Table of Content

05 June 1996, Volume 18 Issue 2

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Brief Report

THE DETERMINATION OF QINGHAI-XIZANG(TIBET) PLATEAU USING GLOBAL POSITIONING SYSTEM

Wang Qi, You Xinzhou, Wang Qilliang

1996, 18(2):  97-103. 

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The present-day crustal deformation of the Qinghai-Xizang plateau and its margins has been intensely studied in geoscience community. The Global Positioning System (GPS) offers a revolutionary method to deepen our knownledge on the crustal thichness that resulted from the collision between Indian and Eurasia plates as well as the subsequent penetration of Indian into the rest of Asia. Since 1991, Institute of Seismology, State Seismological Bureau, has performed several GPS mesurements in the center Qinghai-Xizang plateau with the objectives of monitoring crustal movement using a high-precision GPS geodetic network and these GPS surveys will contribute to the studies of tectonic and geodynamics.

A DISCUSSION ON SOME CALCULATIONS FOR THE ANALYSIS OF OXYGEN ISOTOPE IN MACRO-WATER USING CO₂-H₂O EQUILIBRATION METHOD

Liu Shilin, Yan Zheng

1996, 18(2):  104-108. 

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THE TECTONIC IMPLICATION OF TWO RAPID COOLING EVENTS ON THE SOURTHERN XIZANG(TIBET) PLATEAU

Chen Wenji, Li Qi, Zhou Xinhua, Yin An, T. M. Harrison

1996, 18(2):  109-115. 

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⁴⁰Ar-³⁹Ar analyses and MDD(multiple diffusion domain) model cooling history were performed for 8 K-feldspar samples. They were colleted from Gangdese thrust (GT) in Zedang area and two valleyes of east Nian Qing Tang Gula mountain(NT). Two rapid cooling events at GT and NT were obtained after excess argon(⁴⁰Ar_E) was released from K-feldspar at low temperatures(<800℃) during ⁴⁰Ar-³⁹Ar step-heating experiments corrected by ⁴⁰Ar-Cl ratios. The first rapid cooling event suggested that active time of GT occurred between 27～24Ma. The lower age limit and slip rate were～18 Ma and (12±6)mm/a respetively. The second rapid cooling event at NT suggested that the crustal thickness and elevation may be close to their present level at ～8Ma on the southern Tibetan ploteau.

KINETIC MECHANISM ANDE ITS NUMERICAL SIMULATION OF FORMATION AND EVOLUTION OF LISTRIC FAULT

Chen Kaiping, Ma Jin

1996, 18(2):  116-118. 

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From the viewpoint of progressive deformation, a new kinetic mechanism of formation and evolution of gradually changing into listric is simulated by dynamic finite element method.

PRELIMINARY STUDY ON GEODYNAMICS OF THE NORTHWESTERN EDGE OF THE QINGHAIXIZANG(TIBET) PLATEAU

Zheng Jiandong

1996, 18(2):  119-127. 

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From 1992 to 1995, the author took part in the field investigations in Tarim basin and its surrounding areas, such as the Altun, Kunlun, Karakorum Mts. This paper will briefly deal with geodynamics of the northwestern edge of Qinghai-Xizang(Tibet) plateau based on regional study on neotectonic zonation, active faults and folds, vertical crustal movement, seismic activities and Cenozoic volcanoes and the like. All the features show that the northwestern edge of the Qinghai-Xizang(Tibet) plateau is the most active region within the plateau. From the viewpoint of geodynamics, apart from the northward subduction of the Indian plate, the Tarim basin has southward subducted to the Qinghai-Xizang (Tibet) plateau, whose lithophere is undergoing pushing around and escaping and penetrating to the upper and lower parts respectively.

A STUDY ON RECENT GEODYNAMICS AT THE SOUTHEASTERN MARGIN OF THE QINGHAIXIZANG(TIBET) PLATEAU

Gao Mingxiu

1996, 18(2):  129-142. 

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An united peneplain of Neogene period was broken up into both the surfaces of the Qinghai-Xizang(Tibet) and Yunnan plateau separated on 4500～5000m and 2000～2500m elevations after eafly Pleistocene.At the transitional zone of the block faulting between the two surfaces the landform tilting and steping down from the northwest to the southeast forms the Southeastern Margin of the Qinghal-Xizang plateau.It is also a tectonlcally active zone marked by obvious tectonomorphology,wide manifestation of hydrothermal activity and intensive seismicity.Measurement of the GPS passing through the zone in two times is undergoing extension in NW-SE.Features of the crustal and mantle structure support that the zone belongs to a boundary of thermodynamics and gravity isostatic adjustment.

BUILDING CHINESE ACTIVE FAULT INFORMATION SYSTE USE GIS SYSTEM

Yu Guihua, Deng Qideng, Wu Lun, Cheng Chengqi

1996, 18(2):  156-160. 

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STUDY ON MICROEARTHQUAKES IN THE PROPOSED RESERVOIR OF THREE GORGE AERA

Ma Wentao, Yang Qingyuan, Chen Xiancheng, Hu Ping, Hu Yuliang, Zhao Meng

1996, 18(2):  161-168. 

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In about three years the observation of microearthquakes has been made by setting up three short-distance station networks,separately one of which is along the river, others at Yanguan and along the fault belt in Xiannu mountain,near the place where the dam of the Yangtze Gorge will be made.We have basically studied the features and levels of seismic activity.The seismic activity has been herein presented in order to evaluate the possibility of induced earthquake in the Three Gorge reservoir which will be made in several years.

GEOMORPHIC STUDY ON LATE QUATERNARY IRREGULAR FAULTING ALONG THE NORTHERN PIEDMONT OF LIULENGSHAN RANGE, SHANXI PROVINCE, CHINA

Xu Xiwei, Yonekura Nobuyuki, Suzuki Yasuhiro, Deng Qidong, Wang Yipeng, Takeuci Akira, Wang Cunyu

1996, 18(2):  169-181. 

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Three basic geomorphic units, which were developed in response to the climate changes during the last glaciation, are recongnized along the northern piedmont of the ENE-trending Liulengshan range from airphoto interpretations and field observations.These three units are the inter-stadial fluvial fan (S₃) about 23～53 ka old, the maximum-glacial fluvial fan(S₂) about 10～23 ka old and the post-glacial fluvial fan(S₁) about 1～10 ka old, respectively.Five fluvial terraces(T₀～T₄) were also developed owing to the climatic temperature fluctuations on thousandyear scale.These geomorphic units(S₁～S₃) and fluvial terraces(T₀～T₄) are chronometrically dated by thermoluminescence.Stripped geomorphic mapping shows a natural segmentation in offset-geomorphology along the norhern piedmont fault of Liulengshan range.Six segments can be divided in the mapping areas and they are the Xifutou, Donghouzikou-Dawangcun, Xitunpu-Qiulin, Huoshilin-Qiuchangcheng, Huajialing-Xiejiayao and Longmazhuang-Xinpu segments from the west to the east, respectively.A set of quantitative data (faulting ages, vertical displacements and slip rates) are obtained from long-distance topographic profiles across the offset geomorphic units or fuvial terraces.The average Holocene vertical slip rates are 0.43～0.48mm/a for the Donghouzikou-Dawangcun segment, a bout 0.45 mm /a for t he Xitunpn-Qiulin segment, and 0.53～0.55mm/a for the Longmazhuang-Xinpu segment.The faulting irregularity is demonstrated by temproal and spatial flucturation in vertical slip rates during the Late Quaternary.The period of 15.6～7.6ha B P is the main phase of intensely verical faulting along the northern piedmont of Liulengshan range.

PHANEROZOIC PALEOMAGNETIC DATA FOR THE MAIN BLOCKS OF CHINA

Cheng Guolinag, Sun Yuhang, Sun Qingge, Wang Lihong

1996, 18(2):  182-192. 

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