MINERALOGY AND GEOCHEMISTRY OF DEVONIAN DETRITAL ROCKS FROM THE IBERIAN RANGE (SPAIN)

Two profiles in Devonian marine deposits have been studied, consisting of pelites, subgreywackes, greywackes and quartzites. Quartz and clay minerals are major components and feldspar and calcite are minor ones . Phyllosilicates in the fine fractions are kaolinite and illite; kaol inite has a high degree of ordering; illite is predominantly of a 1Md polytype, with low Na content and poor crystallinity and has a phengit ic composition in greywackes, whereas in pelites it is muscovitic in c omposition. Both phyllosilicates may be inherited from a source area w ith intensive weathering processes, although illite may also be a diag enetic phase. These mineral characteristics indicate that the Devonian rocks did not reach the anchizone boundary in their post-depositional evolution. The chemical composition of pelites and subgreywackes reve als a high degree of chemical maturity. Chondrite-normalized REE patte rns indicate a higher degree of weathering of these Devonian sediments than of Post-Archaean Australian Shales (PAAS), possibly as a consequ ence of sedimentary recycling processes. The REE patterns of the Devon ian rocks in addition to the high Th/Sc, La/Sc and Th/Co ratios sugges t a felsic composition of the primitive source area, probably a K-rich granite.