• Volume 88,Issue 3,2014 Table of Contents
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    • New Editor-in-Chief Professor Degan SHU and Message from the Editor-in-Chief

      2014, 88(3).

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      Abstract:

    • Associate Editors-in-Chief

      2014, 88(3).

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      Abstract:

    • New Fossil Procercopidae (Hemiptera, Cicadomorpha) from the Early Cretaceous of Northeastern China

      2014, 88(3):725-729.

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      Abstract:A new fossil species, Anthoscytina macula sp. nov., of the family Procercopidae is described from the Early Cretaceous Yixian Formation in Huangbanjigou, Chaomidian Village, Beipiao City, Liaoning Province, China. A key to the species of the genus Anthoscytina Hong, 1983 is provided. The diagnosis of the genus is revised.

    • New specimens of Stenocybus acidentatus (Therapsida: Dinocephalia) from the Middle Permian Dashankou Fauna of China

      2014, 88(3):730-737.

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      Abstract:The basal dinocephalian clade Stenocybusidae was known from two incomplete specimens representing one generus, Stenocybus, from Dashankou fanua in Yumen, Gansu Province of China. The holotype of Stenocybus acidentatus is laterally compressed, making some characters unclear. Here we describe two new specimens of Stenocybus acidentatus from the same locality, an anterior portion of skull with articulated jaws, and a right dentary with nearly complete dentition. They show some detailed features on the morphology of the premaxilla, maxilla, nasal, external nares and dentary. The phylogenetic relationship between Stenocybus acidentatus and the relatively large Sinophoneus yumenensis is still difficult to determine, and needs more new complete material and further evidences.

    • Quercus yangyiensis sp. nov. from the Late Pliocene of Baoshan, Yunnan and Its Paleoclimatic Significance

      2014, 88(3):738-747.

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      Abstract:A new Quercus (Fagaceae) morphospecies is described based on well-preserved fossil leaves. The fossils were collected from Yangyi Formation of the Upper Pliocene at the Yangyi coal-mine, Baoshan, western Yunnan, China. Details of the microstructure of mesophyll tissue are preserved because lithification of the fossils was not complete. The fossil laminas possess typical characteristics of Quercus sect. Heterobalanus: quite thick and coriaceous cuticle; secondary veins bifurcating near the margin in the middle and top of the leaf; and upper epidermis with adaxial hypodermis. Based on a detailed morphological and anatomical comparison with all living and fossil species of Quercus sect. Heterobalanus, the fossil leaves prove to be different in their sparse and garland-shaped multicellular trichomes on the lower epidermis, and so it is described as a new species Quercus yangyiensis He, Li et Sun sp. nov. The much sparser trichomes of our fossils compare well with those of living Quercus sect. Heterobalanus and indicate a more humid climate during the deposition of the Yangyi Formation in the Late Pliocene.

    • Hydroxycalciopyrochlore, A New Mineral Species from Sichuan, China

      2014, 88(3):748-753.

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      Abstract:Hydroxycalciopyrochlore, ideally (Ca,Na,U,□)2(Nb,Ti)2O6(OH), cubic, is a new mineral species (IMA2011-026) within the pyrochlore supergroup that was found occurring at the Maoniuping mine, Mianning County, Xichang prefecture, Sichuan Province, southwest China. The mineral is found in an alkali feldspar granite rare-earth ore deposit (26–27 Ma). Associated minerals include calcite, barite, celestine, albite, aegirine, aegirine-augite, fluorite, parasite-(Ce), thorite, thorianite, zircon, galena, sphalerite, magnetite, and pyrite. Crystals occur mostly as octahedra, and less often as dodecahedra and tetrahexahedra or combinations thereof. Some occur with an allotriomorphic habit with a thick triangular tabular form. Crystals generally range from 0.1 to 1 mm in size. The mineral is brownish-black, greenish-black and black on fresh sections with a brown streak. The crystal is translucent, and has a greasy lustre on fresh sections. It is metamict without any observed parting or cleavage and with a conchoidal fracture. The Vickers microhardness is 572 kg/mm2 (5–6 on the Mohs hardness scale). The density measured by hydrostatic weighing is 5.10(3) g/cm3. The strongest four reflections in the X-ray powder-diffraction pattern [d in ? (I) hkl] are: 2.9657 (100) 2 2 2, 1.8142 (34) 0 4 4, 1.5463 (21) 2 2 6, 2.5688 (18) 0 0 4. The unit-cell parameters are a = 10.381(4) ?, V = 1118.7(7) ?3, Z = 8. The structure was solved and refined in the space group Fd3m with R = 0.09. The empirical formula is (Ca0.74Na0.58U0.40Ce0.05Fe0.02□0.21)2.00(Nb1.15Ti0.80Ta0.03Al0.01Mg0.01)2.00O6.02 [(OH)1.01F0.09]1.10, on the basis of 2 atoms of B pfu; the simplified formula is (Ca,Na,U,□)2(Nb,Ti)2O6(OH). Type material is deposited in the Geological Museum of China, Beijing, People’s Republic of China, catalogue number M11800.

    • Petrogenesis of Kejie Granite in the Northern Changning-Menglian Zone, Western Yunnan: Constraints from Zircon U-Pb Geochronology, Geochemistry and Hf Isotope

      2014, 88(3):754-765.

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      Abstract:The Kejie pluton is located in the north of the Changning-Menglian suture zone. The rock types are mainly biotite-granite. Zircon LA-ICP-MS U-Pb dating indicates that the Kejie pluton emplaced at about 80–77 Ma, Late Cretaceous. The Kejie pluton samples are characterized by high SiO2 (71.68%–72.47%), K2O (4.73%–5.54%), total alkali (K2O + Na2O = 8.21%–8.53%), K2O/Na2O ratios (1.36–1.94) and low P2O5 (0.13%–0.17%), with A/CNK of 1.025–1.055; enriched in U, Th, and K, depleted in Ba, Nb, Sr, Ti, P and Eu. They are highly fractionated, slightly peraluminous I-type granite. The two samples of the Kejie pluton give a large variation of εHf(t) values (?5.04 to 1.96) and Hf isotope crustal model ages of 1.16–1.5 Ga. Zircon Hf isotopes and zircon saturation temperatures of whole-rock (801°C–823°C) show that the mantle-derived materials maybe have played a vital role in the generation of the Kejie pluton. The Kejie pluton was most likely generated in a setting associated with the eastward subduction of the neo-Tethys ocean, where intrusion of mantle wedge basaltic magmas in the crust caused the anatexis of the latter, forming hybrid melts, which subsequently experienced high-degree fractional crystallization.

    • Zircon U-Pb age, Lu-Hf Isotopic Characteristics and Origin of the Banshanping Granitoid Rocks in East Qinling Orogenic Belt

      2014, 88(3):766-779.

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      Abstract:The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt. It is a diorite-quartz diorite-granodiorite-granite series, spreading in a NW-SE direction, and intrudes into the Erlangping Group. The SiO2 content ranges from 57.04% to 76.56%, Na2O from 2.05% to 4.65%, K2O from 0.84% to 3.40%. Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids. SREE ranges from 36.51 ppm to 473.25 ppm, and LREE/HREE ratios lie between 3.95 and 22.18. Negative Eu anomalies are not obvious in most samples, though there are obvious Nb, P and Ti positive anomalies. The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma–486.9±9.3 Ma. Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876, εHf(t) values from 8.5 to 14, all positive, and corresponding modal ages (TDM2) range from 559 Ma to 908 Ma. Based on Hf isotope characteristics and existing Sm-Nd and Rb-Sr isotope data, we consider that the Banshanping granitoid rocks originate from mantle-derived material, i.e. the igneous rocks that formed in Neoproterozoic, and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.

    • Geochronology and Geochemistry of the Tinggong Porphyry Copper Ore Deposit, Tibet

      2014, 88(3):780-800.

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      Abstract:We have determined the ages of the ore-bearing Tinggong porphyries and the Eocene granites using the LA-ICPMS zircon U-Pb method. Zircons from one adamellite porphyry and two diorite porphyries yield ages of 15.54±0.28 Ma, 15.02±0.25 Ma and 14.74±0.22 Ma, respectively. The ages of two granites are 50.48±0.71 Ma and 50.16±0.48 Ma. Light Rare Earth Elements (LREE) are enriched in the ore-bearing adamellite porphyries, which are high-K calc-alkaline and metaluminous, while Heavy Rare Earth Elements (HREE) and Y are strongly depleted, indicating an adakitic affinity. The Large Ion Lithophile Elements (LILE) of the adamellite porphyries are highly enriched, whereas some High Field Strength Elements (HFSE) are depleted. The diorite porphyry in this study is chemically similar to the adamellite porphyries, except that the Mg# of the diorite porphyry is a little higher, demonstrating more mantle contamination. Four samples from different rocks are selected for in situ zircon Hf isotopic analyses. The samples show positive ?Hf(t) values and young Hf model ages, indicating their derivation from juvenile crust. However, the adamellite porphyry and diorite porphyry formed in the Miocene exhibit more heterogeneous Hf isotopic ratios, with lower ?Hf(t) values than the granites formed in the Eocene, suggesting the involvement of old Indian continent crust in their petrogenesis. The geochronology and geochemistry of the adamellite porphyries and the diorite porphyries indicate that they formed from the same source region in a post-collisional environment, but contaminated by crust and mantle materials in different ratios. The metallic minerals formed mainly during the older adamellite porphyry stage, but they were recycled and reactivated by the diorite porphyry intrusion.

    • The Kiloton Class Jiaojia Gold Deposit in Eastern Shandong Province and Its Genesis

      2014, 88(3):801-824.

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      Abstract:The recent deep prospecting results in the Jiaojia area of Eastern Shandong Province indicate that the Jiaojia ore field composed of several individual gold deposits as previously suggested is actually an ultra-large gold deposit. This deposit covers an area of ~40 km2, and shows a structural control by the Jiaojia fault and its secondary faults. Gold orebodies generally occur along the same mineralization-alteration belt, and the main orebodies intersect with each other or exhibit a parallel or overlapping distribution. This deposit’s reserves are estimated to be 1, 200t of gold, being the first gold deposit of more than 1000t gold reserves in China. The No. I-1 orebody in the Shaling-deep Sizhuang ore blocks holds gold reserves greater than 350 t, or 29 percent of the total reserves, followed by the No. I orebody in Matang-Jiaojia ore blocks with exceeding 150t gold reserves. This deposit mainly occurs in the footwall of the Jiaojia fault, and presents zoned patterns in mineralization, alteration and structures. The strongly mineralized zones agree with strongly altered and tectonically fractured zones. These orebodies display strataform-like, veinlike or lenticular shapes, and generally show characteristics of pinching out and reappearing, branching and converging, expanding and shrinking. The orebodies commonly occur along positions where the fault strike changes and in gentle locations with dips changing from steep to gentle. The main orebodies are parallel to the main plane of the ore-controlling fault, and tend to be gentle from the surface to the deep. The orebodies mainly plunge to the southwest, with plunge angle of 45°–60°. Orebodies near the main plane of the ore-controlling fault have more gold resource than those away from main fault zone. The slant depth of orebodies is generally larger than the length along its strike direction; orebodies become thick and gold grades become low from the shallow area to the deep area. Ore-forming fluids are H2O-CO2-NaCl±CH4 type with medium-temperature and moderate to low salinity. Sulfur isotopic values (δ34SCDT) for gold ores range between 11.08‰ and 12.58‰, indicating mixed sulfur sources; hydrogen isotopic values (δDV-SMOW) range from ?83.68‰ to ?116.95‰ and oxygen isotopic values (δ18OV-SMOW) range between 12.04‰ and 16.28‰. The hydrogen and oxygen isotopes suggest that ore-forming fluids originated from primary magma, and mixing with a large amount of atmospheric water during the late stage. The Eastern Shandong Province gold deposits are associated with magmatic activities which have mantle-crust-mixed source, and also share some similarities with orgenic and epithermal hydrothermal gold deposits. Because Eastern Shandong Province gold deposits with unique metallogenic features and formation setting which are different from other gold deposit types in the world, we call it the Jiaojia-type gold deposits. The kiloton class Jiaojia gold deposit is related to fluid activities, extension and detachment resulted from thermal upwelling of magmas. The strong magmatic activities in the middle to late stage of early Cretaceous in Eastern Shandong Province lead to active fluids, and provided abundant ore-forming materials for gold depsoits. Moreover, many extensional structures resulting from crustal extension provided favourable space for orebody positioning.

    • Mineralization Styles and Genesis of the Yinkeng Au-Ag-Pb-Zn-Cu-Mn Polymetallic Orefield, Southern Jiangxi Province, SE China: Evidence from Geology, Fluid Inclusions, Isotopes and Chronology

      2014, 88(3):825-844.

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      Abstract:The Yinkeng orefield in Yudu County, Jiangxi Province, SE China, is a zone of concentrated Au-Ag -Pb-Zn-Cu-Mn polymetallic ores. Based on summing up basic geology and ore geology of the orefield, the polymetallic deposits in the orefield have been divided into seven major substyles according to their occurring positions and control factors. The ore-forming fluid inclusion styles in the orefield include those of two-phase fluid, liquid CO2-bearing three-phase and daughter mineral-bearing multi-phase. The homogenization temperatures range from 382o to 122oC, falling into five clusters of 370o to 390o, 300o to 360o, 230o to 300o, 210o to 290o and 120o to 200o, and the clusters of 300o to 360o, 230o to 300o and 120o to 200o are three major mineralization stages, with fluid salinity peaks from 4.14% to 7.31%, 2.07% to 7.31% and 0.53% to 3.90%, respectively. The ore-forming fluids are mainly type of NaCl-H2O with medium to high density (0.74–1.02 g/cm3), or CO2-bearing NaCl-H2O with medium to low density (0.18–0.79 g/cm3). The fluid salinity and density both show a decline tendency with decreasing temperature. According to the measurement and calculation of H- and O-isotopic compositions in the quartz of the quartz-sulfide veins, δDV-SMOW of the ore-forming fluid is from ?84‰ to ?54‰, and δ18OV-SMOW of that is from 6.75‰ to 9.21‰, indicating a magmatic fluid. The δ34SV-CDT of sulfides in the ores fall into two groups, one is from ?4.4‰ to 2.2‰ with average of ?1.42‰, and the other from 18.8‰ to 21.6‰ with average of 19.8‰. The S-isotopic data shows one peak at ?4.4‰ to 2.2‰ (meaning ?1.42‰) suggesting a simple magmatic sulfur source. The ore Pb-isotopic ratios are 206Pb/204Pb from 17.817 to 17.983, 207Pb/204Pb from 15.470 to 15.620 and 208Pb/204Pb from 38.072 to 38.481, indicating characteristics of mantle-derived lead. The data show that the major ore deposits in the orefield have a magmatic-hydrothermal genesis and that the SHRIMP zircon age of the granodiorite porphyry, closely related to the mineralization, is 151.2±4.2 Ma (MSWD = 1.3), which can represent the formation ages of the ores and intrusion rocks. The study aids understanding of the ore-forming processes of the major metallic ore deposits in the orefield.

    • Hydrothermal H?gbomite Associated with Vanadiferous-Titaniferous (V-Ti) Bearing Magnetite Bands in Bhakatarhalli Chromite Mine, Nuggihalli Greenstone Belt, Western Dharwar Craton, Karnataka, India

      2014, 88(3):845-853.

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      Abstract:H?gbomite, a rare exotic mineral, is found to be associated with the vanadiferous–titaniferous (V-Ti) bearing magnetite bands at Bhakatarhalli, Nuggihalli greenstone belt, western Dharwar Craton, India. We report on a second occurrence of h?gbomite from the Dharwar craton in Karnataka, which is the sixth documented occurrence of this mineral from India. We evaluate the chemical characteristics of h?gbomite and associated Fe-Ti-minerals in an attempt to identify its formation as a primary hydrothermal mineral in a metamorphosed magnetite layer.We report here the presence of h?gbomite as a complex oxide of Fe, Mg, Al and Ti with accessory of Zn, V and Sn. Petrographic studies suggest the (V–Ti) bearing magnetite (Mt) contain spinel, h?gbomite, chlorite, martite, ilmenite (Il) and minor amounts of diaspore. The h?gbomite displays euhedral to subhedral textures, and is up to 250 μm along the grain boundaries of magnetite and ilmenite. In the samples studied, h?gbomite is prismatic, irregular and elongated in shape. The genesis of h?gbomite in veins between magnetite and ilmenite implies its precipitation from fluids without involving complicated reactions. Several models were proposed for the formation of h?gbomite; however, the subject is still debatable.

    • Application of Hydrothermal Diamond Anvil Cell to Homogenization Experiments of Silicate Melt Inclusions

      2014, 88(3):854-864.

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      Abstract:The homogenization of silicate melt inclusions (SMIs), small droplets of silicate melt trapped in magmatic minerals, is an important component of petrogenetic and magmatic research. Conventional homogenization experiments on SMIs use microscope-mounted heating stages capable of producing high temperatures at 1 atm and cold-seal high-pressure vessels. Heating stages are generally used for SMIs with low internal pressures and allow in situ observations of the homogenization processes. In contrast, cold-seal high-pressure vessels are generally used to heat SMIs that have high internal pressures, although the homogenized SMIs can only be observed after quenching in this approach. Here we outline an alternative approach that uses a hydrothermal diamond anvil cell (HDAC) apparatus to homogenize SMIs. This is the only current method wherein phase changes in high-internal-pressure SMIs can be observed in situ during homogenization experiments, which represents an advantage over other conventional methods. Using an HDAC apparatus prevents high-internal-pressure SMIs from decrepitating during heating by elevating their external pressure, in addition to allowing in situ observations of SMIs. The type-V HDAC that is currently being used has a shorter distance between the sample chamber and the observation window than earlier types, potentially enabling continuous observation of the processes involved in heating and SMI homogenization through an objective lens with a long working distance. Homogenization experiments using HDAC require that a number of steps, including HDAC preparation, sample preparation, sample loading, preheating, and formal heating, be carefully followed. Homogenization experiments on SMIs within granite samples from the Jiajika pegmatite deposit (Sichuan, China) are best performed using an HDAC-based approach, because the elevated proper external pressure of these SMIs, combined with a short heating duration, helps to suppress material leakage and any reactions within the SMIs, in addition to allowing in situ observations during homogenization experiments. Furthermore, using the HDAC approach has other benefits: heating rates can be precisely controlled, wafer oxidization can be prevented, and samples can be subjected to in situ microbeam analysis. In summary, homogenization using HDAC provides more reliable results than those obtained using conventional heating equipment. Future developments will include improvements to the quenching method and temperature controls for the HDAC apparatus, thereby improving the utility of this approach for SMI homogenization experiments.

    • Structure and Fluid Transportation Performance of Faults in the Changxing-Feixianguan Formation, Xuanhan County, Northeastern Sichuan Basin

      2014, 88(3):865-877.

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      Abstract:On the basis of field observations, microscopic thin-sections and laboratory data analysis of ten faults in Xuanhan County area, northeastern Sichuan Basin, central China, the internal and megascopic structures and tectonite development characteristics are mainly controlled by the geomechanical quality in brittle formation of the Changxing-Feixianguan Formation. The fluid transportation performance difference between the faults formed by different geomechanics or different structural parts of the same fault are controlled by the megascopic structure and tectonite development characteristics. For instance, the extension fault structure consists of a tectonite breccia zone and an extension fracture zone. Good fluid transportation performance zones are the extension fracture zone adjacent to the tectonite breccia zone and the breccia zone formed at the early evolutionary stage. The typical compression fault structure consists of a boulder-clay zone or zones of grinding gravel rock, compression foliation, tectonite lens, and dense fracture development. The dense fracture development zone is the best fluid transporting area at a certain scale of the compression fault, and then the lens, grinding gravel rock zone and compression foliation zones are the worst areas for hydrocarbon migration. The typical tensor-shear fault with a certain scale can be divided into boulder-clay or grinding gravel rock zones of the fault, as well as a pinnate fractures zone and a derivative fractures zone. The grinding gravel rock zone is the worst one for fluid transportation. Because of the fracture mesh connectivity and better penetration ability, the pinnate fractures zone provides the dominant pathway for hydrocarbon vertical migration along the tensor-shear fault.

    • Hydrocarbon Accumulation Process in the Marine Strata in Jianghan Plain Area, Middle China

      2014, 88(3):878-893.

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      Abstract:Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z–?2, ?2–O, S, D–C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle–late period of the Early Yanshanian. In the Lower Triassic–Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area’s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.

    • Effects of Lateral Variation in Vegetation and Basin ‘Dome’ Shape on Tropical Lowland Peat Stabilisation in the Kota Samarahan-Asajaya Area, West Sarawak, Malaysia

      2014, 88(3):894-914.

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      Abstract:Field surveys indicate lateral variation in peat humification levels (von Post) in dominantly occurring fibric, fibric to hemic, sapric and hemic to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes. Cement-peat stabilisation can be enhanced by adding mineral soil fillers (silt, clays and fine sands) obtained from Quaternary floodplain deposits and residual soil (weathered schist). The unconfined compressive strength (UCS) of the stabilised cement-mineral soil filler-peat mix increases with the increased addition of selected mineral soil filler. Lateral variation in the stabilised peat strength (UCS) in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome. The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages (due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome).

    • Present Geothermal Fields of the Dongpu Sag in the Bohai Bay Basin

      2014, 88(3):915-930.

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      Abstract:The Dongpu sag is located in the south of the Bohai Bay basin, China, and has abundant oil and gas reserves. To date, there has been no systematic documentation of its geothermal fields. This study measured the rock thermal conductivity of 324 cores from 47 wells, and calculated rock thermal conductivity for different formations. The geothermal gradient and terrestrial heat flow were calculated for 192 wells on basis of 892 formation-testing data from 523 wells. The results show that the Dongpu sag is characterized by a medium-temperature geothermal field between stable and active tectonic areas, with an average geothermal gradient of 32.0°C/km and terrestrial heat flow of 65.6 mW/m2. The geothermal fields in the Dongpu sag is significantly controlled by the Changyuan, Yellow River, and Lanliao basement faults. They developed in the Paleogene and the Dongying movement occurred at the Dongying Formation depositional period. The geothermal fields distribution has a similar characteristic to the tectonic framework of the Dongpu sag, namely two subsags, one uplift, one steep slope and one gentle slope. The oil and gas distribution is closely associated with the present geothermal fields. The work may provide constraints for reconstructing the thermal history and modeling source rock maturation evolution in the Dongpu sag.

    • Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member (Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

      2014, 88(3):931-948.

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      Abstract:The Asmari Formation deposited in the Zagros foreland basin during the Oligocene-Miocene. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite, argillaceous limestone, some anhydrite (Kalhur Member) and sandstones (Ahwaz Member). This study is based on the analysis of core samples from four subsurface sections (wells Mn-68, Mn-281, Mn-292 and Mn-312) in the Marun Oil?eld in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member. Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz, 1.6% feldspar, and 0.9% rock fragments and all samples are classified as quartz arenites. The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies.Petrographic analysis reveals that mono- and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting. As indicated by the CIW′ index (chemical index of weathering) of the Ahwaz Sandstone (average value of 82) their source area underwent “intense” recycling but “moderate to high” degree of chemical weathering. The petrography and geochemistry results are consistent with a tropical, humid climate and low-relief highlands.

    • Cenozoic Evolution of Sediments and Climate Change and Response to Tectonic Uplift of the Northeastern Tibetan Plateau

      2014, 88(3):949-962.

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      Abstract:Through a comprehensive study of magnetostratigraphy and sedimentology of several basins in the northeastern Tibetan Plateau, we reveal that the study area mainly experienced six tectonic uplift stages at approximately 52 Ma, 34–30 Ma, 24–20 Ma, 16–12 Ma, 8–6 Ma, and 3.6–2.6 Ma. Comprehensive analyses of pollen assemblages from the Qaidam, Linxia, Xining, and West Jiuquan Basins show that the northeastern Tibetan Plateau has undergone six major changes in vegetation types and climate: 50–40 Ma for the warm-humid forest vegetation, 40–23 Ma for the warm-arid and temperate-arid forest steppe vegetation, 23–18.6 Ma for the warm-humid and temperate-humid forest vegetation, 18.6–8.5 Ma for the warm-humid and cool-humid forest steppe vegetation, 8.6–5 Ma for the temperate sub-humid savanna steppe vegetation, and 5–1.8 Ma for the cold-arid steppe vegetation. Comprehensive comparisons of tectonic uplift events inferred from sedimentary records, climatic changes inferred from pollen, and global climate changes show that in the northeastern Tibetan Plateau the climate in the Paleogene at low altitude was mainly controlled by the global climate change, while that in the Neogene interval with high altitude landscapes of mountains and basins is more controlled by altitude and morphology.

    • Geochemical Characteristics of Eolian Deposits on the Eastern Margin of the Tibetan Plateau and Implications for Provenance

      2014, 88(3):963-973.

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      Abstract:Eolian dust deposition is intimately related to atmospheric circulation and environmental setting of the source region, and therefore is an invaluable tool for studying the evolutionary history of atmospheric circulation patterns and paleoclimatic change. Identifying the provenance of any eolian deposit is crucial not only for reconstructing the paleoenvironmental history of the dust source region, but also for understanding the paleoclimatic significance of various indices. Loess and paleosol samples from the Garze region on the eastern margin of the Tibetan Plateau (TP) were analyzed for their elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with those of Northern Chinese (NC) loess formed at the same age. The results show that the geochemical compositions of the Garze loess and paleosol samples are similar to those eolian deposits on the Chinese Loess Plateau (CLP), and also resemble the average UCC. This indicates that the eolian deposits on the eastern margin of the TP were derived from well-mixed sedimentary protoliths that had undergone numerous upper crustal recycling processes, just as with the CLP loess deposits. However, compared with NC loess, the Garze samples have higher ∑REE, Li, Rb, Zr, Cs, Hf and Bi concentrations, higher TiO2/Al2O3, Hf/Nb, La/Nb, Th/Nb and lower K2O/TiO2, Zr/Hf, Ba/Rb ratios. From the Sm-Nd isotopic geochemistry, εNd(0) and 147Sm/144Nd values of Garze loess and paleosol samples are clearly lower than the NC loess. The higher Bi, Zr and Hf concentrations are relevant to the widely distributed acid-magmatic rocks in this region, whereas the higher contents of Li, Cs, Rb are attributed to the high background values of the TP. The geochemical characteristics of the Garze loess and paleosol samples further prove that the local glacial and other Quaternary detrital sediments are predominantly the contributors for the eolian deposits on the eastern margin of the TP. Stable element concentrations and their ratios in the Garze loess and paleosol samples formed at different times have relatively greater variation ranges in comparison with the NC loess, indicating that the source regions for eolian deposits have been unstable since the late Early Pleistocene. We attribute the instability of dust sources to variable earth surface conditions and the changeable TP winter monsoon in direction and intensity, which are in turn related to the uplift of the TP.

    • Spatiotemporal Changes of Vegetation Cover in Response to Climate Change on the Tibetan Plateau

      2014, 88(3):974-983.

      Abstract (847) HTML (0) PDF 10.02 M (1153) Comment (0) Favorites

      Abstract:The Tibetan Plateau is one of the most important ecological barriers in China. Resolving the internal relations and dynamics ruling the association between regional vegetation and climate change is important to understand and protect the regional ecosystems. Based on vegetation, temperature and precipitation data of the Tibetan Plateau from 2001 to 2010, we analyze the spatial and temporal variations of vegetation cover over the past 10 years and discuss the vegetation response to climate change using empirical orthogonal function and singular value decomposition. Our results reveal the following: (1) vegetation cover gradually decreases from the southeast to the northwest of the Tibetan Plateau; (2) vegetation cover has increased on the Tibetan Plateau over the past 10 years, mainly in the central and eastern zones; and (3) a significant positive relationship was suggested between vegetation cover during growing season and the temperature in the entire region and with precipitation in the central and southern zones.

    • Arsenic Distribution Pattern in Different Sources of Drinking Water and their Geological Background in Guanzhong Basin, Shaanxi, China

      2014, 88(3):984-994.

      Abstract (916) HTML (0) PDF 13.07 M (1092) Comment (0) Favorites

      Abstract:To study arsenic (As) content and distribution patterns as well as the genesis of different kinds of water, especially the different sources of drinking water in Guanzhong Basin, Shaanxi province, China, 139 water samples were collected at 62 sampling points from wells of different depths, from hot springs, and rivers. The As content of these samples was measured by the intermittent flow-hydride generation atomic fluorescence spectrometry method (HG-AFS). The As concentrations in the drinking water in Guanzhong Basin vary greatly (0.00–68.08 μg/L), and the As concentration of groundwater in southern Guanzhong Basin is different from that in the northern Guanzhong Basin. Even within the same location in southern Guanzhong Basin, the As concentrations at different depths vary greatly. As concentration of groundwater from the shallow wells (<50 m deep, 0.56–3.87 μg/L) is much lower than from deep wells (110–360 m deep, 19.34–62.91 μg/L), whereas As concentration in water of any depth in northern Guanzhong Basin is <10 μg/L. Southern Guanzhong Basin is a newly discovered high-As groundwater area in China. The high-As groundwater is mainly distributed in areas between the Qinling Mountains and Weihe River; it has only been found at depths ranging from 110 to 360 m in confined aquifers, which store water in the Lishi and Wucheng Loess (Lower and Middle Pleistocene) in the southern Guanzhong Basin. As concentration of hot spring water is 6.47–11.94 μg/L; that of geothermal water between 1000 and 1500 m deep is 43.68–68.08 μg/L. The high-As well water at depths from 110 to 360 m in southern Guanzhong Basin has a very low fluorine (F) value, which is generally <0.10 mg/L. Otherwise, the hot springs of Lintong and Tangyu and the geothermal water in southern Guanzhong Basin have very high F values (8.07–14.96 mg/L). The results indicate that high-As groundwater in depths from 110 to 360 m is unlikely to have a direct relationship with the geothermal water in the same area. As concentration of all reservoirs and rivers (both contaminated and uncontaminated) in the Guanzhong Basin is <10 μg/L. This shows that pollution in the surface water is not the source of the high-As in the southern Guanzhong Basin. The partition boundaries of the high- and low-As groundwater area corresponds to the partition boundaries of the tectonic units in the Guanzhong Basin. This probably indicates that the high-As groundwater areas can be correlated to their geological underpinning and structural framework. In southern Guanzhong Basin, the main sources of drinking water for villages and small towns today are wells between 110–360 m deep. All of their As contents exceed the limit of the Chinese National Standard and the International Standard (>10 μg/L) and so local residents should use other sources of clean water that are <50 m deep, instead of deep groundwater (110 to 360 m) for their drinking water supply.

    • A Microscopic and Nanoscale Understanding of the Formation of Gold Geochemical Provinces

      2014, 88(3):995-1003.

      Abstract (917) HTML (0) PDF 7.36 M (1377) Comment (0) Favorites

      Abstract:Gold geochemical provinces in China were delineated through stream sediment or catchment sediment sampling in this study. Each gold geochemical province delineated by a threshold value of 2.5 ng/g covers an area of thousands of kilometers. It is a dilemma that geochemists traditionally thought that gold could not migrate for a long distance in rivers or streams to form a large-scale geochemical anomaly due to its chemical inertness and high specific density. The quantitative spectroscopic analysis and observations under a scanning electron microscope (SEM) indicate the presence of submicroscopic gold particles (<5 μm in diameter) in large quantities, and observations under a Transmission Electron Microscopy (TEM) further suggest the presence of nanoscale gold particles (several tens of nanometre in diameter) in ores, rocks, soils and stream sediments. Particularly, submicroscopic and nanoscale gold particles less than 5 μm were only found in samples having a low gold content (<10ng/g). This result shows that geochemical provinces, delineated by a threshold value of 2.5 ng/g, are formed by long-distance transport of ultrafine gold in streams. The findings may provide direct microscopic evidence for gold migration to form geochemical provinces.

    • Surface Expressions of Rayleigh-Taylor Instability in Continental Interiors

      2014, 88(3):1004-1016.

      Abstract (857) HTML (0) PDF 14.88 M (1555) Comment (0) Favorites

      Abstract:Two-dimensional thermal-mechanical numerical models show that Rayleigh-Taylor-type (RT) gravitational removal of high-density lithosphere may produce significant surface deformation (vertical deflection >1000 m) in the interior of a continental plate. A reasonable range of crustal strengths and thicknesses, representing a variation from a stable continental interior to a hot orogen with a thick crust, is examined to study crustal deformation and the surface deflection in response to an RT instability. In general, three types of surface deflection are observed during the RT drip event: (1) subsidence and negative topography; (2) uplift and positive topography; (3) subsidence followed by uplift and inverted topography. One key factor that determines the surface expression is the crustal thickness. Models with a thin crust mainly show subsidence and develop a basin. In the thick crust models, surface expressions are more variable, depending on the crustal strength and depth of high-density anomaly. With weak crust and a deep high-density anomaly, the RT drip is decoupled from the overlying crust, and the surface exhibits uplift or little deflection, as the RT drip induces contraction and thickening of the overlying crust. In contrast, with a strong crust and shallow anomaly, the surface is more strongly coupled with the drip and undergoes subsidence, followed by uplift.

    • Status of China’s Land Resources in 2013

      2014, 88(3):1017-1018.

      Abstract (911) HTML (0) PDF 1.83 M (1486) Comment (0) Favorites

      Abstract:

    • Status of China’s Mineral Resources in 2013

      2014, 88(3):1018-1019.

      Abstract (910) HTML (0) PDF 1.85 M (1449) Comment (0) Favorites

      Abstract:

    • Status of China’s Geological Survey and Geological Environments in 2013

      2014, 88(3):1020-2021.

      Abstract (917) HTML (0) PDF 2.59 M (1176) Comment (0) Favorites

      Abstract:

Chief Editor:HOU Zengqian

Governing Body:China Association for Science and Technology

Organizer:Geological Society of China

start publication :1922

ISSN:ISSN 1000-9515

CN:CN 11-2001/P

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