The Laxford Shear Zone: an end-Archaean terrane boundary?

Abstract

22The Lewisian Gneiss Complex of north-western Scotland consists of Archaean 23 gneisses, variably reworked during the Proterozoic. It can be divided into three 24 districts -a central granulite-facies district between districts of amphibolite-facies 25 gneiss to the north and south. Recent work has interpreted these districts in terms of 26 separate terranes, initiating a controversy that has implications for how Precambrian 27 rocks are understood worldwide. The northern district of the Lewisian Gneiss 28Complex (

High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

“…For the mainland Lewisian Gneiss Complex, the Rhiconich block is predominantly composed of migmatitic gneisses of amphibolite grade and of broadly granodioritic composition (Kinny and Friend, 1997;Goodenough et al, 2010). Protolith ages are in the range of 2840-2680 Ma with rare inherited ages of c. 3000 and 3550 Ma (Kinny and Friend, 1997;Friend and Kinny, 2001).…”

“…Protolith ages are in the range of 2840-2680 Ma with rare inherited ages of c. 3000 and 3550 Ma (Kinny and Friend, 1997;Friend and Kinny, 2001). The Rhiconich and Assynt blocks are separated by the Laxford Shear Zone (Evans, 1965;Corfu et al, 1994;Goodenough et al, 2010;. The central region may be further subdivided into Assynt and Gruinard blocks, separated by the Canisp Shear Zone (Coward and Park, 1987;Chattopadhyay et al, 2010;Goodenough et al, 2010).…”

“…The Rhiconich and Assynt blocks are separated by the Laxford Shear Zone (Evans, 1965;Corfu et al, 1994;Goodenough et al, 2010;. The central region may be further subdivided into Assynt and Gruinard blocks, separated by the Canisp Shear Zone (Coward and Park, 1987;Chattopadhyay et al, 2010;Goodenough et al, 2010). The Assynt block features TTG gneisses and metamorphosed mafic and ultramafic lithologies, some of which display granulite mineral assemblages formed during the Badcallian (Park, 1970).…”

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

“…More specifically, Loch Laxford is aligned to the composite Laxford Shear zone (Goodenough et al, 2010), Loch Assynt is partly aligned with the Stoer Shear Zone and the brittle Loch Assynt Fault (Krabbendam and Leslie, 2010) and Loch Inchard and Loch a' Garbh-bhaid Mor are aligned along the WNW-ESE trending Loch Inchard normal fault (Pless, 2011) (Figs. 3, 5A).…”

“…South of Loch Laxford, the original dyke geometry is well preserved and shows a clear WNW-ESE trend (Fig 5B). North of Loch Laxford, the dykes are strongly deformed and occur in irregular shapes (Goodenough et al, 2010). Scourie Dykes are normally finergrained than the surrounding gneiss, with very fine-grained chilled margins.…”