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Original Article |
1 1Reactivation Research Group, Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK (e-mail r.e.holdsworth@durham.ac.uk)
2 2Dipartimento di Scienze della Terra, Università di Siena, Siena, Italy
3 3Universidade Federal do Pará, Centro de Geociências, C.P. 1611, 66000 Belém (PA), Brazil
4 4CognIT a.s., P.B. 610, Busterud, N-1754 Halden, Norway
The partitioning of deformation into wrench- and contraction-dominated deformation domains is a widely reported but poorly described phenomenon in ancient transpression zones. This paper documents spectacularly exposed examples of such partitioning from the Southern Uplands terrane in SE Scotland (Berwickshire), which was deformed during late Llandovery to Wenlock time. A well-exposed coastal section from Eyemouth to Burnmouth preserves a broadly homoclinal sequence in which a highly heterogeneous array of contemporaneous structures formed during regional triclinic transpression. The deformation involved components of NW–SE contraction with subvertical extension, top-to-the-SE thrusting and top-to-the-SW sinistral shear. In the northern third of the section studied these components are partitioned into a series of fault-bounded, metre- to kilometre-scale structural domains that contain geometrically and kinematically distinct assemblages of variably curvilinear folds, strike-slip detachments and locally transecting cleavages. The structures are all broadly contemporaneous and, in individual domains, record either non-coaxial contractional- or sinistral wrench-dominated strains. Similar highly heterogeneous, domainal structural patterns are likely to be found in other regions of oblique convergence in both ancient and modern settings.
Keywords: Southern Uplands, transpression, deformation, strain.
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