GEOCHEMICAL HISTORY AND MAGMATIC PROCESSES OF THE TELICA VOLCANIC COMPLEX, NICARAGUAN VOLCANIC FRONT

The Central American volcanic arc displays a significant range in the geochemical signature of its erupted basalts, which has been linked to variable contributions from the subducting slab and regional changes in subduction parameters, such as the angle of subduction along the arc. The Telica Volcanic Complex (TVC) in NW Nicaragua is unusual in that its basalts exhibit nearly the full range of trace element variability seen amongst mafic lavas along the entire Central American volcanic front. We present here new geochemical data on 45 volcanic rocks that span the entire history of the TVC. ⁴⁰Ar/³⁹Ar ages from basaltic lavas show that volcanism has occurred in the complex for the last 1.6 ± 0.07 m.y.. Current magmatism is centered at Telica, a stratovolcano consisting of several individual vents. U/La and Ba/Th ratios, which are interpreted to represent contributions to the mantle source from Cocos Plate sediments, hemipelagic versus carbonate, respectively (Patino et al., 2000), show little variation over time at Telica. Nonetheless, on average there is an increase in the U/La ratio with time suggesting increased contribution of hemipelagic sediment to magma production beneath the complex. This is perhaps linked to the subduction of deep half-grabens formed in the Cocos Plate (Ranero et al., 2003) or multiple stages of flux extraction from the sediments (Patino et al, 2000). The youngest lavas from Telica form two distinct groups—high-Ti and low-Ti—that differ in their trace element characteristics. The high-Ti lavas are distinctly low in Ba/La and more enriched in Sm/Yb and Nb/Yb ratios suggesting they represent lower degrees of melting with attenuated slab input, whilst their low Zr/Nb and Ba/Nb ratios suggest different mantle sources. The new geochemical data suggest that slab control on magma composition beneath this enigmatic arc volcano has been variable over both short and long time scales.