Abstract

Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are recognized from many localities in the southern Antarctic Peninsula and NE Patagonia and are essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare in or absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed during the Middle Jurassic and the mid-Cretaceous. New U–Pb zircon geochronology from the Antarctic Peninsula and recently published U–Pb ages from elsewhere in the Peninsula and Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight samples are dated here from the central and southern Antarctic Peninsula. They are all moderately to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline basement. They yield ages in the range 188 – 181 Ma, which overlap with published ages of 185 – 180 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic belt of Patagonia (185 – 181 Ma). Whereas Early Jurassic plutons of the Subcordilleran plutonic belt of Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with extension and plume activity during the initial stages of Gondwana breakup. This indicates that subduction was continuing when Chon Aike Province volcanism started. The Early Jurassic plutonism on the Antarctic Peninsula is transitional between subduction-related and breakup-related magmatism.

Supplementary material: Cathodoluminescence images of analysed zircon grains from sites on the Antarctic Peninsula are available at https://doi.org/10.6084/m9.figshare.c.3521973

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