|
Reconstruction of Sub-Ice Volcanoes and Ice Sheet Thicknesses from Geomorphological and Lithofacies Analysis and Volatile Compositions |
University of Colorado at Denver, CB 172, P.O. Box 173364, Denver, Colorado 80217-3364, USA
The Marie Byrd Land volcanic province is a late Cenozoic alkaline basalt-trachyte volcanic field on the Pacific coast of West Antarctica. Most of these volcanoes are partially buried beneath the West Antarctic ice sheet, but in some, a combination of tectonic uplift and lowering of ice level has exposed basal hydrovolcanic sections produced by eruptions in an englacial environment. Some of the largest and best preserved hydrovolcanic structures are delta-like in form, with gentle distal slopes, and foreset bedded deposits composed of hyaloclastites, pillow breccias, pillow lavas, subaerial flows and air fall tephras. Three broad categories of processes related to delta evolution are described here; (1) flow of lava from a subaerial to an englacial environment; (2) intrusion of dykes and sills; and (3) edifice settling, which includes a variety of down-slope movement phenomena. This paper focuses on documenting post-depositional structures that are superbly exposed in these deltas. It describes the apparently province-wide lack of pillow lava cores in Marie Byrd Land englacial volcanoes, and factors that may be related to this anomaly, and it describes characteristics of hyaloclastites that are relevant to future glaciological, sedimentological and geophysical studies of the West Antarctic ice sheet.
