The Mashhad granitoid in the Paleotethys suture zone of northeastern Iran has been widely studied, yet its tectonic setting and magma sources remain debated. Because large granitic bodies within this suture are globally rare, they offer valuable insight into the closure of the Paleotethys Ocean and associated Paleozoic tectonic regime. Here, we present new data on a diverse suite of granitoids exposed along the Paleotethys suture zone. Radiometric ages indicate emplacement at ca. 217–190 Ma, and our new results refine the main magmatic episode to 210–206 Ma. Geochemically, the rocks are predominantly S-type granite, although some samples display A- and I-type affinities. These granites were mainly generated by partial melting of variable metasedimentary sources, including pelitic and clay-rich rocks, as well as clay-poor sediments such as greywacke and arkose, with minor marl or metabasite interlayers. High initial 87Sr/86Sr ratios (0.7062–0.7212) and negative ƐNd(t) values (−7 to −3) argue against significant contributions from the asthenospheric or lithospheric mantle. We infer that collision between Gondwana and Eurasia buried crustal sediments to the depth within the Paleotethys suture, where they were subjected to high temperatures and pressures and locally reached eclogite- and amphibolite-facies conditions. Crustal thickening during collision increased gravitational instability, promoting detachment of the lithospheric mantle, and the subsequent upwelling of hot mantle raised the geothermal gradient and triggered partial melting of shallow crustal metasedimentary rocks in the depth. We therefore conclude that the Mashhad granitoids formed not in a typical syn-collisional or active subduction setting, but in a post-collisional regime related to lithospheric delamination.
This study aims to constrain the ore genesis of two mineralizations situated within the Late Devonian Siljan meteorite impact structure (central Sweden). Meteorite impact event-induced hydrothermal systems are a relatively commonly observed features in larger impact structures – which are evident by local hydrothermal alteration in the target rocks. These hydrothermal fluids circulate the fractured rocks, which may lead to leaching and the formation of epigenetic mineralizations. Although a few known impact structure-hosted Pb-Zn mineralizations have been recognized, their genesis is poorly studied. The Boda deposit and Sollerön mineralization are hosted primarily in Ordovician limestones and, to a lesser extent, occur as interstitial disseminations within the stratigraphically lower Ordovician Obolus Beds conglomerate.Although hosted in different parts of the impact structure, with Boda in the eastern sector and Sollerön in the southwest, both mineralizations display remarkably similar ore mineralogy and textural characteristics, dominated by colloform sphalerite and galena, with subordinate pyrite and chalcopyrite. The application of the Ga-Ge-In-Mn-Fe-in-sphalerite geothermometer yields comparable formation temperatures for the Boda (160–170 °C) and Sollerön (ca. 180 °C) mineralizations. These temperature calculations align with the previously established impact-induced hydrothermal system – which shows an outward radial temperature decrease from the center of the impact structure. Differences in sulfide chemistry between the two mineralizations are attributed to variations in the surrounding country rocks, which likely provided distinct metal sources to the localized, impact-induced hydrothermal system.The involvement of the surrounding Paleozoic sedimentary rocks as a partial metal source is supported by the Co/Ni values of <1 in pyrite, indicative of a sedimentary metal component, from the main Pb-Zn ore, host rock limestone, and the Obolus Beds conglomerate mineralization. Raman spectra of carbonaceous material indicate temperatures of 274 ± 30 °C, which is in accordance with maximum burial temperatures of the surrounding Paleozoic sedimentary rocks rather than the impact-induced hydrothermal system. These temperatures provide additional evidence for interaction between the hydrothermal fluid and the sedimentary rocks. With previously published Pb isotopes showing a Proterozoic basement source for Pb, we conclude a mixed source of metals for the Siljan mineralizations.The cumulative evidence from this study points to a hydrothermal origin induced by the Siljan meteorite impact, where the metals were sourced from both the underlying sedimentary strata and the crystalline basement. Organic-rich fluids mobilized by the impact event, together with pH changes caused by fluid–carbonate rock interaction and fluid mixing, most likely promoted sulfide precipitation and ore formation.
Whole-rock geochemistry of siliciclastic rocks carries a mixed signature of source-rock chemistry, weathering, hydrodynamic sorting, and diagenesis, complicating tectonic-discrimination in Precambrian successions with prolonged post-depositional histories. This study uses the Paleoproterozoic Papaghni sub-basin, Cuddapah Basin, India, as a case study to critically evaluate these discrimination approaches and separate sedimentary-process overprints from primary signals. Bulk major, trace, and rare earth element (REE) compositions were analyzed and compiled with published datasets for all Papaghni sub-basin formations. Forward modelling of chondrite-normalized REE patterns indicates ~60% felsic, ~28% mafic, and ~12% intermediate sediment sources; the intermediate component is interpreted cautiously, as weathered mafic precursors can mimic an intermediate bulk composition. The coarse-grained Gulcheru, Pulivendla, and Gandikota quartzites show pronounced quartz dilution and heavy-mineral enrichment from high-energy, near-shore reworking, whereas the finer-grained Vempalle and Tadpatri shales, deposited in lower-energy shallow-marine settings, retain higher clay-forming-element (Al2O3, Fe2O3, MgO, Na2O) concentrations. Although all five formations share a common felsic-dominated source, a similar weathering-climate regime, and the same basin, elemental redistribution during sorting, reworking, and diagenesis produces substantial scatter on conventional tectonic-discrimination diagrams. Log-ratio-transformed discriminant-function diagrams, applying linear discriminant analysis to volatile-free, closure-corrected major-element data, yield more internally consistent groupings than traditional bivariate plots but remain sensitive to the same process-driven redistribution of elements. This sensitivity is diagnostic rather than incidental: cross-comparing diagrams built on different element subsets identifies the sedimentary process responsible for a given discrepancy, offering a transferable framework for evaluating tectonic-discrimination reliability in other ancient, multiply-overprinted sedimentary basins.
Mantle source heterogeneity in intraplate settings reflects spatial variations in depletion, metasomatism, and melt extraction processes within the lithospheric mantle. Cerro Verde melanephelinites (central Mexico) provide new constraints on these processes through integrated petrographic observations, whole-rock geochemistry, and olivine compositions. The studied rocks display low modal olivine contents (≤10 vol%) and restricted whole-rock compositions, indicating that bulk compositions are not significantly affected by olivine accumulation. Olivine populations record multiple origins, including mantle-derived xenocrysts (Fo 88–90 mol%) and magmatic phenocrysts (Fo ∼84–88 mol%). The mantle-derived olivine xenocrysts, together with orthopyroxene xenocrysts and peridotite xenoliths, constitute a small but distinct mantle crystal cargo entrained by the ascending magmas. Only a subset of intermediate-Fo olivines approaches equilibrium with the most primitive melts (Mg# ≥ 65), supporting the interpretation that the Cerro Verde magmas closely approximate near-primary mantle-derived melts despite carrying a minor mantle-derived crystal cargo. Olivine NiO and CaO systematics further indicate a peridotitic mantle source. Major-element systematics and melting models indicate low degrees of partial melting. Highly incompatible elements (TiO₂ and Na₂O), modeled using near-fractional melting equations and bulk partition coefficients for a spinel lherzolite source, indicate minimum melt fractions of ∼1–3%, whereas thermodynamic modeling and moderately incompatible elements constrain integrated melt fractions of ∼6–15% under upper mantle conditions (∼1.25 GPa and ∼1400 °C). Combined geochemical, mineralogical, and xenolith evidence indicates that the Cerro Verde magmas were derived from a relatively homogeneous and depleted spinel peridotite mantle domain, contrasting with more fertile and metasomatically modified mantle regions in nearby volcanic fields. These results highlight the role of source depletion and melt extraction processes in generating compositional variability in intraplate magmas and provide new insights into the geochemical expression of mantle heterogeneity in continental settings.
Deciphering Paleoproterozoic tectono-magmatic events is fundamental to reconstructing crust-mantle interactions and the tectonic assembly of East Asian continental blocks. However, the Orosirian tectono-magmatic records on the Korean Peninsula remain incompletely constrained, particularly in the southwestern Yeongnam Massif. Here, we investigate the Orosirian mafic xenoliths and metagranitoids from the Gangjin-Wando-Jangheung area to refine the timing of magmatism and evaluate magma sources and tectonic settings. Zircon U-Pb analysis indicates that the mafic xenoliths and metagranitoids formed early (ca. 1.98–1.94 Ga) and middle (ca. 1.89–1.87 Ga) Orosirian, respectively, documenting temporally distinct magmatic episodes.The mafic xenoliths represent mantle-derived magmas characterized by high Mg# (60–64) and elevated Ni and Cr contents. Their enrichment in light rare earth elements and large lithophile elements, coupled with pronounced negative Nb-Ta and moderate zircon εHf(t) values (−6.1 to +2.9) are consistent with derivation from enriched arc-related lithospheric mantle. The metagranitoids are calc-alkaline I-type granitoids interpreted to have formed by partial melting (5–15%) of a mafic igneous protolith compositionally similar to the mafic xenoliths, as supported by thermodynamic phase-equilibrium and numerical modeling. Their arc-like trace element patterns and low zircon εHf(t) values (−12.46 to +0.50) indicate magma generation in an arc-related setting involving old crustal components.These results demonstrate that two-stage Orosirian arc-related magmatism occurred in the southwestern Yeongnam Massif contrasting with contemporaneous tectono-magmatic histories of other major tectonic domains in the Korean Peninsula and the eastern North China Craton. This distinction suggests that the Yeongnam Massif evolved as a discrete tectonic domain during the Orosirian.
Understanding the petrogenesis of Archean potassic granitoids is crucial for grasping how the early continental crust was generated and evolved. However, studying Archean magmatism presents significant challenges-particularly when relying solely on whole-rock geochemical compositions. Complementary mineral-scale analytical approaches are therefore essential to address these limitations. This study conducted textural and in situ geochemical analyses of apatite and zircon from the Mesoarchean (ca. 3117 Ma) monzogranite in the Anshan area, northeastern North China Craton. The apatite and zircon samples largely exist as euhedral-subhedral crystals and preserve primary magmatic chemical signatures, indicative of a magmatic origin. Apatite from the monzogranite yields initial 87Sr/86Sr ratios of 0.7053-0.7124 and epsilon Nd(t) values of-6.53 to 3.06, and has systematically low (La/Yb)N ratios, along with low Sr and high heavy rare earth element and Y concentrations. Coupled with the high-K whole-rock characteristics, the monzogranite was generated under highpressure eclogite facies, with garnet as the dominant residual phase. Zircon two-stage Hf model ages cluster at ca. 3.8 Ga, suggesting that the monzogranite resulted from melts whose source was linked to partial melting of pre-existing Eoarchean tonalite-trondhjemite-granodiorite rocks. Calculations of trace element compositions in melts equilibrated with apatite reveal elevated Rb contents and Rb/Sr ratios, implying a process of dehydration melting. Zircon crystals tend to exhibit unradiogenic Hf isotopes with epsilon Hf(t) ranging from-10.0 to 0.28, and have high ratios of U/Yb and Sc/Yb, overlapping with the arc magma-type zircon field, suggesting that the monzogranite originated in an arc-related magmatic setting. Our findings demonstrate that analyzing the texture and geochemistry of apatite and zircon, alongside comparisons with whole-rock compositions, provides a more comprehensive understanding of the tectonic-magmatic processes of Archean magmas. This integrated approach sheds light on valuable insights into the early Earth's history.
The Chudong PbZn deposit, located in the southern segment of the Ailao Mountain metallogenic belt, is controlled by the coupled effects of fault structures, mafic intrusions, and organic-rich sedimentary strata. The ore body is hosted within a fault-fracture zone developed in the siltstone layers of the Xiamidi Formation of the Carboniferous System. It is spatially associated with a NW-trending F3 fault and basic intrusive rocks. The deposit exhibits an average combined Pb + Zn grade of 5.89%. Rock geochemical analysis indicates that the basic rocks are of island arc tholeiitic basalt origin, reflecting a post-arc extension setting. The mineralization of the Chudong lead–zinc deposit occurred in two main stages, with carbonate–siliceous hydrothermal activity followed by the main sulfide precipitation. Based on geological and geochemical evidence suggests that deep magmatic-hydrothermal fluids mixed with basin brines to generate the primary ore-forming fluids. Organic-rich strata (average TOC = 2.72%) may have provided reduced sulfur that promoted PbZn sulfide precipitation within the fault-fractured zones. This genetic model indicates a close relationship between mineralization, fault-controlled fluid migration, mafic magmatism, and hydrocarbon-bearing sedimentary sequences. Wide-area electromagnetic and dual-frequency induced polarization surveys reveal strong correlations between geophysical anomalies and known ore bodies and delineate several prospective exploration targets. Combined with the regional characteristics of polymetallic mineralization in the Ailao Mountain belt, a structural–intrusive coupling metallogenic model is proposed. In this model, primary faults and intrusions control ore-fluid migration, secondary faults localize mineralization, and fault intersections favor ore accumulation. This model provides an important framework for deep and concealed ore exploration in the Ailao Mountain metallogenic belt.
The Igurubi gold camp, located within the Nzega Greenstone Belt of northern Tanzania, is hosted within the Nyanzian Supergroup, which consists of Neoarchean volcano-sedimentary rocks that are intruded or flanked by intrusions of different ages. The rocks of the Igurubi Gold Camp are largely obscured by lacustrine deposits of the Manonga–Wembere Basin and residual cover, leaving only limited and discontinuous exposures of primary bedrock. Observations along the Mwabomba River and in artisanal mining shafts therefore provide key constraints on the temporal and spatial lithological relationships and structural controls of gold mineralization. Two contrasting granitoid suites occur at Igurubi: trondhjemite with high Al2O3 (mean = 15.6) and Na2O/K2O (mean = 5.3), low heavy REE, high Sr/Y and La/Yb, TTG like affinity), and potassic granites that exhibit lower Al2O3 (mean = 14.8), lower Na2O/K2O (mean = 0.9), low concentrations of heavy REE and variable Sr/Y and La/Yb). Both show enrichment in Zr, Th, and Pb, with negative Nb, P and Ti anomalies in mantle-normalized spidergrams. The geochemical features of the trondhjemites are interpreted as having formed by partial melting of the hydrous basaltic crust within garnet and amphibole stability field, most likely in an Archaean convergent margin. The K-granites on the other hand, are interpreted to have formed by anhydrous partial melting of the pre-existing rocks that include TTG and greenstones.UPb zircon ages indicate emplacement of Igurubi trondhjemites at 2902 ± 15 Ma and potassic granite at 2559 ± 12 Ma. The older trondhjemite predate the ∼2820 Ma mafic volcanism in the Lake Victoria greenstone belts, providing evidence for the first building blocks of the late Archaean continental crust upon which the greenstone succession accumulated. On the other hand, the 2559 ± 12 Ma reported for potassic granites is consistent with the late pulse of granitic magmatism responsible for the stabilization of the Tanzania Craton. Gold mineralization occurs in quartz veins within sheared and hydrothermally altered potassic granites, with sericite-silica alterations and sulphides, pyrite, and associated chlorite, carbonate, and hematite. The maximum age of gold deposition at the Igurubi gold camp is ∼2559 Ma, which is markedly younger than the mineralization ages reported from the Golden Pride Mine (∼2680 Ma) and the Buzwagi Mine (∼2674 Ma). This age disparity indicates that gold mineralization within the region was not the product of a single event but instead reflects multiple mineralizing episodes. The Igurubi mineralization event, therefore, represents a younger phase of hydrothermal activity, demonstrating that ore formation in the Lake Victoria greenstone belts persisted until at least approximately 2.56 Ga. These results reinforce the interpretation that gold deposition at Igurubi is linked to late orogenic processes superimposed on older crustal architecture.
The in-situ micro-area composition of minerals offers critical insights into the source characteristics and mixing processes of granitic magma, while also preserving evidence of late-stage tectono-thermal events and mineralization processes. In recent years, the discovery of large to super-large granite-related pegmatite-type lithium deposits in the Yifeng area, northwestern Jiangxi Province, has drawn increasing attention. Although previous studies have primarily focused on the chronology and bulk geochemistry of granite-related lithium deposits, micro-scale mineralogical processes remain poorly understood. This study investigates muscovite and apatite from three representative granitic intrusions-Ganfang (GF), Guyangzhai (GYZ), and Baishuidong (BSD)-to better understand the lithium mineralization processes. The results show that muscovite from the BSD pluton is significantly enriched in Li, Rb, and Cs, reflecting strong rare metal fertility. This study find the K/Rb ratio below 22 is identified as a reliable geochemical threshold for recognizing Li-mineralized granitic bodies. Furthermore, the Rb content progressive decreases from BSD to GF to GYZ indicates a magmatic evolution trend conducive to lithium enrichment. In addition, apatite geochemistry (delta Ce, Ce4+/Ce3+, and Eu anomalies) not only records a gradually increasing oxygen fugacity from BSD to GF but also reveal the completion of plagioclase fractional crystallization (evidenced by extremely low Eu anomalies in the Guyangzhai pluton). Such oxidizing trends promoted the enrichment of U, Th, Nb, and Ta, whereas prolonged oxidation triggered element mobilization during the magmatic-hydrothermal transition, leading to the formation of barren granites. These findings form a coherent geochemical basis for verifying and evaluating the lithium mineralization potential of the target granitic bodies. Meanwhile, these findings provide new perspectives on the genesis and evolution of lithium-bearing granites and rare metal mineralization in the Yifeng area, offering valuable guidance for future exploration efforts.
Tourmaline-bearing two-mica monzogranite constitutes predominant lithology of the Ke'eryin composite pluton. This study presents in-situ chemical and boron isotopic analyses of tourmaline from the two-mica monzogranite in Ke'eryin rare metal orefield, aiming to decipher the change of tourmaline-forming environment and the granitic magma evolution. Analytical results indicate that the vast majority of tourmaline belong to the alkali group, and all tourmalines exhibit a schorl composition with a magmatic origin. The tourmalines in two-mica monzogranite mainly follow the substitution vector (Na, Mg)(Xvac, Al)- 1, show no correlation between Fe and Al, and exhibit a higher V content, indicating that the tourmalines in two-mica monzogranite were formed in a relatively lower salinity and higher oxygen fugacity conditions than those in Ke'eryin barren pegmatite. The Li, F, and Zn concentrations increase from the tourmalines in two-mica monzogranite to the pegmatitic tourmalines. Boron isotope compositions of analyzed tourmalines in two-mica monzogranite vary in a narrow range between -11.86 and - 10.17 parts per thousand, which is relatively higher compared to those of pegmatitic tourmalines and is mainly attributed to progressive tourmaline crystallization, while fluid exsolution may play a negligible or minor role. Based on the contents of Li, F, and Zn and the boron isotope compositions, we propose that both tourmalines and associated granites may have been derived from metasedimentary source rocks, with pegmatitic tourmalines probably forming later than tourmalines in two-mica monzogranite.
The Gouli gold ore district, located in the eastern part of the East Kunlun orogenic belt in the northern Tibetan Plateau, is an important gold mineralization zone. However, research on the formation age and genesis of gold deposit in this district remains limited, and no consensus has been reached on their genetic mechanism. This study focuses on the Guoluolongwa gold deposit, the largest gold deposit in the Gouli district, and investigates diorite porphyry intrusions that occur nearly parallel to the gold veins. Samples of the porphyry were subjected to U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopic analyses, and in-situ sulfur isotopic analyses of sulfides. Zircon U-Pb dating of pre-mineralization diorite porphyry yielded an age of 202.7 +/- 4.3 Ma (Late Triassic). Geochemical data revealed low SiO2 (51.82-59.03 wt%) and high MgO (5.58-11.26 wt%), Mg# (58-68), Cr (730-1210 & times; 10-6), and Ni (92-196 & times; 10-6) contents, consistent with high-Mg diorite. The samples also exhibited enriched rare earth element patterns with minor negative Eu anomalies. These features show geochemical affinities with sanukitoids, which are thought to form by direct melting of enriched mantle. The epsilon Nd(t) values (+0.4 to +0.8) and trace element ratios indicate that the Guoluolongwa diorite porphyry was produced by partial melting of a metasomatized lithospheric mantle wedge modified by subduction-derived fluids from the Paleo-Tethys Ocean, within a post-collisional extensional tectonic regime. In-situ sulfur isotope analysis of sulfides yielded delta 34S values of 1.0 to 4.1%o, including coarse-grained euhedral pyrite (Py1: 1.3-4.1%o) and fine-grained subhedral pyrite (Py2: 1.0-2.1%o). These sulfur isotope compositions, combined with other geochemical evidence, suggest that the ore-forming materials were primarily mantle-derived. Furthermore, although diorite porphyry dikes and gold-bearing quartz veins are locally distributed along the same orecontrolling structure in the Guoluolongwa deposit, not all gold-bearing quartz veins are spatially associated with the dikes, indicating that these dikes are not essential for gold mineralization. We propose that such structures likely controlled the emplacement of the diorite porphyry and guided the ore fluids, with their occasional spatial coincidence accounted for by shared structural pathways.
Cretaceous magmatism provides key insights into lithospheric reactivation and deep geodynamic processes prior to the Cenozoic uplift of the Tibetan Plateau. However, Cretaceous igneous records are scarce in the East Kunlun Orogenic Belt (EKOB) of the northern Tibetan Plateau, limiting understanding of late Mesozoic lithospheric modification. Here, we present an integrated petrological, geochronological, geochemical, mineralogical, and isotopic study of newly identified high Ba-Sr alkaline quartz monzonites and associated mafic microgranular enclaves (MMEs) from the Xiadawu pluton in the EKOB. Zircon U-Pb dating shows that both lithologies crystallized at ca. 128-129 Ma, recording an Early Cretaceous magmatic event. The MMEs and host quartz monzonites share similar mineral assemblages, trace-element patterns, plagioclase Sr isotopic compositions ((87Sr/86Sr)i = 0.70799-0.70857), and zircon Hf isotopes (epsilon Hf(t) = -7.76 to -1.49), indicating a cogenetic magma system. The MMEs are interpreted as chilled marginal products of the same magma reservoir, although limited late-stage mingling and chemical exchange with the host magma may have occurred locally. Both lithologies are characterized by high Ba and Sr contents (Ba = 844-1947 ppm; Sr = 1054-1332 ppm), indicating derivation from a Ba-Sr-rich parental magma. Combined isotopic and geochemical evidence suggests that the parental magma of the Xiadawu pluton was generated by low-degree partial melting of an enriched lithospheric mantle source previously metasomatized by slab-derived components during earlier Paleo-Tethyan subduction. We further suggest that the Early Cretaceous magmatism in the EKOB formed in a geodynamic setting of localized intracontinental lithospheric reactivation, possibly related to edge-driven mantle convection induced by far-field stress from the Qiangtang-Lhasa collision, thereby providing new insights into pre-uplift geodynamic processes in the northern Tibetan Plateau.
In this paper we report unpublished data on the chemical composition of 36 chondrules from the Allende meteorite. The concentrations of 17 elements were determined by various instrumental neutron activation analysis techniques from 1969 to 1974. Particularly useful are the concentrations of Si determined with fast neutron activation analysis (FNAA), as Si is rarely determined in bulk chondrules. The new Si data confirm the complementarity in Mg/Si ratios between chondrules and matrix of the Allende meteorite. The new Ti data demonstrate non-chondritic Al/Ti ratios in Allende chondrules, in agreement with earlier data. The nonchondritic patterns of refractory lithophile elements in Allende chondrules indicate that the elevated level of refractory elements in chondrules is not the result of addition of Ca,Al-rich inclusions (CAI) to chondrule precursors. It is rather likely that chondrule formation occurred before the addition of CAIs. The non-chondritic ratio of Sc/Ir in Allende chondrules requires an exactly complementary ratio in matrix to achieve a bulk chondritic Sc/ Ir ratio. As Ir is neither correlated with Sc nor with Ni, a large fraction of Ir must have entered chondrule precursors as refractory metal alloys, early nebular condensates. In Allende and other carbonaceous chondrites matrix and chondrules are not independent. Chondrules of carbonaceous chondrites are not chondritic in composition and they are therefore unlikely to represent basic components of planets.
