Abstract:A set of integrated Archean-Paleoproterozoic gneisses and supracrustal rocks are exposed in Huangling area, Yangtze continental nucleus, and are named Kongling Complex. Previous research shows that north and south Huangling had the same material composition and geological evolution process in Ar-Pt1. Zircon dating studies of Archean granitic gneiss from the north and the south of Huangling respectively show that two samples (HL013-1 and HL013-2) from the north huangling contain a large amount of zircons with the development of core-rim structure, and have protolith age of ~2.8 Ga and metamorphic age of ~2.0 Ga, whereas one sample (HL005-3) from south Huangling mainly contains magmatic zircons with oscillatory zones, and has a crystallization age of ~2.9 Ga only. Combined with previous research results, the authors found that the metamorphic age of ~2.0 Ga was widely obtained in the Archean-Paleoproterozoic granitic gneiss and supracrustal rocks from north Huangling, but was not obtained in the similar structures from south Huangling. This is probably due to the fact that north Hangling had widely developed ~2.0 Ga regional metamorphism but south Huangling had not, and they were probably in different massifs or different parts of the same massif in Paleoproterozoic period. The spatial distribution characteristics of 2.1-1.6 Ga tectono-magmatic events in Yangtze block indicate that there may have existed multiple Paleoproterozoic orogenic belts, characterized by the evolution of multi-block collage in Paleoproterozoic. The extensive records of 2.1-1.6 Ga tectono-magmatic events indicate that the Yangtze block is an important part of the global Columbian supercontinent.

Abstract:Based on basic knowledge in geosciences and instances of ore deposits, the authors firstly put forward the argument that gold within rocks in the Xuefeng uplift zone can't be mobilized, migrated and enriched for mineralization by low-grade regional metamorphism of such rocks as slate and meta-sandstone. The fault structure itself cannot be mineralized in the process of dynamic metamorphism. The content of gold in strata in the fracture zone is only 0.123% of that in the orebody. The metallogenic temperature of the gold deposit determined by fluid inclusions mainly ranges from 200 ℃ to 300 ℃, which indicates that the rock gold deposit in the Xuefeng uplift zone was not sourced from underground hydrothermal solutions. The similarity between some ore minerals, associated components, trace elements, and isotopic geochemistry of gold deposits and the similarity of granitic magmatic rocks show their genetic relationships. The gravitational and magnetic data suggest that there might exist a large concealed intrusion under the gold deposit where there are no magmatic rocks exposed on the surface. The above discussion and exclusion suggest that the genetic type of rock gold deposits in Xuefeng uplift belt is magmatic hydrothermal deposit.

Abstract:The Lianhuashan fault zone is an important NE-trending tectonic belt on the southeastern continental margin of China. It is not only an important boundary of secondary tectonic units but also controls the most important tin-copper polymetallic metallogenic belt in Guangdong Province. Previous studies show that the ductile deformation in Lianhuashan fault zone is closely related to the tin-copper polymetallic mineralization. However, there are still some disputes about the distribution of ductile deformation and its contribution to mineralization in Lianhuashan fault zone. In this study, by means of large-scale structural mapping and typical geological profiles of the Lianhuashan fault zone, in combination with the measurement of tensile lineation attitude and the observation of microstructure, the authors have reached the conclusion that the ductile deformation in the fault zone was formed by a series of in-situ shear zones striking nearly 60° in N-S direction, which are roughly parallel to each other. After ductile deformation, these shear zones were cut by brittle faults striking 30°. Ductile deformation controls the shape and scale of orebodies in Lianhuashan fault zone. In the late magmatic and hydrothermal activities, the space of preexisting ductile shear zone was utilized to precipitate and enrich metallogenic elements in the cracks of ductile deformation. The ore-prospecting work in Lianhuashan fault zone should be arranged around the ductile deformation area and should pay attention to the ore-hosting fractures near the ductile deformation.

Abstract:Based on a comprehensive study of 1:50000 regional geological survey and relevant data collection, this paper further discusses the formation and evolution of the Yarluzangbo suture zone. The Tethys Ocean in the Yarlung Zangbo had the nature of the back-arc expanded ocean basin. From Early Triassic to mid Middle Triassic period, the oceanic basin was formed preliminarily, completely formed in late Middle Triassic to Late Triassic period, then gradually shrank from Early Jurassic to Late Cretaceous period, and was finally closed in Paleocene-Eocene period. The ophiolite in the southern belt was mainly of the mid oceanic ridge dilatation type (type MORB) formed in late Middle Triassic to Late Triassic period. The ophiolites in the northern belt seem mainly to have been the upper plate of the subduction zone (type SSZ) related to intra-oceanic subduction, formed in the early Middle Jurassic period. The other Jurassic-Cretaceous magmatic rocks in the belt were mainly fore-arc basalt rocks (type FAB). It is shown that the Tethys Ocean in the Yarlung Zangbo began its intra-oceanic subduction in the Early Jurassic, and synchronously subducted actively northward under the Gangdise belt, subducted passively southward under the Himalaya landmass, and then continued to develop until the Late Cretaceous. The Palaeocene-Eocene subduction and collision and extinction were transformed into a binding zone.

Abstract:Core observation, thin section identification and data test were applied to analyzing the characteristics and quality-controlling factors of reservoirs in braided river delta. 5 parameters of porosity, ratio of sandbody, effective sandbody thickness, stratification coefficient of effective sandbody and matix content were chosen to evaluate the reservoir quantitatively, and gray correlation method was used to determine the weight coefficient and make critical point analysis to confirm the threshold value of various reservoirs. The results show that the lower delta plain is mainly classified as TypeⅠreservoir due to its good reservoir physical property and well-development of effective sandbody, while, in the upper delta plain, conglomerates of high matix content and poor physical property are assigned to typeⅡreservoir. The reservoir quality in delta front varies as its remarkable grain rhythm, with good quality in medium and coarse sandstone and poor quality in fine sandstone. And a limited development scale of the effective sandbody causes the delta front to be more likely recognized as TypeⅡand type Ⅲ reservoir. The results can provide reference for the quantitative evaluation of complex conglomerate reservoirs.

Abstract:The Lianhuashan fault zone is not only an important NE-striking fault zone in Guangdong Province but also a significant tin, tungsten, copper, lead-zinc polymetallic metallogenic belt. Based on geological field observation of the Lianhuashan fault zone and the typical mining area as well as the measurement of the zircon U-Pb age of the granite intrusive with ductile deformation, the authors preliminarily investigated the time of ductile deformation and boundary fault and the relationship between deformation and mineralization in this paper. The result indicates that the ductile deformation time in the Lianhuashan fault zone is around 129-127 Ma, and the brittle boundary fault was developed between the sedimentary time of Guancaohu Formation and the Heshui Formation. The age of ductile shear deformation in the Lianhuashan fault zone was earlier than the mineralization time, and the ductile shear deformation provided the ore-bearing space for mineralization.

Abstract:Qianlishan rock mass is an important rock mass closely related to tin and tungsten mineralization in Nanling region. Studying its spatial characteristics and ore-controlling role is of great significance for deep geological mapping and deep prospecting and prediction. Using medium-scale gravity data the authors determined the hidden boundary of Qianlishan rock mass. Two-dimensional and three-dimensional simulation inversion revealed the connection relationship between Qianlishan rock mass and Wangxianling rock mass, the spatial morphological characteristics and the contact relationship with surrounding rock masses. It is inferred that the Qianlishan rock mass and the Wangxianling rock mass are connected in depth, and were produced in a large basement and controlled by deep and large faults, with the three-dimensional shape of the two rock masses being balloon expansive contour as a whole. On the basis of geological data, the relationship between Qianlishan rock mass and mineralization was discussed. It is concluded that deep bedrock and structure provided ore-forming material source, heat source and ascending channel for the deposit.

Abstract:Numerous Neoproterozoic volcanic-sedimentary rocks, e.g., Wanquan Group, Louqian and Xixi Formation, are outcropped along the Nanping-Ninghua tectonic belt, South China. This paper presents a systematic petrological, geochronological, and geochemical study of metamorphic rocks from the Louqian Formation in Mingxi County of Fujian and Ruijin County of Jiangxi Province. Zircons from meta-dacite in Mingxi County and meta-crystal tuff in Ruijin County yielded U-Pb weighted mean ages of (729±4)Ma and (735±6.7) Ma (by LA-ICP-MS), respectively. The SiO₂ values of these meta-volcanic rocks range from 65.22% to 74.54%, and they have high Al₂O₃ (11.05%-16.80%) and Na₂O + K₂O content (4.88%-10.19%) but low CaO, MgO, and FeO_T content. Their ANK values and A/CNK ratios are 1.23-1.78 and 0.98-1.57 with Nb/Ta being 12.44-17.28, Nd/Th being 2.07-3.51, Ti/Zr being 6.08-10.37 and Ti/Y being 68.51-154.71, implying the S-type igneous rocks. All samples are enriched in large-ion lithophile elements (LILE; e.g., Ba and Rb) and depleted in high-field-strength elements (HFSE; e.g., Nb, Ta, Ti, and P)with Zr/Nb being 16.65-24.07 and Th/Ta being 12.94-16.93. Marked negative Eu anomalies 0.33-0.62 are similar to those in arc igneous rocks. Based on regional geological data and previous studies, the authors hold that the Nanping-Ninghua tectonic belt had been in an active continental margin setting until 713 Ma. The magmatism was caused by the subduction of oceanic crust and formed an intermediate-acid volcanic belt along the Nanping-Ninghua-Ruijin continental margin, which indicates that the collision between the North and South Wuyi blocks did not form a unified Wuyi Block before 713 Ma, and the Cathaysia Block had not a unified pre-Nanhua crystalline basement.

Abstract:Located in northeastern Guizhou of middle Yangtze area, Yanhe County has many low-temperature hydrothermal deposits. It is a good place for studying the provenance-tectonic response of the basin due to its back-bulge position during Ordovician. However, in most area of middle Yangtze, stratigraphic sequence is composed mainly of carbonate rocks intercalated with mudstone, which restricts the development of quantitative analytical methods such as the detrital zircon geochronology. Recently, the authors noticed that there are mudstone and carbonate intercalated with sandstone around Yanhe in the Metitan Formation (O_1-2m) of lower-middle Ordovician. A detrital zircon sample from the sandstone shows that only 8 zircons (12%) are older than 1.0 Ga and they have no age peaks, and the weighted average of the youngest group of zircons ((457.8 ±8.1) Ma) is close to the upper limit of the Meitan Formation. This means that the detritus of the Meitan Formation was mainly derived from a newly formed source area and had a relatively high deposition rate. The age of zircons can be divided into five groups according to their age distribution and peaks: ~461 Ma (Ⅰ), ~580 Ma and ~606 Ma (Ⅱ), ~722 Ma (Ⅲ), ~865 Ma (Ⅳ₁) and ~936 Ma (Ⅳ₂). On the basis of isotope ratio and REE, the authors consider that the ages can be divided into three parts:Ⅰ, Ⅱ and Ⅳ₂, Ⅲ and Ⅳ₁, which are mainly derived from three different source areas. Combined with the previous study, the authors hold that the three source areas are Qianzhong uplift, Kangdian ancient land, and Wuling-Xuefeng uplift, with Qianzhong and Kangdian being newly formed source area. What's more, there are many (73%) hydrothermal zircons in age group Ⅰ (450 ~511 Ma), and this age matches well with low-temperature hydrothermal mineralization, suggesting that it was caused by the activation of the fluid, probably due to the regional tectonic regime converted from extension to compression. This implies that the Caledonian movement had begun to affect the Yanhe area, but was mainly manifested as hydrothermal activity, with no large scale of magmatism.

Abstract:A series of volcanic rocks, such as basalt, andesite and rhyolite, were determined in Xin Barag Right Banner of northern Da Hinggan Mountains. Geological survey reveals that these volcanic rocks should be assigned to Hadataolegai Formation. SHRIMP zircon U-Pb dating indicates that the epidotized andesite from Hadataolegai Formation was formed at(254.3±7.9)Ma(MSWD=4.7). According to geochemical researches, these volcanic rocks of Hadataolegai Formation can be divided into two types, i.e., intermediate-basic rocks and acidic rocks. The magma of intermediate-basic rocks was derived from the lithospheric mantle affected by the southward subduction of Mongolia-Okhotsk plate. The acidic volcanic rocks have a crustal-derived magma source features. Based on tectonic setting analysis, the authors hold that the Hadataolegai Formation volcanic rocks were formed under the continental marginal arc environment and related to southward subduction of Mongolia-Okhotsk plate. The determination of Hadataolgegai Formation improves the stratigraphic sequence of northern Da Hinggan Mountains and provides a favorable evidence for regional tectonic evolution of Da Hinggan Mountains.

Abstract:Tonghua area is a new oil and gas exploration area in the periphery of eastern Songliao Basin and is characterized by low-grade degree oil and gas exploration. The key geological problems such as sedimentary stratigraphic distribution features and deep structure characteristics of the basin remain unknown. Gravity-magnetic-electrical exploration is an important method for revealing the deep structural features and structural framework of the basin. Based on several gravity-magnetic-electrical survey lines, the authors obtained the comprehensive interpretation of Tonghua area tectonic framework. There are 4 class-I faults and 46 secondary faults in the Tonghua area, which control the basic tectonic framework in the study area. For the first time, five faulted basins were identified, namely Hongmiaozi, Huanren, Shajianzi, Guanmozi and Muqi basin. The scale of the basin, the maximum buried depth of the Mesozoic strata, the features of Houjiatun Formation and deep structural framework were determined in this study. In addition, the authors carried out the division of tectonic units in the Huanren Basin and the Guaimozi Basin. This study would provide important basic geological information for further oil and gas exploration, and also have great guiding significance for exploration and deployment in the new periphery areas of eastern Songliao Basin.

Abstract:The intrusive rocks in Tongling area can be separated into a high-K calc-alkaline series and a shoshonitic series. The Jiaochong orefield is one of the seven orefields in Tongling area. The problems as to whether there are two series of intrusive rocks in the Jiaochong orefield or not and whether they have the same age and genesis as compared with the other intrusions in Tongling area are not clear. Therefore, this research was focused on the study of petrography, geochemistry, LA-ICPMS zircon U-Pb dating and in situ Hf isotopic analysis. It turns out that there are two series of intrusive rocks in the Jiaochong orefield. The high-K calc-alkaline series mainly contains quartz monzodiorite and granodiorite, and the shoshonitic series consists of pyroxene monzodiorite. The results of LA-ICPMS zircon U-Pb dating show that the age of the high-K calc-alkaline series in the Jiaochong orefield is about 142 Ma, identical with the age of the other orefields in Tongling area; the age of the shoshonitic series is around 136 Ma, which is younger than that of the other intrusive bodies in Tongling area. In general, the two series of intrusions indicate the features of the multiphase emplacement. Furthermore, lots of zircons having old inherited core in the high-K calc-alkaline series reveal the existence of the materials of old crust in the magma-forming process. Combined with the characteristics of the intrusive rocks in Tongling area and the geochemical features of Jiaochong intrusions, it is obvious that the genesis of the two series of intrusions in the Jiaochong orefield is similar to that of other intrusions in Tongling area. In other word, the intrusive rocks of the shoshonitic series were formed by the fractional crystallization of the alkali-rich basic magma that originated from the deep magma chamber near the Moho. In the meanwhile, the high-K calc-alkaline series is the product of the magma mixing between the felsic magma derived from the shallow magma chamber and the magma that suffered from the fractional crystallization and originated from the deep magma chamber.

Abstract:Extensive lithospheric extensional thinning events occurred during the late Mesozoic in the interior of South China block. As a record of the early Cretaceous ((120.8±1.4)Ma) mantle-derived magmatic activities in the eastern part of the Qingzhou-Hangzhou juncture belt, the Lingshang ultramafic intrusion in Xinyu of northern Jiangxi is a good object for studying the mantle attribute and geodynamic process of the late Mesozoic in central South China. Based on a systematic analysis of the geochronology from La-MC-ICP-MS zircon U-Pb, Lu -hf isotopes and element geochemistry of the Lingshang ultramafic rocks, the authors investigated the intrusion, the source area characteristics of the ultramafic intrusion and the tectonic background reflected by them. Lingshang ultramafic intrusion suffered no significant crustal contamination. The content of MgO is concentrated with no obvious linear relationship with TiO₂, Al₂O₃, Ni, Th, and some other components, implying no significant crystallization differentiation. However, the range of Mg# and La-Sm differentiation indicates that heap crystallization and partial melting might have exerted an effect on magmatic evolution. The characteristics of rare earth and trace elements (Nb, Ta, Zr, Hf, etc.) are similar to those of intraplate basalt (OIB), and the characteristics of low SiO₂, high Ti, high Fe/Mn ratio and Ni are all closely related to asthenosphere mantle. However, the ε_Hf(t) of zircons (6.83-11.41) are less than the value of the depleted mantle, and Nb/Ta ratios are close to the ratio of lithospheric mantle, suggesting low degree partial melting of spinel peridotite mantle source region in the relevant element diagram. All of these data suggest that the Lingshang ultramafic intrusion may be the result of the interaction between asthenosphere mantle and lithospheric mantle under the background of late Mesozoic intracontinental extension. The upwelling asthenosphere material led to the low-degree partial melting of the preexisting spinel peridotite mantle source area, and the deep ultramafic magma was emplaced rapidly along the tectonic weak zone to form the Lingshang ultramafic intrusion.

Abstract:Based on comprehensive geochronological, elemental and isotopic geochemical studies of the Qijianfeng granite in southern Tongbai-Dabie orogenic belt, the authors investigated the petrogenesis as well as the geodynamic settings and Mo mineralization of southern Tongbai-Dabie orogenic belt during Early Cretaceous. LA-ICP-MS zircon U-Pb dating yielded an age of (140±1) Ma for the Qijianfeng granite. The rocks exhibit adakitic characteristics, such as high SiO₂ (72.88%-73.60%), low MgO (0.33%-0.36%), high Sr (620×10^-6-642×10^-6) content and high Sr/Y(107-111) ratios, low Y (5.65×10^-6-5.95×10^-6) and Yb (0.52×10^-6-0.59×10^-6) content, with negligible Eu anomalies. The rocks are enriched in K₂O and depleted in Cr and Ni, and show enriched Sr-Nd isotopic compositions with initial ⁸⁷Sr/⁸⁶Sr and epsilon Nd(t) ranging from 0.7075 to 0.7078 and from -15.5 to -15.1, respectively. The rocks have zircon ε_Hf(t) values of -19.9--13.2 with corresponding two-stage Nd and Hf model ages from 2.15 to 2.19 Ga and from 2.00 to 2.43 Ga respectively, suggesting that the magmas were derived from partial melting of ancient garnet-bearing amphibolites from the thickened lower crust. Combined with the previous studies, the authors propose two-stage magmatic activities and accompanying Mo mineralization during Early Cretaceous in southern Tongbai-Dabie orogenic belt. The first stage Mo-related rocks (>130 Ma) were derived from the partial melting of the thickened lower crust, while the second stage Mo-related rocks (<130 Ma) were generated in a normal crustal environment. It is suggested that the southern Tongbai-Dabie orogenic belt experienced a tectonic transition from collisional compression to post-collisional extension, i.e., collapse, delamination and thinning of over-thickened orogenic crust and lithosphere during early Cretaceous (ca. 130 Ma).

Abstract:The Zhongchuan granitoid pluton is located in the east of the Western Qinling. Zircon LA-ICPMS dating for the porphyritic monzogranite from the Zhongchuan pluton yielded an age of (221±1)Ma (MSWD=0.26), the age of fine-grained monzogranite is (217±1)Ma(MSWD=0.107), that of magmatic enclave include phenocryst is (220±1)Ma(MSWD=0.107), that of magmatic enclave is (216±1)Ma (MSWD=0.26) and that of fine-grained granite vein is 207±1Ma(MSDW=0.29). Magmatic enclave and rock mass have the same age, and the age of granite vein is the youngest, indicating that the ages gradually become younger from the edge to the center. The rock mass and magmatic enclave are respectively of meta-aluminous or weakly peraluminous, high-K calc-alkaline and high-K calc-alkaline or shoshonite series with the Litman index(σ) being 2.20-3.85, 2.24-9.22 and A/CNK being 0.99-1.15, 0.75-1.08. Their REE and trace elements are enriched in large ion lithophile elements (LREE,Rb,Ba,K) and depleted in high-field strength elements(HREE, Zr, Hf, Ta, Nb, P, Ti), with slightly negative to positive anomalies of Eu (δEu=0.29-0.91) and no anomalies of Ce. These characteristics suggest that the granitoids have I type granite features, and the fine-grained monzogranite is located in the center with some highly fractionated I type granite features. The main oxides of rock mass and MME have a good linear relationship in Harker diagram. Nd isotopic compositions of the rock mass and MME are mainly characterized by ε_Nd(t) values of -7.31--8.73 and-5.32--5.69, and T_DM2 of 1.59-1.71 Ga and 1.43-1.46 Ga. Zircon Hf isotopic compositions of the rock mass and MME are mainly characterized by ε_Hf(t) values of-7.02--0.31 and -3.0-0, T_DM2 of 1.27-1.70 Ga and 1.2-1.5 Ga. These characteristics suggest that the rock mass was derived from partial melting of ancient crustal material and magmatic enclave was derived from the lithospheric mantle, with some mixture. The formation of gold deposits was closely related to Zhongchuan granitoid pluton in time and space, and the age of the gold deposit are slightly later than that of Zhongchuan granitoid pluton and close to that of granite vein. Mineralization data indicate that ore-forming material and lithogenous material were similar to each other. These data indicate that magmatism not only provided a thermal source for the mineralization but also offered ore-forming material.

Abstract:The Hejiazhuang-Laohuyao intrusions are located in the north of the Mianlue suture zone, close to the west section of the Shangdan fault zone in the north of the Qinling microplate, and their main lithology is granodiorite. The authors studied the LA-ICP-MS zircon U-Pb ages, geochemical characteristics and Hf isotope characteristics of the Hejiazhuang-Laohuyao intrusions. The results show that the emplacement time of the Hejiazhuang intrusion is 235-240 Ma and that of the Laohuyao intrusions is 239 Ma, suggesting that their emplacement epochs were the early Triassic. The granodiorite in the Hejiazhuang and Laohuyao intrusions are both high-potassium calcareous and alkaline series, showing strong over-aluminum characteristics and belonging to type I granite. The ε_Hf (t) values of both magmatic zircons are mostly negative and contain one or two positive values. The model age of the crust is Mesoproterozoic (1255-1754 Ma), indicating that their source rocks experienced the addition of mantle materials, which might have been magma mixed with mantle materials dominated by partial melting of Mesoproterozoic ancient crust, showing similar geochemical characteristics to adakianrocks and indicating that the magma might have originated from high potassium solution magma mixing produced by partial melting of subducted oceanic crust under high pressure and partial melting of lower crust contaminated by peridotite due to bottom transgression. The emplacement time and genesis of them indicate that the Yangtze plate and Qinling microplates were subducted during the period of 235-240 Ma.

Abstract:In this study, the authors determined a set of volcanic rocks in the Late Paleozoic strata at Huolinhe area, Inner Mongolia. The age of zircon U-Pb isotope based on LA-ICP-MS analysis is (313.7±3.5)Ma, suggesting Late Carboniferous. The characteristics of petrography and petrogeochemical indicate that the Benbatu Formation consists of andesite and andesitic basalt rocks and belongs to aluminous rocks of alkalic series. The SiO₂ values are 52.82%-54.76%, with higher Al₂O₃ content (17.43%-20.79%) and lower TiO₂ content (0.97%-1.41%); Na₂O (3.74%-4.21%)>K₂O (2.37%-3.02%). In addition, rare earth elements (ΣREE) are between 46.78×10^-6 and 124.36×10^-6, light rare earth elements (LREE) are enriched (42.57×10^-6-109.06×10^-6), and heavy rare earth elements (HREE) are relatively enriched (4.21×10^-6-15.30×10^-6). The ratios of LREE/HREE are 6.04-10.43, suggesting obvious fractionation of light and heavy rare earth elements. The ratios of (La/Yb)_N are 6.32-14.56, exhibiting right-inclined shape high on the left and low on the right on the chondrite-normalized REE patterns. Large ion lithophile elements (Rb, Ba, K, Pb, Sr)and LREE are enriched whereas high field-strength elements(Nb, Ta, Ti, P)and HREE are depleted. Magma came from mantle wedge partial melting with underthrust fluid metasomatism. These rocks are characterized by structural environment of island arc and continental edge arc and were formed along the subduction zone at the edge of the plate and related to Paleoasian Ocean subduction.

Abstract:There are few reports of Archean crystalline basement in the eastern part of the Central Asian Orogenic Belt, which impedes researchers' understanding of ancient tectonic evolution of this area. In this study, the authors discovered Paleoproterozoic fine-grained adamellite and sedimentary rocks (Wulanaobao Formation) unconformably covered by the Niqiuhe Formation of Middle Lower Devonian in the Ulikit Obo area along central China-Mongolia border area. The zircon U-Pb dating results (LA-ICP-MS) show that the crystallization age of monzogranite is 1686 ±10 Ma, formed in Paleoproterozoic. The Ulikit Obo granites are high-K calc-alkaline, peraluminous (A/CNK=1.08-1.11). In combination with the existence of muscovite, the Ulikit Obo granites could be classified as S-type granites. They have positive ε_Hf(t) value(+ 2.9-+ 6.7),which is located lower than the 1.7 Ga crustal evolution trend line; besides, the in-situ Hf isotope two-stage model age of zircon is 2.0-2.3 Ga, so the zircon should be derived from partial melting of pelites in syn-collisional tectonic settings. The Wulanaobao Formation was intruded by the Paleoproterozoic Ulikit Obo granites and their detrital zircons yielded a youngest age peak of ca. 1698 Ma. The discovery of Paleoproterozoic Ulikit Obo granites and Wulanaobao Formation indicates the existence of Paleoproterozoic crystalline basement for the microcontinental massifs in the eastern section of the Central Asian orogenic belt.

Abstract:Monzogranites in Fengleishan are located in northern Beishan and situated between two ophiolitic mélange belts of Hongshishan-Baiheshan-Pengboshan and Jijitaizi-Xiaohuangshan, having a special tectonic affinity. Zircons from the monzogranites yielded a weighted mean LA-ICP-MS U-Pb age of (320±1) Ma, representing the intrusion age. The samples are characterized by high content of SiO₂ and Al₂O₃ with Rittmann indexes of 1.58-2.74 (<3.3) and alkaline ratios of 2.35-4.05, belonging to calc-alkaline granitoids. Their A/NCK values range from 0.92 to 1.15 and display metaaluminous to peraalmuinous affinities. They have relatively high content of total REE and are characterized by LREE-enriched patterns ((La/Yb)_N=4.60-8.83)and negative Eu anomalies (δEu=0.56-0.88, 0.72 in average). They also show strong enrichment of incompatible elements (e.g., Th and U) and large ion lithophile elements (e.g., Rb and K) but depletion of high field strength elements (e.g., Nb, Ta, Ti and P). Their normalized patterns are similar to those of upper continental crust (UPC), indicating participation of materials from the UPC in their magma source. High values of Th (8.58-21.62 μg/g) and low ratios of Nb/Ta (8.75-15.72) point to a crust-dominated magma source. On the tectonic discriminant diagrams of Rb-(Nb+Y) and R₁-R₂, most of the samples are plotted in the pre-collisional volcanic arc granite area. Based on associated lithological characteristics, it is proposed that monzogranites in the Fengleishan were formed by pre-collisional volcanic arc magmatism, which was related to oceanic crust subduction in the Hongshishan-Baiheshan-Pengboshan belt. Combined with regional geological background, it is inferred that the closure of the small ocean in the Hongshishan-Baiheshan-Pengboshan belt should postdate the early period of late Carboniferous.

Abstract:North Alun area has experienced complicated tectonic evolution process and, as a result, quite many ultrabasic rocks were formed in a post-collision extension background throughout the area, and geochemical characteristics of these rocks show that ultrabasic rocks in the study area have two kinds of different magmatic sources, evolution processes and tectonic backgrounds. The trace element characteristics show that the first group samples are almost free from the contamination of crustal substances and that the PGE content is lower than that of the primitive mantle. It can be inferred that the first group samples might have come from about 20% partial melting of the primitive mantle and the samples might have been formed in the continental rift tectonic environment because of the rapid rise and emplacement of mantle-derived magma during the quick extension of the oceanic basin, representing the magmatic activity of North Altun Ocean during the initial cleavage period. The geochemical characteristics of the second group samples show that their source region was more complicated and experienced a relatively strong contamination of crustal substances. The research shows that ophiolite belt contained in the samples has the characteristics of ophiolite in a subduction zone environment; therefore, it can be inferred that it was probably formed in a back-arc basin environment under the convergence background, the subduction of oceanic crust that carried a large amount of water and continental crustal substances in the continental margin entered the mantle magma region, suggesting that the subduction process of the ancient oceanic basin of North Altun area occurred in the Early Paleozoic. The average m/f value of the first group samples is 1.64, indicating that the samples are barren iron-rich ultrabasic rocks having no metallogenic potential of Cu-Ni deposits. The analysis of platinum group elements shows that the parental magma might have resulted from the mixing of basaltic magma with ultramafic magma, which was sulfur-unsaturated magma, and the samples experienced limited sulfide liquation. The average m/f value of the second group samples is 17.95, indicating that the samples consist of magnesian ultrabasic rocks associated with chromite, and they have no metallogenic potential of chromite; the values of platinum group elements and Ni are comparatively high, and these elements were mainly from the mantle, and did not experience sulfide liquation. Therefore, the metallogenic potential of Cu-Ni sulfide deposits of the two groups of samples is quite low.

Abstract:The Gutaishan and Longwangjiang quartz vein type gold-antimony deposits, located in Xinhua and Xupu County, respectively, are two representative ones in the middle of Xuefeng arc structure belt. The Gutaishan gold-antimony deposit occurs in the external contact zone of Baimashan composite granite mass, while Longwangjiang gold-antimony deposit is far from Baimashan composite granite mass. Based on the study of fluid inclusions and hydrogen and oxygen isotopic geochemistry,this paper discusses the characteristics and origin of ore-forming fluids so as to provide an insight into the ore genesis. Petrographic observation and microthemometric measurements of fluid inclusions show that ore-forming stage quartz veins in the Gutaishan gold-antimony deposit mainly contain liquid-vapor two-phase aqueous inclusions and CO₂-H₂O three-phase inclusions. The homogeneous temperature and salinity of primary fluid inclusions are in the range of 199 ~298 ℃ and 2.07 ~11.46%NaCl_eqv. The ore-forming stage quartz veins of the Longwangjiang gold-antimony deposit mainly contain liquid-vapor two-phase aqueous inclusions, with the homogeneous temperature from 164 ℃ to 238 ℃ and salinity from 1.40% NaCl_eqv to 8.41% NaCl_eqv. Hydrogen and oxygen isotopic geochemistry shows that the ore-forming fluids of the Gutaishan gold-antimony deposit was composed of the mixture of magmatic water and metamorphic water, and the Longwangjiang gold-antimony deposit was mainly derived from metamorphic water. Based on geological and fluid inclusion characteristics,it is suggested that fluid immiscibility may have been the main mechanism for metal precipitation in the Gutaishan gold-antimony deposit. The mechanism of the ore-forming process in the Longwangjiang deposit was probably caused by the change of temperature and/or pressure, or the addition (mixing) of metamorphic water.

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