ALBERT

Description: The Powell Basin is a small oceanic basin bounded by continental blocks that fragmented during drifting of South America from Antarctica. The basin is limited to the east by the South Orkney Microcontinent, to the north by the South Scotia Ridge, and to the west by the Antarctic Peninsula. The timing of its opening is poorly constrained due to low amplitude magnetic anomalies which hampers their identification and cause large uncertainties in proposed ages that range from the Late Eocene to Early Miocene. The Powell basin has been extensively studied using a variety of geophysical methods including seismic, gravity and magnetic surveys intended to unveil the tectonic domains. The magnetic anomalies and the thermal regime of the basin are of particular interest, as some of these studies have suggested that the absence of clear seafloor magnetic anomalies is the result of impermeable layers that prevent the venting of hot fluids into the water column. Using new magnetic and heat flow data together with geophysical data from international databases, we analyze the thermal structure of the Powell Basin its lithosphere and the upper mantle dynamics and discuss the probable causes of the abnormally small amplitudes of magnetic anomalies.

Description: The last version of the World Digital Magnetic Anomaly Map (WDMAM v. 2.0) was released in 2015 (Dyment et al., EPSL, 2015; Lesur et al., EPS, 2016) with the mandate to update it using the same methodology when new data become available. The new version 2.1, compiled at 5 km interval, at 5 km altitude above the continents and at sea-level over the oceans, includes new datasets: (1) the complete digital aeromagnetic map of Brasil made available by ANP; (2) an improved version of the aeromagnetic map of Russia prepared by V-SEGEI; (3) the second version of the Antarctic Digital Magnetic Anomaly maP (ADMAP; Golynsky et al., GRL, 2018) which results from a remarkable international effort during and after the Second International Polar Year; (4) a new map of the Caribbean Plate and Gulf of Mexico (Garcia and Dyment, EPSL, 2021, 2022); (5) the updated Magnetic Anomaly Map of Eastern Asia prepared by the CCOP (MAMEA; Ishihara and Uchida, 2021); and (6) a new marine magnetic anomaly data compilation prepared by T. Ishihara and coworkers. The remaining data gaps are filled with a satellite anomaly model (Thebault et al., GRL, 2021). Long wavelengths of degree and order lower than 120 are filtered and replaced by those computed between order and degree 16 and 120 using the same satellite magnetic anomaly model from CHAMP and Swarm data. The new map will be presented and its significant improvements over the previous version discussed.

Description: The Powell Basin is a small oceanic basin bounded by continental blocks that fragmented during break up of Antarctica from South America. This basin bounds the South Orkney Microcontinent to the east, the South Scotia Ridge to the north, and the Antarctic Peninsula to the west. The timing of its opening is poorly constrained due to the low amplitude of the oceanic spreading magnetic anomalies which hampers their identification and interpretation causing large uncertainties in proposed ages that range from the Late Eocene to Early Miocene. This basin has been extensively studied using a variety of geophysical methods including seismic, gravity and magnetics surveys intended to unveil the tectonic domains, the particularities of its magnetic anomalies and the understanding of the thermal regime in this area. Here, we show new magnetic and heat flow data integrated with other geophysical data from international databases (multichannel seismic data, bathymetry and free-air gravity), to analyze the thermal structure of the lithosphere of Powell Basin and the upper mantle dynamics as well as to discuss the probable causes of the abnormally small amplitudes of its magnetic anomalies. Our results show that the low magnetic anomaly amplitudes are not widespread but concentrate in the eastern and southwestern part of the basin. We propose that these small amplitudes result from the thermal dependency of magnetic rocks caused by an asthenospheric branch flow that penetrates the Powell Basin through the northern area.