Himalayan leucogranite is an excellent target for understanding the orogenic process of the India–Asia collision, but its origin and tectonic significance are still under debate. An integrated study of geochronology, geochemistry, and in situ Sr-Nd-Hf isotopes was conducted for a tourmaline-bearing leucogranite in the eastern Tethyan Himalaya using LA-ICP-MS, X-ray fluorescence spectroscopy, and ICP-MS and LA-MC-ICP-MS, respectively. LA-ICP-MS U-Pb dating of zircon and monazite showed that it was emplaced at ~19 Ma. The leucogranite had high SiO2 and Al2O3 contents ranging from 73.16 to 73.99 wt.% and 15.05 to 15.24 wt.%, respectively. It was characterized by a high aluminum saturation index (1.14–1.19) and Rb/Sr ratio (3.58–6.35), which is characteristic of S-type granite. The leucogranite was enriched in light rare-earth elements (LREEs; e.g., La and Ce) and large ion lithophile elements (LILEs; e.g., Rb, K, and Pb) and depleted in heavy rare-earth elements (e.g., Tm, Yb, and Lu) and high field strength elements (HFSEs; e.g., Nb, Zr, and Ti). It was characterized by high I Sr (t) (0.7268–0.7281) and low ε Nd (t) (−14.6 to −13.2) and ε Hf (t) (−12.6 to −9.47), which was consistent with the isotopic characteristics of the Higher Himalayan Sequence. Petrogenetically, the origin of the leucogranite is best explained by the decompression-induced muscovite dehydration melting of an ancient metapelitic source within the Higher Himalayan Sequence during regional extension due to the movement of the South Tibetan Detachment System (STDS). The significantly high lithium and beryllium contents of the leucogranite and associated pegmatite suggest that Himalayan leucogranites possess huge potential for lithium and beryllium exploration.
The petrogenesis of the Fanpu diorite can provide new constraints on the activity and deep process of the Paleozoic intermediate magmatism in the North Qinling orogenic belt. Two samples from the Fanpu pluton are dated at 422.1±5.5 Ma and 424.2±5.2 Ma, respectively, indicating that they formed in the Late Silurian.176Hf/177Hf ratios of zircon grains of the Fanpu diorite range from 0.282 272 to 0.282 918, εHf( t) values are between -8.48 and 14.45, and TDM2 are between 1 938 Ma and 488 Ma. The Fanpu diorite belongs to the calc-alkaline series, which are enriched in silicon, alkali, calcium, and magnesium, with Mg# values ranging from 41.7 to 57.4. In the spider diagram of trace elements, the Fanpu diorite has shown the depletion of Nb, Ta and Ti. Total REE contents of the Fanpu diorite are between 117×10-6 and 171×10-6, and ratios of (La/Yb)N range from 6.71 to 18.1. The δEu values are between 0.82 and 0.95. Their REE distribution patterns are characterized by light REE enrichment and heavy REE depletion, without obvious negative Eu anomaly. Magma of the Fanpu diorite might originate from the lower crust and underwent crust-mantle interaction in an island arc tectonic environment, which was related to the northward subduction of the Shangdan Ocean.
The Jiaodong Peninsula is one of the most important gold mineralization areas in China, and the large-scale gold mineralization occurred from 125 Ma to 110 Ma. In this paper, the Early Cretaceous Dazeshan pluton, emplaced coevally with the gold mineralization, is selected to reveal its petrogenesis using detailed lithography, petrogeochemistry and zircon LA-ICP-MS U-Pb chronology. Medium grained monzogranite and fine grained monzogranite are identified in Dazeshan pluton. They have similar petrographic and geochemical characteristics, showing the characteristics of homologous magmatic evolution. Zircon U-Pb dating yields 119.8± 0.8 Ma and 119.3±0.9 Ma for the medium grained monzogranite, 109.2±0.7 Ma and 109.9±0.7 Ma for the fine grained monzogranite. Petrogeochemistry studies show that: monzogranite possess high total alkalis(K2O+Na2O=8.14%~8.72%), with high Al2O3 content(12.42%~15.32%), the granites belong to peraluminious high-K calc-alkaline feature, enrichment in LREEs, relative depletion in HREEs(LREE/HREE=8.46~18.87), as well as significant rare earth element fractionation((La/Yb)N=8.52~24.08)and with pronounced negative Eu anomalies ( δEu=0.33~0.58). The Dazeshan pluton has low zircon εHf( t) values of -26.4~-16.2, and two-stage Hf model ages( TDM2)vary in range of 2 812~2 173 Ma. The diagenetic material is mainly derived from the partial melting of the Paleoproterozoic and Neoarchean crustal materials with the addition of some mantle materials. The diagenetic period of Dazeshan pluton is consistent with the main metallogenic period of Jiaodong gold deposit, suggesting that magmatism and gold mineralization have the same geodynamic setting.
The submarine fan of the Miocene Meishan Formation in the Qiongdongnan Basin is an important target for natural gas exploration in the northern South China Sea. Its sedimentary mechanism and main reservoir controlling factors directly influence the natural gas exploration and production in this area. According to sea level change, seabed topography and geomorphology, syngenetic fault combination etc., the submarine fan of Qiongdongnan Basin has been divided into three categories: shelf fan, slope fan and basin floor fan. Based on a large amount of measured data such as core and sidewall coring, this paper systematically analyzes the submarine fan reservoir revealed by drilling in this area. The study shows that the physical properties of the Meishan Formation submarine fan reservoir in Qiongdongnan Basin are not only affected by the buried depth, but also affected by the provenance and geomorphic units. Specifically, the basin floor fan reservoir from the western East Vietnam provenance and the northwestern Ningyuan River provenance are significantly better than the shelf fan and slope fan reservoir from the northern Lingshui River and Wanquan River provenance. The single submarine fan reservoir is controlled by such factors as provenance, sea level change, the type of fan body and internal composition as well as underflow modification. Among them, the type of submarine fan and its internal composition as well as underflow modification are main factors that affect and control the quality of turbidite reservoir. The gentle slope fault-terrace basin floor fan at the lowstand stage, basin floor fan in the open depression and canyon-cut basin floor fan are important exploration targets for their good-to-high quality reservoir. By contrast, the basin floor fan of steep slope root and gentle slope last-stage fault-terrace basin floor fan possess high exploration risks due to poor reservoir physical properties or undeveloped reservoir. Consequently, the research results of submarine fan reservoir based on provenance system and geomorphic units can be widely applied to the prediction of deep-water submarine fan reservoir.
The Yanshanian metallogenic events occurred frequently in South China, and the granites formed in this period are highly studied, while the study about the Caledonian granites are relatively weak. The deep magma and uranium-polymetallic mineralization in the Xiangshan ore field and its surrounding areas are complex. In recent years, some new metal mineralization spots such as Pb, Zn, Mo and Sn have been found around the Xiangshan area, and massive fine-grained granite has been exposed in its depth. In order to find out the relationship between the fine-grained granite and Mo mineralization, the zircon LA-ICP-MS U-Pb chronology, trace element geochemistry and Re-Os isotope chronology of molybdenite were studied in this paper. The fine-grained granite was formed at 410±2.5 Ma, Late Caledonian Period. The weighted average age of the molybdenite Re-Os isotope is 405±1.2 Ma, which is similar to the fine-grained granite. Combined with the characteristics of trace elements of zircon, the Ti crystallization temperature of zircons are 572 ℃~585 ℃. Oxygen fugacity ΔFMQ=-9.62~-2.52, (Ce4+/Ce3+)zircon=0.9;(Ce/Nd)/Y ratio(0~0.012)is low, Dy/Yb ratio(0.23~0.42)is high, indicating that the water content of magma is not high. It indicates that although the granites are closely related to Sn-Mo poly-metal, they do not have the conditions for forming large Tin-Mo poly-metal deposits. The Caledonian tectonic background of the Xiangshan area in Jiangxi Province is complex. In the discrimination diagram of tectonic background, the samples mainly fall within the transition range of intraplate/non-orogenic environment and magmatic arc/orogenic environment. However, by summarizing the geochemical data of Caledonian granites in central Jiangxi Province, it is found that the tectonic background of Early Caledonian granites is obviously different from that of Late Caledonian granites, and the early orogenic compression environment is dominant, while the later orogenic extension environment is dominant.
The diorite porphyrite in Qixia area is an important material record of Yanshanian magmatic activity in Jiaodong area, and its age and origin are of great geological significance for the inversion of tectonic evolution and mineralization in Jiaodong area. This paper takes Huangyandi diorite porphyrite in Qixia City as the research object. On the basis of field geological survey, petrography, zircon U-Pb dating and petrological geochemistry were studied. The age of diorite porphyrite is 138.5±1.7 Ma. In addition, a large number of inherited zircons with ages of 1 858.3~1 766.7 Ma, 2 538.9~2 351.6 Ma and 2 863.9 Ma are found in the rocks, indicating that there were mixing of crustal materials during magmatic activity. The results of major elements analysis showed that the diorite porphyrite was high K calc-alkaline series. The results of trace element analysis showed that it had the characteristics of enrichment of large ion lithophile elements such as Rb, Sr, Ba and Pb and depletion of high field strength elements such as Ta, Nb and Ti, and it was formed in volcanic arc tectonic environment. The diorite porphyrite in the study area was formed in the tectonic environment of volcanic arc, belonging to typical island arc volcanic rocks, and involved with fluid in the formation process.
On the basis of fully collecting the previous Ordovician stratigraphy, paleontology, sedimentology and other data, the Ordovician system has been systematically combed, and systematic research has been carried out on the Ordovician marine red beds of well WDD1 and the Fengcun section in Guichi in southern Anhui Province, which provides an important scientific basis for stratigraphic correlation, paleoclimate and paleogeographic restoration. The research shows that the Ordovician marine red beds are mainly distributed in the Zitai Formation, Guniutan Formation, Datianba Formation, Baota Formation, Tangtou Formation and Hule Formation, and the age is from the late time of the Early Ordovician Floian Age to the middle time of the Late Ordovician Katian Age. The main rock types are carbonate rocks(nodular argillaceous limestone, reticulated limestone, bioclastic limestone and micrite limestone), and a small amount of clastic rock(mudstone, silty mudstone, silty shale). Most of the marine red beds belong to the semi-deep marine red beds, with some being shallow and deep marine red beds. From northwest to southeast, there is a horizontal variation of one layer type, two layer type, three layer type, two layer type, one layer type, and zero layer type, with a vertical variation of the Katian Age, Darriwiliaan Age and Floian Age. The distribution of marine red beds is closely related to the sedimentary environment, ancient water temperature, and structural properties of different regions. The marine red beds in the study area not only have regional characteristics, but also have global characteristics, which have important research value in stratigraphic correlation.
The Early Paleozoic magmatic rocks in the western Kunlun orogenic belt preserve crucial information regarding the evolution of Proto-Tethys tectonics within the region. Our research group recently recognized the Ordovician gabbros in the Nanpingxueshan area, on the southern West Kunlun orogenic belt. LA-MC-ICPMS zircon U-Pb dating results indicate that the gabbro was formed during the Early Ordovician (476~471 Ma). The gabbro exhibits high Al2O3 (14.32%~16.91%) and TiO2 (1.20%~2.53%), low P2O5 (0.22%~0.55%) and alkali (Na2O+K2O = 4.03%~5.84%), and variable SiO2 (52.27%~56.65%) and MgO (2.98%~7.59%). Some samples exhibit Nb-enriched signatures, with relatively high SiO2 (53.08%~56.86%), low MgO (2.98%~6.05%), high TiO2 (1.48%~2.54%) and Nb (7.64×10-6~14.08×10-6). All samples are characterized by enrichment of large ion lithophile elements (LILEs; Rb, Th, U, K) and light rare earth elements, while depleted in Nb, Ta, Sr. These features are typical of island arc magmatic rocks. Isotopically, the gabbros are depleted in εNd( t) values (2.84~4.04). Based on their similar geochemical characteristics, we hypothesize that the Ordovician gabbros were originated by partial melting of the depleted mantle metasomatized by melts from subducted slabs. Based on regional geological characteristics, we propose that the unique assemblages of continental arc gabbros (530 Ma), Nb-enriched arc-like gabbros (476~471 Ma), and OIB-type pillow basalts (465 Ma) in the Mazar-Tianshuihai terrane are associated with the back-arc extension environment resulting from the retreat of subducted Proto-Tethys oceanic slab.
The Shajingzi fault zone in the northwest margin of Tarim Basin lies between the Wensu Uplift of Tabei Rise and the Awati Sag of the northern depression. It is a first-order fault zone in Tarim Basin, which consists of Shajingzi fault, Yingxiong fault, Wensu fault and Shanan fault. The Shajingzi fault is the main fracture, and the other three are its branches. The Wensu branch fault is a new discovery of this study. And we interpreted the Shanan fault as the front back-thrust fault of the Yingxiong fault, which belongs to the Shajingzi fault zone. The Shajingzi fault zone was formed from the end of Ordovician to the beginning of Silurian, and was finally formed after the Late Devonian to Carboniferous, the end Permian to the beginning of Triassic, the end Jurassic to the beginning of Cretaceous, the end Cretaceous to the beginning of Paleogene and the Neogene to Quaternary multicycle thrust. The Shajingzi fault zone is a fault-controlled oil-gas rich zone, which controls the formation and distribution of Wensu oilfield, Tuotan1, Shanan1 and Xinsudi1 oil and gas reservoirs.
In order to promote the application of hyperspectral technology in seismic-related gas monitoring, this paper selects near-infrared hyperspectral sensors with strong sensitivity to near-surface information to TROPOMI data and evaluates the application effect of near-infrared sensors in seismic-related gas monitoring in the northeast margin of the Qinghai-Tibet Plateau and the Sichuan-Yunnan region. The results show that the CH4 and CO gas in the study area of TROPOMI inversion show obvious seasonal variation in time, which is affected by climate change, landform and human activities, and the high value in Yinchuan, Weihe River and Sichuan Basin is affected by geological background, topography and human activities. Although the time resolution of the near-infrared sensor data and the data efficiency in the Sichuan-Yunnan region are poor, it can't be effectively applied to earthquake monitoring and prediction, but compared with the thermal infrared hyperspectral sensor, the near-infrared sensor can better reflect the near-surface structural characteristics. With the development and application of near-infrared hyperspectral sensors, near-infrared data can gradually make up for the low sensitivity of thermal infrared sensor data to near-surface information and improve the judgment of the relationship between anomalies and earthquakes.
Gulong shale oil is an important replacement resource in Songliao Basin, with an estimated geological reserve of 15.1 billion tons. From the perspective of sedimentary and petrological characteristics, the most prominent feature of Gulong Qingshankou Formation shale is the extensive development of sand dikes, which is not found in shale oil reservoirs in other basins. Therefore, it is also an important information to explore the formation environment of Gulong Qingshankou Formation shale. The sand veins in the Gulong Qingshankou shale oil reservoir are generally small in scale, with a width of 1~2 mm. Visible length(or height)in 1~2 cm, mostly curved like intestine, a few slightly curved. Multi-tilt output, tilt direction has a certain rule, 180° symmetry, generally developed in the gray black mud shale, a small amount of development in siltstone and dolomite (nodules). There is usually a layer of silt on the upper or top of the sand veins, which is closely connected with the sand veins and is the "root" of the sand veins. The bottom of the veins is usually gray black mud shale, and no silt layer can be seen, so it is revealed that the source material forming the veins is from the top silt layer, not the bottom. According to the preliminary study, the dikes in the shale oil reservoir of Qingshankou Formation in Gulong have two kinds of origin: the first is the high pressure liquefaction and filling, forming the large scale sand dikes; the second is caused by density inversion of gravity sedimentation: storm fast handling(powder)sand-size particles to just above the sedimentary clay, as a result of the storm wave oscillation, the silt liquefaction flow, combined with smaller density of clay and silt layer of density is bigger, makes the silt formed in gravity driven sinks down to clay sand vein. The study of sand veins in Gulong shale oil reservoir has four significances: firstly, we can know the sedimentary environment, sedimentary process and sediment state when sand veins were formed; secondly, the diagenetic compaction rate of shale can be known; thirdly, to determine the formation time of dolomite(nodules); fourthly, it can assist reservoir evaluation.
The study on river terraces is an important method to understand the process of regional climate change and tectonic uplift. The Batang section of the Bachu River is located in the southeastern Tibetan Plateau, which belongs to the tributary river system of the Jinsha River and has terraces on both sides. Because of its unique geographical location, it provides a natural place to study the uplift of the Tibetan Plateau since the Quaternary, and it plays an important role in the inversion of the formation and evolution of the Jinsha River system in this area. Field investigation showed that there were four terraces in the Batang area, which are T1~T4 terraces. According to cosmogenic radionuclide dating and optically stimulated luminescence dating of the terrace deposits, the ages of terrace formation from T1 to T4 are 1.7±0.1 ka, 2.3±0.21 ka, 4.5±0.5 ka and 62.3±2 ka, respectively. The T4 terrace was mainly controlled by tectonics, the formation of the terrace T1~T3 and the accumulation of terrace sediments mainly related to climate change. The results provide the reference for the study of climate change and tectonic movement in the Batang area, support the study of the formation and evolution of the Jinsha River system in this area, and promote the study of the uplift process of the Tibetan Plateau since the Holocene.
The formation genetic mechanism and dynamic background of in the Yulong Cu(Mo)ore belt remain controversial. In this study, we present a systematic dataset of whole-rock major and trace elements, zircon U-Pb dating and in situ zircon Hf isotopes, to constrain the petrogenesis of masses in the Duoxiasongduo area. The Duoxiasongduo mass is composed of monzogranite porphyry and alkali feldspar granite porphyry. Monzogranite porphyry is mainly composed of potassium feldspar, plagioclase and quartz, and alkali feldspar granite porphyry is composed of potassium feldspar and quartz. Petrogeochemical analysis shows that both of the rocks belong to high-K calc-alkaline to shoshonitic intrusions with high alkali and potassium. Moreover, these rocks are depleted in high field strength elements(HFSE, e.g., Nb and Ti), but enriched in the large-ion lithophile elements(LILE, e. g., Rb, Th and U)and Pb. Rare earth elements(REE)content ranges from 145.04×10-6 to 290.91×10-6. The ratio of LREE/HREE is relatively high(6~37). Eu varies from weak negative anomalies(Eu/Eu*=0.66~0.84)in the early stage to moderate negative anomalies(Eu/Eu*=0.35~0.39) in the late stage. The zircon U-Pb dating results show that the monzogranite porphyry and alkali feldspar granite porphyry crystallized at 38.3±0.6 Ma and 37.8±1.0 Ma, respectively. Both of them were formed in the same age, belonging to the Himalayan age, indicating that there was an important magmatic hydrothermal Cu-Mo mineralization event in the Eocene in the Duoxiasongduo area. The εHf( t) values of the zircons from the two types of rocks range from +1.3 to +2.6. Combined with the geochemical characteristics of elements and isotopes, the Duoxiasongduo ore bearing porphyry may be the product of juvenile basaltic lower crust which was derived from depleted mantle, which was possibly formed controlled by the Jinshajiang strike-slip fault system induced by the collision between the Indian Plate and the Eurasian Plate.
The 3D geothermal geological modeling can intuitively reflect the temperature field distribution pattern of the geological bodies, which is helpful to determine the favorable target area of geothermal resources. In this paper, geophysical and drillhole data and rock thermal properties data were used to carry out 3D geological modeling and temperature field simulation of the central depression area of Songliao Basin, and verified the reliability of the geothermal geological model through drillhole temperature measurement and measured heat flow data. The results showed that the temperature of the central depression at a depth of 1.0~4.0 km was 30.3℃~62.8℃, 68.2℃~120.2℃, 110.5℃~166.7℃ and 158.4℃~214.2℃, respectively. The 4.0 km depth inland geothermal gradient is between 36.9℃/km~57.4℃/km, and the average geothermal gradient is 48.4℃/km. The temperature of four main thermal reservoir bottom plates of Nenjiang Formation, Yaojia Formation 2-3, Qingshankou Formation 2-3, and Quan Formation 3-4 are 15.8℃~71.4℃, 23.6℃~88.6℃, 31.8℃~107.4℃, and 48.9℃~133.4℃, respectively. Huazijing terrace, Daqing placanticline, and Binxian Wangfu Sag are high value areas of thermal reservoir temperature. The current geothermal field in the research area is mainly controlled by the fluctuation of the basement. The "refraction" effect of heat flow caused by the difference of thermal conductivity (between basement and sedimentary layer) promotes the redistribution of heat flow in the shallow part and the heat flow distribution pattern between concave and convex is formed. In addition, fault structures also have a significant impact on the distribution of high anomaly areas in the geothermal field. Combined with the characteristics of heat source, channel and reservoir cap combination, the Quantou Formation 3-4 in the central area of Daqing placanticline are determined as favorable targets for geothermal resources development in the central depression of Songliao Basin.
The Bainiuchang Ag polymetallic deposit in Yunnan Province is located at the junction of the Cathaysia, Yangtze and Indosinian blocks. It has favorable conditions for mineralization due to the influence of multi-phase geological effects. In this paper, the analysis data of major element formed in the course of exploration and development of the deposit for many years has an in-depth mining on the basis of the establishment of prospecting database and ore body model by the method of geochemistry and statistics. The triangle plots of the ore-forming elements show that the Zn/Pb values are concentrated between the 0.70 and 3.50 range, with higher grades of Ag, Sn and Cu in this range, and that the Zn/Pb values are indicative of ore-forming fluid. The results of the principal component analysis show that two principal components, P1 and P2 are able to explain most of the information in the original variables, and the element assemblage of P1 is Ag-Pb-Zn, which represents the mesothermal ore-forming element assemblage. The element assemblage of P2 is Sn-Zn/Pb, representing high temperature ore-forming element assemblage. Therefore, the source of the ore-forming fluid is located in the southern part of the mining area, and the ore-forming fluid was transported and deposited from south to north to form the above mineralization zoning regularities. The metal-element assemblages and spatial mineralization regularities obtained based on geostatistical analysis will provide a theoretical basis for the studies of deposit genesis, and resource exploration and development in mining areas.
Longtan Formation in eastern Sichuan Basin has large potential for shale gas exploration and development. This formation deposited under marine-continental environment has complex rock types and rapidly changing sedimentary sub-facies, which leads to the problems on how to identify and classify the rock-combinations by normal means. However, the present classification of rock-combination is not precise enough. These problems set limits and troubles on identifying the favorable rock-combinations and exploration activities for Longtan Formation in this area. On the basis of core observation, field profile measurement and thin section identification, combined with the mud-to-ground ratio and single-layer lithology thickness of the well, seven lithological combination types were established for the first time, namely: shale, rich shale containing sandstone, rich shale containing limestone, shale-limestone interbedding, rich limestone containing shale, dense limestone and igneous rock types. Based on the characteristic parameters of shale reservoirs such as TOC, porosity, gas content and brittleness index, the planar distribution of different lithological combinations in each section of the Longtan Formation was studied. The results show that the longitudinal dominant lithology combinations are mainly rich shale containing limestone and shale in Longtan section, and the second section of Longtan is mainly shale, shale-limestone interbedding and rich limestone containing shale. On the plane, the dominant lithological combination of mud-rich and mud-containing types in Longtan is mainly distributed in the Kaizhou-Yunyang area, and the shale is mainly distributed in the Chongqing-Qijiang area. The dominant shale type of Longtan Section Ⅱ is distributed in the Banan-Qijiang area, the shale-limestone interlayer is distributed in the Dazhou area, and the mud-rich limestone is distributed in the Wanzhou-Liangping-Shizhu area. The research results provide an important basis for the exploration of shale gas in the Longtan Formation in eastern Sichuan.
Although regional geohazard risk assessment has been carried out for many years, due to the difficulty in evaluating and quantifying the risk of geohazards, and the difficulty in investigating and obtaining data from risk elements, the quality of regional risk assessment has always been low, and research progress has been slow. In addition, the natural conditions of the northern Tibetan Plateau are harsh, with high cold and anoxic conditions, and many peaks covered by glaciers. Most areas are rarely visited, and the level of research is extremely low, the basic geological data and research results on geohazards are relatively scarce, and the risk assessment of regional geohazards is close to blank, making it difficult to meet the needs of local governments for geohazards reduction, prevention, and emergency management. This paper takes Bangor County of Nagqu City, Tibet Autonomous Region as the research area. Using remote sensing image data from GF-1 and GF-2 in 2020 and 2021, as well as GIS technology, the number, types, scales, developmental characteristics, and distribution laws of geohazards within a 2.8×104 km2 area of Bangor County are identified. Information volume method is used to systematically carry out high-precision and large-scale risk assessment of geohazards throughout the county. The susceptibility, hazard, vulnerability and risk of geohazards in the entire county are comprehensively evaluated. The study shows that due to its location on the Qinghai-Tibet Plateau and sparse population, the overall level of geohazard risk in Bangor County is not high, with 98% of the area being low-risk zones. Medium and high-risk zones are mainly concentrated around towns. These evaluation results provide scientific basis for reducing and preventing geohazards in Bangor County.
The Gemalong area is located in the southern part of the eastern section of the East Kunlun orogenic belt. The tectonic activity and magmatic activity in this area are strong. In this paper, LA-ICP-MS zircon U-Pb geochronology and whole-rock element composition of two granodiorites and two tonalite diorites are studied. The genetic types and magmatic source characteristics of the rocks are discussed, and the tectonic evolution environment of the diorites is analyzed. The results show that the diagenetic ages of two representative diorite samples are 405.3±1.1 Ma and 405.8±1.2 Ma, respectively, indicating that the diagenetic age is Early Devonian. The four diorite samples have the characteristics of high silicon, high aluminum, high alkali, poor calcium, poor magnesium and weak peraluminous, belonging to the weak peraluminous high potassium calc-alkaline series rock. The representative minerals of S-type granite are not developed in the four samples, and the Rb/Sr value is 0.32~0.43, which is less than 0.9, and the A/CNK value is 0.98~1.09, which is less than 1.1, which is consistent with the geochemical characteristics of I-type granite. By analyzing the La-La/Sm diagram and(Zr+Nb+Ce+Y)-(Na2O+ K2O)/CaO diagram, combined with Nb/Ta, Zr/Hf, Nb/U, Rb/Sr, Ti/Y, Ti/Zr values, it can be concluded that the diorite in Gemalong area is formed by partial melting of crustal rocks, and may be accompanied by the participation of mantle-derived materials. Combined with previous studies, (Y+Nb)-Rb diagram and Rb/30-Hf-Ta*3 diagram, it can be seen that the diorite in Gemalong area was formed in the post-collisional extensional environment formed in the Early Devonian East Kunlun orogenic belt.
The North China Craton preserves Mesoproterozoic magmatic records related to the breakup of the Columbia supercontinent. In this paper, the temporal and spatial distribution, petrological and geochemical characteristics of the A-type granites in the main rifts and their surrounding areas of the North China Craton in the Mesoproterozoic are reviewed. The genesis and tectonic background of the A-type granites in each period are discussed, and their indicative significance for the breakup events of the North China Craton in the Mesoproterozoic is discussed. Four stages of A-type granites are mainly developed in the North China Craton: 1)~1.78 Ga A-type granites are mainly distributed in the Xiong'er Rift and Shanxi-Shaanxi area; 2)~1.70 Ga A-type granites are mainly distributed in the northern Zha'ertai-Bayan Obo and Yanliao rifts; 3)~1.60 Ga A-type granites are mainly distributed in the southern Xiong'er Rift; 4)~1.32 Ga A-type granites are mainly distributed in the northern Zha'ertai-Bayan Obo and Yanliao rifts. These four A-type granites are derived from the partial melting of crustal materials, which may be related to the heat source provided by the crustal melting of magma underplating caused by the same period of extension. As a whole, there is an evolution sequence from post-orogenic extension to intracontinental rift environment, and there are obvious spatial and temporal differences in the region. The A-type granites of the Mesoproterozoic in the North China Craton recorded four major breakup events, providing evidence that the North China Craton might have participated in the breakup of the Columbia supercontinent.
构建地质知识图谱对深化现有地质数据分析和推进地质大数据的构建至关重要.地质命名实体识别作为构建地质知识图谱的核心技术,仍然面临着地质命名实体不断被引入、符号分隔的命名实体、同一实体表达形式不同等挑战.针对上述问题,本文提出了GeoERNIE-BiLSTM-Attention-CRF的地质领域命名实体识别模型,其中预训练模型GeoERNIE学习了地质领域的先验语义知识,并结合自定义地质领域主体词表对复杂命名实体进行准确分词,能够提升模型整体性能和地质命名实体未登录词以及复杂实体的识别效果.然后通过BiLSTM充分学习地质实体上下文语义信息来帮助对命名形式多样的地质命名实体进行识别,接着引入Attention机制对地质实体相关语义增加特征权重,最后由CRF层输出最佳实体标注结果.本文以测试集数据对模型性能进行了评估,模型的准确率、精确率、召回率和F1值分别达到了 96.35％、96.90％、96.87％和96.95％.实验表明相比其他模型,本文模型在地质命名实体识别方面效果更优,能有效识别符号分隔和同一实体表达形式不同等复杂地质命名实体.
