DI31A-2559
Does a Superswell Exist Between Antarctica and Australia?
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Sung-Hyun Park1, Charles H Langmuir2, Sean R Scott3, Kenneth W W Sims3, Jian Lin4, Seungsep Kim5, Peter J Michael6 and Doshik Hahm7, (1)Korea Polar Research Institute, Incheon, South Korea, (2)Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA, United States, (3)University of Wyoming, Laramie, WY, United States, (4)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (5)Chungnam National University, Daejeon, South Korea, (6)University of Tulsa, Tulsa, OK, United States, (7)KOPRI Korea Polar Research Institute, Incheon, South Korea
Abstract:
The Australian-Antarctic Ridge (AAR) is located between the Australian-Antarctic Discordance (AAD) of the Southeast Indian ridge (SEIR) in the west and Pacific-Antarctic Ridge (PAR) in the east. The AAR has intermediate spreading rate (~70 mm/yr) and consists of a series of 1st order segments bounded by parallel transform faults. KR1, a southernmost segment (63°S) of the AAR, is a 300-km-long super-segment with shallow axial depth (~2000 m). KR1 is bounded by the Macquarie transform fault in the east and the Balleney transform fault in the west, which connects KR1 with KR2 at ~ 200 km north. KR2 is 180 km long with axial depth (~2300 m) deeper than KR1. Both KR1 and KR2 are shallow relative to global mid-ocean ridges. Most of the basaltic rocks from the two segments show enriched geochemical characteristics that differ from both the AAD (Southeast Indian Ridge) and the PAR. La/Sm ratios vary from N-MORB to T-MORB; however, K2O/Nb ratios of all samples are consistently low like OIB. Their Pb isotopes are mostly more radiogenic than the N-MORB samples from PAR (and EPR) and SEIR, with 206Pb/204Pb mostly >18.6. At a given 206Pb/204Pb, their 87Sr/86Sr are higher than the PAR, but lower than the SEIR. The basalts from the two segments are geochemically similar to Cenozoic volcanoes erupted on southeast Australia, Zealandia and northwest Antarctica, suggesting a genetic relationship. According to tectonic reconstruction models, these three continents were originally joined, but separated from each other after ~80 Ma. Notably, the KR1 and KR2 segments are located at the boundary of this continental separation. The ages of Cenozoic volcanoes span from ~ 60 Ma to the recent, and the volcanoes might be related to a plume head that caused the breakup of the continents. Seismic tomography studies show that there is a low velocity zone (LVZ) in the shallow mantle (> 250 km) between Antarctica and Australia where the AAR is located. The AAR would be sampling this LVZ, and this implies that plume-like material is distributed at a 3,500 km scale in the shallow depths of the mantle. Such large-scale mantle anomaly in the Southern Ocean is of similar size to proposed “super-swells” beneath Africa and the South Pacific Ocean.
