High-precision U–Pb monazite geochronology of the c. 806 Ma Grampian Shear Zone and the implications for the evolution of the Central Highlands of Scotland

Abstract

Two pegmatites and mylonitic rocks from the Grampian Shear Zone yield U–Pb monazite ages of 806 ± 3 Ma, 808 –9 +11 Ma, and 804 –12 +13 , respectively. These confirm that shearing and pegmatite crystallization was essentially synchronous. Lower intercepts of c. 440 Ma indicate disturbance during Ordovician reworking. These new data question the concept of a single latest Proterozoic–early Palaeozoic orogeny in the Grampian terrane and the significance of the Great Glen Fault.

A composite C-isotope profile for the Neoproterozoic Dalradian Supergroup of Scotland and Ireland

“…However, 87 Sr/ 86 Sr data for the Kincraig Formation (Thomas et al 2004), which is stratigraphically older than the Ballachulish Limestone, are consistent with an age of c. 750 -800 Ma when compared with the latest compilation of Neoproterozoic 87 Sr/ 86 Sr data (Halverson et al 2007b). Thus the age of the base of the Dalradian is still uncertain and further work is required to resolve this issue, including a circumspect consideration of the basement-cover relationships and the 800 -840 Ma age dates for the sheared gneissose rocks in the Central Highlands of Scotland (Highton et al, 1999;Noble et al 1996).…”

How the Neoproterozoic S-isotope record illuminates the genesis of vein gold systems: an example from the Dalradian Supergroup in Scotland

“…2; Thomas et al 2004;Prave et al 2009;Rooney et al 2011). The base of the Dalradian sequence is dated at a maximum age of c. 800 Ma by the presence of Knoydartian deformation in the basement rocks, combined with no evidence of pre-Caledonian mineral ages in the Dalradian Supergroup (Noble et al 1996). The Leny Limestone within the Southern Highland Group is dated at 510-515 Ma (Cowie et al 1972) based on the presence of the rare Mid-Cambrian trilobite Pagetides (Pringle 1940;Cowie et al 1972).…”

“…Gravity anomaly after Hussein & Hipkin (1981) and interpretation in Pattrick et al (1988). should be noted that correlation of the Ballachulish Limestone with the Bitter Springs anomaly would make the formations below too old if it is accepted that the base of the Dalradian is ,800 Ma. Prave et al (2009) (Noble et al 1996).…”

“…(1) The base of the Dalradian is c. 800 Ma (Noble et al 1996) and, following Prave et al (2009), the Port Askaig Tillite is correlated with the Sturtian glacial episodes and the mid-Easdale Subgroup is correlated to Marinoan glacial episodes. (2) The base of the Dalradian is c. 700 Ma based on 87 Sr/ 86 Sr variation (Thomas et al 2004;Stephenson et al 2013); this is consistent with the Re-Os date for the Ballachulish Slate (Rooney et al 2011), which in turn suggests that the Port Askaig Tillite represents the Marinoan glacial episodes.…”

87 Sr/ 86 Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales

“…This interpretation is supported by evidence from regional mapping Smith et al 1999) and the absence of 800-900 Ma monazite ages in proven Grampian Group rocks . Others have inferred that the Grampian Group and possibly parts of the Appin Group were deformed and metamorphosed along with the sub-Grampian Group rocks by Neoproterozoic tectonothermal activity in the Scottish Central Grampian Highlands dated at between c. 800 and c. 900 Ma (Noble et al 1996;Highton et al 1999).…”