Geochemistry of metabauxites in the Bergstrasser Odenwald (Mid Germam Crystalline Rise) and palaeoenvironmental implications

Pre- to early Variscan metamorphosed volcano-sedimentary series of the west ern (Bergstrasser) Odenwald have been intruded by Variscan calc-alkaline ma gmatites with plate margin affinities. Within the NE-SW trending metabasic and metapelitic series, intercalations of anomalously aluminous- and iron-r ich compositions representing former bauxites are distinguishable. Geochemi cal data indicate that the Al-, Fe-rich rocks are the metamorphic equivalen ts of a former bauxitic-ferralitic weathering profile, now comprising spine l fels (top) with relies of pisolitic structures, corundum-chlorite fels, c orundum-cordierite-plagioclase gneiss, sillimanite-cordierite-plagioclase g neiss, cordierite-plagioclase gneiss and kinzigite (base) displaying a decr ease of weathering in the order as listed. The evolution of such terrestria l sediments is related to specific climatic, environmental, and physico-che mical conditions similar to those of the present-day tropical to subtropica l humid regions with high seasonal rains and intensive drainage. Comparison with palaeomagnetic and palaeoclimatic data indicate that the Odenwald met abauxites originally formed during the Lower to Mid-Devonian. Our results i mply that, during this geological time span, parts of the precursors of the Mid-German Crystalline Rise not only transversed low latitudes but also we re exposed to terrestrial weathering.