Petrology and geochemistry of the ophiolitic and volcanic suites of the Taitao Peninsula — Chile triple junction area

This paper presents detailed petrologic and geochemical analysis of mafic and ultramafic rocks from the Taitao Peninsula, South Chile, and contributes to improve the knowledge of the Taitao ophiolite. These data allow us to identify three different units on the Taitao Peninsula, which include an ophiolitic body (peridotites, gabbros and dykes) and two Pliocene to Pleistocene volcanic-sedimentary units which accumulated as subduction of the Chile ridge occurred. The petrologic, mineralogical and geochemical data strongly suggest an oceanic origin of the peridotites and the gabbros, possibly at an active spreading center; harzburgites and CPX-bearing harzburgites can be considered as fragments of obducted mantle, whereas werhlites could represent a different magma source, enriched in K, Ti, Na and water, that impregnated the peridotites in a later stage. The two volcanic-sedimentary units, termed the Main Volcanic Unit (MVU) and the Chile Margin Unit (CMU) are geochemically unconnected with the ophiolite. They range in composition from basaltic to dacitic and can be subdivided into three groups: (i) a group with MORB affinities (ii) a group with calc-alkaline affinities (iii) a group with intermediate characteristics. MVU exhibits greenschist facies mineral assemblages whereas CMU shows assemblages ranging from zeolite facies to very low temperature conditions. We suggest that these different metamorphic overprints are a consequence of the collision of two different ridge segments with the South-America margin in front of the Taitao Peninsula.