Structural trend line pattern and strain partitioning around the Gibraltar Arc accretionary wedge:: Insights as to the mode of orogenic arc building

[ 1] Mediterranean tectonics results in tight orogenic arcs enclosing back-arc basins of oceanic or thinned continental lithosphere. The Gibraltar Arc cannot be explained solely by the Europe- Africa plate convergence; therefore complementary mechanisms have been proposed. Most of them imply a westward motion of the arc and a general transpressive regime on both branches ( Betic and Rif chains). A structural revision made along the western Gibraltar Arc allows us to generate a detailed kynematic map and to introduce new constraints on the possible arc formation mechanisms. Our results suggest that the strain partitioned into two main types of structures: structures accommodating suborthogonal shortening ( folds and thrusts) and structures accommodating arc-parallel stretching ( normal faults, conjugate strike- slip faults, and distributed minor structures). On the basis of the fan pattern depicted by the slip direction of contractional structures and the homogeneous distribution of arc-parallel stretching, an arc formation mode close to the piedmont glacier type is suggested.