Upper Allochthon
Structurally overlying the eclogites of the Western Gneiss Region is a tract of
metamorphic rocks and Devonian sediments.
The metamorphics ("Upper Allochthon")are chiefly metavolcanics
etc. which experienced peak conditions of no more than greenschist facies. They
contain mineral assemblages that imply peak pressures of 4.1±1.8 kbar.
Faulted (and locally unconformable upon) the metavolcanics
are thick sequences of siliciclastic sediments of early to mid Devonian (405-385
Ma) age. At the locality here these sediments fill the Hornelen Basin.
Although there is a measured stratigraphic thickness in excess of 20 km for these
sediments, they occur as off-lapping packages, characteristic of growth
strata accumulating in rifts. Hence the full stratigraphic thickness is never
developed at a single site. Individual sedimentary packages show growth into the
fault contact. This in turn clearly places younger, shallower-level rocks against
older, deeper level ones. So the fault is a normal fault as is the
tectonic contact between the metavolcanics and the eclogites.
Use the section to zoom into the specific geology.
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