Petrological and Geophysical Characterization of Exhumed Subcontinental Mantle from the Australian-Antarctic Ocean-Continent Transition Zone

Brief description

The final lithospheric breakup of the Australian-Antarctic rift system remains controversial due to sparse geological constraints on the nature of the basement along the ocean-continent transition zones. We present new interpretations of multichannel seismic reflection transects, as well as new petrological data of dredged mantle rocks along the East Antarctic margin (Seamount B, offshore Terre Adélie). By combining both datasets, we show that a 50–100 km wide domain of cold (900°C), fertile subcontinental mantle was exhumed along the non-volcanic Antarctic margin. The dredged peridotites preserve characteristics similar to mantle xenoliths found in syn- to post-rift volcanism at the eastern end of the Australian margin (Victoria and Tasmania), indicating the sampling of a common fertile subcontinental mantle during rifting between Australia and Antarctica. Seamount B represents the initial stages of exhumation of cold subcontinental lithosphere along an ocean-continent transition during rifting. This thick mantle domain was likely affected by syn-rift melt impregnation at high-pressure (8 kbar), leading to the formation of plagioclase-pyroxenites. Overall, the combination of continental rifted blocks, a 50-100 km wide domain of volcanic-poor subcontinental mantle and (ultra)-slow spreading implies that ocean-continent transition zones along the Australian-Antarctic margins represent a recent analogue to ocean continent transition zones from the Jurassic Western Tethys. Additionally, evidence of syn-rift melt stagnation at high pressure suggests that magmatism along the Australian-Antarctic rifted margins was sufficient to form magnetic anomalies that can be used as isochrons despite their formation in lithosphere other than mature, steady-state ocean crust.

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Maintenance and Update Frequency: notPlanned

Statement: This Dataset contains mineral chemistry (major and trace elements) of plagioclase, olivine, spinel, orthopyroxene, clinopyroxene and amphibole from dredged samples from Seamount B (offshore Terre Adélie, Japanese dredging expeditions TH91, TH95).

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Credit
A.M. acknowledge the support of SNSF grant P2LAP2_171819. I.S. was supported under Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (Project ID SR140300001). J.M.W. acknowledges support from Australian Research Council grant DP180102280. We are also grateful to the support from the SCAR community as well as to Dr. M. Yuasa of the Geological Survey of Japan for having carried out the initial studies on Seamount B. The seismic reflection data is freely available through the Seismic Data Library System of SCAR and geochemical analyses of minerals are accessible in the supporting information data set.