Metallogenic Mechanism and Tectonic Setting of Tungsten Mineralization in the Yangbishan Deposit in Northeastern China

The Yangbishan iron–tungsten deposit in the Shuangyashan area of Heilongjiang Province is located in the center of the Jiamusi Massif in northeastern China. The rare earth element and trace element compositions of the scheelite show that it formed in a reducing environment and inherited the rare earth element features of the ore-forming fluid. The geochemical characteristics of the gneissic granite associated with the tungsten mineralization show that the magma formed in this reducing environment and originated from the partial melting of metamorphosed shale that contained organic carbon and was enriched with tungsten. In addition, in situ Hf isotopic analysis of zircons from the gneissic granite indicates that they probably originated from the partial melting of a predominantly Paleo–Mesoproterozoic crustal source. According to LA-ICP-MS zircon dating, the Yangbishan orerelated gneissic granite has an Early Paleozoic crystallization age of 520.6 ± 2.8 Ma. This study, together with previous data, indicates that the massifs of northeastern China, including Erguna, Xing'an, Songliao, Jiamusi, and Khanka massifs, belonged to an orogenic belt that existed along the southern margin of the Siberian Craton during the late Pan-African period. The significant continental movements of this orogeny resulted in widespread magmatic activity in northeastern China from 530 Ma to 470 Ma under a tectonic setting that transitioned from compressional syn-collision to extensional postcollision.     

A New Ootype of Dinosaur Egg (Faveoloolithidae: Duovallumoolithus shangdanensis oogen. et oosp. nov.) from the Late Cretaceous in the Shangdan Basin,Shaanxi Province,China

A new ootype collected from the Upper Cretaceous Lijiacun Formation in the Shangdan Basin, Shaanxi Province is described in this paper. Based on general external shape, size, eggshell thickness and honeycomb‐like eggshell microstructure, eggs are referable to the oofamily Faveoloolithidae. Compared with other members of Faveoloolithidae, specimens described in this paper show special characteristics: adjacent pores are usually separated by two eggshell units between which often develop interspaces; columnar eggshell units are relatively closely arranged in radial view. According to these characteristics, we erect a new oogenus and a new oospecies: Duovallumoolithus shangdanensis oogen. et oosp. nov. The new discovery expands the diversity of Faveoloolithidae.     

The Late Triassic I–Type Granites from the Longmu Co–Shuanghu Suture Zone in the interior of Tibetan Plateau, China: Petrogenesis and Implication for Slab Break–Off

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between P_2 O_5 and SiO_2, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO_2, MgO, FeOt, MnO, CaO) and SiO_2. Almost all ε_(Hf)(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low Na_2 O/K_2 O ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.     

Isotope Geochronologic and Geochemical Constraints on the Magmatic Associations of the Collisional Orogenic Zone in the West Kunlun Orogen,China

The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision–related intrusive rock series, i.e., a gabbro–quartz diorite–granodiorite series that formed at 224±2.0 Ma and a monzonitic granite–syenogranite series that formed at 222±2.0 Ma. The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin(material source and thermal source), tectonic setting, genesis and geotectonic implications of these rocks. The results of this analysis indicate that the parent magma of the first series, representing a transition from I-type to S-type granites, formed from thermally triggered partial melting of deep crustal components in an early island–arc–type igneous complex, similar to an I-type granite, during the continental collision orogenic stage. The parent magma of the second series, corresponding to an S-type granite, formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic–Triassic. During continued collision, the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region, forming an immiscible puncture-type complex. The deep tectonothermal events associated with the continent–continent collision during the orogenic cycle are constrained by the compositions and origins of the two series. The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.     

First Report of Zircon U‐Pb Ages from Lubei Cu‐Ni Sulfide Deposit in East Tianshan of Central Asian Orogenic Belt,NW China

正Objective The East Tianshan mafic-ultramafic rocks belt mainly produced in the eastern Jueluotage belt is an important part of the Central Asia Orogenic Belt(CAOB).The wellknown deposits including Huangshan,Huangshandong,Tulaergen,Hulu,Xiangshan were have been consecutively discovered in this belt(Duan Xingxing et al.,2016).The new discovery of the Lubei Cu-Ni sulfide deposit in recent     

Comparative Study of Hydrogen and Carbon Isotopic Composition of Gases Generated from the Pyrolysis of a Peat under Saltwater and Freshwater Conditions

To understand the influence of the diagenetic water medium on the isotopic compositions of thermogenic coalbed gas, both hydrous and anhydrous closed-system pyrolyses were performed at temperatures of 250°C to 650°C on an herbaceous marsh peat. Compared to the results of anhydrous pyrolysis, the hydrocarbon gases generated from hydrous pyrolyses have very different hydrogen isotopic compositions. However, the carbon isotopic compositions of the hydrocarbon gases became only slightly heavier in hydrous pyrolysis, compared to that from anhydrous pyrolysis. With the progress of thermal evolution from peat to a more advanced thermal maturity of vitrinite reflectance values (Ro) of 5.5% during the pyrolysis, the difference in the average δD value increased from 52‰ to 64‰ between the hydrous pyrolysis with saltwater and anhydrous pyrolysis and increased from 18‰ to 29‰ between the hydrous pyrolysis with freshwater and anhydrous pyrolysis, respectively. The difference in the average δ13C value was only 1‰–2‰ between the hydrous and anhydrous pyrolysis. The relationships between the δD values of the generated hydrocarbon gases and Ro values as well as among δD values of the hydrocarbon gas species are established. The close relationships among these parameters suggest that the water medium had a significant effect on the hydrogen isotopic composition and a minimal effect on the carbon isotopic composition of the hydrocarbon gases. The results of these pyrolyses may provide information for the understanding of the genesis of coalbed gas from herbaceous marsh material with the participation of different diagenetic water media.     

南海北部潮汕坳陷侏罗系沉积特征及对储层的控制作用研究

南海北部潮汕坳陷侏罗系具有很大的油气勘探潜力,沉积特征对其储层的发育具有明显的控制作用。通过对研究区最新地震资料精细解释,可以划分出4个典型地震反射界面和3个地震反射层,根据层序界面圈出侏罗系分布特征和残留厚度;通过地震相-沉积相转换对比分析研究,识别出侏罗纪地层不同时期的沉积相类型及其分布特征,重塑了潮汕坳陷侏罗系沉积演化史。该区主要发育5类沉积相、8种沉积亚相,其中滨岸三角洲前缘亚相和深水扇中亚相分别控制了碎屑流砂岩优质储层的发育;此外,浊流砂岩储层主要受控于物源供给的影响,距离三角洲砂体朵叶越近,滑塌浊积体数量越多,面积也越大。总体上,滨岸三角洲前缘亚相、深水扇中亚相和滑塌浊积体是研究区良好的储集相带,该类储集体由于埋藏较深加之被泥岩覆盖,对油气聚集较为有利。