Volcanic record of the subduction of an active spreading ridge, Taitao Peninsula (southern Chile)

During the Pliocene, the Taitao Peninsula was the locus of the subduction of the Chile active spreading ridge beneath the South American margin. New field data allow us to distinguish within the Taitao ophiolite a genuine ophiolitic body of undetermined age and two volcanic and volcaniclastic units. One unit shows evidence for deposition in a shallow-water environment, and it unconformably overlies the Chilean continental basement. Its established Pliocene age demonstrates that it was deposited during the subduction of the Chile ridge. Lavas from both units include enriched mid-oceanic ridge basalts (MORBs) together with Nb-depleted basalts, andesites, and dacites. La/Nb ratios vary randomly from 1 to 4 in both units and are positively correlated with SiO2 content. These chemical characteristics are consistent with upper-crustal contamination of MORB-type basalts by the Chilean crust as already suggested from isotopic data. We consider these volcanic suites to be the result of eruptions of MORB magmas that originated from the downgoing, shallowly buried, active spreading center and were contaminated during their rise through the Chilean continental basement.