COMPOSITIONAL VARIATION OF DETRITAL GARNETS IN QUATERNARY RHINE, MEUSE AND BALTIC RIVER SEDIMENTS IN THE NETHERLANDS

Electron microprobe analysis of detrital garnets from Quaternary Rhine , Meuse and Baltic River sediments in the Netherlands area is used to trace back the provenance and relative contributions from different so urce lithologies in each drainage basin. In the Late Pliocene, high-gr ade metamorphic almandine- and pyrope-rich garnets from the Vosges and Black Forest dominate the Rhine garnet suite. With the onset of the P leistocene, the Alpine Foreland Molasse is connected to the Rhine drai nage area, supplying grossular- and probably also spessartine-rich gar nets. The connection of the Aare and other Alpine tributaries to the R hine in the Middle Pleistocene (Menapian-Bavelian) finally introduces large amounts of almandine-rich garnets derived from high-grade region ally metamorphosed inner Alpine source lithologies. The garnet suite o f the Meuse sediments almost entirely consists of spessartines and Mn- rich almandines. They are derived from Mn-rich tow-grade metamorphic p elites of the Libramont anticlinal region and the Stavelot Massif in t he Ardennes. A small association of Mn-poor almandines is ascribed to a Vosges supply from before the capture of the Upper Meuse by the Mose lle. The Baltic River garnet assemblages are characterized by a wide c ompositional spectrum, indicative of a large differentiated source are a. The almandine- and pyrope-rich garnets are most likely derived from the extensive Fennoscandian Shield, while the spessartine-rich specim ens are thought to originate from the mid-German Variscan massifs.