). Along structural planes such as shear planes, hydrothermal solutions gain its F− from the decay of these minerals, fluorite in particular. Fluorine is combined with CO2 from possible descending meteoric waters along fractures to form bastnäsite as a secondary hydrothermal mineral. They are oxidizing fluids that percolated downwards in the granite and form peculiar Fe-chlorite (chamosite) indicating 214–232 °C crystallization temperature. Two varieties of bastnäsite are distinguished (F-free/poor and F-rich) due to fluctuation of F- in the hydrothermal solutions and changes in the physicochemical conditions. Depletion of zircon in U and Th is attributed to the original mantle source of the melt and its infertility in radioelements. Mode of occurrences, abundance and mineral chemistry of REEs-bearing accessory minerals in the Nu'man granite at Wadi Rahjan suggest their potentialities for applications in a variety of technological applications such as clean/green energy production, for example solar cells and wind mills, in addition to the use in highly demanded electric vehicles and powerful Nd-magnets.
