In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system： one data set was from the ＇Geological-geophysical map series of Chin...In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system： one data set was from the ＇Geological-geophysical map series of China Seas and adjacent areas＇ database and the other was newly collected by R/VKexue Ⅲ in 2011. Magnetic and gravity data were reorganized and processed using the software MMDP, MGDP and RGIS. In addition to the description of the anomaly patterns in different areas, deep and shallow structure studies were performed by using several kinds of calculation, including a spectrum analysis, upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly. The depth of the Moho and magnetic basement were calculated. Based on the above work, several controversial tectonic problems were discussed. Compared to the shelf area and Ryukyu Arc, the Okinawa Trough has an obviously thinned crust, with the thinnest area having thickness less than 14km in the southern part. The Taiwan-Sinzi belt, which terminates to the south by the NW-SE trending Miyako fault belt, contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough. As an important tectonic boundary, the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments. A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate. Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area. The gravity and magnetic data support the existence of a Great East China Sea, which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions, and might have extended southwestward and connected with the northern South China Sea shelf basin.展开更多
Study of the characteristics of the crustal magnetic anomaly in the Qinghai-Tibet Plateau and the adjacent areas helps better understand the lithospheric structure and evolution, as well as the regional geodynamic pro...Study of the characteristics of the crustal magnetic anomaly in the Qinghai-Tibet Plateau and the adjacent areas helps better understand the lithospheric structure and evolution, as well as the regional geodynamic processes. Here we analyze the distri- bution laws of the crustal magnetic anomaly and its vertical gradient, the decay characteristics of the anomaly, the contribu- tions from different wavelength bands to the anomaly, and the relationship between the anomaly and the crustal regional tec- tonics in the plateau and nearby, based on a new and higher degree geomagnetic model NGDC-EMM-720-V3 constructed from the surface, aeromagnetic, marine and satellite survey data. The results reveal that the positive and negative anomalies in the Qinghai-Tibet Plateau are weak, while those of the surrounding areas are strong. The boundary agrees well with the border of the plateau regional tectonics. The anomaly is nearly east-west in the central and western plateau, arc-shaped in the south- western and eastern, and nearly north-south in the southeastern, consistent with the tectonic trends. There are strong negative anomaly loci in the east and west syntaxis, whereas no significant differences exist among the Cenozoic blocks in the plateau interior. No direct correspondence exists between the anomaly and the crustal depth. On the background of a weak magnetic anomaly in the plateau, relatively stronger short wavelength fields from the shallower crust are overlapped in the Lhasa, Qilian, Qaidam, and Sichuan-Yunnan rhombic blocks. A strong negative anomaly in the east-west direction is distributed along the Himalayas, mainly caused by the middle and long wavelength bands in the deep and central crust. The magnetic structural lay- ers are stable in the Sichuan and Tarim basins. The anomalies at different altitudes over the southern plateau vary strongly, showing a drastic variation in the magnetic structure from the deep crust to the shallow crust.展开更多
基金funded by the National Key Basic Research Program of China (973 ProgramGrant No.2013CB429701)National Natural Science Foundations of China (Grant Nos.41206050 and 41202081)
文摘In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system： one data set was from the ＇Geological-geophysical map series of China Seas and adjacent areas＇ database and the other was newly collected by R/VKexue Ⅲ in 2011. Magnetic and gravity data were reorganized and processed using the software MMDP, MGDP and RGIS. In addition to the description of the anomaly patterns in different areas, deep and shallow structure studies were performed by using several kinds of calculation, including a spectrum analysis, upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly. The depth of the Moho and magnetic basement were calculated. Based on the above work, several controversial tectonic problems were discussed. Compared to the shelf area and Ryukyu Arc, the Okinawa Trough has an obviously thinned crust, with the thinnest area having thickness less than 14km in the southern part. The Taiwan-Sinzi belt, which terminates to the south by the NW-SE trending Miyako fault belt, contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough. As an important tectonic boundary, the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments. A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate. Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area. The gravity and magnetic data support the existence of a Great East China Sea, which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions, and might have extended southwestward and connected with the northern South China Sea shelf basin.
基金sponsored by National Natural Science Foundation of China (Grant Nos. 40464001 and 40864002)
文摘Study of the characteristics of the crustal magnetic anomaly in the Qinghai-Tibet Plateau and the adjacent areas helps better understand the lithospheric structure and evolution, as well as the regional geodynamic processes. Here we analyze the distri- bution laws of the crustal magnetic anomaly and its vertical gradient, the decay characteristics of the anomaly, the contribu- tions from different wavelength bands to the anomaly, and the relationship between the anomaly and the crustal regional tec- tonics in the plateau and nearby, based on a new and higher degree geomagnetic model NGDC-EMM-720-V3 constructed from the surface, aeromagnetic, marine and satellite survey data. The results reveal that the positive and negative anomalies in the Qinghai-Tibet Plateau are weak, while those of the surrounding areas are strong. The boundary agrees well with the border of the plateau regional tectonics. The anomaly is nearly east-west in the central and western plateau, arc-shaped in the south- western and eastern, and nearly north-south in the southeastern, consistent with the tectonic trends. There are strong negative anomaly loci in the east and west syntaxis, whereas no significant differences exist among the Cenozoic blocks in the plateau interior. No direct correspondence exists between the anomaly and the crustal depth. On the background of a weak magnetic anomaly in the plateau, relatively stronger short wavelength fields from the shallower crust are overlapped in the Lhasa, Qilian, Qaidam, and Sichuan-Yunnan rhombic blocks. A strong negative anomaly in the east-west direction is distributed along the Himalayas, mainly caused by the middle and long wavelength bands in the deep and central crust. The magnetic structural lay- ers are stable in the Sichuan and Tarim basins. The anomalies at different altitudes over the southern plateau vary strongly, showing a drastic variation in the magnetic structure from the deep crust to the shallow crust.
