Publication Date:
2010-06-21
Description:
The Rosemarkie Inlier is a small fault-bounded lens of interleaved Moine psammites and possible Lewisianoid orthogneisses with distinctive leucogranite veins and pods that lies adjacent to the Great Glen Fault (GGF). The basement rocks and most of the leucogranites are strongly deformed and tightly folded with foliations generally steeply dipping and a locally well-developed NE-plunging rodding lineation. Mid-Devonian sandstone and conglomerate unconformably overlie the inlier on its western side. Monazite from a deformed leucogranite vein gave a mean ID-TIMS 207Pb/235U age of 397.6{+/-}2.2 Ma and acicular zircons gave a compatible concordant ID-TIMS U-Pb age of 400.8{+/-}2.6 Ma, dating emplacement as mid-Devonian. Xenocrystic zircons from the leucogranites and complex zoned zircons from two adjacent tonalitic gneisses gave LA-MC-ICP-MS concordant ages between 2720 and 2930 Ma confirming their Archaean Lewisianoid origin. Leucogranite emplacement is interpreted to mark the onset of Acadian transpression and sinistral strike-slip movement on the GGF that resulted in multi-phase deformation and oblique exhumation of the Rosemarkie Inlier. The sequence and structure of the Early-Devonian Meall Fuar-mhonaidh Outlier, 32 km farther SW along the GGF, are also linked to this tectonic event, which was apparently localized along the main terrane-bounding faults in Scotland.
