Abstract

Mr W. B. Harland commented on the clear description of the Trollfjord–Komagelv fault as an example of transpression in which strike-slip coupled with compression seemed to have acted together judging by the appearance in cross-sections of steeply dipping strata and minor high angle faults near the major fault. The authors confirmed that the intensity of deformation decreased away from the main fault. Transpressive tectonics should, in theory, be very common, occurring at any plate margin oblique to plate motion and yet the structures were often not so easily interpreted. Mr Harland was surprised at the relatively small amount of breccia and mylonite in so important a transcurrent fault and he suggested that the fault surface irregularities might not only be accommodated by supplementary strike-slip and splay faulting but possibly by squeezing out of material, in reverse dip-slip motion, that would then be lost to view.

The Authors Reply: The fault zone was, in fact, initially interpreted as a reverse fault system (Siedlecka & Seidlecki 1967) on the basis of the associated steep dips and small-scale reverse faults. Although there is no evidence of the amount, or even the direction of any dip-slip movement on the fault, it is entirely probable, to judge from recent strike-slip fault systems, that dip-slip did occur. This could have been related to a regional transpression or a local compression across the fault. However the lack of regional fold axes parallel to the fault zone perhaps suggests that the regional transpressive component was minor.

The small

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