Table of Content

20 March 2014, Volume 20 Issue 1

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Magma-dynamic Evidence for Indosinian Emplacement and Tectonic Implication of the Early Yanshanian Granite Batholiths, South China: Based on Estimates of Emplacement Age for the 8 Granite Batholiths in Nanling Range

ZHANG Bangtong, WU Junqi, LING Hongfei, CHEN Peirong

2014, 20(1):  1. 

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Based on the geological-tectonic features,the related thermophysical parameters and the radioactive element concentrations for each granite batholith, the simplified cubic mathematic model calculation results suggest that the cooling time from initilal temperature to crystallization temperature (Δtcol) for the 8 Early Yanshanian batholiths in Nanling (NR) Rang were 3.9 Ma(Jingjiling batholith)~5.5 Ma (Jiufeng batholith), the prolongation time caused by latent heat generated from crystallization (ΔtL) were 2.6 ~3.5 Ma and the prolongation time caused by radiogenic heat from decay of the radioactive elements (ΔtA) were 5.2 Ma (Pitou batholith)~45.1 Ma (Guposhan batholith). The time difference elapsed from the magma emplacement to the crystallization (△tECTD) were12.1 Ma (Pitou batholith)~52.2 Ma (Guposhan batholith)for the 8 Early Yanshanian batholiths in Nanling Rang and in combination with the zircon U-Pb ages of these granitoids and inversion calculation, the emplacement ages were 194.4 Ma (Pitou batholith)~219.3 Ma (Jiufeng batholith). These data provide important magma-dynamic evidence for the Indosinian emplacement of the Early Yanshanian batholiths in Nanling Rang and display the double magmatic-tectonic features in NR i.e., the E-W trending Indosinian tectonic framework( represented by t E ) and the Early Yanshan granite batholiths(represented by t C).

Petrogenesis of Ophiolite-type Chromite Deposits in China and Some New Perspectives

HU Zhenxing, NIU Yaoling, LIU Yi, ZHANG Guorui, SUN Wenli, MA Yuxin

2014, 20(1):  9. 

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Ophiolites of varying ages are widespread in China, some of which contain chromite deposites of industrial value. However, compared with some of the world’s large ophiolite chromite deposites (e.g., Kempirsai, Bulquiza, Guleman), the Chinese chromite deposits are small (e.g., Sartohay, Dongqiao, Luobusa). Recent research recognizes that most ophiolites with significant chromite reserves are all formed in a surpasubduction zone environment. Melt-rock interaction is a popular interpretation for the origin of podiform chromite deposits, but the actual mechanism in this model for chromite enrichment remains unclear. It remains the primary task to understand process or processes of chromium enrichment towards the formation of chromite deposits. Is the formation of chromium-rich melts necessary? If so, when, where, how, and under what conditions could this take place? These are additional processes beyond the well-understood aspects of the petrogenesis that need to research towards an effective chromite mineralization model.

Sulfur Isotope Geochemistry of the Lala IOCG Deposit in Sichuan Province

ZHU Zhimin, LI Tingxue, CHEN Liang, TAN Hongqi, LIU Yingdong

2014, 20(1):  28. 

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The source of sulfur is vital to understand the ore-forming process and genesis of IOCG deposits. We summarize the data of sulfur isotope from the Lala deposit in Sichuan Province, and discuss sulfur isotope compositions of sulfide and their sources on the basis of geologic and ore microscopic studies. The large variability in sulfur isotope indicates that the ore-forming sulfur was multi-sourced. The δ34S value of pyrite ranges from -1.4‰ to 4.9‰ with a mean value of 1.8‰ and the δ34S value of chalcopyrite ranges from -5.9‰ to 9‰ with a mean value of 1.5‰. Together with sulfide formation analysis and comparison with some type IOCG deposits worldwide, these data demonstrate that sulfur from seawater evaporate is important to precipitation of pyrite and chalcopyrite. But there is no evidence to support that the variation of sulfur isotope composition is reduced during metamorphism in the Lala deposit.

The Fluid Inclusions Study on Zhilingtou Molybdenum Deposit in Southwest Zhejiang Province

ZHAO Chao, NI Pei, WANG Guoguang, CHEN Hui, CAI Yitao

2014, 20(1):  38. 

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Since pyrite was found in the Zhilingtou deposit, Zhejiang Province in the mid-20th century, lead-zinc and gold-silver ore-bodies have been discovered as well. In recent years, a porphyry molybdenum deposit has been found beneath the gold- silver orebodies in Zhilingtou area. Molybdenum ore bodies mainly occur in the Badu Group in the outer contact zone of the granite porphyry. Similarly with the typical porphyry-type alteration zoning, the alteration types from molybdenum ore body to wall rock is from potassium-biotitization through beresitization to chloritization-carbonation. Ore fluids can be divided into early mineralization stage, the main mineralization stage, and the late mineralization stage. Fluid inclusions in the early mineralization stage are mainly Ia type ones with the homogenization temperatures from 354 to 442 °C and salinities from 12.3 to 19.4 wt% NaCl. Fluid inclusions in the mineralization stage include type II and III. The homogenization temperatures of type II range from 329 to 406 °C and the salinities vary between 3.5 and 6.2 wt% NaCl; the homogenization temperatures of type III range from 305 to 375 °C and the salinities vary between 30.6 and 45.8 wt% NaCl. Fluid inclusions in late mineralization stage belong to type Ib with the homogenization temperatures from 187 to 285 °C and the salinities from 3.5 to 8.4 wt% NaCl. Fluid boiling processes played an important role in metal precipitation of the Zhilingtou molybdenum deposit. The Raman spectra show that ore fluids are H2O-NaCl fluids. The hydrogen-oxygen isotopes data show that mineralizing fluids were magmatic fluids during the early and main mineralization stages and meteoric water was added in the late stage.

Identification of the Complete Cu-S Series Minerals from the Zijinshan Cu-Au Deposit, Fujian Province

HUANG Hongxiang, WANG Shaohuai, CHI Changyan

2014, 20(1):  50. 

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This paper presents a new study of the complete Cu-S minerals from the Zijinshan Cu-Au deposit, based on electron- microprobe and X-ray diffraction analyses. All copper sulfide minerals present in the Cu-S series were identified here, including covellite, yarrowite, spionkopite, geerite, anilite, digenite, djurleite, and chalcocite. The cell parameters of covellite, anilite, digenite, djurleite, and chalcocite were calculated using the X-ray diffraction data. The sequence of crystallization and phase variations of the Cu-S minerals exposed in this deposit are established according to their systemic mineralogical study for the first time in China. This study also contributes to enrich the materials of mineralogical study of Cu-S series minerals.

Geochronology, Petrogenesis and Geological Significance of the High-K Calc-alkaline Granites in the South Tianshan

MAO Youliang,FAN Shuanghu,CHEN Shue,SU Chunqian,ZHI Rongjun, RUI Ting,WANG Jiang

2014, 20(1):  58. 

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The Dongquangebi pluton is located in the Wushitala area of the northern margin of the South Tianshan, and is comprised mainly of porphyraceous monzonitic granite and a small amount of mafic microgranular enclaves. SHRIMP zircon U-Pb dating of porphyraceous monzonitic granite indicates that the weighted mean 206Pb/238U age is 305±1 Ma. These rocks are characterized by high-alkali (K2O+Na2O=7.58%~8.44%) and high-K (K2O/Na2O=1.09~1.33) and high Mg number (Mg#=51.6~58.5), with the A/CNK values between 0.92 and 1.00, which fall into the metaluminous high-Mg# and high-K calc- alkaline series. These rocks are also characterized by enrichment of LREE and LILE (Rb, K, Th and U) and depletion of HREE and HFSE (Nb, P and Ti), with slightly negative Eu anomaly (0.60~0.99) and strong depletion of Y (10.17×10-6~14.84×10-6) and Yb (1.054×10-6~1.374×10-6). These features suggest that the petrogenesis of the Dongquangebi pluton is magma mixing and the geochemical features of the Dongquangebi pluton belong to granitic rocks formed in the late-stage of a collisional orogeny. Combined with regional geological data, it is concluded that the Dongquangebi granitic pluton was derived from partial melting of the lower crust,with minor mixing with mantle-derived magma,due to the underplating of mantle-derived magma during the late-stage collision between the Tarim plate and Yili-Central Tianshan plate. The collisional magmatism in the South Tianshan indicates that the South Tianshan Late Paleozoic residual basin was closed in the Late Carboniferous, and the establishment ofmagma mixing of the Dongquangebi pluton indicates an important event of vertical growth of the continental crust in the South Tianshan.

Geochemical Features and Significance of the Late Permian Granites in Northern Sonid Zuoqi, Inner Mongolia

CHEN Junlin, HE Yuli, YANG Guolin, SUN Bainian*, LIU Kenan

2014, 20(1):  68. 

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The Late Permian granites in northern Sonid Zuoqi occur on the north of the Solonker suture. They are part of the Late Paleozoic suture zone in the southeastern margin of the Siberian plate. Research on the Late Permian granites in this area is helpful to understand the tectonic evolution of the Late Paleozoic in central Inner Mongolia. Major and trace element analyses reveal that the granites are characterized by high silica, high alkali, low magnesium, and low calcium, and the content of Na2O is higher than that of K2O. They belong to the high-K calc-alkaline series. The granites are rich in LREE and LILE, and have a negative europium anomaly. Trace elements Nb, Ta, Sr, P, Ti are poorly concentrated and Pb, Hf, Dy, etc. are well concentrated. Petrologic and geochemical characteristics indicate that these rocks are highly fractionated I-type granites, which were produced in a continental arc setting. This result suggest that the Solonker suture had not yet closed, and the Siberian plate had not completely conjoined to the North China plate during the Late Permian. The northern Sonid Zuoqi region might be formed during a transitional stage from subduction to collisional orogeny.

Apatite Fission Track Evidence for the Mesozoic-Cenozoic Tectonic Uplift of Aqishan-Yamansu Area, East Tianshan: With Discussion of Tectonic Activity and Geological Disposal of Radioactive Waste

LIU Hongxu, YAN Danping, He Jianguo, CHEN Feng, GAO Honglei, SUO Shixin,WANG Xun

2014, 20(1):  81. 

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Tectonic activity is a fundamental discriminant factor in site assessment for radioactive waste. The tectonic activity of geological repository of radioactive waste which is located at Aqishan-Yamasu in the East Tianshan was evaluated through model studying the uplift and exhumation history by the apatite fission track dating. The result shows that apatite fission track pool-agedata range from 81.7 to 51.4 Ma which recorded a cooling event of the East Tianshan during the Late Cretaceous to Eocene, which is consistent with a tectonic uplift and denudation event in the Late Cretaceous in the Tianshan. The mean track lengths range from 13.60±0.11 to 14.36±0.10 μm with the standard deviations of 0.98 ~1.22 μm, which suggests that most tracks didn’ t experience thermal annealing process after they were formed. Based on evaluated geothermal gradient, the mean exhumation rate in the East Tianshan during the Late Cretaceous to Eocene was calculated to reach 270~580 m/Ma. The geological data and further temperature-time modeling of apatite was conducted, indicating that an exhumation event existed from the Late Cretaceous to Eocene (84~49 Ma); after 50 Ma, the crust of the east Tianshan has been in a steady state, and the Cenozoic tectonic activity in Aqishan-Yamansu area has become significantly weaker than other area of Tianshan. The study shows that the geomorphologic features of present Tianshan inherit that from the Late Cretaceous, and weak tectonic activity conforms to the tectonic requirements of geological disposal of radioactive waste.

The Fault System and its Fault Sealing Properties of the Dome Structure in Dongying Sag, East China

LI Wei, WANG Zhibo, WANG Guangzeng, XUE Yan, ZHAO Wenrui, ZHANG Xiaoqing

2014, 20(1):  93. 

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Fracture is the most important controlling factor for fault-block reservoirs. So clarifying fault system development characteristics and its sealing properties is a key step in fault-block reservoirs’exploration and development and favorable zones prediction. Many methods have been used to deal with the dome structure in Dongying Sag, such as the detailed interpretation of three-dimensional seismic data, the coherence cube analysis,and the fault activity analysis techniques. Based on those processing methods, the fault system spatial characteristics and its evolution of the study area were analyzed. Combined with the single factor analysis and comprehensive fuzzy evaluation, the sealing properties of the main faults in work area were analyzed. Based on all the above, the relationship between hydrocarbon accumulation and distribution and the fault sealing was discussed. The results show that, the Dongying dome structure originated from the upwarp of salt gypsum and plastic mudstone in Kongdian and the fourth member of the Shahejie formation, the reverse drag of the northern boundary fault and the latter dextral transtension and then was complicated by multi-stage superimposition, multi-directional trending and multi-type array fault systems. The sealing properties of different strata and different parts of the faults show difference. As a whole, in the third to the lower second member of the Shahejie formation, the sealing properties of the second-grade faults were quite good, but those of the third-grade faults were not so good. While in the upper second member of the Shehejie to the Dongying formation, the study of the sealing properties of these faults show that there is a good correlation between fault sealing properties and the reservoirs accumulation and distribution, that is, reservoirs are usually located by the faults with good sealing properties.

Constraints and Controls of Fault Related Folds on the Development of Tectonic Fractures in Sandstones

JU Wei, HOU Guiting, HUANG Shaoying, SUN Xiongwei, SHEN Yinmin, REN Kangxu

2014, 20(1):  105. 

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The studies on the development laws of tectonic fractures in sandstones are significant to the reservoir prediction. In order to better know the development and distribution of tectonic fractures around the fault related folds, this paper studied the relationship between tectonic fracture density and its distance to the fault with the examples of a fault bend fold and a fault propagation fold developed in the Jurassic sandstones of the Kuqa Depression. The results show that (1) an exponential relationship between tectonic fracture density and its distance to the fault is established, and the tectonic fracture density decreases as the distance from the fault increases; (2) there is a damaging region where the tectonic fracture density decreases sharply, and this region is a fracture zone controlled by the fault related fold, which is named a“s fault and hinge controlling tectonic fracture zone”. The recognition of this tectonic fracture zone is of great importance to the quantitative study of tectonic fractures and numerical simulation of reservoir.

Formation of Multiple Episodes of Paleo-weathering Crust of Tuff-buried Hills and its Effect on Hydrocarbon Accumulation Erlian Basin, Inner Mongolia, China

LI Hao,GAO Xianzhi,YANG Dexiang,WANG Huilai,WANG Miao

2014, 20(1):  114. 

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Multiple episodes of volcanic eruptions lead to the development of multiple layers of weathering crust vertically in tuff buried hill. Geochemical, petrologic and logging data jointly demonstrate the existence of multiple episodes of weathering crust in the tuff buried hill. For well Ha-31, weathering crusts were developed at 1062 ~ 1080 m and 1165 ~ 1179 m and show K, Na, Ca leaching, larger CIA index, smaller S / A index, and relatively rich Al, Fe, Mn, P, etc content which are in accordance with the response to conventional well logging. Additionally, for singe well in logging, it shows some degree of cyclicity vertically, and this kind of cyclicity can be correlated among multi-wells. Moreover, tuffs originated from different eruption periods show different structures, composition, and sizes. From above, we can conclude that tuffs were formed in multiple episodes and multiple weathered crusts were developed vertically. The effects of multiple episodes of paleo-weathering crusts of tuff buried hills on hydrocarbon accumulation include vertical reservoir of zonal distribution , weathering crust reservoirs (late weathering crusts) and inner buried reservoirs (early weathering crusts) with vertical overlay, and complex hydrocarbon accumulation mode. The proposition of multiple episodes of tuff weathering crust related reservoirs extends the volcanic hill exploration depth and provides a theoretical basis for volcanic rocks inner buried hill exploration.

Sequence Stratigraphic Framework and Sedimentary System Distribution in the Lishu Rift, Songliao Basin

CHEN Xianliang,JI Youliang,FAN Tailiang,WANG Hongyu,YAN Ning,CHEN Xiaoyan

2014, 20(1):  122. 

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Based on seismic data, logging, drilling data, cores and characteristic of structure evolution, sequence framework of faulted layer in the Lishu rift is established. The faulted layer of the Lishu rift includes the Late Jurassic-Early Cretaceous strata of Huoshiling, Yingcheng, Shahezi and Denglouku formations, and is subdivided into three second-order sequences (I-III) and seven third-order sequences (SQ1-SQ7). Furthermore, sedimentary facies and sedimentary system are studied within the sequence frameworks. The results show that it mainly developed alluvial fan, fan delta, braided river delta, nearshore subaqueous fan, and lacustrine sedimentary system. Alluvial fan system mainly developed in the SQ2 sequence. Fan delta system mainly developed in the SQ3 and SQ4 sequences. Braided river delta system was found in the SQ5, SQ6 and SQ7 sequences. Nearshore subaqueous fan system mainly developed in the steep-slope zone of the SQ4, SQ5 and SQ6 sequences. The lateral and vertical evolutions of sedimentary systems were controlled by palaeostructure and palaeogeomorphology. The sand bodies of the SQ4 and SQ5 sequences are more favorable exploration area in the Lishu rift.

High-resolution Sequence Stratigraphic Characterization and Sand Body Prediction of the Lower Triassic Formatin in Xiquan(XIQ) Area of Eastern Junggar Basin

GUO Juanjuan,WEI Dongtao,PAN Jianguo,XU Xuelong,KONG Xu,WANG Yanjun,WEI Cairu

2014, 20(1):  131. 

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Based on core logging and 3D-seismic data, the high-resolution sequence stratigraphy of the Jiucaiyuanzi formation of the Lower Triassic Formatin in XIQ area of Eastern Junggar Basin is studied. Three kinds of short-term base-level cycles, five intermediate-term base-level cycles, and two long-term base-level cycles can be identified with the technology of division and correlation of the high-resolution sequence stratigraphic theory. Based on the base-level cycles, reservoir sands in different sequences are predicted with the technology of the frequency-divided inversion. Base-level changes control the spatial distribution of the sandstone of the Jiucaiyuanzi formation of the lower Triassic Formatin in XIQ area. The favorable sand bodies are predicted. The targets for further exploration and evaluation are identified.

Discussion on the Southern Boundary of the Permian Shihezi Formation in the Ordos Basin

LUO Tingting, ZHOU Lifa

2014, 20(1):  139. 

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he aim of this paper is to discuss the original southern boundary of the Permian Shihezi Formation in the Ordos Basin. Based on field observation and laboratory works, through petrological and provenance analyses, this paper discusses its provenance and tectonic affinity of the Shihezi Formation in southern Ordos Basin and North Qinling. The results suggest that rock lithics of the Shihezi Formation from both areas are similar and is characterized by epimetamorphic rock and granite, with few tectonite; the detrital mode compositions are similar and both are associated with collisional orogenic belt and foreland uplift provenance; In SiO2/Al2O3-K2O/Na2O and K2O/Na2O-SiO2, Zr-Th,La-Th-Sc,and Th-Sc-Zr/10 diagrams, both areas show the same tectonic background. F1-F2 distinguish diagram shows the consistent provenance of these two areas. They also have similar REE distribution patterns. Therefore, metamorphic rock and magmatic rock in Proterozoic of North Qinling as well as the low- grade metamorphic rocks of recycled orogen to its southern area may most probably the potential sources for the Shihezi Formation in southern Ordos Basin and North Qinling. It is inferred that the south border of the Ordos Basin had crossed Luonan tectonic belt and maybe reached to North Qinling.

Advances in Characterization of Pore System of Gas Shales

JIAO Kun, YAO Suping, WU Hao, LI Miaochun, TANG Zhongyi

2014, 20(1):  151. 

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Shale gas is the free, adsorbed and dissolved gas accumulated in dark shale beds. The nature of pores is a key factor to decide gas storing of shale gas reservoir. The structure of gas shales pores is complex, and the pore diameters are mainly in nano-scale. The methods used in conventional gas system study cannot explain high production of shale gas systems in USA. The characterization of nanopores in gas shales plays a key role in shale gas system evaluation. The studies of nanopores in gas shales are reviewed and compared with each other. There are three kinds of shale gas system characterization: (1) Image analysis is based on a stereological analysis, using various types of microscopes such as scanning electron microscopes (SEM), transmission electron microscopes (TEM), scanning tunneling microscope (STM) and atomic force microscopes (AFM); (2) Intrusive methods are based on gas adsorption, mercury porosimetry, and calorimetric methods; (3) Nonintrusive methods are based on radiation scattering, wave propagation, positron lifetime spectroscopy, etc. Image analysis can obtain the morphologic information directly, rapidly and conveniently. Intrusive methods have advantages in characterization of fractal features of pore system. Because of in-situ, non- invasive analysis and high penetrability of neutron and X-ray, nonintrusive methods can simulate the pore system evolution under multi-geological settings. As each method has its own advantages, multi-scale detection using multi-technology is recommended in shale gas pore system characterization.

Laboratory Simulation of the Morphological and Chemical Compositional of Kelp During the Early Diagenesis

LU Shanshan,LIU Wenhui,LI Yucheng,WU Juan,WANG Ning, TENG Geer,WANG Jie,MA

2014, 20(1):  162. 

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Amorphous bodies by the transformation of microbial were obtained during the simulation of early diagenesis of kelp in this paper. The morphology of the samples was observed, the content of biochemical components, carbon, hydrogen, nitrogen, and the trace metal elements were determined. The experimental results provided important experimental reference data for hydrocarbon source rocks of marine benthic macroalgae. Kelp was constantly degraded in the simulation experiment, the cells was completely broken as amorphous bodies by the 67th day. The microorganism promoted the transformation of biochemical component. In the late anaerobic stage, the content of polysaccharide and protein decreased, but the crude lipid increased up to 8.16%. Kelp had significant effects on the adsorption of the trace metal elements, and the content of the trace metal elements fluctuated. The results show that the microorganism promotes the transformation of kelp to amorphous bodies, and is beneficial to the increase of lipid and hydrocarbon generation, and the content of elements varied regularly. But there are still problems in using the trace metal elements for oil and source rock correlation directly, So further studies are needed.