1997 Vol. 3, No. 2

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THE GEOLOGICAL EFFECT OF RIDGE SUBDUCTION IN ARC AREA
Zhang Jian, Shi Yaolin
1997, 3(2): 1-10.
Abstract (159) PDF (402KB)(9)
Abstract:
Ridge subduction is an important stage of Wilson cycle.If the spreading rate of the active ridge is smaller than the rate of subduction,the subducting oceanic plate will decrease in size,and the ridge itself will be eventually subducted.There are four possible kinematic scenarios of ridge subduction,we investigate one of the possibility:both the leading and the trailing plates are subducted.Subduction of a hot active ridge will significantly affect the thermal state of the subduction zone,and leave tectonic and petrologic signatures.In this study,we use twodimensional finite element method to calculate the thermal consequence of an active ridge subduction.Upwind technique is adopted to secure a stable and accurate solution for advective heat transfer.Frictional/shear heating is included in our modeling.The shear stress is limited by the friction law in the brittle regime and by the flow law in the ductile regime.Sequential changes of temperature created by ridge subduction are calculated,and the resulting geological consequences at arc areas are discussed.The results of computation can well explain cessation of arc volcanism,low-temperature metamorphism,uplift and subsidence of arc-trench margin.
THE HIGH-RESOLUTION LATE PLEISTOCENE LOESS STRATIGRAPHY IN TAOHUAYU,MANGSHAN,ZHENGZHOU
Jiang Fuchu, Wu Xihao, Xiao Huaguo, Wang Sumin, Xue Bin
1997, 3(2): 11-17.
Abstract (152) PDF (336KB)(7)
Abstract:
For its characteristic high-resolution the eolian Manshan loess is exposed along the south bank of Huanghe River,situated on the northwest suburbs of Zhengzhou City,Henan Province,which is wholly composed of loess strata,over 160 m thick,upward from loess L15 or paleosol WS1.The loess sequence in this area are perfect and the typical loess profiles are exposed in Taohuayu and Zhaoxiayu,in which the strata upward from paleosol S2 at Taohuayu profile have been preliminary studied.According to the lithology,susceptibility,TL and 14C dating,the stratigraphical units have been subdivided into S0,L1,S1,L2 and S2 with 0.6m,70.8m,9.9m,12.4m and 1.0m thick respectively.It is of great significance that there exist quite a thickness of Malan Loess (L1) formed in the Late Pleistocene.
We have sampled at an interval of 10cm and measured the profile magnetic susceptibility in the field and mass magnetic susceptibility in the laboratory respectively.The values of magnetic susceptibility of the Mangshan Loess is smaller than that inside the Loess Plateau.We have correlated the magnetic susceptibility profile with the SPECMAP marine oxygen isotope time series and inferred that the rapid changes in susceptibility values at the L1/S0,S1/L1 stratigraphic boundaries correspond with the oxygen isotope stage 2/1 (12.05ka) and 5/4(73.91ka) transitions respectively.With the two marked points,by using the Kukla's susceptibility age model to calculate the age of successive stratigraphic levels we then derived a chronology.Grain size of the loess during the last glaciation (L1) was analyzed at an interval of 40cm,and depositional rate of each unit has also been calculated.
The susceptibility of Chinese loess mainly manifests the prosperity or decline of the southerly summer monsoon from the low latitude ocean,so the susceptibility values may be used as a proxy index for the change strength of summer monsoon climate.Average deposit rate and resolution in late Pleistocene loess at Mangshan reveal a great difference of dust deposit blown and entrained by the northerly winter monsoon from the high latitudes area between glaciation and interglaciation or stadial and interstadial.The maximum mean deposit rate is up to 2.47mm/a during the last glaciation,whereas the minimum is 0.18mm/a yet during the last interglaciation.The frequency and amplitude of winter monsoon variations revealed by the grain size record whose mean resolution come to 40.5 a/10cm dring the last stadial in the last glaciation at Mangshan are more detailed than that by the Greenland ice core.
The late Pleistocene loess strata in Mangshan are both related to and different from that inside the Loess Plateau.For its high-resolution the Mangshan loess during last glaciation can reflect the abrupt climate changes of East Asian monsoon,and is a excellent record for the Past Global Changes study on high-resolution and short timescale.
QUATERNARY GLACIATION IN SHENNONGJIA
Zhao Zhizhong, He Peiyuan
1997, 3(2): 18-23.
Abstract (163) PDF (240KB)(6)
Abstract:
Shennongjia located in central China is an important area to study Quaternary geology.Based on the distribution of glacial vestiges,we make a discussion of the Shennongjia Quaternary glaciation.There are three glacial substages,i.e.Songbai glaciation,Muyu glaciation,Longtan glaciation,and two epiglacidtions,i.e.Songxiangping epiglaciation,Shennongjia epiglaciation.A study of the Shennongjia Quaternary glaciation provides new data for solution of the dispute over the Quaternary glaciation in eastern China. Quaternary climatic stratigraphic sequence in Shennongjia is established for the first time.
DISCUSSION ON THE EFFECTIVE ELASTIC MODULI IN THE UNSYNMMETRICAL MULTI-LAYER PLATE
Wu Hongling
1997, 3(2): 24-32.
Abstract (127) PDF (330KB)(8)
Abstract:
In order to adapt plate and shell models in applying the finite element method to tectonic analysis problems in representing crustal layer,this paper relaxes the synmmetrical restrictions on the geometry and elasticity in the multi-layered structure.According to the effective principle we re-determine the location of the neutral plane of the plate,which is no longer in the middle of the plate as in the synmmetrical case.General expressions for effective bending stiffness and elastic moduli are given,they are expressed in terms of each layer's thickness and elastic moduli of the plate.Two examples are given for three-layer crustal model.We also discuss the difference between the effective bending or membrane stress distribution and those obtained by treating each layer in their own moduli.
A THREE DIMENSINAL ELASTOPLASTIC FINITE ELEMENT MODEL FOR PREDICTING DYNAMICALLY RESERVOIR EFFECTIVE STRESS
Ran Qiquan, Gu Xiaoyun
1997, 3(2): 33-40.
Abstract (130) PDF (297KB)(5)
Abstract:
A three dimensinal elastoplastic model for predicting dynamically reservoir effective stress is established based on the coupled interaction mechanism of reservoir stress and multiphase fluid flow.The model is characteristic of two important aspects:the coupled effect of stress and seepage,and the elastoplastic properties of reservoir rocks under alternative loads of injection and production.The model is solved using elastoplastic incremental finite element method and an example is given.
THE ROLE AND SIGNIFICANCE OF CRUSTAL STRESS IN PETROLEUM GEOLOGY AND ITS PRESENT SITUATION
Ma Yinsheng
1997, 3(2): 41-46.
Abstract (223) PDF (238KB)(19)
Abstract:
The author discusses the role of crustal stress and its significance in petroleum geology from four aspects:crustal stress and the formation and evolution of oil-bearing basins,crustal stress and the structures of the basins,crustal stress and the migration of oil and gas,and crustal stress and the oil development.A systematic exposition of the study situation of the crustal stress is made.The magnitude and direction of present crustal stress can be obtained by stress measurement and focal mechanism solution.The magnitude and direction of fossil crustal stress can be determined only by the analysis of structure deformations and microfabrics.
THE STUDY OF FAULT CLOSURE BY USE OF ENTRY PRESSURE AND ITS APPLICATION IN NORTH TARIM
Zhou Xingui
1997, 3(2): 47-53.
Abstract (181) PDF (300KB)(10)
Abstract:
The entry pressure is the minimum driving force which is responsible for oil and gas secondary migration and also major index that measures the secondary migration and the blocking capability of a fault.Opening and closing of a fault depends on the difference of the entry pressure in the fault zone and that in its two sides.This paper puts emphasis on the study of closing of southern Keping fault,Yinggan fault and Kulukejumo fault in the north Tarim basin with reference to the pressure-closed lower limit of mudstone cover and rc30 lower limit of oil-gas migration.The result is consistent with what were observed in the field.
SEGMENTATION OF THE SHAOWU-HEYUAN FAULT ZONE AND THEIR ACTIVITY ASSESSMENT
Liu Daren
1997, 3(2): 54-60.
Abstract (378) PDF (330KB)(19)
Abstract:
The Shaowu-Heyuan active fault zone bordering Fujian,Jiangxi and Guangdong Provinces,forms the west boundary of the sub-seismic zone of the southeast coastal area of China.It includes three sub-zones different in geometry and features.They are the northern Shaowu-Shicheng Fault Zone,the central Ruijing-Xunwu Fault Zone,and the southern Longchuan-Heyuan Fault Zone with a total length of about 750km.The three are not connected end to end,but en echelon arranged with the southern one overlapping successively the northern in a right manner.This article deals mainly with the activity of the part running through the Jiangxi Province in connection with the distribution of earthquakes,hot springs,and ground fissures and the effect on the stability of the earth's crust.The author comes to the conclusion that there is little possibility for a large earthquakes to occur along the Shaowu-Heyuan Fault Zone,though some scattered smaller ones not excepted.
A STUDY OF INTRUSIVE CONTACT STRUCTURES
Yi Shunhua, Li Zhen
1997, 3(2): 61-65.
Abstract (129) PDF (278KB)(12)
Abstract:
This paper gives the major conclusions of intrusive contact structures achieved by authors by applying the theory and methods of geomechanics:(1) the intrusive contact structures themselves form a system which,falling into three basic types,results from the combined action of the emplacement of intrusives and regional tectonic stress;(2) multi-phase activity of ore-controlling structures is related to hydrofracturing;(3) the outer contact structures generally are referred to essentially as thermodynamic metamorphic origin.
TECTONIC DEFORMATION AND GOLD MINERALIZATION IN ZHAOYUAN-YEXIAN AREA,SHANDONG PROVINCE
Zhu Dagang
1997, 3(2): 66-72.
Abstract (158) PDF (300KB)(7)
Abstract:
The geology of the Linglong-Jiaojia type gold deposits in Zhaoyuan-Yexian gold belt,Shandong Province,is discussed in this paper.The stress is laid on the characteristic features of the ore-controlling fault in the gold belts.The role of the ductile-brittle faults in the gold mineralization at different stages of their deformation is also discussed.
DEFORMATION FEATURES OF CHONGLI-LONGHUA-FUXIN STRUCTURAL ZONE AND ITS CONTROL OF MINERALIZATION
Wu Zhenhan
1997, 3(2): 73-81.
Abstract (147) PDF (370KB)(7)
Abstract:
The Chongli-Longhua-Fuxin structural zone is of importance controlling magma intrusion and gold mineralization in the northern Yashan area.In late Variscan-Indosinian stage,it was dominated by ductile shearing and formed a series of discontinuous east-west trending ductile shear zones.In Ysashanian stage,it was characterized by ductile-brittle and brittle faulting and formed a series of east-west trending high-angle thrust faults superposed on the early mylonite zones.In Himalayan stage,fault activity succeeded.
The Chongli-Longhua-Fuxin structural zone has exerted a notable control over gold mineralization,such as the spatial distribution of Zhangjiakou-Longhua-Fuxin gold mineralization and the five gold concentrations.Temporally different types of deformation within the zone are accompanied by different types of gold mineralization.Its compounding with northeast and northwest trending faults is favorable for gold mineralization.
ORE-CONTROLLING STRUCTURE IN THE PLOY-METALLIC ORE DEPOSITS IN SHALIUHENANQU,DULAN,QINGHAI PROVINCE
Cheng Zhengle, Zhou Xianqiang, Song Yougui
1997, 3(2): 82-89.
Abstract (143) PDF (327KB)(12)
Abstract:
Based on the study of the mega and micro ore-controlling structures in the polymetallic ore deposits in Shaliuhenanqu,Dulan,Qinghai Province,the deformation histories of variously trending structures were determined:E-W-trending structure experienced at least three stages of deformation,the NW-trending and the NE-trending structures two stages of deformation each.Therefore,the authors proposed the tectonic development of that area and also discussed the role of the variously oriented structures in the formation of the deposit.
STUDY OF THE PROPERTIES OF SYNTECTONIC PORPHYROBLASTS IN DABEIWU AREA,JIANGXI PROVINCE
Chen Bailin, Dong Faxian
1997, 3(2): 90-97.
Abstract (102) PDF (421KB)(7)
Abstract:
The syntectonic porphyroblasts of pyrite and siderite in the ductile shear zone developed in epimetamorphic clastic rocks in Dabeiwu area are the products and marks of ductile shear deformation during progressive metamorphism.The porphyroblasts being of syntectonic origin have attained the following features:their growth is correlated with deformation intensity,content of sericite and size of the crystal,and the porphyroblasts have their distinct crystal forms and retain the schistosity of groundmass.From the rotation of the pophyroblasts,the authors reconstruct the evolution of Dabeiwu ductile shear zone:from left-lateral reverse-slip through flattening deformation to right-lateral normal-slip.

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