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This stretch of coast was first recognised as an area of interest in the mid-1800’s by the likes of Sir Roderick Murchison and James Nicol (1810 – 1879). The presence of mafic and ultrabasic rocks and basaltic pillow lavas caused great debate. Various theories on their presence were put forward, however, it wasn’t until the 1970’s that the area was identified as an obducted ophiolite complex, emplaced during the (overall) subduction of the Iapetus Ocean crust during the Caledonian Orogeny. In other words, it was a fragment of ocean crust and underlying mantle that had become detached from the ocean floor and was stuck to the Scottish landmass as the Iapetus closed.
The Ballantrae Complex outcrops along the coast between Girvan and Ballantrae but is also exposed on higher ground inland. It represents rocks from various levels in the crust, extending to perhaps 40 – 50km in depth. The main components of the Ballantrae Complex are:
– Obducted oceanic crust and island arc remains – Late Tremadoc to early Arenig (approximately 490 – 480Ma)Pillow lavas, lava conglomerates, cherts and fossiliferous black shales, gabbros and trondhjemites (representing the magma chambers)Obducted ocean mantle – Middle Arenig (approximately 480Ma)Ultramafic rocks (mostly dunites and harzburgites), generally serpentinised
– Uncomformably overlying Ordovician (Llanvirn) and younger fossiliferous sediments.
– Basal conglomerates (volcanogenic), shallow-marine limestones and deep water greywackes and shales; this represents a fault controlled fore-arc succession to the northwest of the complex
Lawson, J.D. & Weedon, D.S. 1992. Geological Excursions around Glasgow & Girvan. Geological Society of Glasgow.
Stone, P. & Smellie, J.L. 1988. The Ballantrae Area. Description of the solid geology of parts of 1:25,000 sheets NX 08, 18, and 19. British Geological Survey (Her Majesty’s Stationery Office, London).
Stone, P (editor). 1996. Geology in south-west Scotland – An Excursion Guide. British Geological Survey.