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The asthenosphere plays a fundamental role in present-day plate tectonics as its low viscosity controls how convection in the mantle below it is expressed at the Earth’s surface above. The origin of the asthenosphere, including the role of partial melting in reducing its viscosity and facilitating deformation, remains unclear. Here we analysed receiver-function data from globally distributed seismic stations to image the lower reaches of the asthenospheric low-seismic-velocity zone. We present globally widespread evidence for a positive seismic-velocity gradient at depths of ~150 km, which represents the base of a particularly low-velocity zone within the asthenosphere. This boundary is most commonly detected in regions with elevated upper-mantle temperatures and is best modelled as the base of a partially molten layer. The presence of the boundary showed no correlation with radial seismic anisotropy, which represents accumulated mantle strain, indicating that the inferred partial melt has no substantial effect on the large-scale viscosity of the asthenosphere. These results imply the presence of a globally extensive, partially molten zone embedded within the asthenosphere, but that low asthenospheric viscosity is controlled primarily by gradual pressure and temperature variations with depth.

Intraplate magmatic provinces found away from plate boundaries provide direct sampling of the composition and heterogeneity of the Earth’s mantle. The chemical heterogeneities that have been observed in the mantle are usually attributed to recycling during subduction1–3, which allows for the addition of volatiles and incompatible elements into the mantle. Although many intraplate volcanoes sample deep-mantle reservoirs—possibly at the core–mantle boundary4—not all intraplate volcanoes are deep-rooted5, and reservoirs in other, shallower boundary layers are likely to participate in magma generation. Here we present evidence that suggests Bermuda sampled a previously unknown mantle domain, characterized by silica-undersaturated melts that are substantially enriched in incompatible elements and volatiles, and a unique, extreme isotopic signature. To our knowledge, Bermuda records the most radiogenic 206Pb/204Pb isotopes that have been documented in an ocean basin (with 206Pb/204Pb ratios of 19.9–21.7) using high-precision methods. Together with low 207Pb/204Pb ratios (15.5–15.6) and relatively invariant Sr, Nd, and Hf isotopes, the data suggest that this source must be less than 650 million years old. We therefore interpret the Bermuda source as a previously unknown, transient mantle reservoir that resulted from the recycling and storage of incompatible elements and volatiles6–8in the transition zone (between the upper and lower mantle), aided by the fractionation of lead in a mineral that is stable only in this boundary layer, such as K-hollandite9,10. We suggest that recent recycling into the transition zone, related to subduction events during the formation of Pangea, is the reason why this reservoir has only been found in the Atlantic Ocean. Our geodynamic models suggest that this boundary layer was sampled by disturbances related to mantle flow. Seismic studies and diamond inclusions6,7have shown that recycled materials can be stored in the transition zone11. For the first time, to our knowledge, we show geochemical evidence that this storage is key to the generation of extreme isotopic domains that were previously thought to be related only to deep recycling. The formation of Bermuda sampled a previously unknown mantle reservoir that is characterized by silica-undersaturated melts enriched in volatiles and by a unique lead isotopic signature, which suggests that the source is young.

The recent discovery of some ancient evolved rocks in Gale crater by the Curiosity rover has prompted the hypothesis that continental crust formed in early Martian history. Here we present petrological modeling that attempts to explain this lithological diversity by magma fractionation. Using the thermodynamical software MELTS, we model fractional crystallization of different Martian starting compositions that might generate felsic igneous compositions like those analyzed at Gale crater using different variables, such as pressure, oxygen fugacities, and water content. We show that similar chemical and mineralogical compositions observed in Gale crater felsic rocks can readily be obtained through different degrees of fractional crystallization of basaltic compositions measured on the Martian surface. The results suggest that Gale crater rocks may not represent true liquids as they possibly accumulated and/or fractionated feldspars as well as other phases. In terms of major element compositions and mineralogy, we found that the Gale crater felsic compositions are more similar to fractionated magmas produced in Earth's intraplate volcanoes than to terrestrial felsic continental crust as represented by tonalite‐trondhjemite‐granodiorite suites. We conclude that the felsic rocks in Gale crater do not represent continental crust, as it is defined on Earth. Recent in situ data changed our understanding of the crustal composition of MarsAlkaline and felsic rocks can also be reproduced through different degrees of fractional crystallizationContinental crust, as defined by large amounts of quartz‐bearing felsic rocks, is unique to Earth

Large igneous provinces and some hotspot volcanoes are thought to form above thermochemical anomalies known as mantle plumes. Petrologic investigations that support this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500 °C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350 °C). Earth’s mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700 °C). Here we use geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400 °C hotter than the modern ambient mantle. These results are also supported by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 ± 20 °C. As mantle plumes are chemically and thermally heterogeneous, we interpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Our results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.

Volcanism is one of the main mechanisms transferring mass and energy between the interior of the Earth and the Earth's surface. However, the global mass flux of lava, volcanic ash and explosive pyroclastic deposits is not well constrained. Here we review published estimates of the mass of the erupted products from 1980 to 2019 by a global compilation. We identified 1,064 magmatic eruptions that occurred between 1980 and 2019 from the Smithsonian Global Volcanism Program database. For each eruption, we reported both the total erupted mass and its partitioning into the different volcanic products. Using this data set, we quantified the temporal and spatial evolution of subaerial volcanism and its products from 1980 to 2019 at a global and regional scale. The mass of magma erupted in each analyzed decade ranged from 1.1–4.9 × 1013kg. Lava is the main subaerial erupted product representing ∼57% of the total erupted mass of magma. The products related to the biggest eruptions (Magnitude ≥6), with long recurrence times, can temporarily make explosive products more abundant than lava (e.g., decade 1990–1999). Twenty‐three volcanoes produced ∼72% of the total mass, while two different sets of 15 volcanoes erupted >70% of the total mass of either effusive or explosive products. At a global scale, the 10 and 40‐year average eruptive rates calculated from 1980 to 2019 have the same magnitude as the long‐term average eruptive rates (from thousand to millions of years), because in both cases rates are scaled for times comparable to the recurrence time of the biggest eruptions occurred. The impact of volcanism on the Earth system depends on how the magma is erupted at the surface. Lava effects are very strong locally, while ash emissions can impact larger areas. However, the total mass of magma erupted, as well as the mass of each volcanic product (effusive: lava; explosive: ash and pyroclastic flows) remain poorly constrained. Here we investigated the temporal and spatial evolution of global subaerial volcanism by quantifying the mass of each solid volcanic product erupted above the sea level from 1980 to 2019. Results show that at a global scale the subaerial volcanism produced 1.1–4.9 × 1013kg of magma per decade from 1980 to 2019. Lava is the main subaerial product representing ∼57% of the total erupted mass of magma. Combined with already available datasets, our work furthers future investigations of the relationship between the erupted masses of magma and of volatiles, the variation of the eruptive rates after an earthquake, the impact of the erupted mass on the Geospheres at local and global scales. Finally, mass balancing between the erupted and intruded mass could provide information of whether a volcano or a magmatic province is accumulating magma, potentially increasing future eruptive hazards on a decadal timescale. Global estimation of the mass and products erupted from 1980 to 2019Lava is the main subaerial product erupted from 1980 to 2019Twenty‐three volcanoes produced ∼72% of the total mass erupted from 1980 to 2019 Global estimation of the mass and products erupted from 1980 to 2019 Lava is the main subaerial product erupted from 1980 to 2019 Twenty‐three volcanoes produced ∼72% of the total mass erupted from 1980 to 2019

Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intra-oceanic subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge, which formed above an intra-oceanic subduction system over the past 70 Myr. We find that the geochemical signature of erupted lavas evolved from basaltic to andesitic about 10 Myr ago—coincident with the onset of subduction of more oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally. We conclude that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone—a process probably more common in the Archaean—can produce juvenile continental crust.

Melt inclusions (MI) are considered the best tool available for determining the pre-eruptive volatile contents of magmas. H2O and CO2concentrations of the glass phase in MI are commonly used both as a barometer and to track magma degassing behavior during ascent due to the strong pressure dependence of H2O and CO2solubilities in silicate melts. The often unstated and sometimes overlooked requirement for this method to be valid is that the glass phase in the MI must represent the composition of the melt that was trapped at depth in the volcanic plumbing system. However, melt inclusions commonly contain a vapor bubble that formed after trapping owing to differential shrinkage of the melt compared to the host crystal, and/or crystallization at the inclusion-host interface. Such bubbles may contain a substantial portion of volatiles, such as CO2, that were originally dissolved in the melt. In this study, we determined the contribution of CO2in the vapor bubble to the overall CO2content of MI based on quantitative Raman analysis of the vapor bubbles in MI from the 1959 Kilauea Iki (Hawaii), 1960 Kapoho (Hawaii), 1974 Fuego volcano (Guatemala), and 1977 Seguam Island (Alaska) eruptions. We found that the bubbles typically contain 40 to 90% of the total CO2in the MI. Reconstructing the original CO2content by adding the CO2in the bubble back into the melt results in an increase in CO2concentration by as much as an order of magnitude (thousands of parts per million). Reconstructed CO2concentrations correspond to trapping pressures that are significantly greater than one would predict based on analysis of the volatiles in the glass alone. Trapping depths can be as much as 10 km deeper than estimates that ignore the CO2in the bubble. In addition to CO2in the vapor bubbles, many MI showed the presence of a carbonate mineral phase. Failure to recognize the carbonate during petrographic examination or analysis of the glass and to include its contained CO2when reconstructing the CO2content of the originally trapped melt will introduce additional errors into the calculated volatile budget. Our results emphasize that accurate determination of the pre-eruptive volatile content of melts based on analysis of melt inclusions must consider the volatiles contained in the bubble (and carbonates, if present). This can be accomplished either by analysis of the bubble and the glass followed by mass-balance reconstruction of the original volatile content of the melt, or by re-homogenization of the MI prior to conducting microanalysis of the quenched, glassy MI.

The Nain Ophiolite is one of the most complete harzburgitic-ophiolite suites exposed along the Nain-Baft Fault, around the Central-East Iranian Microcontinent (CEIM). It is a remnant of the Nain Ocean (Early Jurassic to upper Early Cretaceous-Paleocene). During the Cretaceous (~Albian to Cenomanian), ascending melts and serpentinization overprinted the Jurassic melt-rock reactions and metamorphism of peridotites in most of the ophiolite. However, metamorphosed peridotites of the Darreh Deh massif in the eastern part of Nain Ophiolite remained intact, with the lowest degree of alteration and serpentinization and slightly higher degrees of partial melting and melt – rock reactions. Clinopyroxene and Cr-spinel compositions together with bulk rock geochemistry of Darreh Deh peridotites indicate a mid-ocean ridge affinity for lherzolite but later compressional tectonics led to an intra-oceanic subduction and supra-subduction zone (SSZ) in which harzburgite and dunite formed due to ascending melt reacting with the mantle lherzolite. Further indications are the presence of replacive olivine, incongruent melting of orthopyroxene and increase of Cr# of Cr-spinel in harzburgite. The extensional to compressional evolution in the Jurassic ended with accretionary and/or collisional processes induced by convergence between the Sanandaj – Sirjan zone and the CEIM. These caused a regional metamorphism that affected the Darreh Deh massif by forming antigorite, talc, metamorphic olivine, tremolite and chlorite metamorphic assemblages in mantle peridotites at amphibolite facies (~630-700 °C / 7-15 kbar) conditions, similar to the metamorphosed diabasic dikes, basalts and pillow lavas of this ophiolite.

The granitoids of Dehnow in NE Iran are part of a calc-alkaline plutonic series (diorite-to-nalite-granodiorite) that intruded the remnants of the Paleo-Tethys oceanic crust during the Triassic. New major and trace element data together with isotopic compositions elucidate their I-type nature and a deep magma origin. P-T calculations based on amphibole and plagioclase suggest crystallization stages in the upper lithosphere at an approximate pressure of 6.4 kbar and temperature of 708 °C. The Dehnow granitoids are characterized by high concentrations of LILE, LREE, HFSE and low concentrations of HREE, similar to some worldwide I-type granites, including examples from Harsit (along the Alpine-Himalayan suture zone), Iberia and the Martins Pereira plutons. The new geochemical data in combination with mineral parageneses and field observations suggest that the origin of the low temperature, Caledonian-type, arc-related granitoids of Dehnow resulted from the subduction of the Paleo-Tethys oceanic slab beneath the Turan block (along the Alpine-Himalayan suture zone) and involved the contribution of lower crust and mantle melts in this collisional setting.

To better estimate the extrusive flux of the Central American Arc, from 2002-2008, we obtained sixty one high precision 40Ar/39Ar ages on geographically well-situated lavas and tephra from Costa Rica and Nicaragua. Here, we describe a number of observations encountered during this study using four examples that well document the precision, accuracy and general reliability of the 40Ar/39mAr ages. First, low K2O values, particularly in samples from Nicaragua, is a major limitation in or attempts to obtain reliable dates on samples under 1 My. Second, extensive weathering of samples due to the tropical climate of Central America has resulted in various levels of argon loss even when the hand sample appeared unaltered. Third, our field and geochronological data lead us to conclude that eruptive rates have not been constant over the past 15 to 20 My, but rather appears punctuated by gaps of up to several million years. We attempted to address the temporal gaps in several ways. First, geochemical analyses were used to identify samples that may have erupted during time periods without known volcanism. For example, U/Th values in the active Central American arc are significantly higher than those obtained from the Miocene Coyol Group except for four samples with intermediate values that were dated to determine if their ages were intermediate as well. However, all of these samples were found to be from a period with known volcanism. Second, we sought to locate the oldest sections of the active arc and the youngest sections of the Coyol Group in order to better constrain the timing and duration of the apparent gap in volcanic productivity. This approach also failed to locate samples from periods without known volcanism. When these methods proved largely unsuccessful, our focus shifted to dating regions of minor volcanism between the active and Coyol volcanic fronts as well as between Cosigüina and San Cristóbal, the longest stretch of the Central American Volcanic Front without active volcanism. This effort yielded ages on samples ranging from 1.1 to 3.6 Ma and, thus, substantially reduced the apparent volcanic gap in Nicaragua. [ABSTRACT FROM AUTHOR]

The present study defines the stratigraphy of Poá s volcano by using geologic, petrographic, geochrono-logic and geochemical analyses made on the Poás units. The northern flank of the volcano is comprised of the following units: Rio Sarapiquí, La Paz Andesites, Tiribi Formation (from Barva volcano, but interdigitated with Poás stratigraphy), Rio Cuarto Lavas, Von Frantzius, Cerro Congo, Bosque Alegre and Laguna Kopper. The units on the southern flank are Colima Formation, La Paz Andesites, Tiribi, Achiote, Poasito, Sabana Redonda and Poás Lapilli Tuff. The central part of the volcano is made by the Poás Summit Unit, which includes the Main and Botos craters. The composition of the rocks spans the range from basalts to dacites. These units were geochemically correlated with two magmatic components: 1. The Sabana Redonda Geochemical Component (TiO2 > 1%) enriched in HSFE and other trace elements, present in La Paz Andesites, Lavas Rio Cuarto, Poasito, Sabana Redonda, Poás Lapilli Tuff and some from Botos crater lavas. 2. The Von Frantzius Geochemical Component (TiO2 < 0.8 %) is present in lavas of the Main crater, Von Frantzius, Achiote, Bosque Alegre, Cerro Congo and some Botos crater lavas. During the last 600 ka the content of K2O and other oxides (TiO2 and P2O5) and traces (Zr, Ba) have varied significantly through time, suggesting the presence of these two geochemical end-members since the beginning of the magmatic activity of Poás. Within similar ranges of time, units with high and low values of these elements have coexisted; the latter is true for Botos lavas and the Main crater. For units that possibly shared a common vent, such as La Paz Andesites, Achiote and Main crater, the percentages of K2O and TiO2 have decreased through time. Nevertheless, more geochronological data are needed to improve the interpretations given above. [ABSTRACT FROM AUTHOR]

We describe the stratigraphy and geochemistry of tephras and lavas related with 5 cinder cones in a north-south alignment on the southern flank of Poás volcano. The local geologic basement is composed mainly by lava flows, with the northwest dominated by the Achiote basaltic-andesites and the rest of the area by Poasito andesites, this last cogenetic with the cinder cones. All of these units are generally covered by a thin layer of the upper section of the Poás Lapilli Tuff. Field evidence suggests that the cinder cones were not contemporaneous but represent different magmatic pulses. The magmas that produced these cinder cones represent the most enriched magmatic component of Poás volcano. Based on the available geochemical data, we define two magmatic components for Poás: 1) The Sabana Redonda component (TiO2 >1%, relatively enriched in HFSE and other incompatible elements), which is also present in the Paleo-Poás, Poás lapilli tuff y and some Botos crater lavas. 2) The von Frantzius component (TiO2 <0.8%), which is present at lavas from the main crater, von Frantzius cone, Hule maar, and in some Botos crater lavas. Intermediate lavas (TiO2 0.8-1%) are hybrids between these two components. Both components share the same OIB-like source, although the Sabana Redonda component requires a relatively lower degree of partial melting, produced primarily by a decompression mechanism, which may be related with the extension generated within the Poás volcano-tectonic fracture. The von Frantzius component represents magmas produced primarily by flux melting related with the subduction processes. [ABSTRACT FROM AUTHOR]

The eastern margin of North America has been shaped by a series of tectonic events including the Paleozoic Appalachian Orogeny and the breakup of Pangea during the Mesozoic. For the past ∼200 Ma, eastern North America has been a passive continental margin; however, there is evidence in the Central Appalachian Mountains for post‐rifting modification of lithospheric structure. This evidence includes two co‐located pulses of magmatism that post‐date the rifting event (at 152 and 47 Ma) along with low seismic velocities, high seismic attenuation, and high electrical conductivity in the upper mantle. Here, we synthesize and evaluate constraints on the lithospheric evolution of the Central Appalachian Mountains. These include tomographic imaging of seismic velocities, seismic and electrical conductivity imaging along the Mid‐Atlantic Geophysical Integrative Collaboration array, gravity and heat flow measurements, geochemical and petrological examination of Jurassic and Eocene magmatic rocks, and estimates of erosion rates from geomorphological data. We discuss and evaluate a set of possible mechanisms for lithospheric loss and intraplate volcanism beneath the region. Taken together, recent observations provide compelling evidence for lithospheric loss beneath the Central Appalachians; while they cannot uniquely identify the processes associated with this loss, they narrow the range of plausible models, with important implications for our understanding of intraplate volcanism and the evolution of continental lithosphere. Our preferred models invoke a combination of (perhaps episodic) lithospheric loss via Rayleigh‐Taylor instabilities and subsequent small‐scale mantle flow in combination with shear‐driven upwelling that maintains the region of thin lithosphere and causes partial melting in the asthenosphere. For the past 200 million years, the east coast of North America has been situated in the middle of a tectonic plate. Contrary to the expectations for this setting, a region of the Central Appalachian Mountains centered near the boundary between the U.S. states of Virginia and West Virginia exhibits atypical properties. The unusual observations include volcanic activity in the geologic past far away from a plate boundary, elevated rates of erosion associated with high topography in the Central Appalachians, and anomalous structure in the upper mantle that has been detected using geophysical methods. This article describes, synthesizes, and compares a suite of observations that show that this part of the Central Appalachians is unusual compared to other so‐called passive continental margins. We discuss a range of different models that might describe how the lithosphere, or the rigid part of the crust and upper mantle that defines the tectonic plate, has evolved through time beneath our study region. We show that the lithosphere today is thin, and that past episodes of lithospheric loss involving a portion of dense lithosphere “dripping” into the mantle under the force of gravity may provide a good explanation for the observations. There is a present‐day geophysical anomaly in the upper mantle co‐located with unusually young volcanism in the Central AppalachiansWe synthesize constraints from geophysics, petrology/geochemistry, and geomorphology to constrain possible models for lithospheric lossWe favor one or more Rayleigh‐Taylor lithospheric instabilities, perhaps in combination with shear‐driven upwelling There is a present‐day geophysical anomaly in the upper mantle co‐located with unusually young volcanism in the Central Appalachians We synthesize constraints from geophysics, petrology/geochemistry, and geomorphology to constrain possible models for lithospheric loss We favor one or more Rayleigh‐Taylor lithospheric instabilities, perhaps in combination with shear‐driven upwelling

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

We present a geologic map of the Tapantí quadrangle, which is located in the central region of Costa Rica and belongs to the Central Costa Rica Deformed Belt (CCRDB). The CCRDB is a consequence of the interaction of the Cocos Ridge and the Western edge of the Panama microplate. The oldest rocks mapped in this work are Miocene in age and theyvbelongs to Pacacua, Peña Negra and Coris formations, than form the western edge of the Candelaria basin. Three igneous events were distinguished. First, the Miocene volcanic arc, which is represented by the rocks of La Cruz Formation and the clasts of Pacacua Formation. Another period of igneous activity was recorded in Grifo Alto and Doán formations and the Tapantí Intrusive, with an age range of 0.6-0.03 Ma. From a geochemical point of view is remarkable a change between 10 to 6 Ma, enrichment of K and Si and changes in U, Sr, Ba and La concentrations. This change corresponds with the Cocos Ridge arriving to the Middle America Trench and it is visible because the Pliocene magmatic arc, the Pliocene intrusive of Tapantí and the nowadays volcanic arc. The structural model suggests the existence of two deformation events, the first occurred during the period of time between Late Miocene and Pliocene and it formed the Folding Zone Orosi-Patarrá, and the second one corresponds to the establishment of CCRDB, from Pliocene to present, which is constituted by left lateral faults bearing ENE and right lateral faults bearing NW. [ABSTRACT FROM AUTHOR]

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 significantly 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-Golito-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. [ABSTRACT FROM AUTHOR]

In the Talamanca Cordillera, the widespread magmatic products record Neogene and Quaternary intrusive and extrusive phases. Generally, it is possible to recognize three magmatic stages: 1) Volcanic series older than Upper Miocene, ranging from ~17 to 11 mya; 2) Plutonic events during the Middle-Upper Miocene, between 12,5 and 7,5 mya, known as Talamanca Intrusive Group or Granite-Gabbro Series of Talamanca; c) Post-intrusive magmatic pulses from Neogene-Quaternary, whose temporal range extends from ~5 to 2 mya. For the first time it is proposed here a differentiation of post-intrusive magmas into three units by petrographic criteria: a) Kamuk Unit, andesites with labradorite-type plagioclase and occasional orthopyroxene. b) Durika Unit, defined by andesine-type plagioclase and the presence of biotite phenocrysts as the predominant ferromagnesian phase. c) Rio Lori Unit, whose products were not sampled in this study, but based in previous work they are characterized by the presence of quartz, amphibole and biotite phenocrysts. Additionally, we provide a new contribution to the geologic cartography of the Talamanca Cordillera, with a geological description of the summits of Cuerici, Ena, Durika, Utyum, Kamuk, fila Pittier and Echandi. We also present new data referring to the geology of the summit of Chirripo. [ABSTRACT FROM AUTHOR]