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Central America has a rich mix of conditions that allow comparisons of different natural experiments in the generation of arc magmas within the relatively short length of the margin. The shape of the volcanic front and this margin's architecture derive from the assemblage of exotic continental and oceanic crustal slivers, and later modification by volcanism and tectonic activity. Active tectonics of the Cocos-Caribbean plate boundary are strongly influenced by oblique subduction, resulting in a narrow volcanic front segmented by right steps occurring at ∼150-km intervals. The largest volcanic centers are located where depths to the slab are ∼90–110 km. Volcanoes that develop above deeper sections of the subducting slab are less voluminous and better record source geochemical heterogeneity. Extreme variations in isotopic and trace element ratios are derived from different components of thesubducted oceanic lithosphere. However, the extent that volcanoes sample these signatures is also influenced by lithospheric structures that control the arc segmentation. The architecture of Central America derives from the assemblage of exotic continental and oceanic crustal slivers modified by arc magmatism and tectonic processes. Active tectonics in Central America are controlled by oblique subduction. The lithospheric architecture and tectonics define the segmentation of the volcanic front, and thus the depth to the slab below a volcanic center. The composition of the subducted material is the main control of the along arc geochemical variations observed in Central American volcanoes. Geochemical heterogeneity in each segment is highlighted by extreme compositions representing the smaller centers with variations up to 65% of the total observed range. [ABSTRACT FROM AUTHOR]

The Rutgers University Central American geochemical dataset focuses on the active volcanoes related to the Cocos-Caribbean convergent plate boundary that extends from Guatemala to Costa Rica in Central America. The RU prefix signifies that the data and samples are primarily from the long-term Central American research project started at Dartmouth College in 1970 and continued at Rutgers University from 1974 to the present. The database is decidedly uneven because of the impressive improvement of analytical techniques over the span of data collection. Further complications arose because most of the sampling and analysis were part of the educational process for many different undergraduate and graduate students using different types of instruments. This note presents, as a reasonably coherent whole, geochemical data and metadata for about 1400 samples collected by at least 40 students and colleagues. Many unpublished Sr, Nd, and Pb isotopic ratios are included here but most of the new data are metadata that provide greatly improved descriptions of the tectonic settings, locations, and status of the samples as well as estimates of data quality. [ABSTRACT FROM AUTHOR]

Abstract: The volcanic record of western Nicaragua documents a significant lull in volcanic activity that has persisted from the late Miocene (~7Ma) to the formation of the modern volcanic front around 350ka. This study fills this gap for the first time with samples collected in Northwest Nicaragua between Cosigüina and San Cristóbal volcanoes and with samples collected from the Nicaraguan Depression. We found two previously unknown volcanic units ranging from 3.6 to 1.3Ma and the improved volcanic record allows us to reconstruct the geochemical evolution of the Nicaraguan arc. U/Th values increased by nearly threefold since the Miocene following the “carbonate crash” at 10Ma, when dominantly carbonate sediment deposition shifted toward hemipelagic sediment deposition. This transition was thought to be abrupt, however our new data show that it took place gradually over the last 7Ma. Northwest Nicaragua is a particularly interesting case study because it contains Middle Miocene volcanism on either side of the Nicaraguan Depression, the Coyol Formation (25–7Ma) to the East and the Tamarindo Formation (14.7–11.7Ma) to the West. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to the hypothesis that the two coeval units, currently separated by ~100km, were once connected and have since been separated by extension. Here, we present data suggesting that the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit. [Copyright &y& Elsevier]

Abstract: The volcanic front in southern Central America is well known for its Galapagos OIB-like geochemical signature. A comprehensive set of geochemical, isotopic and geochronological data collected on volumetrically minor alkaline basalts and adakites were used to better constrain the mantle and subduction magma components and to test the different models that explain this OIB signature in an arc setting. We report a migration of back-arc alkaline volcanism towards the northwest, consistent with arc-parallel mantle flow models, and a migration towards the southeast in the adakites possibly tracking the eastward movement of the triple junction where the Panama Fracture Zone intersects the Middle America Trench. The adakites major and trace element compositions are consistent with magmas produced by melting a mantle-wedge source metasomatized by slab derived melts. The alkaline magmas are restricted to areas that have no seismic evidence of a subducting slab. The geochemical signature of the alkaline magmas is mostly controlled by upwelling asthenosphere with minor contributions from subduction components. Mantle potential temperatures calculated from the alkaline basalt primary magmas increased from close to ambient mantle (~1380–1410°C) in the Pliocene to ~1450°C in the younger units. The calculated initial melting pressures for these primary magmas are in the garnet stability field (3.0–2.7GPa). The average final melting pressures range between 2.7 and 2.5GPa, which is interpreted as the lithosphere–asthenosphere boundary at ~85–90km. We provide a geotectonic model that integrates the diverse observations presented here. The slab detached after the collision of the Galapagos tracks with the arc (~10–8Ma). The detachment allowed hotter asthenosphere to flow into the mantle wedge. This influx of hotter asthenosphere explains the increase in mantle potential temperatures, the northwest migration in the back-arc alkaline lavas that tracks the passage of the hotter asthenosphere, and the presence of a slab melting signature in the volcanic front caused by recycling of Galapagos Hotspot tracks. [Copyright &y& Elsevier]

Six to five Myr. old continental-arc shoshonites and other high-K igneous rocks crop out among the summits of the Talamanca Cordillera, Central America. These rocks fill a previously assumed volcanic gap in eastern Costa Rica, showing that the Late Miocene-Pliocene magmatic arc was almost continuous along the current Talamanca Cordillera. Their trace element compositions (e.g., Sr ~ 1700 ppm at Rb ~ 120 ppm concentrations) together with fractional crystallization modeling, and isotopic signatures suggest a genesis related to subduction processes rather than lower crustal melting. Here we present a comprehensive geochemical study that integrates Monte Carlo simulations of trace element geochemistry and isotopic evidence in order to explain the origin of these highly enriched igneous rocks. The trace element budget of the Talamanca arc rocks requires the input of an incompatible element-enriched component, similar in composition to the Cocos Island Province (Pacific Ocean). We interpret the presence of this component to be the result of slab melting of subducted seamounts. Our model suggests that in southern Central American, contribution of OIB-related seamounts is a critical step for the generation of continental crust-like rock compositions. • A juvenile continental arc fills a Late Neogene gap between Costa Rica and Panama. • This suite includes shoshonitic lavas highly enriched in incompatible elements. • Their trace element budgets require a melt component from subducted seamounts. [ABSTRACT FROM AUTHOR]