Table of Content

26 October 2019, Volume 33 Issue 05

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Structural Geology and Stratigraphy

Late Mesozoic Paleotectonic Stress Fields Inferred from Fault-slip Data in Central and Western Yanshan Orogenic Belt: Implications for Destructive Geodynamics of North China Craton

GAO Jianweng, LIN Yi, ZHANG Changhou, DING Zhaoyue, HOU Liyu, HUANG Yingzhu

2019, 33(05):  919-936.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.01

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A dataset of 2,321 fault-slip data were collected from 116 sites in Late Mesozoic plutons in the central and western Yanshan orogenic belt. Paleostress field inversion was carried out via Tensor from these data. A five-generation sequence of paleostress fields has been established from the inversion results combined with regional tectonic deformation analysis. We found that: (1) Latest Jurassic-Earliest Cretaceous (148-127 Ma) compression with N-S-trending maximum principle stress (σ₁) (D₁); (2) Early Cretaceous (143-127 Ma) compression with NW-trending σ₁ (D₂); (3) Multidirectional extension with a nearly vertical σ₁ (D₃, ~120-110 Ma); (4) Compression with NE-trending σ₁ (D₄), and (5) Compression with E-trending σ₁ (D₅). D₁ and D₂ are interpreted as the far-field effects correlated with the closing of Mongol-Okhotsk Ocean and west-dipping subduction of paleo-Pacific plate, respectively. These two tectonic systems have major impact on the deformation of the Yanshan orogenic belt. D₃ may have reflected the vertical compression derived from deep mantle activity. Tectonic events unambiguously related to D₄ and D₅ have not been reported so far, which implies relatively weak paleostress field, and their geodynamic setting remains unclear. We suggest that a model of multidirectional extension induced from vertical compression may be applicable to the peak destruction of the North China Craton, instead of a passive rifting model dominated by subduction roll-back of the paleo-Pacific plate as previously proposed.

Neoproterozoic Post-orogenic Tectonic Transformation in Eastern Margin of the Yangtze Block:Petrologic and Geochronologic Constraints of the Weng’an Dome

SONG Zhidong, YAN Danping

2019, 33(05):  937-956.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.02

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The timing and processes of the transformation from the Rodinian post-orogenic tectonics to extension in the Yangtze block have been an important question in the Neoproterozoic Yangtze tectonic evolution. The Weng’an Dome in the southeastern Yangtze block has preserved the complete stratigraphic sequence, and the unconformity between the Neoproterozoic Banxi Group and the Nantuo Formation in the Nanhua period, and is thus an ideal target to investigate the Neoproterozoic post-orogenic tectonic transformation. We study the sedimentary sequence of the low-grade metamorphosed sedimentary rocks of the Neoproterozoic Banxi Group and Nantuo Formation (Nanhua period), via detrital zircon U-Pb dating and whole-rock geochemical analyses. Field geology shows that the Nantuo Formation (Nanhua period) lies unconformably on the Banxi Group. Age dating results indicate the maximum depositional ages for the Banxi Group and Nantuo Formation are 772 Ma and 691 Ma, respectively. Neoproterozoic rocks in the Weng’an Dome (Banxi Group) have intermediate SiO₂ contents, with the average values of SiO₂/Al₂O₃=5.53, K₂O/Na₂O=7.14 and (TFeO+MgO)=3.47%. The Neoproterozoic Banxi Group sedimentary rocks may have sourced from the feldspar-quartz-dominated upper crust. The Weng’an Dome may have formed in an active continental margin, and the clastic material may have derived from the western margin of the Neoproterozoic Yangtze block. The Nantuo Formation sedimentary rocks have intermediate SiO₂ contents, with average values of SiO₂/Al₂O₃(4.69), K₂O/Na₂O (20.41) and (TFeO+MgO) (6.64 %). The REE chondrite-normalized patterns of the clastic rocks resemble those of the upper continental crust, as characterized by LREE-enrichment, flat HREE patterns and negative Eu anomalies. The Nantuo Formation sediments may have come from the feldspar-quartz-dominated (with minor intermediate rocks) upper crust. The Weng’an Dome was likely formed in a rifting-related tectonic setting. In summary, we suggest that the stratigraphic transition from the Banxi Group to the Nantuo Formation represents the tectonic transformation from syn-collisional orogeny (till ~772 Ma) to post-orogenic rifting (after ~691 Ma). Therefore, the syn-to post-orogenic tectonic transition occurred at about 772-691 Ma.

Zircon U-Pb Ages for Volcanic Rocks in Bayan Har Group in the Northern Tibetan Plateau and Its Geological Significance

XIA Mengmeng, GAO Wanli, HU Daogong, ZHANG Yaoling, XU Jiusheng, JIA Liyun, WANG Chaoqun

2019, 33(05):  957-969.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.03

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Using laser ablation multiple collector inductively coupled plasma mass spectrometry(LA-ICP-MS)method, the authors determined zircon U-Pb isotopes of the dacitic rock interlayers of Bayan Har Group in Kabaniuerduo area of northern Tibetan Plateau. The authors conducted dating of six samples and obtained ages of (208.1±0.8) Ma, (206.1±1.2) Ma,(208.2±1.3) Ma, (207.5±1.1) Ma, (203.8±1.9) Ma, and (205.1±1.8) Ma, respectively, precisely showing the Early Rhaetian age of the Late Triassic. These dating results of the volcanic rocks would benefit the stratigraphic classification and correlation of the Upper Triassic flysch within the Bayan Har Group and could provide evidence and age constraints for the collision and orogeny between blocks of Baryan Har block and Kunlun block.

Late Pleistocene Tectonic History of the Western Segment of Maniao-Puqian Fault: Evidence from the Laocheng Section, Northern Hainan Island

LI Wei, JIA Liyun, HU Daogong, ZHANG Xujiao, XIA Mengmeng, LIN Wenjie, YUAN Yue

2019, 33(05):  970-978.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.04

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Maniao-Puqian Fault is an important seismogenic fault for the M7.5 Qiongshan earthquake in Hainan in 1605. Its tectonic history is of great significance for evaluating the crustal stability, earthquake risk mitigation, and the engineering of major construction projects such as the bridge connecting Hainan island and Leizhou peninsula. Geological and geomorphic studies show that the western segment of Maniao-Puqian Fault zone is about 2.5 km wide from north to south, and composed of three near-E-W-trending subparallel stepped normal faults. Fault profile excavation in Laocheng town exposed a wide (~70 m) N-S-trending fault zone, which reveals the fault tectonic history. Optically stimulated luminescence (OSL) dating results of the Daotang Formation indicate that the fault had experienced two tectonic events in 16-31 ka BP: an earlier N-/S-dipping normal faulting with a 3.3 m cumulative vertical displacement, followed by an intensive S-dipping normal faulting. Stratigraphic displacement in different ages indicates that the Maniao-Puqian Fault has been active since Pliocene, and its activity is strong in the Quaternary. It remains an important active fault in northern Hainan island.

Milankovitch Cycles of the Precambrian Hongshuizhuang-Tieling Formations at Jixian Section in Tianjin

REN Chuanzhen, CHU Runjian, WU Huaichun, FANG Qiang

2019, 33(05):  979-989.  DOI: 10.19657/j.geoscience.1000-8527.2019.007

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Sedimentary cycles preserved in the Phanerozoic Eon can be associated with the changes in the ellipticity of Earth’s orbit, the tilt and the precession of Earth’s rotational axis, but evidence from the Precambrian sequences is still lacking. The Mesoproterozoic Hongshuizhuang-Tieling formations at the Jixian section in Tianjin were deposited in the lagoonal-tidal flat environment, and are dominated by rhythmic sand-shale interbeds. To explore whether the rhythmic sequences are related to the Milankovitch cycles, a high-resolution cyclostratigraphy study was conducted on the paleoclimate-paleoenvironment proxies of the lithology, magnetic susceptibility (MS), and gamma-ray (GR) features of the Hongshuizhuang-Tieling formations. Spectral analyses show that the wavelength ratios of the cycles in these stratigraphic units correspond to the hierarchies of the Mesoproterozoic Milankovitch cycles. The sedimentary cycles of 1.2-1.5 m, 0.4 m and 0.17-0.19 m can be associated with the short eccentricity, obliquity and precession, respectively, in the lower part of Member 1 of the Tieling Formation. The 0.1 m sedimentary cycle may be associated with semi-precession cycle in the Tieling Formation. The major sedimentary cycles of 1.1-1.8 m, 0.34-0.54 m, 0.14-0.16 m and 0.08-0.09 m are considered to be caused by long and short eccentricity, obliquity, and precession in the upper part of Member 2 of the Hongshuizhuang Formation, respectively. After calibrating to the 405 ka long eccentricity cycles, the spectra represent periods of the 100 ka short eccentricity, 22-24 ka obliquity and 15 ka precession, respectively. Moreover, the eccentricity amplitude modulation cycles show main periodicities of ~2.0 Ma, which is shorter than that at present (~2.4 Ma).

Petrology

Discovery and Significance of Early Jurassic Bimodal Volcanic Rocks in Huoshaoyun, Karakoram

ZHOU Nengwu, CHEN Bangxue, DENG Zhongfei, SANG Mingshuai, BAI Quanjin

2019, 33(05):  990-1002.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.06

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The Karakoram volcanic rocks are close to the Qiao’er Tianshan Fault, and the two are closely space-time related. The SiO₂ contents of the basalt and dacite are of 48.84%-52.44% and 62.22%-65.63%, respectively. They have obvious Daly intercepts and are typically bimodal. Basalt has a low content of Al₂O₃, and high contents of MgO, CaO, TiO₂. Some trace elements (Sr, Ba) are strongly depleted, whereas the high field strength elements (HFSEs, e.g.Ta, Nb, Ti, Zr) are not depleted. Dacite has relatively high Al₂O₃, Na₂O and K₂O contents, but low MgO, CaO and TiO₂ contents, and are enriched in large ion lithophile elements (LILEs, e.g.Rb, Th, U, K), depleted of HFSEs, showing typical island arc geochemical affinity. Both the basalt and dacite are calc-alkaline, co-magmatic and likely formed in back-arc basins. Dacite may have formed from the fractionation of basaltic magma. LA-ICP-MS zircon U-Pb dating of the dacite yielded Early Jurassic age of (195.5±1.1) Ma. Considering the regional tectonic evolution, it is concluded that the Qiao’er Tianshan area may have been a developing backarc basin. We suggest that the lithospheric mantle of the basin during the volcanism had not been broken off and no oceanic crust was formed.

LA-ICP-MS Zircon U-Pb Age and Geological Significance of the Early Cretaceous Monzogranite in Xiaowulangou, Xilinhot, Inner Mongolia

TENG Chao, ZHANG Xiaofei, ZHOU Yi, FENG Junling, LI Shucai

2019, 33(05):  1003-1014.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.07

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Based on 1∶50,000 regional geological survey, we studied the monzogranite in the southern Central Asian Orogenic Belt (CAOB) at Xiaowulangou (Xilin Hot, Inner Mongolia)based on its petrology, zircon U-Pb age and geochemistry. LA-ICP-MS zircon U-Pb dating yielded Early Cretaceous age of (121.29±0.63) Ma. Petrological and geochemical data reveal that the monzogranite is characterized by high Si and K, low Mg, Ca, P and Ti. The rocks are high-K calc-alkaline and peraluminous. The rocks are enriched in large ion lithophilic elements (LILEs, e.g.Rb) and some high field strength elements (HFSEs, e.g.Th and Ta), but depleted in Nb, Sr and Ba. Rare earth element (REE) compositions are characterized by slight LREE enrichments and negative Eu anomalies. Geochemical characteristics suggest that the monzogranite is A-type, and may have been a product of partial melting of continental crustal rocks. Tectonic discrimination diagrams show that these rocks resemble post-orogenic A₂-type granite, indicating that the region was likely in a post-orogenic extensional setting during the Early Cretaceous.

Geochemical Characteristics and U-Pb Age of Redamen Granites in Western Sichuan, China: Petrogenesis and Tectonic Significance

YUE Xiangyuan, YANG Bo, ZHOU Xiong, GONG Daxing, YE Yakang, TAN Hongqi, ZHOU Yu, ZHU Zhimin

2019, 33(05):  1015-1024.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.08

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The Redamen quartz diorite is located in the northeastern part of the Songpan-Ganzi orogenic belt. LA-ICP-MS zircon U-Pb dating of the pluton yielded Late Triassic age of (206.4±1.4) Ma. The quartz diorite contains SiO₂ contents of 50.62% to 56.66%, K₂O/Na₂O of 0.32 to 1.20, aluminum saturation index of 0.59 to 0.86, and Rittermann index of 0.40 to 1.20. The samples are subalkaline, metaluminous, and high-K calc-alkaline to calc-alkaline. Total REE (∑REE) contents are of 81.45×10^-6 to 222.39×10^-6, with LREE/HREE of 5.38 to 10.45 and (La/Yb)_N values of 5.98 to 12.99. The rocks show Eu anomalies (δEu=0.66-1.01) and Ce anomalies (δCe=0.81-0.93). The Redamen quartz diorite may have emplaced in a collisional orogenic setting, via magma upwelling and partial melting of the lower crust.

Petrogenesis and Tectonic Implications of the Jintonghu Granitic Porphyry in Zijinshan Orefield, Fujian Province

ZHANG Qian, WU Xiangbin, YANG Mu, QIAN Meiping, DIAO Qian, MENG Feisi

2019, 33(05):  1025-1035.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.09

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Genesis of Mesozoic granites in South China is important for studying the evolution of the lithosphere, as well as the regional granite petrogenesis and related mineralization. In this contribution, in-situ LA-ICP-MS U-Pb, trace element and Hf isotope analyses of zircon were conducted to constrain the emplacement age and petrogenesis of the granitic porphyry at the Jintonghu Cu-Mo deposit, western Fujian, China. The Jintonghu granitic porphyry is U-Pb dated to be Early Cretaceous (101.1±1.9 Ma). The zircon ε_Hf(t) values (-6.1 to 0.7) and the two-stage Hf model ages (1.09 to 1.51 Ga) preclude the possiblilty that the parental magmas of the Jintonghu granitic porphyry was dominantly sourced from the basement materials or metasedimentary rocks. The low zircon Ce⁴⁺/Ce³⁺ ratios suggest that the Jintonghu granitic porphyry mimics fractionated I-type granites in the Nanling Range, and the magmas were likely derived from older felsic igneous domains with little juvenile material contributions. Interpretations of the elemental and isotopic data suggests that the Jintonghu granite was most likely derived from partial melting of old deep-seated magmatic rocks due to the subduction of Paleo-Pacific Plate in an active continental marginal setting.

Geochemistry

The Alteration Characteristics and Element Migration Law of the Jinchiling Gold Deposit, Shandong Province

GAO Jianwei, TENG Chao, ZHAO Guochun, LIU Wenqing, ZHOU Yi

2019, 33(05):  1036-1045.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.10

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Jiaodong area,the most important gold province in China,is an area with concentration occurrence of large and super large gold deposits,the proved reserves in Jiaodong Peninsula account for nearly 1/3 of the country. Among them, the quartz vein type gold deposit is an important type of deposits in the area, and the Jinchiling gold deposit in Shandong is the representative of this type. Based on the detailed geologic observations in the field and indoor research, this paper found out the alteration type and mineral combination characteristics of the gold deposit, collected rock samples of different alteration types, conducted geochemical analysis of rock elements, and summarized the migration law of elements during hydrothermal alteration by using mass balance method. The surrounding rock of the deposit is granite, and the ore-bearing hydrothermal fluid surges along the fault, which has a strong alteration effect on the surrounding rock. This paper argues that the alteration types are mainly potash-alteration, silicification-sericitization and pyritization silicification-sericitization. The material exchange in the alteration process changes the composition of the fluid and so on. The fluid provides a large amount of SiO₂ to the altered rock. At the same time, the surrounding rock of the alteration process provides a large amount of K and Na to the fluid, which promotes the activation of Au in the fluid, causing the stability of AuH₃SiO₄ in the hydrothermal fluid to decrease, and causing the decomposition of AuH₃SiO₄, and then the Fe²⁺ and Fe³⁺ are consumed to form pyrite, resulting in gold mineralization.

Distribution Characteristics of Selenium Cultivated Soil and Its Influencing Factors in Hailun County of Heilongjiang Province

ZHANG Li, LIU Guodong, LÜ Shijia, CUI Yujun, WANG Enbao

2019, 33(05):  1046-1054.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.11

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Heilongjiang Province is considered to be a region with severe selenium deficiency in China, and the distribution of selenium in soil is extremely uneven. Large-scale selenium-enriched soil was first discovered through agricultural geological surveys in recent years. Through the statistical analysis of soil selenium content in the farming area of Hailun County, the distribution characteristics and influencing factors of soil selenium were discussed, which provided a scientific basis for rational development of local selenium-rich resources. 15,608 surface soil samples of 0-20 cm depth and 976 deep soil samples of 150-200 cm depth were collected in the study area, and chemical indicators such as total selenium content and selenium morphology were analyzed. The soil selenium content in the study area was evaluated according to the national selenium-enriched soil standard. The selenium content in the surface soil was between 0.02-0.87 mg·kg^-1 with the average content 0.29 mg·kg^-1. 93.87% of the soil was selenium-sufficient soil, and 4.9% of the soil was selenium-rich soil. There was almost no potentially selenium deficient or deficient soil. The average content of selenium in different soil types from high to low: paddy soil>black soil>meadow soil>aeolian sandy soil>dark brown soil. Relevant analysis results showed that the main factors affecting soil selenium content in the study area were soil pH, organic matter and soil parent material. The main forms of selenium in soil were organic-bound forms. Total selenium, organic matter and pH were also the main factors affecting the selenium availability.

A Study on the Variation of Plant Nutrient Elements in Soils at the North of Longyou County,Zhejiang Province

HE Ling, ZHOU Guohua, SUN Binbin, JIAN Zhonghua, HUANG Chunlei, KANG Zhanjun

2019, 33(05):  1055-1062.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.12

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The concentration and their balance of nutrient elements in arable soils are of important influence on crop growth. Identifying the temporal and spatial change of nutrient elements in soils is a key task to monitor geo-chemical change of land quality. The temporal and spatial variation of nutrient elements in soils at the north of Longyou County was recognized through statistical and spatial analysis based on the two sets of data respectively obtained in 2008 and 2014 after eliminating systemic analytical bias. The results showed that the contents of N and K₂O in soils decreased and the net relative accumulation rates were -4.40% and -13.81% respectively during the past six years. The variation of B and P concentration in soils was not obvious. The accumulation rates of different nutrient elements in soils were mainly controlled by the types of soil and land use. For example, N content in paddy fields showed an obvious trend of enrichment but depletion in woodland, vegetable fields and dry land. P concentration in vegetable fields, garden fields and dry land presented significant enrichment, while in paddy fields shows a trend of depletion.

Establishment of A Geochemical Model for Different Se-enriched Crops in Yinkeng-Qiaotou-Ma’an Area,Yudu County,Jiangxi Province

MA Ming, YAO Lingyang, XIE Shuyun, TANG Molan, BAO Zhengyu, CHEN Guoguang

2019, 33(05):  1063-1069.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.13

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In this paper, 61 sets of rice, peanut samples and their root soils were collected and systematically studied in the geological background of sandstone and mudstone in Yudu region of Jiangxi Province. The results showed that the average content of selenium in rice was 0.062 μg/g, the average content of selenium in rice roots was 0.39 μg/g, the average content of selenium in peanut was 0.051 μg/g, and the average content of selenium in peanut roots was 0.44 μg/g. In addition, the selenium enrichment rates of rice and peanut were 30.00% and 16.10%, respectively, corresponding to the root soil selenium content exceeding 0.4 μg/g accounted for 36.07%. Correlation analysis showed that there was a positive correlation between selenium content and TFe₂O₃, MnO, TOC, S, LOI, N, CaO, MgO, Na₂O and negative correlation with SiO₂. Crop selenium content was positively correlated with total selenium, bioavailable selenium, TOC, Fe-Mn oxides, calcium-magnesium compounds and sulfur contents, and use these properties to establish the geo-geochemical fitness model of selenium-enriched crops. Therefore, under the geological background that the soil parent material is sandstone and mudstone, the development of selenium-enriched agricultural products should not only be based on the total selenium content in the soil, but also consider the available selenium, TOC, Fe-Mn oxide, calcium and magnesium oxide, and sulfur content.

Mathematical Geology and Remote Sensing

Geomorphic Features and Its Constraint to Sandstone-hosted U Deposits Occurrence in Mid-Kezelkum, Uzbekistan

SUN Yue, PAN Jiayong, CHEN Zhengle, HAN Fengbin, LIU Wenheng, XIAO Weifeng

2019, 33(05):  1070-1078.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.14

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The region of Mid-Kezelkum, located at the western of Tianshan orogenic belt in Central Asia, is a famous sandstone-hosted uranium metallogenic province in the world. In order to clean up the controls of the topographic and geomorphic conditions on both formation and conservation of sandstone-hosted U deposits. The elevation, slope, aspect, surface rolling, swath profile, and other kinds of geomorphic features are extracted from digital elevation model (DEM) data using geographic information system (GIS) technology, and geomorphic features with sandstone-hosted U deposits are quantified in this paper. The results show that the favorable landforms for sandstone-hosted U deposits are the elevation of 100 m, the slope of 0°-5°, the topographic relief of 10-35 m, and the sub-basin hypsometric integral (HI) of 0.3-0.6. There are 4 clear planation surfaces in Mid-Kezelkum, and the elevation are 2 200 m (I), 1 600 m (II), 1 100 m (III), and 330-400 m (IV), respectively. The sandstone-hosted U deposits were developed near the IV planation surface. By analyzing the correlation of different geomorphic factors, the sandstone-hosted U deposits are concentrated in the low-altitude and low-relief regions. Both of which can be used as the main factors for prediction of prospecting for sandstone-hosted U deposits. In addition, the favorable sandstone-hosted U deposit areas are delineated by means of spatial analysis and geomorphic features which provide the basis for further prospecting in Mid-Kezelkum.

The Extraction of Alteration Information with Remote Sensing Image of Semi-exposed Area: A Case Study of the Maqu Area in Gansu

LIAN Chenqin, YAO Fojun, YANG Jianmin, GENG Xinxia, CUI Shunyao, PU Wanfeng, ZHANG Zhigang

2019, 33(05):  1079-1085.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.15

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Aiming at the problem of remote sensing alteration information extraction in semi-exposed area, this paper proposes a method based on partition processing to extract alteration information. Using Aster image as the main data source, the study area is divided into vegetation area and exposed area by using the normalized vegetation index (NDVI). The exposed area extracts alteration information by using the combining method of lossless linear stretching, principal component analysis(PCA) , abnormal cutting and abnormal filtering. The vegetation area extracts alteration information by using the combining method of vegetation suppression, lossless linear stretching, principal component analysis, abnormal cutting and abnormal filtering. The extracted information is analyzed and verified by using the known geological and mineral data. The results show that the alteration information extracted by this method is in good agreement with the known gold deposits. Based on remote sensing and other information, the remote sensing target areas are optimized, and the target areas are verified in the field. Four mineralized areas are discovered. In summary, this method is feasible for the alteration information extraction in this area, and has important guiding significance for gold exploration.

Environmental Geology

Remote Sensing Survey on Glacial Dynamic Evolution in the Himalayas in China During 1999—2015

AN Guoying, HAN Lei, TU Jienan, ZHI Ruirong, HUANG Shuchun, TONG Liqiang

2019, 33(05):  1086-1097.  DOI: 10.19657/j.geoscience.1000-8527.2019.05.16

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Using the two-phase remote sensing images based on the ETM in 1999 and the GF-1/OLI in 2014/2015 in the Qinghai-Tibet region, the glacial cataloging is completed and the glacial changes in the Chinese Himalayas during 1999-2015 is summarized. The results show that glaciers were generally retreating in the Himalayas from 1999 to 2015. There were 85 (1.53% of total)retreating glaciers with a total decrease in size and volume of 42.00 km²(0.67%)and 2.385 km³(0.50%), respectively.Along the Himalayas from east to west,the number of glaciers decreased more in the east, whereas the size and volume decreased more in the west with glaciers relatively stable in the middle.On one hand, the glaciers retreated in the north, northeast and east, with the loss of the number and size being the highest in the north, followed by the northeast and the east. Meanwhile, the reduction rate of the glacier number and size was the highest in the east and northeast, respectively, and lowest in the north. While the size decreased mostly in the average slope of 10° to 15°, the number decreased mostly in the slope of 30° to 35°. The glacial retreat was most significant at 5,500 to 6,000 m elevations, followed by 5,000 to 5,500 m.The reduction rate was the highest at 3,500 to 4,000 m elevations,and lowest at 6,000 to 6,500 m elevations.Decreases in the glacial number and size were obvious in the Yarlung Zangbo River Basin (5O2), followed by Langqin River Basin (5Q2)and Pengqu (5O1), but least in Zhari Nanmucuo (5Z3). The retreat or disappearance of a large number of smaller glaciers, accompanied by the retreat of larger ones, is the main cause of glacier changes in the Himalayas. There is a close relation between glacial retreat and climate change in the Himalayas. Analyzing the annual mean temperature and annual precipitation over the past decades, the annual average temperature has increased significantly since the 1961’s, whilst the annual precipitation has increased or decreased. The temperature rise and precipitation drop may have caused the glacial retreat in the survey period.

Construction of DEM in Baiyangdian Wetland Based on Remote Sensing Thematic Interpretation

WANG Kailin, LI Haitao, LI Wenpeng, LI Muzi, CHEN Yichao, ZHANG Baoyun

2019, 33(05):  1098-1105.  DOI: 10.19657/j.geoscience.1000-8527.2019.006

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Based on multi-temporal Landsat Remote Sensing imaging, a synthetic method suitable for extracting Baiyangdian Wetland was used. Considering the wetland range as the submerged area, and its boundary line is regarded as the contour line of the surface water level. According to remote sensing images, elevation control points, the regions affected by human activities in wetlands are adjusted, and the Digital Elevation Model (DEM) of the Baiyangdian Wetland is generated by interpolation. Through verifying the remote sensing images and ground elevation control points, the DEM accuracy is estimated to be over 80%, and the verifying error of the ground control point (-0.5 m to 0.5 m) reaches 80%. The DEM extraction from a series of remote sensing images can make up the defects of insufficient digital elevation information in the Baiyangdian Wetland. This study is important to improve the water balance calculation of the Baiyangdian wetland and the accuracy of the coupled model between the lake and groundwater.

Hydrochemical Feature Genesis and Hydrocarbon Exploration Significance of Chang 8 Tight Sandstone Reservoir in Longdong Area,Ordos Basin

SI Yang, ZHANG Wenxuan, LUO Anxiang, SUN Bo, ZHU Yushuang

2019, 33(05):  1106-1117.  DOI: 10.19657/j.geoscience.1000-8527.2019.005

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Domestic studies on the relationship between formation water and reservoirs are mostly concentrated in fault block depressions, and such studies are relatively rare in lithologic reservoirs. Based on a large data set of the formation water chemical compositions,thin-section petrography and scanning electron microscopy of the Chang 8 tight sandstone reservoir in Longdong area of Ordos Basin, the chemical characteristics and genesis of the Chang 8 formation water were analyzed and their hydrocarbon exploration implications were discussed. The study shows that the average salinity of formation water in the reservoir is 33.6 g/L. The formation water is mainly of CaCl₂ type, and the hydrogeological system is closed, conducive to oil preservation. Ionic characteristics of the formation water are closely linked with the Chang 8 sandstone diagenesis. The Mg²⁺ depletion and slight Na⁺ enrichment/depletion may have mainly related to chloritization, albitization and dissolution of plagioclase. The Ca²⁺ excess is unlikely only related to albitization and plagioclase dissolution, but also related to the Ca²⁺ release by volcanic ash in mudstone. The {{\mathrm{SO}}_4}^{2-} and {{\mathrm{HCO}}_3}^{-} contents may have been controlled mainly by desulfurization and carbonate cementation. Since the diagenesis of the Chang 8 sandstone was much affected by hydrocarbon charging, the water chemistry characteristics of the western/central/eastern sequences of the study area are different. The Na/Cl coefficient of the formation water in the western part is lower than that of the central and eastern parts, whereas the {{\mathrm{SO}}_4}^{2-} content and desulfurization coefficient of the formation water are higher. We suggested that this is closely related to the different filling conditions of the reservoir.

Study on Physical and Mechanical Characteristics and Stability Analysis of Ancient Landslide Deposit in East Tibet

ZHAN Meiqiang, GE Yonggang, JIA Lirong, YAN Hua

2019, 33(05):  1118-1127.  DOI: 10.19657/j.geoscience.1000-8527.2019.003

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The proposed Sichuan-Tibet Railway is the most complicated railway in nature and geological environment. The geological disaster, as a key control node of local and even the whole line, is related to the success or failure of Sichuan-Tibet Railway construction. Field investigation shows that the Denongnongba ancient landslide is located on the first order land of the right bank in Zangqu River, and has attracted much attention in the process of railway line selection or construction in Sichuan and Tibet, and its stability is a necessary condition for railway selection line. Based on field investigation, this paper systematically calculated and analyzed the physical and mechanical parameters and stability of the ancient landslide deposit. The results show that under natural conditions, the dry density of gravel is above 1.75 g/cm³, and the water content is less than 4%, and the cohesion and internal friction angle of the deposit are significantly correlated with water content, which decreases with the increase of water content. Based on FLAC^3D numerical simulation and GEO-SLOPE stability result, it is shown that the landslide deposit is stable under natural and rainstorm conditions, but the stability of toe and the posterior edge of slope is poor under heavy rainfall condition, and the stability coefficient of toe is only 0.761. Under the action of rainstorm, earthquake and human activity, the deposit is likely to be local instability, which affects the safety of railway construction and the residents on the slope, and it is necessary to take comprehensive management and stability monitoring to the landslide.

Research on the Surface Textures of the Quartz Sand in Diamictons

CHEN Ruichen, CHEN Jian, CUI Zhijiu

2019, 33(05):  1128-1136.  DOI: 10.19657/j.geoscience.1000-8527.2019.004

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Due to the characteristics of quickness and no-sorting in the transport and deposition processes, the cause of formation identification of diamictons has become the main concern among domestic and foreign scho-lars. The comprehensive study on the surface textures of quartz sands in diamictons is one of the common me-thods to reconstruct sedimentary environment, which plays an important role in the identification of diamictons. This paper summarized the previous studies to construct an interpretation scheme and combination mode to differentiate among deposits of till, landside, debris, and dam-break flood deposits based on micro-textures. Moreover, the relationship between the particle contact mode and quartz sand surface micro-texture of these high-energy events was analyzed. Based on the current difficulties in the study of surface textures of quartz sands in diamictons, the future research direction and the key problem to be solved were proposed.