Trace element studies of the origin of igneous rocks

Abstract

TRACE ELEMENT STUDIES are increasingly important in igneous petrogenetic investigations in as much as they place constraints on possible modes of origin of igneous rocks and also give evidence of the nature and composition of the mantle/crust systems within which magmas are generated and modified. The conference saw trace element studies applied to a wide range of igneous rock compositions, occurring within a wide range of environments. Four papers were concerned with areas in which basalt lavas predominate, i.e. Mull (Beckinsale et al.), the islands associated with the axial trough of the Red Sea (Henderson & Parry), the East Scotia Sea (Saunders & Tarney) where basalts are generated within an intra-oceanic marginal basin and the South Shetland Islands and Antarctic Peninsula (Weaver et al.) where different periods of magma genesis have been related to subduction and extension. Other papers dealt with metabasalts from ophiolite complexes (Pearce), K-rich volcanics (Parker), diorites and granodiorites (Brown et al), granites and charnockites (Petersen) and the ultramafic to granitic rocks of the Fongen-Hyllingen Gabbro Complex (Esbensen). An important recent development in geochemistry has been to extend the range of material which can be usefully analysed. For example, important petrogenetic information is now being obtained from altered and metamorphosed igneous rocks using ratios based on trace elements such as Ti, Zr, Y, Nb, P, Ce, Sm, Yb, abundances of which appear to be unchanged by secondary processes (Pearce). Volcanic rock geochemistry, which until recently was virtually synonymous with lava geochemistry, has now expanded its scope to