My Blogs (olelog) are mainly based on my daily reading of earth science news.
Here on whatonearth.olehnielsen.dk I try to weave some of the pieces together to a greater whole with added background info.
It is of great help that Google Maps is now covering the bottom of the oceans as well. A quick look at the area in the Drake Passage between the southern tip of South America and the northern tip of Antarctica may make you suspicious. Do we see a tectonic plate bordered by two fracture zones, a subduction zone and a spreading ridge? It looks like it.
Drake Passage between the South America and Antarctic Peninsular opened during the development of the Scotia Arc from about 41 million years ago. In Drake Passage, the Phoenix Ridge has three extinct spreading ridge segments (P1, P2 and P3 in the figure below). These segments separated the Phoenix plate from the Antarctic plate. Previous magnetic studies suggested that the seafloor spreading in each of the ridge segments stopped at the same time about 3.3 million years ago. The figure below is taken from a study published as U.S.Geological Survey and The National Academies; USGS OF-2007-1047, Extended Abstract 110, and available for download as PDF file: http://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea110.pdf
The figure cover approximately the same area, and I hope you can recognise the same features as seen in the Google map above. There are plenty of parallel fracture zones in the area. Of importance here are the Shackleton Fracture Zone (SFZ) and the Hero Fracture Zone (HFZ) (bordering two sides of the Phoenix Plate). SST finally is The South Shetland Trench northwest of the South Shetland Islands. It is the only trench along the Pacific margin of the Antarctic Peninsula. Subduction here almost stopped after the cessation of spreading in Drake Passage about 3.3 million years ago. The red lines are survey lines from the mentioned study (so just ignore them).
The Phoenix Plate is also known as the Aluk Plate. It was an ancient tectonic plate that existed during the mid-Cretaceous through early Tertiary time. The Phoenix Plate began subducting under the Antarctic Plate. The Phoenix Ridge is a mid-oceanic ridge between the Pacific and the Phoenix Plates which had a spreading rate of 18-20 cm per year until around 84 million years ago. A major decrease in spreading rate, and the convergence rate with the Antarctic Plate occurred around 52.3 million years ago. Today the Phoenix Plate is part of the Pacific Plate, as the spreading ridge, the Hero Fracgure Zone and the South Shetland subduction zone are no longer active. The only movement now is along the Shackleton fracture Zone (active boundary).
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