G. Groppelli and L. Viereck-Goette (eds.): Stratigraphy and geology of volcanic areas. The Geological Society of America Special Paper, 2010, 464 pages, ISBN 978-0-8137-2464-5 (pbk)

Abstract

This 291-page long volume consists of a collection of 14 articles that are an outcome of a scientific session “devoted to the methodology in field mapping of volcanic areas” held at the 32nd International Geological Congress (IGC Florence, 2004). It also includes an accompanying CD-ROM not available to the reviewer. Field-work based “hard-rock geologists” mapping in volcanic areas are invariably faced with the problem of choosing how to establish map units and their contacts and then display them. In the early 1970s of the last century, when I was a young geologist myself, enrolled in mineral exploration and geological mapping in the Neogene volcanic areas in the East Carpathians (Romania), the major issue was to establish effective rock map divisions in a petrographically quite monotonous volcanic field, so that amphibole–pyroxene andesites were distinguished from pyroxene–amphibole andesites, and hypersthene-dominant andesites from augitedominant ones within the larger class of pyroxene andesites. Moreover, rocks containing opacitized and/or resorbed amphiboles were further distinguished, and the presence of accessory quartz crystals was a sufficient feature to map “quartz andesites”, even though the quartz was xenocrystic in origin. Textural criteria (e.g., separating “aphanitic” rocks from the “normal” porphyritic ones) completed the scheme. As whole-rock chemical analyses became accessible, petrochemical criteria were introduced to supplement the petrographical ones. The resulting maps, looking like mosaics of variously colored patches representing “petrotypes” of volcanic rocks, were frustratingly irrelevant from a volcanological point of view; volcanic structures and edifices were hardly seen in such maps. Later, in the 1980s, we introduced genetic criteria among the mapping tools, so that belonging to a certain volcanic structure and the genetic type of the volcanic products were both considered higher-order map entities than those based on precise petrographic features of the mappable rock units. The maps became more volcanologically relevant. Interestingly, the possible Cover used with permission; © 2010 Geological Society of America.