Geochemical composition of sedimentary rocks and imprint of hydrothermal fluid flow at the Variscan front - an example from the RWTH-1 well (Germany)

摘要

The mineralogical and chemical characteristics of Palaeozoic rocks in the northern Eifel Mountains provide information on the sedimentary provenance in the NW Rbenohercynian Basin and on the mineralogical and hydrothermal control of trace element abundance. Elements mainly bound to illite (i.e. V, Ni, Rb, Sr, Cu. Ba) can be distinguished from elements predominantly controlled by chromite (Cr) and zircon (Zr). Lower Devonian and Upper Carboniferous units have similar chemical characteristics indicating similar sources of detritus and in part resedimentation of Lower Devonian detritus during Upper Carboniferous times. Their high Chemical Index of Alteration points to intensive weathering in the source area and/or recycling during transport. The existence of an ophiolitic source of detritus situated in the NE of the Rhenohercynian Basin can be supported in this study by the abundance of Cr and Ni. A marked change of the sedimentary input is recorded in the Upper Devonian Famennian shales and Condroz Beds. Here, chemically unweathered rocks with felsic composition of the Brabant Massif dominate the source rocks. Chemical evidence for fluid flow is observed at fault zones indicated in the RWTH-1 well. Input of Cu, Ba and NH, is attributed to Variscan hydrothermal fluid flow. Fluid flow was caused by dewatering of sedimentary rocks during the Variscan compressive deformation and was focussed along larger thrust faults within the footwall of the Aachen Thrust.