Endeavor research into evolving paradigms around Ophiolites: The case of the oceanic igneous complexes of Costa Rica
More than one century of studies were done on the radiolarite-igneous ("ophiolitic") complexes in Costa Rica that range from Jurassic to Eocene. These studies can be grouped in four main stages of knowledge: 1) from 1904 to 1957 were recognized the cherts, and the mafic and ultramafic igne...
|Main Authors:||Alvarado Induni, Guillermo E., Denyer Chavarría, Percy, Gazel Dondi, Esteban|
Universidad de Costa Rica
More than one century of studies were done on the radiolarite-igneous ("ophiolitic") complexes in Costa Rica that range from Jurassic to Eocene. These studies can be grouped in four main stages of knowledge: 1) from 1904 to 1957 were recognized the cherts, and the mafic and ultramafic igneous complexes, the first regional maps were done, and the first time were recognized ellipsoidal basalts, now widely known as pillow lavas. 2) From 1958 to 1978, the complexes were seen under the concept of the association of ophiolites (serpentine, gabbro, diabase, basalts, and related rocks), and interpreted the radiolarites as deep-sea sediments. This stage is characterized by the seminal work of Gabriel Dengo and by the first geochemical analyses in the framework of the plate tectonics. 3) From 1979 to 1994, a huge amount of geochemical data, paleontological and K/Ar ages were published and it was the stage of more controversial papers. Their interpretation varied for the same locality (i.e. Nicoya Peninsula) from a relative simple stratigraphic model to a very complex nappe slices, and from a simple tectonic evolution (in situ and formed by a mid-oceanic ridge volcanism) to a multistage evolution (terrains, and mid-oceanic ridge, aseismic ridge, intraplate and island arc volcanism). The situation was similar in the other Costa Rican oceanic complexes. 4) From 1995 to present, the panorama and mutual agreement between the different groups was clearer. This stage is characterized by joint collaboration, the use of modern laboratory techniques as Sr, Nd, and Pb isotopes, major, trace and complete rare earth elements, 40Ar/39Ar dating, and volcanological criteria, together with detailed field mapping. The main new result of these studies was that the radiolarites (164-84 Ma) in the Nicoya Peninsula were significatively older than the basic igneous rocks (140-84 Ma), indicating a complex magmatic event intruding and erupting into the thick sedimentary sequence. For other areas, like Santa Elena Peninsula, Tortugal, Herradura and Quepos, the picture on these oceanic complexes are more or less clear. In the case of Osa-Golfito-Burica area, more studies are necessary. In general, the detailed field mapping is a powerful tool in combination with the modern techniques. The similarity in age, petrology, geochemistry and tectonic context for other oceanic complexes in Guatemala, Antilles and the northern part of South America, is more than a coincidence, they have a similar evolution. Therefore, a multidisciplinary study of the chrono- and bio-stratigraphic relations, together with modern petrology, geochemical and micropaleontology approach is necessary to provide a solid base for a robust plate tectonic reconstruction and geologic history. The aim of this paper is to summarize the historical ideas and data available of the oceanic complexes of Costa Rica, to clarify the evolution of the interpretations and evidences in the frame of the paradigms and the state of the art of knowledge at different moments.