5:15 PM - 7:15 PM
[SCG55-P16] Formation Process of the Lyra Basin in the Western Equatorial Pacific Ocean
Keywords:Lyra Basin, 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 thought to be formed by the breakup of the super-large oceanic plateau, Ontong Java Nui, during the Cretaceous Normal Superchron (e.g., Taylor, 2006). To verify this hypothesis, it is indispensable to expose the tectonics of the surrounding ocean basins, Lyra, East Mariana, Nauru, Stewart, and Ellice basins. Previous studies suggest that the East Mariana and Nauru Basins were formed between 159 Ma and 123 Ma, based on magnetic anomaly lineations (e.g., Nakanishi et al., 1992), and that the Ellice Basin is thought to have formed between approximately 123 Ma and 112–108 Ma, based on radiometric ages of dredged samples (Davidson et al., 2023). On the other hand, the formation age of the Lyra and Stewart basins, are unknown because of the lack of magnetic anomaly lineations or radiometric ages.
The Lyra Basin is located west of the Ontong Java Plateau and deepens westward from with 4000 to 5500 m. The Lyra Trough, situated in the western part of the basin, is the most remarkable topographic feature in the basin. Several seamounts exist in the eastern margin of the trough. The strike of the trough is N36°W. In our last presentation in JpGU Meeting 2024, we examined the subsurface structure and formation age of the Lyra Basin by an analysis of bathymetry and gravity anomalies around the Lyra Trough. The results supported the hypothesis by Hegarty and Weissel (1988) that the Lyra Trough is originated from a fracture zone. After the meeting, we reexamined our results by three-dimensional modeling of the subsurface structure and admittance analysis without the load of the Lyra Trough.
We used multibeam bathymetry data acquired in the cruises from 1996 to 2022, the latest free-air gravity anomaly data by Sandwell et al. (2014), the multi-channel seismic data collected by R/V Mirai in 2014 (MR14-06, Shimizu et al., 2017), and the latest sediment thickness data in the world’s oceans by Straume et al. (2019).
To examine the subsurface structure model, we constructed a 3D model using IGMAS+ (Götze and Lahmeyer, 1988; Schmidt et al., 2011, 2020). Consequently, we exposed more detailed subsurface structure. For admittance analysis, we conducted 1D analysis along the survey line crossing multiple seamounts near the trough. The elastic thickness of the plate in the Lyra Basin is estimated to be about 8-9 km. According to the relationship between the elastic thickness and the loading age of seamounts in the eastern margin of the Lyra Trough (Watts et al., 2006; Watts, 2011), seamounts in the basin are thought to be formed about 30 Myr after the formation of the basin. We conducted that the Lyra Basin is thought to be formed around 95 Ma because the seamounts were formed at 65 Ma (Shimizu et al., 2015).
The Lyra Basin is located west of the Ontong Java Plateau and deepens westward from with 4000 to 5500 m. The Lyra Trough, situated in the western part of the basin, is the most remarkable topographic feature in the basin. Several seamounts exist in the eastern margin of the trough. The strike of the trough is N36°W. In our last presentation in JpGU Meeting 2024, we examined the subsurface structure and formation age of the Lyra Basin by an analysis of bathymetry and gravity anomalies around the Lyra Trough. The results supported the hypothesis by Hegarty and Weissel (1988) that the Lyra Trough is originated from a fracture zone. After the meeting, we reexamined our results by three-dimensional modeling of the subsurface structure and admittance analysis without the load of the Lyra Trough.
We used multibeam bathymetry data acquired in the cruises from 1996 to 2022, the latest free-air gravity anomaly data by Sandwell et al. (2014), the multi-channel seismic data collected by R/V Mirai in 2014 (MR14-06, Shimizu et al., 2017), and the latest sediment thickness data in the world’s oceans by Straume et al. (2019).
To examine the subsurface structure model, we constructed a 3D model using IGMAS+ (Götze and Lahmeyer, 1988; Schmidt et al., 2011, 2020). Consequently, we exposed more detailed subsurface structure. For admittance analysis, we conducted 1D analysis along the survey line crossing multiple seamounts near the trough. The elastic thickness of the plate in the Lyra Basin is estimated to be about 8-9 km. According to the relationship between the elastic thickness and the loading age of seamounts in the eastern margin of the Lyra Trough (Watts et al., 2006; Watts, 2011), seamounts in the basin are thought to be formed about 30 Myr after the formation of the basin. We conducted that the Lyra Basin is thought to be formed around 95 Ma because the seamounts were formed at 65 Ma (Shimizu et al., 2015).