Table of Content

05 December 1984, Volume 6 Issue 4

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Brief Report

THE PLASTIC DEFORMATION CHARACTERISTICS AND REGIONAL STRAIN FIELD ON THE SOUTHERN SEGMENT OF THE TANCHENG-LUJIANG FAULT ZONE

Xu Jiawei, Wang Ping, Ching Rengao, Ye Zhoujie

1984, 6(4):  1-16. 

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The studied segment shows its major,transcurrent ductile shear zone with a considerable sinistral displacement.The rock formation (Pt-T₁₊₂) at a depth of 5—15km may have cropped out in this area during its and subsequent erosion,many plastic-deformed strctures in it.The deformed zone was involved in the Indo-China orogeny.On the basis of measurements and analyses on a lot of pebbles within the shear zone,it is known that K₁ (the Flinn') is 1.178 and 1.053,which suggests a variation of simple shear and a plain strain with a constant volume of the studied zone.The intensely deformed belts are generally 40—50km in width,with an average a/c ratio of 27.68 and the maximum more than 87.37.The intensity of strain decreases rapidly with increasing distance from the shear fault zone,as well as with decreasing".depth to which the fault goes.For the Pt formation at the greatest depth,a/c value ranges from 30.58,Z₁-12.71-12.98,Z₂-2.54,and G-1.50.It follows that the differential horizontal slip may occur between various structures.On the condition that the elongation strain e1 and e3 are 4.95 and -0.817 within the intensely deformed belt,respectively,the belt in question has been elongated 164.23km in length and shortened 272.5km in width,to a corresponding 200km and 50km for the time being.The deformed belt was associated with syntectonic dynamothermal metamorphism,represented by greenschist facies and retrogressive metamorphism of early amphibolite ones.The internal belt was formed by high shear strain,with an angle ranging from 0—20°and a shear strain culculated to be more than 11.34.Developed here are four sorts of models involving viscous shear,ductile shear,ductile-brittle shear and brittle shear within the earth's crust.

HORIZONTAL DEFORMATION AND ITS GEOTECTONIC IMPLICATION IN THE BEIJING AREA

Wang Ruobai, Huang Liren

1984, 6(4):  17-24. 

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Processing of data,obtained from repeated measurements of ground deformation by use of the Beijing Ⅰ-triangulation network during 1966 and 1976—1980,was conducted to relate the characteristics of lateral component of the deformation field in this area to the regional structures.In terms of extensional tectonics,generation of compression-deformed zones may be accounted for,such as 1) Both the Babaoshan and Xiadian fault zones are dominant and the boundaries between the extensional tectonic elements; 2) Compression-deformed zones close to the fault zones are likely to be associated with the tilting motion of the fault blocks; and; 3) NW—NNW—trending fault(Nankou-Sunhe) is a transform strike-slip fault in this area.

OFFSET GULLIES AND RECURRENCE TIME OF M8.5 STRONG EARTHQUAKS ALONG THE FAULT ZONE OF NORTHERN PIEDMENT OF NANHUA MOUNTAIN,HAIYUAN,NINGXIA

Cheng Shaoping, Peng Gui, Li Hongchun

1984, 6(4):  25-37. 

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Because of recent activity of the fault zone of northern piedment of Nanhua Mountain,21 gullies along the fault zone within 16 kilometers from Caiyuan to Luanduizi were obviously offsetted,showing well oriented sinistral displacements.This paper studies geological and geomorphological features,precoss and offsets of the gullies,and determines for the fault zone the average slip rate (4.3mm/yr,since Late Pleistocene),on the basis of ¹⁴C dating of deposits and data on the rate of head-ward erosion.Moreover,according to observations in the field,the maximum displacement for the seismic fault in the epicentral area of Haiyuan M 8.5 Earthquake of 1920 is about 6.9m.On the basis of above data,the recurrence time of 8.5 strong earthquake along the fault zone has been estimated as about 1600 years.

RECURRENCE OF INDUCED EARTHQUAKES AT THE DENJIAQIAO RESERVIOR,YIDU COUNTY,HUBEI

1984, 6(4):  38-38. 

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THE ACTIVITY OF FAULT ZONE INFERRED FROM MICROSTRUCTURAL STUDY OF DEFORMED ROCKS

He Yongnian, Lin Cbuanyong, Shi Lanbin

1984, 6(4):  39-44. 

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The neotectonic activity of a minor fault zone on the Southwest margin of Yangzi platform has been studied based on the analysis and comparison of the microstructural features of deformed rocks within and outside the fault zone.The fault developed in Permian Emei basalt,striking NE40—50°,dipping toward Southeast at an angle of 70—80°,with a total length of 250m and horizontal displacement of 1.5m.Within the fault developed a zone 3—30cm in width consisting of fault gouge and fractured lenticular rock fragments,which along with the country rocks were cut by the late calcite veins.The samples were collected from the veins within the fault and the veins within the country rocks of different distance from the fault.The optical microscopic observation has shown that almost all of the calcite posseses twin lamellae,while U-stage measurement has shown that the space index of twin lamellae varies with the increasing distance from the fault.The space index is highest in the fault (50/mm),and decreases rapidly with the increasing distance from the fault (10/mm in the sample 20m away from the fault).The differential stress during the deformation process has been estimated from the developement degree of twin lamellae by using Jamison and Spang's method.The Result is in good agreement with that estimated from dynamically recrystallized grain-size.It is shown that the stress within the fault(700 bars) is much higher than that outside the fault(300 bars).According to thermoluminenscence dating the calcite veins were formed in Pleisto-cence.It is proposed that after Pleistocene there would be more than one active period of the fault.The stress of the main period was up to 700 bars.The strain and stress of the rocks within the fault during the faulting process were significantly greater than those in the rocks outside the fault.

STRUCTURAL ANALYSIS OF THE MOZITIANXIAOTIAN FAULT

Xu Lei, Wu Yongsheng

1984, 6(4):  45-53. 

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The study fault is located on the northern piedmmont of the Dabie mountain in the western part of Anhui Province with a variety of mylonite zone found on the both flanks.The mylonite zones are parallal to foliations on the axial plane of early fold zone,which was deformed through late folding.The mylonites prove to have formed in the priod of the second-stage tectonic slip in the Proterozoic rather than a cause of the fault rock.A suite of brittle-deformation related imbricate thrust can be found on the southern side of the fault in question along with some ramps.The study fault and these imbricate thrusts cut through the folds consisting of the mylonites.This paper also discusses active block in this region.

ON THE FUNCTION OF TWO SORTS OF PROGRAMMING PALEOMAGNETIC MAP RELATED TO BASIC CODES

Bai Yunhong, ChengGuoliang, Sun Qingge, Li Suling, Sun Yuhang

1984, 6(4):  54-54. 

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PETROLOGICAL CHARACTERISTICS AND GENESIS OF ALKALI BASALTIC BRECCIA PIPES IN THE LUOTUOFENG AREA, PINQUAN OF HEBEI PROVINCE

Fan Qicheng

1984, 6(4):  55-69. 

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The alkli basaltic breccia pipes at the Lutuofeng area are late Tertiary volcanic rocks,composed of breccia,dikes and cones,suggesting a multi-stage volcanism.The sequence of eruption was from alkali olivin-basalts to basanite,olivine nephelites and quartz tholeiites.Based on petrography,mineralogy,major and trace elements,especially on REE and Sr isotopic composition,the petrological characteristics and petrogenetic relation of the basalts have been well discussed.It has been postulated that the alkali olivin basalt-basanite magma requires low-degree(5—8%)melting of the garnet lherzolites,while the olivin nephelites magma may be derived from differentiations of the alkali olivin basalt basanite magma under high pressure in the lithospheric mantle.The quartz tholeiites may be the products of the melts of lithospheric mantle.The author has concluded that the spinel lherzolite xenolith is mantle fragments that were trapped by alkali basalts at a time when they were uprising from the mantle.

SOME ASPECTS OF NEOTECTONIC ACTIVITY AND PLATE MOTION IN 27TH INTERNATIONAL GEOLOGICAL CONGRESS,MOSCOW,USSR

1984, 6(4):  70-70. 

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STUDY ON THE SOUNDING OF DEEP-SEATED CRUSTAL STRUCTURES BENEATH THE LIAYANG AREA

Liang Zhonghua, Tang Rongyu, Song Jianjun, Zhu Meng

1984, 6(4):  71-78. 

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This paper describes the structural profiles across such main boundaries between earth's crust and mantle as: granitic layer (G),inner granitic layer (G₁),Conrad boundary (C),M discontinuity (M),and M₁ and M₃ in upper mantle,for which a coverted wave has been used in the study area (E118°56′—119°40′,N31°10′—31°50′).The results obtained indicate that NE-trending structures are dominant beneath this area,and then NW-trending structures.The deep faults have been well developed and the two shocks have occurred at the granite layer.It has been concluded that the earthquakes tend to have occurred along the edge of the uprising zone or along the gradient zone where the depths to the boundaries vary,abruptly or at the intersections of the deep fault in different directions.

DISCUSSION ON EPICENTRAL"LOCATIONS FOR THE TIBET M=8 EARTHQUAKE ON 29,SEPTEMBER 1411

Han Tongling

1984, 6(4):  79-79. 

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《SELECTED WORKS ON REMOTE SENSING SEISMOGEOLOGY》 WILL BE PUBLISHED

Yao Gan

1984, (4):  80-80. 

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