Search Results (57)

There are many controversies over the material sources of the Late Paleozoic strata in the Lower Yangtze region, and there is a lack of consensus on the basin source–sink system, which hinders the reconstruction of Late Paleozoic paleogeography and exploration of energy and mineral resources in the area. This study aimed to clarify the sedimentary provenance and tectonic background of the Upper Permian Longtan Formation in the Chizhou area of southern Anhui Province. The key objectives were to: (i) analyze the geochemical characteristics of sandstones using major, trace, and rare earth elements; (ii) determine the tectonic setting of the sediment source region based on discrimination diagrams; and (iii) integrate geochemical, sedimentological, and paleocurrent data to reconstruct the source-to-sink system. The geochemical data suggest that the sandstone samples exhibit relatively high SiO₂, Fe₂O₃, MgO, and Na₂O content and relatively low TiO₂, Al₂O₃, and K₂O content, consistent with average values of post-Archean Australian shale (PAAS) and the upper continental crust (UCC). The chondrite-normalized rare earth element patterns resemble PAAS, with enrichment in light REEs and depletion in heavy REEs. Tectonic discrimination diagrams indicate a provenance from active continental margins and continental island arcs, with minor input from passive continental margins. Combined with regional tectonic context and paleocurrent measurements, the results suggest that the Longtan Formation sediments primarily originated from the Neoproterozoic Jiangnan orogenic belt and the Cathaysia Block, notably the Wuyi terrane. These research results not only provide new geological data for further clarifying the provenance of Late Paleozoic sedimentary basins in the Lower Yangtze region but also establish the foundation for constructing the Late Paleozoic tectonic paleogeographic pattern in South China. Full article

The southern Great Xing’an Range is located in the overlap zone of the Paleo-Asian Ocean metallogenic domain and the Circum-Pacific metallogenic domain. It hosts numerous Sn-polymetallic deposits, such as Weilasituo, Bianjiadayuan, Huanggang, and Dajing, and witnessed multiple episodes of magmatism during the Late Mesozoic. The study area is situated within the Huanggangliang-Ganzhuermiao metallogenic belt in the southern Great Xing’an Range. The region has witnessed extensive magmatism, with Mesozoic magmatic activities being particularly closely linked to regional mineralization. We present petrographic, zircon U-Pb chronological, lithogeochemical, and Lu-Hf isotopic analyses of the Yexilinhundi granites. The results indicate that the granite porphyry and granodiorite were emplaced during the Late Jurassic. Both rocks exhibit high SiO₂, K₂O + Na₂O, differentiation index (DI), and 10,000 Ga/Al ratios, coupled with low MgO contents. They show distinct fractionation between light and heavy rare earth elements (LREEs and HREEs), exhibit Eu anomalies, and have low whole-rock zircon saturation temperatures (T_zr), collectively demonstrating characteristics of highly fractionated I-type granites. The εHf(t) values of the granites range from 0.600 to 9.14, with young two-stage model ages (T_DM2 = 616.0~1158 Ma), indicating that the magmatic source originated from partial melting of Mesoproterozoic-Neoproterozoic juvenile crust. This study proposes that the granites formed in a post-collisional/post-orogenic extensional setting associated with the subduction of the Mongol-Okhotsk Ocean, providing a scientific basis for understanding the relationship between the formation of Sn-polymetallic deposits and granitic magmatic evolution in the study area. 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 present study aims to characterize complex geological structures and significant mineralization using remote sensing and aeromagnetic studies. Structural lineaments play a crucial role in the localization and concentration of mineral deposits. For the first time over the study district, a combination of aeromagnetic data, Landsat 9, ASTER, and PRISMA hyperspectral data was utilized to enhance the characterization of both lithological units and structural features. Advanced image processing techniques, including false color composites, principal component analysis (PCA), independent component analysis (ICA), and SMACC, were applied to the remote sensing datasets. These methods enabled effective discrimination between Phanerozoic rock formations and the complex basement units, which comprise the island arc assemblage, Dokhan volcanics, and late-orogenic granites. The local and deep magnetic sources were separated using Gaussian filters. The Neoproterozoic basement rocks were estimated using the radial average power spectrum technique and the Euler deconvolution technique (ED). According to the RAPS technique, the average depths to shallow and deep magnetic sources are approximately 0.4 km and 1.6 km, respectively. The obtained ED contacts range in depth from 0.081 to 1.5 km. The research area revealed massive structural lineaments, particularly in the northeast and northwest sides, where a dense concentration of these lineaments was identified. The locations with the highest densities are thought to signify more fracturization in the rocks that are thought to be connected to mineralization. According to the automatic lineament extraction methods and rose diagram, NW-SE, NNE-SSW, and N-S are the major structural directions. These trends were confirmed and visually represented through textural analysis and drainage pattern control. The lithological mapping results were validated through field observations and petrographic analysis. This integrated approach has proven highly effective, showcasing significant potential for both detailed structural analysis and accurate lithological discrimination, which may be related to further mineralization exploration. Full article

We report information on the protolith, the Triassic retrograde metamorphism, and anatexis recorded in zircons extracted from granitic gneiss and biotite schist in the Sulu orogenic zone, central China. The schist is enclosed within the granitic gneiss in the form of a lens. Zircon grains from the schist sample indicate anatexis occurred at 214.6 ± 3.6 Ma (MSWD = 5.1), with ε_Hf (t) values ranging from −22.6 to −18.3, corresponding to T_DM^C(Hf) ages between 2675 Ma and 2407 Ma. The granitic gneiss originated from magmatic rock formed at 774 ± 32 Ma (MSWD = 5.7) and subsequently underwent metamorphism at ~211 Ma. Three zircon cores from the granitic gneiss exhibit ε_Hf (t) values ranging from −13.6 to −6.3, with T_DM ^C(Hf) ages spanning 2487–2075 Ma. Six zircon rims from the gneiss yield ε_Hf (t) values of −14.7 to −13.3, and T_DM ^C(Hf) ages ranging from 2176 to 2092 Ma. We believe that the protolith of granitic gneiss is the Neoproterozoic magmatic rock, whose tectonic affinity is the northern margin of the Yangtze craton. The granitic gneiss experienced Triassic collisional orogeny-related metamorphism and subsequent retrograde metamorphism, with the timing of retrograde overprinting consistent with zircon-recorded anatexis in the schist. In addition, the protoliths of both the gneiss and schist exhibit close affinity to Archean-Paleoproterozoic crustal sources. Full article

The granitic rocks and the Dokhan Volcanics at the transect between Safaga and Qena, the Egyptian Northern Eastern Desert represent the northern termination of the Arabian–Nubian Shield (ANS), which, in turn, represents the northern part of the East African Orogeny (EAO). The geochronological development of the magmatic activities that constructed the ANS is critical in understanding these orogenies. The ANS was constructed through pre-collisional, syn-collisional, and post-collisional magmatic phases. The transition between these magmatic phases marks tectonic shifting from subduction to compressional and extensional tectonic settings, respectively. The chronological constraints of these tectonic–magmatic phases are still questionable. Our study aims to refine these chronological constraints through the dating of four calc-alkaline granitic rocks (722 ± 5 Ma–561 ± 4 Ma), five alkaline granitic rocks (758 ± 5 Ma–555 ± 4 Ma), and three Dokhan Volcanic rocks (618 ± 5 Ma–606 ± 5 Ma). Our results suggest the absence of any pre-collisional rocks. The syn-collisional magmatism extended here from 758 ± 5 Ma to 653 ± 7 Ma, demonstrating the chronological domination of the syn-orogenic compressional regime in the NED. The Dokhan Volcanic activity marked the shifting of the tectonic setting from a compressional to an extensional regime at 618 ± 5 Ma. Post-collisional plutonism dominated between 583 ± 5 Ma and 555 ± 4 Ma in the studied region, suggesting that ANS magmatic activity was extended to the Phanerozoic edge. These findings refute the classical interpretations of older magmatism as calc-alkaline granitoids and younger magmatism as alkaline granitoids. Pre-Neoproterozoic (pre-ANS) xenocrysts with ages of 1879 ± 22, 1401 ± 25, 1385 ± 12, 1232 ± 27, 1210 ± 18, and 1130 ± 15 Ma were yielded, which might support a local reworked ancient magmatic source. Full article

The North Qilian Orogen experienced a series of late Neoproterozoic to early Paleozoic tectonic events, including the opening and closure of the Proto-Tethyan Qilian Ocean, as well as post-subduction processes. This study investigated the Shandan adakites in the Longshoushan area of the North Qilian Orogen, focusing on zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf–O isotopic compositions. The Shandan adakites yield ages of ca. 446–440 Ma, suggesting they crystallized during the collision between the Alxa and Qilian blocks following the closure of the Proto-Tethyan North Qilian Ocean. High Sr/Y (40.9–117) ratios and enrichments in light rare earth elements indicate that the Shandan adakites were formed by partial melting of thickened magnesian lower crust. They have relatively rich ε_Nd (t) (−7.66 to −6.32), ε_Hf(t) (3.30 to −12.4), and δ¹⁸O (5.34‰–7.52‰). Zircon Hf–O and whole-rock Sr–Nd isotopes confirm significant contributions from the ancient crust and mantle-derived melts, suggesting complex crust–mantle interactions in their magma sources. We propose that the Shandan adakites formed during the (early) post-collisional stage of orogenesis. Based on regional geological evidence and previous studies, we suggest the Alxa and Central Qilian blocks collided during ca. 446–440 Ma, leading to the thickening of the lower crust. After ca. 440 Ma, the tectonic setting of the Northern Qilian Orogen transitioned from a collisional to a post-collisional stage. Full article

In order to better constrain the specific depositional age and provenance of the Danzhou Group and understand the geological evolution of the Jiangnan Orogenic Belt, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from the Gongdong and Hetong formations of the Danzhou Group in the Longsheng area of the Western Jiangnan Orogenic Belt. Detrital zircons from the Gongdong Formation yield three age populations of 2658–2517 Ma, 2427–1678 Ma and 891–781 Ma, and the youngest ages suggest that the sedimentation began after ca. 783 Ma. U-Pb ages of detrital zircons from the Hetong Formation yield major populations at 2769–2502 Ma, 2492–2100 Ma, and 991–731 Ma, and the youngest ages redefine the maximum depositional age of this unit is 760 Ma, much younger than previously considered. Thus, the upper part of the Hetong Formation in the Longsheng area is newly subdivided into the Sanmenjie Formation, which is characterized by a large amount of 765–761 Ma volcanic rocks. The dominant 991–731 Ma detrital zircons for all samples were likely sourced from the Neoproterozoic igneous rocks of the southeast margin of the Yangtze Block. The subordinate 2494–1678 Ma detrital zircons were probably sourced from the Cathaysia Block. Minor amounts of 2769–2502 Ma detrital zircons may have been sourced from the Yangtze Block. Detrital zircons from the Gongdong Formation have mainly negative εHf (t) values (−1.1 to 21.8, 90%), suggesting that the detritus of the Gongdong Formation is dominated by the recycling of old crustal materials. The εHf (t) values of detrital zircons from the Hetong Formation have a large spread of −22.2 to +9.7, indicating that the source material of the Hetong Formation includes both the juvenile crustal materials and the recycled ancient crustal materials. The above age populations and Hf isotopic characteristics are consistent with the magmatic rocks in the Jiangnan Orogenic Belt and the Southeast Yangtze Block. Taking into account the lithostratigraphic features, provenances, and depositional ages, the Danzhou Group in the Western Jiangnan Orogenic Belt was deposited in a back-arc basin. Full article

Gem-quality garnets, with their high closure temperature (750–800 °C), high transparency, uniform composition, and purity, offer promising prospects for U-Pb dating. Despite decades of recognition that garnets can be dated using the U-Pb method, direct dating remains extremely limited. Tsavorite is a rare gem-quality green vanadium-rich grossular hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). Until now, the accurate crystallization age of the tsavorite in Kenya and Lemshuku (Tanzania) has remained unknown. Here, we conducted in situ laser U-Pb geochronological analysis on gem-quality tsavorite samples from Tanzania and Kenya. U-Pb dating of tsavorite sourced from the Lemshuku mine (Tanzania) and the Tsavorite mine (Kenya) yielded ages of 643.9 ± 3.2 Ma and 617.4 ± 4.8 Ma, respectively. The high closure temperature of the U-Pb system within garnets renders it more inclined to preserve crystallization ages rather than documenting cooling events or metamorphic overprinting. Consequently, these ages are indicative of the tsavorite mineralization epochs. These findings align with the most significant metamorphic period documented in the Mozambique Belt, known as the East African Orogen, which occurred between 640 and 600 Ma. U-Pb data have revealed distinct formation times for each district. Dating specific deposits can provide more precise information about the origin of tsavorite, rather than solely relying on isotope or trace element data that have long been used for provenance studies of tsavorite. Full article

The Paleoproterozoic basement underlying the Cathaysia Block remains relatively understudied, and its contribution to the region’s tectonic evolution requires further investigation. In this study, we examined Jurassic Laiziling and Jianfengling A-type granites and identified a significant number of zircon grains exhibiting varied CL imaging characteristics. These zircons yielded four distinct age groups: <100 Ma, 200–100 Ma, 500–200 Ma, and >700 Ma. Detailed trace element analysis revealed that these age groups correspond to different zircon types: metamorphic recrystallized zircons (<100 Ma), primary magmatic zircons (200–100 Ma), and inherited zircons (500–200 Ma and >700 Ma). Through host rock and tectonic setting discrimination, we consider that the inherited zircons have host rocks of S-type granites and basic rocks, and these were formed in subduction-compression tectonic environments. In comparison to local significant geological events in history, we propose that these zircons record multiple tectonic events in the South China Block, including the amalgamation of the Yangtze and Cathaysia Blocks during the Neoproterozoic; an intracontinental orogenic event that occurred during the Middle Paleozoic; and subduction–exhumation processes related to the Paleo-Pacific slab; as well as extensional metamorphic events from the Cretaceous to Tertiary events. A comparison of Hf isotopic compositions revealed that zircons aged 500–200 Ma and >700 Ma share a 2.5–1.6 Ga crustal evolution zone, indicating that multiple re-melting events have occurred within the Paleoproterozoic basement of the Cathaysia Block. Full article

The Mingshan reservoir of the Dabie Orogen has a number of Neoproterozoic bimodal intrusive rocks. We focused on the zircon U-Pb chronology, Hf isotopes, and bulk-rock geochemistry of these rocks. The results showed the following: (1) The bimodal intrusive rocks mainly consist of monzogranitic gneiss and plagioamphibolite, with zircon U-Pb ages of 785.0 ± 7.1 Ma and 787.3 ± 6.1 Ma, respectively. These ages indicate that they were formed in the late Qingbaikou epoch of the Neoproterozoic era. (2) The monzogranitic gneiss was dominated by peraluminous features and displayed a strong right deviation of REE (rare-earth element) patterns and a negative δEu anomaly. It is enriched in the LILEs (large-ion lithophile elements) Rb, Ba, and K, but slightly depleted in Nb, Sr, P, and Ti, with low 10,000* Ga/Al values, indicating that it is similar to Al-type granite. The plagioamphibolite belongs to the metaluminous, peraluminous series. It has a Mg^# (molar ratio of Mg to Mg + Fe) of 36.1~55.9 and is enriched in the LILEs Rb, Ba, and K, with a slight positive anomaly of Ba, and is depleted in Nb and Sr. (3) The monzogranite shows negative zircon εHf(t) values ranging from −13.4 to −7.2 and a Paleoproterozoic T_DM2(Hf) (two-stage depleted mantle model age) of 1969–2298 Ma. The zircon εHf(t) values and T_DM2(Hf) of the plagioamphibolite were concentrated around 2.9–5.7 and 1257–1410 Ma, respectively. The geochemistry and Hf isotopes show that the monzogranitic gneiss and plagioamphibolite have distinct magmatic sources. The plagioamphibolite formed from mantle and partial continental crustal materials. The monzogranitic gneiss, on the other hand, was formed as a result of the partial melting of the shallow ancient felsic crust caused by mafic rock heating or upwelling. Taking into account regional correlation, the middle Neoproterozoic bimodal intrusive rocks originated in the structural framework of an extensional setting. Full article

Complex Neoproterozoic tectonic processes greatly affected the West Congo Basin, resulting in a series of dispersed copper deposits in the Niari Sub-basin, Republic of the Congo. Structural observation and analysis can help in understanding both the transportation pathways for copper accumulation and the detailed tectonic evolution processes. This study examines cases from four copper mine sites in the Luangu region of the Niari Basin, using a set of codes that consider the three regional tectonic regimes (extension, extrusion, and contraction) and three deformation criteria (maximum effective moment criterion, tensile fracture criterion, and the Coulomb criterion). By combining these two aspects, nine new codes are introduced: the extension maximum effective moment criterion (EM), extension tensile fracture criterion (ET), extension Coulomb criterion (EC), strike-slip maximum effective moment criterion (SM), strike-slip tensile fracture criterion (ST), strike-slip Coulomb criterion (SC), compression maximum effective moment criterion (CM), compression tensile fracture criterion (CT), and compression Coulomb criterion (CC). By analyzing and applying these codes to the selected sites, we show that the new codes can present a geometric coordination catering to an exhumation-related inversion process from extension, strike-slipping, to contraction. The existence of SM- and CM-related structures that occurred during regional extrusional and contractional events may indicate a deeper level of exhumation for layers related to copper deposits in the field sites. A new tectonic evolution model is presented, considering the hypothesis of vertical principal stress changes while the two horizontal principal stresses remain relatively constant during copper mineralization affected by the Western Congo Orogen. The application of the nine codes facilitates the determination of interrelations between different tectonic regimes. Full article

The Huangjindong gold deposit in northeastern Hunan is one of the most representative gold deposits in the Jiangnan Orogenic Belt. The orebodies are mainly hosted in the Neoproterozoic Lengjiaxi Group, which comprises carbonaceous slates. Abundant carbonaceous material (CM) can be found in the host rocks and ore-bearing quartz veins, but its geological characteristics and genesis, as well as its association with gold mineralization, are still unclear. Systematic petrographic observation demonstrated two types of CM in host rocks and ores, i.e., CM1 and CM2. Among them, CM1 is the predominant type and mainly occurs in the layered carbonaceous slates, while CM2 is mostly present in quartz veins and mineralized host rocks. Laser Raman spectroscopic analyses of CM1 were performed at higher temperatures (376–504 °C), and CM2 was generated at similar temperatures (255–435 °C) to gold mineralization. Combined with previous studies, we can conclude that CM1 was produced by Neoproterozoic to early Paleozoic metamorphism before gold mineralization, while CM2 is of hydrothermal origin. Geochemical modeling indicates that CM1 could promote gold precipitation through reduction, as well as facilitate structure deformation and metal absorption as previously proposed. However, hydrothermal CM2 is favorable for gold mineralization because it triggers sulfidation, similar to other Fe-bearing minerals (such as siderite) in the host rocks. Consequently, both types of CM in the Huangjindong deposit are favorable for gold mineralization and carbonaceous slates could be important gold-bearing units for future ore prospecting in the Jiangnan Orogen as well as other places in South China. Full article

Although considered a crucial component of the Rodinia supercontinent, it remains uncertain how the Yangtze craton relates to the accretion and breakup of Rodinia. Here, the Huanglingmiao granitic complex (HGC), an intermediate-acid rock series that intruded on the southern Kongling terrane of the northern Yangtze craton margin, is investigated to help resolve this conundrum. Our analysis indicates that these rocks consist of tonalite, trondhjemite, granodiorite, oligoporphyritic granodiorite, porphyric biotite granodiorite, and fine- to medium-grained granodiorite dyke compositions. Collectively, this assemblage is further subdivided into two categories by their temporal, spatial, and geochemical features into early TTG-like and later granitic–dioritic units, which are composed of tonalite, trondhjemite, granodiorite, porphyritic granodiorite, and the fine- to medium-grained granodiorite dykes, respectively. Zircon U-Pb dating yields ages of 865~850 Ma for the TTG-like rocks, 844~825 Ma for the porphyritic granodiorites, and ~800 Ma for the granodiorite dykes. Combined with geochemical evidence, the data suggest that the early- and late-series rocks were formed by a partial melting of Mesoproterozoic and Paleoproterozoic crustal materials, respectively, suggesting that the vertical layering of the crust controlled the composition of the independent units. In addition, isotopic evidence points to different sources for the various rocks in the Kongling terrane and that mantle-derived materials influenced the early-series lithologies. Combined with previous studies on the northern margin of the Yangtze craton, it is inferred that the early-series rocks formed in an active continental margin environment, while the late-series rocks display within-plate boundary formation characteristics. The multiple magmatic activities revealed by this study record sequential partial melting with tectonic transition characteristics from an Andean-type to within-plate magmatism in the northern margin of the Yangtze craton. Taken together, these observations point to a strong association between these rocks, convergence, and incorporation of the northern Yangtze craton margin into the Rodinia supercontinent during the Tonian Period. Full article

The South China Plate is an important part of the Rodinia supercontinent in the Neoproterozoic. The Rizhao area, located on the northeastern margin of the South China Plate, records multiple periods of magmatism, among which Neoproterozoic granitic gneiss is of great significance to the tectonic evolution of the South China Block. In this study, systematic petrology, geochemistry, isotopic chronology, and zircon Hf isotopic analyses were carried out on gneisses samples of biotite alkali feldspar granitic and biotite monzogranitic compositions in the Rizhao area. Geochemical analyses suggest that these granitic rocks belong to the sub-alkaline series and have high potassium contents. They are enriched in large-ion lithophile elements K, Rb, and Ba; depleted in high field strength elements P, Nb, and Ti; enriched in light rare earth elements and moderately depleted in heavy rare earth elements; and have weak to moderate negative Eu anomalies and weak negative Ce anomalies. These rocks are post-orogenic A-type granites. LA-MC-ICP-MS U-Pb dating of zircons from two biotite alkali-feldspar granitic gneiss samples yielded weighted mean ages of 785 ± 8 Ma (MSWD = 3.0) and 784 ± 6Ma (MSWD = 1.5), respectively, and a biotite monzogranitic gneiss sample yielded a weighted mean age of 789 ± 6 Ma (MSWD = 2.3). Lu-Hf isotopic analyses on zircon grains from the two types of Neoproterozoic-aged gneisses yielded negative ε_Hf(t) values ranging from −19.3 to −8.8 and from −18.3 to −10.4, respectively, and the corresponding two-stage Hf model age ranges are 2848–3776 Ma and 2983–3682 Ma, respectively. These granites are the product of Neoproterozoic magmatic activity and are mainly derived from the partial melting of Archean continental crust. Combining the geochemical characteristics and zircon U-Pb-Lu-Hf isotopic analyses, these A-type granitic gneisses appear to have formed in an intracontinental rift extension environment during the initial break-up of the Rodinia supercontinent, as part of the supercontinent break-up process at the northeastern margin of the South China Block. Full article