School Seminar - Professor Robert Loucks - University of Western Australia
Professor Robert Loucks - University of Western Australia
Coutts Lecture Theatre - Room 3.31 - Wills Memorial Building
We are pleased to welcome Professor Robert Loucks from the University of Western Australia and our visiting Benjamin Meaker Fellow who will be delivering the School Seminar:-
Title: Chemical compositions of felsic igneous rocks preserve a record of the tectonic stress regime in which they formed
The across-arc horizontal tectonic stress regime varies along intra-oceanic and continent-margin magmatic arcs, with some being tensional, as is commonly the case along substantial segments of Western Pacific arcs. Other arc segments are undergoing lithosphere-shortening orogenic deformation under strong horizontal compressive stress. A review of variations in whole-rock chemical composition along adjacent compressive and non-compressive segments of modern arcs shows that asthenosphere-derived parental basalts of essentially identical starting composition follow divergent trends of chemical differentiation to residual felsic compositions in compressive and non-compressive arc segments. Among the differences is a tendency for zircon to begin precipitating in compressive segments at an earlier (more mafic, less siliceous) stage of magmatic differentiation, and for plagioclase to saturate in compressive segments at a later, more siliceous stage of magmatic differentiation. Consequently, the whole-rock ratio Sr/Zr is usefully sensitive in discriminating magmatic-differentiation series in compressive arc segments from those in non-compressive arc segments. Time series of Sr/Zr in igneous suites spanning a substantial time range along a segment of a convergent plate margin can be useful for constraining temporal variations in its tectonic stress regime, which should be useful for time-constrained tectonic reconstructions.
All staff and students welcome. Lunch and further discussion will be held in the Earth Sciences Common Room after this event.
For further information please contact Dr. Benjamin Moon.