DETERMINING TECTONIC TRANSPORT DIRECTIONS AND SHEAR SENSES IN THE SOUTHERN PART OF THE NORTHERN HIGHLANDS TERRAIN, SCOTLAND

The Moine metasedimentary rocks in northern Scotland have played an important role in characterizing tectonic transport directions associated with thrust faulting in the Northern Highland Terrane (NHT) during Caledonian orogenesis (450-435 Ma). Microstructural, quartz crystal fabric, and isotopic analyses of samples in the northern part of the NHT show that local tectonic transport changed from top to the north at 450-440 Ma in the core of the orogen to top to the west at 435 Ma along the western foreland margin (Law et al. 2021). To extend these studies to cover the southern part of the NHT we are conducting similar kinematic analyses along four E-W oriented transects crossing the Sgurr Beag thrust (SBT), a major NE-SW striking fault within the high temperature (amphibolite facies) core of the southern NHT. From north to south these transects include: Loch Monar, Glen Shiel, Kinloch Hourn and Lochailort.

Preliminary analyses on the Loch Monar transect indicate a top up to the NE shear sense in present day coordinates. Preliminary analyses from the three transects located further to the south indicate a top down to the SSE shear sense in present day coordinates. All four transects are located in the NE-SW trending Caledonian age Steep Belt within which the SBT is locally folded. Dynamically recrystallized quartz grain sizes are being measured along these transects to determine if shearing is locally focused on the SBT itself or if shearing is more homogeneously distributed and may post-date motion on the SBT.

In the southern part of the NHT we are also conducting kinematic analyses on samples collected from the structurally relatively simple Flat Belt located between the Steep Belt to the NE and the Great Glen fault to the SW. In this structural domain, our preliminary microstructural and quartz crystal fabric analyses of amphibolite facies Moine metasedimentary rocks indicate a top up to the NNW sense of shearing and tectonic transport. At least in map view this domain of top to the NNW tectonic transport appears to extend northward into the 450-440 Ma northward-directed transport domain previously recognized in the northern NHT.