The provenance of granite boulders in conglomerates of the Northern and Central Belts of the Southern Uplands of Scotland

Abstract

Rb–Sr whole rock isochrons from several suites of granite boulders which occur in Ordovician and Silurian conglomerates in the Southern Uplands of Scotland yield ages of around 1200 Ma, 600 to 700 Ma and 470 to 490 Ma. The plutonic and tectonic history recorded by these clasts corresponds more closely with that of NW Newfoundland than with that of Scotland. The petrography of the clasts can also be matched with exposed granite plutons in Newfoundland. Since the conglomerates were derived from the NW it is concluded that the Southern Uplands lay to the SE of Newfoundland. A total of 1500 km strike-slip displacement occurred between the Caradoc and the Early Devonian, consistent with oblique subduction of the Iapetus Ocean below the North American continental margin.

Age and provenance of granitoid clasts in Moeatoa Conglomerate, Kawhia Syncline, New Zealand

“…In applying conventional Rb-Sr whole-rock dating to conglomerate cIasts, careful attention to petrography and geochemistry is necessary to ensure that all cIasts used on any isochron R7Srf6Sr for NBS987 = 0.71010 ± 0.00005 87Rbf86Sr precision = ±1 % (lcr) R7Srf6Sr precision = ±O.07% (lcr) plot are from the same source (cf Elders, 1987). Here, four groups of clasts have been isolated from those collected for study.…”

The Lamington Conglomerate: further evidence for an ophiolitic source for the Ordovician Marchburn Formation, Northern Belt, Southern Uplands

“…Estimates of the amount of displacement along the fault range from no more than a few hundred km (and possibly much less -Owen and Clarkson 1992) up to c. 1500 km (e.g. Elders 1987). Some of the basaltic lavas within the Ballantrae complex contain unaltered clinopyroxene phenocrysts, with the associated gabbroic and microgabbroic rocks displaying a similar style of alteration/metamorphism to that of the gabbro lithic clasts in the Lamington Conglomerate; namely saussuritised plagioclase and replacement of clinopyroxene by brown amphibole and later secondary actinolitic amphibole (Jelinek et al, 1984).…”

Evidence for seamount accretion to a peri-Laurentian arc during closure of Iapetus 1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2 Geological Survey of Canada Contribution 20100465.

“…These collectively constitute an accretionary complex that formed outboard of the composite Laurentian margin, prior to the closure of Iapetus and the arrival of peri-Gondwanan crust. The disparity between this large accretionary complex in the British Isles and its absence in Newfoundland combined with extensive evidence for strike-slip displacements in the Ordovician (e.g., Elders 1987;Hibbard and Waldron 2009), led van Staal et al (1998) to propose that the Newfoundland Appalachians experienced strike-slip excision, whereas the British Isles underwent strike-slip duplication. Our suggestion of subduction erosion in Newfoundland implies that an accretionary prism did not form in Newfoundland.…”