Journal of Conference Abstracts

Negative Thermal Expansion in Beta-Quartz

Patrick R. L. Welche¹ (prlw1@cam.ac.uk), Volker Heine¹ (vh200@phy.cam.ac.uk) & Martin T. Dove²

¹ Theory of Condensed Matter, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE.

² Dept. of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ.

Computer modelling and theoretical analysis are used to explain the nearly zero and slightly negative coefficients of thermal expansion in beta-quartz well above the alpha/beta phase transition temperature. Quartz was selected for study as an archetypal material with a framework structure of stiff units, namely SiO₄ tetrahedra, linked through shared oxygen atoms. The contributions of the soft mode, the Vallade mode, the TAxz phonon branch and the phonon spectrum as a whole are discussed in detail.

Measuring the Pulse of a Plume from the Sedimentary Record

Nicky White (nwhite@esc.cam.ack.uk), Bryan Lovell, Ben Clarke & Steve Jones

Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, U.K.

Surface uplift and subsequent denudation gives rise to sedimentary deposition. The resultant stratigraphic record therefore contains indirect information about rates of uplift. Such rates are of particular interest in regions where large-scale magmatic underplating of the continental crust because melt production rates associated with mantle plume activity can be determined We establish a connection between the occurrence of discrete pulses of Palaeogene submarine fan deposition and the timing of magmatic underplating on the northwest continental shelf of Europe. Magmatism was closely associated with activity of the Iceland plume, so the pulses of sedimentation are potentially a sensitive measure of plume activity. Our hypothesis is supported by independent evidence of plume temperature variation determined from satellite free-air gravity data.