Chromite-bearing serpentinite bodies within an arc–backarc metamorphic complex near La Cabaña, south Chilean Coastal Cordillera

Abstract

Lithology, metamorphism, and deformation of the host rocks of chromite-bearing serpentinite bodies are described. The metasedimentary rocks and the intercalated metabasalts were metamorphosed under greenschist facies conditions. Several metamorphic and deformational phases are distinguished. The first three developed under constant strain directions with NNE–SSW to NE–SW trending fold axes. E–W trending fold axes formed in a later phase, still under ductile conditions. Only after the Carboniferous/Permian boundary were kink bands formed that indicate transition to brittle deformation. Block-stream-like arranged chromitite boulders indicate the occurrence of major chromitite layers within a large serpentinite body. The emplacement of the serpentinite body into the host rocks took place between the third and fourth folding phase. Cr/(Cr+Al) ratios of chromite ores indicate an island arc position for the chromitites, whereas data from neighbouring areas point to backarc conditions. A polyphase, more or less continuous, subduction process from the Carboniferous up to the end of the Permian is thought to be responsible for tectonically mixing up these units.