Fault and stress patterns at different stages of development of oceanic transform zones: the South Iceland seismic zone and the Tjornes fracture zone(Iceland) as case example

Two transform zones connecting the Icelandic rift segments and the Mid-Atla ntic ridge are described and compared in terms of faulting and stress patte rns. One is a diffuse shear zone of Riedel type, The other, formed by three major lineaments, reflects an alternance of moderate and very low mechanic al couplings. Comparing these two transform zones at different stages of ev olution shows that (1) the trend of the transform motion, as expressed in m ajor structures, appears only when the zone is mature, and (2) a rather sim ple stress pattern exists at early stages of the process whereas a complex stress pattern prevails at later stages. ((C) 1999 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.)