Archive

2015, Volume 22 Issue 6
15 November 2015 Previous Issue    Next Issue
---
Article


For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Article

Select

Precambrian geodynamics (Ⅰ): From universal environment to protoEarth. LI San-Zhong, ZHANG Zhen, SUN Wen-Jun, DAI Li-Meng, ZHANG Guo-Wei 2015, 22(6): 1-9.  DOI: doi: 10.13745/j.esf.2015.06.001 Abstract ( 1734 )   PDF (1614KB) ( 1967 )   The origin of everything is the eternal theme of natural science and scientific research in frontier. Modern natural science in the promotion of keeping pace with the sophisticated technology continuously accumulated many new discoveries, very much new knowledge and new theories in recent 100 years. The exploration of origin to everything is no longer confined to an exploration stage of a single phenomenon, and is at the cognitive age of interdisciplinary research for the unified origin of all things origin. This paper systematically integrates these advances to the Earthrelated origins, especially in the recent 10 years, from the professional popularization perspective. Focusing on the origins of large phenomena in the establishment of astronomy theory as the main line, this paper describes concisely the origins of the universal, elements, star, protoEarth and others. The latest studies suggest that the universe originates from the Big Bang at 13.7 billion years ago and the spatial expanding rate is faster than the speed of light; thus the cosmic inflation theory has become the recent advance of the Big Bang theory. At 10-35s after the Big Bang the primitive “superforces” starts to break up due to spontaneous broken, and strong nuclear force, electroweak force and gravitational force are generated, meanwhile Deuteriumtype and Heliumtype stable atoms starts to turn up. At 10-34s the universe is still small which is only comparable with the presentday solar system, but its temperature has dropped to 1027K and the nuclear force isolates from the other two forces, the universe finished its expanding period and turned into standard Friedman expansion period. The plasma entropy of the freequarks and gluon and lepton constitute the universe; the concentrations of the free quarks produce protons and neutrons; matter annihilated with antimatter but exceeded by about one billionth part. The primitive universe was glutted with different microscopic particles and elements were originated from the collision and fusion of these particles, and the formation of elements are considered to have undergone 8 stages. After one billion years since the Big Bang, the universe went into the stage of star condensation; the temperature of the universe dropped to 18 K and the first galaxy and star appeared; the vast clouds of the galaxy dust and gas in the galaxy were condensed to form stars. The latest “Zero Time” of the solar system derived from U - Pb method is 4567±1 Ma. It takes about 9 billion years from the initiation of the universe to the formation of the solar system. Hundreds of generations of the explosion of the big stars may have occurred. The modern nebular hypothesis proposes that the formation of the protoEarth begins with embryo of a planet which is the assemblage of the planetesimals, and then the embryo gradually accreted to about more than 1/2 of the present day Earth at 4550 Ma. Then the Earths protocore appeared at about 4530 Ma. The relatively cold primary planet embryo became warmer and warmer due to the effects of impact, compression and radioactive decay processes, the protoEarth continuously generated heat accumulation and global developing process started. In summary, the paper briefly introduces the essences and frontiers of many academic achievements for both to popularly satisfy the lovers of natural science and to help professional experts profoundly understand different fields of scientific frontiers and new achievements. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅱ): Early Earth. LI San-Zhong, HU Li-Jing, ZHANG Zhen 2015, 22(6): 10-26.  DOI: 10.13745/j.esf.2015.06.002 Abstract ( 1783 )   PDF (2611KB) ( 2068 )   The early Earth refers to the Hadean or dark ages of the Earth. The Hadean Earth is also known as the Earth of 4.56 to 4 Ga. The early Earth is a scientific frontier of Earth Science and a basic problem related to many theories on geology and geochemistry. This paper systematically integrates the early Earthrelated research advances, especially in the recent 10 years, from the professional popularization perspective. Focusing on the origins of large geological phenomena in the establishment of geological theory as the main line, this paper describes concisely the origins of the protoEarth core, protocrust, mantle convection, lithosphere, mantle heterogeneity, continental and oceanic crusts, water and atmosphere and oceans, plate tectonics, the origin of early life and others that are major frontier scientific issues of Earth Science. These problems are closely associated with some origins of the universe and elements related to origin of matter in the Earth. The protocore of the Earth occurred after a few million years at the beginning of the formation of the ProtoEarth; the last time global largescale melting event in the Earth happened at 4450 Ma; the Earths protomantle and protocore was again under homogenization; and the protocore may disappear. After 4450 Ma, the primitive core size is similar to the size of the present core. Only the liquid outer core was under cooling and its size decreased, while the solid inner core increased. Based on the earliest crustal zircon ages that are greater than 4408 Ma, and the earliest crustal age obtained from the Sm - Nd system is 4470 Ma; the formation of the crust is earlier than that of the late core. Therefore, the time of the protocrust separated from the protomantle is about 4.45 Ga. Based on the geochemical characteristics of Hf and Nd, some of the oldest zircons occurred at 4.3 Ga ago. The upper part of the primitivemantle after assimilation of the magma was cooled, which may constitute the primitive lithospheric mantle that can become the lower part of the protocrust. However, there is no differential oceanic and continental lithospheres in the original 4 billion years ago. There are three different theories for the origin of mantle convection which is most likely to occur in the event of accidental impact at 4.45 Ga. The origin of the mantle heterogeneity may be related to the mantle convection. The mantle heterogeneity happened earlier than the plate tectonics, which can be only explained by the theory of mantle plume or mantle overturn, and then it has been enhanced by the late plate tectonics. The origins of water, atmosphere and oceans are possibly earlier than the origins of continental and oceanic crust. The earliest water has the most reliable and direct evidence from the discovery of the oldest zircon oxygen isotope, suggesting that the water in the primary Earths surface is stable at 4.0 Ga. However, the records of the Earths earliest minerals remaining in the Western Australia Yilgan Craton (Mt. Narryer and Jack Hills area) is one 4.4 Ga zircon. The earliest zircon also means that the earliest felsic crust (continental crust) should occur at 4.4 Ga ago. Therefore, the origin of continental crust is far earlier than that of plate tectonics, and the mechanism of early continental crust origin is likely to be independent of the plate tectonics regime, triggered by the tectonicmagmatic processes and the three generations of magmatic differentiation processes under preplate tectonics regime that eventually led to the formation of largescale TTG (continental crust). Water is a prerequisite for the origin of life, so the origin of life on Earth should be later than 4.0 Ga, and the reliable fossil confirms that life at least originated before 3.7 Ga. Furthermore, early life may appear in the submarine hydrothermal vents. In summary, this paper briefly introduces the essences and frontiers of many academic achievements to help professional experts profoundly understand different fields of scientific frontiers and new achievements on the component, structures, evolution and dynamics of Early Earth. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅲ): General features of Precambrian geology. 2015, 22(6): 27-45.  DOI: 10.13745/j.esf.2015.06.003 Abstract ( 1840 )   PDF (3189KB) ( 1982 )   During the 4.560.543 Ga Precambrian period, it has a lot of unique geological features of sedimentation, magmatism, metamorphism, deformation, mantle and lithospheric geodynamics. In order to understand the Precambrian geodynamics, this paper introduces some scientific advances on the composition and properties of the Precambrian crust and lithosphere, and their episodic growth, variation of Archean mantle temperature and viscosity, thickness, strength and rheological structure evolution of crust and lithosphere. The heat flow value of the Earth during 3.82.5 Ga is 2.54 times tham the presentday heat flow value. During the heat early Earth period, lower mantle heat accumulation is larger than the upper mantle heat loss, resulting in cyclic mantle overturn. Coevally the rising lower mantle went through the dry peridotite solidus, resulting in largescale melting at more than 150 km depth. This is the formation mechanism and energy background of Archean continental lithospheric mantle, but due to the Earths longterm cooling, this mechanism terminated after the Archean. The Archean high heat flow values caused the heat Archean mantle difficult to support the large terrain elevation; the Archean lithospheric strength is small, and fast terrain responses happened under the action of gravity. However, the giant mafic dyke swarms first appeared (at about 2.75 and 2.45 Ga), and supracrustal rocks occurred; the late Archean crust had gradually enough rigidity to allow melts ascending through the crust which is cooled and solidified. The fundamental cause of the major geological events in the Precambrian period is the result of the attenuation and oscillations of the Earths heat；all the Precambrian crustal growth (accretion), the formation of the supercontinent, the magmatism and the mineralization are characterized by different periods and nonlinear evolution. The formation of largescale TTG in a short time implies that they were possibly derived from vertical accretion. Finally this paper discusses the Hadean characteristics, origin, growth and preservation mechanisms of the continental crust, supercontinent reconstruction and mechanism, and coevolution of early life and environment, and other key scientific problems. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅳ): Preplate regime. 2015, 22(6): 46-64.  DOI: 10.13745/j.esf.2015.06.004 Abstract ( 1549 )   PDF (4125KB) ( 2413 )   Precambrian geodynamics focuses on kinetics mechanism of sedimentation, magmatic, metamorphic and deformation, mantle and lithosphere of the Earth during 4.560.543 Ga, being the eternal frontier and research focus of Earth Science. The presentday study shows that the early Precambrian tectonics is difficult to adopt the theory of plate tectonics to be interpreted reasonably; origin time of plate tectonics through the Earth history may vary at various positions, but the mainstream understanding is that the plate tectonics regime occurred during 2.72.1 Ga, and so is the North China Craton. The preplate regimes appearing before plate tectonics has been proposed, including many kinds of understanding: mantle plume, mantle overturn, gravitational tectonics, and platelets, of which the gravitational tectonics was considered at the stage of layering or stratification on the Earth in the Hadean, especially 4.544.45 Ga of the core formation and mantle magma ocean. So far, for the origin of oval structures of crustal levels, there are 8 original models: diapirism, middlelower crust flow, horizontal channel flow, polyphase fold superposition, deformation partitioning, crackingsag subduction, multilayer topdown rheological flow and batholith intrusionderived bucklingpartitioning, they all can appear under extension, compression and strike slipping backgrounds. No matter what both plate tectonics and preplate regimes, global tectonic process seems to be top down mechanism. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅴ): Origin of plate tectonics. 2015, 22(6): 65-76.  DOI: 10.13745/j.esf.2015.06.005 Abstract ( 1540 )   PDF (2154KB) ( 2879 )   This paper summarizes different views and their corresponding evidence of the starting time of plate tectonics, and explores three requirements of starting plate tectonic system: rigid plate, subduction and mantle convection, and then further discusses the differences between the Precambrian subduction or plate tectonics regime and modernstyle subduction or plate tectonics regime. The three requirements of starting plate tectonic system met at the same time until during 2.72.1 Ga in different places around the world. But the modernstyle plate tectonic system and regime have a starting time of between 1.0 (or 1.9) to 0.8 (or 0.6) Ga; the remarked material records or identification markers are still ophiolite suites, HPUHP metamorphic rocks, and arc magmatic rocks. At last, we describe possible starting mechanisms and processes of plate tectonics to provide a constraint for understanding the differences of preplate tectonics and plate tectonics, and to provide some latest insights for promoting thoughts and explorations of a unified theory of geodynamics as well. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅵ): Formation of North China Craton. 2015, 22(6): 77-96.  DOI: 10.13745/j.esf.2015.06.006 Abstract ( 1892 )   PDF (3904KB) ( 1687 )   The research on the North China Craton has made a series of great progress in recent 20 years, but it still has many unresolved problems. Firstly, this paper discusses the existing problems in the Precambrian tectonic unit division of the North China Craton, and then proposes some principles of dynamic tectonic unit division, and preliminarily makes dynamic tectonic division of PaleoarcheanMesoarchean, Neoarchean, Paleoproterozoic and MesoNeoproterozoic tectonic units, respectively. Based on these tectonic divisions, this paper determines the different periods of unique deformation styles and tectonic evolution. According to the new tectonic divisions and a series of major Precambrian geological events recorded in the North China Craton, different stages of evolution of the unique structural styles and tectonic regimes and their transition are also discussed. This paper proposes the rigid cratonization of some Archean continental nuclei in the North China Craton occurred at about 2.5 Ga, however, the obvious and earliest linear tectonic belts or rifts occurred at about 2.2 Ga. Therefore, this paper concludes the judgment of the Neoarchean initiation of plate tectonic regime in the North China Craton and provides the related structural evidences. Finally, based on our longterm structural analysis, this paper discusses the final assembly processes of the North China Craton in 1.85 Ga. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅶ): Formation and evolution of early continental crust. 2015, 22(6): 97-108.  DOI: 10.13745/j.esf.2015.06.007 Abstract ( 1835 )   PDF (1676KB) ( 3766 )   The Hadean to Paleoarchean continental crust consists of both granitoid gneiss terrenes and greenstone belts. A number of investigations revealed the ~4.4 Ga oldest detrital zircon ages of continental crusts marked by granitic rocks, and the earliest tonalitic and granodioritic gneisses were formed at ~4.03 Ga as well as the oldest greenstone belts at ~3.8 Ga. The Hadean to Paleoarchean granitoid gneiss terranes are chiefly composed of TonaliticTrondhjemiticGranodioritic gneisses (TTG). The TTG gneisses still are major lithological assemblages in the Meso to Neoarchean, however, lithological compositions of granitoid gneiss terranes exhibit significant diversity, especially the late Neoarchean marked by many granodioritemonzogranitesyenogranite suites. The greenstone belts display complicated compositions, komatiitic to tholeiitic rocks dominated during the Eo to Paleoarchean associated with BIF sedimentary sequences, whereas the Meso and Neoarchean greenstone belts decrease the ratios of the utramafic to mafic komatiites but raised the ratios of tholeiitic and calcalkaline mafic to felsic volcanic compositions with BIF and detrital sedimentary sequences, locally, boninitic, Nbriched basaltic and adakitic volcanics that are generally considered as the criteria of slab subductions. Geodynamic investigations suggested that the mantle plume regime dominated in the Hadean to Paleoarchean. The mantle convections and crust/mantle interactions led to the formation and thickening of the lithosphere 3.0 Ga ago. Locally significant thickening of mafic crust in downwelling areas due to dragging of mantle convection and thrusting slice stack in upper levels, leading to granulite to eclogite facies metamorphism and partial melting in deep level, which derived the formation of TTG granitoid magmas and initially hot subductions of bottom slabs. However, the Meso to Neoarchean dynamic regimes appeared dominant modernstyle plate tectonics, which were revealed by the discoveries of more and more eclogites and calcalkaline volcanics although the mantle plume regimes still play important roles locally. Related Articles | Metrics

Select

Precambrian geodynamics (Ⅷ): Late Archean crustal growth models recorded in the North China Craton. 2015, 22(6): 109-124.  DOI: 10.13745/j.esf.2015.06.008 Abstract ( 2380 )   PDF (2218KB) ( 1487 )   The early Precambrian crustal growth models and related crustmantle geodynamics have always been the research focus of international Precambrian community. Although it is generally accepted that the continental crust was dominantly formed during the Archean period, the definite crustal growth models and crustmantle geodynamic regimes remain largely controversial. Some researchers advocate the vertical tectonic regimes, e.g., plume or lower crust delamination models, whereas others favor the lateral subductionaccretion processes or plumearc interaction models. Recent studies reveal that several essential changes occurred during the late Archean crustal evolution history of the earth, i.e., rapid decrease in the ratio of komatiites within metavolcanic sequences; the wide emplacement of potassiumrich granitoid gneisses; and the apparent increase of the crustal recycling processes. All the above lines of evidence indicate that the crustmantle geodynamic regimes may have significantly changed during the late Archean. The North China Craton (NCC) is characterized by intense ~2.52.6 Ga tectonothermal events, which offers valuable opportunities for us to investigate the transitional regimes of early Precambrian crustmantle geodynamic evolution. In this study, we provide a timely review of recent early Precambrian studies along the northwestern margin of the Eastern Block (EB), especially focusing on the petrogenesis and crustmantle interaction processes recorded by the late Neoarchean (~2.52.6 Ga) metavolcanic rocks in the Western and Northern Liaoning Provinces, Eastern Hebei Province, and the Wutai granitegreenstone belt. It is suggested that the metamorphosed mafic rocks in these areas can be subdivided into three petrogenetic types of MORB (Midocean ridge basalt)type, IAT (Island arc tholeiite)type and the CAB (calcalkaline basalt)type. These Neoarchean metavolcanic rocks are considered to be formed by the partial melting of the asthenospheric mantle underneath an Archean spreading ridge and of the mantle wedge peridotites variably metasomatized by slabderived fluids, respectively. On the other hand, the metamorphosed andesitic to dacitic rocks may be generated by the partial melting of the subducted oceanic slabs and the interactions between melts from the slab and mantle wedge materials, showing analogous to either high magnesian andesites (HMAs) or Phanerozoic adakites. Integrated with recent early Precambrian studies of entire EB, we propose that the NCC has experienced intense crustal growth during the late Archean period (~2.5 and ~2.7 Ga), of which, the early Neoarchean episode (~2.7 Ga) of crustal growth is controlled by the plumearc interaction processes, whereas the late Neoarchean episode (~2.52.6 Ga) is dominated by the lateral subductionrelated intraoceanic arc and arccontinent accretion processes. Similar late Neoarchean tectonothermal events related to lateral subductionaccretion processes have been widely reported from the Tarim Craton, southern India, Vestfold Hills terrane of East Antarctica, and the Gawler Craton of Australia, and they may represent the key geological responses to the arrival of Phanerozoiclike plate tectonic regimes and the first global supercontinent (i.e., Kenorland) during the terminal Archean. Related Articles | Metrics

Select

Natural gas hydrate accumulation elements and drilling results analysis in the eastern part of the Pearl River Mouth Basin. 2015, 22(6): 125-135.  DOI: 10.13745/j.esf.2015.06.009 Abstract ( 2090 )   PDF (2074KB) ( 1239 )   Natural gas hydrate is generally considered to be one of the most promising new type of clean energies to replace coal, oil and natural gas, and it has enormous reserves but still untapped. Guangzhou Marine Geological Survey carried out geophysical, geochemical and comprehensive geological investigation in the northern slope of the South China Sea from the year of 1999, obtained a lot of geological information about gas hydrate occurrence, and implemented drilling in year 2007 in the Shenhu area and in year 2013 in the eastern part of the Pearl River Mouth Basin; both of them acquired gas hydrate samples successfully, especially the voyage of drilling in year 2013 in the eastern part of the Pearl River Mouth Basin had gotten high purity, new type of gas hydrate samples. The result of above investigation and drilling confirmed the existence of a huge resource prospects of gas hydrate in South China Sea. This paper gives a brief introduction of the main results of the drilling in year 2013 in the eastern part of the Pearl River Mouth Basin. This study makes contrastive analysis between several hydrate drilling areas worldwide and the accumulation condition in the eastern part of the Pearl River Mouth Basin before the drilling. The result indicated that gas source, stable environment, gas migration and reservoir conditions are essential factors of gas hydrate accumulation. According to the analysis of the characteristics of these factors, we forecasted the formation of seeped hydrate in this area. The drilling in year 2013 revealed the coexistence of the disseminated hydrate and seeped hydrate in this area and illustrated that the controlling factors of the formation and distribution of gas hydrate in this area were more complex. Related Articles | Metrics

Select

A new method for making the quasisimultaneous lithofacies palaeogeographic map. 2015, 22(6): 136-147.  DOI: 10.13745/j.esf.2015.06.010 Abstract ( 1511 )   PDF (2486KB) ( 1076 )   In this paper, on the basis of “sequence stratigraphy”, the principles of “spatial orderliness of facies sequence” and “temporal synchronism of environmental change” were applied to solving the problems of regional stratigraphic isochronal or quasiisochronal correlation. That the isochronal or quasiisochronal stratigraphic unit was adopted as the compilation unit of lithofacies paleogeographic maps was basically realized. Additionally, the drawbacks of the “distortion” of the lithofacies paleogeographic maps and the concealment of the change of vertical sedimentary environment caused by the nonisochronous lithostratigraphic units, i.e. “formation, member”, used in the traditional compilation, were overcome. The “new compilation method of quasisimultaneous lithofacies paleogeographic map” may be divided into three studying phases, i.e. single profile sequence stratigraphic column, highresolution sequence stratigraphic column correlation diagram and quasisimultaneous lithofacies paleogeographic series maps. In a marine basin, the sea level synchronously lifts; therefore, the corresponding threelevel sequences were isochronous in whole region. Also isochronous were the low water level, transgression, high water level, compulsive regression wedge and other system tracts, which were marked off by sequence boundary, first flooding surface, maximum flooding surface, regressive surface and other physical boundaries. For these reasons, the corresponding physical boundaries mentioned above in the single profile sequence stratigraphic column in the whole region may be linked together to form the isochronal correlation framework diagram of the studying area, to begin with. Then the strata in the isochronal framework would further be compared to form the correlation diagram. Finally, on the basis of the above work, the isochronous stratigraphic units were selected to compile the lithofacies paleogeographic series maps. The authors took as an example the research results of the early Lopingian lithofacies paleogeography of the west segment of the Pingle depression in central Jiangxi for further expounding. Accuracy of the isochronous correlation was improved after using the “new compilation method of quasisimultaneous lithofacies paleogeographic map”. The compiled lithofacies paleogeographic series maps fully reflected not only vertical and horizontal changes of lithofacies paleogeography in this period, but also the control of the sedimentary environment exerted by the combined effect of crustal movement and sea level eustacy. In addition, it shortened the map compilation units to the least possible, thus making the paleogeographic map more accurate, informative and practical. Related Articles | Metrics

Select

The structure and formation of the Cenozoic fault basin in the Lower Yangtze region. 2015, 22(6): 148-166.  DOI: 10.13745/j.esf.2015.06.011 Abstract ( 1471 )   PDF (3303KB) ( 2423 )   In an effort to further advance our understanding of the characteristics and dynamics of the Cenozoic fault basins in the Lower Yangtze region, we characterize the geological structures and formation mechanism of the fault basins by the interpretations of the seismic, drilling and geological data. Based on the regional cross sections perpendicular to the axis of the basins and their comparisons in time and space, we found that the scale of the basins gradually expanded from the land to the sea, and the rifting sequences increased in the thickness, and that the structures became more complex. All of these facts show us that the extensional amount and intension of the basins gradually increase from the west to the east. Constrained by the approximately wedge geometry of the Lower Yangtze block and boundary condition of the eastern lateral extrusion, the block approaches to expand in the southnorth direction, which could reactivate the preexisting faults of the preCenozoic basement, and then induced regional rifting process and basin subsidence, suggesting that the formation of the fault basins in the Lower Yangtze region was constrained by the two basic factors: the basement and the stress. The Cenozoic extension in the Lower Yangtze region and the dextral movement of the TanLu fault are all the geological responses to the tectonic deformation of the Lower Yangtze block, which can be explained well by the subduction of the Pacific Plate. Related Articles | Metrics

Select

Study on the Silurian sedimentary system of Western Hunan and the formation mode of typical foreland basin. 2015, 22(6): 167-176.  DOI: 10.13745/j.esf.2015.06.012 Abstract ( 1423 )   PDF (1868KB) ( 1418 )   Western Hunan region has deposited clastic rocks of Silurian. Except the strata of Upper Silurian are missing, other interfaces between strata are mostly of integrated contacts. Based on comprehensive stratigraphy study, many sedimentary system types, such as deep water retention basin, foreland basin turbidite fan, delta, shoreland and tidal flat, can be distinguished at western Hunan region, and the sea level turns shallow upwards. The sediment source was from the Xuefeng uplift in the southeastern of Western Hunan. The structural evolution of the Silurian foreland basin in Western Hunan has undergone several periods: the basin formation period, the development period, the shrinking period, and the extinction period of the foreland. The relationship between sedimentary and tectonic evolution is that the deep water retention basin sedimentary system was formed in the initial period of the foreland basin, the marine turbidite fan sedimentary system was formed in the developed period of the foreland basin, the delta sedimentary system was formed in the shrinking period of the foreland basin, and the tidal flatsand damshoreline sedimentary system was formed in the extinction period of the foreland basin. Related Articles | Metrics

Select

Poststack geostatistics inversion in the application of the carbonate rocks reservoir prediction: In Xinken area, Halahatang oil field as an example. 2015, 22(6): 177-184.  DOI: 10.13745/j.esf.2015.06.013 Abstract ( 1498 )   PDF (1474KB) ( 1212 )   Based on method of poststack geostatistical inversion, some key techniques, such as construction of the fine geological model, classification of reservoir and analysis of statistics parameters, equivalent simulation for porosity and geostatistical inversion，have been discussed in details. Aimed at the problem resulted from prediction of carbonate reservoir, the further study procedures which are to optimize systematically the relevant inversion parameters and their reasonable distribution in local reservoirs were carried out in order to get the better prediction precision through well seismic reservoir fine calibration. The prediction results showed this method performed well in spatial distribution of reservoir and nonreservoir; 35 wells were used to test the precision of inversion results; the accumulative thickness of the reservoir when their total porosity is above 1.8% was quantitatively analyzed combined with the local geologic features，it showed high conformity to the real situation of reservoir distribution. The conformity rate is over 80% between the prediction results and practical drilled reservoirs occurrence, so that the prediction results from poststackbased geostatistical inversion have the better precision and approach the actual geologic situation; it has better prediction identification between the reservoir and nonreservoir heterogeneity than conventional wave impedance inversion in practical field operation. Related Articles | Metrics

Select

Tight reservoir characteristics of sedimentary organic matterbearing tuff in Tiaohu Formation of Santanghu Basin. 2015, 22(6): 185-196.  DOI: 10.13745/j.esf.2015.06.014 Abstract ( 1581 )   PDF (2195KB) ( 841 )   Sedimentary organic matterbearing tuff is a special type of tight reservoirs in the Santanghu Basin. The study of sedimentary organic matterbearing tuff in the Santanghu Basin will provide a good opportunity to improve our knowledge of unconventional tight reservoir. Based on thin section examination, field emission environmental scanning electron microscopy (SEM), Xray diffraction (XRD) analysis, measurements of quartz crystallinity index, reservoir physical property, etc., the reservoir characteristics of sedimentary organic matterbearing tuff in Tiaohu Formation are studied in this paper. The results indicate that vitric tuff and crystalvitric tuff are the main rock types of tight reservoirs in Tiaohu Formation. The most important mineral in tuffs is quartz, with average content over 50%. Reservoir space types are mainly micronano scale interparticle pores caused by the devitrification of tuffs, as well as dissolution intraparticle pores, interparticle pores of inorganic minerals and clays, and pores within organic matter. Besides, fractures are also important reservoir space. Tight tuff reservoirs are characterized by high porosity ranging from 10% to 25% and low permeability mainly in the range of (0.010.5)×10-3 μm2. High total porosity is caused by small volume but large quantities of micronano scale pores from the devitrification, and low permeability is attributed to the very small throat radius of pores. The physical property of tuffs is mainly affected by the composition of the volcanic ash and the degree of devitrification which can be characterized by quartz crystallinity index. The physical property of vitric tuff is better than that of crystalvitric tuff. The degree of devitrification is mainly controlled by the depth (temperature) of tuff and the organic acid content. Related Articles | Metrics

Select

Characteristics of marinecontinental transitional organicrich shale in the Ordos Basin and its shale gas significance. 2015, 22(6): 197-206.  DOI: 10.13745/j.esf.2015.06.015 Abstract ( 1831 )   PDF (1521KB) ( 969 )   In this study, the CP marinecontinental transitional organicrich shale in the Ordos Basin was investigated by means of rock pyrolysis analysis, rock extraction and group analysis, organic element analysis and coal optical analysis to test the geochemical parameters, such as organic matter type, abundance, maturity and hydrocarbon generation potential. Utilizing SEM, XRD and physical property measurement, the mineral composition and the characteristics of porosity and permeability have been analyzed. The results proved that the marinecontinental transitional organicrich shale in the Ordos Basin distributes widely and has the characteristics of diminutive individual thickness but huge cumulative thickness. The content of TOC is about 2.5%, organic matter type is mainly Ⅲ, and RO is about 1.2%. Hydrocarbon potential(S1+S2) is at the stage of massive gas generation. Percentage of quartz and feldspar is high, various porosity and crack type could be found, and preservation of shale reservoir is well. All of these conditions provide the favorable environment of shale gas formation. Related Articles | Metrics

Select

Main controlling factors of Paleogene hydrocarbon accumulation of Termit Basin, West African rift system. 2015, 22(6): 207-216.  DOI: 10.13745/j.esf.2015.06.016 Abstract ( 1441 )   PDF (1832KB) ( 822 )   The Termit Basin, which is located in the southeastern Niger and tectonically belongs to the northern part of West African Rift System (WARS), is a MesozoicCenozoic rift basin developed on the PrecambrianJurassic basement. Since 1974, many foreign oil companies have made exploration in Termit Basin and found seven reservoirs in Dinga Faulted Terrace. CNPC began exploration in the basin in 2008. It is a very difficult issue that how to evaluate the potential and find abundant petroleum. Based on the tectonic evolution of the Late Cretaceous great transgression and two rifts superimposition, this study mainly focuses on analyzing the main controlling factors of Paleogene hydrocarbon accumulation. The petroleum accumulation model of the Paleogene shows the following six characteristics: (1) hydrocarbon generation is controlled by the large area of marine source rocks; (2) sandstone distribution is influenced by superimposition of two phases rifting; (3) secondary migration of oil and gas is controlled by faults and thick carrier beds; (4) fluid potential is decided by structural relief; (5) petroleum accumulation is determined by the relationship between faults and sandstone; (6) preservation of oil and gas is defined by cap rocks and lateral blockages. The analysis of main controlling factors reveals the petroleum accumulation principles of the Paleogene, and facilitates the exploration of the Termit Basin. Related Articles | Metrics

Select

Hydrodynamic condition and response of formation water chemical fields of geothermal water in North China Basin. 2015, 22(6): 217-226.  DOI: 10.13745/j.esf.2015.06.017 Abstract ( 1679 )   PDF (1549KB) ( 1008 )   The hydrogeochemical zonations of geothermal water in North China Basin can be used to indicate the hydrodynamic zoning because the latter actively responded to the former. The quality of geothermal water is deteriorating and the deuteriumexcess parameter decreases from surrounding mountains to the basin and from shallow to depth in North China Basin, suggesting that the rate of groundwater circulation become slower and slower. The distribution characteristics of high salinity zoning of geothermal water indicate that the Taihang Mountains and Yanshan Mountains in the west and north are predominant recharge area of geothermal water in North China Basin, while a small recharge amount is from the mountains in the southwest of Shandong Province. In addition, whether in the horizontal or vertical direction in the basin, the hydrogeochemical zonations also indicate that there is hydrodynamic equilibrium zone between the centripetal flow (infiltration original water) and acentric flow (sedimentary original water) of geothermal water in sandstone. This indicates that there is transient equilibrium between the centripetal flow and the acentric flow. Related Articles | Metrics

Select

Origin of the Ashi volcano, Western Kunlun Mountains: Evidence from seismic tomography. 2015, 22(6): 227-232.  DOI: 10.13745/j.esf.2015.06.018 Abstract ( 1531 )   PDF (1259KB) ( 1157 )   We carried out a highresolution Pwave velocity tomography of the Tibetan Plateau, Ashikule volcano clusters and surrounding areas by using arrivaltime data obtained from the nationwide seismic network, International Seismological Centre (ISC) as well as temporary seismic arrays deployed on the Tibetan Plateau. Our highresolution tomography shows that the Indian plate is revealed as a highvelocity anomaly and it is subducted beneath the Tibetan Plateau. The northern limit of the highvelocity anomaly has reached to the northern boundary of western Tibet, to the BangongNujiang suture under central Tibet and around the Jinsha River suture under eastern Tibet, suggesting the different northsouth distance that the Indian plate subducted northward. Our tomographic results suggest that the Indian plate has subducted to western Kunlun, around the Ashi volcano. To the north, the Tarim block shows a prominent high velocity anomaly. We found obvious low velocity anomalies and magma upwelling path beneath the Ashi volcano. In the mantle transition zone, there is a low velocity zone beneath the Ashi volcano. The Ashikule volcano clusters could be formed by the decompression melting of asthenospheric materials and magma upwelling. Related Articles | Metrics

Select

Seamounts in West Junggar ocean and its geological effects on the subduction zone. 2015, 22(6): 233-240.  DOI: 10.13745/j.esf.2015.06.019 Abstract ( 1466 )   PDF (1631KB) ( 3043 )   With deepening of the study, the oceanic island basalts (OIB) formed in different times have been identified in Central Asian Orogenic Belt (CAOB). West Junggar is located in southwestern margin of the CAOB, and contains many ophiolitic mélange belts with OIB basalts. The basalts show pillow structure and closely associate with ultrabasic rock, gabbro, massive basalt, limestone and purple siliceous rock. Geochemical studies show pillow basalts are characterized by alkaline affinity with high TiO2 (major > 2.5%), light rare earth elements (LREE) enrichment, no obvious Nb and Ta negative anomalies. They are very similar to typical OIB, suggesting that they may have been formed in the oceanic plate and plumerelated seamount setting. Based on developmental stage analysis for seamounts, we think that the seamounts in West Junggar at least had grown into the explosive stage, because of lots of pillow lavas. The volcanic rocks or volcaniclastic sediments in seamounts were enriched in large ion lithophile elements (LILE) and high field strength elements (HFSE). Therefore, the subduction of seamounts would have strongly affected the geochemical properties of volcanic rocks in arc and backarc area. In fact, the DevonianCarboniferous volcanic rocks in West Junggar contain seamount signal. Therefore, seamount subduction model may be better to explain the petrogenesis of volcanic rocks with OIB in West Junggar. In addition, there is a potential resource effect by seamount subduction, so we should study the indicator of the subduction of the paleoseamounts and island chains, in order to provide a reliable basis for exploring gold, copper, and some other mines. Related Articles | Metrics

Select

Changes of soil carbon pool in typical areas of Changjiang drainage basin and its influencing factors. 2015, 22(6): 241-250.  DOI: 10.13745/j.esf.2015.06.020 Abstract ( 1683 )   PDF (1517KB) ( 728 )   Soil carbon pool is an important part of global surficial carbon pool, which will influence global climate change as a carbon source or sink for greenhouse gases. Taking areas covered by the multipurpose regional geochemical survey (MPRGS) in the Changjiang drainage basin as an example, the soil carbon density and soil carbon storage and their changes have been calculated by combining MPRGS data and the second national soil survey data. And also, the factors that caused the carbon sinks and sources were analyzed. The results show that the soil organic carbon density (SOCD) significantly increased at most regions of the study area from the 1980s to 2000s, especially in the Longmen Mountain region of western Chengdu, southern region of Yaan and the surrounding region of Guiyang. The amount of soil carbon increase is about 312.38 TgC. Recovery of vegetation in woodland and grassland, and improved land management in paddy fields and dry farmland are the major factors that increased soil carbon storage in the respective land use area. The land use change has relatively little impact to soil carbon stock changes in the study area. Soil erosion had almost no effect on paddy field, but it had obviously restrained the increase of SOCD in the dry farmlands. And also, the climate change had no obvious influence on soil carbon stock in this region. Related Articles | Metrics

Select

Discovery of the Late Silurian granodiorite and its tectonic significance in the Tuwu-Yandong porphyry copper deposits, DananhuTousuquan island arc, Eastern Tianshan. 2015, 22(6): 251-266.  DOI: 10.13745/j.esf.2015.06.021 Abstract ( 1683 )   PDF (2065KB) ( 2171 )   The DananhuTousuquan island belt, located along the southern margin of the TurpanHami basin, is an important part of the Central Asian Orogenic Belt and ranks one of the most important metallogenic belts in Xinjiang, NW China. However, its precise formation age and tectonic setting are still controversial. In this study, we identified for the first time a Late Silurian granodiorite in the largest Tuwu Yandong porphyry Cu belt in this island belt. The zircon U - Pb dating indicated that the granodiorite was emplaced at about 420 Ma. The granodiorite is characterized by metaluminous to weakly peraluminous, medium Mg values and calcalkaline compositions; it is enriched in light rare earth elements, Rb, Ba, K, U, Th, and Pb, and depleted in Nb, Ta and Ti; its εNd(t) value is between 4.05 and 4.07, its ISr(t) value is between 0.704149 and 0.704520 and its εHf(t) value is between 8.91 and 11.66. These geochemical data indicate that the magma that formed the granodiorite was produced through partial melting of juvenile crust under the setting of island arc without obvious contamination of ancient continental crust. The discovery of the Late Silurian granodiorite, combined with previous studies, shows that the Dananhu Tousuquan island arc belt and the Harlik island arc belt belong to the same island arc in the Early Paleozoic and constructed an integrated arc basin system with the KalatageXiaorequanzi backarc basin. This knowledge is of great significance to the Late Paleozoic arcbasin evolution of the Eastern Tianshan Mountains. Related Articles | Metrics