13:45 〜 15:15
[SCG52-P24] 背弧拡大におけるデタッチメント断層の役割：フィリピン海の海洋コアコンプレックス
キーワード：背弧拡大、海洋コアコンプレックス、デタッチメント断層、フィリピン海
Detachment faulting is now recognized as an essential style of seafloor spreading under melt-starved environments and a key feature in understanding the magmatic-tectonic cycle of mid-ocean ridges. Oceanic core complexes (OCCs) and smooth seafloor exposed along long-lived detachments are investigated in global slow-spreading systems; however, the studies of OCCs in back-arc spreading centers are still limited to the back-arc systems are an indispensable part of global divergent boundaries. The OCCs in back-arc basins can provide important information about the melt supply rate during back-arc evolution and the mantle beneath back-arc areas.
Limited back-arc basin OCC studies have been done in the Philippine Sea. Along the Parece Vela remnant back-arc rift (PVR) in the Parece Vela Basin, many OCCs are distributed. The rift axis is highly segmented and hosts anomalous massifs, though the well-ordered abyssal hills dominate in the far off-axis. Intensive studies have been done in the Mado Megamullion area, the junction between the Shikoku and the Parece Vela Basin, and the Godzilla Megamullion area at 15°N, the center of the PVR.
We now compile all available geophysical data in the Philippine Sea back-arc basins and try to identify the OCCs, smooth seafloor, and NTO massifs using multibeam bathymetry and gravity anomalies. In some cases, the age and/or spreading rate are estimated by magnetic anomalies and rock age dating. The most notable feature is that detachment faulting is the most dominant style at the cessation of back-arc spreading. Most OCCs and other structures are located just at the remnant axis, suggesting the waning of melt supply at the end of one back-arc opening cycle. Along the PVR, very long, continuous corrugations on the OCCs sometimes develop over the whole segment. Along the CBF Rift in the West Philippine Basin, another group of OCCs developed.
The second category of back-arc OCCs is discovered along the remnant arc crust. They were formed at the beginning of the back-arc spreading or the transition between rifting and spreading. Typical OCCs at mid-ocean ridges are the size of 20-30 km, and the length (flow-line direction) is longer or about the same as the width. However, some OCCs along the remnant Kyushu-Palau Ridge and Daito Ridge have wide widths, likely indicating the different lithosphere/asthenosphere environment and mechanical features.
The third group is the Chaotic Terrain in the Parece Vela Basin, located at the center of the basin.
We describe the morphological and geophysical features of these detachment-derived structures, estimate the melt supply rate, and discuss the implications for back-arc basin formation and lithosphere beneath the back-arc areas.
Limited back-arc basin OCC studies have been done in the Philippine Sea. Along the Parece Vela remnant back-arc rift (PVR) in the Parece Vela Basin, many OCCs are distributed. The rift axis is highly segmented and hosts anomalous massifs, though the well-ordered abyssal hills dominate in the far off-axis. Intensive studies have been done in the Mado Megamullion area, the junction between the Shikoku and the Parece Vela Basin, and the Godzilla Megamullion area at 15°N, the center of the PVR.
We now compile all available geophysical data in the Philippine Sea back-arc basins and try to identify the OCCs, smooth seafloor, and NTO massifs using multibeam bathymetry and gravity anomalies. In some cases, the age and/or spreading rate are estimated by magnetic anomalies and rock age dating. The most notable feature is that detachment faulting is the most dominant style at the cessation of back-arc spreading. Most OCCs and other structures are located just at the remnant axis, suggesting the waning of melt supply at the end of one back-arc opening cycle. Along the PVR, very long, continuous corrugations on the OCCs sometimes develop over the whole segment. Along the CBF Rift in the West Philippine Basin, another group of OCCs developed.
The second category of back-arc OCCs is discovered along the remnant arc crust. They were formed at the beginning of the back-arc spreading or the transition between rifting and spreading. Typical OCCs at mid-ocean ridges are the size of 20-30 km, and the length (flow-line direction) is longer or about the same as the width. However, some OCCs along the remnant Kyushu-Palau Ridge and Daito Ridge have wide widths, likely indicating the different lithosphere/asthenosphere environment and mechanical features.
The third group is the Chaotic Terrain in the Parece Vela Basin, located at the center of the basin.
We describe the morphological and geophysical features of these detachment-derived structures, estimate the melt supply rate, and discuss the implications for back-arc basin formation and lithosphere beneath the back-arc areas.