bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extensional Structures in the Ophiolites from Cuba and China: New Constraints to Slowly‐Spreading Ancient Oceanic Lithosphere
Authors: GUO Zhaojie 
Published: May 2019

AbstractA group of low‐angle normal faults developed in banded gabbro of Moa Ophiolite, Cuba. The dark gabbro was cut into puddings by several normal faults, while light gabbro was just swelling in layer thickness. In Hongliuhe ophiolite at eastern segment of South Tien Shan Suture Zone in China, the extensional deformation concentrates on fine cumulus gabbro which is typically mylonitized. Abundant structural features were discovered in HLH ophiolite such as S‐C foliation, C’ foliation, extensional crenulation cleavage, small toughness normal fault, low‐angle normal faults and high‐angle normal faults. According to the above tectonic phenomenon from the ophiolite belts in Cuba and China, we will get the conclusion: the maximum principal compressive stress (b1) is vertical to cumulus bedding, and the maximum tensile stress (b3) is paralleling to cumulus bedding. Considering of the above evidence, the extensional tectonic event should developed at mid‐ocean ridge. Due to seafloor spreading, the maximum tensile stress is paralleling to cumulus layer, and extensional tectonic is kept in cumulus gabbro. In this way, normal faults developed in dark gabbro, while brittle‐ductile extensional developed in light gabbro. A large number of domes, folds paralleling to ocean ridge and detachment faults represented by low angle normal fault were discovered near ocean ridge in Indian Ocean and Atlantic Ocean. In this way, materials from deep oceanic lithosphere (e.g. gabbro, mantle peridotite) outcrop at the crust surface of ocean basin. The above evidences from China and Cuba are consistent with extensional tectonic and metamorphic core complex from slowly and super‐slowly spreading Indian Ocean and Atlantic Oceanic lithosphere based on ODP. Therefore, extensional deformation in the ophiolite belt is of significant meaning for clarifying the formation process and mechanism of ancient oceanic basin.
The Wenquan Ultramafic Rocks in North Terrane, East Kunlun Mountains, NW China – Arc Cumulates of the Paleo‐Tethys
Authors: MENG Fancong , JIA Lihui , FENG Huibin 
Published: May 2019

AbstractThe Wenquan ultramafic rocks, located in the East Kunlun Orogenic belt in the northeastern part of the Qinghai‐Tibet Plateau, consist of dunite, wehrlite, olivine‐clinopyroxenite and clinopyroxenite, and exhibit cumulate textures. Olivine from dunite has high Fo (forsterite, 90–92) and NiO (0.15–0.42 wt%) contents. Cr‐spinels from all of the rocks in this suite are characterized by high Cr# (100×[Cr/(Cr+Al)], 67–91), low Mg# (100×[Mg/(Mg+Fe2+)], 17–35) and low TiO2 contents (mostly < 0.5 wt%). Clinopyroxenes display high Mg# (92–98) and low TiO2 contents (0.002–0.099 wt%), similar to those in ophiolitic cumulates. Geochemically, the Wenquan ultramafic rocks show enrichment of LILE, Sr, and Ba, and depletion of Nb and Th. Mineral chemistry and geochemistry indicate that the Wenquan cumulates were generated from a depleted mantle and likely evolved from high‐Mg basaltic magmas (Mg#=78) that underwent fractional crystallization and crustal contamination. Zircons from clinopyroxenites yield a U–Pb weighted mean age of 331 ± 2 Ma, which is nearly coeval with the formation age of the Buqingshan and A'nyemaqen Carboniferous ophiolites. The Wenquan Carboniferous ophiolites are confirmed to exist in the Central East Kunlun Fault zone, whereas previous studies have considered them to be the Proterozoic ophiolites. The Wenquan ultramafic rocks might be an arc cumulates of the Paleo‐Tethyan ocean, indicating that there were two cycles of oceanic–continental evolution along the Central East Kunlun Fault zone. Keywords Ultramafic rock, Cumulate, Ophiolite, East Kunlun Orogenic belt.
Metamorphic Evolution of High‐pressure Politic Granulite from the Ailaoshan Orogenic Belt, Northeastern Margin of Indochina Block, West Yunnan, China
Authors: QI Xuexiang , ZHAO Yuhao , ZHU Luhua 
Published: May 2019

AbstractAilaoshan orogenic belt located at the northeastern margin of the Indochina block, southeastern Tibet, was formed by subduction and collision between the Indochina and South China blocks in Triassic and slip shearing resulted from the extrusion of the Indochina block in Cenozoic.The high‐pressure pelitic granulite is located at the southeastern margin of the Ailaoshan metamorphic belt, occurs as a slice of about 500∼700m in thickness, consists of garnet, sillimanite, feldspar, biotite and quartz with accessory of kyanite, sapphirine, spinel, rutile, ilmenite, zircon and apatite.The petrography and mineral chemistry show that the high‐pressure pelitic granulite had suffered three stages of metamorphism: 1) the prograde metamorphism recorded by the mineral assemblage of garnet, kyanite, feldspar, biotite and rutile; 2) the peak metamorphism shown by the mineral assemblage of garnet, sillimanite, sapphirine, ternary feldspar, K‐feldspar, plagioclase, biotite, spinel, quartz, rutile and zircon mantle; 3) the retrograde metamorphism recorded by the mineral assemblage of biotite, muscovite, plagioclase, quartz and zircon rim. Zircon SHRIMP U‐Pb dating indicates that the protolith of the pelite granulite was deposited before 336 Ma, the prograde to peak metamorphism occurred at P‐T conditions of ≥10.4 kbar at 850∼919 °C in 235 Ma, and the retrograde metamorphism occurred at the P‐T condition of 3.5∼3.9 kbar at 572∼576 °C until to 33 Ma. They are consistent with the times of Indochina separated from Gondwanaland during late Paleozoic, the amalgamation of the south China and Indochina blocks during the Triassic, and the sinistral slip‐shearing since the Early Cenozoic respectively. It is inferred that that the sedimentary rock was subducted to the lower continental crust (30 km) and suffered granulite‐facies metamorphism due to the collision during Indosinian, then exhumed quickly to middle‐upper crust (10–12km) and superimposed retrograde metamorphism since the Cenozoic.
Geodynamic Setting of the Xigaze Ophiolite in Yarlung‐Zangbu Suture Zone, South Tibet
Authors: SHE Yuwei , ZHU Xiangkun , HE Yuan , SUN Jian 
Published: May 2019

AbstractThe geodynamic setting of the Xigaze ophiolite has long been debated. Structural and geochemical evidence suggest the Xigaze ophiolite was formed at a slow‐spreading ridge (Nicolas et al., 1981; Liu et al., 2016). Based on incompatible element concentrations, the Xigaze ophiolite volcanics are consistent with the ubiquitous subduction signature in suprasubduction zone (Bedard et al., 2009; Hebert et al., 2012; Dai et al., 2013). It is noteworthy that the Xigaze ophiolite is different from the Geotimes and Lasail and Velly units from Oman ophiolite, respectively. The mafic rocks of the Xigaze ophiolite generally resemble typical N‐MORB and Geotimes volcanics in composition except for slight depletions of Th and Nb (Fig.1a). Although the Xigaze rocks have similar Th and Nb concentrations to Lasail and Velly rocks, most incompatible elements in the Xigaze rocks are comparable to N‐MORB. Petrography in gabbro of Xigaze ophiolite shows that euhedral plagioclases are enclosed by clinopyroxenes suggesting that these minerals have crystallized from an anhydrous magma (Sisson and Grove, 1993). Although the Xigaze volcanic rocks are slightly depleted in Th and Nb, they have MORB‐like trace element characteristics implying that they are derived from an anhydrous MORB magma at spreading centre. Godard et al. (2006) suggested that the mantle source of the Oman ophiolite have element and isotopic characteristics similar to Indian Ocean MORB, where the mantle preserved some older slab materials. A negative Nb anomaly of Oman Geotimes volcanic rocks may be resulted from contamination of the slab materials via decompression melting of the convecting mantle. Moreover, the Xigaze rocks have 1.27–3.18 of (Th/Nb)N ratios similar with those of Geotimes volcanics ((Th/Nb)N =0.51–2.77) and lower than those of Lasail and Velly units ((Th/Nb)N =2.12–6.35). These features suggest that the Xigaze ophiolite may have formed at the spreading centre.
Petrological sStudies of Jilang Eclogite and Constraints on the Subduction and Exhumation Processes of the Paleo‐Tethys Oceanic Crust
Authors: SHEN Tingting , ZHANG Cong , TIAN Zuolin , LI Yang , YANG Jingsui 
Published: May 2019

AbstractThe (ultra‐) high pressure eclogites from Sumdo area, recorded the subduction and exhumation process of the Paleo‐Tethys oceanic crust. Previous studies showed that there are significant differences in temperature and pressure conditions of the eclogites in four regions, e.g. Sumdo, Xindaduo, Bailang and Jilang. The cause of this differences remains unclear. Studying the peak metamorphic conditions and P‐T path of Sumdo eclogite is of great significance to reveal the subduction and exhumation mechanism of Paleo‐Tethys ocean. In this paper, we choose the Jilang eclogite as an example, which has a mineral assemblage of garnet, omphacite, phengite, hornblende, rutile, epidote, quartz and symplectit (diopside + amphibole + plagioclase), and minor biotite. Garnet has a “dirty” core with abundant mineral inclusions and a “clear” rim with less mineral inclusions, showing typical growth zoning. From the core to the rim, Prp content in garnet increasing while Grs content decreasing. P‐T pseudosection calculated with Domino constrained peak P‐T conditions of Jilang eclogite as 563°C, 2.4 GPa. Combined with petrographical observation, four stages of metamorphism have been recognized: (1) early stage prograde metamorphism represent by the core of garnet and mineral inclusions therein; (2) peak metamorphism represent by the rim of garnet, omphacite, phengite, glaucophane, rutile and quartz; (3) first stage of retrograde metamorphism characterized by decomposition of lawsonite to zoisite; (4) second stage of retrograde metamorphism characterized by symplectites surrounding omphacite and cornona rimmed garnet. Jilang eclogite shows a clockwise P‐T path, and near isothermal decompression during exhumation. It differs from eclogites in other area, which are hosted by garnet‐bearing mica schists or serpentinites. Jilang eclogites are enclosed in metamorphic quartzites, with relatively low P‐T conditions. We infer that the Jilang eclogite was derived from the shallow part of the subduction zone, and was exhumated by low density materials in the subduction channel.
Assimilation of the mafic‐ultramafic magma: a case study of diabase dyke at the Beidaihe, North China Craton
Authors: XU Haijin 
Published: May 2019

AbstractAssimilation serves as a significant part in magma's evolution. Because of rapid cooling of ultramafic‐mafic magma, assimilation between mantle‐derived magma and crustal rocks (wall‐rocks) is often neglected. The Beidaihe diabase dikes in North China Craton suggest that assimilation of the rapidly cooled mantle‐derived magma can not be ignored. The diabase dikes are very thin (0.5 to 2 m in width) and discordantly intrude into Ordovician limestone. Center of dyke is porphyritic texture while chilled margin of it is aphanitic texture, suggesting a rapid crystallization process. Moreover, limestone close to the dyke was transformed into marble because of contact‐thermal metamorphism. From the center to margin of the dykes, contents of SiO2 (48.9→ 41.6 wt.%) and MgO (8.3 → 4.0 wt.%) are obviously decreased, but contents of CaO (6.4→8.3 wt.%) and CO2 (0.8 → 5.2 wt.%) are distinctly increased. Meanwhile, calcites in the wall rocks adjacent to and far from the dykes are also greatly different. The calcites close to the dykes have high MgO and FeO contents but low CaO and CO2 contents. All these suggest an assimilation process of the mantle‐derived magma with wall‐rock limestone. Calculating CO2 contents in the dyke and wall rock suggest that the extent of assimilation is thought to reach up to 8 ‐ 12 %. Therefore, when the wall rocks of the mantle‐derived magma are carbonate rocks, its components are obviously influenced by assimilation, although it often rapidly chilled. Simultaneously, this study provides possible explanation for some mantle‐derived rocks in carbonate areas with high LOI.
The Open of the Paleo‐Tethys Ocean: Inferred from the Early Paleozoic Ophiolite in the Qiangtang Area, Northern Tibetan Plateau
Authors: ZHAI Qingguo , LI Cai , WANG Jun , HU Peiyuan , TANG Yue , WANG Haitao 
Published: May 2019

AbstractThe Paleo‐Tethys Ocean was a Paleozoic ocean located between the Gondwana and Laurasia supercontinents. It was usually consider to opening in the early Paleozoic with the rifting of the Hun superterrane from Gondwana following the subduction of the Rheic Ocean/proto‐Tethys Ocean. However, the opening time and detailed evolutionary history of the Paleo‐Tethys Ocean are still unclear. The Paleozoic ophiolites have recently been documented in the middle of the Qiangtang terrane, northern Tibetan Plateau, and they mainly occur in the Gangma Co area. These ophiolites are composed of serpentinite, pyroxenite, isotropic and cumulate gabbros, basalt, hornblendite and plagiogranite. Whole‐rock geochemical data suggest that all mafic rocks were formed in an oceanic‐ridge setting. Furthermore, positive whole‐rock εNd(t) and zircon εHf(t) values suggest that these rocks were derived from a long‐term depleted mantle source. The data allow us to conform that these rocks represent an ophiolite suite. Zircon U‐Pb dating of gabbros and plagiogranites yielded weighted mean ages of 437‐501 Ma. The occurrence of the ophiolite suite suggests that a Paleozoic Ocean basin (Paleo‐Tethys) existed in middle of the Qiangtang terrane. We hypothesize that the ophiolite in the middle of the Qiangtang terrane represents the western extension of the Sanjiang Paleo‐Tethys ophiolite in the east margin of the Tibetan Plateau, and they mark the main Paleo‐Tethys Ocean. This is the oldest ophiolite from the Paleo‐Tethyan suture zones and the Paleo‐Tethys Ocean basin probably opened in the Middle Cambrian, and continued to grow throughout the Paleozoic. The ocean was finally closed in the Middle to Late Triassic as inferred from the metamorphic ages of eclogite and blueschist that occur nearby. The Paleo‐Tethys Ocean was probably formed by the breakup of the northern margin of Gondwana, with southward subduction of the proto‐Tethys oceanic lithosphere along the northern margin of the supercontinent.
Let Me Drill a Coring Hole for You, and I will Return You a Telescope Inserted into the Earth
Authors: ZHANG Xiaoxi , ZHANG Hui 
Published: May 2019

AbstractThere was a famous saying by Sage Archimedes over 2,000 years ago that giving him a long enough lever and a fulcrum, he would tilt the entire earth. As an old driller, I propose another non‐famous saying that giving me a chance to drill a coring hole, and I will create a telescope to insert the deepest earth for you. Nowadays, drilling is one of most significant methods to collect samples from the deep earth. Those samples are extremely important for geoscientists to focus on the dynamic evolution of deep earth. Therefore, drilling engineering is thought to be inseparable for the geosciences. Unfortunately, some young geologists, especially students majoring on geology, have no meanings of what the drilling is, and of the importance for their geological researches. In this case, education popularization drilling knowledge should be strengthened in future. And we hope that sufficient attention of drilling engineering will be taken by geologists in the world. Moreover, in order to obtain high‐quality cores by various coring drilling methods. Drilling techniques and special coring tools must be continuously developed to successfully perform with regard to a variety of complex geological conditions. We have developed coring tools these years as follows: Splitted core barrel Triple tube coring drill tool, Advanced tube coring tool, Vacuum suction coring tool, Shock‐type coring tool, Long core barrel coring tool, WL‐drilling system with hydro‐hammer, WL‐drilling system with mud motor. These new coring tools have played a very important role in China's scientific drilling program. All in all, without advanced drilling technology, pickup of high quality samples from the deep Earth and geological research on the dynamic evolution will be restricted.
Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China
Authors: AN Yanfei , ZHANG Shuai , JDN Nenzhelele 
Published: May 2019

AbstractAs a widely‐developed mineral in various types of rocks, pyrite features important geological information such as temperature and pressure during its formation and evolution (An et al., 2014; An et al., 2018). It is an important geological formation for studying the origins of rocks, mineralization, and deposits (Xue et al., 2014; An et al., 2016). The study of the genesis of gold deposits is a research hotspot in current geology and mineral deposits not only because of high economic value, but also because of important practical significance (An et al., 2017; Yang et al., 2014). Shandong Zhaoyuan, as the third largest gold production area in the world, has important research significance of the origin and generation of gold‐bearing minerals (Xue et al., 2014; Wen et al., 2014). In this study, pyrite from augen granite (figure 1a), syenite (figure 1b), basite (figure 1c) and gold ore (figure 1d) at Zhaoyuan gold deposit Shandong Province, was selected as the research object. The morphological and structural micro‐fabrics were analysed by polarized light microscopy (PLM) and Raman spectroscopy to reveal the source and process of gold further.
Micro‐fabrics and Genesis of Pyrite from Zhaoyuan Golden Deposits in Shandong Province, North China
Authors: GAO Biao , LI zhong 
Published: May 2019

AbstractNorth China Craton experienced significant lithospheric destruction or delamination during the Late Mesozoic, accompanied with the emergence of numerous basins and intensive volcanic activities. Extensional basins also formed in eastern Shandong Province. Even though they have been researched for decades, the relation between basin development and deep tectonic processes still remains obscure. Recently, a set of Early Cretaceous strata, characterized by translating from turbidite deposits to terrestrial strata unit and ending up with a unique volcanicalstic formation within a pretty short time span, has been found on Lingshan Island. Previous Studies have reached an agreement that Lingshan Island strata was formed in a distinct sedimentary background compared with the coeval sedimentary units in Jiaolai Basin. Essential information about basin development and its tectonic setting in the region during Early Cretaceous are preserved in the Lingshan Island strata. In this article, we show the characteristic of heavy mineral assemblage from the bottom to the top, and the characteristic of detrital minerals’ chemical component in the two representative samples. Based on these new works, we indicate that the Lingshan Island basin was developed in transpressional tectonic setting with complex provenance materials mainly from Qianliyan‐Uplift during the period ca.123∼120Ma. Then, the basin evolved within a extensional region and filled with locally derived clastics during 120 to 105Ma. Additionally, the basin was evolved during the procedure of progressive lithospheric thinning and asthenosphere upwelling, which could be proven by stratigraphic characteristics and chemical component of detrital spinels.
Geochemical Characteristics and Their Geological Significance of the Sterane in the Crude oil of Chang 2 Oil Group in Yanchang Formation in Xifeng area, Ordos Basin
Authors: HE Jinxian , ZHANG Xiaoli , WU Caifang 
Published: May 2019

AbstractXifeng area is a key oil and gas exploration and development area in the Ordos Basin. The Chang 2 oil group of Yanchang Formation is an important replacement oil‐bearing horizon in this area. The sterane compounds in the saturated hydrocarbons of crude oil contain abundant geochemical information and can reflect the source of parent materials and the maturity of crude oil, so they are important information carriers for oil source correlation(Huang et al., 1991; Duan, et al., 2001). In this paper, the crude oil samples were systematically collected from the reservoirs of Chang 2 oil group in 10 production wells in Xifeng area and the group compounds of crude oil were separated. The separated saturated hydrocarbon components were tested by chromatography‐mass spectrometry (GC‐MS) and the sterane compounds were identified and analyzed. The geochemical characteristics of the sterane in the saturated hydrocarbons of crude oil and their geological significance could provide a scientific basis for the oil source correlation of Chang 2 oil group at late stage.
Numerical Modeling the Formation Mechanism of L Tectonites
Authors: HU Chengliang , WANG Tao , XIANG Biwei 
Published: May 2019

AbstractL‐tectonite is the deformed rock characterized by extremely developed lineation and weaker foliation. From the geometric, Flinn (1965) believed that a contracting rheological field may be a necessary condition for the development of L‐tectonite. In an ideal contracting field, only the maximum principal strain axis was stretching, and the other two principal strain axes were equally shortened. Obviously, this field is an end‐member solution in maths, and is difficult to be observed in nature. Sullivan (2013) summarized the possible tectonic settings in which a contracting field might develop and considered that the most likely contracting field would develop in macroscopic region of the orogenic belt. However, the appearance of L‐tectonites in nature is not widespread but often isolated. The previous analysis of the development mechanism of L‐tectonites still were focused on strain geometry and lacks of rock rheological mechanism.
Characteristics and Hydrocarbon Accumulation Periods of the Fluid Inclusions in the Sandstone Reservoirs of Chang 9 Oil Groups in Yanchang Formation, Huaqing Area
Authors: Xiaoli Zhang , Jinxian He , Caifang Wu 
Published: May 2019

AbstractHuaqing area is an important area for oil and gas exploration and development in the Ordos Basin, within which, the Chang 9 oil group of Triassic Yanchang Formation is one of the main intervals for exploration and development (Zhang et al., 2011). Fluid inclusions record abundant oil and gas accumulation information and important oil and gas migration and accumulation history information(Parnell et al., 1998; Parnell, 2010; Jiang et al., 2018). The occurrence, distribution and intersection of the fluid inclusions in diagenetic minerals were observed under microscope. The accurate formation periods of inclusions are key to determine hydrocarbon accumulation periods (Burrus et al., 1985; Zhou et al., 2000; Zhao, 2002). In addition, the fluorescence color and brightness of organic inclusions observed by fluorescence microscopy could be used to roughly identify the oil and gas evolution stages (Zhang et al., 2010). Therefore, the occurrence, distribution and fluorescence characteristics of oil and gas inclusions were important evidence for judging the hydrocarbon accumulation periods. The fluid inclusions in sandstone reservoirs of Chang 9 oil group in Huaqing Area were observed in detail, and the observation results revealed that fluid inclusions were widespread in Chang 9 sandstone and exhibited various types. Through comprehensive analyses, it was considered that the fluid inclusions in Chang 9 sandstone reservoirs indicated three hydrocarbon accumulation periods.