Abstract
Rifting of continental lithosphere leading to oceanic basins is a complex process conditioned by different factors such as the rheology and thermal structure of the underlying lithosphere, as well as underlying asthenospheric dynamics. All these processes, which finally lead to oceanic domains, can better be recognized in small oceanic basins. Powell Basin is a small oceanic basin bounded to the north by the South Scotia Ridge, to the east by the South Orkney Microcontinent, and to the west by the Antarctic Peninsula. It was formed between the Oligocene and Miocene, however, its age is not well defined, among other reasons due to the small amplitude of its spreading magnetic anomalies. This basin is an ideal framework to analyze the different rifting and spreading phases, which leads from continental crust to the formation of an oceanic domain through different extensional regimes. To identify the different boundaries during the formation of Powell Basin from the beginning of the rifting until the end of the spreading, we use different data sources: magnetic, gravity, multichannel seismic profiles and bathymetry data. We use seismic and bathymetry data to estimate the Total Tectonic Subsidence (TTS). TTS has proven to be useful to delineate the different tectonic regimes present from early rifting to the formation of oceanic seafloor. This result together with magnetic data has been used to delimit the oceanic domain and compare with previous authors’ proposals. This method could be applied in any other basin or margin to help delimiting its boundaries. Finally, we analyze the role that an asthenospheric branch intruding from the Scotia Sea played in the evolution of the magnetic anomaly signature on an oceanic basin.
Highlights
The formation of the Drake Passage is considered a remarkable event in Earth’s climate history leading to the formation of several small oceanic basins along its southern part
The northern and western part of Powell Basin are characterized by large and long-wavelength positive magnetic anomalies (>300 nT) (Figure 2B). These anomalies correspond to the Pacific Margin Anomaly (PMA), which runs sub-parallel along the Antarctic Peninsula margin (Garrett, 1990; Ghidella et al, FIGURE 4 | A) tectonic subsidence (TTS) map
We will firstly discuss the tectonic boundaries. To achieve this we extrapolate to a 3D our previous 2D results using the TTS, Bouguer gravity anomaly, and Analytical signal information altogether to discuss the nature of the crust in three different margins of Powell Basin
Summary
The formation of the Drake Passage is considered a remarkable event in Earth’s climate history leading to the formation of several small oceanic basins along its southern part. Powell Basin is a byproduct of the opening of the Drake Passage, resulting after the fragmentation of the NE extremity of the Antarctic Peninsula. This basin is characterized by a smooth relief that varies from 3,000 to 2,400 m below sea level (Figure 1), in the northwestern sector of Weddell Sea. This basin is characterized by a smooth relief that varies from 3,000 to 2,400 m below sea level (Figure 1), in the northwestern sector of Weddell Sea It constitutes an elliptically shaped oceanic domain bounded by a continental block known as the South Orkney. Microcontinent (SOM) to the east, the South Scotia Ridge (SSR) to the north, and north-western tip of the Antarctic Peninsula to the west. It is limited by a bathymetric ridge bordering the northern margin of the Weddell Sea.
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