The TICOSECT program aims to investigate the crustal structure of the active continental margin of Costa Rica and to understand the geodynamic processes within the subduction system. With the help of a comprehensive wide-angle seismic data set, composed of an onshore/offshore experiment as well as refraction measurements on land in northern Costa Rica, the lithospheric structure from the Middle America Trench (MAT) to the Caribbean lowland have been modelled. The cross-section includes also the ophiolitic Nicoya complex and the volcanic arc. The modelling yields an angle of about 6 degrees off-shore for the subduction of the Cocos plate beneath the Caribbean plate. Below the Nicoya peninsula the subduction angle steepens to ca. 20 degrees and the subducting Cocos plate can be identified down to 50 km depth. The velocity distribution at the margin wedge indicates that there is no sedimentary accretion. Rather, the velocities suggest that the wedge is built up from material of the Nicoya complex which forms the landmass of the Nicoya peninsula. In the eastern part of the Nicoya peninsula lateral velocity gradients within the upper and upper-lower crust indicate a transition between two different crustal blocks, which have been juxtaposed together, thus forming a border of the ophiolitic Nicoya body. In the area of the volcanic arc a low velocity body, possibly containing some percentage of magma, can be observed at about 10 km depth. At depths greater than 10 km in the Caribbean plate the velocities between 6.6 km/s and 7.4 km/s possibly represent a crust formed mainly by mafic intrusive material. Evidence for Caribbean plate mantle material is found at depths of about 40 km.
Methods & Equipment