Large volume silicic volcanism along the proto-Pacific margin of Gondwana:lithological and stratigraphical investigations from the Antarctic Peninsula

Jurassic magmatism in western Gondwana produced the most voluminous episode of continental volcanism in the Phanerozoic era During the Early to Middle Jurassic, some 2.5-3 million km(3) of dominantly basalt, and to a lesser e xtent rhyolite, were erupted onto a supercontinent in the early stages of b reak-up. The major silicic portion of the Gondwana magmatic province is exp osed in Patagonian South America. The volcanic rocks of Patagonia have been collectively termed the Chon-Aike Province and constitute one of the world 's most voluminous silicic provinces. The volcanic rocks are predominantly pyroclastic, dominated by ignimbrite units of rhyolite composition. Volcanic rocks crop out sporadically across much of the once contiguous Ant arctic Peninsula, and are considered to form an extension of the Chon-Aike Province. A continuation of the province to include the Antarctic Peninsula would extend its strike length along the active Pacific margin by c. 2000 km. Volcanic rocks exposed along the east coast of the Antarctic Peninsula, defined here as the Mapple Formation, are also dominated by rhyolitic igni mbrite flows, with individual units up to 80 m in thickness, and a total th ickness of c. I lan. The ignimbrites vary in degree of welding, from high-g rade rheomorphic ignimbrites with parataxitic textures, to unwelded, lithic -rich ignimbrites. Rhyolite lava flows, air-fall horizons, debris flow depo sits and epiclastic deposits are volumetrically minor, occurring as interbe dded units within the ignimbrite succession. The lithology and stratigraphy of the Jurassic volcanic rocks of the Mapple Formation are presented, and comparisons are made to the Chon-Aike Provinc e. A consistent stratigraphy of Permo-Triassic metasedimentary rocks, uncon formably overlain by terrestrial mudstone-siltstone sequences, which are in turn conformably overlain by largely silicic, subaerial volcanic rocks, is present at several localities along the Antarctic Peninsula, and at locali ties in the Chon-Aike Province. Precise (zircon U-Pb) Middle Jurassic ages exist for two volcanic formations from the Antarctic Peninsula, and a Middl e-Lower Jurassic age has been suggested for the underlying sedimentary form ations based on fossil flora analysis. The Antarctic Peninsula chronostrati graphy, coupled with lithological similarities, indicate a close relationsh ip to those sequences of the Chon-Aike province.