ANALYSIS OF A COMPLEX HIGH-STRAIN ZONE AT CAP DE CREUS, SPAIN

The structural analysis of a high-strain zone developed in medium- to high-grade metamorphic micaschists from the Cap de Creus area, Spain p rovides an example of the complex relationships between geometry, stra in and kinematics to be found in deep crustal shear zones. This high-s train zone is composed of E-W trending structural domains characterize d by different strain intensities and associated with syntectonic empl acement of pegmatite dykes. The main phase of deformation discussed he re, D-2, affects steeply dipping bedding, boudinaged quartz veins and S-1 developed parallel to bedding. D-2 deformation of these features a nd of syn-D-2 pegmatite dykes gives rise to fold/boudin structures. In map view, a D-2 high-strain zone coincides with a km-scale dextral fl exure of S-0, S-1 and S-2, although all small-scale structures on outc rop surfaces close to horizontal indicate a prevalent sinistral shear sense. In addition, a subvertical stretching lineation is present appr oximately parallel to the axis of the foliation-deflection and thus no rmal to the apparent 'displacement' direction in the high-strain zone. It is proposed that this high-strain zone did not form by horizontal dextral simple shear with a flow plane parallel to the boundaries of h igh- and low-strain zones but acted as a zone of highly vortical sinis tral non-coaxial flow with a strong vertical extension component. The dextral flexure of S-0, S-1 and S-2 can be explained by considering th at sinistral non-coaxial flow in the low-strain zones was either slowe r or earlier that in the high-strain core. This example stresses the n ecessity of being careful when interpreting displacement directions fr om the deflection of older fabric elements in deep-seated high-strain zones.