A cross section of the convergent Pacific margin of Nicaragua

Prestack depth migration of multichannel seismic reflection lines across th e Pacific margin of Nicaragua has yielded an accurate depth image to about a 9-km depth from the deep ocean basin to the coast. The margin contains th e Sandino forearc basin, probably underlain by oceanic igneous basement and fronted by a small prism accreted at the seaward end of the continental ba sement. Seismic stratigraphy and drill hole information indicate that sedim ent has been accumulating since Late Cretaceous. The margin configuration f ormed between late Cretaceous and Paleocene time and has endured since that time. Uplift of the outer high and slope was probably coeval with subsiden ce of a deep basin beneath the shelf. From middle-late Eocene time to Oligo cene time, the outer high was a barrier to sediment transport. A similar La te Cretaceous to Oligocene tectonic history has been described for the Guat emalan and Costa Rican segments of the Pacific margin. We speculate that th e structure of the Pacific forearc basin formed by subduction initiation at the edge of the Caribbean igneous province. Since late Oligocene time, mar gin-wide subsidence occurs in the Nicaraguan margin, perhaps related to sub duction erosion of the upper plate. Coeval steep reverse and normal faultin g along local structures in the forearc basin might occur by transpression along margin-parallel strike-slip faults. These faults have been active sin ce the early development of the basin, but the greatest rate of vertical di splacement along them was in early - middle Miocene time, probably related to a plate kinematic reorganization involving the collision of Central and South America.