Murray McClintock
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Supervisor: Assoc. Prof. James White
See also Murray's PhD webpage. |  |
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Fieldwork at Coombs Hills. Geologist stands on Mawson Formation pyroclastic rocks intruded by Ferrar Supergroup sills (black). |
Development of a volcano-tectonic rift system during Jurassic-Early Cretaceous fragmentation of Gondwana created a setting in which voluminous basaltic magmas intercepted wet, poorly consolidated terrestrial sediments, leading to the formation of a regional hydrovolcanic field. At Coombs Hills, Victoria Land, Antarctica(click on images to see a larger view), extensive peperites, hyaloclastites and irregular intrusive masses are intermixed with tuffs and tuff-breccias of the Mawson Formation. These rocks, and correlatives 1500 km along strike in the Transantarctic Mountains, form regional pyroclastic deposits transitional between Beacon Supergroup terrestrial sedimentation and Ferrar Supergroup flood basalt volcanism. Study of the phreatomagmatic system represented by the Mawson Formation provides insights into how magmatism is initiated and evolves during continental rifting.
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Ferrar dike cutting Mawson Formation pyroclastic rocks. |
The Mawson Formation records initial sub-volcanic, non-explosive mixing of magma and sediment along with explosive phreatomagmatism within a vent complex kilometres to tens of kilometres in extent. Widespread accidental debris derived from the underlying and surrounding Beacon Supergroup suggests shallow-seated 'wet' phreatomagmatism developed as the precursor to Ferrar Supergroup flood volcanism. A declining water supply rate and an increasing magma flux as rifting accelerated led to a long-term transition from explosive phreatomagmatic eruptions, the later stages of which are marked by further subaerial tuffs and base surge deposits, to voluminous effusion of the Ferrar flood basalts. The nature and spatial relationships of vent-proximal lithofacies and syn-volcanic intrusions suggests generation of peperites and pyroclastic deposits at intrusive contacts both within and at the margins of small, unstable, short-lived vents, with crater size increasing largely by lateral quarrying of the upper vent walls. Minor pyroclastic traction and suspension sequences preserved within the Mawson suggest that widespread country rock disruption and localised hydroclastic fragmentation and peperite formation was intimately associated with periods of explosive subaerial phreatomagmatic activity. Local lake development provides a record of the interaction between extensional tectonics, magmatism and sedimentation during emplacement of the flood basalts.
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View NE across the Odell Glacier to Coombs Hills from Allan Hills, with the Convoy Range behind. The Allan Hills are reached by a four hour ski from the Coombs Hills along the margin of the Polar Plateau. |
Geologist engaged in fieldwork, Coombs Hills. Tan-coloured pyroclastic rocks of the Mawson Formation (foreground) are capped by Ferrar flood basalts. |
This Mawson Formation is part of a regional, rift-related phreatomagmatic province erupted along the Pacific margin of Gondwana immediately prior to rapid outpouring of the flood basalts. The Mawson overall is an extension of the Ferrar-Karoo phreatomagmatic province, underlying exposures of Ferrar Supergroup flood basalts up to 1500 km along strike in Victoria Land, and Karoo basalts on a similar scale in southern Africa. This phreatomagmatic province records explosive hydrovolcanism at a scale orders of magnitude larger than that of typical phreatomagmatic volcanic fields.
Published Work
- McClintock, M K & White, J D L. 2002. Granulation of weak rock as a precursor to peperite formation: coal peperite, Coombs Hills, Antarctica. Journal of Volcanolgy and Geothermal Research V 114: 205-217.