Abstract
ORDOVICIAN and Silurian marine clastic sequences containing boulder bearing conglomerates overlie the Ballantrae ophio-lite complex in South-west Ayrshire, Scotland. These conglomerates are thought to have been emplaced by submarine slides1 or less viscous marine currents2. The Ordovician conglomerates accumulated at the toes of contemporary submarine faults downthrowing to the south3 and in both their stratigraphy and palaeocurrents there is substantial evidence for a northerly source. The conglomerates contain clasts of the underlying ophiolite, metamorphic rocks, acid and intermediate volcanic and hypabyssal rocks and clasts of undeformed pink granite some of which are >80 cm in largest dimension. Dewey4 and many subsequent workers5 envisage these sediments as having accumulated on the southern margin of a continent under which oceanic plate was being consumed in a northerly dipping subduction zone. The time span of this subduction is subject to much speculation6 but is generally thought to have ceased by Devonian time. We report here our investigations of the clasts in the southern Ayrshire conglomerates to elucidate (1) the nature and extent of plutonic activity in the area to the north of the subduction zone, and (2) the nature of the crust into which the plutons were emplaced.
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LONGMAN, C., BLUCK, B. & VAN BREEMEN, O. Ordovician conglomerates and the evolution of the Midland Valley. Nature 280, 578–581 (1979). https://doi.org/10.1038/280578a0
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DOI: https://doi.org/10.1038/280578a0
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