A cross section of the convergent Pacific margin of Nicaragua

Abstract

Prestack depth migration of multichannel seismic reflection lines across the 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 the Sandino forearc basin, probably underlain by oceanic igneous basement and fronted by a small prism accreted at the seaward end of the continental basement. Seismic stratigraphy and drill hole information indicate that sediment has been accumulating since Late Cretaceous. The margin configuration formed between late Cretaceous and Paleocene time and has endured since that time. Uplift of the outer high and slope was probably coeval with subsidence of a deep basin beneath the shelf. From middle‐late Eocene time to Oligocene time, the outer high was a barrier to sediment transport. A similar Late Cretaceous to Oligocene tectonic history has been described for the Guatemalan and Costa Rican segments of the Pacific margin. We speculate that the structure of the Pacific forearc basin formed by subduction initiation at the edge of the Caribbean igneous province. Since late Oligocene time, margin‐wide subsidence occurs in the Nicaraguan margin, perhaps related to subduction erosion of the upper plate. Coeval steep reverse and normal faulting along local structures in the forearc basin might occur by transpression along margin‐parallel strike‐slip faults. These faults have been active since the early development of the basin, but the greatest rate of vertical displacement along them was in early ‐ middle Miocene time, probably related to a plate kinematic reorganization involving the collision of Central and South America.