A probable Early Triassic age for the Miers Bluff Formation, Livingston Island, South Shetland Islands

• Published in: Antarctic Science
• Main Authors: Willan, R. C. R., Pankhurst, R. J., Hervé, F.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Cambridge University Press 1994
• Subjects: Earth Sciences; South Shetland Islands; Livingston Island; Miers; Hurd; Hurd peninsula; Miers Bluff; Antarctic Science
• Online Access: http://nora.nerc.ac.uk/id/eprint/516575/; https://doi.org/10.1017/S095410209400060X

Fifteen samples of very low-grade mudstones from two widely separated sections in the Miers Bluff Formation on Hurd Peninsula yield an Rb-Sr errorchron (MSWD=8.9) corresponding to an age of 243 ± 8 Ma. This age is interpreted as representing effective homogenization, on a kilometres scale, during turbidite deposition and diagenesis in early Triassic times. The initial 87Sr/86Sr ratio 0.7085 ± 0.0003 represents a mature crustal source and is consistent with the re-working of material comparable to that eroded from the Chilean fore-arc accretionary complex. Four further samples, collected near to a zone of quartz-carbonate veins, lie to the right of the errorchron, with two samples having unusually low Sr contents. These samples fall on a 113 Ma reference line and indicate metasomatic disturbance in Cretaceous times. Metasomatism was probably related to hydrothermal alteration accompanying widespread silicification and quartz veining on western Hurd Peninsula. A mid-to late Cretaceous age for metasomatic disturbance agrees with field relations which indicate that the hydrothermal activity preceded or was coeval with the mid- to late Cretaceous period of volcanism on Livingston Island. Hence the hydrothermal rocks are not related to the Eocene Barnard Point pluton, as previously suggested.