The Lithosphere

Magma-supply dynamics of the Ferrar large igneous province

Principal Investigator: James White
Organisation: University of Otago

What we do: This study uses physical features of Ferrar Dolerite dikes and sills to constrain interpretations of magma flow in Large Igneous provinces (LIPs) because the mode of magma distribution in the subsurface plumbing system of LIPs is important to know in order to better understand surface eruptions and their effects.

Why we do it: Large Igneous provinces form by the movement of large volumes of magma from the mantle to the crust and earth’s surface. Distribution of the magma takes place both in surface lava flows (so-called flood basalts) and through subsurface sheets whose solidified remnants are dikes and sills. In addition to magma-flow directions, this approach will allow assessment of injection style (single or multiple). The combined dataset will powerfully constrain interpretations of emplacement and eruption dynamics for the intrusive, extrusive and pyroclastic rocks of the Ferrar and other LIPs, and hence of their environmental effects and potential hazards in the unlikely event of near-future continental LIP eruptions.  It will also help us understand past climate changes associated with the huge eruptions that characterise large igneous provinces.

What we've found so far:  We find that many intrusions change their shape and orientation along their length, and the form of the fractures occupied by magma varies widely across small areas.  The rather chaotic pattern we see suggests that country rock forms a 'floated' lid on top of or partly within a fluid magma, with magma-filled cracks formed in response to floating of the lid, rather than to regional tectonic stresses.  If so, it implies for areas with thick sills that dike orientations mapped by remote sensing can't be used to infer regional stress regimes.  On the other hand, local patterns of dike alignment near and above sills may be useful in inferring magmatic processes, such as directions of sill propagation.

Recent Publications:
Ross, P.-S. and White J.D. 2005. Unusually large clastic dykes formed by elutriation of a poorly sorted, coarser-grained source. Journal of the Geological Society of London 162: 579-582, 2005. View Abstract.

Ross, P.-S. Volcanology of the Mawson Formation at Coombs and Allan Hills, South Victoria Land, Antarctica. Ph.D., University of Otago, 2005. View Abstract.

Reubi, O.,  Ross, P-S, White, J.D.L. 2005. Debris avalanche deposits associated with large igneous province volcanism: an example from the Mawson Formation, central Allan Hills, Antarctica. Geol Soc Am Bull 117: 1615-1628.