Table of Content

20 August 2022, Volume 28 Issue 4

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Calculating Equilibrium Temperatures and Pressures of Peridotite Xenoliths from the Slave Craton in Canada

CHEN Yao, WANG Qin

2022, 28(4):  457-472.  DOI: 10.16108/j.issn1006-7493.2020199

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Peridotite xenoliths from the Jericho kimberlite pipe in the Slave Craton in Canada provides a window to investigate composition and thermal structure of the subcontinental lithospheric mantle. Here we summarized the recent progress in thermometers and barometers of mantle rocks, then measured major and trace element concentrations of 9 fresh peridotite xenoliths from the Jericho kimberlite pipe, and calculated their equilibrium temperatures and pressures using different thermometers and barometers. The results indicate that the garnet-orthopyroxene barometer of Nickel and Green (1985) can yield reliable pressure estimates, and two-pyroxene thermometer of Taylor (1998) and clinopyroxene thermometer of Nimis and Taylor (2000) give consistent temperature estimates. Coarse-grained granoblastic spinel-garnet peridotites and garnet peridotites have equilibrium temperatures of 575-843℃ and pressures of 2.4-3.6 GPa. In contrast, prophyroclastic spinel-garnet lherzolite records temperature of 1109℃ and pressure of 5.0 GPa, and probably experienced an early exhumation event from ~156 km to the middle lithospheric depth by kimberlite magmas and the final exhumation by the eruption of the Jericho kimberlite pipe in the Jurassic. The temperatures estimated from the REE-in-garnet-clinopyroxene are higher than the corresponding values from the major-element based thermometers, indicating a cooling history of the lithospheric mantle beneath the Slave Craton. In addition, spinel peridotites preserved the signature of the high-degree partial melting in the shallow mantle, whereas the lower part of the lithospheric mantle have been modified by metasomatism of kimberlite and silicate melts.

Discovery of Mafic Microgranular Enclaves in the Indosinian Caijiang Pluton, Jiangxi Province, and Its Geological Implications

LIU Yunchao, JIANG Yaohui, QING Long, DU Foguang

2022, 28(4):  473-483.  DOI: 10.16108/j.issn1006-7493.2020115

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In this work, mafic microgranular enclaves have been found in the Caijiang granitic pluton, Jiangxi Province. This paper reports the geological and petrographic, as well as LA-ICP-MS zircon U-Pb geochronology and element geochemistry characteristics of these enclaves. Most of the enclaves are elliptical, showing quenched margin and back veins. They have typical magmatic texture and acicular apatite. Some enclaves contain feldspar xenocrysts. These enclaves have relatively lower SiO₂ (as low as 57.05 wt%) and higher MgO + Fe₂O₃ (up to 14.21 wt%). LA-ICP-MS zircon U-Pb dating shows that these enclaves were formed at 224 Ma, and there is a time gap of about 4-6 Ma with the host granite (230-228 Ma). Characteristics above indicate these enclaves are the masses of discrete mantle-derived basic magma or mixing products of mantle-derived magma and host magma. It is likely that the enclave magma was injected when the host granitic magma was in a state of crystal mush. The discovery of MMEs provide direct evidence for the underplating of mantle derived magma, and the formation of Caijiang granitic rocks at a high temperature. This work is of great significance to further study the heat source mechanism of Indosinian granites in South China.


Ce-in-zircon Oxybarometer and the Redox State of the Early Earth

XIAO Luyi, YANG Xiaozhi

2022, 28(4):  484-492.  DOI: 10.16108/j.issn1006-7493.2020114

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Oxygen fugacity (f O₂), a quantitative factor in rendering the redox state of a given system, is a key thermodynamic parameter in Earth sciences. The oxygen fugacity of the early Earth and its variation with time, which is a prime goal of Earth sciences, plays important roles in understanding the origin and evolution of the atmosphere, hydrosphere, biosphere and even the whole Earth. Zircon provides the oldest samples yet found on the planet, and is almost the only survivor of the Hadean period. Studies in recent years have demonstrated that the Ce content of zircon is able to record the prevailing f O₂ of its parent magma, leading to the so-called Ce-in-zircon oxybarometer. This provides a unique probe into the redox state of the early Earth. We provide a brief introduction of this technique, and then outline the recent advances on the redox state of the early crust and mantle, followed by a discussion on the f O2 evolution of the early atmosphere, crust and upper mantle and the coupling relation of f O₂ between them.


Geochemical Behaviors of Uranium and Thorium during Weathering of Carbonate Rocks

LIN Fali, HE Shouyang

2022, 28(4):  493-505.  DOI: 10.16108/j.issn1006- 7493.2020225

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Uranium and thorium, as lithophile, are ubiquitous in earth crust and bedrock. The weathering of bedrock makes uranium and thorium participate extensively in various surficial geochemical processes. Both weathering-pedogenesis and erosion of carbonate rocks are important sources of uranium-series radionuclides in karst-ecological systems. Also be key process of global biogeochemical cycling of uranium-series radionuclides. Bedrock and soil samples are collected from 6 typical carbonate rock profiles in Houzhai catchment. The content, distribution and characterization of mobility of uranium and thorium are analyzed


during weathering process of carbonate rocks. Carbonate rocks profiles are characterized by extreme mass defect which dominated by chemical-weathering. Chemical-weathering depletion fraction (CDF) is more than 70% due to dissolubility of carbonate rocks, and the CDF of pure limestone and dolomite is more than 90%. A sudden enrichment of uranium and thorium appear in the rocksoil interface because of chemical weathering and residual dissolution. Thorium-rich is more obvious than uranium, and both have secondary distribution in profile. Uranium is easily dissolved and more mobile, yet thorium is mostly adsorbed by soil particles less mobility in the process of weathering. The CDF indicates obvious difference in chemical mobility of uranium and thorium. Multi-stage variation of Th/U implies weathering intensity and more potential geochemical information during weatheringpedogenic process of carbonate rocks.

Study on the Spatial Variation and Driving Factors of Copper, Cobalt, Molybdenum and Zinc in Top Soil of Typical Agricultural Region in Sichuan Basin

YUAN Yuyang, LIU Shuling, LUO Kunli, LIU Yonglin, TANG Ye

2022, 28(4):  506-515.  DOI: 10.16108/j.issn1006-7493.2020214

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In order to quantitatively analyze the effects of geographical factors on the spatial variation of copper (Cu), cobalt (Co), molybdenum (Mo) and zinc (Zn) in surface soil, 156 soil samples from the Jiangjin district with high longevity population in Sichuan Basin were collected and measured. The spatial variation and driving factors of Cu, Co, Mo and Zn in surface soil were studied using mathematical statistics, geostatistics and geographic detectors. The mean content of Cu, Co, Mo and Zn in surface soil, Jiangjin district were 27.0×10^-6, 18.5×10^-6, 0.4×10^-6 and 216.8×10^-6, respectively, and were 1.19-fold, 1.45-fold, 0.20- fold and 2.17-fold of background values of China soils. The variation coefficients of soil Cu, Co, Mo and Zn content were in the moderate intensity. Whereas, spatial distribution of Zn and Mo in surface soil from the Jiangjin district was more uneven. As a whole, the content of Cu, Co, Mo and Zn in top soil from northern Jiangjin was higher than those of southern Jiangjin. Iron (Fe), manganese (Mn), parent rocks and soil types were driving factors affecting spatial variation of the soil Cu, Co, Mo and Zn but vary in extent. Generally, the iron (Fe) and manganese (Mn) in soil exerted the highest effect and played an important role in the distribution, enrichment, and migration of Cu, Co, Mo and Zn in top soil from the Jiangjin district, Sichuan Basin.

Geochemistry and Genetic Analysis of Chert of the Piyuancun Formation in Western Zhejiang

YUAN Yuyang, CAI Chunfang, LIU Yonglin, LUO Wei, TANG Ye

2022, 28(4):  516-526.  DOI: 10.16108/j.issn1006-7493.2020063

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A series of layered black chert was deposited in the lower Yangtze region during the Ediacaran-Cambrian (E-C) transition period. In the western Zhejiang, the Diben section consists of the Piyuancun Formation, which corresponds roughly to the Liuchapo Formation or the Laobao Formation in the upper Yangtze region. The chert generally has highly organic carbon content, and is highly enriched in uranium (U), vanadium (V), molybdenum (Mo) and other redox sensitive elements. The chert, together with the black mudstone deposited in early Cambrian, is called black rock series. But there is still some debate about its genesis. The major and trace (rare earth) elements in the black chert are measured and analyzed to probe into the source and origin of the chert of the Piyuancun Formation in the western Zhejiang. The results show that: (1) It is not possible for chert deposited in such a large range of deep water to be formed only by hydrothermal sources. (2) The late Ediacaran biodegradation products have a significant impact on the formation of chert. However, it is still not possible to determine whether the materials that constitute chert is mainly derived from organisms due to the lack of reliable palaeontological evidence. We infer that biological activities exerted certain influence on the formation of chert. (3) The chert of Piyuancun Formation was mainly products of chemical deposition, and silica mainly came from the weathering of continental silicate minerals.

The Earliest Denudation Record of the Dabie Orogenic Belt Evidenced from the Middle Triassic Huangmaqing Formation in the Ningwu Basin

LI Chao, HU Xiumian

2022, 28(4):  527-538.  DOI: 10.16108/j.issn1006-7493.2020104

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Due to post-orogenic multi-stage tectonic events and long-term massive denudation, there are poor precise constraints to limit the initial denudation time of the Dabie orogen, that is, timing of starting to provide a source for the peripheral basins. In this work, we conduct field investigations on the Huangmaqing Formation, a set of Middle Triassic delta facies terrigenous clastic rock in Ningwu Basin, northeastern South China, and presents sedimentologic and provenance analysis. Lithologies of the Huangmaqing Formation are dominated by the litho-quartzose sandstone and feldspathic-litho-quartzose sandstone, with quartz of 76%-84%, lithic fragment of 10%-14%, and feldspar of 6%-11%. Among the lithic fragments, quartz-rich metamorphic rock fragments or metapelite grains rock debris are dominant, indicating the existence of special sources of metamorphic rocks. The detrital zircon age spectrum shows the main peaks at 350-250 Ma、420-400 Ma、900-700 Ma、2000-1600 Ma、2500-2100 Ma. The Susong Complex belt located in the southern orogenic belt is the main source of the Huangmaqing Formation. Compared with the sedimentary records of other early Mesozoic basins around the Dabie orogen, it is found that these basins have similar provenance in the Middle-Late Triassic. The early exhumation of the lower metamorphic belts in the Dabie orogenic belt led to the initial denudation of the orogenic belt. At least part of the sediments of the Huangmaqing Formation were derived from the early uplift and denudation of the orogenic belt.

Paleosalinity Characteristics and Geological Significance of the Upper Bayingobi Formation in Yingejing Depression, Bayingebi Basin

GAO Hongxia, LIU Xiaodong, LIU Pinghui, MENG Pinghong, XIANG Long, RAO Gengwei

2022, 28(4):  539-553.  DOI: 10.16108/j.issn1006-7493.2021072

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The mudstone of the upper Bayingobi formation in Bayingobi basin is one of the research targets for the deep geological disposal of high-level radioactive waste in China. At present, the combination characteristics of clay minerals and the factors affecting the paleosalinity of the mudstone are less studied. In this paper, the paleosalinity of the upper Bayingobi formation is comprehensively distinguished by the methods of B content, Sr/Ba ratio, Rb/K ratio, Na+K mass fraction and X-ray diffraction. The results are as follows：(1) The upper member of Bayingobi formation is dominated by semi deep lake-deep lake sedimentary environment with thick dark grey mudstone developed. And it mainly ranges from semi deep lake to deep lake facies. (2) The lithologic characteristic of the target formation in the study area is argillaceous and silty. Illite, montmorillonite and mixed layer of illite and montmorillonite are well developed while chlorite and kaolinite are relatively rare. (3) The values of Sr/BA, Rb/K, B/GA and Na+K of the selected samples are similar to the paleosalinity changes restored by Couch formula, and the water is mainly featured by brackish and saline water. (4)With increasing sample depths from TZK-1 and TZK-2 boreholes, the paleosalinity changes regularly, with the characteristics of increase-decrease, which is consistent with the change of illite content. The paleosalinity change is coupled with paleoclimate and redox research in this lithologic section. The results show that: The study of paleosalinity in the target formation is not only conducive to the restoration of paleosedimentary environment in the lake basin, but also helps to reveal the influence of paleosalinity variation on clay mineral assemblage characteristics and evolution. These results may provide a certain basis for the later in-depth study of clay mineral’ s nuclide adsorption performance and nuclide migration in mudstone.

Influence of Flow Velocity and Dip Angle on Perchloroethylene Migration in Fractured Media

LU Yue, LIU Yichao, XU Hongxia, SUN Yuanyuan, WU Jichun

2022, 28(4):  554-564.  DOI: 10.16108/j.issn1006-7493.2020223

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Perchloroethylene (PCE) was selected as the representative dense non-aqueous phase liquid (DNAPL) to investigate its migration and distribution characteristics under different flow velocities and dip angles in single fractured media. By using the light transmission method, we could monitor the migration and saturation distribution of PCE dynamically, and therefore the change process of PCE source zone architecture could be characterized. The results showed that PCE separated from the injection needle in the form of lumps, and was nearly elliptical and not continuous with each other in the process of migration. In this paper, Fs refers to the square of the initial pollutant separated from the injection needle. The larger the flow velocity was, the larger Fs was, and the smaller PCE centrifugal rate e was; the larger the dip angle was, the smaller Fs was, and the smaller the centrifugal rate e was. When the infiltration process became stable, the area and centrifugal rate of agglomerated PCE decreased  significantly. The increase of flow velocity and dip angle promoted the vertical migration of PCE, which accelerated the front-end migration rate of PCE and made PCE move to the bottom of the fracture system more quickly. The increase of flow velocity promoted the distribution of PCE, and the peak saturation decreased, while the increase of dip angle suppressed the distribution and made the peak saturation increase during the process.


Tectonic Setting and the Peak Metamorphic Conditions of the Xingxingxia Group in the Central Tianshan Block, Xinjiang

ZHU Mixi, ZHU Wenbin, GE Rongfeng, WANG Yiqiong

2022, 28(4):  565-581.  DOI: 10.16108/j.issn1006-7493.2020219

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The Central Tiansan Block is an important part of the Chinese Tianshan Orogenic Belt, and the formation age of Precambrian basement in the Central Tianshan Block becomes older as it goes east. The Xingxingxia Group is located in the easternmost of the Central Tianshan Block and has the oldest Precambrian basement of the Chinese Tianshan Orogen. In this paper, the metamorphic schist and gneiss in the Xingxingxia Group were observed and sampled in the field, and thin section observation, mineral electron probe analysis and whole-rock geochemistry test were carried out in the laboratory. The geochemical analysis of the whole rock major element indicates that the protoliths of the metamorphic schist and gneiss in the Xingxingxia Group are mainly argillaceous rocks and sandstone. The results of trace elements and REE indicate that the Xingxingxia Group was deposited in continental arc or active continental margin environment based on the results of EPMA and major elements. The temperature and pressure conditions of the peak metamorphism of the Xingxingxia Group were 610-730℃ and 6.8-8.5 kbar. In addition, according to the latest metamorphic age of the basement rock, the time of peak metamorphism of the Xingxingxia Group is about 380 Ma.


Tectono-thermal Chronology of the Xingxingxia Complex in Eastern Tianshan

WANG Yiqiong, ZHU Wenbin, LUO Meng

2022, 28(4):  582-591.  DOI: 10.16108/j.issn1006- 7493.2020112

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The Xingxiaxia region is located in the easternmost part of the central Tianshan block in Chinese Tianshan. The Tianshan orogenic belt has recorded numerous micro-continents, oceanic crust and island arc complex accretional orogeny since the Neoproterozic. In order to further understand the basement evolution and later uplift-denudation of the Tianshan orogenic belt, this study uses ⁴⁰Ar/³⁹Ar and apatite fission track methods to analyze the Precambrian basement rocks, Paleozoic and Mesozoic intrusive rocks in the Xingxingxia area. The results of muscovite and biotite ⁴⁰Ar/³⁹Ar experiments of Xingxingxia Precambrian samples are 239.74±1.54 Ma and 266.20±2.77 Ma. The apatite fission track ages of the precambrian basement and later intrusive rocks are range from 92.5 to 70.5 Ma. Combined with previous results, we suggest that the results of biotite ⁴⁰Ar/³⁹Ar experiments, 239.74±1.64 Ma represents the time of ductile shearing in the area, while the results of muscovite ⁴⁰Ar/³⁹Ar experiments, 266.20±2.77 Ma has many explanations. One is that it represents another period of ductile shearing, and the other is just a cooling time. However, at least one period of ductile deformation occurred in the Xingxingxia area during 260~240 Ma, which may represent the post-collision strike-slip in the Tianshan area after the closure of the North Tianshan Ocean. Thermal simulation results of apatite fission track indicate that, a rapid uplift happened in 90 Ma, which may be influenced by the long-distance effect of the Lhasa block collision or the simultaneous Mongolia-Okhotsk orogeny.

Structural Fractal Texture Characteristics and Its Prospecting Significance for the Yadu-Mangdong Metallogenic Belt in NW Guizhou Province

CUI Zhongliang, YAO Yanling, CHENG Jinhua, LUO Kai, ZHOU Jiaxi

2022, 28(4):  592-605.  DOI: 10.16108/j.issn1006- 7493.2020218

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The fractal geometry method is used to finely determine the structural fractal texture characteristics of the Yadu-Mangdong metallogenic belt in NW Guizhou Province. Combined with the structural ore-controlling characteristics and Fry analysis, the favorable ore prospecting area is delineated and the future ore prospecting direction of Pb-Zn resources in the study area is proposed. The results show that the statistical self-similarity of fault structure is good in the range of 3.371 to 26.965 km. The overall capacity dimension of faults is 1.6052 and the information dimension is 1.6051. The distribution of Pb-Zn deposits has two features, that is high fractal dimension and relative blocking-trap fluid area. Small Pb-Zn deposits are developed in the area that has capacity dimension greater than 1.29 and information dimension greater than 1.39, and medium-large Pb-Zn deposits are developed in area that has capacity dimension greater than 1.58 and information dimension greater than 1.42. The Pb-Zn deposits and their metal resources are significantly clustered and the fractal dimensions of spatial distributions are 1.0096 and 0.9313, respectively. According to the fractal dimension, structural ore-controlling characteristics and Fry analysis, the study area can be divided into four favorable metallogenic grades, of which grade I region has the highest ore prospecting potential. Such a region shows a spatially NW-trending distribution, including the newly discovered Zhugongtang Pb-Zn deposit.

Characteristics and Genesis Mechanism of the Dolomite Reservoir in the Ordovician Majiagou Formation in the Ordos Basin

WU Dongxu, LI Chang, ZHOU Jingao, HU Cong, HUANG Zhengliang, YU Zhou, LI Weiling, GUO wei

2022, 28(4):  606-616.  DOI: 10.16108/j.issn1006-7493.2020222

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The Ordovician dolomite in Ordos basin is an important natural gas reservoir. Studying the genesis of dolomite and reservoir development is of great significance to the development of the deep carbonate exploration theory. Based on observations of a large number of cores and thin sections, combined with geochemical analysis of stable carbon and oxygen isotopes, rare earth elements, order degree of dolomite, formation water and inclusions, the developmental characteristics and formation mechanism of two Ordovician type dolomite reservoirs in the basin were studied in detail. The analyses reveal that the dolomicrite containing anhydrite nodules or columnar crystals is mainly sabkha genesis in an evaporitic environment of tidal flat. The development of its large-scale reservoir was mainly controlled by the long-term unconformity surface, below which plenty of dissolved mold holes of the anhydrite nodules and columnar crystals were developed. The granular beach dolomite is mainly genesis result of seepage reflux and the development of its reservoir pores is primarily affected by the high-frequency fluctuations of the sea level, generating multi-cycle intergranular (intercrystalline) porous reservoirs. Although the dolomitization fluids of both types of dolomite were concentrated seawater, the original pore types and characteristics of the two dolomites are different due to their different mechanisms and rates of dolomitization. In the subsequent diagenetic transformation and evolution, the two types of dolomite pores show both similarities and obvious differences. This finding will provide useful guidance for the exploration of deep dolomite reservoirs.

Reservoir Characteristics of the Qiongzhusi Shales and Their Influencing Factors in the Qujing Area, Yunan Province

HU Lin, XUE Xiaohui, DU Wei, CHENG Peng, ZI Jieneng

2022, 28(4):  617-622.  DOI: 10.16108/j.issn1006-7493.2020210

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Using mudstone and shale samples of the Qiongzhusi Formation in the Qujing area of Yunnan Province as an example, the types and characteristics of microscopic reservoir space of the shales were investigated by combined methods, including Argon ion polishing-field emission scanning electron microscopy (FESEM), high-pressure mercury injection and conventional scanning electron microscopy (SEM). Results show that the pores in shale samples of the Qiongzhusi Formation have complex formation mechanisms and different types including organic pores, clay mineral pores, grain mineral pores and microfratures, of which the organic pores dominate. The porosity is between 1.59%-11.33% with an average value of 5.0%. The reservoir space proportions of micro- and transitional pores are about 56.5%, mesopores and macropores are about 34.0%, while macropores are relatively undeveloped. TOC contents, mineral compositions and diagenesis are the main controlling factors for the development of shale pores in the Qiongzhu Formation. TOC is the main control for the development of shale pores in the Qiongzhu Formation.


Evaluation of Sealing Properties of Multi-stage Extensional Abutting Faults in Bohai Sea

REN Jian, HAN Rui, HUANG Zhen, HAN Zijun, HOU Dongjia, CHEN Xingpeng

2022, 28(4):  623-633.  DOI: 10.16108/j.issn1006-7493.2020109

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Bohai Sea area experienced a complex tectonic evolution history including the multi-stage extension which led to the development of a complicated abutting faults system. Although the formation of abutting faults has been demonstrated to contribute significantly to the hydrocarbon accumulation in the fault block traps, while strong hydrocarbon productivity heterogeneity has appeared in lots of drilling practices, and hydrocarbon leakage was the main cause for some drilling failure. Comprehensive analyses and comparisons combining the 3D seismic, well data, and analogue modeling reveal that three factors are related to the sealing ability of abutting faults: (1) the evolution level of abutting faults determines the degree of leakage in fault intersection; (2) the time interval between charge and leak controls the effective charging timing; (3)difference in stress among faults resulted from oblique extension of pre-existing faults determines the ability of stress sealing. The height of trapped hydrocarbon column derived from drilling data in the structures with abutting faults of Bohai Oilfield shows excellent correlation with the sealing ability analysis based on the above three factors, demonstrating that this method has good application prospects in petroleum exploration in areas with similar structures.