Search Results (429)

Magmatic activity is crucial for identification of the tectonic framework of the ancient oceanic crust. In this study, systematic investigation, including a field survey, zircon LA-ICP-MS U-Pb dating, and whole-rock geochemical analysis, has been carried out on the intrusive quartz- and granodiorites within the Meso-Tethyan Shiquanhe Ophiolitic Mélange (SQM), Tibet. Zircon U-Pb dating yields the weighted mean ages of 174.7 ± 1.4 Ma (quartz diorite) and 178.9 ± 1.2 Ma (granodiorite), respectively, demonstrating the Early Jurassic formation age. The quartz diorite samples are metaluminous (A/NKC = 0.77–0.95) (molar/Al₂O₃/(CaO + Na₂O + K₂O)), while the granodiorite samples are weakly peraluminous (A/NKC = 0.95–1.21), and both of them exhibit tholeiitic to calc-alkaline geochemical characteristics and can be classified as I-type granites. The right-dipping rare-earth element (REE) patterns, enrichment in large ion lithophile elements (LILEs: Rb, Ba, Th), and depletion in high-field-strength elements (HFSEs: Nb, Ta, Ti), as well as relatively high (La/Yb)_N ratios, are features compatible with an island arc setting. Combined with previous works, we suggest that the Shiquanhe ophiolitic mélange not only preserves records of mid-late Jurassic island arc magmatic activity but also contains evidence of island arc magmatism from the late Early Jurassic. Full article

The Huxu Au-dominated deposit is a representative intermediate sulfidation epithermal deposit in the middle section of the Gan-Hang belt. The formation of such deposits is commonly closely related to deep magmatism. However, the specific relationship between the formation of the Huxu deposit and the magmatic rocks, and the tectonic setting of the related magmatism and mineralization in this deposit still remains unclear. In this study, we present the results of U-Pb dating, major and trace element analysis, and Nd isotope analysis of the magmatic zircon and apatite from the ore-bearing quartz diorite porphyry in the Huxu deposit. The results show that the U-Pb ages of zircon and apatite from the quartz diorite porphyry are 137.9 ± 1.3 Ma and 130 ± 16 Ma, respectively; the total content of rare earth elements (ΣREEs) in the zircons ranges from 446.66 to 2752.92 ppm, exhibiting enrichment in heavy REE and depletion in light REE, with a slightly negative Eu anomaly and a slightly positive Ce anomaly; the ΣREEs in the apatite is relatively high, ranging from 3252.02 to 13,155.92 ppm, averaged 5604.16 ppm, and exhibits a right-leaning mode with light REE enrichment and heavy REE depletion, with a moderate degree of negative Eu anomaly; the distribution of ¹⁴³Nd/¹⁴⁴Nd ratios of the apatite is rather concentrated (0.512145–0.512271), and the εNd(t) value calculated based on the U-Pb age of apatite ranges from −8.31 to 5.79. By combining the geological characteristics and the geochemical data of the deposit and the ore-bearing magmatic rocks, we propose that the ore-bearing quartz diorite porphyry of the Huxu Au-dominated polymetallic deposit belongs to I-type granite; the parental magma is the mixture of juvenile and ancient crustal melts; the tectonic setting of the intrusion and mineralization is the continental margin arc related to the subduction of the ancient Pacific Ocean Plate in the Early Cretaceous Epoch; and the ore-forming fluids and metals are provided by deep magma. Full article

Ultrapotassic lamprophyre dykes are spatially closely related to gold deposits in collision tectonic belts. However, the potential implication of these lamprophyre dykes to gold deposits remains poorly constrained. Abundant ultrapotassic lamprophyre dykes in the Baiyun gold deposit of Liaodong Peninsula, NE China, are closely associated with Au orebodies. This presents an excellent opportunity to investigate the genesis and tectonic significance of these dykes, as well as their potential connection to gold mineralization. Here, based on LA-ICPMS zircon U-Pb age, petrogeochemistry, and Sr-Nd-Hf isotopic composition characteristics, we studied the ultrapotassic lamprophyre dykes in the Baiyun gold deposit. Zircon U-Pb dating of lamprophyre dykes is 225.7 ± 1.3 Ma, which is consistent with the previous auriferous pyrite Re-Os data results within error, indicating that the lamprophyre dykes and gold deposits formed simultaneously in the Late Triassic, which coincided with the exhumation of the deeply subducted South Chin Block (SCB). The lamprophyre dykes belong to the shoshonitic series (K₂O + Na₂O = 6.39–7.57 wt.%, K₂O/Na₂O = 3.99–8.74) and are enriched with magnesium (MgO = 5.33–6.40 wt.%, Mg^# = 58–65), barium (Ba = 2225–3046 ppm), and strontium (Sr = 792–927 ppm), and their (⁸⁷Sr/⁸⁶Sr)_i isotopic composition ranges from 0.712514 to 0.714831, ε_Nd(t) ranges from −15.4 to −14.1, and zircon ε_Hf(t) values range from −14.3 to −12.5. These correspond to Paleoproterozoic model ages between 2.1 and 2.3 Ga, which are comparable to the ultra-high-pressure metamorphic rocks with the SCB nature found in the Dabie–Sulu orogenic belt. The results demonstrate that the overlying lithospheric mantle was possibly metasomatized by subducted SCB-derived melts before magma generation under the North China Block (NCB) in the Late Triassic. The lamprophyre dykes with high Nb/U and Th/Yb values, enriched Ba, Sr, REE, Na₂O + K₂O, K₂O/Na₂O, and the LOI demonstrate that the metasomatic agents were hydrous, high-pressure melts. These melts likely resulted from the partial melting of subducted continental crust, which is attributed to phengite breakdown in the subduction continental channel. The silica-rich melts migrate from the plate into the sub-continental lithospheric mantle (SCLM) and form potassic- and volatile-enriched metasomatized SCLM. Subsequently, the partial melting of metasomatized SCLM due to the decompression and thinning may be the main mechanism to generate the syn-exhumation ultrapotassic magma in a post-collision setting. This study suggests that the SCLM, metasomatized by melts derived from continental crust, plays a key role in generating volatile-rich hydrous SCLM during the continental subduction and collision stage. In contrast, during the post-collision stage, as tectonic forces transition from compressional to extensional, the abundant volatiles and ultrapotassic magma produced from the partially melted and metasomatized lithospheric mantle may significantly contribute to the transportation, enrichment, and precipitation of gold through magmatic-hydrothermal processes, facilitating the formation of gold deposits. Full article

The northern part of the Naomugeng Sag in the Erlian Basin shows favorable sandstone-type uranium mineralization in the lower member of the Saihan Formation. The sandstone thickness ranges from 39.67 to 140.36 m, with an average sand content ratio of 76.33%, indicating broad prospecting potential. This study focuses on samples from uranium ore holes and uranium-mineralized holes in the area, conducting grain-size analysis of uranium-bearing sandstones, heavy mineral assemblage analysis, and detrital zircon U-Pb dating to systematically investigate provenance characteristics. The results indicate that the uranium-bearing sandstones in the lower member of the Saihan Formation were primarily transported by rolling and suspension, characteristic of braided river channel deposits. The heavy mineral assemblage is dominated by zircon + limonite + garnet + ilmenite, suggesting that the sedimentary provenance is mainly composed of intermediate-acid magmatic rocks with minor metamorphic components. Detrital zircon U-Pb ages are mainly concentrated in the ranges of 294–217 Ma (Early Permian to Late Triassic), 146–112 Ma (Middle Jurassic to Early Cretaceous), 434–304 Ma (Late Carboniferous to Early Permian), and 495–445 Ma (Middle–Late Ordovician to Early Silurian). Combined with comparisons of the ages of surrounding rock masses, the provenance of the uranium-bearing sandstones is mainly derived from intermediate-acid granites of the Early Permian–Late Triassic and Middle Jurassic–Early Cretaceous periods in the southern part of the Sonid Uplift, with minor contributions from metamorphic and volcanic rock fragments. The average zircon uranium content is 520.53 ppm, with a Th/U ratio of 0.73, indicating that the provenance not only supplied detrital materials but also provided uranium-rich rock bodies that contributed essential metallogenic materials for uranium mineralization. This study offers critical insights for regional prospecting and exploration deployment. Full article

The Mianhuakeng deposit, located within the Zhuguangshan batholith in the Nanling area, is currently recognized as the largest granite-related uranium deposit in China. A portion of the uranium ore bodies is spatially associated with NE-trending mafic veins within the granite. In this study, the field investigation, zircon U-Pb dating, S and Pb isotope analysis, and whole-rock geochemical analysis were conducted on these mafic veins to explore their crystallization age, petrogenesis, tectonic setting, and relationships with uranium mineralization. The weighted mean result of zircon U-Pb is 189 ± 3 Ma, suggesting that the mafic dyke was crystallized during the Early Jurassic. The whole-rock geochemistry and isotopes exhibit characteristics of intraplate basalts, suggesting that the mafic dykes originate from an enriched mantle source consisting of garnet–spinel lherzolite, with an estimated partial melting of 1%–5%. Mafic magmas underwent low-degree contamination from the lower crust during upwelling, induced by the extension of the lithosphere during the Early Jurassic. The analyses of pyrite sulfur isotopes in mafic samples vary between −2.9‰ and 1.8‰, significantly different from that of pyrite (−14.4‰ to −7.8‰) formed during the uranium mineralization. Furthermore, the ages of the pitchblende of 127–54 Ma are much younger than the crystallization ages of mafic dykes, indicating that the mafic magmas did not contribute to the uranium mineralization of Mianhuakeng deposit during magmatism. However, the abundant reducing minerals (e.g., pyrite, hornblende, and Fe²⁺-bearing minerals) in the mafic dykes can act as a redox barrier, reducing mobile U⁶⁺ to immobile U⁴⁺ during fluid–rock interaction, thereby facilitating uranium precipitation from the hydrothermal ore-forming fluids. The secondary fractures created by the intrusion of mafic magma probably provided favorable pathways for the movement of hydrothermal fluids. Full article

The island of Mindoro forms the northeastern part of the Palawan Continental Terrane, a terrane that is considered to have formed at the southwestern margin of SE China and subsequently drifted into its present position as a consequence of the opening of the South China Sea. Using U-Pb age determinations of detrital zircon in sedimentary rocks and of current river sediments, this study aims to establish the relationships between the various geological units exposed on this island. The results indicate that some established units have left no trace in the current river sediments. On the other hand, some ages found in the age distributions of river sediments have no known source in the studied units. The data presented support the concept that the Northeast Mindoro Block is distinct from the Southwest Mindoro Block. Both blocks contain units that may be correlated with units exposed in northern and southern Palawan, and thus both appear to be related to the SE China margin of the South China block. Full article

Cr and Platinum-Group Elements (PGEs), critical metallic elements, are mainly hosted in mafic and ultramafic rocks, but determining these rocks’ mineralization age has long been challenging. Zircon, the primary geochronological mineral, is scarce and fine-grained in such rocks, hindering conventional separation techniques (heavy liquid separation, magnetic separation, manual hand-picking) with low efficiency, poor recovery, and significant sample bias. This study develops an integrated workflow: mixed acid leaching enrichment (120 °C), powder stirring for mount preparation, automated mineral identification, and in situ Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA–ICP–MS) dating. Validated on the Xiugugabu diabase in the western Yarlung–Tsangpo Suture Zone (southern Tibet), the workflow yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 120.5 ± 3.3 Ma (MSWD = 0.13) and 120.5 ± 2.0 Ma (MSWD = 3.2) for two samples. Consistent with the published Yarlung–Tsangpo Suture Zone (YTSZ) diabase formation ages (130–110 Ma), these confirm the Xiugugabu diabase as an Early Cretaceous Neo–Te–thys oceanic lithosphere residual recording mid-stage spreading. The workflow overcomes traditional limitations: single-sample analytical cycles shorten from 30–50 to 10 days, fine–grained zircon recovery is 15x higher than manual picking, and U–Pb ages are stable. Suitable for large-scale mafic–ultramafic geochronological surveys, it can extend to in situ zircon Hf isotope and trace element analysis, offering multi-dimensional constraints on petrogenesis and tectonic evolution. Full article

Detrital zircon U–Pb dating from the Muti Formation sheds light on sediment sources and foreland basin development along the northeastern Arabian margin during the Late Cretaceous. The siliciclastic-rich Muti Formation was deposited in a syn-obduction foreland basin that formed as the Semail Ophiolite advanced. Zircon age spectra from eastern (Nakhal and Sayga) and western (Murri) sections are dominated by Neoproterozoic–Cambrian ages (450–900 Ma), linked to the Pan-African orogeny and the Arabian–Nubian Shield, indicating these as the main sediment sources. The Murri section also contains older Mesoproterozoic to Archean zircons, likely recycled from the Nafun Group (part of the Huqf Supergroup), suggesting reworking of ancient Gondwanan cover sequences rather than direct input from the Indian craton. Additional Permian zircons reflect input from Arabian Plate magmatic rocks, while Jurassic–Cretaceous grains indicate material derived from the Semail Ophiolite and related arc terranes. Overall, the Muti Formation records a mixed sediment supply from the Arabian Shield, reworked Gondwanan sandstones, and ophiolitic detritus, marking the transition from a passive margin to a flexural foreland basin. The dominance of Pan-African zircon ages highlights continued recycling of Gondwanan sequences and refines models of Late Cretaceous basin evolution in northern Oman, underscoring the complex, multi-cycle nature of sedimentation in this tectonically active setting. Full article

Geochemical whole-rock variations in the Kovdozero complex in the Lapland–Belomorian Belt (LBB) are compared with those observed in the Pados-Tundra layered complex in the Serpentinite Belt (SB) in the complementary structure in the Fennoscandian Shield. A great variety of coronitic associations exists in the entire LBB–SB system. The Kovdozero complex largely consists of more evolved products of crystallization. Our results of U–Pb dating (zircon and baddeleyite) give the dates of 2514 ± 5 and 2478 ± 6 Ma, leading to the revised age ~2.5 Ga for the Kovdozero complex. It is thus considered to be coeval with Pados-Tundra, Perchatka, and gabbro–anorthosite associations of the Belomorian province in the White Sea region. The variation trends are generally extensive, continuous and close to linear at Kovdozero, which point to crystallization of chonolithic bodies of the complex from a single portion of melt, in separate reservoirs that likely communicated to develop as a whole in the connected system. The extreme degree of differentiation of derivatives of the initial komatiitic magma occurred in the large-scale plume. It led to the development of shallowly emplaced complexes grading from dunitic rocks and associated chromitites with Ru–Os–Ir mineralization at Pados-Tundra (the center) to leucocratic gabbroic rocks at Kovdozero, and likely to gabbro–anorthosite rocks of the Belomorian province (the periphery); these are considered the final products in the megastructure. The εNd(T) values are slightly negative at Kovdozero: −0.43 and −0.60. They imply some degree of crustal contamination of the initial magma. The generalized date of 2.5 Ga likely represents the age of the coronitic complexes of ultrabasic–basic rocks that crystallized from portions of komatiite-derived melts in hypabyssal settings of the LBB–SB megastructure in the eastern Fennoscandian Shield. Full article

The voluminous Mesozoic volcanic rocks developed in the Great Xing’an Range, northeastern China, have received extensive attention in recent decades. However, the timing and petrogenesis, as well as the related geodynamic processes of the Late Mesozoic volcanism, are still controversial. In this paper, we present the whole-rock geochemistry and zircon U–Pb ages for the Late Mesozoic volcanic rocks from the western part of the central Great Xing’an Range, which provide considerable insights into the geodynamic setting of the region. The zircon U-Pb dating results indicate that two main episodes of volcanism occurred in the central Great Xing’an Range, including in the Late Jurassic (ca. 147 Ma) and Early Cretaceous (ca. 142–125 Ma). These Late Mesozoic volcanic rocks display similar geochemical compositions, which are mainly intermediate–felsic, alkaline, peraluminous to metaluminous, enriched in large ion lithophile elements and light rare earth elements, and depleted in high-field-strength elements, indicating arc affinities in the subduction zone. The trace element compositions suggest that the magmatism was related to a post-collisional extensional environment. Combined with the spatial distribution and temporal migration of the Mesozoic magmatic events in the whole northeastern China region, we propose that these Late Jurassic–Early Cretaceous volcanic rocks formed in a continental arc setting, which was mainly related to the rollback of the subducted Paleo-Pacific oceanic plate. Full article

The Jiulongnao W–Sn ore field in the eastern Nanling Range is characterized by large-scale early Yanshanian magmatic activity and W–Sn mineralization. In recent years, increasing attention has been given to the close relationship between Indosinian magmatic activity and Sn mineralization. The Aotou quartz vein-type Sn deposit is unique for only Sn mineralization without W during the Indosinian period. Seventeen thin-to-thick cassiterite–quartz veins are densely distributed in Ordovician metasandstone and slate, and these veins extend down to the top of the concealed granite. However, both the diagenetic age and the petrological characteristics of the concealed granite remain unclear. This contribution shows that the Aotou muscovite intrusion is a highly fractionated S-type pluton, characterized by a peraluminous, high-K composition, enrichment in LREEs, and depletion of Ba, Sr, Ti, and Eu. In this study, LA–ICP–MS zircon U–Pb dating of the concealed muscovite granite yields emplacement ages of 238.7 ± 1.0 Ma and 225.4 ± 0.9 Ma, indicating that at least two stages of magmatic intrusion occurred in the Triassic, with the diagenetic environment transitioning from a compressional setting to an extensional setting. The ε_Hf(t) values during the two stages are −0.98 to −0.95 and −0.98 to −0.96, and the T_DM2 values are 1.78–2.08 Ga and 1.78–2.06 Ga, indicating that two-stage magma was derived from the late Paleoproterozoic lower crustal materials. Comprehensive analysis reveals that the second stage of Indosinian magma intrusion (232–225 Ma) in the Jiulongnao ore field is closely related to Sn mineralization, and the northern Wenying pluton has good prospecting potential for quartz vein-type Sn(–W) deposits. Full article

The Wunuer deposit is an important hydrothermal Zn-Pb-Ag-Mo polymetallic deposit in the central Great Xing’an Range, NE China. The zinc–lead polymetal mineralization is closely hosted by the volcanic rocks of the Manketouebo formation (rhyolite and lithic crystal tuff) and related to the Mesozoic granite porphyry. Field evidence and petrographic observations have identified three mineralization stages within this deposit from deep to shallow: (1) late magmatic stage with vein-type Mo mineralization characteristics and mainly related to the deep granite porphyry; (2) magmatic–hydrothermal transition stage characterized by breccia-type Zn mineralization, which occurred within a steep cryptoexplosive breccia; and (3) hydrothermal stage featured by vein-type Zn-Pb-Ag mineralization hosted by the ore-bearing fractured zone. In this contribution, we present the mineralogy, zircon U-Pb age, sphalerite Rb-Sr dating, whole-rock geochemistry, and Hf-S-Pb isotopes of the Wunuer deposit. LA-ICP-MS zircon U-Pb dating of the ore-related granite porphyry, rhyolite, and lithic crystal tuff suggests that the Mo mineralization from the late magmatic stage occurred between 144.8 Ma and 145.8 Ma. The Rb-Sr isochron dating of sphalerite indicates that the hydrothermal stage Zn mineralization age is 121 ± 2.3 Ma, which is related to the volcanism of Baiyin’gaolao Formation in the Wunuer area. The concentrated and positive δ³⁴S_V-CDT values (0.17‰~5.40‰) of sulfides, as well as uniform Pb isotope compositions of granite porphyry intrusion and galena, jointly imply a magmatic source of metallogenic materials for Pb-Zn mineralization. Whole-rock geochemistry and Hf-Pb isotopes reveal that the granite porphyry and rhyolite both originated from a mantle-derived juvenile component and assimilated by minor ancient crustal material in an extensional setting. Our study demonstrates the prospect of further exploration for two mineralization events in the hydrothermal polymetallic deposits of the central Great Xing’an Range. 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

Mesozoic granitic rocks are widely developed in the Great Xing’an Range, and determining their emplacement age and genesis is crucial for reconstructing the tectonic-magmatic evolution of Northeast China. This paper reports the petrographic, geochronological, geochemical and zircon Hf isotopic characteristics of granites in the Huolin Gol area of the southern Great Xing’an Range to determine the formation age, source nature and geodynamic background of the rocks in this area. Zircon U–Pb dating results show that the granites in the study area were formed in the Early Cretaceous (134–130 Ma), rather than the Late Jurassic as previously thought. The granites have SiO₂ contents ranging from 75.02 to 78.53 wt.%, Na₂O = 3.55–3.89 wt.%, K₂O = 3.98–5.11 wt.%, Na₂O/K₂O = 0.72–0.97, A/CNK = 1.04–1.14. Their rare earth element (REE) distribution patterns are all right-inclined, with LREE/HREE = 3.89–12.41, (La/Yb)_N = 2.39–18.86, Eu/Eu* = 0.02–0.17. Trace element spider diagrams show significant enrichment in Rb, Th, U, K, Pb and LREEs, and depletion in Ba, Nb, Ta, Sr, P, Ti and HREEs. The zircon εHf(t) values range from +6.4 to +15.0, and the two-stage Hf model ages (T_DM2) range from 773 to 226 Ma. These characteristics indicate that the granitic rocks belong to the weakly peraluminous high-K calc-alkaline I-type granite, derived from partial melting of newly generated juvenile continental crust materials. Combined with the coeval magmatic associations, spatial distribution patterns, and regional tectonic evolution, we propose that the Early Cretaceous granitic rocks in the study area formed in an active continental margin setting, with their geodynamic mechanism linked to the subduction of the Paleo-Pacific Plate beneath the East Asian continent. Full article