Loading...
Welcome to Geological Journal of China Universities ! Today is
Share:

Table of Content

    20 March 2012, Volume 18 Issue 1
    Origin and Paleozoic Tectonic Evolution of the Lhasa Terrane
    Zhu Dicheng, Zhao Zhidan, Niu Yaoling, Wang Qing, Dilek Yildirim, Dong Guochen,
    2012, 18(1):  1-15. 
    Asbtract ( 2932 )   PDF (2626KB) ( 2561 )  
    References | Related Articles | Metrics

            The history of breakup, drift, subduction, and collision of the Lhasa Terrane during the Paleozoic remains poorly
    understood because of the scarcity of data. This paper reviews the Mesozoic lithospheric architecture and explores the origin
    and Paleozoic evolution of the Lhasa Terrane on the basis of geological and geochemical data currently available. Abundant
    zircon Hf isotope and whole-rock Nd isotope data of silicic rocks indicate that the southern and northern Lhasa subterranes

    are dominated by juvenile crust with possible Precambrian crystalline basement locally preserved, while the central Lhasa subterrane
    is a microcontinental ribbon with ancient basement rocks as old as Archean. Over 3000 U-Pb ages of detrital zircons from Late
    Neoproterozoic-Paleozoic strata define an age peak of ca. 1170 Ma for the Lhasa Terrane and identical age peaks of ca. 950 Ma
    for the Amdo, Southern Qiangtang, and Tethyan Himalaya. Thus the most plausible explanation for the origin of the Lhasa Terrane
    is that it came from the northern Australia. The ca. 492 Ma bimodal metavolcanic rocks identified in the central Lhasa subterrane
    were likely developed in an active continental margin representing a part of a magmatic arc paleogeographically located in the
    northern Australian continent and may be a result of slab break-off of the subducting proto-Tethyan oceanic lithosphere. The Late
    Devonian to Early Carboniferous gneissic granitoids in both the southern margin of the Lhasa Terrane and Southern Qiangtang are
    S-type granitoids with significant contributions from mantle-derived materials. These rocks may have been emplaced in a back-arc
    setting that ultimately evolved to what is known as the Songdo Tethyan Ocean. The Lhasa-northern Australia collision at the end of
    the Middle Permian may have triggered the southward subduction of the Bangong-Nujiang oceanic lithosphere, imposing a critical
    role on the subsequent tectonomagmatic evolution of the Lhasa Terrane during the Mesozoic.

    Crustal Recycling and Genesis of Continental Alkaline Basalts: Case Study of the Cenozoic Alkaline Basalts From Shandong Province, Eastern China
    CHEN Lihui, ZENG Gang, HU Senlin, YU Xun, CHEN Xiayu
    2012, 18(1):  16-27. 
    Asbtract ( 3772 )   PDF (668KB) ( 2469 )  
    References | Related Articles | Metrics

             Geochemically, continental alkaline basalts are similar to those oceanic island basalts, and are viewed as the representative of intraplate basalts in continents. Here we provide a case study of the Cenozoic basalts in Shandong Province,eastern China, to discuss the genesis of continental basalts. Spatially, the Cenozoic basalts can be divided into two kinds, the early three parallel volcanic belts and the late small and isolated volcanoes. The three belts including the Weifang belt and the Yishui belt in western Shandong, and the Penglai belt in eastern Shandong are less alkaline and are mainly composed of alkali olivine basalts and basanites, which show broad ranges of incompatible element ratios and isotopic values. The small and isolated volcanoes are more alkaline and are mainly composed of basanites and nephenilites, which are more homogenous in incompatible element ratios and isotopic values. Therefore, compared with oceanic island basalts, the parallel volcanic belts in Shandong can be regarded as shield-building stage basalts, while the small and isolated volcanoes correspond to the posterosional or rejuvenescent basalts. On the isotopic plots of Sr vs. Nd and Nd vs. Hf, both the Weifang belt and the Yishui belt show a two-endmember mixing array. However, there is minor difference of the enriched endmembers of these two arrays. The enriched endmembers are characterized by smaller Ce/Pb and elevated Ba/Th ratios, suggesting a signature of lower continental crust. However, such materials have much lower Th/La ratios and have excess radiogenic Hf contents relative to radiogenic Nd. Such geochemical signatures cannot be produced by assimilation of lower continental crust but by recycled lower continental crust (eclogite or garnet pyroxenite), which had undergone early melting in the mantle. The different arrays in isotopic plots of the two belts are alike those of the KEA chain and the LOA chain of Hawaii islands. Therefore, we propose that the parallel volcanic belts of Shandong be attributed to the plume activity and the recycled lower continental crust be important components of the plume. Geochemically,basanites and nepheninites of the late small and isolated volcanoes share many signatures with the carbonatite, e.g. the depletion of K, Pb, Zr, Hf, Ti in the primitive mantle-normalized grams. Therefore, we conclude that their mantle sources have been carbonated recently. The moderately depleted Sr, Nd, Hf isotopic compositions of these alkaline rocks indicate that the carbonated liquids might be derived from recycled young (Mesozoic?) oceanic crust.

    An Overview of the Tectonic Evolution of North Qaidam UHPM Belt: from Oceanic Subduction to Continental Collision
    ZHANG Guibin, ZHANG Lifei, SONG Shuguang
    2012, 18(1):  28-40. 
    Asbtract ( 3510 )   PDF (1245KB) ( 3164 )  
    References | Related Articles | Metrics

            The North Qaidam UHPM belt is a typical continental type subduction zone. Coesite inclusions were found from
    eclogite and country gneiss, and diamond inclusion from garnet peridotite. This paper is focused on the progress of petrology,thermobarometry, geochemistry and geochronology studies of Yuka, Luliangshan, Xitieshan and Dulan terranes in the North Qaidam UHPM belt. This belt is unique because subducted oceanic relics prior to the continental subduction and collision are well preserved, Combined with the published data, especially the two protolith sources for eclogites, we conclude that the North Qaidam UHPM belt experienced a tectonic evolution from an oceanic subduction to a continental collision.

    Partial Melting of Hydrous Lower Continental Crust: Discussion on the Petrogenesis of C-Type Adakites From the Dabie Orogen
    Zhang Chao, Ma Changqian, Francois HOLTZ
    2012, 18(1):  41-51. 
    Asbtract ( 2805 )   PDF (714KB) ( 2407 )  
    References | Related Articles | Metrics

             On the basis of continental composition, principles of partial melting of hydrous mafic rocks, and the published
    experimental data, we discuss the partial melting mechanism of lower continental crust. By comparing the Dabie C-type adakites with experimental melts, we provide constraints on the magma source, melting conditions (temperature and pressure), and the melting degree. Overall, the lower continental crust of East China, including the Dabie orogen, is basic to intermediate (50~60% SiO2) and slightly hydrous. Thus, fluid-absent dehydration melting of hydrous minerals is a major mechanism for the lower continental crust generating hydrous felsic melts and anhydrous residues. More than ~20% garnet in the residues could be formed by partial melting of amphibolite at a medium pressure (1.0~1.2 GPa, equivalent to 35~40 km), which is essential to make the coexisting melt to possess adakitic signatures (especially low Y, high Sr/Y and La/Yb). Based on a H2O activity model and solidus of metamafic rocks, dehydration partial melting, which occurs at ~950 ℃, could lead to a maximum melting proportion of 15~20%, meeting the requirement for efficient melt segregation. The Dabie C-type adakitic rocks, are of high-K calc-alkaline series (3.5~5% K2O), and it is very clear, when compared with experimental melts, that they cannot be derived from low-K protoliths with reasonable melting degrees. In the light of the highly incompatible behavior of K in the course of partial melting,our calculation based on the partition coefficients between melt and possible residues indicates that high-K calc-alkaline melts similar to the Dabie C-type adakitic rocks can be generated by 15~20% (mass basis) partial melting of amphibolites with~1 wt% K2O.

    Effects of Melt Refertilization on the Subcontinental Lithospheric Mantle
    Sun Jing, Liu Chuanzhou, Wu Fuyuan
    2012, 18(1):  52-61. 
    Asbtract ( 2456 )   PDF (1386KB) ( 3399 )  
    References | Related Articles | Metrics

    The lherzolites have been commonly regarded as mantle residues after low degrees of partial melting. However, melt
    refertilization, which refers to transform the refractory harzburgites to fertile lherzolites through adding asthenosphere-derived
    basaltic melts, provides a new explanation for the fertile lherzolites. Besides the enrichment in major elements, this process also transforms the enriched characteristics in trace elements and Sr-Nd isotopes of the harzburgites to the depleted characteristics of lherzolites. It is still highly debated as to whether melt refertilization can change the Os isotopic compositions of mantle peridotites, which depend on the ratios of the refertilizing melts, the sulfur saturation of the melt, and the time of refertilization, etc. The melt/rock ratios in the sub-continental lithospheric mantle are commonly low. Therefore, effects of melt refertilization on the Os isotopic compositions of the peridotites are probably limited. In addition to chemical compositions, addition of refertilizing melts changes the physical properties. Melt refertilization would destabilize the lithospheric mantle through increasing the permeability and decreasing the viscosity. Although it can change the chemical-physical properties of the lithospheric mantle, it is unclear whether the melt refertilization process is responsible for lithospheric thinning and craton destruction.

    Anomalous Lithium Isotopic Compositions of the Cenozoic Lithospheric Mantle Beneath Penglai, Shandong Province:The ion Probe Analyses of Peridotite Xenoliths
    Li Pei, Xia Qunke, Etienne DELOULE
    2012, 18(1):  62-73. 
    Asbtract ( 1401 )   PDF (1534KB) ( 1332 )  
    Related Articles | Metrics

           Li contents and isotopic compositions of minerals in the peridotite xenoliths hosted by Cenozoic basalts from Penglai,
    Shandong Province have been measured using ion probe. The results show that the Li abundance ranges from 2.0 to 10.4×10-6,2.8 to 23.8×10-6 and 3.3 to 59.7×10-6 in olivine (ol), orthopyroxene (opx) and clinopyroxene (cpx), respectively, and the δ7Li values varies from-28.6 ‰ to +0.5 ‰, -12.7 ‰ to +12.8‰ and -41.5 ‰ to +22.6 ‰ in ol, opx and cpx, respectively. Both the Li contents and isotopic ratios deviate strongly from the normal mantle range and the equilibrated trend. These extreme disequilibria imply that the strong Li enrichments were induced by strong mantle metasomatic events. The high Li and δ7Li enrichments of pyroxene reflected the nature of the recent mantle metasomatism that fed them, whereas the moderate Li enrichment and strong δ7Li depletion in the olivines may record a relatively ancient low-δ7Li signature. The reproduction of the measured profiles and the decoupling of Li enrichment from the LREE-depleted pattern in cpx suggest that both enrichment processes were relatively recent and transient. Accordingly, we conclude that the“ pristine” recycled components with anomalous Li composition existed in the upper mantle beneath the eastern North China Craton (NCC). The fractionation of Li isotopic compositions in the recycled components was linked to the subduction of the Pacific plate beneath East Asia since the Mesozoic, and the recycled components were reactivated recently to feed these anomalous Li enrichments as recorded by the Penglai peridotite xenoliths.

    Pyroxenites: High-Pressure Segregates or Recycled Oceanic Crust?
    Zhang Yaling, Xu Yigang 
    2012, 18(1):  74-87. 
    Asbtract ( 2801 )   PDF (838KB) ( 2623 )  
    Related Articles | Metrics

            There are three petrogenetically different pyroxenites, namely cumulate pyroxenite, metamorphosed oceanic crust, and
    metasomatic pyroxenite. Type I pyroxenites formed as crystallization segregates from mantle-derived melts under pressure
    of 1.5~2.5 GPa. They commonly show cumulated or igneous textures and do not form perfect linear correlations in a CaO/MgOSiO2/ MgO plot. Type I pyroxenits show no Eu anomaly and their Sr-Nd-O isotopes are similar to those of mantle rocks. Type II pyroxenites are metamorphic products of recycled oceanic crust. They commonly show a deformed texture, forming a linear correlation in a CaO/MgO-SiO2/MgO plot and show a positive Eu anomaly. While theirεNd values are identical to those of the MORB, their Sr-O isotopes show distinct features. Metasomatic pyroxenites result from interactions between melts and peridotite. They are commonly surrounded by harzburgite or dunite. Minerals in metasomatic pyroxenites are less variable than other two types of pyroxenites. Dispersed in the CaO/MgO-SiO2/MgO plot, theirεNd values are lower than those of the Type II pyroxenites,and their Sr isotopic ratios show a restricted range. The δ18O values of metasomatic pyroxenites are variable, either lower than,higher than, or similar to the mantle value. To explain the co-existence of pyroxenites of different origins within a single ultramafic massif, the following model is conceived: the oceanic upper crust, including basalts and sediments, produces considerable elementally variable fluids and magmas, which react with surrounding peridotites and convert it to pyroxenites and also form type I pyroxenites by high-pressure crystal segregation along magma conduits in the peridotites. The oceanic lower crust consisting of troctolite and gabbroic rocks retained their original compositions and translated to type Ⅱ pyroxenites without partial melting or other significant metasomatic reaction during subduction and exhumation at subsolidus conditions.

    Zircon U-Pb Chronology and Assemblages of Mesozoic Granitoids in the Manzhouli-Erguna Area, NE China: Constraints on the Regional Tectonic Evolution
    Wang Wei, Xu Wenliang, Wang Feng, Meng En 
    2012, 18(1):  88-105. 
    Asbtract ( 2380 )   PDF (3593KB) ( 3069 )  
    Related Articles | Metrics

          LA-ICP-MS zircon U-Pb dating data of the Mesozoic granitoids from Lingquan, Baogedewula and Shanghulin basins
    in Manzhouli and Erguna area are obtained to constrain the regional tectonic evolution. Zircons from 12 representative granitoids are euhedral-subhedral in shape and display typical oscillatory zoning in CL images as well as high Th/U ratios of 0.31~3.63, implying their magmatic origin. The dating results indicate that the Mesozoic granitic magmatism in the region can be divided into three stages, i.e., the Middle Triassic, Early-Middle Jurassic, and Early Cretaceous magmatism. The Middle Triassic granitoids can be further subdivided into two stages, 241 Ma biotite syenogranite and 229 Ma syenogranite, which could be formed under an extensional environment after the final closure of the Paleo-Asian ocean in the late Paleozoic or early Mesozoic. The Early-Middle Jurassic granitoids can be further subdivided into two stages, 180±5 Ma biotite monzogranite and 171±2 Ma syenogranite. Combined with the existence of the coeval porphyry-type Mo deposit, our data suggest that the Early-Middle Jurassic magmatism could be formed under an active continental margin which was related to the subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif. The Early Cretaceous magmatic rocks consist of 140-150 Ma granite porphyry and 134±2 Ma quartz-monzonite porphyry. The former is similar to the Jixiangfeng Formation in time, the latter occurs as crater fills and could belong to the late evolutionary products of this magmatism. Combined with the lack of coeval volcanic rocks in the eastern Jilin- Heilongjiang provinces, the data suggest that these volcanic rocks could be formed under an extensional setting related to the evolution of the Mongol-Okhotsk orogen.

    Muscovite 40Ar/39Ar Dating of the Quartz Porphyry Veins from Northwest Guangxi, China, and its Geological Significance
    Chen Maohong, Lu Gang, Li Xinhua 
    2012, 18(1):  106-116. 
    Asbtract ( 2518 )   PDF (2915KB) ( 2769 )  
    References | Related Articles | Metrics

             The late Yanshanian magmatite in the Youjiang Fold Belt of western China is represented by basic-ultrabasic dyke
    swarms and ultra-acid rock veins. The 40Ar/39Ar dating of muscovite phenocryst from quartz porphyry veins, which are located in the Bama-Fengshan-Linyun area of northwestern Guangxi, yields a plateau age of 95.59±0.68 Ma and an isochron age of 95.0±1.0 Ma for a NE-striking quartz porphyry vein in Longhuang of Fengshan county, and a plateau age of 96.54±0.70 Ma and an isochron age of 95.91±1.1 Ma for a NW-striking quartz porphyry vein in Bama county. These ages are interpreted as an emplacement age for quartz porphyry veins. The new data support that the Yanshanian magmatic activity concentrated on 80-100 Ma in the Youjiang Fold Belt and the surrounding area, indicating large scale extension and lithospheric thinning in western China during the late Cretaceous. Since the granitic magmatic activity of late Cretaceous was related to a large scale Sn-(Cu-Pb- Zn) mineralization in western China, it is worth considering the prospecting potential for Sn-(Cu-Pb-Zn) in the area where quartz porphyry occurs within the Youjiang Fold Belt. We further discuss whether Carlin-type gold deposits and other epithermal ore deposits are related to this episode of magmatic activity within the Youjiang Fold Belt.

    Isolation of a Siderophore-Producting Bacterial Strain and Mica-bacterial Interactions
    HE Linyan, ZHANG Yin, SHENG Xiafang, HUANG Zhi
    2012, 18(1):  117-124. 
    Asbtract ( 2164 )   PDF (1390KB) ( 2722 )  
    References | Related Articles | Metrics

         studies on the interactions between siderophore-producting bacteria and mica minerals will help us understand the
    mechanism of bio-weathering, the formation of soil, global cycle of several elements, and local environmental contamination. A siderophore(pyoverdins)-producting bacterial strain Z6 was isolated from rhizosphere soil of advantage wild plants sheep sorrel (Rumex acetosa L.) growing in Longshan potassium mine tailings in Nanjing, which was identified as Pseudomonas sp. by checking the individual morphology, colony characteristics, and 16S rDNA sequencing. Using the test cultures containing biotite or muscovite inoculated with Pseudomonas sp. Z6, we found that a strong increase in the amount of siderophore in the fiest 15 days and bacteria could influence silicon and iron mobilization from mica minerals consistently until 75 d of culture. The amounts of iron released from biotite in the presence of Z6 increased by 211 times and the silicon increased by a factor of 27.8, much higher than that in the negative control without minerals. SEM analysis revealed the formation of erosion and bacteria-mineral aggregates on the surface of mica. Cellular growth, siderophere production and pH change by Pseudomonas sp. Z6 cultivated in biotite were directly and quickly influenced, more significantly than that in muscovite experimental setup. The siderophore(pyoverdins)- producting bacterial strain Z6 might play an important role in the process of mica weathering. Production of bacterial siderophore may be related to the presence of different mica minerals.

    Application of the PVTX Simulation of Reservoir Fluid Inclusions to Estimate Petroleum Charge Stages: A Case Study in the Tuoputai Area of Tarim Basin
    SHI Weijun, JIANG Hong, XI Binbin
    2012, 18(1):  125-132. 
    Asbtract ( 1905 )   PDF (1909KB) ( 2283 )  
    References | Related Articles | Metrics

           PVTX simulation of reservoir fluid inclusions has been widely applied to determine trapping pressures and
    temperatures of inclusions, and in turn to reveal charge histories in petroleum reservoirs. In this paper, we present a case studyof the Middle Ordovician Yijianfang Formation carbonate reservoir in the Tuoputai area of Tarim Basin, using the VTFlinc
    simulation method. Based on an integrated study of petrography, microthermometry, laser Raman spectrum, and confocal laser scanning microscope analyses, the inclusions were studied for forming stages, compositions, and thermodynamics. These further indicate the paleo-temperature and pressure of the inclusion formation. The petroleum charge time and stages are inferred. There were two stages in general, i.e., 420-405 Ma of the late Caledonian stage and 8-2 Ma of the late Himalayan stage. Previous work suggests that the Himalayan petroleum charge event of the Tahe oilfield did not reach here, but this study using the new method shows otherwise. Thus, the method is promising in applications.

    Petrogenesis of Indosinian High Ba-Sr Granites in Laoniushan Batholith, Shaanxi Province and Their Tectonic Implications
    Wang Yanfen, Shao Yi, Jiang Shaoyong, Zhang Zunzhong, Hu Jian, Xiao E, Dal Baozh
    2012, 18(1):  133-149. 
    Asbtract ( 3718 )   PDF (5683KB) ( 2293 )  
    References | Related Articles | Metrics

           The Laoniushan complex granitic batholith occurs in Xiaoqinling orogen along the southern margin of the North China
    Craton. Zircon LA-ICP-MS U-Pb dating yields an age of 207.9±0.72 Ma for the Kangping pluton, which is the early-stage
    granites in Laoniushan batholith, indicating that they were generated from the Early Mesozoic magmatism. These granites are characterized by metaluminous, high silica and total alkalinity with high FeO*/(FeO*+MgO) ratios, LILEs (especially Sr and Ba) and LREEs, low HREEs and Y contents, and insignificant Eu anomalies, similar to the high Ba-Sr granites. In comparison to the typical slab-derived adakites, the Kangping granites have low compatible elements (such as Cr, Ni) and high K2O contents with high-K calc-alkaline features, and display insignificant fractionation of HREEs. During the diagenetic processes, the geochemical behaviors of these granites were mainly constrained by the fractional crystallization of amphibole (clinopyroxene), plagioclase (K-feldspar), and minor garnet. Element and isotope compositions suggest that the sources of the Kangping granites in Laoniushan complex batholith are the mixture of the ancient basement materials of Taihua Group and small amounts of enriched lithospheric mantle metasomatised by fluid/melt that was derived from pelagic sediments-bearing subducted slab. These granites were generated by partial melting of the lowest part of the crust due to the subducted slab break-off during the post-collision extensional stage of the continental collision and orogenic processes.

    40Ar-39Ar Plateau Ages of Biotite and Plagioclase from Xinwuli Granitoids in Tongling Area, Anhui Province and its Geological Significance
    Wang Yonglei, Pei Rongfu, Wang Haolin, Qu Hongying, Li Jinwen
    2012, 18(1):  150-157. 
    Asbtract ( 2074 )   PDF (2276KB) ( 1586 )  
    References | Related Articles | Metrics

           Biotite and plagioclase samples from the quartz monzodiorite of Xinwuli granitoids yield 40Ar-39Ar plateau ages of
    152.1±1.7 and 135±1 Ma. Samples from the granodiorite give 40Ar-39Ar plateau ages of 143.8±0.9 Ma and 140.4±0.9 Ma.
    The similar ages suggest an important stage of Yanshanian magmatic activity in the Middle and Lower Yangtze regions. The 40Ar-39Ar age of biotite from quartz monzodiorite is older than the previous zircon U-Pb isotopic ages, which is probably due to excess argon. Together with the age data of Xinwuli granitoids, we obtain the cooling curves of the granodiorite and quartz monzodiorite. The cooling curves show that the cooling rates of Xinwuli granitoids have been fast since the Late Jurassic, indicating an extensional tectonism. The formation of Xinwuli granitoids may be related to the Late Mesozoic lithosphere thinning in Eastern China.

    Zircon U-Pb Dating of the Yishichun Mafic-Ultramafic Complex From Southern Qilian and its Geological Significance
    YU Jiyuan, LI Xiangmin, MA Zhongping, WANG Guoqiang, TANG Zhuo,
    2012, 18(1):  158-163. 
    Asbtract ( 2176 )   PDF (1247KB) ( 2296 )  
    References | Related Articles | Metrics

          The study area is located at the southern margin of the Middle Qilian, south of the Qinghai Lake—GuLei deep fault
    belt, which is a favorable area for copper-nickel deposits in Qilian metallogenic belt. Yishichun Copper-nickel ore occurs within the homologous and contemporaneous basic-ultrabasic intrusions, and copper-nickel mineralization is spatially and temporally related to the intrusive rocks. The cathodoluminescence (CL) images and the Th/U ratios of zircons from the basic-ultramafic rocks suggest that zircon crystals are of magmatic origin; The LA-ICP-MS U-Pb dating of these zircons yields a weighted mean age of 455.1±1.7 Ma. Therefore, the ore-bearing rock emplacement and copper-nickel mineralization occurred during the late Ordovician, and the metallogenic dynamic process was probably related to an ancient continental margin rifting.

    Characteristics and Distribution of Reservoir Spaces of the Carboniferous Volcanic Rocks in Dixi Area, Junggar Basin
    Xiong Yixue, Xi Aihua, Ran Qiquan, Ge Yuhui, Liu Xiaohong, Sun Yuanhui
    2012, 18(1):  164-173. 
    Asbtract ( 1956 )   PDF (7476KB) ( 1285 )  
    References | Related Articles | Metrics

           Reservoir space types, forming factors, and distribution of the Carbonferons volcanic rocks in Dixi area are investigated
    by core inspection, thin section analyses, imaging logging, and seismic data interpretations. The results show that rock types of carboniferous volcanic reservoir in Dixi area include mainly basalt, syenite porphyry, volcanic breccia, and ignimbrite. Reservoir space can be divided into four types, namely primary pores, secondary pores, primary fractures, and secondary fractures. The primary pores are mainly gas pores and intergranular pores. Primary fractures include shrinkage induced joints and explosion related cracks. Intragranular dissolved pores and groundmass dissolution pores predominatec the secondary pores, and secondary fractures are prevailing tectonic fractures. The controlling factors of the reservoir space are volcanic lithology and facies, weathering and leaching, tectonism and dissolution. The types and distribution of primary reservoir space are controlled by lithology and facies, while secondary pore space and fracture are governed by the later three factors. From the northwest to the southeast, the controlling factors changed from the volcanic lithology and facies to the weathering and leaching, tectonism and dissolution. According to these, the gas pores and intergranular pores in Dixi 17 and 14 well area, are controlled by lithology and facies, resulting in a northeast-trending long strip. The secondary dissolved pores in ignimbrite and volcanic breccia from Dixi 10 well area occur along the fractures. The development of intragranular and groundmass dissolution pores are controlled by both the subvolcanic intrusives and fractures in Dixi 18 well area.

    Raman Spectroscopic Characteristics of Different Hydrocarbon-Forming Organisms
    Bao Fang, Tenger , Yang Yunfeng, Xie Xiaomin, Zhang Meizhen, Wang Rucheng 
    2012, 18(1):  174-179. 
    Asbtract ( 1536 )   PDF (998KB) ( 2498 )  
    References | Related Articles | Metrics

           This study proposed a method to distinguish the bio-precursors of organic matter in hydrocarbon source rocks. Through
    analysis of the Raman spectra of two common types of organisms, phytoplankton and benthic algae, in hydrocarbon source rocks, we found that the organic matter originated from different organisms have different Raman spectra characteristics. The difference in Raman shift between G-mode peak and D-mode peak normally indicates the polymerization degree of aromatic structures, and the intensity ratio of D-mode peak to G-mode peak reflects the order degree of aromatic structures. By comparing the spectra parameters of different hydrocarbon-forming organisms, we found that the polymerization degrees of the macerals originated from benthic algae are greater than those of phytoplankton as well as the order degree of phytoplankton is also greater than benthic algae. Our research shows that the difference in Raman shift between G-mode peak and D-mode peak of different hydrocarbon organisms sampled from the same layer displays significant difference. The polymerization degree of aromatic structure of organic matter can be detected by Raman spectroscopy to distinguish different organisms. Although the intensity ratio of D-mode peak to G-mode peak is not only subject to the thermal maturity of materials but also sensitive to their structure properties of bio-precursor organism, it may also serve as a reference for distinguishing different hydrocarbon-forming organisms in practice.

    Relationship Between Micro-sedimentary Environment and Morphology of Molar Tooth: Taking the Molar-tooth of Neoproterozoic in Dalian, China as an Example
    Peng Nan, Llu Yongqing, Kuang Hongwei
    2012, 18(1):  180-188. 
    Asbtract ( 1747 )   PDF (7770KB) ( 1737 )  
    References | Related Articles | Metrics

          Molar Tooth (MT), is a special sedimentary phenomenon and only developed in carbonates in Precambrian. It has been
    found in many areas of the world. Abundant MTs with complicated morphology were found in the Neoproterozoic carbonate rocks of Dalian, Liaoning Province, China. The MT from Dalian was divided into autochthonous MT and allochthonous MT, according to its morphology. The autochthonous MT was further divided into four subtypes containing ribbons, bars, worms, spots and the allochthonous MT consists of fragments only. The MTs from Dalian were mainly developed in a shallow subtidal to intertidal zone. Based on the analysis of different types of MT and their distribution in a micro-sedimentary environment zone, a special relationship between morphology and micro-sedimentary environment was found. MT1-1 and MT1-2 types mainly occur in a lagoon; MT1-3 and MT4 are the principal types in the middle of a tidal zone; MT2 and MT3 dominate the middle to upper pare of a tidal zone, while MT5 type appears in a shallow subtidal zone (around base of storm waves) or lower of an intertidal zone.Therefore we infer that wide and long MT ribbons were probably easily produced in a low-energy environment without substance from land, but a high energy environment with plenty of land-substances is favorable for short and small MT. It is concluded that hydrodynamic force and land-substances can influence the morphology of MT. Besides, considerable land-substances can inhibit the formation of micro-spars or reduce the sizes of MT.

    Automated Computation of Sandstone Ratio with Massive Logging Data
    Li Bin, Zhu Xiaomin, Li Yang
    2012, 18(1):  189-192. 
    Asbtract ( 1444 )   PDF (503KB) ( 1605 )  
    References | Related Articles | Metrics

          Comparative analysis of sandstone content in terrestial strata is an effective method to determine directions of sources
    and to reveal sedimentary environments in sequence stratigraphy studies. It is also an important index that is used to delineate sequence stratigraphy and lithofacies in palaeogeography studies. This article uses an Access database to achieve fast calculation of sandstone radio using massive logging data of sequence stratigraphy. The new method improves efficiency and enhances data accuracy and reliability as compared with the traditional methods. It is proved that the method is a feasible means of scientific compuation and can be used in other earth science research.