Simone Hood Hills
MSc topic: Magma-sediment interaction, southern Victoria Land, Antarctica
Email: hoosi925@student.otago.ac.nz
Supervisor: Assoc. Prof. James White
Abstract for Geological Society of New Zealand conference, 2002
Mawson Formation, Allan Hills, Southern Victoria Land, Antarctica.
S.B. Hood Hills, Geology Department, University of Otago, P.O. Box 56 Dunedin, hoosi925@student.otago.ac.nz
J.D.L. White, Geology Department, University of Otago, P.O. Box 56 Dunedin, james.white@stonebow.otago.ac.nz
Prior to Jurassic Ferrar Supergroup Kirkpatrick flood-basalt effusion, explosive volcanism occurred along the length of the Transantarctic Mountains. Evidence for this explosive activity, the Mawson Formation, is well exposed in the Allan Hills, southern Victoria Land.
Detailed field mapping of Mawson Formation tuff breccias revealed a small diatreme like vent structure, with steep, near vertical contacts [above photo] with the host tuff breccia also of the Mawson Formation.
Well indurated intra vent tuff breccia [lower right] dominantly comprises randomly orientated sandstone and coal clasts derived from the underlying country rock, the Beacon Supergroup, along with dolerite and rare granitoid clasts with varying amounts of fluidal juvenile clasts.Thorough mixing of fluidal juvenile material and Beacon sandstone and coal has occurred, with the vent tuff breccia matrix dominantly consisting of sand grains, which are sometimes incorporated within juvenile fragments. Incorporation of large blocks of the host Mawson tuff breccia within the vent breccia is indicated by varying amounts of fluidal juvenile material [below] and accidental lithic clasts throughout the exposed vent tuff breccia. Evidence for heating of accidental lithics is given by vitrinite reflectance data for coal incorporated within the vent breccia. The occurrence of magma-water interaction is provided by abundant peperite fragments, and peperitic dyke margins. This vent structure is thought to be one of many similar structures throughout the area that were formed within a large volcanic complex.
