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Simultaneous U–Pb and U–Th dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on the ca. 0.1 Ma Toya tephra and the ca. 0.08 Ma SS14-28 U–Th zircon reference material. In U–Pb dating, both Th/U and Pa/U partitioning between magma and minerals were considered. In U–Th dating, both abundance sensitivity and molecular interferences on 230Th were reevaluated. As a result, the Toya tephra yielded an accurate weighted mean U–Pb age of 0.103 ± 0.029 Ma (2σ) using zircon and monazite. Conversely, the SS14-28 zircon yielded an inaccurate U–Pb age (0.25 ± 0.10 Ma), which was attributed to low 206Pb signal intensity. Both the Toya tephra zircon and the SS14-28 zircon yielded accurate U–Th model ages of 0.108 ± 0.014 Ma and 0.078 ± 0.007 Ma, respectively. The agreement of U–Pb and U–Th ages for Toya indicates that simultaneous U–Pb and U–Th dating is possible and viable. The inappropriate age of SS14-28 U–Pb age and appropriate U–Th model age also indicates it is preferable to apply both U–Pb and U–Th dating simultaneously for young (<0.4 Ma) zircons to check internal consistency. The proposed double dating approach may be especially useful for small grains when it otherwise would be impossible to obtain multiple ages from a single grain. By adopting simultaneous U–Pb and U–Th dating using LA-ICP-MS, zircon crystallization ages as old as 4.5 Ga to as young as 0.1 Ma (or even younger) can be obtained in a quick and cost-effective manner with a reasonable (~5% at 1σ) uncertainty. [ABSTRACT FROM AUTHOR]

The large-sized Tarangaole uranium deposit and its neighboring Daying and Nalinggou deposits, located in the northeastern margin of the Ordos Basin, constitutes a major uranium resource base in northern China. In order to further clarify the sedimentary material source, uranium source and regional sediment–tectonic setting of the uranium-fed clastic rocks (i.e., Zhiluo Formation(J2z)) in the district, this paper carried out whole-rock geochemistry, heavy minerals composition and in situ U-Pb dating of detrital zircons for sandstones from the lower section of the Zhiluo Formation. The results have shown that the average chemical differentiation index (CIA) for the host rocks is 73.16 and the chemical weathering degree is moderate. Heavy minerals are mainly composed of ilmenite, garnet, chlorpyrite, zircon, pyrite, apatite, hematite, etc. The U-Pb dating of detrital zircon generally indicates three age peaks, i.e., 260~Ma, 1850~Ma and 2450~Ma, respectively. In conclusion, the source rocks may have been formed at active continental margins, e.g., in a continental margin arc environment. The sedimentary materials mainly come from khondalite series, TTGs, granulite, and mafic–ultramafic intrusive rocks distributed among the Daqing–Ula Mountains and adjacent areas, etc. The Late Paleozoic U-rich intermediate and acidic magmatic rocks spreading over the eastern part of the Ula–Daqing and Wolf mountains have provided the main uranium sources for the formation of major U deposits in the northern Ordos Basin. [ABSTRACT FROM AUTHOR]

The Wunugetu deposit, a large-scale porphyry copper–molybdenum deposit, is located in the southern Erguna block. Its ore bodies are primarily found within monzogranites, granite porphyries, and biotite monzogranites. Additionally, the deposit contains late-stage intrusive dykes of rhyolitic porphyries. This study examined the deposit's monzogranites and rhyolitic porphyries using lithogeochemistry, zircon U-Pb dating, and Hf isotopic analysis. The main findings include: (1) Zircon U-Pb dating showed that the monzogranites formed around 209.0 ± 1.0 Ma, whereas the rhyolitic porphyries in the northern portion formed around 170.49 ± 0.81 Ma, suggesting magmatic activity in the deposit spanned from the Late Triassic to the Middle Jurassic. (2) The monzogranites exhibited high silicon content (73.16–80.47 wt.%) and relatively low aluminum content (10.98–14.37 wt.%). They are enriched in alkalis (content: 3.42–10.10 wt.%) and deficient in magnesium and sodium, with aluminum saturation indices (A/CNK) ranging from 1.1 to 2.9. In addition, the monzogranites are enriched in large-ion lithophile elements (LILEs) such as Rb, K, and Ba and deficient in high-field-strength elements (HFSEs) like Nb, P, and Ti. (3) The monzogranites have low Zr + Nb + Ce + Y contents of (151.3–298.6 ppm) × 10−6 and 10,000 × Ga/Al ratios varying between 1.20 and 2.33, suggesting that they are characteristic of I-type granites. (4) Positive zircon εHf(t) values ranging from +0.3 to +7.6 in both rhyolitic porphyry and monzogranite samples, increasing with younger emplacement ages, imply that the deposit's rocks originated from magmatic mixing between mantle-derived mafic magmas and remelts of the juvenile crust. Considering these results and the regional geological evolution, this study proposes that the Wunugetu deposit was formed in an active continental margin setting and was influenced by the Late Triassic–Middle Jurassic southeastward subduction of the Mongol-Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

It has been accepted that granitoids of the Irizar unit in the Central Victoria Land (Antarctica), as an important part of the Granite Harbour Intrusives, were formed in a post-collisional setting during the Ross orogeny along the margin of east Gondwana. However, the emplacement ages of the Irizar unit remain poorly constrained, making it difficult to form a more complete picture of the geodynamic evolution of the Ross orogen and its counterpart (Delamerian orogen) in southeast Australia. In this work, four syenogranite samples from the Irizar unit were chosen for SHRIMP zircon U-Pb dating, which yielded ages of 507.8–489.7 Ma. The new geochronological data indicate that the post-collisional extension in the Central Victoria Land had begun by ~508 Ma, much earlier than previously thought (i.e., 490–480 Ma). Integrated with U-Pb ages for Early Paleozoic granitoids from the literature, the Ross–Delamerian orogen shows that the post-collisional granitic magmatism initiated at ~515 Ma in the Central Transantarctic Mountains and northward systematically decreased to ~508 Ma in the Victoria Land, and then to ~487 Ma in southeast Australia. This can be explained well by the propagating northward transition from pre- and syn-collisional compression to post-collisional extension. [ABSTRACT FROM AUTHOR]

The intensive variables, geochemical, mineralogical, and petrogenetic constraints of the Iberian peraluminous rare metal granites (RMGs), many of them unknown, are presented. The mineral chemistry of ore and gangue minerals, whole rock analyses, geothermobarometry, melt water and phosphorus contents, mass balance, and Rayleigh modeling were performed to achieve these objectives. These procedures allow us to distinguish two main contrasting granitic types: Nb-Ta-rich and Nb-Ta-poor granites. The former have lower crystallization temperatures, higher water contents, and lower emplacement pressures than Nb-Ta-poor granites. Nb-Ta-rich granites also have higher fluoride contents, strong fractionation into geochemical twins, higher Na contents, and different evolutionary trends. At the deposit scale, the fractional crystallization of micas properly explains the variation in the Ta/Nb ratio in both Nb-Ta-poor and Nb-Ta-rich RMGs, although in higher-grade granites, the variation is not as clear due to the action of fluids. Fluid phase separation processes especially occurred in the Nb-Ta rich granites, thus transporting halogens and metals that increased the grades in the top and sometimes in the core of granites. Gas-driven filter pressing processes facilitated the migration of fluid and melt near solidus melt in Nb-Ta-rich granites. The geochemical signature of the Iberian rare metal granites mainly follows the trends of two-mica granites and P-rich cordierite granites, but also of granodiorites. [ABSTRACT FROM AUTHOR]

The Bilong Co oil shale is one of the most significant source rocks in the Mesozoic Qiangtang Basin (Northern Tibet); however, its absolute chronology remains controversial. In this study, in situ carbonate U–Pb isotope dating analysis was carried out for the first time. Detailed field geological investigations yielded some age-diagnostic ammonites, enabling a re-evaluation of the stratigraphic age of the Bilong Co oil shale. A total of 61 spots of U–Pb isotope dating from the middle part of the Bilong Co oil shale section suggests an average age of 181 ± 13 Ma. Elemental geochemistry and diagenetic analysis indicate that the proposed age represents the early deposition of the calcite, and the oil shale was deposited during the Early Jurassic time. This estimated age is further supported by the newly discovered ammonite assemblage of Hildoceratidae–Tiltoniceras sp. at the top part of the oil shale section, which confirms the deposition of the oil shale during the Toarcian age of the late Early Jurassic. Consequently, the Bilong Co oil shale can be assigned to the Quse Formation, which is attributed to the Lower Jurassic rather than the Middle Jurassic. The re-assessment of the stratigraphic age of the Bilong Co oil shale is of great significance for regional evaluation and exploration activities of hydrocarbon source rock layers in the Qiangtang Basin as well as for global stratigraphic correlation of the late Early Jurassic Toarcian oceanic anoxic event. [ABSTRACT FROM AUTHOR]

Cenozoic dolomitization of reefal carbonates has been widely found on many tropical islands worldwide. However, most ages and geochemical data obtained from bulk samples prevent a clear understanding of the previous complex diagenetic processes of these island dolostones due to a lack of in situ age and fluid composition. In this study, one deep borehole penetrated Cenozoic carbonates on Meiji Island in the southern South China Sea and massive dolostones with thicknesses over 400 m were uncovered. The in situ U–Pb geochronology and elemental analysis were conducted on the lower Nanwan Formation (upper Miocene) comprising undolomitized calcite (bioclast), replacive dolomite, and dolomite cement. Strontium isotope ages and U–Pb dates show that the penecontemporaneous replacive dolomitization occurred at 11.0–8.5 Ma, close to the deposition of precursor limestone. The dolomite cement precipitated at 8.5–6.0 Ma. In situ elemental analyses indicate that the formation of replacive dolomite and dolomite cement in the Nanwan Formation was probably controlled by seawater. The higher Mg/Ca ratio and lower Mn and Sr contents in dolomite cements show that their fluid underwent more evaporation. The dolomite content is positively related to the porosity of reefal limestones in the Nanwan Formation, suggesting that primary voids play an important role in fluid transportation during following dolomitization. Coralline algae and lime mud with algal fragments are beneficial for the rapid nucleation of dolomite. This study demonstrates that in situ elemental analysis using laser ablation has great potential for identifying the source of multistage dolomitizing fluids and can help refine the existing dolomitization model of isolated atolls. [ABSTRACT FROM AUTHOR]

Granulite facies rocks provide important keys to evaluating collisional metamorphism in orogenic belts. The mafic granulites of Baoding in the Fuping Complex of the North China Craton occur within the Trans-North China Orogen (TNCO), a major Paleoproterozoic collisional orogen. Here, we present results from detailed investigations on newly discovered garnet pyroxenite, garnet two-pyroxene granulite, and garnet-bearing-plagioclase amphibolite using petrographic, mineralogical, geochemical, and zircon U-Pb dating methods. Our results show that the Fuping Complex metamorphic evolution in this study evolved in four stages: prograde (M1), high-pressure granulite facies (M2), granulite facies (M3), and retrograde (M4) stages. The mineral assemblage of the prograde stage (M1) consists of Amp + Pl + Q within garnet cores. The mineral assemblage of high-pressure granulite facies at the peak stage (M2) consists of Gt + Cpx + Pl + Q ± Amp, forming the garnet pyroxenite. The granulite facies stage M3 is characterized by the occurrence of orthopyroxene, with a mineral assemblage of Gt + Cpx + Opx + Amp+ Pl + Q. The early retrograde stage M4-1 includes clinopyroxenes scattered inside amphiboles, following the breakdown of garnet and clinopyroxene. The mineral assemblage of this stage comprises Amp + Pl + Q + Ilm ± Cpx. Later, in the late retrograde stage M4-2, the composition of amphiboles changed to actinolite, and epidote and chlorite started to appear in the matrix. Traditional geothermobarometry yielded P-T conditions of 700~706 °C and 6.0~6.2 kbar for prograde stage M1, 854~920 °C and 13.0~13.8 kbar for high-pressure granulite facies stage M2, 912~939 °C and 8.1~9.9 kbar for M3, 661~784 °C and 3.1~4.4 kbar for M4-1, and 637~638 °C, 1.1~1.3 kbar for M4-2, along a clockwise P-T path with a nearly isothermal decompression (ITD) and slight heating. Zircon LA-ICP-MS U-Pb dating constrains the timing of the high-pressure granulite facies metamorphic event to be between 1.83 and 1.86 Ga. Geochemical features suggest that the protoliths of the high-pressure granulites may have formed in an island arc environment within a convergent margin setting. Together with results from previous studies, our data suggest that the ~1.85 Ga metamorphic age recorded in the Fuping Complex represents a regional metamorphism in the TNCO, associated with the subduction–collision and assembly of the Eastern and Western Blocks of the NCC. [ABSTRACT FROM AUTHOR]

Permian intermediate–felsic igneous rocks, widely distributed in the southern Beishan orogen, provide crucial constraints on the geodynamic process of the late Paleozoic Paleo-Asian Ocean. New zircon U–Pb dating using LA–ICP–MS determines the age of the northern Qingshan diorites, the Heishantou quartz diorites, and the southern Qingshan biotite granodiorites at 300 Ma, 294 Ma, and 291–286 Ma, respectively. Their whole-rock compositions exhibit arc-like geochemical features. Moreover, their zircon trace elements show the characteristics of continental arc zircons. The diorites, characterized by low SiO2, high MgO with Mg# (50–52), and low Cr, Co, and Ni, display enrichment in Sr-Nd-Hf isotopes (87Sr/86Sr = 0.7060 to 0.7061; ℇNd(t) = −1.4 to −1.7; ℇHf(t) = −4.7 to −0.6), originating from the fractionation process of magma derived from the enriched mantle. The quartz diorites show moderate SiO2 and variable MgO (2.75–3.84 wt%) and exhibit enrichment in Sr-Nd (87Sr/86Sr = 0.7048–0.7050; ℇNd(t) = −1.5–+0.9) and depletion in zircon Hf isotopes (ℇHf(t) = 3.8 to 7.8). Combined with their high Y (20.0–21.0 ppm) and low (La/Yb)N (6.0 to 17.2), we conclude that they originated from the juvenile lower crust previously influenced by oceanic sediments, with the input of enriched mantle-derived materials. The biotite granodiorites display low A/CNK (0.91–0.97), 10000*Ga/Al (1.8–1.9), and Ti-in-zircon temperatures (average 711 °C), indicating that they are I-type granitoids. These rocks show enrichment in Sr-Nd isotopes (87Sr/86Sr = 0.7054 to 0.7061; ℇNd(t) = −2.0 to −1.6) and many variable zircon Hf isotopes (ℇHf(t) = −2.3 to +4.5). Geochemical studies indicate that they originate from the mixing of magmas derived from the enriched mantle and preexisting juvenile lower crust. All these data imply the existence of oceanic subduction in southern Beishan during the early Permian. Integrating these results with previous studies, it is inferred that the retreating subduction of the Liuyuan Ocean contributed to early Permian intermediate–felsic rocks becoming widespread in the Shibanshan unit, the southernmost part of the Beishan orogen, and also why the Paleo-Asian Ocean in southern Beishan did not close during the early Permian. [ABSTRACT FROM AUTHOR]

The influence of the paleo-Tethys or paleo-Pacific oceanic plate subduction on Early Triassic South China has long been debated. We have studied the zircon U-Th-Hf isotopes, trace elements, and whole-rock geochemistry of Early Triassic peraluminous granitoids in the Qinzhou Bay area, South China Block. LA–ICP–MS zircon U–Pb dating has revealed the Jiuzhou granodiorites and Dasi-Taima granite porphyries formed between 248.32 ± 0.98 and 246.6 ± 1.1 Ma. These rocks are characterized by high K2O and Al2O3, and low MgO, CaO, and P2O5 contents with A/CNK = 1.06–1.17, showing high-K calc-alkaline S-type affinities. The Early Triassic intrusive rocks and adjacent silicic volcanic rocks in the Qinzhou Bay area were found to be comagmatic and derived from a common magma pool, detached in an undifferentiated melt instead of indicating remarkable crystal—melt separation. Although the analyzed granitoids have highly enriched zircon Hf isotopic compositions (εHf(t) = −23.9 to −7.8), they cannot originate solely from metasedimentary protoliths. Source discrimination indicators have revealed enriched lithospheric mantle-derived magma was also an endmember component of the S-type silicic magma, which provided a heat source for the crustal anatectic melting as well. We inferred the studied Early Triassic granitoids formed under the paleo-Tethys tectonic regime before the collision of South China and Indochina blocks, as the oceanic plate subduction would have created an extensional setting which further caused the mantle-derived upwelling and volcanic eruption. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Weideshan granites are associated with large-scale Au and polymetallic Cu-Mo-Pb-Zn mineralization. To investigate the petrogenesis of the Weideshan granite and constrain its tectonic setting during the Early Cretaceous, we conducted a zircon U-Pb-Hf isotope and whole-rock geochemical and Sr-Nd isotopic study of the granite. In situ zircon U-Pb dating of three granite samples yielded Early Cretaceous ages of 112.83 ± 0.80, 112.64 ± 0.91, and 111.82 ± 0.78 Ma. The samples had high-K calc-alkaline compositions and were enriched in the light rare earth and large-ion lithophile elements (e.g., K, Rb, Ba, Th, and U) and depleted in high-field-strength elements (e.g., Nb, Ti, and P). The samples had small negative Eu anomalies and initial 87Sr/86Sr and εNd(t) values of 0.70853–0.71029 and –18 to –14, respectively. The zircon εHf(t) values varied between −16 and −12, with corresponding two-stage model ages (tDM2) of 2180–2000 Ma. These characteristics indicated that the Weideshan pluton was formed in a back-arc extensional environment caused by subduction of the Paleo-Pacific Plate toward the Asian continent during the early Cretaceous. The magma was generated by crust–mantle interaction during lithospheric thinning. The diagenetic age of the Weideshan granites was the same as the formation age of gold and polymetallic ores in the Jiaodong area. The extensive fluid circulation induced by the magma emplacement may be the main source of ore-forming materials for the gold and polymetallic Cu-Mo-Pb-Zn deposits. [ABSTRACT FROM AUTHOR]

As the world's largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) underwent continuous juvenile crustal growth in the Phanerozoic. The northern margin of the North China Craton (NCC) and its adjacent area form the eastern segment of the CAOB, which is a key area for learning about the geological evolution of the Paleo-Asian Ocean (PAO). In the Permian, the west of the northern margin of the NCC was a post-collision extensional environment, while the east was in a subduction stage. As a connecting area, the Permian evolution of the PAO in the middle of the northern margin of the NCC has not been systematically studied. In order to fill the gap and understand the continuous temporal and spatial evolutionary process of the PAO, this paper focuses on the Permian granitic rocks in the Chifeng area. Zircon U-Pb dating and the geochemical analysis of whole-rock major and trace elements were conducted to build a granite chronological framework, and to discuss the genesis and tectonic background of the granitic rocks, along with tectono-magmatic evolutionary history in the Chifeng area. The respective LA-ICP-MS zircon U-Pb dating results from eight samples are 269 ± 1, 268 ± 3, 260 ± 4, 260 ± 1, 260 ± 1, 255 ± 2, 254 ± 2 and 256 ± 1 Ma, respectively. These results, combined with previous data, revealed that the Permian granitic rocks had undergone three events of magmatism: (1) monzogranitic-syenitic phase (294–284 Ma; Cisuralian); (2) monzogranitic phase (269–260 Ma; Guadalupian) and (3) late monzogranitic-syenitic phase (256–254 Ma; Lopingian). From the Early Permian (294–284 Ma) to the Middle Permian (269–260 Ma), granites with fine-medium-grained locally porphyritic texture and massive structure showed a high-potassium calc-alkaline series formed in a compressional setting, indicating a continuous collision between the Xing'an-Mongolian Orogenic Belt (XMOB) and the NCC. During the Late Permian-Early Triassic (256–248 Ma), granites with massive structure and medium-grained texture in the Chifeng area were magmatism dominated by A- and I-type granites of high-potassium calc-alkaline series, combined with the coeval basic rocks, which constituted a typical "bimodal" rock assemblage. This suggests that the Chifeng area was located in an extensional setting where the subducting slab broke off during the collision between the XMOB and NCC. These granitic plutons from the Permian are believed to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the NCC, according to emplacement time and occurrence location. Our findings provide strong evidence for Permian continuous temporal and spatial tectonic evolution and the characterization of the eventual closure of the PAO in Chifeng area at the northern margin of the NCC. [ABSTRACT FROM AUTHOR]

Various magmatic–hydrothermal activities have resulted in different styles of polymetallic mineralization in South China. Shuikoushan is a large Fe-Cu-Pb-Zn-Au-Ag orefield situated in fold-and-thrust belts within the South China Block. Two types of granodiorite have been identified in recent drilling work. The early-stage, coarse-grained granodiorite has developed magnetite-bearing skarns in the deep level. The late-stage, fine-grained granodiorite is associated with garnet-hematite–magnetite–pyrite–sphalerite–chalcopyrite-bearing skarns in its contact zone. Away from the garnet-bearing skarn are calcite–quartz–pyrite–sphalerite–galena veinlets in faulted breccia. Fieldwork has identified iron mineralization in both skarns, whereas copper mineralization was only discovered in the garnet-bearing skarns. Lead, zinc, gold, and silver mineralization were observed in the garnet-bearing skarns and faulted breccia. Zircon U–Pb analyses suggested the emplacement of two granodiorite at 167.8 ± 0.8 Ma (MSWD = 1.1, N = 31) and 163.6 ± 0.7 Ma (MSWD = 1.3, N = 32). Apatite and garnet U–Pb dating further indicated the magnetite-bearing skarns of 166.2 ± 1.9 Ma (MSWD = 4.5, N = 27), the hematite–magnetite–sulfide-bearing skarns of 158.6 ± 2.8 Ma (MSWD = 1.3, N = 34), and the calcite–quartz–sulfide veinlets of 159.5 ± 5.2 Ma (MSWD = 1.7, N = 24). The time–space relationship between the two intrusions and hydrothermal activities suggests that the fine-grained granodiorite is responsible for polymetallic mineralization. Whole-rock geochemistry analyses demonstrated the enrichment of LILEs and the depletion of Nb and Ta in two granodiorites, with a slight enrichment in LREEs and flat HREE patterns. These granodiorite bodies therefore belong to high-K calc-alkaline magma generated via the crust's partial melting. The fine-grained granodiorite generally has a lower HREE and higher Dy/Yb, Sr/Y ratios than coarse-grained granodiorite, corresponding to the source of magma in garnet stable lower crust. The residual garnet keeps ferric iron in melts, leaving the fine-granodiorite more oxidized for copper and gold concentration. Through these analyses and our drilling work, a continuous skarn–hydrothermal–epithermal system has been identified for Cu-Pb-Zn-Au-Ag targeting in Shuikoushan. [ABSTRACT FROM AUTHOR]

The Yongfeng composite granitic pluton, located in the southern section of the Nanling area, is composed of the Yongfeng and Longshi biotite monzonitic granites. In order to reveal the genesis of this composite granitic pluton and its relationship with mineralization, this study conducted zircon U-Pb dating, whole-rock major and trace element analysis, and biotite electron probe analysis. The results show that the Yongfeng composite granitic pluton is rich in silicon and alkali, weakly peraluminous, and poor in calcium and iron. It shows the enrichment of light rare earth elements and a significant fractionation of light and heavy rare earth elements. It also shows the enrichment of large ion lithophile elements and depletion of Ba, K, P, Eu, and Ti relative to the primitive mantle. The contents of TFe2O3, MgO, CaO, TiO2, and P2O5 are low and decrease with increasing SiO2 content. The Yongfeng composite granitic pluton does not contain alkaline dark minerals. Its average zircon saturation temperature is 776 °C, average TFe2O3/MgO is 4.81, and average Zr + Nb + Ce + Y is 280.6 ppm, which correspond to a highly fractionated I-type granite. The Yongfeng and Longshi granites were respectively formed at 152.0 ± 1.0 Ma–151.3 ± 1.1 Ma and 148.9 ± 1.2 Ma. They were formed in the extensional tectonic setting during the post-orogenic stage, under the control of the breakup or retreat of the backplate after the subduction of the Pacific Plate into the Nanling hinterland. The magmatic system of the Yongfeng composite granitic pluton is characterized by high fractionation, high content of F, high temperature, and low oxygen fugacity, which is conducive to mineralization of Sn, Mo, and fluorite. [ABSTRACT FROM AUTHOR]

Devonian magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt (CAOB). However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Devonian granitoids in the eastern Southern Beishan Orogenic Belt (SBOB). Early-Devonian granitic magmatism has been recognized from the Luotuoquan area, and the granites were emplaced between 404.9 Ma and 399.4 Ma according to LA-ICPMS zircon U–Pb dating. Geochemically, the granites exhibit high SiO2 and Al2O3 contents and are enriched in light rare earth elements as well as Rb, Th, Nd, Zr, and Hf, while being depleted in heavy rare earth elements and Ba, U, Sr, and Ti, with distinct rare earth element fractionation and pronounced negative Eu anomalies. According to the comprehensive analysis, they closely resemble the features typically associated with A-type granites. The zircons εHf(t) values are within the range of +0.90–+5.19 (averaged 3.23) for the monzogranite and syenogranite, whereas their TDM2 values fall between 1.05 and 1.34 Ga, suggesting that the magma source of the monzogranite–syenogranite originated from the partial melting of the Mesoproterozoic crust dominated by metagreywackes. Furthermore, the monzogranite and syenogranite exhibit high temperatures (average 782 °C), thin crustal thickness (average 30 km), and A-type characteristics, suggesting their formation in post-collision extensional settings. We propose the closure of the Beishan Ocean occurred before the early Devonian, followed by a transition in the Southern Beishan Orogenic Belt from a compressional to an extensional setting. [ABSTRACT FROM AUTHOR]

The Paleoproterozoic gneiss domes are important structures of the Khondalite Belt in the northwestern North China Craton. However, less attention has been paid to their formation and evolution, and it thus hampers a better understanding of the deformation history of the Khondalite Belt. In this paper, we conducted structural and geochronological studies on the Qianlishan gneiss domes of the Khondalite Belt. The field observations and zircon U–Pb dating results show that the Qianlishan gneiss domes consist of 2.06–2.01 Ga granitoid plutons in the core, rimmed by granulite facies metasedimentary rocks (khondalites) of the Qianlishan Group. Both of them were subjected to two major phases of deformation (D1–D2) in the late Paleoproterozoic. Of these, D1 deformation mainly generated overturned to recumbent isoclinal folds F1 and penetrative transposed foliations/gneissosities S1 at ~1.95 Ga. Subsequently, D2 deformation produced the NW(W)–SE(E)-trending doubly plunging upright folds F2 at 1.93–1.90 Ga, and they have strongly re-oriented S1 gneissosities, giving rise to the Qianlishan gneiss domes. Combined with previous studies, we argue that the Qianlishan gneiss domes were the products of the Paleoproterozoic collisional orogenesis between the Yinshan and Ordos Blocks. Additionally, the development of doubly plunging antiforms is considered an important dome-forming mechanism in the Khondalite Belt. [ABSTRACT FROM AUTHOR]

Super-deep drilling in the central Sichuan Basin encountered volcanic rocks of the Suxiong Formation, which are overlain by multiple hydrothermal alterations within the upper section of the Ediacaran Dengying Formation. This provides an excellent research opportunity to understand the pre-Cambrian hydrothermal activity and geological evolution of the western margin of the Yangtze Craton. Observations revealed the development of a series of hydrothermal dolomite aggregates characterized by the presence of brown sphalerite within fractures and pores of the carbonate rock. Microscopically, the dolomite exhibited fibrous columnar crystallization, forming radial bands with a gradual decrease in crystallization intensity from the center to the periphery. Cathodoluminescence analysis revealed the presence of approximately eight dolomite bands within the aggregate. U–Pb dating from the inner to outer bands yielded isotopic ages of 781 ± 12 Ma for the second band, 683 ± 12 Ma for the fifth, 562 ± 12 Ma for the sixth, and 545.4 ± 6.9 Ma for the seventh. The in situ rare earth element (REE) distribution patterns of the 781 and 683 Ma dolomite bands exhibited similarities. They both showed low total REE content (∑REE), with significant fractionation between light and heavy REEs. Additionally, they exhibited negative anomalies in cerium (Ce) and europium (Eu), while heavy REEs were relatively enriched. The dolomite bands at 562 and 545 Ma also exhibited similar REE characteristics, with low ∑REE and weak fractionation between light and heavy REEs. They also displayed distinct negative anomalies in Ce and Eu, indicating similar distribution patterns. These findings suggested that formation of the banded hydrothermal dolostone occurred during different tectonic events, and the presence of heavy REE-enriched hydrothermal fluids suggested a deep-seated origin. This study has provided preliminary evidence that the Dengying Formation, previously considered to be of the Ediacaran age, has undergone multiple episodes of deep-seated fluid infiltration and alteration since the Mesoproterozoic Era. Importantly, these events coincide with the rifting of the Rodinia and Pannotia supercontinents, aligning with their respective timeframes. This finding raises questions regarding the stratigraphic division and correlation of the formations in the deeply buried core area of the basin. [ABSTRACT FROM AUTHOR]

The geodynamic mechanisms that controlled magmatic activity in South China during the late Mesozoic have been a cutting-edge focus of recent research. Southeastern Guangxi, which is located at the juncture between the Pacific and Neo-Tethyan tectonic domains, is a transitional zone characterized by the occurrence of widespread Jurassic–Cretaceous magmatic rocks. Investigation of this region can shed light on the late Mesozoic tectonic setting of South China. We conducted U–Pb geochronological and geochemical analyses of the Liuwang granodiorite and quartz porphyry, which are exposed in southeastern Guangxi. Zircon U–Pb dating yielded an age of 161.8 ± 1.2 Ma for the granodiorite and 97.89 ± 0.68 Ma for the quartz porphyry, indicating that they formed during the Late Jurassic and Late Cretaceous, respectively. The Liuwang granodiorites are weakly peraluminous high-K calc-alkaline rocks characterized by enrichment in large ion lithophile elements (including Rb) and high field strength elements (including Th, U, Pb, and Ta) and depletion in Ba, Nb, and Sr. The granodiorites also exhibit weak rare earth element (REE) fractionation and slightly negative Eu anomalies. Conversely, the Liuwang quartz porphyry is weakly peraluminous and belongs to the potassic syenite series, transitioning into the high-K calc-alkaline series. It is characterized by enrichment in Rb and high field strength elements (including Th, U, Pb, and Ta), with depletion in Ba, Nb, Sr, and Zr. It does not exhibit REE fractionation but does yield prominent negative Eu anomalies. The granodiorite and quartz porphyry yield εHf(t) values of −23.26 to −2.48 and −4.4 to +0.8, respectively, with tDM2 ages of 2642–1270 and 1411–1081 Ma, respectively. These data suggest that the Liuwang granodiorite formed under a background of Late Jurassic lithospheric extension–thinning and was derived from partial melting of Palaeoproterozoic–Mesoproterozoic metasedimentary sandstones with a minor contribution from mantle-derived melts. In contrast, the Liuwang quartz porphyry was derived from partial melting of Mesoproterozoic pelitic rocks and formed in a Late Cretaceous tectonic setting linked to the northward subduction of the Neo-Tethys Ocean beneath South China. [ABSTRACT FROM AUTHOR]

The Middle Permian Maokou Formation in the Sichuan Basin has huge resources and is an important target for natural gas exploration. In recent years, significant exploration breakthroughs have been made in the dolomite field of member Mao-2 in central Sichuan, and the gas production of several wells has exceeded 1 × 106 m3/d, indicating promising prospects for exploration. However, the origin of the dolomite reservoir in member Mao-2 remains ambiguous, which restricts the accurate prediction of favorable reservoirs. This study focuses on drilling in the Hechuan area as its research object, by using a detailed description of the cores from member Mao-2 of seven wells; samples were selected for tests of the degree of dolomite cation ordering, stable carbon and oxygen isotopic compositions, strontium isotopic composition, rare earth elements, LA-ICP-MS element mapping and U-Pb dating. It is clarified that: (1) The crystalline dolomite of member Mao-2 in the Hechuan area is the main reservoir rock, and the heterogeneous vugs and fractures are the main reservoir space. The dolomite in member Mao-2 has been characterized by a low degree of cation ordering value (avg. 0.59), with values of δ13C (avg. 3.87‰), δ18O (avg. −7.15‰) and 87Sr/86Sr (avg. 0.707474) having similar geochemical characteristics to Middle Permian seawater; the REEs normalized distribution patterns have similar characteristics to limestone; and the U-Pb age (261.0~262.0 Ma) corresponds to the age in the Capitanian stage of the Permian Guadalupian Series. (2) Petrological studies show that member Mao-2 has vertical karstification zonation characteristics; syngenetic karstification controls the formation of a large-scale fracture-cave system in the phreatic zone; the dolomitization of sediment in the fracture-cave system occurred during the penecontemporaneous period with locally restricted seawater. (3) The main controlling factors of the reservoir were syngenetic karstification, early dolomitization and hydrothermal dissolution related to Emei taphrogenesis. The research results are of great significance for dolomite reservoir prediction; the highlands of paleogeomorphology with syndepositional faults are favorable areas for dolomite reservoirs. [ABSTRACT FROM AUTHOR]

The Qinling Complex is located in the core of the northern Qinling Orogen and plays a key role in understanding the tectonic evolution of the Qinling Orogen, but its metamorphic evolution remains controversial. The combined investigation of petrographic observation, zircon U-Pb dating, and phase equilibria modeling for garnet amphibolites from the Tianshui area in the West Qinling Orogen is reported in this study. The results show that the garnet amphibolites record a clockwise P-T path characterized by a pre-TMax decompression heating stage, a temperature peak at P-T conditions of 0.84–0.99 GPa and 869–886 °C, followed by a decompression cooling stage. Zircon U-Pb dating yields four age populations of ~479 ± 4 Ma, ~451 ± 8 Ma, ~411 ± 4 Ma, and ~377 ± 6 Ma. The 479–450 Ma reflects the timing of the pre-TMax high–medium pressure upper amphibolite-facies metamorphism. The metamorphism at peak temperature condition occurred at c.411 Ma and was followed by decompression cooling to c.377 Ma. The Ordovician high–medium pressure metamorphism is related to the continental collision, which is slightly later than the HP–UHP eclogite-facies metamorphism in the East Qinling Orogen. The HT granulite-facies metamorphism at peak temperature condition took place at reduced pressures, suggesting thinning of the collision-thickened orogenic crust. Therefore, the northern West Qinling Orogen experienced a tectonothermal evolution from initial crust thickening to thinning during the Paleozoic collisional orogeny. [ABSTRACT FROM AUTHOR]

The early Paleoproterozoic (ca. 2.2–2.1 Ga) tectonic evolution of the Jiao–Liao–Ji belt (JLJB) is a continuous hot topic and remains highly controversial. Two main tectonic regimes have been proposed for the JLJB, namely arc-related setting and intra-continental rift. Abundant ca. 2.2–2.1 Ga volcanic rocks were formed in the JLJB, especially in the Liaodong Peninsula. These ca. 2.2–2.1 Ga volcanic rocks therefore could host critical information for the evolution of the JLJB. In this study, we report a suit of ca. 2.2–2.1 Ga felsic metavolcanic rocks in the Liaodong Peninsula of the JLJB to provide new insights into the above issue. Zircon U-Pb dating reveals that the felsic metavolcanic rocks were erupted at 2185–2167 Ma. They have variable εHf(t) values (−0.70 to +9.69), high SiO2 (66.30–75.30 wt.%) and relatively low TiO2 (0.03–0.78 wt.%), tFe2O3 (0.55–5.03 wt.%), MgO (0.17–8.76 wt.%), Cr (9.16–67.30 ppm), Co (2.01–7.00 ppm) and Ni (3.90–25.70 ppm) contents with enrichments in light rare earth element (REE) and large ion lithophile element (LILE), and depletions in heavy REE and high field strength element (HFSE). Geochemical and isotopic results indicate that the felsic metavolcanic rocks were sourced from partial melting of ancient Archean TTG rocks and juvenile lower crustal materials. Combined with coeval A-type granites, bimodal volcanic rocks and the absence of typical arc magmatism, the most likely tectonic regime at ca. 2.2–2.1 Ga for the JLJB is an intra-continental rift. [ABSTRACT FROM AUTHOR]

Understanding the composition, formation and evolution of the oldest continental crust is crucial for comprehending the mechanism and timing of crustal growth and differentiation on early Earth. However, the preservation of the ancient continental crust is limited due to extensive reworking by later tectonothermal events. In the Lulong area of eastern Hebei, abundant ca. 3.8–3.4 Ga detrital zircons of the fuchsite quartzite have been previously identified. Nonetheless, the provenance and Hf isotopic compositions of the fuchsite quartzite remain unclear. In this study, we present new detrital zircon ages and Hf isotopic for the fuchsite quartzite in the Lulong area to establish the timing of deposition, the provenance and the regional stratigraphic relationship. Zircon U-Pb dating indicates that the fuchsite quartzite was deposited between 3.3–3.1 Ga and most grains were sourced from the 3.8 Ga TTG gneisses and Paleoarchean magmas. Field investigations and regional correlations reveal that the fuchsite quartzite from the Lulong area is equivalent to that of the Caozhuang area. Zircon Hf isotopic data from eastern Hebei Province (Lulong and Caozhuang areas) and Anshan and Xinyang areas indicate that the oldest crustal growth event of North China Craton occurred in the Hadean. [ABSTRACT FROM AUTHOR]

The Zhangbaling tectonic belt (ZTB), one of the most representative tectonic belts in East China, has experienced uplift since the Early Cretaceous and is, thus, an excellent object for understanding the tectonic uplift and topographical evolution of East China and the whole of East Asia. On the basis of field observations, in this contribution to the literature, we carried out detrital zircon LA-ICP-MS U–Pb dating for the Upper Cretaceous sediments in the basins adjacent to the ZTB and zircon (U–Th)/He dating for the Early Cretaceous plutons along the western flank of this belt. Detailed field observation showed that the orthogneiss of the Feidong Complex experienced sinistral strike–slip activities, while the marbles underwent thrusting; thrust faults were developed in the Early Cretaceous plutons and volcanic rocks, and normal faults were superimposed on thrust or strike–slip faults. The detrital zircon dating results showed that the Upper Cretaceous sediments are characterized by an Early Cretaceous major cluster with just a minor cluster from the middle Neoproterozoic ages, indicating that the Zhangbaling Group and the Feidong Complex of the ZTB are not their main provenance. Zircon (U–Th)/He dating results showed that the ZTB experienced rapid uplifting during the mid-Cretaceous and recorded another rapid uplifting after 30 Ma. Combining existing research with our new data, it can be concluded that the ZTB was characterized by thrust activity in the mid-Cretaceous, which occurred under regional compression setting and was the basis of the formation of a watershed after 30 Ma. [ABSTRACT FROM AUTHOR]

Continental arc is characterized by alternant magmatic flare-ups and lulls. From the Permian to the Middle Jurassic period, two flare-ups with a lull developed in NE China, but the tectonic controls that caused the flare-ups remain unclear. Sedimentary rocks of the Heilongjiang Complex were derived from these magmatic rocks; thus, we employed detrital zircon U-Pb dating and trace elements analyses to unravel the regional tectono-magmatic evolution. Eu anomaly, (Dy/Yb)N and Th/U ratios of the detrital zircons and Sr/Y and (La/Yb)N of the regional granitoids together indicate the occurrence of two episodes of crustal thickening during the two flare-ups, accompanied with a westward migration of magmatism. We propose that the Permian flare-up was caused by the shallowing subduction from the east, which thickened the upper plate and enhanced the deep crustal melting. During the Middle Triassic period, the mantle wedge was expelled by the flat slab and thickened crust, leading to the magmatic lull. However, the westward subduction of the back-arc oceanic plate occurred before the lull, gradually producing the Jurassic magmatic flare-up and crustal thickening. Closure of the back-arc ocean caused by the outboard Paleo-Pacific oceanic plate subduction was important in the formation of the episodic magmatic flare-ups and crustal thickening in NE China. [ABSTRACT FROM AUTHOR]

Northeast China composes the main part of the Central Asian Orogenic Belt. Traditionally, Northeast China has been considered a collage of several microcontinental blocks. However, the tectonic evolution of these blocks remains uncertain. Igneous rocks can be used to infer the magmatic histories of the blocks and thus help reconstruct their evolution. In this study, we present new zircon U–Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing'an Range, Northeast China, to constrain the Carboniferous amalgamation of the united Xing'an–Erguna and Songnen–Zhangguangcai Range massifs. On the basis of zircon U–Pb dating results, we identify two main stages of magmatism, i.e., early Carboniferous (332–329 Ma) and late Carboniferous (312–310 Ma). The early Carboniferous igneous rocks include diorites and granodiorites, with the former being classified as calc-alkaline to tholeiitic and the latter as tholeiitic. Both rock types are enriched in Th and U and depleted in Nb and Ti. The rocks display slightly fractionated rare earth element (REE) patterns, with an enrichment in light REEs and a depletion in heavy (H)REEs. The geochemical characteristics of the early Carboniferous rocks indicate that they formed in a subduction-related continental-arc setting. The late Carboniferous igneous rocks include monzogranites and syenogranites, both of which are classified as high-K calc-alkaline rocks and show enrichment in Th, U, and Rb and depletion in Nb and Ti. The rocks display strongly fractionated REE patterns, with an enrichment in light REEs and a depletion in HREEs. The geochemical characteristics of the late Carboniferous rocks indicate that they formed in a syn-collisional tectonic setting. Combining the new geochronological and geochemical results and inferred tectonic settings with regional magmatic data, we propose a new three-stage model to interpret the late Paleozoic tectonic evolution of the united Xing'an–Erguna and Songnen–Zhangguangcai Range massifs of Northeast China: (1) early Carboniferous (360–340 Ma) subduction of the Paleo-Asian oceanic plate beneath the united Xing'an–Erguna Massif and formation of the Wunuer oceanic basin in the Yakeshi area; (2) early to late Carboniferous (340–310 Ma) sustained subduction of the Paleo-Asian oceanic plate beneath the united Xing'an–Erguna Massif and initiation of subduction of the Wunuer oceanic basin; and (3) late Carboniferous–early Permian (310–275 Ma) syn-collisional to post-collisional tectonic transition between the united Xing'an–Erguna Massif and the Songnen–Zhangguangcai Range Massif. [ABSTRACT FROM AUTHOR]

In this study, we present the results of U–Pb (ID-TIMS) geochronological studies of calcic garnet from the alkaline ultramafic complexes of Eastern Sayan province (eastern Siberia). New U–Pb ID–TIMS garnet ages obtained from different rocks of Bolshaya Tagna (632 ± 2 Ma) and Srednaya Zima intrusions (624 ± 5 Ma), as well as previously published garnet ages of the Belaya Zima complex (646 ± 6 Ma), allow us to constrain the timing and duration of episodes of alkaline ultramafic magmatism in Eastern Sayan province (619–651 Ma). Variations in the chemical compositions of rocks from three massifs indicate that the parental melts were separated from different magmatic chambers generated during the same episode of mantle melting. This study further highlights garnet U–Pb dating as a potentially robust, high-resolution geochronometer to constrain the evolution of the main pulse of alkaline ultramafic magmatism in the large magmatic provinces. [ABSTRACT FROM AUTHOR]

Detrital zircons in the matrix of an accretionary complex play an important role in providing evidence to reconstruct oceanic plate subduction and accretion processes. The Nadanhada accretionary complex (NAC) dominated by the Yuejinshan, Raohe and Tongjiang accretionary complexes provides significant geological evidence to better understand the Paleo-Pacific subduction–accretion process. Most previous studies have focused on the Yuejinshan and Raohe accretionary complexes, while those of the Tongjiang accretionary complex on the north side have focused on blocks. In this study, we present zircon U–Pb dating and Hf isotopic data for the matrix of metasedimentary rock in the Tongjiang accretionary complex. The analysis results show that the zircons in the fine silty mudstone, phyllonite and fine argillaceous siltstone define the youngest weighted mean ages (youngest detrital zircon ages) of 261.4 ± 2.9 Ma (247 Ma), 175.2 ± 4.9 Ma (169 Ma) and 168.6 ± 2.1 Ma (162 Ma), respectively, and yield a younging trend of the accretion materials from west to east. Provenance analysis indicates that the matrix was mainly sourced from the neighboring Jiamusi and Xingkai blocks. Based on previous results of the Permian and Late Triassic blocks in the Yuejinshan region, the Permian and Early Jurassic blocks in the Tongjiang region, and the Late Triassic and Early–Middle Jurassic blocks in the Raohe region, as well as the lower limit of the depositional age of the Late Triassic matrix in the Yuejinshan region and the Middle Jurassic and Early Cretaceous matrices in the Raohe region, we propose that the NAC may record the Late Permian–Triassic, Jurassic and Early Cretaceous oceanic accretion events, representing the westward subduction and accretion process of the Paleo–Pacific Ocean Plate. [ABSTRACT FROM AUTHOR]

The superlarge Huaaobaote Ag–Pb–Zn deposit is located on the western slope of the southern Great Xing'an Range (SGXR). The deposit includes four ore blocks, namely, ore blocks I, II, III, and V. Except for the no. I orebody of ore block I, which is hosted in the contact zone between the Carboniferous serpentinized harzburgite and the Permian siltstone, the other orebodies all occur as veins controlled by faults. The mineralization process at the deposit can be divided into four stages: cassiterite–arsenopyrite–pyrite–quartz stage (stage I), cassiterite–chalcopyrite–pyrite–freibergite–arsenopyrite–pyrrhotite–quartz stage (stage II), sphalerite–galena–jamesonite–stibnite–freibergite–silver mineral–quartz–calcite–chlorite stage (stage III), and argentite–pyrargyrite–pyrite–quartz–calcite (stage IV). Cassiterite U–Pb dating of the Huaaobaote deposit yielded ages of 136.3–134.3 Ma, indicating that the deposit formed in the Early Cretaceous period. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich FIs, have been distinguished in the quartz vein and sphalerite. The homogenization temperature during the four stages gradually decreases, with temperatures of 302–340 °C for stage I, 267–304 °C for stage II, 186–273 °C for stage III, and 166–199 °C for stage IV, respectively. The salinity (wt% NaCl eqv.) at stages I, II, III, and IV is 3.7–6.6, 0.2–4.5, 0.2–5.0, and 0.4–1.6, respectively, indicating that the ore-forming fluid is characterized by low salinity. The δ18Owater and δD values of the ore-forming fluid range from −11.9‰ to 7.9‰ and −168‰ to −76‰, respectively, indicating that the ore-forming fluid was dominantly derived from a mixture of magmatic and meteoric water. The calculated δ34SH2S values range from −3.6‰ to 1.2‰, indicating that the sulfur mainly came from granitic magma. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of sulfides are in the ranges of 18.195–18.317, 15.509–15.667, and 37.965–38.475, respectively, implying that the ore-forming material was mainly derived from felsic magma that may be formed by the partial melting of orogenic materials. Fluid mixing, cooling, and immiscibility were the three primary mechanisms for mineral precipitation in the Huaaobaote deposit. [ABSTRACT FROM AUTHOR]

Hardly any previous studies have focused on the granitic dykes which intrude into the Paleoproterozoic Liaohe Group in the Liaodong Peninsula, northeast of the North China Craton. In situ zircon U-Pb dating, Lu-Hf isotopic and geochemical analyses on three representative monzogranite dykes were taken in this study. These dykes have relatively high content of SiO2 (72.20%–74.78%) and K2O (2.83%–6.37%), and have characteristics of high-K calc-alkaline to shoshonite series. Two dyke samples have I-type granite features and have high Sr/Y ratios and positive Eu anomalies, showing an adakitic feature. Another dyke has a high ratio of Ga/Al, but has a low Zr saturation temperature, which differs from the typical A-type granite. Zircon grains from these three dykes have typical magmatic zoning in CL images and yield consistent U-Pb ages of ~1859–1852 Ma, which are interpreted as the crystallization ages of these dykes. Hf isotopic analyses yield mainly negative εHf(t) values and TDM2 ages of 2782–2430 Ma, similar to those of the 2.2–2.1 Ga granitoids and meta-sedimentary rocks (the Liaohe Group), indicating these monzogranitic dykes may have been sourced from melting of Paleoproterozoic granitoids and meta-sedimentary rocks. The monzogranitic dykes were generated under a post-collisional geological setting after the Jiao-Liao-Ji orogeny process. [ABSTRACT FROM AUTHOR]

The Fengcheng Formation of the Mahu Sag is an unconventional reservoir that is of paramount importance for exploration and development of hydrocarbon resource. However, current research on natural fractures in the Fengcheng Formation remains limited, posing challenges for exploration of hydrocarbon resource in the region. This study is based on core observations, thin section identification, geochemical testing and the evolution of regional tectonic movements to investigate the characteristics and periods of formation of natural fractures to address this gap. According to the characteristics of natural fractures in the drilling core samples and microsections, the natural fractures in the Fengcheng Formation can be grouped into structural fractures and atectonic fractures. Structural fractures can be further divided into three subtypes: high-angle interlayer shear fractures, along-layer shear fractures, and tensile fractures. Additionally, non-tectonic fractures in this studied area are primarily bedding fractures, hydraulic fractures, and hydrocarbon-generating overpressure fractures. Vertically, fracture development is more prominent at the bottom of Feng #2 Formation and at the top of Feng #3 Formation. Results also indicate that natural fractures primarily formed during three distinct tectonic movement periods. The initial stage of fracture evolution pertains to the Late Permian period (243–266 Ma), filled with fibrous calcite, and exhibiting a uniform temperature of 70–100 °C. The second stage of fracture evolution occurred during the Late Indosinian to Early Yanshanian period (181–208 Ma), mostly filled or semi-filled with calcite, with a uniform temperature of 110–130 °C. The third stage of fracture development happened during the late Yanshanian to early Himalaya period (50–87 Ma), predominantly filled with calcite, and presenting a uniform temperature of 130–150 °C. Among the various types of structural fractures, the density of high-angle interlayer shear fractures demonstrates a positive correlation with daily gas production, indicating their vital role in promoting hydrocarbon resource production and transportation. Furthermore, microfractures generated by hydrocarbon-generating overpressure fractures exhibit small pore sizes and strong connectivity. These microfractures can create an effective permeability system by connecting previously isolated micropores in shale reservoirs, thus establishing interconnected pore spaces in the shale formation. [ABSTRACT FROM AUTHOR]

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems. [ABSTRACT FROM AUTHOR]

The Chigbrak Formation in the Upper Ediacaran is one of the important exploration targets in the Tarim Basin, NW China. However, no significant discoveries have been made in this field, and unclear reservoir genesis is one of the important factors restricting exploration breakthrough. This study examined the outcrops of the Aksu area in northwestern Tarim Basin by using systematic descriptions of petrologic features in the Upper Ediacaran Chigbrak Formation. Samples were selected for tests of stable carbon and oxygen isotopic compositions, strontium isotopic compositions, rare earth elements, LA–ICP–MS element mapping and U–Pb dating. It was found that (1) the Chigbrak Formation is mainly composed of dolomitic microbialite, with average values of δ13C (PDB), δ18O (PDB) and 87Sr/86Sr of 3.50‰, 2.95‰ and 0.709457, and has similar geochemical characteristics to the coeval seawater. The dolomites have also been characterized by a medium degree of cation ordering (avg. 0.68), a low content of ΣREEs (avg. 9.03 ppm) and a chondrite standardized curve of REEs showing enrichment of LREE and depletion of HREE. The U–Pb ages range from 538 to 618 Ma, corresponding to the age of Ediacaran period. (2) Dolomitization occurred in a marine diagenetic environment during the penecontemporaneous period, with seawater as the dolomitization fluid. (3) Vugs are the dominant pore type of Chigbrak Formation, and they are the products of the dissolution of meteoric water in penecontemporaneous period. (4) The main controlling factors of reservoir were lithofacies, meteoric water dissolution controlled by fourth– or fifth–order sequences and tectonic movement, and early dolomitization. The research results are of great significance to the dolomite reservoir prediction of the Upper Ediacaran Chigbrak Formation of the Tarim Basin. [ABSTRACT FROM AUTHOR]

With the northward subduction and final closure of the Neo-Tethyan oceanic crust, the Indian and Eurasian plates finally collided together and underwent a strong collision orogenic event, resulting in large-scale crust–mantle magmatic interactions. In order to clarify the controversies about tectono-magmatic activities after the Indian–Eurasian continental collision, we report the newly dated Eocene Qiongduojiang gabbro explored in the Tethyan–Himalaya belt, southern Tibet. LA-ICP-MS zircon U-Pb dating shows that the crystallization age of the Qiongduojiang gabbro is 46.1 ± 1.7 Ma. The whole-rock major and trace elements, as well as Rb-Sr, Sm-Nd, and Pb isotopic data results, show that the Qiongduojiang gabbro is apparently depleted in Nd isotopes, is enriched in Pb isotopes, and has maintained a consistent 87Sr/86Sr(t) value. This paper argues that the E-MORB-like Qiongduojiang gabbro originated from asthenosphere upwelling caused by slab breakoff of the Neo-Tethyan oceanic plate. This event caused large-scale magmatic activities, a magmatic mixing process between ancient crust and deep mantle, and wild distribution of Eocene Gangdese plutons along the Yarlung–Tsangpo Suture Zone, and it rendered the subduction-modified Tibetan lithosphere fertile from the Gangdese porphyry Cu deposits. [ABSTRACT FROM AUTHOR]

This paper describes the potential industrial use of zircon from Nigeria (Plateau, Nasarawa, Kano, Kaduna, Bauchi, and Adamawa states). Different techniques, equipment, and indices such as scanning electron microscope, energy dispersive X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, specific gravity, refractive index, pH, and hardness were used to examine the samples. The X-ray diffraction showed predominantly quartz, zirconium oxide, and other heavy minerals. All twelve samples showed the presence of Zr-O, SiO 4 2 − , Zr-OH, and OH, with pH values ranging from 7.3 to 7.8. Six of the zircon samples had a refractive index between 1.4 and 12.5. The hardness values ranged from 0.0021 to 0.0703 GPa, while the elastic moduli were between 0.00558 and 0.9593 GPa. Four of the twelve untreated zircon samples with specific gravities above 4.2 g/cm3, which is the United States Geological Survey minimum recommended standard for zircon sand, needed to be upgraded to increase the ZrO2 weight percentages and purity toward improving their suitability for zircon-reinforced composites applications in aerospace and also for ceramic, foundry, building and construction, and refractory industries. The study's findings can be incorporated by the industries into their businesses for the development of novel industrial materials as well as the processing methods and procedures for beneficiation of the mineral for value-addition. [ABSTRACT FROM AUTHOR]

The Alxa Block is an important component of the North China Craton, but its metamorphic basement has been poorly studied, which hampers the understanding of the Alxa Block and the North China Craton. In this study, we conducted geochronological and geochemical studies on three TTG (tonalite–trondhjemite–granodiorite) gneisses and one granitic gneiss exposed in the Langshan area of the eastern Alxa Block to investigate their crustal evolution. The zircon U-Pb dating results revealed that the protoliths of the TTG and granitic gneisses were formed at 2836 ± 20 Ma, 2491 ± 18 Ma, 2540 ± 38 Ma, and 2763 ± 42 Ma, respectively, and were overprinted by middle–late Paleoproterozoic metamorphism (1962–1721 Ma). All gneiss samples had high Sr/Y ratios (41–274) and intermediate Mg# values (44.97–55.78), with negative Nb, Ta, and Ti anomalies and moderately to strongly fractionated REE patterns ((La/Yb)N = 10.6–107.1), slight Sr enrichment, and positive Eu anomalies, displaying features of typical high-SiO2 adakites and Archean TTGs. The magmatic zircons from the 2.84 Ga and 2.49 Ga TTG rocks had low εHf(t) values of −1.9–1.7, and −3.83–2.12 with two-stage model ages (TDMC) of 3.24–3.11 Ga and 3.10–3.01 Ga, respectively, whereas those from the 2.54 Ga TTG rock exhibited εHf(t) values ranging from −1.1 to 3.46 and TDMC from 3.0 Ga to 2.83 Ga, suggesting that the crustal materials of the basement rocks in the eastern Alxa Block were initially extracted from the depleted mantle during the late Paleoarchean to Mesoarchean era and were reworked in the late Mesoarchean and late Neoarchean era. By contrast, the Alxa Block probably had a relative younger crustal evolutionary history (<3.24 Ga) than the main North China (<3.88 Ga), Tarim (<3.9 Ga), and Yangtze (<3.8 Ga) Cratons and likely had a unique crustal evolutionary history before the early Paleoproterozoic era. [ABSTRACT FROM AUTHOR]

Late Paleozoic–early Mesozoic intrusive rocks are distributed widely along the northern margin of the Qaidam Basin in the northern Tibetan Plateau. To constrain the tectonic evolution, we carried out petrological, chronological, and geochemical studies of the Chahannuo gabbros. LA-ICP-MS Zircon U–Pb dating yields an age of 255.0 ± 0.9 Ma for the gabbros, which confirms the existence of Indosinian tectono-magmatic activity on the northern margin of the Qaidam Basin. The Chahannuo gabbros have low whole-rock SiO2, Fe2O3 contents, and high Al2O3 contents, which suggests a calc-alkaline affinity. In addition, the gabbros have high MgO, Cr, and Ni contents and Mg#, similar to those predicted of the regional basaltic melts, and indicating that they were affected mainly by fluid from the subducted slab. The Chahannuo gabbros are characterized by arc-like trace element patterns, with enrichment in LREE and LILE, and depletion in HREE and HFSE. No obvious negative Eu anomalies also indicate that no significant magmatic differentiation has occurred. The low Nb/La ratio and Ti content in gabbros samples suggests that the Chahannuo gabbros were partially contaminated by the crust during their formation. The Chahannuo gabbros have high incompatible element ratios (Rb/Sr, Th/Nd, and Th/La), which are closer to the category of enriched mantle. Combing our data with previous data from contemporaneous magmatism in the region, we suggest that the Chahannuo gabbros formed in a continental arc environment related to the northward subduction of the Paleo-Tethyan oceanic plate. [ABSTRACT FROM AUTHOR]

This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl−, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs' parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested. [ABSTRACT FROM AUTHOR]

Garnet is the most common alteration mineral in skarn-type deposits, and the geochronological research on it can limit the mineralization age. The Longwan Pb–Zn deposit, situated within the Fozichong Pb–Zn ore field in Guangxi, lacks precise geochronological data, limiting the in-depth comprehension of its genesis and tectonic setting. This study employs LA-ICP-MS U–Pb dating of garnets developed in the skarn orebody and zircons in the associated granitic porphyry to determine the deposit's mineralization age. Backscatter electron images and electron probe microanalysis reveal common zonation characteristics in garnets from the Longwan Pb–Zn deposit, with dominant end-member compositions of Andradite and Grossular. The values of U concentrations range from 1.8 ppm to 3.7 ppm, and a garnet U–Pb age of 102.6 ± 1.9 Ma was obtained, consistent with the zircon U–Pb age of 102.1 ± 1.2 Ma from the granite porphyry within the deposit. The Longwan Pb–Zn deposit formed during the late Early Cretaceous as a skarn deposit resulting from contact metasomatism between the granite porphyry and the host rock. The deposit likely formed in response to the Neo-Tethys plate subducting beneath the South China continent during the Cretaceous, followed by a retreat during the Late Cretaceous. The Cenxi-Bobai Fault experienced reactivation under the extensional tectonic regime induced by the Neo-Tethys Ocean's retreat, leading to a series of magmatic activities along the NE-trending direction within the Fault. The Longwan Pb–Zn deposit formed during the processes of magma emplacement and contact metasomatic reactions with the country rock. [ABSTRACT FROM AUTHOR]

Centimeter-scale magmatic enclaves are abundant in peralkaline felsic volcanic rocks in the Sanshui Basin. Their lithology is mainly syenite and syenitic porphyry, and they mainly comprise alkali feldspar and amphibole, which is similar to the mineral assemblage of the host trachyte and comendite. The SiO2 content in the syenitic enclaves is ~63 wt%, which is similar to that of the host trachyte but lower than that of the comendite. Thermobarometric calculations showed that the syenitic enclaves crystallized at similar temperature and pressure conditions as their host trachyte. The results of mass-balance modeling and MCS modeling indicate that the syenitic enclaves likely experienced an approximately 74% fractional crystallization from the basaltic parental magma. Combined with the similar mineral assemblages and geochemical characteristics of the host trachyte, we think that the enclaves resulted from the in situ crystallization of trachytic magma in the shallow crust and that they had a cogenetic origin with their host volcanic rocks, which means that they were likely to derived from the identical magma chamber which was formed from different batches of magma mixing/mingling. The recharge and mixing of basaltic magma triggered the eruption of trachytic magma eruption. The syenitic crust may have been disaggregated by the ascending trachytic magma and brought to the surface as syenitic enclaves. The syenitic enclaves in volcanic rocks provide unique information on the magmatism of the shallow crust as evidence of magma mixing/mingling. [ABSTRACT FROM AUTHOR]

Studies on post-collisional magmatic rocks can provide key clues to researching the crust–mantle interactions and the tectonic evolution of collisional orogenic belts. This study investigated a suite of newly discovered mafic intrusions in the middle of the East Kunlun orogenic belt through integrated analysis of petrology, petrography, and zircon U–Pb dating. The data could offer new insights into the generation of the Proto-Tethyan tectonic evolution. The result shows that these mafic intrusions are mainly gabbro and diabase, formed in the Early Devonian, with zircon U–Pb ages of 408.9 ± 2.0 Ma for gabbro and 411.1 ± 3.1 Ma for diabase. It consists of plagioclase, pyroxene, and dark minerals, and a small number of calcite and chlorite. Diabase has a small amount of amygdale. Their Na2O + K2O contents range from 3.47 wt.% to 5.45 wt.%, with Na2O/K2O ratios from 1.39 to 3.09, suggesting that they are calc–alkaline rocks. These rocks have an Fe2O3ᵀ content of 7.68 wt.%–11.59 wt.% and Mg# of 50.58–59.48, belonging to the iron-rich and magnesium-poor type. The chondrite-normalized rare earth elements show similar patterns that are characterized by enrichment of light rare earth elements, with (La/Yb)N of 3.27–6.75 and no significant europium anomaly, indicating the rocks are homogenous. The studied rocks are characterized by low contents of compatible elements Cr and Ni, enrichment of large-ion lithophile elements such as Rb, U, Sr, and Nd, and high-field-strength elements such as Nb, Ta, Zr, Hf, and Th. The mafic magma originated from the partial melting of the enriched mantle and was assimilated and mixed with crust materials during the process of migration. Based on the regional tectonic evolution, we interpret that the Proto-Tethys Ocean had closed in the Early Devonian, and that the East Kunlun region was in a post-collisional extensional tectonic setting. [ABSTRACT FROM AUTHOR]

Abundant hydrocarbon resources were discovered in the Xiazijie fan-delta in the Triassic Baikouquan Formation in Mahu sag, Junggar Basin. However, the maximum depositional age of Baikouquan Formation and provenance of this fan-delta are still unclear, which would be unfavourable for further hydrocarbon exploration. In this study, we used detrital zircon U-Pb dating and composition statistics of conglomerate clast and sandstone grain from Baikouquan Formation to constrain the maximum depositional age and provenance of the Xiazijie fan-delta. The results showed that (1) the conglomerate clast compositions of Xiazijie fan-delta mainly consisted of tuff and intermediate-felsic magmatic rocks, and sandstone samples could be classified as litharenite type with the lithic fragments were almost entirely volcanic lithic fragments; (2) the average Qt:F:L values of sandstone samples (M152-S1 and M152-S2) were 26:7:67 and 21:8:71, respectively, and they plotted in the magmatic arc domain in the Qt-F-L ternary diagram, indicating the tectonic setting of source area of Xiazijie fan-delta was magmatic arc; (3) M152-S1 yielded U-Pb ages ranging from 417 Ma to 253 Ma, with a dominant age peak at 313 Ma and two secondary age peaks at 411 Ma and 268 Ma, respectively, while M152-S2 yielded U-Pb ages ranging from 467 Ma to 256 Ma, with a dominant age peak at 307 Ma and two secondary date peaks at 405 Ma and 262 Ma; (4) the mean age of youngest two zircon grains of M152-S1 was 254.8 ± 4.7 Ma, while that of M152-S2 was 257.6 ± 3.8 Ma, suggesting the Baikouquan Formation might be deposited after the Changhsingian to Olenekian; (5) the magmatic rock ages of central West Junggar were distributed mostly between 450–260 Ma, with a dominant age peak at 307 Ma. The ages distribution between magmatic rock of central WJ and detrital zircons of M152-S1 and M152-S2 were similar, indicating the central WJ domain should be the major source area of the Xiazijie fan-delta; (6) the magmatic rock of Hakedun–Hongguleleng area in the Central WJ was characterized by a peak age at 305 Ma, which was consistent with the peak ages of M152-S1 and M152-S2, indicating the Hakedun-Hongguleleng area was likely to be their major source area; and (7) one minor peak age at 411 Ma and another at 405 Ma were obtained from M152-S1 and M152-S2, respectively, and a zircon grain with Middle Ordovician age at 467 Ma was obtained from M152-S2, indicating Late Silurian–Early Devonian Chagankule pluton in the Saier Mountain and Ordovician Honggleleng ophiolite mélange in the Sharburt mountain were the minor source areas. This research has significant implications for stratigraphic correlation in Junggar Basin and hydrocarbon exploration in the Xiazijie fan-delta conglomerate reservoir. [ABSTRACT FROM AUTHOR]

A-type granites are typically formed in stable intra-plate, back-arc or postcollisional settings and are characterized by highly ferroan and potassic major element compositions, and by strong enrichment in incompatible trace elements. Unlike I-, S- and M-type granites, where the letters denote the dominant source material (igneous, sedimentary or mantle derived), there is no consensus on the source and processes giving rise to A-type magmas. In this contribution, a conceptual model for the origin of A-type granitoids, using the Bornholm A-type granitoid complex in southern Fennoscandia as an example, is presented. In this model, underplated mantle-derived basaltic magma may develop into intermediate and siliceous A-type magma, which is ferroan, potassic and highly enriched in incompatible trace elements, through a combination of fractional crystallization leading to cumulate formation, and partial melting and crustal assimilation, in a process akin to zone refining in metallurgy. The key factor is a relatively stable tectonic environment (postcollisional, anorogenic, or extensional), where there is little or no replenishment of more primitive basaltic magma to the system, allowing it to attain more evolved, enriched and extreme compositions. The A-type granitoids may then be viewed as a more evolved counterpart of subduction-related I-type granitoids. [ABSTRACT FROM AUTHOR]

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems. [ABSTRACT FROM AUTHOR]

Several orogenic/sediment-hosted gold deposits are widely distributed in the Central Belt of Peninsular Malaysia. This study combines U-Pb dating with the isotope composition of lead as well as gold content in ore and magmatic rock-hosted pyrite. It aims to investigate the age of gold mineralization and possibly establish a link between gold mineralization and magmatic intrusion in the district. The results show that the S-type magmatic rocks yield crystallisation ages ranging from 204.1 ± 4.7 Ma to 223 ± 3.2 Ma with low magnetic susceptibility measurements below 3 × 10−3 SI unit. These ages fit within the 200–250 Ma Pb-Pb model age of the Pb isotopic composition of K-feldspars. Pyrite trace element mapping has shown that gold and lead show zoning patterns occurring at the same time in pyrite. The Pb isotope composition of the cores of pyrite grains indicate that the approximate model age of gold mineralization is 200 Ma. This age is close to 197–199 Ma (Early Jurassic), previously determined by K-Ar dating of sericite which was interpreted to be the age of gold mineralization. In this study, gold content varies up to 793 ppb in the analysed magmatic rock-hosted pyrites, indicative of a likely magmatic contribution to gold mineralization. [ABSTRACT FROM AUTHOR]

The Chakabeishan (CKBS) deposit is the first pegmatite-type Li-Be deposit discovered in the eastern North Qaidam Tectonic Belt (NQTB) of Tibetan Plateau. The correct understanding of its petrogenesis and the precise determination of its formation age are of great significance for further regional prospecting and the discovery of new economically valuable rare-metal deposits. Therefore, a systematic study of texture, major-element composition, and U-Pb dating of columbite-tantalite group minerals (CGMs) in the spodumene pegmatite dyke from the CKBS deposit was undertaken. Three types of CGMs were identified, including concentric oscillatory ferrocolumbite (CGMs-1), homogeneous ferrocolumbite (CGMs-2), and irregular ferrotantalite (minor manganocolumbite) with abundant early ferrocolumbite replacement remnants (CGMs-3). The zoning patterns and chemical compositions in the CGMs record the complex evolutionary history of their host pegmatite from the magmatic stage (CGMs-1, disequilibrium crystallization) to the magmatic-hydrothermal transition stage (CGMs-2, equilibrium crystallization) and then to the late metasomatic stage (CGMs-3, replacement/re-equilibrium). CGMs U-Pb dating results suggest that the spodumene pegmatite dyke (No.15) emplaced at 230.1 ± 2.6 Ma. Subsequently, it experienced fluid metasomatism at 221 ± 5.3 Ma. Based on the new age data and published geochronological data, it can be concluded that the spodumene pegmatite dykes in the CKBS deposit formed in an oceanic subduction-related setting, representing a new metallogenic event in western China. Except for the CKBS deposit, a large number of rare-metal pegmatite dykes have also been discovered in the eastern NQTB, indicating that the eastern NQTB may be an important potential rare-metal metallogenic belt that should be explored in detail and arouse painstaking attention. [ABSTRACT FROM AUTHOR]

The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine websterite, gabbro and diorite intrusions, and new zircon U–Pb dating, Lu–Hf isotope and whole-rock geochemical data are presented herein to further confirm the Late Triassic mafic–ultramafic magmatism with Cu–Ni mineralization and to discuss the petrogenesis and geodynamic setting. Zircon U–Pb dating shows that the Late Triassic ages, corresponding to 220 Ma and 222 Ma, reveal the mafic–ultramafic and dioritic magmatism in Kaimuqi, respectively. Zircon from gabbro has εHf(t) values of −3.4 to −0.2, with corresponding TDM1 ages of 994–863 Ma. The mafic–ultramafic rocks generally have low SiO2, (Na2O+K2O) and TiO2 contents and high MgO contents and Mg# values. They are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy REEs (HREEs) and high-field-strength elements (HFSEs), indicating that the primary magma was derived from the metasomatized lithospheric mantle. The diorites show sanukitic high-Mg andesite properties (e.g., MgO = 2.78%–3.54%, Mg# = 50–55, Cr = 49.6–60.0 ppm, Sr = 488–512 ppm, Y = 19.6–21.8 ppm, Ba = 583–722 ppm, Sr/Y = 23.5–25.4, K/Rb = 190–202 and Eu/Eu* = 0.73–0.79), with LREEs and LILEs enrichments and HREEs and HFSEs depletions. We suggest that the primary Kaimuqi diorite magma originated from enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments. The Kaimuqi mafic–ultramafic and dioritic intrusions, with many other mafic–ultramafic and K-rich granitic/rhyolitic rocks in the EKO, formed in a dynamic extensional setting after the Palaeo-Tethys Ocean closure. [ABSTRACT FROM AUTHOR]

The Ordos Basin's southern part is a composite zone made up of numerous continental blocks and has long been influenced by surrounding tectonism. However, only a few studies have investigated the existence of southern provenance supply and the basin's southern boundary in the Middle Jurassic Zhiluo Formation. Based on sandstone detrital zircon U-Pb dating and zircon rare earth element analyses, net-sand ratio maps, paleocurrent direction and the field outcrop survey, this study establishes the source area and boundary of the Zhiluo Formation in the southern basin, and discusses the tectonic events. The study shows that the four main age peaks in the detrital spectra occurs at 2283 Ma, 1788 Ma, 432.5 Ma and 218.7 Ma, with a few of the zircons dated at 794.5–1235.2 Ma. The North Qilian orogenic belt (N-QLOB), the western part of the North Qinling orogenic belt (NQOB), and the southern margin of the North China Block (SNCB) contributed to the provenance. According to an integrated analysis of the provenance and tectonic background of continental blocks in the basin's southern margin, the boundary of the basin in the depositional period of the Zhiluo Formation should reach the N-QLOB in the southwest, the NQOB in the south, and the Sanmenxia–Lushan fault belt in the southeast. On the basis of the aforementioned findings, the tectonic evolution of the continental blocks at the southern periphery of the Ordos Basin was restored. [ABSTRACT FROM AUTHOR]

The Lushan Massif has been considered an extensional dome which represents a typical extensional structure in South China. However, the composition and structure of the Lushan Massif are still unclear. In this study, we identified the eastern detachment fault (EDF) for the first time. In addition, many sinistral strike-slip structures have also been recognized in the Lushan area, such as the Xingzi shear zone (XZSZ) and Lianhua shear zone (LHSZ). Detailed field observation and structural analysis revealed that the former sinistral faults are tectonic boundaries of the later Lushan extensional dome (LSED). The tectonic evolution sequence was established after the structural analysis combined with zircon U-Pb dating and mica 40Ar-39Ar dating of metamorphic rocks, veins, and intrusive rocks from the strike-slip fault and detachment fault. The Lushan Massif has undergone sinistral ductile shearing within 162–150 Ma. The LSED was then formed in an extensional tectonic setting from 140 to 114 Ma. Together with the regional geological setting, we believe that the sinistral strike-slip structures, represented by the XZSZ and LHSZ, are coeval with the Tanlu fault system and could be controlled by a transpressional stress field resulting from the subduction of the Pacific Plate. The LSED was formed in a back-arc extension setting resulting from the rollback of a subducted slab. The tectonic transition from compression to extension in the South China Block took place at 150–140 Ma. [ABSTRACT FROM AUTHOR]

Complex microstructures of zircon recrystallisation have been discovered in igneous and metamorphic zircons from the Jack Hills Metasedimentary Belt in Western Australia, and the granitic injection complex of Harris in north-west Scotland. Cathodoluminescence (CL), electron backscatter diffraction (EBSD) and wavelength dispersive spectroscopy (WDS) analysis reveal that recrystallisation in the studied zircons is often characterised by (1) translation, bending and fading of the oscillatory zoning; (2) structural recovery of the zircon; (3) an enrichment in Hf and depletion in Y in recrystallised zircon; and (4) the formation of a recrystallisation interface with a minor (<2°) misorientation. A new, composite recrystallisation model in which trace element and dislocation migration occurs shortly after crystallisation during magmatic cooling and pipe diffusion along dislocation arrays formed by the accumulation of dislocations allows enhanced diffusion to enrich Hf and leach U, Pb and Y. After the recrystallisation event, subsequent metamictization of primary zircon (typically with oscillatory zoning) creates zones that can structurally recover through a diffusion-reaction re-equilibration mechanism, resulting in further trace-element mobility. These mechanisms can create complex microstructures in zircons, suggesting that a detailed understanding of the crystallisation and recrystallisation history of a zircon may be required to accurately interpret its U-Pb ages. [ABSTRACT FROM AUTHOR]

The Chang'an Chong Cu-Mo deposit is located in the Chang'an Cu-Mo-Au ore cluster in the southern Ailaoshan tectonic belt in southwestern China. There are six intrusive bodies in the mining area, among which the No.Ⅱ intrusive body is the largest and most closely related to Cu-Mo mineralization of skarn. The No. 1 main orebody is composed of the No. 1 copper orebody and No. 1 molybdenum orebody, which are distributed in parallel with similar shapes. In this paper, the age of skarn is determined by the LA-SF-ICP-MS U-Pb dating of garnet, and it is nearly consistent with the age of alkaline porphyry in this region (41–32 Ma). Compared with the U-Pb age of zircon from the ore-bearing porphyry and the Re-Os age of molybdenite, the U-Pb age of garnet was consistent with them within error, indicating that they were the same mineralization event, which further proves that the porphyry-skarn Cu-Mo-Au mineralization event along the Ailaoshan-Red River fault zone mainly occurred at 38~32 Ma. In-situ S isotope results show that the δ34S mean values of disseminated pyrite (PyI), pyrite of sulfide veins (PyⅡ) and chalcopyrite (Ccp) in the main mineralization period are 2.35‰, 3.60‰ and 0.55‰, respectively. These δ34S values are similar to those of magma and slightly enriched in δ34S, and the δ34S value of chalcopyrite is mainly concentrated near 0‰, so it can be considered that the S of the ore-forming fluid came from magmatic-hydrothermal fluids. Based on the comprehensive analysis of the regional metallogenic background, deposit chronology and isotope geochemistry, it is concluded that the Chang'an Chong Cu-Mo deposit was formed in an intra-plate post-collision strike-slip environment. [ABSTRACT FROM AUTHOR]