136 ANTARCTIC Figure Middle Jurassic mafic sills related to the initial breakup of Gondwana, emplaced within a Triassic sedimentary sequence within the Theron Mountains, which are located in the Transantarctic Mountains leaves and fossilized stems and roots of the nowextinct glossopterid tree The rapid and virtually complete disappearance of Late Palaeozoic ice is recorded in the earliest Permian strata The Glossopteris leaves, dropped from the widespread woody deciduous tree or shrub, indicate a cool and wet rather than cold climate Following the end-Permian extinction event and the disappearance of the Glossopteris flora, the Triassic cross-bedded sandstones and mudstones were deposited by low-sinuosity rivers on a northwest-sloping plain The reversal in palaeoslope is attributed to uplift associated with a Late Permian– Early Triassic Gondwanian folding that deformed the Cape Fold Belt and also the Permian and older strata of the Ellsworth and Pensacola mountains in Antarctica The climate was mild and arid with a varied reptilian and amphibian fauna, and a flora characterized by the fossil fern known as Dicroidium Beacon sedimentation culminated in the Early Jurassic with explosive rhyolitic volcanism and volcanic debris flows, and ultimately by basaltic flows and associated intrusive rocks of the Ferrar Supergroup West Antarctica: A Collage of Crustal Blocks The basin and range topography of West Antarctica can be used to delineate five physiographically defined crustal blocks (Figure 3) that have distinctive geological features and that may have existed as distinct microplates during the Mesozoic breakup of Gondwana Haag Nunataks: Part of the East Antarctic Shield This small crustal block is situated between the southern tip of the Antarctic Peninsula and the Ellsworth Mountains It is formed entirely of Proterozoic basement amphibolites and orthogneiss of Grenvillian ages (dating to between 1176 and 1003 Ma) Although the gneisses are exposed only on three small nunataks, aeromagnetic surveys show the full extent of the block and suggest that similar Proterozoic basement may underlie part of the Weddell Sea embayment region Isotopic studies also suggest that this basement may be present beneath the neighbouring Antarctic Peninsula region The gneisses correlate with Proterozoic basement gneisses within the East Antarctic Shield and may represent a fragment of the East Antarctic Shield displaced during the breakup of Gondwana Ellsworth Whitmore Mountains: A Displaced Fragment of the Gondwanian Fold Belt The Ellsworth Mountains form a 415-km-long NNE– SSW-trending mountain range that contains the highest mountain in Antarctica The mountains are situated along the northern periphery of the crustal block of the Ellsworth–Whitmore Mountains, which represents part of a displaced terrane once situated along the palaeo-Pacific margin of Gondwana, prior to supercontinent breakup, adjacent to South Africa and the Weddell Sea coast of East Antarctica It was assembled in its present position by Late Cretaceous