Table of Content

20 March 2001, Volume 7 Issue 1

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Article

Regional Tectonic Evolution Around Yinggehai Basin of South China Sea

GUO Ling-zhi, ZHONG Zhi-hong, WANG Liang-shu, SHI Yang-she, LI Hua, LIU Shao-wen

2001, 7(1):  1-12. 

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Yinggehai basin is located in the northwest of South China Sea， and formed in the Cenozoic The Cenozoic sedimentary thickness in the basin is more than 15km ，therefore，the structural features related to rifting phase are difficult to reveal by seismic profiling In order to understand its origin an d evolution， we analysed the regional characteristics of the Cenozoic tectonic evolution surrounding Yinggehai basin，an d obtained the Cenozoic tectonic stress field of the basin. The formation and tectonic stress field of Yingehai basin can be divided into four phases. The first phase, from the later Paleocene to the early Oligocene，Indochina block extruded toward southeast fast，with a clockwise rotation movement Yinggehai basin origined in this stage. The second phase， from the later Oligocene to the early Miocene， Indochina block’s southeastward extrusion slowed down gradually. However， South China block was relatively stable and Yinggehai basin was under a left-slip shearing condition. The third phase, during the middle and the later Miocene， with the Indochina block intruding into Eurasia plate gradually，Indochina peninsula’s extrusion slowed down further . At the end of the middle Miocene，South China block began to extrude integrally. The last phase，from the Pliocene to the Quaternary period，Indochina block was relatively stable，South China block’s extrusion continues ，the relative movement of these two blocks is right-slip shearing The Cenozoic evolution of tectonic stress field of Yinggehai basin is controlled by the interaction between Pacific plate， India plate and Eurasia plate. Most of all， the relative movement between Indochina and South China block resulted from the India-Eurasia collision is the dominate factor of the Cenozoic tectonic stress field controlling the origin an d evolution of Yinggehai basin.

Structural Features and Origin of Changma Basin，Gansu Province

WANG Sheng-li, LU Hua-fu, JIA Dong, SHI Huo-sheng, YE Shang-fu

2001, 7(1):  13-20. 

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The Altyn fault is a major strike-slip fault system that consists of the main fault and the second-order faults with a distribution pattern corresponds to the 1eft-lateral strike-slip transpression model. The Changma basin is located to the south flank of the eastern segment of the A1tyn fault zone. whose paleo-stress field is in accordance with kinematic direction of the Altyn fault. The northern border fault of the Changma basin is the east segment of the Altyn main fault. The south border makes up the zigzag Banjiezijing-Yemashan fault，the Yerneshan mountain fault，the Shibandun. Gongchakou fault，and the north border fault of the central Oilian mountain，which ere S fracture，smal1 Y fracture，P shear，and S second-order fracture of the Altyn fault respectively The eastern border is composed of the west Xiangmaoshan fault. The Meshetou fault，and the Qingshiyan fault，which ere X fracture，S fracture，and R’s shear of the Altyn fault respectively. The Changma basin is a narrow triangle in map view surrounded by those fauls Therefore. we conclude that the Changma basin is a strike-slip branch basin formed by interaction of the Altyn main fault and its branch faults. During the Jurassic-Cretaceous，the Changma area was tensioned and buried by thick deposits. From the later Tertiary to Quaternery， the Changma strike-slip branch basin inversed and was pressed horizontally caused by the emplacement of the sinistral strike-slip Altyn fault. Having analyzed the petroleum geological features of the Changma basin，the authors emphasize that there are advantageous conditions of hydrocarbon genesis in the Changma basin，and more attention and investment should be devoted to the exploration in this area.

Deep Geological Conditions Constraning the Late Mesozoic Magmatism in SE China

XU Ming-jie, SHU Liang-shu

2001, 7(1):  21-33. 

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Analyses of regional geologic settings and geophysic data have yielded following results: 1. The regional tectonism and material composition of basement had influence on the Late Mesozoic magma activity，and the magmatic division at the surface is consistent with that in the deep. 2. Based on the types of magmatic rocks，three tectonic-magma regions are recognized: (a)low-K and high-A1 calc-alkaline intermediate-acid volcanic-intrusive complex region, i.e., SE China Coastal Region; (b)high-K granitic volcanic-intrusive complex region，named as the Wuyishan region and (c)high-K S-type granite region in the west to Ganjiang without acid volcanic intrusive complex These three regions are separated by Zhenghe-Dapu and Ganjiang fault zones respectively. The crusta1 thickness in the SE China Coastal Region is thinner, whose basement is mostly volcanic and granite belongs to I-type; the crustal thicknesses for other two regions are greater than the first，their basements are mostly melted sedimentary rock series and the granitic rock is S-type. The Ganjiang fault zone is called as the Late Mesozoic Volcanic Rock Line 3. In the SE China Coastal Region，there is a local-low-resistivity-layer，which was related to a pullrifting The underplating of basaltic magma an d the formation of alkaline granit were closely related to the pull-rifting in the Late Cretaceous. 4 .Zhenghe-Dapu，Ganjiang and Changle-Nan ’ao fault zone have apparent geophysic features，which are both the gravity gradient zones and ultra-crust fault zones where the geological interaction along the crust. mantle boundary is most common. 5. There is a low-velocity zone of 2-4km thick in the middle crust, and is considered as a result of a part melting of ductile deformation，which is probably a local magrnatic source 6. Our study supports the model of plate subduction combining with underplating of basalt magma For the origin of the Late Mesozoic magmatism in the SE China . The fault zone from the Japanese Central Tectonic Line to Taiwan Longitudinal zone is a Mesozoic subduction and suturing zone where the Mesozoic Pacific plate subducted to the East Asian continental margins to form a wide volcanie-intrusive arc.

The Relationship between Linear Weak-Information of Radar Image and Subordinate Faults in Landslide Area of Hong Kong

LIN Hui1, SHI Huo-sheng1;2, SHAN Yin1

2001, 7(1):  34-42. 

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By processing the Airborne L-SAR image of the study 0xea，we selected the weak-information of SAR image as indicator of subordinate faults，and traced the structural background of landslides in the region. The regional fault in the study area is the NE strike-slip fault Its sinistral movement forming a serial subordinate faults，including R plan，P plan and R’ plan，which are represented as weak information of lineation in radar image and related to the development of micro-geography. By selecting and enhancing the weak information， we made the deformation frame of subordinate shear faults. Together with field investigation, we found that the location of P shear plan on the northeastern Jubilee Reservoir can form 1ands1ides of gravity unbalanced alluvium, with a background of strong strain deformation belt. The newly formed landslide of bou1der falls was 1oeated at southeast of Jubilee Reservoir It has features of structural tension background，and relates to the subordinate faults with pull-apart action on the direction of the R shear plan.

Current Situation in Study on the Archean-Proterozoic Boundary

LI Jiang-hai, HUANG Xiong-nan, QIAN Xiang-lin, LIU Shu-wen

2001, 7(1):  43-49. 

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Based on a large amount of data，we analyzed the results of recent studies on the Archean-Proterozoic boundary(A/P boundary), related tectono-magmatic events and discussed the significances of these studies Considering the current situation of study related to the A/P boundary in north China，we believe it is necessary to conduct a synthetic investigation on the tectonic setting，geochronology and sedimentary features in the metamorphic regions of the Wutai Mountain and Taihang Mountain A multidisciplinary study in the future using data from typical sections in these regions will provide important constrains for defining the A/P boundary in China.

Geology and Magma-Dynamical Features of Jingjiling Composite Granitic Batholith in the Western Nanling Region

ZHANG Bang-tong, DAI Yong-Shan, WANG Ju, BAI Chou-Yong, LIU Hong-lei

2001, 7(1):  50-61. 

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Jinjling composite batholith in the west Nanling Region consists of three granite bodies with different ages of intrusion: I stage，amphibole-bearing biotite adamellite; Ⅱ stage，biotite granite; II stage，two-mica granite. The ages and initial strontium ratios for the I stage andⅡ stage granites by Rb-Sr whole-rock isochron method are 169 .5 Ma and 0.7163, and 150.7 Ma and 0.7206，respectively. It indicates that they are intrusions of early Yanshanian period. Granites of the Jinjiling hatholith belong to calc-alkaline rock series and show a general evolution trend from I stage admmellite, to Ⅱ stagegranite and Ⅲ stage bimicaceous granite as follows: aluminium saturation index increases from metaluminous(I)to peraluminous(Ⅱ)and highly peraluminous; ordering degree of K-feldspar increases from 0.33(I) to 0.69(Ⅱ)and 0.80(Ⅲ); An of plagiaclase decreases from 37(I)to 26(Ⅱ)and 7(Ⅲ); chemical composition of biotite varies from Fe-hiotite(I)，to lepidomelane(Ⅱ)and Fe-mica(Ⅲ); oxides (Si02， Al2O3 ，TFe，MgO，TiO，CaO)versus DI diagrams show a linear evolution features; rock-forming temperatures gradually drop down form 745℃(I) to 673℃(Ⅱ) and 505℃(Ⅲ). By means of geochemical and geobarometric methods，it is estimated that the depth of emplacement for Jinjiling batholith was about 6.5km, and the rock-forming pressure was about 180MPa Jinjiling composite granitic batholith belongs to S-type granitoids，forming in collision orogeny environment.

Nd Isotopic Systematics of the Late Mesozoic Volcanic Rocks from Southeastern Zhejiang Province，China: Implications for Stratigraphic Study

YU Yun-wen, XU Bu-tai, CHEN Jiang-feng, DONG Chuan-wan

2001, 7(1):  62-69. 

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Late Mesozoic volcanic rocks in southeastern Zhejiang Province can be subdivided into three stratigraphic cycles. The εNd(t)values for these three cycles，from bottom to top，are -14.1 to –6.2, with an average of –10.0; -7.7 to –6.3，with an average of –7.0; and -7.5 to 0，with an average of –4.6，respectively. T2DM for the three cycles are 1.6 to 1.8， with than average of 1.72Ga; 1.4to 1.6，with an average of 1.48Ga; and 0.9 to l.5 with an average of 1.3lGa，respectively. Vo1canic rocks from different cycles show significant variation in Nd isotopic compositions, indicating that the tectonic environment of formation and the magma source of volcanic rocks varied with time. Therefore. Nd isotopic compositions of the volcanic rocks are very important in stratigraphic division and comparison

A Discussion on Petrological Characteristics and Genesis of Yueshan Intrusion，Anhui Province

ZHOU Tao-fa, YUE Shu-cang, YUAN Feng, LIU Xiao-dong, ZHAO Yong

2001, 7(1):  70-80. 

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Yueshan ore field is a typical skarn-hydrothermal type of Cu(Fe)，Au polymetallic ore field in the mineralisation belt of the Middle and Lower reaches of the Yangtze River area . Copper-gold deposits in this ore field have close relationship with the Yueshan intrusion The intrusion consists of diorites. quartz diorites and quartz monzonitic diorites. The geological and geochemical characteristics，especially the petrochemistry，REE，trace elements and Pb，Sr，Nd，O isotope geochemistry of this intrusion， as well as geochemical modeling of its petrogenetic Process, are discussed. The results show that the Yueshan intrusion is a MC-type granite with 70% of mantle-derived material an d 30% of crust. derived materia1. It was formed by the process of combined wall-rock assimilation of the crustal material and fractional crystallization of the mantle-derived alkaline basalt. An open magnetic system of the Yueshma dioritic body is essential to formation an d evolution for the ore-forming fluid of the metallic ore deposits in this field.

Gas Geochemistry of Warm Springs in Tan-Lu Fault Belt

LIU De-liang; TAO Shi-zhen; ZHANG Chao-ming

2001, 7(1):  81-86. 

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The gas compositions and isotope compositions of warm springs in fault structure zones directly indicate structure activity and hydrogeochemical characteristics in the fault zones. N2 is the major gas component(90% or so) of warm springs in Tan-Lu fault belt. There is an obvious difference in δ13C CO2 for different sections of the fault zone. Theδ13C CO2 values in northern section are –4.3‰ ～7.8‰ ，and the CO2 is inorganic in origin，produced by petrochemical evolution of the rocks. Theδ13C CO2 values in central and southern sections are lower than -10‰ ，and the CO2 is organogenic. 40Ar/36Ar vary from 295 to 363，in which the lower ratios stem from atmosphere. and the higher ratios from the decay of K in the rocks of the earth crust. This paper not only studies the gas compositions of warm springs in different sections of Tan-Lu fault belt and their origin，but also is important in revealing the tectono-magmatic activity and hydrogeochemical characteristics of the fault belt.

Analysis on Mesozoic-Caenozoic Ultrabasic Rocks in Northeast Jiangxi Province and Perspective of Diamond Prospecting

LOU Fa-sheng, HUANG Zhi-zhong, WU Xin-hua, LUO Xiao-hong, WU Ming-ren, XIE Qing-hui

2001, 7(1):  87-91. 

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The ultrabasic rocks of Mesozoie-Caenozoic era have been found in the northeastern Jiangxi Province They are mainly 1imburgite and breccia-like 1imburgite and intruded the Cretaceous red basins. The breccia-like 1imburgite is pipe shaped. The results of petrochemical Analyses indicate that these ultrabasic rocks contain 38.19～44.28% Si02，2.01～2.93% K20+Na2O，7.67～11.10% MgO，8.25-12.67% CaO and 11.94-14.51% Al2O3 etc. These ultrabasic rocks aye quite similar to the typical limburgite in chemical composition. The discovery of Mesomic-Caenomic ultrabasic rocks provides an important information for reevaluation of the perspective for the diamond prospecting in the northeastern Jiangxi Province.

REE-Geochemistry of Mesozoic Volcanic-Intrusive Complex and Dark Inclusions in Xiangshan District，Jiangxi Province

DUAN Yun, ZHAO Lian-ze, FAN Hong-hai, WANG De-zi

2001, 7(1):  92-98. 

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The dark-coloured enclaves were found in subvocanic dike for the first time in the Xiangshan district，Jiangxi Province，which provides a new information for studying Mesozoic vocanic-intrusive complex in this region. This kind of enclaves exsit in smal1 amounts，with chilled margin，back veins，and other obvious quenching characteristics. Petrologically they aye mainly dioritoids. We colleted 14 samples ，including the basemental rocks，volcanic rocks，subvolcanic rocks and dark enclaves，and made detailed REE analyses on them. Combining with the previous study， we tried to explain the genetic relations hip and difference between them in a more integrated and systematic way. The data and diagrams demonstrate that: 1)as a whole，the magmas which formed various volcanic rocks with slight to intermediate fractionation degree of REE and strong europium negative anomalies ，were differentiated an d evolved in the same magmatic reservoir， The latter was originated from the continental crust; 2)products of the bicyclic volcanic activity. Rhyodacite and porphymclast lava，represent double emptying of magma reservoir; 3)REE data of dioritic enclaves don’t show strong europium negative anomalies . Conseguently we concluded that the magma of these enclaves was derived from a deeper level，and could be a mixture of lower crust and enriched mantle with a higher mixing proportion. Furthermore，Pb，Si，Nd isotope data also provided similar information. εNd(t) of volcanics and subvolcan cs are –8.8 and –11.2，respectively，which are very close to the upper crust va1ue in southeast China，while that for the dioritic enclaves is –6.5，which indicates involvement of a deeper source component. Mesozoic volcanic-intrusive complex in Xianshan district was generated by the partial melting of sialic lithosphere and belongs to the S-type in origin，which is consistent with the popular point of view. However，discovery of dioritic enclaves implies possible participation of lower crust or even upper mantle component

Study on the Erosion Amount of Hiatus Surface between Neogene and Eogene in North Part of East Depression，Liaohe Basin

WU Zhi-ping, LIU Ji-guo, ZHANG Wei-hai, ZHA Ming

2001, 7(1):  99-105. 

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The hiatus surface between Neogene and Eogene in the east depression of Liaohe basin was formed in the transition period from the rifting stage to post-rifting of the basin evolution. Beneath the surface，sediments formed in faulted depression were eroded due to tectonic uplift in the last stage of Eogene. Basing on calculated erosion amount of some wells in different tectonic positions and analyzing the relation between erosion and topography， the thickness of eroded sediments of N/E in the north region of this depression had been recovered The result indicated that，with regard to the whole region，the erosion amount in the north was larger than that in the south. It also suggested that the erosion amount was smaller in the area where paleo-river bed located than that in the river banks.

Late Cretaceous Foraminiferal Faunas and Eustatic Change in Gamba Area，Southern Tibet

ZHAO Wen-jin

2001, 7(1):  106-117. 

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The Zongshan section in Gamha of southern Tibet has long been considered as the standard section for the Cretaceous of the Tethyan Himalayas The Late Cretaceous strata are well exposed in this area and contain abundant foraminiferal fossils，from which 130 species of 52 genera have been identified. The rocks are mostly marine carbonates. Systematic studies of the microfauna and petrology have been conducted to establish a new stratigraphic framework for this area and the relationship between the foraminifera1 faunas and the sea level changes.The Late Cretaceous strata in this area can be subdivided into three Formations, which are(in ascending order)the Lengqingre Formation，Gangbacunkou Formation and Zongshan Formation. They are roughly of the Cenomanian to early Turonian，middle Turonian-Santonian and Campanian-Maastrichtian age. Ten planktonic foraminiferal zones were recognized，which can be correlated with similar zones in Pakistan， Europe and America In addition，5 foraminlferal faunas， represented by Rotalipora fauna， Whiteinella-Helvetoglobotruncana fauna ，Dicarinella-M arginotruncana fauna ，Globotruncana-Globotruncanita fauna and Orbitoides-Omphalocyclus fauna，can be recognized. The evolution of the foraminiferal faunas in this area occurred mainly in response to the eustatic changes which have affected biological niche of the microplankton.

Recognition of the Oulituozhi Porphyry-Type Oil and Gas Reservoir in Liaohe Basin and Its Significance

GU Lian-xing, REN Zuo-wei, WU Chang-zhi, Zhao Ming

2001, 7(1):  118-120. 

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The Oulituozhi oil-gas field in the Liaohe Tertiary basin，Northeast China，has a daily output of more than 200 tons of crude oil and a significant amount of gas Oil and gas are accumulated in the top portion of a subvolcanic trachytic porphyry which intruded in the Eocene Shahejia Formation Reservoir space is dominated by crypto-explosive breccias，crack networks，vertical open cracks an d tensional microfissures. These varieties of space were produced by explosions of water and other volatiles below an crystalline rind, by upwelling forces of the magma from the depth, and by cooling an d volume contraction of the solidified rocks. Because such a combination of space is characteristic of a subvolcanic porphyry，the reservoir at Oulituozhi could be designated as a porephyry-type reservoir. Such a model should be taken into account during exp1oration work for oi1 and gas in the O1ituozhi area.