Search Results (208)

The age, provenance, and evolution of some terranes in the Klamath Mountains are poorly constrained because of low detrital zircon yields. We present petrography and 947 new detrital and igneous zircon U-Pb ages from the North Fork (NFT), Eastern Hayfork (EHT), and Western Hayfork (WHT) terranes in the central and southern Klamath Mountains. Chert and argillite are abundant in the NFT and EHT, but matrix sandstones with abundant Proterozoic-to-Archean zircon ages indicate that the EHT received more sediment from North America. Detrital zircon ages from the WHT are ~171 Ma with scattered pre-Mesozoic ages, consistent with previous ages and continental input. A younger population of three grains at 145 Ma is interpreted as Pb loss during metamorphism. In the southernmost EHT, a 143 Ma dike correlates with plutons in the northern Sierra Nevada, which were offset from the Klamath Mountains 140–130 Ma. A 158 Ma metavolcanic/metavolcaniclastic rock in the EHT is a possible extrusive equivalent of the Wooley Creek intrusive suite. The metamorphosed EHT matrix has a young population of six ages at 69 Ma, which we tentatively interpret may represent Pb loss during metamorphism. This study documents an exposure of Late Jurassic arc cover sequence and suggests there may be previously unrecognized local metamorphism/magmatism ≤69 Ma. Full article

The Rzhanski granitoid pluton and Ignatitsa diorite porphyry bodies are considered Late Paleozoic in age, belonging to the Western Balkan Zone (WBZ) in Northwestern Bulgaria. Here, we provide U-Pb zircon geochronology of these magmatic bodies, together with their geochemistry complemented by the geochemistry of the overlying volcanic rocks. Geochemical data indicate that the intermediate to acid magmatic rocks are mostly peraluminous, calc-alkaline diorite/andesite to granite, that have an origin in a continental magmatic arc tectonic environment. All plutonic, subvolcanic and volcanic rocks exhibit uniform LILE- and LREE-enriched characteristics of an arc-related igneous suite. Zircons in the Ignatitsa diorite porphyry yield a magmatic crystallization age of 315 Ma, while the zircons in the Rzhanski aplitic metagranite pluton crystallize at 294 Ma. The record of the Variscan intrusive magmatism encompasses a region-wide, well-defined time interval 332–294 Ma in the WBZ, which coincides with those of the Central Balkan Zone and the adjacent Sredna Gora Zone. The age of the Variscan greenschist facies metamorphism using the metagranite and host greenschists relationships is limited between 294 Ma and the unpublished depositional age of 268 Ma for the overlying clastic formation in the studied part of the WBZ. Full article

The Tuzla area, located in the Ayvacık district of Çanakkale (Biga Peninsula, northwestern Türkiye), hosts a Oligocene-Miocene volcanic system comprising andesitic, dacitic, rhyolitic lavas, trachyandesite, pyroclastics, and ignimbrites, and the Kestanbol Pluton. Petrographic and X-ray diffraction (XRD) analyses indicate that the altered volcanic units are dominated by porphyritic dacitic/rhyodacitic and trachyandesitic rocks, with silicification, iron oxide formation, and opacification. XRD results reveal smectite, smectite–illite/mica, illite–mica, kaolinite, cristobalite–opal, K-feldspar, plagioclase, dolomite, hematite, and quartz as the principal mineral phases. Geochemical data, including rare earth elements (REEs), suggest that fractional crystallization of primary mineral phases played a major role in controlling magmatic evolution. Chondrite-normalized REE patterns display enrichment in light REEs relative to heavy REEs, indicating derivation from a common magma source. K₂O–Na₂O and (Na₂O + K₂O)–FeOᵗ–MgO (AFM) diagrams show high-K calc-alkaline, calc-alkaline, and tholeiitic affinities, with most rhyodacite/dacite and all trachyandesite samples plotting in the tholeiitic field. Tectonic discrimination diagrams indicate formation in both volcanic arc and intraplate tectonic settings. Moderate enrichments in Ba and Sr reflect magmatic evolution and source characteristics, whereas the highest concentrations are attributed to post-magmatic fluid–rock interaction. Overall, the Tuzla volcanic rocks originated from a collision-related enriched lithospheric mantle source and subsequently evolved through fractional crystallization and assimilation processes, accompanied by crustal contamination and variable hydrothermal overprint. Full article

(1) Background: Geothermal resources are enriched in Jiangsu Province, particularly in its mid-deep geothermal reservoirs. The thermal properties and thermal effects of magmatic rocks, which are largely unknown in Jiangsu Province, are fundamental for analyzing the genetic mechanisms of geothermal resources and evaluating resource potential. (2) Methods: Representative magmatic rock samples from different geological periods and different tectonic settings are collected from the main tectonic units of Jiangsu Province. Key thermophysical parameters such as thermal conductivity, heat production rate, rock density, and porosity are systematically tested. (3) Results: The variation patterns of these thermal property parameters are analyzed, and the sources and spatiotemporal evolution characteristics of radiogenic heat production, and the thermal effects of magmatic rocks, are specifically explored. (4) Conclusions: Magmatic rock lithology from acidic to basic is negatively correlated with thermal conductivity, thermal diffusivity, and radiogenic heat production rate, and positively correlated with volumetric heat capacity. The radiogenic heat production of magmatic rocks is primarily controlled by the contents of U and Th, increasing with the increasing SiO₂ content. The formation of geothermal anomalies in areas with thin or absent sedimentary cover is significantly influenced by the thermal effect of magmatic rocks, especially by the high heat-producing granites. The radioactive thermal contribution of the Taolin and Suzhou plutons was calculated. Full article

The tectonic evolution of the Paleo-Asian Ocean during the Early to Middle Permian remains a key issue in understanding the geodynamic history of the Central Asian Orogenic Belt. To address this, we conducted petrological, whole-rock geochemical, zircon U–Pb geochronological, and Hf isotopic analyses of Early Permian biotite granodiorite and Middle Permian porphyritic granite from the south-central Great Xing’an Range. Zircon U–Pb dating yields ages of 273.2 ± 1.4 Ma and 264.4 ± 1.5 Ma, indicating that these intrusions emplaced during Early and Middle Permian. Geochemical analyses show that the rocks are characterized by high SiO₂ and Al₂O₃ contents, and low MgO and CaO contents and belong to the metaluminous to weakly peraluminous series, typical of I-type granites. The rocks are enriched in light rare earth elements and large-ion lithophile elements (e.g., Rb, Ba, K), but depleted in heavy rare earth elements and high field strength elements (e.g., Nb, Ta, P, Ti), with weakly negative Eu anomalies. The Early Permian pluton exhibits low-Sr and high-Yb characteristics and thus fall in the plagioclase stability field. In contrast, Middle Permian pluton was derived from magmas generated by partial melting under high-pressure conditions and that, underwent crystal fractionation during ascent to the mid-upper crust, ultimately forming low-Sr and low-Yb type granites. All zircon ε_Hf(t) values are positive (+4.84 to +14.87), with the corresponding two-stage Hf model ages ranging from 345 Ma to 980 Ma, indicating that the magmas were predominantly derived from juvenile crustal materials accreted during the Neoproterozoic to Phanerozoic. Considering these results, we propose that the Paleo-Asian Oceanic plate continued to subduct beneath the Songliao–Xilinhot block to the north during the Early to Middle Permian, with intense subduction and crustal thickening occurring in the Middle Permian. This suggests that the south-central segment of the Great Xing’an Range was situated in an active continental marginal setting during the Early-Middle Permian. Full article

The Baoshan Terrane, as a passive continental margin during the subduction of the Paleo-Tethys Ocean and the lower plate during collision, exhibits a poorly understood magmatic history. This region is characterized by limited magmatic activity and scarce field outcrops, which has hindered a comprehensive understanding of its petrogenesis and geological evolution. This paper presents a chronological and geochemical study of two different types of syn-collisional granites identified in the Mengnuo and Muchang areas in the southern Baoshan Terrane. Our results show that the two types of granites are high-fractionated S-type granites in Bangdong pluton from Mengnuo (zircon U-Pb ages of 230.3 ± 1.4 Ma, 228.7 ± 1.6 Ma and 230.2 ± 1.1 Ma) and A-type granites in Muchang (zircon U-Pb ages of 232.3 ± 1.8 Ma), respectively. Their formation ages are close to the timing of collision, belonging to syn-collisional granites. The Mengnuo high-fractionated S-type granites have SiO₂ contents ranging from 75.15 to 77.78 wt.% with A/CNK of 1.14 to 5.09, and are strongly peraluminous, high-K calc-alkaline granites. They display negative zircon εHf(t) values (−7.72 to −12.32), indicating derivation from partial melting of ancient crustal materials followed by extensive fractional crystallization. In contrast, the Muchang A-type granites contain 73.26 to 76.41 wt.% SiO₂, exhibit low A/CNK ratios (0.92–1.46, average = 1.07), and high Zr + Nb + Ce + Y abundances (313.7 to 3000.3 ppm), characterizing them as weakly peraluminous A-type granites. Further classification reveals that the Muchang granites belong to A1-type granites with positive εHf(t) values (+4.01 to +8.46), indicating the involvement of mantle-derived materials in their magma sources. In this case, combined with results from relevant studies in the Changming-Menglian suture zone, we propose that the Late Triassic magmatism in the Baoshan Terrane was likely triggered by slab break-off during syn-collisional stage. Slab break-off might cause mantle upwelling, resulting in large-scale Lincang batholith and associated volcanic rocks in the upper plate as well as various magmatism activities (S-type and A-type felsic rocks and intraplate basalts) in the Baoshan Terrane. Full article

We present ID-TIMS U-Pb single zircon ages and major and trace element data for granitoid plutons from the Imorona–Itsindro and Kiangara suites in central Madagascar, in order to constrain the timing of igneous emplacement and investigate the petrogenesis and tectonic settings of these Neoproterozoic plutons. A U-Pb crystallization age of 779 ± 7 Ma was determined from an Imorona–Itsindro intrusion, while a Kiangara intrusion yields 777 ± 4 Ma, older than previously reported. The identical U-Pb ages suggest contemporaneous emplacement of some Kiangara and Imorona–Itsindro intrusions. Elemental data indicate that the two suites display trace element patterns similar to those of arc-type magmas. Some distinct geochemical features are apparent between these two suites. The Imorona–Itsindro sample displays I-type affinity with low REE abundances, whereas the Kiangara samples exhibit A-type signatures with higher REE contents. We suggest that the elemental differences between A-type and I-type reflect the contamination of mantle-derived magma by lower and upper crustal rocks, respectively. We suggest that the coeval A-type and I-type granitoids in central Madagascar were generated in a subduction system associated with slab rollback and back-arc extension like extension. The compositional diversity in these Neoproterozoic plutons reflects the evolution of the tectonic regime within a single geodynamic environment, similar to that proposed for plutons in other Precambrian and younger terranes. Full article

Hainan Island has experienced a superposition of multiple phases of tectonic movements and magmatic activities, leading to numerous controversies regarding the genesis, spatiotemporal distribution, and tectonic setting of its Yanshanian granites. Accurately determining the characteristics of magmatic rocks during this period is crucial for clarifying the regional tectonic evolution. This study focuses on Diaoluoshan granite in the southeastern part of Hainan Island. Through petrological, mineralogical, zircon U-Pb geochronological, and geochemical analyses, it aims to identify the genetic type, formation age, and magma source properties of this pluton, thereby revealing the Late Yanshanian tectonic setting of Hainan Island. The results show that the zircon U-Pb dating of Diaoluoshan granite yields an age of 102.5 ± 2.8Ma, indicating its formation in the late Early Cretaceous. This granite is a high-K calc-alkaline I-type granite, with silica (SiO₂) content ranging from 63.9% to 77.3%. The pluton exhibits significant negative anomalies of Ta, Nb, P, and Ti, as well as relatively obvious positive anomalies of Rb, Th, U, and K. The biotite in the granite has a magnesium oxide (MgO) content ranging from 12.84% to 13.13%, showing characteristics of crust–mantle material mixing. The magma of this pluton was derived from the partial melting of the lower continental crust mixed with the uprising and underplating mantle mafic magmas, driven by the subduction of the Paleo-Pacific Plate and its slab rollback. This study confirms that during the Late Yanshanian, Hainan Island was in an extensional rift environment driven by the subduction of the Paleo-Pacific Plate and its slab rollback, but without a well-developed volcanic front. It provides key geological evidence for the study of Yanshanian tectono-magmatic evolution in South China. Full article

This study presents the first detailed investigation of pyroxene zoning within polymetallic skarn zones of the Elazığ region. Skarns develop along contacts between plutonic rocks (diorite and granite) and carbonate rocks, forming two main zones: endoskarn and exoskarn. Endoskarns exhibit clear mineralogical zoning, including pyroxene–garnet, pyroxene–scapolite, and epidote–garnet assemblages, while scapolite occurs in both endoskarn and exoskarn zones. Minor serpentinized olivine within endoskarns is attributed to localized magnesium enrichment due to partial assimilation of low-Mg magma by dolomitic marbles. Geochemical analyses reveal systematic variations in pyroxene composition related to ore type: Cu-Fe skarns show low Mn/Fe ratios (<0.1) and low Zn (~200 ppm), Fe skarns have high Mn/Fe ratios (>0.2) and elevated Zn (>200 ppm), and W-bearing skarns display intermediate Mn/Fe ratios (~0.15) with high Zn (>500 ppm). These findings highlight the value of pyroxene Mn/Fe ratios and Zn contents as indicators of hydrothermal fluid evolution and skarn-forming processes. Overall, this study provides the first evidence of oscillatory zoning in pyroxenes from polymetallic skarns in the region, demonstrating the interplay between magmatic differentiation and hydrothermal mineralization. Full article

The Gangdese Belt is sandwiched between the Yarlung–Zangbo Suture Zone (YZSZ) and the Bangong–Nujiang Suture Zone (BNSZ), and witnessed large-scale magmatic activity during the Early Cretaceous period. Currently, controversies remain regarding the petrogenetic mechanism and tectonic setting of the Early Cretaceous magmatism in the eastern Gangdese Belt. To clarify these controversies, this study conducted systematic petrogeochemical analysis on the Ranwu pluton in the eastern Gangdese Belt. The results show that the main rock types of the Ranwu pluton are monzogranite and granodiorite. The LA-ICP-MS zircon U-Pb ages of the monzogranite (sample CZTW1105) and granodiorite (sample CZTW2051) are 116.3 ± 0.5 Ma and 114.6 ± 0.6 Ma, respectively, collectively indicating that the Ranwu pluton formed during the Early Cretaceous period. The results of in situ zircon Hf isotope analysis show that the εHf(t) values range from −5.0 to 0.5, with corresponding Hf crustal model ages (T_DMC) of 1139–1494 Ma. The Ranwu pluton belongs to the high-K calc-alkaline series and is classified as I-type granite. Combined with geochemical characteristics and tectonic setting discrimination diagrams, it is determined that the granites of this period have geochemical signatures of post-collisional granites and formed in a tectonic setting during the transition from a compressional to an extensional regime. The occurrence of Early Cretaceous post-collisional granites marks the end of the main orogenic stage in the Bangong–Nujiang Suture Zone, and the Gangdese Belt has since transitioned into a tectonic environment of the post-orogenic extensional stage. Full article

The consistency between geochemical discrimination diagrams and the modal Quartz–Alkali feldspar–Plagioclase (QAP) classification scheme was investigated by evaluating the accuracy of three diagrams—the Quartz–Plagioclase coordinates (P-Q), the SiO₂–CaO/(CaO + K₂O) (SCK), and the Silica–Total Alkali (TAS) diagrams—for granitoid rocks. A global dataset of 1981 samples, each containing both whole-rock geochemical data and quantitative modal mineralogy, was employed. The results indicate that the P-Q and SCK diagrams have relatively low overall accuracy (~50%–55%) in reproducing the QAP classification. Their accuracy is acceptable for granites but notably lower for basic and intermediate rock types. The SCK diagram achieves higher accuracy (~80%) for tonalite but exhibits considerable dispersion for other lithologies. Despite the IUGS recommending the TAS diagram for volcanic rocks only, it is commonly used for intrusive rocks; this study, however, finds that it yields low accuracy rates for most common plutonic rocks and is therefore unsuitable for their reliable classification. This limited accuracy is attributed to the use of only three or four oxides to estimate major mineral proportions, a practice equivalent to dimensionality reduction that results in substantial information loss. Full article

Thorium-rare earth-iron oxide deposits of the Lemhi Pass district, Idaho and Montana, are enriched in the middle rare earth elements (REE), and particularly neodymium (Nd). Overall, thorium (Th) and total rare earth oxide (TREO) grades of the deposits are sub equal at 0.4 wt. % but locally exceed 1 wt. % TREO. Nd-monazite, the major REE phase (35 wt. % Nd₂O₃) occurs in hydrothermal Th-REE mineralized quartz veins and biotite-rich shear zones of enigmatic origin. Hosted in Mesoproterozoic metasedimentary rocks, the deposits are modest in size but present over a large area with no obvious source pluton exposed. This paper documents the geochemistry of the monazite and provides the first geochronological data to constrain its origin. Elemental mapping and U-Th-total Pb EPMA dating of the monazite and thorite document a Paleozoic age for mineralization centered in the Late Devonian at approximately 355 Ma ± 20 Ma. A second period of volumetrically minor Th and REE remobilization is dated as Mesozoic (ca. 100 Ma). For context, a reactivated passive continental margin was present during the Devonian in eastern Idaho, while the Mesozoic was a time of major accretionary tectonics and arc magmatism further west. Nd and Pb isotopic data require a significant interaction of the fluids with an ancient crustal component represented by regional Mesoproterozoic metasedimentary rocks and granitoids. A source–transport–deposition model is hypothesized with metasomatic fractionation and enrichment of Nd during regional hydrothermal circulation. The aqueous fluids were hot, oxidizing, and likely saline, but the exact source of the Th and REEs and the mechanism of enrichment remains problematic. Additional analytical work and increased knowledge of the regional and district geology will improve this unconventional hypothesis for formation of Lemhi Pass’ unusual Nd-rich Th-REE-Fe mineralization. Full article

Large-scale Mesozoic granites are widespread in the offshore area of eastern Shandong Province, China. This study aims to refine the granite classification and explore the degree of granite differentiation and ore-bearing potential in the study area. We conducted field investigations in Dazhushan, Xiaozhushan, and Laoshan plutons. The analytical methods included petrography, whole-rock geochemistry, Sr–Nd–Pb–Li isotopes, zircon U–Pb dating, in situ Hf isotopes, and microanalysis (LA-ICP-MS) of plagioclase. The results reveal high-silica (SiO₂ > 70%), highly differentiated (DI > 90) granites emplaced during the Early Cretaceous (113.12–121.78 Ma). Sr–Nd–Pb isotopes indicate magma derived from a crustal source (I_Sr = 0.7032–0.7242; εNd(t) = −12.45~−20.46). Critically, the spodumene-bearing Dazhushan granites exhibit high Li content with limited isotopic fractionation (δ⁷Li = 1.00–4.62‰; Li = 8.64–93 ppm), signaling high ore potential. In contrast, the Xiaozhushan granites are barren (δ⁷Li = 3.31–4.92‰; Li = 0.66–4.01 ppm). This study identified I-type (Laoshan) and I-S type (Dazhushan and Xiaozhushan) highly differentiated granites formed by plagioclase fractionation, with Dazhushan being the most promising for mineralization. Full article

This study documents the first A1-type granite identified on the southern margin of the central Lhasa terrane: a two-mica syenogranite pluton in the Meibaqieqin region. Because A-type granite provides sensitive records of crustal melting and lithospheric extension, this pluton offers important insights into magmatic processes and tectonic evolution along the southern margin of the Lhasa terrane. We analyzed two sample suites collected from different sites within the same pluton using zircon U–Pb geochronology and Hf isotopes, whole-rock geochemistry and Nd isotope. Zircon U–Pb weighted mean ages were 130.5 ± 0.7 Ma and 130.0 ± 0.7 Ma, placing emplacement in the Early Cretaceous. Zircon ε_Hf(t) values ranged from −11.29 to −9.00 and −11.04 to −7.27, with two-stage Hf model ages (T_DM2) of 1.76–1.90 Ga and 1.65–1.89 Ga. Whole-rock ε_Nd(t) values clustered between −11.77 and −11.36, yielding two-stage Nd model ages (T_NdDM2) of 1.85–1.88 Ga. Geochemically, the pluton is high-K calc-alkaline. These isotopic signatures indicate derivation predominantly from ancient crustal sources with a little mantle material. Chondrite-normalized REE patterns are overall right-inclined and display a V-shaped profile. Together with trace-element characteristics, these features support classification as A1-type granite. Regional comprehensive data suggest that pluton emplacement was controlled mainly by lithospheric extension related to northward subduction of the Neo-Tethyan oceanic plate, with a lesser contribution from southward subduction along the Bangongco–Nujiang suture. The source characteristics and geodynamic context differ markedly from A2-type granites on the northern margin of the central Lhasa terrane, which reflect distinct magmatic sources and tectonic regimes. Full article

The heavy mineral-rich wadi deposits sourced from various wadis close to Gabal Homret Waggat in the central eastern Desert of Egypt are being analyzed to assess their genesis and paleoenvironment. This study integrates remote sensing (ALOS/PALSAR DEM and ASTER imagery), mineralogical, and geochemical analyses (XRF and SEM-EDX). Remote sensing analysis (ASTER and ALOS/PALSAR) delineated three main watersheds and identified granitic plutons as the primary source rocks. Mineralogical analysis revealed a diverse heavy mineral assemblage, including zircon, rutile, ilmenite, magnetite, staurolite, and sillimanite, indicative of a provenance dominated by granitic and metamorphic rocks. Grain size analysis shows that the samples range from very platykurtic to extremely leptokurtic (Kg: 0.598–5.350 φ), indicating deposition in predominantly fluvial environments. Geochemical data show enrichment in SiO₂, Al₂O₃, K₂O, and Na₂O, indicating a felsic (granitic) source with low Chemical Index of Alteration (CIA: 41.89–51.83) and Plagioclase Index of Alteration (PIA: 37.97–52.78) values, and indicating that the source rocks show low to moderate chemical weathering. Tectonic discrimination diagrams suggest that the source rocks were formed in a continental island arc or active continental margin, consistent with the Arabian–Nubian Shield. The presence of economically valuable minerals like zircon and rare-earth-element-bearing monazite and columbite highlights the significant resource potential of these placer deposits. Full article