Heydolph, Ken (2010) Spatial variations in the geochemistry of arc volcanism in Central America. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, 153 pp.

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Abstract

Volcanism in Central America results from the subduction of the Cocos plate beneath the Caribbean plate. The resulting central American Volcanic arc (CAVA) extends for ~1500 km parallel to the Middle American Trench from Guatemala in the northwest to Costa Rica in the southeast. Characteristic for the CAVA are systematic variations in tectonic parameters (e.g. subducting angle of the Cocos plate), the composition of the subducting plate and the overlying crust. Various partly still active volcanoes and volcanic centers are located along and across the arc and have been subject to intensive research for the past years. The numerous and often contradicting individual models for the origin of arc volcanics in Central America propose a variety of distinct magmatic sources. This dissertation provides new models for the magmatic sources of northwestern and southeastern CAVA rocks. A new and comprehensive dataset of main and trace elements concentrations and ratios, and isotope ratios (Sr-Nd-Pb and for the first time for Central American volcanics Hf) of mafic volcanics und potential magmatic endmembers from the subducting Cocos plate and the overlying Caribbean Plate has been established. Systematic along and across arc geochemical variations of trace element concentrations and ratios and isotope ratios (in particular of Hf and Pb) clearly show that subducting Cocos plate sediments have no influence on the magmatic source components for NW CAVA rocks, as has been proposed by several already published models. The new dataset provides a system of three magmatic endmember components which can explain the observed systematic geochemical variations of NW CAVA rocks. The northwestern CAVA endmember is an enriched magmatic component in the lithosphere beneath Guatemala. The southeastern part of the arc is characterized by the offshore Costa Rica subducting Cocos and Coiba ridges and a neighboring subducting seamount province, which all show an enriched Galapagos hotspot influenced ocean island basalt (OIB) signature (i.e. radiogenic Pb and Hf but unradiogenic Sr and Nd isotopic ratios). New data from mafic volcanics from Costa Rica and Panama show a strong, though systematically from Costa Rica to Nicaragua decreasing influence of the subducting Galapagos hotspot seamount province on the magmatic source composition of the volcanics.

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