Endeavor research into evolving paradigms around Ophiolites: The case of the oceanic igneous complexes of Costa Rica

Abstract

aBtract: 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, 40 Ar/ 39 Ar 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 Looking into the geotectonic panorama of the Caribbean and its geological significance, the Nicoya Complex sensus latus has occupied a special place in Caribbean geology since its original description by Dengo (1962a). In the 1970's and early 1980's the Nicoya Complex was the focus of extensive research; corresponding with a historical moment in which the ophiolites studies took relevance into the geosciences carpet (e.g. Coleman, 1977). These first studies constituted an effort to understand a very complex picture but with traditional tools, leading to misinterpretation and confusion. Today, the endeavor of more than four decades of research have produced a pile of work, which were done using di...

Síntesis geocronológica del magmatismo, metamorfismo y metalogenia de Costa Rica, América Central

“…En Costa Rica afloran rocas ígneas básicas y ultrabásicas con diferentes grados de metamorfismo, que a lo largo de más de 50 años de estudios se han ido paulatinamente agrupado en diferentes unidades con base en su geoquímica elemental e isotópica, geocronología y correlaciones con las rocas suprayacentes, a las que intruyen o que las envuelven a modo de matriz (sedimentaria, tectónica o ígnea). De norte a sur las expondremos brevemente, pero aquel lector que desee profundizar, se le recomienda los trabajos recientes y sinópticos de Hauff et al (2000), Baumgartner et al (2008), Alvarado et al (2009a), Denyer & Gazel (2009) y Tournon & Bellon (2009), así como la extensa literatura allí citada. Todo este ensamblaje de rocas ígneas (básicas y ultrabásicas) y sedimentarias asociadas, representantes de una litosfera oceánica anexada al continente, generalmente producto de una dorsal medio-oceánica, pero que puede ser de cualquier ambiente geotectónico -en la mayoría de los casos incompleta y desmembrada por tectonismo-, posteriormente emplazada y expuesta por tectonismo, es lo que se agrupa dentro de las ofiolitas (Figs.…”

The Caribbean Lowland Evergreen Moist and Wet Forests

“…These differences have accumulated (but fluctuated) for the past many millions of years, as the wide abyssal Central American Seaway (CAS) between the oceans underwent a series of shoaling events throughout the Miocene and into the Pliocene. The primary engine for these changes has been tectonic activity for more than the past 70 my in one of the world's most complex intersections of oceanic and continental plates (Alvarado et al 2009, Van Avendonk et al 2011, Buchs et al 2010, Hoernle et al 2002, Hoernle et al 2008, Sadofsky et al 2009, Wegner et al 2011, Werner et al 1999.…”

“…The parent material for most of the Caribbean lowland soils is derived from the episodic volcanic lava flows from the mountains of the Central Cordillera, in addition to contributions made by volcanic mud flows (lahars) and volcanic ash (Sollins et al 1994;Alvarado and Mata, chapter 4 of this volume). Even the sands of the Caribbean beaches are composed of volcanic material due to a process whereby:…”

Peperitas en Costa Rica

“…La anterior interpretación no fue tomada en consideración o como relevante por los subsiguientes investigadores, quienes optaron por una gran diversidad de modelos, prevaleciendo estos sobre las evidencias de campo, en gran parte bajo la conceptualización válida, pero no única, de que las radiolaritas se deben de depositar sobre un basamento ígneo básico. Aunque lo anterior es cierto, impidió que se visualizaran las evidencias de campo que indicaban que las radiolaritas, en su mayor parte, estaban claramente intruidas por cuerpos diabásicos y nunca en contacto sedimentario con los depósitos de coladas de lava (ver discusión histórica en Alvarado et al, 2009a). No fue sino hasta que las dataciones radiométricas argónargón aportaron las evidencias de que los eventos magmáticos eran en gran parte más jóvenes que las radiolaritas (Sinton et al, 1997;Hauff et al, 2000), por lo que Hauff et al (2000) propone a modo más regional que los contactos, tanto tectónicos como magmáticos, prevalecían con respecto a los contactos sedimentarios, aspectos previamente observado por otros autores (Gursky & Gursky, 1989), pero no conceptualizado de modo regional, ni interpretado como peperitas o como intrusiones contemporáneas (i.e., Schwarzer & Gursky, 2007).…”

“…No fue sino hasta que las dataciones radiométricas argónargón aportaron las evidencias de que los eventos magmáticos eran en gran parte más jóvenes que las radiolaritas (Sinton et al, 1997;Hauff et al, 2000), por lo que Hauff et al (2000) propone a modo más regional que los contactos, tanto tectónicos como magmáticos, prevalecían con respecto a los contactos sedimentarios, aspectos previamente observado por otros autores (Gursky & Gursky, 1989), pero no conceptualizado de modo regional, ni interpretado como peperitas o como intrusiones contemporáneas (i.e., Schwarzer & Gursky, 2007). Todo lo anterior, más nuevos trabajos de campo, permitieron readecuar los modelos (ver Alvarado et al, 2009a).…”