Specific gravity field and deep crustal structure of the Himalayas east structural knot

Transcription

1 CHINESE JOURNAL OF GEOPHYSICS Vol. 49, No. 4 Jul., 2006,,.., 2006, 49 (4) : Teng J W, Wang Q S, Wang GJ, et al. Specific gravity field and deep crustal structure of the Himalayas east structural knot. Chinese J. Geophys. (in Chinese), 2006, 49 (4) : ,2, 1, 1, 1, 1 1, , (92 E 97 E,26 N 30 N),, ( ).,,. 3. > 70 km ; 55 km ; km ; km, 3.,,.,,.,,,, (2006) P , Specific gravity field and deep crustal structure of the Himalayas east structural knot TENGJi2Wen 1,2, WANG Qian2Shen 1, WANG Guang2Jie 1, XU Ya 1, ZHANG Xue2Mei 1 1 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing , China 2 College of Geoexploration Science and Technology, Jilin University, Changchun , China Abstract More than a half of the Himalayas east structural knot area (92 E 97 E, 26 N 30 N) that straddles boundaries between China, India and Burma has no ground gravity measuring point yet. Here it is hard to research directly the gravity field characteristic and the deep crustal structure. In this paper, the satellite gravity anomaly data are employed as pseudo free air gravity anomaly to calculate Bouguer gravity anomaly. The calculated Bouguer gravity anomaly exhibits well mirror correlation with the topography altitude of this district. Three profiles of deep crustal structure according to above calculation are obtained. In the Qinghai2 Xizang Plateau the crust thickness is more than 70 km, in the orogenic belt of Himalayan Mountains it is about 55 km, in the Brahmaputra basin valley it is 33 to 35 km, and in the Naga mountain it is 40 to 45 km. The east structural knot is composed of high2density matter, moves northward after the collision and extrusion by the Indian Ocean plate, and then inserts into the eastern margin of the Qinghai2Xizang Plateau. This dynamic process results in violent tectonic movement of the southeastern and northeastern edges of the Qinghai2Xizang ( ) (2005 ).,,1934,1962 -,. E2mail : iggcas. ac. cn

2 1046 (Chinese J. Geophys. ) 49 Plateau, induces a series of earthquakes frequently, and accumulates a large amount of mineral resources. Keywords Himalayas, East structural knot, Gravity field, Deep crustal structure, Wedge insertion 1, ( 1),,., -.,., [1 8 ].,.,,.. 92 E 97 E,26 N 30 N [9 ],.,,, [10 ].,.,.,,.,, ,,,.,.,,.,,,, [11],.,,,, [5] ( 2 3)., ( 2 7 ),,.,.,,.,..,,,!

3 4 : Fig. 1 Geographic position and topographic altitude characteristics of the east structural knot area [12 ] Fig. 3 Distribution of orders satellite gravity anomaly [12 ] 4 Fig. 4 Distribution of calculated Bouguer gravity anomaly on the east structural knot area

4 1048 (Chinese J. Geophys. ) 49 2 Fig. 2 Blank area of gravity data of the east structural knot and adjacent area 212 [12 ],. 1 1 :.,,.,.,,.,, ;,. [13,14 ],.,.,,,.,, [12 ] ( ),,.,. [12 ], ( 2, 3 [12 ] ),.,,, [13 ]. [12 ],.,,.,,. : 3500 m, (2 3 ) m, 1900 m. (2 3 ),. ( ). 3,

5 4 : 1049,.,,.,. ( ),., 214 g cm - 3,. ( 4),,. 3 ( 5 7) :,.,,., ( 4),. : ( m ) mgal ; ( 3000 m 1500 m) mgal ; ( m ) mgal - 50 mgal ; ( m ) mgal mgal ; ( 1000 m) mgal. [10,12,15 ] ( )., [10,12,15 ],., [12 ] Bowin [16 ], km [12 ],.,,. 411, 3 ( 5 A - A, 6 B - B, 7 C - C ). A - A 92 E,30 N 9515 E,2515 N, 700 km,.,. B - B 95 E, 600 km, A - A, A - A,. C - C 93 E,, 600 km. C - C ;,,. 4, 5 A - A Fig. 5 Crustal structural profiles A - A inversed from gravity field data of the east structural knot area and its adjacent

6 1050 (Chinese J. Geophys. ) 49 6 B - B Fig. 6 Crustal structural profiles B - B inversed from gravity field data of the east structural knot area and its adjacent 412,,. 3,, ( 5 7). A - A ( 5) Moho 70 km. Moho, km ;, km ;,Moho 45 km ; ( ). B - B ( 6),Moho 70 km,, km ; km ; 45 km ;. C - C ( 7) Moho 70 km, 55 km, 7 C - C Fig. 7 Crustal structural profiles C - C inversed from gravity field data of the east structural knot area and its adjacent 33 km :,, ( > 70 km), (45 km), (33 35 km)., ( ), mgal., 30 km., NEE EW..,,,,,. - NS,,

7 4 : 1051,. 5 (1),,,,,.,. (2),,,.,. (3),.,.,, 70 km., km., km. 45 km.,, - -, - -., ( ),, ( ),. (4) 3, g cm - 3, 2178 g cm - 3.,, (3138 g cm - 3 ).,,,. (5),,. (6) :,,,, ( ).,,, ( ). -,. (7),. Moho,,,,,. 6, ( ). -.,,,. (References) [ 1 ] Teng J W. Characteristics of geophysical fields and plate tectonics of the Qinghai- Xizang Plateau and its neighbouring regions. Proceeding of Symposium on Qinghai- Xizang (Tibet) Plateau (Beijing, China). Geological and Ecological studies of Qinghai- Xizang Plateau. Beijing : Science Press, Vol. 1, [ 2 ], Barchfiel B C,.. (D ), 2001, 31 (1) : 1 9 Wang E Q, Barchfiel B C, Ji J Q. Estimation of Cenozoic crust shortening and its geological evidence in Himalayas structure knot. Science in China (Series D) (in Chinese), 2001, 31 (1) : 1 9

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