Mawson Breccias Intrude Beacon Strata at Allan Hills, South Victoria Land: Regional Implications

At Allan Hills, south Victoria Land, Antarctica, Mawson tuff breccias are intrusive into Permian and Triassic Beacon strata, contrary to previous reports of the relationship. North of Watters Peak, Mawson intrusive and extrusive rocks, a megaclast unit consisting principally of beds of Member C of the Triassic Lashly Formation, and

in situ

brecciated Permian and Triassic country rock, taken together, comprise an assemblage of Jurassic rocks interpreted as a magmatically-driven collapse structure. At adjacent Coombs Hills the contact at one locality is intrusive but at another the relationships are less clear. The intrusive, rather than stratigraphic, relationship between Mawson tuff breccias and Beacon strata leads to reinterpretation of the Prebble Formation field relations at Otway Massif as also intrusive. Previous interpretations, based on a major unconformity at Allan Hills, of an episode of Early Jurassic pre-Ferrar erosion that created significant topography can no longer be supported.