Stratigraphic and structural reappraisal of the metamorphic complex from northeastern Cordillera Darwin, Tierra del Fuego, Chile

Abstract

New petrographic and structural studies in NE Cordillera Darwin have impact on previous stratigraphic determinations regarding the distinction between basement and cover of the Rocas Verdes basin. Our results reveal that the metasedimentary and metavolcanic rocks mapped in the hanging wall and footwall of the first-order Glaciar Marinelli thrust were affected by the same episodes of Mesozoic-Cenozoic deformation than the cover rocks of the Fuegian Andes, with no evidence of pre-Jurassic deformation. The key to determine the sequence of deformation relies on the correct distinction of the primary sedimentary layering in fine-grained metasedimentary rocks. These results indicate that the rocks in the study area are part of the sedimentary and volcanic fill of the Rocas Verdes Basin. Two new U-Pb age determinations indicate that early Paleozoic and older detrital zircon grains prevail in these cover rocks, consistent with the provenance from an eroded Paleozoic basement during the early development of the rift basin. Careful petrographic studies are thus required to assess the validity of detrital zircon maximum depositional ages in the area.