REQUIREMENT CONDITIONS FOR PULL-APART BASINS DOMINATED BY AXIAL SEDIMENT SUPPLY AND CONTINUOUS DEPOCENTER MIGRATION

Pull-apart basins in plate convergent margins are closely related to strike-slip faults along subduction zone or continental collision. The Izumi Group in Japan (Cretaceous) is considered as deposits in an elongate basin (300 km long by 10–20 km wide) along the Median Tectonic Line, which at the time of deposition was a sinistral strike-slip fault related to oblique subduction along a forearc margin. It typically has that (1) axial sediment supply is primary and marginal supply is secondary and that (2) depocenter progressively migrates in opposite direction of sediment supply. Both characters are similar to classical examples of Ridge Basin, California and Hornelen Basin, Norway; they are considered as strike-slip fault-related basins, but are in some aspects similar to rift basins. This paper is focused on required condition for the two characters in strike-slip basins.

Modern examples of transform-related pull-apart basins, such as Dead Sea basin and Gulf of California do not show the two characters together. Because of inherence of rapid subsidence in pull-apart basins, they are generally deficient in sediments or dominated by marginal sediment supply. In addition, depocenters sometimes develop at the same time in different places, and the direction of its migration is not only unidirectional but bidirectional.

For the above two characters, it is considered that large sediment supply into the basins along the strike-slip faults and continuous generation of accommodation space during the deposition are needed. It indicates intense uplift and erosion in the source area along the primary fault. An interpretation is rotational strike-slip faults that yield both transpression and transtension along the primary fault. Another interpretation is indent-related strike-slip faults causing large uplift. The latter is represented by a collision of Indian subcontinent induced large uplift of Himalaya and generated fault-terminated strike-slip basins of Gulf Tonkin Basin and Yinggehai Basin related to Red River shear zone, southeast Asia, in which most of sediments were supplied along the shear zone.