Abstract:Mesoproterozoic magmatic rocks are extensively exposed along the southwestern margin of the Ordos Basin. Relevant studies are of great significance for revealing the breakup process of the Columbia Supercontinent. To clarify the magmatic genesis and the tectonic evolution characteristics of this era, this paper conducts systematic petrological, zircon U-Pb geochronological, and geochemical studies on the bimodal igneous rocks in the Qi'angou area of the southwestern Ordos Basin. Zircon U-Pb dating results show that the ages of the granite porphyry and basaltic andesite are 1 794±10 Ma and 1 803±21 Ma, respectively, indicating their formation in the Mesoproterozoic. Geochemical characteristics reveal that the granite porphyry is a peraluminous A₂-type granite, enriched in largeion lithophile elements (LILE) and depleted in high field strength elements (HFSE), with relatively high Rb/Sr ratios (2.95~3.55), reflecting its origin from crustal melting.The basaltic andesite belongs to the calc-alkaline series, exhibiting island arc-type distribution characteristics of selective LILE enrichment and significant HFSE depletion, with right-inclined rare earth element (REE) distribution patterns. Compared with the continental crust, it has higher La/Nb (3.83~4.01) and La/Ta (342~355) ratios, indicating its derivation from the enriched lithospheric mantle and influence of crustal material contamination (Nb/Ta=17.8~18.6, obvious Rb-Th enrichment). The insignificant Eu anomaly (δEu=0.96~0.97) suggests that the magma did not undergo obvious plagioclase fractional crystallization during its evolution.Comprehensive analysis based on tectonic discrimination diagrams and regional tectonic settings indicates that this set of bimodal igneous rocks formed in a post-orogenic intracontinental extensional environment during the Mesoproterozoic, reflecting the breakup event of the North China Craton around 1.80 Ga.

Abstract:Based on the 1∶50 000 regional geological and mineral survey in Jianshui area of Yunnan Province, a set of pillow lava was determined in the study area, which was scattered on the Triassic clastic rock strata. The weighted average age of 14 zircons obtained by LA-ICP-MS zircon U-Pb dating is 352.3±5.9 Ma (MSWD=1.7), which belongs to the early period of Early Carboniferous and represents the eruption time of lava. The lava has the characteristics of high alkali (Na₂O>K₂O, Na₂O/K₂O=2.93～65.7, average 23.1), high Al(Al₂O₃=11.43%～16.67%)and low Ti(TiO₂=1.71%～2.62%,average 2.16%). It belongs to the subalkaline basalt series. The total amount of rare earth elements of the lava is low, ∑REE = 101.81×10^-6~138.50×10^-6, and it is enriched in large ion lithophile elements such as Rb, Ba, Th, K and high field strength elements such as Nb, Ta, etc., showing the characteristics of the large uplift distribution pattern unique to the intraplate basalt, which is similar to the characteristics of OIB. The normalized rare earth element distribution pattern of lava shows a right-leaning distribution pattern enriched in light rare earth elements, which is similar to the characteristics of intraplate basalt or oceanic island basalt. Combined with the regional geological background, this paper believes that the Jianshui pillow lava may be a product of the Yangtze and Cathaysian continental blocks controlled by the Paleo-Tethys multi-island ocean system under the early extension of the Late Paleozoic, along with the basic volcanic rocks in the northern section of Shizong-Mile, and the Early Carboniferous pillow basalts in the Longlin area of Jingxi, western Guangxi.

Abstract:The Late Neoarchean witnessed a significant compositional transition of the continental crust in the North China Craton from sodium-rich to potassium-rich, marking a key stage of crustal maturation. However, the precise timing and processes of this transition remain unclear. In this study, we present an integrated analysis of petrography, geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope for Late Neoarchean sodium-rich and potassium-rich granites from the southwestern Zhongtiao Mountains. The purpose of this study is to constrain their formation ages and source characteristics, and to explore their dynamic background and implications for continental crust maturation. Zircon U-Pb dating indicates that both the trondhjemitic gneiss and the monzogranite were formed in the late Neoarchean, with crystallization ages of 2 531±18 Ma and 2 527±54 Ma, respectively. Whole-rock major and trace element data, together with zircon Lu-Hf isotopes, suggest that the trondhjemitic gneiss was mainly formed by the partial melting of the mafic rocks in the lower crust in the early Neoarchean, while the monzogranites were primarily derived from partial melting of ancient high- to medium-K basaltic lower crust, with a minor contribution from metasedimentary rocks (mainly graywacke). Combined with regional geological evidence, we propose that the diverse Late Neoarchean granitoids in the Zhongtiao Mountains were generated by partial melting of sources at different crustal depths, including mafic lower crust, and minor metasedimentary rocks, likely triggered by mantle plume activity. The emplacement of the potassium-rich granite at ~2.53 Ga signals crustal maturation in this region, reflecting the stabilization of the local continental crust.

Abstract:This study presents a systematic petrological, LA-ICP-MS zircon U-Pb geochronological, and whole-rock geochemical investigation on the Neoproterozoic augen- and granitic gneisses from the Wenquan Group, West Tian-shan. Results show that these granitic gneisses crystallized at 904.5±4.1 Ma to 902±4 Ma, representing an early Neoproterozoic magmatic event. The rocks are characterized by high silica (SiO₂ = 65.23%~68.75%), high alkali (ALK=7.46%~8.89%), high potassium (K₂O/Na₂O = 1.01~2.24), and strong peraluminous affinity (A/CNK= 1.05~1.18), belonging to the high-K calc-alkaline series and typical S-type granites. They are enriched in Rb, Ba, Th, and light rare earth elements (LREE), depleted in Nb, Sr, Ti, and P, and exhibit moderate negative Eu anomalies. Comprehensive analysis indicates that the magmas were derived from high-temperature dehydration melting of greywacke with minor pelitic rocks from the Paleoproterozoic Wenquan Group, and formed in a syn-collisional tectonic setting related to the Grenvillian orogeny during the assembly of the Rodinia supercontinent. This study provides precise geochronological and geochemical constraints on the Precambrian basement of the Yili Block and offers important insights into the tectonic affinity between the Yili Block, the Central Tianshan Block, and the Tarim Craton.

Abstract:Carbonate reservoirs play a pivotal role in petroleum exploration endeavors within the Tarim Basin. However, due to limited core sampling, severe dolomitization, and challenges associated with conventional well logging interpretation, the classification and correlation of Cambrian-Ordovician carbonate strata have long remained contentious. Stable carbon isotopes offer a promising avenue for facilitating global or basin-scale stratigraphic correlation, thereby presenting a novel approach to addressing this issue. This study systematically investigates the carbon and oxygen isotopes of 116 carbonate samples sourced from the Upper Cambrian to Lower-Middle Ordovician in Well GC8, situated in Gucheng area, Tarim Basin, NW China. The results show that the distribution of δ¹³C values ranges from -2.32 ‰ to +0.53‰, with an average of -0.95‰. The overall δ¹³C exhibits a negative trend from bottom to top with a small change in amplitude, typified by two cycles of gradual negative excursions succeeded by abrupt positive excursion. The δ¹⁸O values portray a predominantly negative trend with limited variability, characterizing by two weak positive excursions followed by strong positive excursions. Based on the conodont biostratigraphy, comparative analysis with other representative sections elucidates the presence of TOCE (top of Stage 10 isotopic carbon excursion), COTICE (Cambrian-Ordovician transition isotopic carbon excursion) and MDICE (mid-Darriwilian isotopic carbon excursion) through the Upper Cambrian to Lower-Middle Ordovician in Well GC8. Notably, the documentation of TOCE and COTICE excursions within the Tarim Basin represents a pioneering discovery, with potential implications for positioning the Cambrian-Ordovician boundary at the inflection point of δ¹³C positive excursion after the TOCE. Furthermore, regional disparities in the MDICE development across the Tarim Basin hint at potential sedimentary hiatus of the Yijianfang Formation in Well GC8, with likely exhibiting the absence of the Pygodus anserinus conodont zone and a substantial portion of the Pygodus serra conodont zone in the Yijianfang Formation in Gucheng area.

Abstract:The Neoproterozoic strata in the southeastern North China Craton are primarily distributed in the western part of Shandong, the Xuzhou-Suzhou area, and the Huainan area, spanning several administrative regions and tectonic units. The coeval Neoproterozoic strata in these areas have been named differently within separate areas, which has created significant challenges for regional stratigraphic correlation. This has further hindered the comprehensive and systematic studies on the sedimentary environment evolution, paleogeographic patterns, and geothermal resource distribution in the southeastern North China Craton during the Neoproterozoic. Based on the historical stratigraphic classification and abundant data of specific stratigraphic sections, especially the field sections measured by this study, we establishes a stratigraphic correlation framework for the Neoproterozoic strata of the southeastern North China Craton. Through field-based lithological and sedimentary structural descriptions, combined with the microscopic identification of sedimentary components and textures, five sedimentary facies zones have been identified within the Neoproterozoic carbonate strata. They are Evaporitic facies, Platform interior restricted, Open marine, Platform-margin reef and shoals, and Carbonate ramp slope facies zones. The statistic of the carbonate strata thicknesses from various sections reveals that the relatively deep-water Platform-margin reefs and shoals facies zone are predominantly distributed in the southeastern part of the study area. Toward the western and northwestern parts of the study area, the depositional environment shallows progressively and Open marine and Platform interior restricted facies zones developed, accompanied by a gradual thinning of the strata. This facies zone transition reflects a Neoproterozoic paleogeographic pattern of low in southeast and high in northwest, with marine water transgressed from the southeastern part to the northwestern part of the study area. Based on the facies and paleogeographic analysis, and in combination with geothermal reservoir evaluation criteria, it can be inferred that the reef-shoal facies bearing Niyuan, upper Wangshan, and Jinshanzhai formations on the southern part of Huaibei, the dolostones bearing Sidingshan Formation on the northwestern part of Huainan, and the Platform-margin reefs and shoals facies zone bearing Jiuliqiao and Sidingshan formations on the eastern part of Bengbu have great potential for the development of karst geothermal reservoir. These findings provide targeted areas for future geothermal exploration and development.

Abstract:In spodumene pegmatite veins, spodumene exhibits a distinctive spodumene-quartz intergrowth (SQI) texture. Studying its microstructure, textural characteristics, and genetic mechanism is of great significance for further revealing the metallogenic mechanisms of granitic pegmatite-type lithium deposits. This paper takes the Late Triassic to Early Jurassic spodumene pegmatite veins in the Lijiagou area, Markam, western Sichuan, as an example. By integrating optical microscopy, scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction, we investigated the mineral composition, major element geochemistry, and crystal-lographic orientation of the rocks. Combined with the regional geological background and previous research findings, this study provides the following preliminary insights into the formation mechanism of the SQI texture in the Lijiagou spodumene pegmatites in western Sichuan: ① The fine-grained spodumene within the SQI shows high consistency with the host spodumene in terms of major element composition and crystallographic orientation. Moreover, cleavage planes of the host crystal extend continuously into the SQI domains, indicating that both originally belonged to the same crystal and share identical compositional and structural features; ② The SQI did not form through magmatic-hydrothermal metasomatism or undercooling crystallization. Instead, early spodumene phenocrysts underwent brittle ductile deformation under regional tectonic stress, leading to shearing and fragmentation into fine-grained spodumene aggregates. Subsequently, siliceous melt infiltrated along the fracture systems and crystallized as quartz, ultimately forming the intergrowth texture; ③ The morphology of quartz is controlled by the interstitial spaces between spodumene grains and shows no obvious signs of deformation. It is interconnected with surrounding quartz, suggesting that its formation occurred after the syn deformational period, representing crystallization of siliceous melt within the interstitial gaps along spodumene grain boundaries. In summary, the spodumene-quartz intergrowth texture in the Lijiagou spodumene pegmatite veins formed under an orogenic compressional setting and is a deformation-induced product.

Abstract:Rutile is one of the common solid inclusions in quartz crystals. In addition to existing as a single mineral inclusion, there is also a special growth phenomenon of the intergrowth of rutile and hematite forming "rutile star". This study investigates the crystallographic orientation relationship and formation mechanism of rutile inclusions within quartz crystals through various analytical techniques including optical microscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and crystallographic structure analysis. The results indicate that the rutile inclusions in quartz crystal samples are either protogenetic or syngenetic inclusions. Microscopic observations revealed two distinct morphological types of rutile: one is the oriented arrangement of rutile with irregular bamboo-joint-like fractures, and the other is the elongated prismatic rutile growing with hematite as the core, forming a "rutile star" with an approximate 60° angle. Since the {100} or {010} plane nets of rutile are structurally similar to the {001} plane net of hematite, the {100} or {010} plane of rutile can be joined and grow with the {001} plane of hematite. There are two possible crystallographic orientation relationships for the intergrowth of rutile and hematite: the c-axis of rutile is parallel to the <210> direction of hematite, and the <101> direction of rutile is parallel to the <210> direction of hematite. The formation of "rutile star" inclusions originates from the parent hematite-ilmenite solid solution. As the temperature decreases, the solid solution decomposes into ilmenite and hematite. The Fe²⁺ in ilmenite is oxidized to Fe³⁺, resulting in the formation of hematite and rutile. The rutile nucleates perpendicular to the {001} planes of hematite and grows progressively along {001} planes of hematite, ultimately forming "rutile stars" with hematite as the core and rutile crystals intersecting at 60°.

Abstract:Carbonatite-alkaline complex-associated rare earth element (REE) deposits are the principle sources of REEs. The enrichment and mineralization processes of REEs during such magmatic-hydrothermal systems are currently the most highly debated issues in metallogenic studies. Due to the widespread occurrence of bastnäsite and monazite in nature, most studies are focused on the mineralogical and geochemical properties of REE phosphates and fluorcarbonates. Unfortunately, experiment results demonstrate that the solubilities of REE phosphates and fluorcarbonates are insufficient for the formation of REE mineralizing fluids. By contrast, REEs also occur as Na-rich REE carbonate minerals in carbonatites, including carbocernaite and burbankite. These minerals are formed from some unique fluids, meanwhile easily altered during later hydrothermal processes, hence attracting limited research interests. However, according to the results from latest experiments, the transition from bastnäsite to carbocernaite via reacting with Na⁺ and CO^2-₃ is the essential process that leads to the exceptional enrichment of REEs in aqueous liquids. Furthermore, REEs precipitate preferentially as carbocernaite or burbankite from Na-enriched carbonate fluids, and crystallization of bastnäsite occurs either during a relatively early stage where Na is insufficiently enriched, or after Na precipitating substantially as alkaline silicate minerals during interaction with silicate wall rocks. These findings are consistent with REE occurring as burbankite in isolated systems (such as fluid inclusions), but as bastnäsite in carbonatite ore veins or other open systems, and indicate that such Na-rich REE carbonate minerals have clear implications for REE mobilization and mineralization processes. In this paper, we reviewed the crystal structures and chemical properties of carbocernaite and burbankite, and compared the occurrence of both minerals in carbonatite REE deposits to those in high pressure-temperature experiments, aiming to reveal the roles of such minerals during REE mobilization and mineralization processes, and provides clues for establishing a comprehensive REE metallogenic model in carbonatite systems.

Abstract:Continental collisional orogens represent a critical component of Earth's deep carbon cycle, with their decarbonation processes exerting a profound influence on global carbon budgets and long-term climate evolution. In contrast to oceanic subduction zones, continental collision belts are characterized by higher geothermal gradients, more felsic (sialic) compositions, and weaker fluid activity. Their decarbonation mechanisms are dominated by metamorphic reaction-driven decarbonation and anatexis-induced carbon release. This contribution systematically reviews decarbonation mechanisms in continental collisional orogens, with a focus on thermodynamic modeling of Paleoproterozoic "hot" orogens (exemplified by the Khondalite Belt, North China Craton) to elucidate carbon cycling characteristics under early plate tectonic regimes. Modeling results reveal that high geothermal gradients promoted intense and rapid metamorphic decarbonation during the early prograde stage in Paleoproterozoic orogens, whereas Phanerozoic cold orogens experienced decarbonation predominantly during exhumation. Under high-temperature and fluid-present conditions, carbonate rocks may undergo partial melting (generating anatectic carbonatites). These carbonatitic melts are highly mobile, and their degassing during formation, ascent, and interaction with country rocks constitutes a significant pathway for carbon release. We propose that the widespread continental collisional orogeny and supercontinent assembly events in the late Paleoproterozoic, due to their elevated thermal regimes, may have triggered large-scale carbon emissions, profoundly influencing contemporary global carbon cycling and climate evolution. The associated carbon fluxes quantitative constraints are needed in future models.

Abstract:The exhumation of geological bodies is a product of interactions among Earth's spheres. Precisely determining the timing and processes of exhumation has become a crucial aspect of modern Earth system science. Thermochronological techniques, particularly fission-track and (U-Th)/He dating, play a central role in this endeavor. Conventionally, for the same mineral type within a single rock sample, the fission-track age should be greater than or equal to the corresponding (U-Th)/He age. However, the phenomenon of the (U-Th)/He age appears older than the fission-track age, and significant dispersion of single-grain (U-Th)/He ages beyond analytical error are common yet often overlooked anomalies in low-temperature thermochronology. This paper aims to clarify potential misconceptions in interpreting thermochronological data and provides a concise yet systematic review of the interplay among factors such as the accumulation and annealing of radiation damage, the U-Th zonation, thermal history, and mineral chemical composition. These factors can significantly alter the annealing behavior of fission tracks and the diffusion behavior of ⁴He within crystals, leading to a decrease in the fission-track annealing temperature and an increase in the (U-Th)/He closure temperature, thereby resulting in age inversion. The dispersion of single-grain (U-Th)/He ages and the inversion between fission-track and (U-Th)/He ages often carry important geological information, providing key clues for interpreting complex thermal histories.

Abstract:Natural pink diamonds have attracted significant attention due to their stunning color, complex geological background, and extreme rarity. Their main coloration mechanisms include the 550 nm absorption band (accounting for approximately 99%) and NV color centers (accounting for approximately 0.6%). The former is found in Type Ⅰa and Ⅱa diamonds, while the latter only exists in Type Ⅱa diamonds. Currently, there is no artificial method capable of simulating natural plastic deformation to introduce the 550 nm absorption band. However, NV color centers can be introduced through multi-stage treatments including HPHT, irradiation and annealing, which are used for color modification of natural diamonds (predominantly Type Ⅰa, supplemented by Type Ⅱa) and synthetic diamonds (Type Ⅰb-Ⅱa and Type Ⅱa). Additionally, NVH and SiV color centers are also found in some chemical vapor deposition (CVD) synthetic diamonds. This paper systematically compares the gemological and spectroscopic characteristics of natural pink diamonds, treated natural diamonds, and synthetic diamonds (produced by CVD or HPHT methods), and proposes a rapid identification method based on ultraviolet-visible spectroscopy (UV-Vis) and infraredspectroscopy (IR). Furthermore, comprehensive identification of pink diamonds is achieved by combining photoluminescence spectroscopy (PL) and DiamondView.