Abstract
Neoproterozoic siliciclastic-dominated sequences are widespread along the eastern margin of Laurentia and are related to rifting associated with the breakout of Laurentia from the supercontinent Rodinia. Detrital zircons from the Moine Supergroup, NW Scotland, yield Archean to early Neoproterozoic U-Pb ages, consistent with derivation from the Grenville-Sveconorwegian orogen and environs and accumulation post–1000 Ma. U-Pb zircon ages for felsic and associated mafic intrusions confirm a widespread pulse of extension-related magmatism at around 870 Ma. Pegmatites yielding U-Pb zircon ages between 830 Ma and 745 Ma constrain a series of deformation and metamorphic pulses related to Knoydartian orogenesis of the host Moine rocks. Additional U-Pb zircon and monazite data, and 40Ar/39Ar ages for pegmatites and host gneisses indicate high-grade metamorphic events at ca. 458–446 Ma and ca. 426 Ma during the Caledonian orogenic cycle.
Highlights
The assembly and breakup of Neoproterozoic supercontinents Rodinia and Pannotia led to the development of a series of evolving sedimentary sources and sinks for sediment accumulation (Cawood et al, 2007a, 2007b)
The North Atlantic realm occupied an external location on the margin of Laurentia, and this region acted as a locus for accumulation of detritus (Moine Supergroup and equivalents) derived from the Grenville-Sveconorwegian orogenic welt, which developed as a consequence of collisional assembly of Rodinia
In contrast in eastern North America, which lay within the internal parts of Rodinia, sedimentation did not commence until the mid-Neoproterozoic during initial stages of supercontinent fragmentation
Summary
The assembly and breakup of Neoproterozoic supercontinents Rodinia and Pannotia led to the development of a series of evolving sedimentary sources and sinks for sediment accumulation (Cawood et al, 2007a, 2007b). The rift and passive-margin successions are well preserved within, and their development heralds the initiation of, the Appalachian-Caledonian orogeny, which extends along the east coast of North America, through Ireland, Britain, East Greenland, and Scandinavia (Fig. 1A; Dalziel, 1997; Dewey, 1969; van Staal et al, 1998; Williams, 1984) The character of these successions, in terms of both original depositional lithology and age range, and subsequent orogenic deformational and metamorphic history, varies along and across the orogen and likely reflects variations in nature of basement lithologies, the nature and timing of the continental breakup record, and the timing and drivers of the orogenic record. Our aim is to present new data on provenance and timing of orogenic activity for the Moine Supergroup in Scotland, so as to constrain the development of the northeast Laurentian margin in the Neoproterozoic and to relate along-strike
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