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

Lithology, metamorphism, and deformation of the host rocks of chromite-bear ing serpentinite bodies are described. The metasedimentary rocks and the in tercalated metabasalts were metamorphosed under greenschist facies conditio ns. Several metamorphic and deformational phases are distinguished. The fir st three developed under constant strain directions with NNE-SSW to NE-SW t rending fold axes. E-W trending fold axes formed in a later phase, still un der ductile conditions. Only after the Carboniferous/Permian boundary were kink bands formed that indicate transition to brittle deformation. Block-st ream-like arranged chromitite boulders indicate the occurrence of major chr omitite layers within a large serpentinite body. The emplacement of the ser pentinite body into the host rocks took place between the third and fourth folding phase. Cr/(Cr + Al) ratios of chromite ores indicate an island are position for the chromitites. whereas data from neighbouring areas point to backarc conditions. A polyphase, more or less continuous, subduction proce ss from the Carboniferous up to the end of the Permian is thought to be res ponsible for tectonically mixing up these units. (C) 2001 Elsevier Science Ltd. All rights reserved.