Imbricated ocean-plate stratigraphy and U-Pb zircon ages from tuff beds in cherts in the Ballantrae complex, SW Scotland

Abstract

Ocean-plate stratigraphy (basalt, chert, clastics) of the Balcreuchan Group in the Ballantrae complex is repeated by layer-parallel thrusts to form duplex structures south of Bennane Head, ~5 km north of Ballantrae. Five tuff beds, all in chert, have similar U-Pb zircon ages of ca. 470 ± 10 Ma. The geometrical polarity of the duplexes and the zircon ages provide new constraints on the tectonic evolution of the accretionary wedge of the Ballantrae complex. Northwestward thrusting of the duplexes suggests that subduction was from the northwest to the southeast, and this polarity at the leading edge of the main ophiolite body is consistent with the northward younging of the volcanic arc rocks of the Ballantrae complex.

Provenance and exhumation of an exotic eclogite-bearing nappe in the Caledonides: a U–Pb and Rb–Sr study of the Jæren nappe, SW Norway

“…Records of this 'Taconian' tectonometamorphism are prominent in North America (e.g. Tucker & Robinson 1990;Karabinos et al 1998;Robinson et al 1998) and are well documented from the British Isles (Friedrich et al 1999;Kinny et al 1999;Friend et al 2000;Oliver et al 2000;Rogers et al 2001;Chew et al 2003;Flowerdew et al 2005;Chew et al 2008;Sawaki et al 2010). In Scandinavia, these processes were identified only in the Laurentian metamorphic rocks in the North Norwegian mainland (Fig.…”

Episodic arc-ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny

“…484-480 Ma from Ballantrae and the Tyrone Plutonic Group; (2) their suprasubduction-zone characteristics (Cooper et al, 2011); (3) a close association among ophiolites, islandarc volcanics, and within-plate lavas at both; and (4) the occurrence of early to late Arenig graptolitic faunas (Floian to early Darriwilian; Sadler et al, 2009) and tuffs dated at ca. 470 Ma (with large analytical errors) from Ballantrae (see Oliver et al, 2002;Sawaki et al, 2010). However, despite these similarities, the Ballantrae Ophiolite Complex may also represent a young ophiolite of the Lough Nafooey-Baie Verte arc system associated with a reentrant along the Laurentian margin that was emplaced ca.…”

A review of geological origins and relationships in the Ballantrae Complex, SW Scotland

“…The age of the within-plate components overlaps this range. The sedimentary strata interbedded with the basalt lavas contain early Arenig (Floian, 471-478 Ma: Figure 7) graptolite faunas, whilst zircons from tuff interbeds at Bennane Head have been dated (U-Pb) at 470±10 Ma (Sawaki et al 2010). The Millenderdale gabbro is also thought to have had a withinplate origin (Smellie & Stone 2001) and has been dated (K-Ar) at 487±8 Ma .…”

“…Mitchell 1978). Sawaki et al (2010) & Rushton, 1983) and so formed relatively late in the overall development of the Complex. By that time, arc-continent collision would have been incipient, and any physical barriers to a terrestrial input may have broken down.…”