The Origin of Spatial and Temporal Geochemical Variations in the Central American Volcanic Arc

Variations in age and composition of the subduction input, slab dip, crustal thickness and crustal composition are likely to be the major controls on spatial and temporal variations along the Central American Volcanic Arc (CAVA). Our extensive new geochemical data set from volcanic rocks and olivine-hosted melt inclusions, combined with published data, shows systematic variations along two sections of the CAVA. Along the volcanic front (VF) from NW Nicaragua to Guatemala and across the arc from El Salvador to Honduras, variations in trace element (e.g. decrease in Ba/La and U/Th and increase in La/Yb) and isotopic composition (decrease in 143Nd/144Nd and increase in 206Pb/204Pb) suggest a decreasing role for a hydrous fluid component and an increasing role of a sediment melt component in the arc magmas to the NW along the VF and behind the VF. Since the age and composition of the subduction input are similar along this part of the arc, the decreasing slab dip angle, increase in crustal thickness and/or transition from mafic oceanic to evolved continental type basement are likely to control the observed geochemical variations. From NW Nicaragua to central Costa Rica, the most mafic lavas and melt inclusions show an increase in SiO2, La/Yb and 206Pb/204Pb and a decrease in FeO*, Ba/La, U/Th and 143Nd/144Nd, consistent with an increasing role of hydrous melts with Galapagos hotspot-type geochemical signatures contributing to the arc magmas to the SE. These geochemical variations correlate with an increasing overprinting of the incoming Cocos Plate by the Galapagos hotspot. There is a dramatic increase in Pb isotopic composition beginning at Arenal, which is coincident with the projection of the northern morphological boundary of the subducting Galapagos hotspot track. The fluid-mobile nature of Pb and the high Pb concentrations in the arc magmas indicate that the Pb isotopic composition (and the other geochemical variations) is primarily controlled by the subduction input. The Galapagos type component decreases behind the VF in Costa Rica. Temporal variations in isotopic composition in Panama record the complex interaction of the Galapagos hotspot track with the Panamanian arc over the last 70 Ma.