11:00 AM - 11:15 AM
[SCG48-07] Spreading process of the Mariana Trough using geomagnetic anomaly data
Keywords:back-arc basin, magnetic anomaly, Mariana Trough
The Mariana Trough is an active back-arc basin formed by the subduction of the Pacific Plate beneath the Philippine Sea Plate. The Mariana Trough can be divided into three regions based on its topographic features: northern, central, and southern regions. Although the age and spreading rate of the Mariana Trough have been investigated based on the analysis of geomagnetic anomaly data in each region, there has been no comprehensive study on the formation history. In this study, we examine the whole history of back-arc spreading of the Mariana Trough from its beginning to the present by interpreting the morphology and geomagnetic anomalies. The Mariana Trough is a well-studied region in the back-arc basins, and geomagnetic anomalies can be interpreted over the entire area. Since there are only a few such basins in the Shikoku and Lau Basins, this study is expected to provide new insights into the formation process of back-arc basins.
We used bathymetry data and z-component of vector magnetic anomaly. We compiled multibeam bathymetry data collected during the total 14 cruises (Y96-13, YK99-11-Leg2, YK00-13, YK01-11, YK03-09, YK09-08, YK10-10, YK10-15, KR98-12, KR02-14, KR03-13, KR05-17, KR06-12, KH92-1) and created a 50 m grided bathymetry. The blank nodes were complemented by 0.1 arc-minute grided bathymetry data from Kitada et al (2005). Geomagnetic anomaly data were obtained during the total 24 cruises (Y96-13, YK99-11-Leg2, YK01-11, YK03-09, YK08-08 Leg1,2, YK09-08, YK10-10, YK10-12, YK10-15, YK12-11, YK14-13, YK15-11, KR97-11, KR98-12, KR00-03, KR02-01, KR02-14, KR03-13, KR05-17, KR16-14, KH92-1) by shipboard three-component magnetometers. We use only the z-component of vector magnetic anomaly because the Mariana Trough is an east-west spreading near the magnetic equator and the horizontal component is relatively inaccurate due to the insufficient accuracy of the gyrocompass. The effect of ship magnetization was corrected and then the obtained anomaly was converted to the equivalent magnetization intensity of the seafloor.
Based on the detailed bathymetric maps, we identified the spreading axis, off-axis segment boundaries, and boundary between the stages of rifting and seafloor spreading. The present spreading axis is divided into 18 second order segments, but the segment lengths have not been constant since the beginning of spreading, and it is clear that there have been separation and fusion of the segments. Especially in the central region, the strike of the lineation of the seafloor topography changed drastically in about 4 Ma. We summarized the length, strike, and offset of each segment. We also identified the magnetic lineations over the whole basin floor. The oldest chron in each area is identified only on the west side of the spreading axis, and is C3An.2n_old (about 6.7 Ma), in the central area, C2An.3n_old (about 3.6 Ma) in the northern area, and C2An.3n_young (about 3.3 Ma) in the southern area. We also performed a 2-D forward modeling, assuming 1 km-thick magnetized layer draping the bathymetry to examine the spreading rate, the oldest chron, and the process in detail. The style of asymmetric spreading is also discussed.
We used bathymetry data and z-component of vector magnetic anomaly. We compiled multibeam bathymetry data collected during the total 14 cruises (Y96-13, YK99-11-Leg2, YK00-13, YK01-11, YK03-09, YK09-08, YK10-10, YK10-15, KR98-12, KR02-14, KR03-13, KR05-17, KR06-12, KH92-1) and created a 50 m grided bathymetry. The blank nodes were complemented by 0.1 arc-minute grided bathymetry data from Kitada et al (2005). Geomagnetic anomaly data were obtained during the total 24 cruises (Y96-13, YK99-11-Leg2, YK01-11, YK03-09, YK08-08 Leg1,2, YK09-08, YK10-10, YK10-12, YK10-15, YK12-11, YK14-13, YK15-11, KR97-11, KR98-12, KR00-03, KR02-01, KR02-14, KR03-13, KR05-17, KR16-14, KH92-1) by shipboard three-component magnetometers. We use only the z-component of vector magnetic anomaly because the Mariana Trough is an east-west spreading near the magnetic equator and the horizontal component is relatively inaccurate due to the insufficient accuracy of the gyrocompass. The effect of ship magnetization was corrected and then the obtained anomaly was converted to the equivalent magnetization intensity of the seafloor.
Based on the detailed bathymetric maps, we identified the spreading axis, off-axis segment boundaries, and boundary between the stages of rifting and seafloor spreading. The present spreading axis is divided into 18 second order segments, but the segment lengths have not been constant since the beginning of spreading, and it is clear that there have been separation and fusion of the segments. Especially in the central region, the strike of the lineation of the seafloor topography changed drastically in about 4 Ma. We summarized the length, strike, and offset of each segment. We also identified the magnetic lineations over the whole basin floor. The oldest chron in each area is identified only on the west side of the spreading axis, and is C3An.2n_old (about 6.7 Ma), in the central area, C2An.3n_old (about 3.6 Ma) in the northern area, and C2An.3n_young (about 3.3 Ma) in the southern area. We also performed a 2-D forward modeling, assuming 1 km-thick magnetized layer draping the bathymetry to examine the spreading rate, the oldest chron, and the process in detail. The style of asymmetric spreading is also discussed.