STRAINS AT THE INTERSECTIONS OF SYNCHRONOUS CONJUGATE NORMAL FAULTS

Processes accommodating the mutual offsetting of intersecting conjugat e faults are investigated by outcrop examination of three pairs of con jugate normal faults with maximum throws from 5 min to 10 cm. In two c ases resolved fault throws decrease sharply towards the intersection z ones which, on the scale of observation, are zones of ductile thinning of inter-fault layers that accommodate the throw reductions. Strain w ithin the intersection zone of conjugate faults in fluvio-glacial sand s is accommodated by inter- rain slip. and layer thinning is complemen ted by layer-parallel extension at constant volume. In a second exampl e, strain within the intersection zone of conjugate faults in inter-la yered chalk and marl is accommodated by volume reduction, without laye r extension. In a third example, also in fluvio-glacial sands, strain in the intersection zone is accommodated by small faults (throws great er than or equal to 1 mm): when throws on all resolvable faults are ag gregated, there is no decrease in throw towards the conjugate intersec tion. The presence or absence of a decrease in resolved throw towards conjugate intersections and of a complementary ductile zone accommodat ing the change in throw. is a function not only of the resolution limi t of the observations but also of the scale of the deformation process within the conjugate zone. (C) 1998 Elsevier Science Ltd. All rights reserved.