C. Basile et Jp. Brun, Transtensional faulting patterns ranging from pull-apart basins to transform continental margins: an experimental investigation, J STRUC GEO, 21(1), 1999, pp. 23-37
Seventeen small-scale experiments were performed to study the deformation i
nduced in brittle-ductile models by a releasing stepover between two transf
orm faults, and by intersection between transform and divergent plate bound
aries. In both cases, faulting depends on the rheological layering (presenc
e and strength of a ductile layer at depth) and the width of the basal step
over. Successive types of pull-apart basins are observed in the first set o
f experiments, which are compared with natural examples. Firstly, a lazy Z-
shaped basin appears, which is bounded by Y faults above transform boundari
es and R faults propagating from each corner of the stepover. Then, R' Faul
ts replace R faults, leading to a rhomb-shaped graben. At every stage, the
basin length-to-width ratio remains between 2.2 and 3.8, suggesting that sc
ale independence of pull-apart basins is related to the geometrical shape o
f bounding faults. In a second set of experiments, deformation at the end o
f a transform boundary is characterized by a horsetail splay bounding a div
ergent basin. Within the horsetail splay, block tilting and block rotation
about vertical axes lead to a surface slope perpendicular to the slope of t
he divergent basin, a feature that can be compared with marginal ridges at
transform margins. (C) 1998 Elsevier Science Ltd. All rights reserved.