Search Results (218)

Kimberlite has attracted considerable interest among geologists as the primary source of natural gem-quality diamonds. The term “transitional kimberlite” was previously introduced to categorize rocks that exhibit bulk geochemical and Sr–Nd isotopic characteristics intermediate between those of archetypal kimberlite (formerly Group-I) and orangeite (formerly Group-II). Nevertheless, the petrogenesis of transitional diamond-bearing kimberlites remains poorly understood due to limited research. The diamondiferous transitional Wafangdian kimberlite in the North China Craton (NCC) thus provides a valuable opportunity for a detailed case study. We investigated fresh hypabyssal transitional Wafangdian kimberlites using bulk-rock major and trace element geochemistry to constrain near-primary parental magma compositions and decipher their petrogenesis. Geochemical compositions identify samples affected by crustal contamination based on elevated SiO₂, Pb, heavy rare earth element (HREE) concentrations, and Sr isotopic ratios. Compositional variations among macrocrystic samples (MgO: 29.7–31.5 wt.%; SiO₂: 30.6–34.7 wt.%; CaO: 3.9–7.5 wt.%; Mg^# [atomic Mg/(Mg + Fe²⁺) × 100]: 85–88) result from substantial entrainment and partial assimilation of peridotite xenoliths (up to 35%). In contrast, variations within aphanitic samples (MgO: 24.0–29.7 wt.%; SiO₂: 27.7–30.9 wt.%; CaO: 6.0–11.8 wt.%; Mg^#: 81–85) are attributed to fractional crystallization of olivine and phlogopite (~1–32%). Based on these constraints, the near-primary parental magma composition for the Wafangdian kimberlite is estimated as ~29.7 wt.% SiO₂, ~29.7 wt.% MgO, and Mg^# 85. Trace element concentrations in the transitional Wafangdian kimberlites resemble those of archetypal kimberlites globally (e.g., Nb/U > 26, La/Nb < 1.4, Ba/Nb < 16, Th/Nb < 0.25), indicating a shared convective mantle source. However, the Wafangdian kimberlites exhibit distinct characteristics: ε_Nd(t) values ranging from −3.44 to −1.77, higher Al₂O₃ and K₂O contents, and lower Ce/Pb ratios (10–20) compared to archetypal kimberlites. These features suggest the mantle source region was profoundly influenced by deeply subducted oceanic material. Full article

The profound Phanerozoic destruction of the eastern North China Craton (NCC) is well documented, yet its mechanism remains debated due to limited constraints on thermal state and lithospheric thickness during the Early Cretaceous—the peak period of cratonic destruction. We address this gap through integrated geochemical analysis (major/trace elements, Sr-Nd-Pb isotopes, olivine chemistry) of Early Cretaceous (~125 Ma) Fangcheng basalts from Shandong. These basalts possess high MgO (8.14–11.31 wt%), Mg# (67.23–73.69), Ni (126–244 ppm), and Cr (342–526 ppm). Their trace elements show island arc basalt (IAB) affinities: enrichment in large-ion lithophile elements and depletion in high-field-strength elements, with negative Sr and Pb anomalies. Enriched Sr-Nd isotopic compositions [⁸⁷Sr/⁸⁶Sr(t) = 0.709426–0.709512; ε_Nd(t) = −12.60 to −13.10], unradiogenic ²⁰⁶Pb/²⁰⁴Pb(t) and ²⁰⁸Pb/²⁰⁴Pb(t) ratios (17.55–17.62 and 37.77–37.83, respectively), and slightly radiogenic ²⁰⁷Pb/²⁰⁴Pb(t) ratios (15.55–15.57) reflect an upper continental crustal signature. Covariations of major elements, Cr, Ni, and trace element ratios (Sr/Nd, Sc/La) with MgO indicate dominant olivine + pyroxene fractionation. High Ce/Pb ratios and lack of correlation between Ce/Pb or ε_Nd(t) and SiO₂ preclude significant crustal contamination. The combined isotopic signature and IAB-like trace element patterns support a lithospheric mantle source that was metasomatized by upper crustal material. Olivine phenocrysts exhibit variable Ni (1564–4786 ppm), Mn (903–2406 ppm), Fe/Mn (56.63–85.49), 10,000 × Zn/Fe (9.55–19.55), and Mn/Zn (7.07–14.79), defining fields indicative of melts from both peridotite and pyroxenite sources. High-MgO samples (>10 wt%) in the Grossular/Pyrope/Diopside/Enstatite diagram show a clinopyroxene, garnet, and olivine residue. Reconstructed primary melts yield formation pressures of 3.5–3.9 GPa (110–130 km depth) and temperatures of 1474–1526 °C, corresponding to ~60 mW/m² surface heat flow. This demonstrates retention of a ≥110–130 km thick lithosphere during peak destruction, arguing against delamination and supporting a thermo-mechanic erosion mechanism dominated by progressive convective thinning of the lithospheric base via asthenospheric flow. Our findings therefore provide crucial thermal and structural constraints essential for resolving the dynamics of cratonic lithosphere modification. Full article

The Changning-Menglian suture zone, as the remnant of the main Paleo-Tethyan oceanic basin in its southern segment, lacks direct magmatic evidence constraining the timing of subduction initiation in its northern segment. The petrogenesis and tectonic setting of the newly discovered Early Permian (~280 Ma) Wayao granodiorite in the northern segment remain unclear, hindering our understanding of the timing of subduction initiation and processes of the Paleo-Tethyan Ocean in the Changning-Menglian suture zone. This study presents systematic petrographic, zircon U-Pb geochronological, whole-rock major and trace element geochemical, and Sr-Nd-Hf isotopic analyses on the newly discovered Early Permian granodiorite in the Wayao area, northern segment of the Changning-Menglian suture zone, western Yunnan. Zircon U-Pb dating yields a crystallization age of ca. 280 Ma, confirming its emplacement during the Early Permian. The petrogeochemical characteristics indicate that it belongs to the metaluminous, calc-alkaline series of I-type granite. It is enriched in large-ion lithophile elements (LILEs; e.g., Rb, Th, U, La, Pb) and depleted in high-field-strength elements (HFSEs; e.g., Ba, Nb, Sr, Ti), exhibiting a pronounced negative Eu anomaly. Whole-rock Sr-Nd isotopes (εNd(t) = −5.6–−6.1) and zircon Hf isotopes (εHf(t) = −1.34–−10.01) suggest that the magma was predominantly derived from the partial melting of ancient crustal material (primarily metamorphosed basic rocks, such as amphibolite), with a minor addition of mantle-derived components (magma mixing). Combined with petrogeochemical discriminant diagrams (e.g., Sr/Y vs. Y, Rb vs. Yb + Ta) and the regional geological context, this granodiorite is interpreted to have formed in an active continental margin tectonic setting associated with the eastward subduction of the Paleo-Tethys Ocean (represented by the Changning-Menglian Ocean). This discovery fills the gap in the record of Early Permian subduction-related magmatic rocks in the northern segment of the Changning-Menglian suture zone. It provides crucial petrological evidence constraining that the eastward subduction and consumption of the northern Paleo-Tethys Ocean had already commenced by the Early Permian. Full article

The Xiaobaihegou fluorite deposit is located in the southwest of the Altyn-Tagh Orogen, NW China. However, the provenance, thermodynamic properties, and enrichment mechanisms of the ore-forming fluids in this deposit remain unclear. Fluorite mineralization primarily occurs in the vicinity of the contact zone between the granite and the wall rocks. The zircon U-Pb age of the alkali-feldspar granite in the Xiaobaihegou fluorite deposit is 482.3 ± 4.1 Ma. The ore-hosting lithologies are mainly calcareous rock series of the Altyn Group. The ore bodies are controlled by NE-trending faults and consist primarily of veined, brecciated, massive, and banded ores. The ore mineral assemblage is primarily composed of calcite and fluorite. The rare earth element (REE) patterns of fluorite and calcite in the Xiaobaihegou deposit exhibit right-dipping LREE enrichment with distinct negative Eu anomalies, which closely resemble those of the alkali-feldspar granite. This similarity suggests that the REE distribution patterns of fluorite and calcite were likely inherited from the pluton. The ore-forming process can be divided into an early stage and a late stage. The massive ores formed in the early stage contain mainly gas-rich two-phase fluid inclusions and CO₂-bearing three-phase inclusions, with homogenization temperatures ranging from 235 °C to 426 °C and salinities from 28.59% to 42.40% NaCl equivalent. In the late stage, brecciated and stockwork ores were formed. They host liquid-rich two-phase and gas-rich two-phase fluid inclusions, with homogenization temperatures ranging from 129 °C to 350 °C and salinities from 0.88% to 21.61% NaCl equivalent. The results of hydrogen and oxygen isotope studies indicate that the ore-forming fluids were derived from a mixture of magmatic–hydrothermal and meteoric water. Fluorite precipitation in the early stage was mainly due to the mixing of magmatic–hydrothermal solution and meteoric water, as well as a water–rock reaction. In the late stage, fluid mixing further occurred, resulting in a decrease in temperature and the formation of brecciated and stockwork ores. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of fluorite from the deposit range from 0.71033 to 0.71272 and 0.511946 to 0.512073, respectively, indicating that the ore-forming material originates from the crust. Based on the ore-forming characteristics, it is proposed that Ca may be primarily leached from the strata formation, while F may predominantly originate from magmatic–hydrothermal solutions. The formation of fluorite deposits is closely related to the transition of the Central Altyn-Tagh Block and Qaidam Block from a compressional orogenic environment to an extensional tectonic environment. Full article

The Chating Cu-Au and Magushan Cu-Mo deposits in Anhui province are two representative deposits within the recently defined Nanling-Xuancheng ore concentration area in the Middle and Lower Yangtze River Metallogenic Belt (MLYB). Magmatism and mineralization for the area are not well known at present due to a lack of in-depth studies on the petrogenesis of ore-bearing intrusive rocks and their relationship with deposits. Here, the ore-bearing intrusive rocks of the two deposits are investigated through analyses of whole-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages, and zircon Hf isotopes. The results reflect the two intrusions, both formed in the Early Cretaceous (138.9 ± 0.8 Ma and 132.2 ± 1.3 Ma). They belong to the sub-alkaline high-K calc-alkaline series, while trace elements are enriched in LILEs and LREE and depleted in HFSEs. However, the intrusions of the Chating deposit (I_sr = 0.7064–0.7068; ε_Nd(t) = −8.5–−7.3; ε_Hf(t) = −11.9–−7.0) have obviously different Sr-Nd-Hf isotopic compositions from the intrusions of the Magushan deposit (I_sr = 0.7079–0.7081; ε_Nd(t) = −5.7–−5.4; ε_Hf(t) = −5.4–−3.6). The characteristics indicate that the two intrusions were formed in the same diagenetic ages and tectonic settings and derived from a crust–mantle mixture with predominant mantle-derived materials. But the crust materials of sources are different, which further leads to different metallogenic elements, showing that the Chating deposit is enriched in Cu and Au, while the Magushan deposit is enriched in Mo. Moreover, the characteristics and magma sources of two intrusions and metallogenic elements correspond respectively to the Tongling Cu-Au polymetallic ore concentration area in the MLYB and the southern Anhui Mo polymetallic ore concentration area in the Jiangnan orogen. The correlation implies differences in magmatism and mineralization between the northwestern and southeastern parts of the Nanling-Xuancheng ore concentration area, demarcated by the Jiangnan Deep Fault. These variations were mainly controlled by the Pre-Sinian crustal basement. Full article

Isotopic investigations focused on determining the mobility and provenance of ancient human civilizations and sourcing of archeological artifacts continue to gain prominence in archeology. Most studies focus on the premise that the geographic variation in isotope systems of interest (e.g., Sr, Pb, Nd, O) in the natural environment is recorded in both human hard tissues of local individuals and raw materials sourced for artifacts within the same region. The introduction of multi-collection–inductively coupled plasma mass spectrometry (MC-ICP-MS) and laser ablation systems are techniques that consume smaller sample sizes compared to previous mass spectrometric approaches due to their higher ionization efficiency and increased sensitivity. This development has facilitated the isotopic measurement of trace elements present at low abundances (e.g., Pb, Nd, <1-to-low ppm range) particularly in human tooth enamel. Accurate interpretation of any isotope ratio measurement for the proveniencing of such low-abundance samples requires the adequate evaluation of post-mortem diagenetic alteration. A synopsis of practices currently in use for identifying post-mortem alteration in human archeological samples is discussed here. Post-mortem shifts in radiogenic isotope signatures resulting from secondary alteration are distinct from those potentially related to the impact of climate change on the bioavailable budgets for these elements. This topic is of interest to the archeological community and discussed here in the context of Holocene-aged samples from burial sites within the Nile River Valley System, and preferred dust source areas from the neighboring Sahara Desert. Full article

The Chagai porphyry copper belt is a major component of the Tethyan metallogenic domain, which spans approximately 300 km and hosts several giant porphyry copper deposits. The tectonic setting, whether subduction-related or post-collisional, and the deep dynamic processes governing the formation of these giant deposits remain poorly understood. Mafic microgranular enclaves (MMEs), mafic dikes, and multiple porphyries have been documented in the Saindak mining area. This work examines both the ore-rich and non-ore intrusions in the Saindak porphyry Cu-Au deposit, using methods like molybdenite Re-Os dating, U-Pb zircon ages, Hf isotopes, and bulk-rock geochemical data. Geochronological results indicate that ore-fertile and barren porphyries yield ages of 22.15 ± 0.22 Ma and 22.21 ± 0.33 Ma, respectively. Both MMEs and mafic dikes have zircons with nearly identical ²⁰⁶Pb/²³⁸U weighted mean ages (21.21 ± 0.18 Ma and 21.21 ± 0.16 Ma, respectively), corresponding to the age of the host rock. Geochemical and Sr–Nd–Hf isotopic evidence indicates that the Saindak adakites were generated by the subduction of the Arabian oceanic lithosphere under the Eurasian plate, rather than through continental collision. The adakites were mainly formed by the partial melting of a metasomatized mantle wedge, induced by fluids from the dehydrating subducting slab, with minor input from subducted sediments and later crust–mantle interactions during magma ascent. We conclude that shallow subduction of the Arabian plate during the Oligocene–Miocene may have increased the flow of subducted fluids into the sub-arc mantle source of the Chagai arc. This process may have facilitated the widespread deposition of porphyry copper and copper–gold mineralization in the region. Full article

The Great Xing’ an Range is located in the eastern part of the Xing’ an-Mongolian Orogenic Belt, which is an important component of the Central Asian Orogenic Belt. To determine the emplacement age and petrogenesis of the granitoids in the Gegenmiao and Taonan areas of the central Great Xing’an Range, and to investigate its tectonic setting, petrographic studies, zircon U-Pb geochronology, whole-rock Sr-Nd isotopic analysis, zircon Hf isotopic analysis, and detailed geochemical investigations of this intrusion were carried out. The results indicate the following, in relation to the granitoids in the study areas: (1) The zircon U-Pb dating of the granitic rocks in the study areas yields ages ranging from 141.4 ± 2.0 Ma to 158.7 ± 1.9 Ma, indicating their formation during the Late Jurassic to Early Cretaceous; (2) the geochemical characteristics indicate that these rocks belong to the calc-alkaline series and peraluminous, classified as highly fractionated I-type granites with adakite features; (3) the Sr-Nd isotopic data show that the εNd(t) values of Gegenmiao granitic rocks are 2.8 and 2.1, while those of Taonan granitic rocks range from −1.5 to 0.7; (4) the Zircon εHf(t) values of the granitic rocks from Gegenmiao and Taonan vary from 2.11 to 6.48 and 0.90 to 8.25, respectively. They are interpreted to have formed through partial melting of thickened lower crustal material during the Meso-Neoproterozoic. The Gegenmiao and Taonan granitic rocks were formed in a transitional environment from post-orogenic compression to extension, which is closely associated with the Mongolia–Okhotsk tectonic system. Full article

The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly identified Late Carboniferous adakitic granodiorite from the South Tianshan, incorporating geochronological, zircon U-Pb and Lu-Hf isotopic, whole-rock geochemical, and Sr-Nd isotopic data. Zircon U-Pb analysis indicates that the granite was emplaced at 310 ± 2.5 Ma. Based on major element compositions, the granodiorite belongs to medium-K calc-alkaline weakly peraluminous series (A/CNK = 0.95–1.09). The samples exhibit typical high-silica adakitic affinity, as evidenced by the elevated contents of SiO₂ (67.75–69.27 wt.%), Al₂O₃ (15.29–15.90 wt.%), Sr (479–530 ppm), and Ba (860–910 ppm); low concentrations of Yb (0.43–0.47 ppm) and Y (7.12–7.44 ppm); high Sr/Y ratios (67–72); and slight Eu anomalies (δEu = 0.89–1.03). The sodium-rich composition (K₂O/Na₂O = 0.48–0.71) is comparable to adakitic rocks from slab-derived melts. Elevated concentrations of Ni (22.12–24.25 ppm), Cr (33.20–37.86 ppm), Co (6.32–6.75 ppm), and V (30.33–32.48 ppm), along with high Mg# values (55–57), suggest melt–mantle interaction during magma ascent. The slightly enriched isotopic signatures, characterized by higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.706086–0.706205) and lower ε_Nd(t) (−3.09 to –2.47) and ε_Hf(t) (−3.11 to +7.66) values, point to notable sedimentary contributions, potentially through source contamination and/or shallow-level crustal contamination. By integrating the new results with previously published data, we consider that the adakitic granodiorite was generated by partial melting of the subducted oceanic crust, triggered by asthenospheric upwelling associated with the southward rollback of the north-dipping South Tianshan oceanic lithosphere. Our data provide new insights into Late Carboniferous retreating subduction along the southern active margin of the Yili-Central Tianshan and the accretionary architecture of the southern Altaids. Full article

The tectonic evolution of the Paleo-Pacific Ocean and the destruction mechanism of the North China Craton (NCC) are still controversial. In this study, we conducted zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd-Hf isotope analyses on the Weiyuanpu mafic–ultramafic intrusions in the eastern segment of the northern margin of the NCC to discuss their petrogenesis and tectonic implications. The Weiyuanpu mafic–ultramafic intrusions consist of troctolite, hornblendite, hornblende gabbro, gabbro, and minor diorite, anorthosite, characterized by cumulate structure. The main crystallization sequence of minerals is olivine → pyroxene → magnetite → hornblende. The zircon U-Pb ages of hornblendite, hornblende grabbro, and diorite are ~170Ma. Geochemical characteristics exhibit low-K tholeiitic to calc-alkaline series, enriched in light rare-earth elements (LREE) and significant large-ion lithophile elements (LILE), and depleted in high-field-strength elements (HFSE). Sr-Nd isotopic compositions are I_Sr = 0.7043–0.7055, εNd(t) = −0.7 to +0.9, and zircon εHf (t) values range from +3.4 to +8.7. These results suggest that the source region was a phlogopite-bearing garnet lherzolite mantle metasomatized by subduction fluids. The study reveals that the northeastern margin of the NCC was in a back-arc extensional setting due to the subduction of the Paleo-Pacific Ocean during the Middle Jurassic, which caused lithosphere thinning and mantle melting in this region. Full article

Haigou deposit, located in Dunhua City, southeast Jilin Province, NE China, is a large-scale gold deposit. The gold ore body is categorized into two types: quartz-vein type and altered rock type, with the quartz-vein type being predominant. The vein gold ore body primarily occurs within the monzonite granite and monzonite rock mass in the Haigou area and is controlled by fault structures trending northeast, northwest, and near north-south. In order to constrain the age and tectonic setting of quartz vein-type gold mineralization, we conducted a detailed underground investigation and collected samples of monzonite granite and pyroxene diorite porphyrite veins related to quartz-vein-type gold mineralization for LA-ICP-MS zircon U-Pb dating and whole-rock main trace element data testing to confirm that monzonite granite is closely related to gold mineralization. Pyroxene diorite porphyry and gold mineralization were found in parallel veins. The zircon U-Pb weighted mean ages of monzonite and pyroxene diorite porphyrite veins are 317.1 ± 3.5 Ma and 308.8 ± 3.0 Ma, respectively, indicating that gold mineralization in monzonite, pyroxene diorite porphyrite veins, and quartz veins occurred in the Late Carboniferous. The monzonite granite and pyroxene diorite porphyrite veins associated with quartz vein-type gold mineralization have high SiO₂, high K, and high Al₂O₃ and are all metaluminous high-potassium calc-alkaline rock series. Both of them are relatively enriched in light rare earth elements (LREE) and macroionic lithophile elements (LILE: Rb, Ba, K, etc.), but deficient in heavy rare earth elements (HREE) and high field strength elements (HFSE: Nb, Ta, P, Ti, etc.), the monzonitic granite Eu is a weak positive anomaly (δEu = 1.15–1.46), the pyroxene diorite porphyre dyke Eu is a weak positive anomaly (δEu = 1.09–1.13), and the Nb and Ta are negative anomalies. The Th/Nb values are 0.28–0.73 and 1.48–2.05, and La/Nb are 2.61–4.74 and 4.59–5.43, respectively, suggesting that diagenetic mineralization is the product of subduction in an active continental margin environment. In recent years, scholarly research on Sr, Nd, and Pb isotopes in Haigou rock masses has indicated that the magmatic source region in the Haigou mining areas is complex. It is neither a singular crustal source nor a mantle source but rather a mixed crust-mantle source, primarily resulting from the partial melting of lower crustal materials, with additional contributions from mantle-derived materials. In summary, the metallogenic characteristics, chronology data, geochemical characteristics, and regional tectonic interpretation indicate that at least one phase of magmatic-hydrothermal gold mineralization was established in the Late Carboniferous as a result of the subduction of the Paleo-Asian ocean plate at the northern margin of the North China Craton. Full article

Amphibole-rich cumulates provide crucial information pertaining to the petrogenetic history of suprasubduction zone ophiolites and are, therefore, helpful in constraining the evolution and closure of the Neo-Tethys during the late Cretaceous to the early Tertiary period. Following this, the present contribution examines the meta-hornblendite and meta-hornblende-gabbro lithologies in the Mayudia ophiolite complex (MdOC), NE Himalaya, based on their field and petrographic relations, constituent mineral compositions, whole rock major and trace element chemistry and bulk strontium (Sr)—neodymium (Nd) isotope systematics. MdOC cumulates potentially represent the fossilized record of an island arc root, where amphibole + titanite + magnetite was fractionally crystallized from a super hydrous magma (10.56–13.61 wt.% melt water content) prior to plagioclase in a stable physico-chemical condition (T: 865–940 °C, P: 0.8–1.4 GPa, logfO₂: −8.59–−11.19 unit) at lower crustal depths (30–38 km). Such extreme hydrous nature in the parental magma was generated by the flux melting of the sub-arc mantle wedge with aqueous inputs from the dehydrating slab. A super hydrous magmatic reservoir was, therefore, extant at sub-arc mantle depths in the eastern Neo-Tethys, which has likely modulated the composition of the oceanic crust during intraoceanic subduction. Full article

The Yanbian area of Jilin Province is situated in the eastern segment of the southern margin of the Xing-Meng Orogenic Belt, representing a region that has been superimposed and reworked by the Paleo-Asian Ocean and Circum-Pacific tectonic event. To determine the emplacement age and petrogenesis of the quartz diorite in the Fudong area of Yanbian, Jilin Province, and to investigate its tectonic setting, petrographic studies, zircon U-Pb geochronology, whole-rock Sr-Nd isotopic analysis, zircon Hf isotopic analysis, and detailed geochemical investigations of this intrusion were carried out. The results indicate that the Fudong quartz diorite has: (1) A weighted mean zircon U-Pb age of 186 ± 1.7 Ma, corresponding to the Late Early Jurassic; (2) geochemically high concentrations of Sr (average: 1146 ppm) and Ba (average: 1213 ppm), and enrichment of light rare earth elements (LREE), along with notably high Th/Yb and Rb/Y ratios; (3) geochemically, the quartz diorite is enriched in large-ion lithophile elements (LILEs; e.g., Ba, K) and light rare earth elements (LREEs), while being depleted in high-field-strength elements (HFSEs; e.g., Ta, Ti). These features are consistent with magma formed in a subduction-related setting. In summary, the Fudong quartz diorite formed within an active continental margin tectonic environment associated with the subduction of the Paleo-Pacific Plate. Its primary magma likely originated from an enriched lithospheric mantle that had been metasomatized by fluids released from the subducted slab. Full article

The Kesikköprü iron deposit, located in the Central Anatolian Crystalline Complex, occurs in the triple contact of Kesikköprü granitoid, mafic–ultramafic rocks, and marble. The causative Kesikköprü granitoid, consisting of diorite, granodiorite, and granite, is classified as sub-alkaline, calc-alkaline, and shoshonitic, displaying metaluminous to partially peraluminous properties. Sr-Nd isotope data and the geochemical characteristics of the Kesikköprü granitoid indicate a metasomatized mantle origin, with its ultimate composition arising from crustal contamination and magma mixing along with fractional crystallization in a post-collisional setting. The ⁴⁰Ar/³⁹Ar geochronology reveals a total fusion age of 73.41 ± 0.32 Ma for the biotite of the Kesikköprü granitoid. The alteration pattern in the deposit is characterized by an endoskarn zone comprising garnet–pyroxene (±phlogopite ± epidote) and an exoskarn zone displaying a zoning of garnet (±pyroxene ± phlogopite), pyroxene (±garnet ± phlogopite ± epidote), epidote–garnet, and epidote-rich subzones. Magnetite is extracted from massive lenses within the exoskarn zones and shows vein, disseminated, banded, massive, and brecciated textures. The low potassium content of phlogopites which are associated with magnetite mineralization prevents the determination of a reliable alteration age. δ¹⁸O thermometry reveals a temperature range between 462 and 528 °C for the magnetite mineralization. According to geochemical (trace and rare earth elements), stable (δ¹⁸O, δ²H, δ³⁴S, and δ¹³C), and radiogenic (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) isotope data, the hydrothermal fluid responsible for the alteration and mineralization is related to the Kesikköprü granitoid, from which a significant magmatic component originates initially, followed by meteoric fluids at lower temperatures (123 °C) during the late-stage formation of calcite–quartz veins. Full article

The Junqueira massif is a syn- to late-kinematic Variscan batholith intruded into Ediacaran-Cambrian metasedimentary rocks of the Douro-Beiras Supergroup (DBSG) in the Central Iberian Zone. The batholith occupies the axial zone of the Porto-Viseu antiform, a large NW-SE trending megascopic domal structure formed during the last Variscan ductile deformation event. Field and petrographic evidence reveals that the Junqueira batholith comprises several units of leucocratic granites distinguished by variations in grain size and relative proportions of the main rock-forming minerals. This work provides new petrographical, geochemical, Sr–Nd isotope data and ID-TIMS U–Pb ages for the Junqueira batholith. U–Pb dating of zircon and monazite by ID-TIMS gives a crystallization age of ca. 312–309 Ma for this batholith. Combined geochemical and Sr–Nd isotopic data for the different granite units (ASI > 1.1; high SiO₂ and K₂O contents, low CaO, MgO, Ba, Sr, moderately fractionated REE patterns, Eu negative anomalies, ⁸⁷Sr/⁸⁶Sr_i > 0.713, εNd₃₁₀ = −3.5 to −5.9; T_DM = 1.1–1.4 Ga) support a provenance by fluid-absent melting processes of exclusively supracrustal sources (mainly metapelites), similar to the adjoining country rocks of the Beiras Group of the DBSG. Full article