The Petrography of the Austral or Tubuai Islands (Sourthern Pacific)
1927; Geological Society of London; Volume: 83; Issue: 1-5 Linguagem: Inglês
10.1144/gsl.jgs.1927.083.01-05.12
ISSN2058-105X
AutoresL. J. Chubb, W. Campbell Smith,
Tópico(s)Geology and Paleoclimatology Research
ResumoI. Introduction. The following account of the petrography of the islands of Rapa and Rurutu in the Austral Group is based on the collections made by one of us in April and May 1925 during the St. George Expedition to the Southern Pacific. A general account of the geology of these islands has already been given by one of us (Chubb, 1927), and references to previous literature will be found in that paper. In Rapa the district most thoroughly worked was that between Mount Vairu and Mount Taga and the head of the harbour, though collections were made from many other parts of the island. In Rurutu only the area between Moerai Bay and the districts of u and Avera was explored. The few occurrences of sedimentary rocks have been described in the paper already mentioned. A brief account will be given of the pyroclastic rocks which were found at a few localities, after which the small intrusions and the volcanic rocks, forming the main bulk of the island, will be described in detail. The volcanic rocks are often deeply weathered to a red clay, especially in the higher parts of Rurutu, where no expesures of fresh rock were found above 600 feet. Elsewhere, however, exposures of unweathered rocks are fairly common, and the rocks selected for description are remarkably fresh and very suitable for chemical and petrographical study. II. Rapa Pyroclastic Rocks. A brown-drab basalt-breccia [840] containing numerous crystals of augite (5 mm. long) and small olivines, in a
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