Basin modelling of the Limon Back-arc Basin (Costa Rica): burial history and temperature evolution of an island arc-related basin-system

摘要

The Limon back-arc basin belongs to the southern Central American arc-trench system and is situated at the east coast of Costa Rica. The basin-fill consists of Late Cretaceous to Pleistocene sedimentary rocks. A northern and a southern sub-basin can be defined, separated by the E-W-trending Trans Isthmic Fault System. The North Limon Basin is nearly undeformed, whereas the South Limon Basin is characterized by a fold-and-thrust belt. Both sub-basins have a very similar sedimentary fill and can act as a natural laboratory for reconstructing controlling factors of arc-related sedimentary basins as well as the influence of deformation on a basin system. Modelling focused on burial history and temperature evolution. Two-dimensional simulations were carried out with the software PetroMod((R)). The geohistory curve of the North Limon Basin is overall linear, indicating continuous subsidence. The South Limon Basin is also characterized by continuous subsidence, but rates strongly increased at the beginning of the Neogene. Despite a rapid Plio-Pleistocene deformation of the fold-and-thrust belt, the present-day temperature field is not disturbed in that area. The modelling results indicate a mean heat flow of 60 mW m(-2) for the North Limon Basin and 41 mW m(-2) for the South Limon Basin. These values are low compared with other back-arc basins. The lower values are attributed to the following effects: (1) underlying basaltic crust, (2) the lack of an initial rift phase, (3) the low extension rates, (4) absence of volcanic activity and (5) insulation effects of a thick sediment pile. The reasons for the locally lower heat flow in the southern sub-basin can be found in the low-angle subduction of the Cocos Ridge. Owing to the low subduction angle, the cool fore-arc mantle-wedge below the island-arc is pushed backwards increasing the cooled area.