10:45 AM - 11:00 AM
[SCG48-06] Bathymetric Feature and Crustal Structure of the Lyra Trough in the western equatorial Pacific Ocean
Keywords:Lyra Trough, Ontong Java Plateau, bathymetric feature, gravity anomaly, crustal structure
The Ontong Java Plateau is located near the equator in the western Pacific Ocean. The plateau is known to be the largest oceanic plateau among the present oceanic plateaus in the world. The plateau is hypothesized to be formed by the breakup of the super-large oceanic plateau, Ontong Java Nui, during the Cretaceous Normal Superchron (e.g., Taylor, 2006). However, the detailed process of the breakup has not been exposed. To settle the discussion of the formation of the Ontong Java Plateau, it is indispensable to expose the tectonics of the surrounding basins, Lyra, East Mariana, Nauru, Stewart, and Ellice basins. Magnetic anomaly lineations indicate that the East Mariana and Nauru basins were formed between the Late Jurassic and Early Cretaceous (159-123 Ma, Nakanishi et al., 1992). The formation of the Lyra and Stewart basins still remains unsettled because of lack of magnetic anomaly lineations and radiometric ages. We will present new evidence about the tectonics of the Lyra Basin from the bathymetric and gravity data and the seismic reflection data.
The Lyra Basin deepens westward from the Ontong Java Plateau, with a water depth from 4000 to 5500 m. The Lyra Trough extends linearly across the western part of the Lyra Basin, with an overall strike of NNW-SSE. Hegarty et al. (1983) proposed that the trough is a track of the subduction between the Caroline and Pacific plates. On the other hand, Hegarty and Weissel (1988) proposed that the trough was a transform fault between the Caroline and Pacific plates. The origin of the Lyra Trough as well as Lyra Basin remains a subject of controversy.
We used multibeam bathymetry data acquired in the cruises from 1996 to 2022, the last free-air gravity anomaly data by Sandwell et al. (2014), and the multi-channel seismic data collected by R/V Mirai in 2014 (MR14-06, Shimizu et al., 2017). To model the crustal structure across the Lyra Trough, we used the method of Talwani et al. (1959).
Several ridges and seamount are situated around the eastern margin of the Lyra Trough. The strike of the ridges is different from that of the Lyra Trough. The seamounts are divided into multiple segments at the eastern margin of the Lyra Trough. Our gravity modeling along the seismic survey line indicates that the crustal structure west of the Lyra Trough is not distinctly different from that east of the trough, implying that the Lyra Trough is not a trace of a subduction zone but a fracture zone.
The Lyra Basin deepens westward from the Ontong Java Plateau, with a water depth from 4000 to 5500 m. The Lyra Trough extends linearly across the western part of the Lyra Basin, with an overall strike of NNW-SSE. Hegarty et al. (1983) proposed that the trough is a track of the subduction between the Caroline and Pacific plates. On the other hand, Hegarty and Weissel (1988) proposed that the trough was a transform fault between the Caroline and Pacific plates. The origin of the Lyra Trough as well as Lyra Basin remains a subject of controversy.
We used multibeam bathymetry data acquired in the cruises from 1996 to 2022, the last free-air gravity anomaly data by Sandwell et al. (2014), and the multi-channel seismic data collected by R/V Mirai in 2014 (MR14-06, Shimizu et al., 2017). To model the crustal structure across the Lyra Trough, we used the method of Talwani et al. (1959).
Several ridges and seamount are situated around the eastern margin of the Lyra Trough. The strike of the ridges is different from that of the Lyra Trough. The seamounts are divided into multiple segments at the eastern margin of the Lyra Trough. Our gravity modeling along the seismic survey line indicates that the crustal structure west of the Lyra Trough is not distinctly different from that east of the trough, implying that the Lyra Trough is not a trace of a subduction zone but a fracture zone.