LATERAL VARIATION IN QUARTZ C-AXES PATTERNS ALONG THE MOINE THRUST, NW SCOTLAND: IMPLICATIONS FOR THE KINEMATICS OF NON-PLANAR FAULT SYSTEMS

In map pattern, fault traces are typically curvi-linear suggesting that in three dimensions, faults have non-planar geometries. Such three-dimensional "irregularities" in the fault surface may have important implications for the overall kinematics of the system. Quartz c-axes patterns examined in a prominent salient-recess pair along the Moine thrust suggest that the local kinematics within the deformation zone of the thrust varies with respect to fault geometry.

The sample localities extend from the Stack of Glencoul (at a salient along the fault) to just north of Loch Srath nan Aisinnin (within a recess). Law (1987) demonstrated at the Stack of Glencoul how quartz c-axes patterns show a transition from an asymmetric kinked girdle to symmetric cross girdles with increased distance from the thrust surface; the transition takes place by at most 70 cm from the thrust. However, our data suggests that elsewhere along the thrust this transition may not be taking place quite so close to the thrust. The rest of the samples collected from the footwall portion of the salient are 10's to 100's of meters from the thrust surface. These samples have very weak to indistinguishable c-axes patterns. Within the recess in the fault near Loch Srath nan Aisinnin, the c-axes patterns maintain an asymmetry up to 4 m away from the thrust surface as well as maintaining distinguishable patterns as far away as 400 m from the thrust. In addition, within the recess there are abundant meter to 10's of meters-scale folds where along the salient the beds have a relatively constant dip of 26 degrees to the ESE. Thus, deformation behavior is significantly different at different locations within this salient-recess pair that represents three-dimensional irregularities in the thrust surface geometry. Such variability will have system-wide implications for the overall kinematics of thrust sheet emplacement.