The Geology of the South Shetland Islands
Description / Table of Contents:
King George Island is almost entirely composed of igneous rocks; four volcanic episodes and one intrusive phase are represented. The oldest volcanics, which are believed to be Upper Jurassic in age, form a calc-alkaline suite with an andesite-rhyolite association. Recent field investigations indicate there is no evidence for the extensive areas of sedimentary rocks previously recorded. The presence of regionally metamorphosed xenoliths in the Jurassic Volcanos indicates that they rest upon a Basement Complex. The early Tertiary Andean Intrusive Suite, which is petrographically similar to that of Graham Land, forms an axial core to the island. The majority of the Jurassic Volcanics have been metasomatized by these intrusions and the significance of the resultant secondary minerals is discussed. A linear pattern of Tertiary and Quaternary vulcanicity has been demonstrated and lavas of three distinct episodes are described. One of these volcanic groups is of unknown age, whilst the others are known to be Middle Miocene and Recent. The lavas include dominant pyroxene-andesites, basaltic andesites, olivine-basalts and rare trachyandesites. The petrogenesis of the volcanic site is discussed and crystal separation is suggested as the most important factor in their evolution. A geological map, compiled from all the available rock collections and field notes, shows the distribution of the volcanic and intrusive groups.
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28 S. : Ill., Kt.