Geological Journal of China Universities

A DISCUSSION ON THE EXHALATIVE SEDIMENTARY MASSIVE SULFIDE DEPOSITS OF SOUTH CHINA

Xu Keqin, Wang Henian, Zhou Jianping, Zhu Jinchu

1996, 2(3): 241-256.

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The seafloor exhalative sedimentary mineral deposition is a very important process by which many copper, lead, zinc, iron, tin, silver and gold deposits in South China were formed. Many polymetallic massive sulfide deposits in this area, previously thought to be of magmatic hydrothermal type or skarn type, have been studied and recognized by the present authors as the exhalative sedimentary deposits, These deposits can be subdivided into five groups according to the tectonic environments of their formation and types of their host rocks: 1) Cu an Cu-Pb-Zn massive sulfide deposits related to spilite-keratophyre series, such as Xiqiu Cu deposit in Zhejiang Province; 2) Sedimentary rocks-hosted massive sulfide deposits, such as Dajiangping pyrite deposit in Guangdong Provinces; 3) The Kuroko-type deposits in island-arc rift, such as Xiacun Ag-Pb-Zn deposits in Sichuan Province; 4) Massive polymetallic sulfide deposits in ancient fault depressions, such as Dabaoshan Cu-Pb-Zn deposit and Fenglin Cu deposit in Guangdong and Jiangxi Provinces respectively; 5) Exhalative sedimentary deposits in fault-controlled Mesozoic-Cenozoic continental basins, such as the massive sulfide deposits in Nanjing-Wuhu area. These sedex deposits are widespread and usually form extensive metallogenic belts, such as Fe-Cu (Au) belt of middle-lower reaches of Yangze River, Sn-polymetallic belt in NW Guangxi province, and Sn-Ag polymetallic belt in SE Yunnan province. The major features of mineralizations and the space-time distribution of the massive sulfide deposits in South China are also discussed. It has been emphasized in this paper that the exhalative sedimentary massive sulfide deposits in ancient fault depressions are extremely specific for South China. In addition, the group of exhalative sedimentary deposits in the fault-controlled Mesozoic-Cenozoic continental basins are worthy to be further studied in the future.

A DISCUSSION ON THE GENESIS AND TECTONIC SETTING OF ALKALI GRANITES IN THE ULUNGUR ALKALI-RICH GRANITE BELT, XINJIANG

Liu Jiayuan, Yuan Kuirong

1996, 2(3): 257-272.

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A series of alkali and meta-alkali granitic intrusives occur along Zahebar-Sarterik-Tasgark-Almat on the south bank of Ulungur River and are controlled by Ulungur deep fault in the northwest part of Eastern Junger, Xinjiang, which form a distinctive alkali granite belt in the area. This belt, in association with Ulungur ophiolite belt nearby, has important significance in tectonics of the area. Evidences from geology, mineralogy, petrology and geochemistry show that these granites in the Ulungur alkali granite belt fall into Type A in granitoid classification. However, they contain high contents of Fe2O3, MnO and have higher ratio of Na2O/K2O, in comparison with typical A-type granitoids known at home and abroad. On the basis of comp0rehensive study and previous works on the Ulungur alkali granites, the authors suggest a composite model of “mantle material transport + partial melting of dehydrated sial source +granitic magma differentiation + tensional tectonics” to explain well the petrogenesis of A-type granites in this area. Geochemical plots, together with the analysis on evolution of the regional tectonics, show that the Ulungur alkali granites intruded during the post collision-orogeny tensional tectonic significance because not only they mark the termination of Easter Junger orogeny, but also their spatial distribution, together with the Kalimaili alkali granites in the south, demonstrates the presence of grand suture between the Siberia plate and the Khazakstan plate. It again proves that the study of granitoids plays an important role on geotectonics in certain area.

THE TREND SURFACE ANALYSIS OF ORE BODY DITRIBUTION AND ITS RELATION WITH THE ORE-CONTROLLING STRUCTURES IN SHAXI PORPHYRY COPPER DEPOSIT, ANHUI PROVINCE

Yang Xiaoyong1 2, Wang Kuiren1 2, Sun Murong1, Wang Xiangyun3

1996, 2(3): 273-283.

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This paper presents the morphological feature of the ore bodies in Shaxi porphyry copper deposit by means of trend analysis and with the help of computer program. Considering the geological structures and the thermal fluid alteration which control the ore bodies, the authors dicuss the relationship between the distribution of ore bodies and the ore-controlling structures and thermal fluid alteration in the ore deposit. The results show that there exists good correlation between the ore bodies derived from the trend surface analysis and those from exploration.

INTERMITTENTLY LATERAL TRANSFERRED RIFTING AND PROGRESSIVE- LEAPING INVERSION: A CASE STUDY FROM THE FUXIN BASIN

Wang Guiliang1, Ma Xingyuan2, Jing Huilin3, Yun Wu1, Wang Daqing1, Tan Haiqiao1, Li haiyu1

1996, 2(3): 284-294.

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The Fuxin fault basin is located on the western side of the uplifted core of Lushan anticline. Since Early Cretaceous intermediate volcanic rocks of the upper Yixian Formation had been accumulated in the graben defined by fault F”1 and fault F2 at the eastern and western margins respectively. After volcanic eruption ceased, terrestial clastic sediments of the Jiufutang Formation were then deposited in the F”1-F2 bounded graben. Following the early rifting, the crust in the areas tilted and uplifted, as a result, structural inversion initiated and deposition stopped in the southern part of the basin, the Yixian district. At the same time, the fault F2 at the western margin stopped its activities. During the Shahai episode, the basin evolved from a graben to a half-graben controlled by the fault F’1,with down-faulting at the eastern boundary and overlapping at the western boundary. As soon as the Shahai episode rifting ceased and the fault F”1 rested, the rifting of Fuxin episode occurred in the half-garben which had transferred eastwards and been controlled by the marginal fault F’1. After the Fuxin episode rifting ended, the basin undergone a leaping inversion, which many normal faults became the compound faults, namely, reserve fault at upper and normal ones at lower parts, and many positive flower structures were developed. The subsidence of Sunjiawan episode in Middle Cretaceous are further transferred eastward, and the half-graben defined by the fault F1 was formed. After the Sunjiawan episode, a basinwide uuplift and fold-fault took place, and finally the evolution history of the basin ended. The intermittently lateral-transferred rifting and progressive leaping inversion of the Fuxin basin provides a new tectonic models for basin inversion.

FAULT ROCKS AND FAULTING MODEL

Aiming Lin

1996, 2(3): 295-306.

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Based on a review of previous work on the textures, microstructures, and origin of fault rocks, this paper gives some new interpretations and suggestions on the classifications of fault rocks and faulting model as following. (1) Fault rocks formed at some specific tectonic regions and provided a record of the nature of deformation. So, it is generally believed that the regional tectonic history can be understood by studying the textures of fault rocks. (2)The textures such as lineations and foliations found in fault rocks not only formed in ductile shear zone, but also formed in brittle shear zone. Therefore, the lineations and foliations can not be used as an only criterion in the classification of fault rocks. (3) The original grain size of crystals included in host rocks must be considered in the classification of fault rocks and the deduction of deformational degree of fault rocks from the grains size, because the original grain size of crystals included in host rocks affects the changes of grain size in fault rocks. (4) It is possible to understand the formation mechanism of fault rocks and related seismic faulting, and to build a relative fault model by studying the mechanical mechanism of fault rocks and related subjects such as seismology, tectonics, rheology and mechanics of materials.

PHYSICAL MECHANICAL MECHANISM FOR THE WHOLE UPLIFTING OF THE QINGHAI-XINZANG PLATEAU AND THE LATERAL SHORTENING AND VERTICAL THICKENING OF THE CRUST

Teng Jiwen, Zhang Zhongjie, Hu Jiafu, Yin Zhouxun, Liu Hongbin, Wan Zhichao, Yang Dinghui, Zhang Bingming and Zhang Hui

1996, 2(3): 307-323.

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The Himalayan movement is the latest strong movement of the crust and the most important geological event in Asia during the Mesozoic and Cenozoic Eras. This movement, which has built up the Himalayan Mountains and is still in progress, affects a wide are of eastern Aisa and is regarded as the cause for whole uplifting of the Qinghai-Xizang Plateau. A variety of hypothesis have been suggested for this uplifting mechanism, but none of them is convincible. In order to investigate the physical-mechanical mechanism for the whole establish and to establish a geodynamic model for crustal shortening and thickening, this paper, starting from discussions on the tectonic framework, crust and mantle structure and geophysical field, will be concentrated on the following five problems: 1. The basic models for the formation of thick crust, thin lithosphere, deep faults of varying features and for thrusting, intersecting and collisional orogeny. 2. Earthquake activities, fault plane solution and stress fields. 3. Plate movement, terrain amalgamation and continental accretion. 4. Physical mechanical mechanism for uplifting of the Qinghai-Xizang Plateau. 5. Geodynamic model for the uplifting. As a result of the northward movement of the India plate and its collision with the Eurasia continent, the long-term tectonic compression has rendered the plateau area anomalous earthquakes and stress fields, strong hydrothermal activities, rapid southward declining of Lg wave energy and strengthening of the Q value, as well as the pattern of southward increasing of crustal temperature and “hot” crust relative to “cold” mantle in the lithosphere. Gravity isostasy has not yet been reached at both south and north piedmonts, and high mountains have been continuously uprising. The ophiolite suite emplaced along the Yaluzangbu River extends 1700km in length. A series of strike-slip faults were formed and rocks were strongly deformed. A transitional zone, 300 to 500km in width between the north margin og the Ganges Plain and the Yaluzangbu River, has been developed by collisional compression. All these facts appears to indicate that the physical mechanical mechanism for the uplifting of the Qinghai-Xizang Plateau and the shortening and thickening of the crust could be understood in terms of the asthenosphere dragging and the consequent long-term collision and compression between the India and Asia Plates. The dynamic model could be explained by the wedging of crustal materials from India plate into that under the Qinghai-Xizang Plateau along the low-velocity zones in the middle part of the crust during collision and compression, which has produced the present Himalayan collisional orogenic belt and caused the uplifting of the Qinghai-Xizang Plateau.

GEOCHEMICAL VARIATION ACROSS THE CAMBRIAN-ORDOVICIAN BOUNDARY AT CHANGSHAN SECTION OF ZHAOGEZHUANG, TANGSHAN

Shen Weizhou, Fang Yiting, Ni Qisheng, Li Yuping, Liu Yan

1996, 2(3): 324-331.

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The Cambrian-Ordovician boundary section at Changshan is one of the well-established sections in stratigraphic region of North China. Zhou and Zhang (1978) studied the trilobites in detail across this boundary in Zhaogezhuang area. They discovered conspicuous difference in trilobite fauna cross the Cambrian-Ordovician boundary (between bed 6 and bed 7 at Changshan section). This paper deals with the variation of isotopes (δ13C and δ18O) and trace elements across the Cambrian-Ordovician boundary at same section. The authors discovered that, besides the conspicuous difference in trilobite fauna, there is also variance at different ranges in isotope compositions and almost all trace element contents across the Cambraian-Ordovician boundary in Changshan section. This indicates the change of sedimentary environment in that time. Based on the analyses of C and O isotopes it is concluded that the carbonate rocks from the strata across the Cambrian-Ordovician boundary in Changshan section were formed in submarine environment.

A STUDY ON THE UPPER PERMIAN OF THE YILY BASIN, XINJIANG

Cui Zhilin1, Mei Zhichao1, Qu Hongjun1, Chen Shiyue1, Zheng Guoqiang1, Yang Lei1, Liu Junxia2, Wu Yahong2, Xiong Liping2

1996, 2(3): 332-338.

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The Yily Basis in the central Tianshan orogenic belt accommodates a huge thickness (about 5000-9000m) of continental Permian strata. The Upper Permian is chiefly composed of fluvial-lacustrine deposits bearing fossils of sporo-pollen, bivalves, ostracodes, and plants. The Xiaoshansayi Formation discordantly overlying the Wulang Group of Lower Permian consists of 419m thick lacustrine mudstone, sandstone and conglomerate with the Cordaitina-Hamiapollenites-Vittatina sporo-pollen assemblage. The Hamist Formation comprises volcanic rocks and coarse clastic sedimentary rocks yielding bivalve Palaeonodonta, Anthraconauta. Argillaceous rocks of lacustrine facies dominate the Tiemulike and the Bakaluesayi Formation, but are frequently interbedded with massive conglomerate beds in the latter. “MPPAO” bivalve fauna and a similar sporo-pollen assemblage occur in these two formations. The Basrgan Formation of the uppermost Permian is composed of fluvial-alluvial conglomerate and sandstone, and reaches 650m thick. The fossil assemblages, lithological features and sedimentary facies of Upper Permian in the Yily Basin show a strong similarity to those of the Junggar Basin.

A STUDY ON ORDOVICIAN SEQUENCE STRATIGRAPHY IN YICHANG DISTRICT, HUBEI PROVINCE AND SEDIMENTARY ENVIRONMENT OF THE WUFENG FORMATION IN YANGTZE AREA

Xiao Chuantao1, Jiang Yanwen1, Zhu Zhongde1, Li Yibin1, Pan Yuntang2

1996, 2(3): 339-347.

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The Ordovician system in Yichang district is divided into three II type sequences by using the principle and method of outcrop sequence strtigraphy. The characteristics and their sedimentary dynamic mechanism of the individual system tractst, the controls of sea level changes on sedimentary process, organism migration and the environment are elucidated as well. It is believed that there are three sea level change cycles during the Ordovician period in the study area: the first one occurred from early to late Lianghekou age; the second one from the end of Lianghekou to the beginning og Dawan age; and the third one from early Dawan age to terminal Wufeng age. Two keep-up type carbonate systems are recognized. The result shows that the Lower Ordovician bioreefs in Yichang district formed during high sea level periods. The early Wufeng age reached the maximum of sea level rising, and the Wufeng shale is considered to be a typical condensed section, while the Guanyingqiao Member formed within high sea level period. Based on the analysis of the sedimentary rate, ecologic and sedimentary aspects, it is believed that both the Wufeng shale Member and the Guanyingqiao Member are formed in deep sea basin environment.

GEOCHEMICAL CHARACTERISTICS OF PERMIAN SEQUENCE IN LOWER YANGTZE REGION

Du Xiaodi, Huang Zhicheng, Cheng Zhina, Liu Jiaren

1996, 2(3): 348-356.

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Permian in Lower Yangtze Region is a typical sequence of mixed carbonate, chert and terrigenous clastics. Taking the Permian profiles in Chaoxian, Anhui as examples, the authors discuss its petrological and REE distribution characteristics. Seven sedimentary facies are divided, namely: restricted platform, open platform, continental slope, basin, delta, neritic and continental marginal lagoon facies, The Permian can be divided into seven third-order sequences. Four of them are type I sequences, other three agre type II sequences. Then the authors elaborate geochemical characteristics of these sequences. With the rising of sea level, δ13C is gradually increased and δ18O decreased. When sealevel changed, the high stand systems tract (HST) and the trangresivestand systems tract (TST) have different REE compositions. The total REE of TST is greater than that of HST. The trace element distribution characteristics in TST is different from that of HST. Based on above work, the authors conclude that geochemical parameters such as O and C isotopes, REE and trace elements are helpful to sequence analysis.

A BRIEF INTRODUCTION FOR QUANTITIATIVE DYNAMIC STRATIGRAPHY

Wu Zhiyong, Jiang Yanwen

1996, 2(3): 357-360.

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The quantitative dynamic stratigraphy (QDS) is a new synthetical subject which studies the geologic dynamics, stratigraphy, sedimentology and hydrodynamics of a sedimentary basin by using quantitative mathematical methods, and finally obtains the distribution model of sedimentary facies and strata of the basin. This paper briefly introduces the advancing, theoretical basis and the research methods of the quantitative dynamic stratigraphy, and clarifies its main applications through some practical examples.

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