11:00 〜 11:15
[SCG55-19] Near-bottom magnetic survey of the Central Indian Ridge for paleomagnetic and tectono-magmatic reconstruction
キーワード：深海磁気異常、古地磁気強度変動、海底マグマ活動、海洋底テクトニクス
During the R/V Hakuho-maru KH-24-4 cruise in October 2024, we conducted a deep-tow magnetic survey across the Central Indian Ridge to investigate long-term variations in Earth’s magnetic field and refine seafloor age models. This ridge segment, characterized by an intermediate spreading rate and well-defined abyssal hills (indicating stable magma supply), is particularly suitable for recovering high-quality paleo-intensity records spanning over four million years.
We employed a cesium deep-tow magnetometer developed by the Atmosphere and Ocean Research Institute, University of Tokyo. The sensor was positioned 30 m away from the main stainless-steel frame, which housed a pressure sensor, a motion sensor, and a 13 kHz acoustic transponder for precise depth and horizontal positioning. The frame was deployed 15 m below a 360 kg weight attached to the vessel’s wire. All measurements (total magnetic field, depth, and attitude) were recorded at 2 Hz and monitored in real time to ensure data quality and stable sensor depth. Over 29 hours of towing, the system traversed a survey line of approximately 140 km at water depths ranging from about 1,800 to 2,700 m.
Our results indicate that the measured magnetic field intensity varied between 41,300 nT and 44,600 nT—approximately five times the range detected at the sea surface in the same region. Numerous short-period fluctuations in the data suggest a detailed record of geomagnetic reversals, paleo-intensity changes, and sensor-altitude variations. Notably, these fluctuations exhibit finer resolution than previous profiles from the Central Indian Ridge (Pouliquen et al., 2001) and are comparable to deep-tow data collected along the East Pacific Rise during the Brunhes normal polarity chron (Gee et al., 2000). Furthermore, preliminary interpretation based on the geomagnetic reversal history identifies geomagnetic polarity chrons C1n (0.00–0.77 Ma) to C4An (8.69-9.03 Ma), suggesting that this dataset represents the longest deep-sea magnetic anomaly record observed to date—more than twice as long as existing records.
In this presentation, we also compare these data with continuous relative paleo-intensity records from drilled marine sediments (Valet et al., 2005; Channel et al., 2009; Yamazaki et al., 2018). In addition, we discuss potential insights into temporal variations in magma activity and crustal structure by integrating rock magnetic and geochemical analyses.
We employed a cesium deep-tow magnetometer developed by the Atmosphere and Ocean Research Institute, University of Tokyo. The sensor was positioned 30 m away from the main stainless-steel frame, which housed a pressure sensor, a motion sensor, and a 13 kHz acoustic transponder for precise depth and horizontal positioning. The frame was deployed 15 m below a 360 kg weight attached to the vessel’s wire. All measurements (total magnetic field, depth, and attitude) were recorded at 2 Hz and monitored in real time to ensure data quality and stable sensor depth. Over 29 hours of towing, the system traversed a survey line of approximately 140 km at water depths ranging from about 1,800 to 2,700 m.
Our results indicate that the measured magnetic field intensity varied between 41,300 nT and 44,600 nT—approximately five times the range detected at the sea surface in the same region. Numerous short-period fluctuations in the data suggest a detailed record of geomagnetic reversals, paleo-intensity changes, and sensor-altitude variations. Notably, these fluctuations exhibit finer resolution than previous profiles from the Central Indian Ridge (Pouliquen et al., 2001) and are comparable to deep-tow data collected along the East Pacific Rise during the Brunhes normal polarity chron (Gee et al., 2000). Furthermore, preliminary interpretation based on the geomagnetic reversal history identifies geomagnetic polarity chrons C1n (0.00–0.77 Ma) to C4An (8.69-9.03 Ma), suggesting that this dataset represents the longest deep-sea magnetic anomaly record observed to date—more than twice as long as existing records.
In this presentation, we also compare these data with continuous relative paleo-intensity records from drilled marine sediments (Valet et al., 2005; Channel et al., 2009; Yamazaki et al., 2018). In addition, we discuss potential insights into temporal variations in magma activity and crustal structure by integrating rock magnetic and geochemical analyses.