Tectonic evolution and regional setting of the Cuu Long Basin, Vietnam

Abstract

Abstract The Cuu Long Basin is situated off the southeastern coast of Vietnam. This study utilizes all available seismic data in the Cuu Long Basin, Vinh Chau Basin and coastal Mekong Delta to constrain the tectonic history of the area. The linkage between the Mae Ping Fault Zone and deformation in the Cuu Long Basin is also examined in detail. Two major deformational events are observed: a transtensional rifting event from the mid Eocene to mid-Early Oligocene (40–31\u202fMa) followed by transpression from mid-Early Oligocene to mid-Late Oligocene (31–25\u202fMa). The data strongly suggest that all the very straight major tributaries of the Mekong River Delta follow northwest trending faults that link into to the southwestern end of the Cuu Long Basin fault system and that the basin opened between where the Mekong Delta faults enter and a point of zero extension at the NE termination of the basin. The Mekong Delta Fault Zone exhibited left-lateral displacement during extension in the Cuu Long Basin and right-lateral displacement during younger transpression. The orientation, age and sense of displacement of the Mekong Delta Fault Zone are consistent with slip on the Mae Ping Fault Zone in Thailand and Cambodia, and hence are considered to be part of the same regional fault system. Based on a Chainat Duplex analogue and other data, the Mekong Delta and Mae Ping fault zones appear to be linked by a NNW-striking step-over zone, referred to here as the Mekong-Ton Le Sap step-over zone. This zone follows the eastern boundary of the Paleocene to Early Eocene Kampot Fold Belt. Based on structural and stratigraphic similarities, it appears the adjacent Vinh Chau Basin shares a common tectonic history with the Cuu Long Basin, but the linkage to the Mekong Delta Fault Zone is less clear.