The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides

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Abstract
It has long been known that the Highland Border includes an assemblage of altered serpentinites, gabbros, spilitic lavas, ferruginous and manganiferous cherts, black phyllites, quartzose clastics and amphibolites. New work confirms that many of these rocks represent a dismembered tectonically emplaced ophiolite of Caledonian age, which originated in a narrow oceanic basin within or bordering the Dalradian sedimentary pile. The ophiolitic rocks were expelled from the basin as thrust sheets transecting D1 structures. Studies in the SW Highlands suggest emplacement during D2 synchronous with SE translation of the Tay Nappe. This implies that the ophiolite originated in the N. The Highland Border rocks are seen as marginal to a long-lived northward-dipping subduction zone within the Southern Uplands. The evolution of the Ballantrae ophiolitic complex, the Midland Valley and the Dalradian sedimentary basin are considered within this framework.