RT Journal Article
SR Electronic
T1 Late Proterozoic rifting in NW Scotland: the genesis of the ‘Torridonian’
JF Journal of the Geological Society
JO Journal of the Geological Society
FD Geological Society of London
SP 413
OP 420
DO 10.1144/gsjgs.139.4.0413
VO 139
IS 4
A1 Stewart, A. D.
YR 1982
UL http://jgs.lyellcollection.org/content/139/4/413.abstract
AB The two major “Torridonian” successions, viz. the Stoer Group (~968 Ma) and the Sleat–Torridon Groups (~777 Ma) occupy NNE-trending rifts cutting Archaean and early Proterozoic crust. Palaeocurrents, pebble petrography and age, and the initial 87Sr/86Sr ratios of clay-rich sediments indicate derivation from flanking areas of this old crust, rather than from late Proterozoic Grenville or Morarian metamorphic rocks. The earlier rift seems to be roughly contemporaneous with Grenville metamorphism but genetically unrelated to it. The rifts perhaps mark initiation of an Iapetus-related ocean in the same way as very similar fault-bounded Triassic and Lower Jurassic sediments mark the start of continental break-up and initiation of the present Atlantic. The western margin of both rifts probably coincides with the Outer Hebrides Thrust and the eastern margin with the Moine Thrust Zone. Reactivation of the old rift-margining faults by Caledonian compression may have generated the lower thrusts of the Moine Thrust Zone, while the Moine nappe itself, by analogy with Lower Devonian events in southern Appalachia, represents a slice of the Grenville microcontinent emplaced after closure of the intervening ocean.