Ellsworth Land Volcanic Group

The Antarctic Peninsula has been traditionally interpreted as a native continental arc, yet more recent studies suggest it is a collection of terranes merged onto the Gondwana margin. In the Antarctic Peninsula and eastern Ellsworth Land, volcanic and plutonic rocks formed during the subduction of oceanic lithosphere, marking different periods of volcanic activity. These rocks, part of the Antarctic Peninsula Volcanic Group, range from Early Jurassic to Tertiary age and exhibit various facies and ages, though their relationships are not fully understood. Plutonic rocks, forming widespread outcrops, dominate the Antarctic Peninsula's igneous landscape, with their full extent and connectivity still not fully understood due to limited exposure and data availability. The Ellsworth Land Volcanic Group underlies parts of the southern Antarctic Peninsula and eastern Ellsworth Land. At Mount Poster, these volcanic rocks, up to 600 meters thick, and probably exceeds 2 kilometers in total thickness, yet is difficult to know. Ellsworth Land intertongues with the Sweeney Fm and is overlaid by the Latady Group, marked by intense folding, thrust faulting, and pluton intrusion during the Late Jurassic to Early Cretaceous period. The Ellsworth Land VG shows considerable alteration and metamorphism, leading to challenges with volcanic sections correlation due to variations in rock types and minor faulting, with an estimated thickness of roughly 1000 meters in the Sweeney Mountains, where is present in most peaks, where is characterized by silicic ignimbrite, featuring diverse weathering patterns and lithology dominated by feldspar-rich ignimbrite. Additionally, it contains lithic-rich sections with quartzite fragments and traces of red mudstone, along with late-stage epidote and quartz veining. Well-consolidated units exhibit distinguishable fiamme, while less consolidated ignimbrites contain flattened pumices, occasionally found alongside deformed ignimbrites. The sedimentary facies are more typically tens of metres thick, with a maximum of ~300 m black finely laminated mudstone and sandstone. Age Analyses of intracaldera ignimbrites in the Mount Poster Formation yielded an age of 183.4 ± 1.4 Ma, around the same time as volcanic activity in other regions like Karoo-Ferrar. Zircon analysis were conducted on eight samples of silicic ignimbrite spanning from the Sweeney Mountains to Lyon Nunataks, with ages ranging from 185.2 ± 1.5 Ma to 177.5 ± 2.2 Ma, while detrital zircons from sedimentary rocks at Potter Peak West indicate again 183 ± 4 Ma. These findings indicate that volcanic activity began either slightly before or at the same time as the initial non-volcanic sedimentation in the Sweeney Formation. More recently, volcanic tuffs at Mount Peterson have been dated at 181.9 + 2.4 Ma and are likely correlated to the other sections. == Paleoenvironment ==

The Toarcian Latady Basin was bracketed between the Ellsworth-Whitmore block, that was located in the Paleopacific along the Marie Byrd Land, Thurston Island, the Antarctic Peninsula and Southern Patagonia, being either islands or a peninsular landmass connected with mainland South America. The Mount Poster Formation rhyodacitic ignimbrites emplaced in an intraplate, a major silicic flare-up within the Chon Aike Province setting in southern Palmer Land, influenced heavily by upper crustal melting, being supply to both the Atoll Nunataks Formation and parts of the Latady Group. Local vulcanism was likely dominated by large-volume (Ultra-Plinian) eruptions, providing a potential rhyolitic volcanic source to nearby Transantarctic Area (ex. Mawson Formation). The Mount Poser layers suggests they were likely deposited within a Volcanic crater, indicated by similar composition, strong bonding, extensive layering, and the presence of faults and dykes around the edges that mark the boundaries of such crater, resembling units recovered in western United States and Alaska, where volcanic activity created similar landscapes. The differences seen on the layers might indicate different volcanic events from various centers, possibly forming a series of connected or nested craters. The sedimentary layers near the volcanic ones often show signs of heat damage or disturbance by the volcanics: red mudstone next to basaltic flows turns black, and disrupted bedding underlies lava bodies. Sedimentary layers mainly consist of well-sorted sandstone and siltstone with ripple patterns, suggesting deposition in freshwater, likely in a lacustrine body with associated subaerial fluvial units. Fossil plant remains indicate a terrestrial environment, with conifers dominating and suggesting a preference for volcanic-rich soil. Lacustrine layers with volcanic influence are recovered in the connected Cañadón Asfalto Formation. == Fossil content ==

The fossil palaeoassemblage is dominated by plants, suggesting a fully terrestrial or lacustrine setting, without any marine evidence. The material is dominated by wood trunks and root horizons. The leaf-based macroflora is conifer-dominated and corresponds to genera recovered in the Argentinian Cañadón Asfalto Formation, where cuticular analysis of the same taxa suggests common environmental stress. This fits also with the local foliar remains, that are consistent with growth between eruptive phases. Equisetales Pteridophyta Peltaspermales Cycadeoidopsida Coniferophyta == See also ==