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Title: Geology of Volcan Las Navajas, a pleistocene trachyte/peralkaline rhyolite volcanic center in Nayarit, Mexico

Volcan Las Navajas, located in the northwestern portion of the Mexican Volcanic Belt has produced a sequence of volcanic rocks with compositions in marked contrast to the predominantly calc-alkaline volcanoes which predominate in this part of Mexico. The oldest exposed lavas consist of trachytes with 63% SiO/sub 2/, 6% FeO*, and 500 ppm Zr along with comenditic rhyolites with 68% SiO/sub 2/, 5% FeO*, 800 ppm Zr, and an agpaitic index of 1.0. These lavas were followed by the eruption of a comenditic ash-flow tuff and the formation of a caldera 2.7 km in diameter. This caldera was subsequently filled by eruptions of pantelleritic rhyolite obsidian lava flows with 72% SiO/sub 2/, 8% FeO*, 1100 ppm Zr, and an agpaitic index of 1.5 to 1.9. A second caldera was then formed which is offset to the south of the main eruptive vents for previous eruptions. This younger caldera has a diameter of about 4.8 km and its southern walls have been covered by calc-alkaline andesitic lavas erupted from nearby Sanganguey volcano. Volcanoclastic sediments in the floor of the younger caldera have been tilted and faulted in a manner suggestive of late stage resurgence. Subsequent eruptions within the caldera, however, havemore » been restricted to calc-alkaline andesites. Tectonically, the area in which this volcano occurs appears to have been undergoing a crustal rifting event since the Pliocene. The occurrence of these peralkaline rocks lends further support to such a hypothesis.« less
Authors:
;
Publication Date:
OSTI Identifier:
6458495
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Resource Relation:
Journal Name: Geol. Soc. Am., Abstr. Programs; (United States); Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Research Org:
Tulane Univ., New Orleans, LA (USA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; MEXICO; VOLCANIC REGIONS; RHYOLITES; CHEMICAL COMPOSITION; TRACHYTES; GEOLOGIC HISTORY; CALDERAS; GEOCHEMISTRY; GEOLOGY; LAVA; PLEISTOCENE EPOCH; VOLCANISM; CENOZOIC ERA; CHEMISTRY; DEVELOPING COUNTRIES; GEOLOGIC AGES; IGNEOUS ROCKS; LATIN AMERICA; NORTH AMERICA; QUATERNARY PERIOD; ROCKS; VOLCANIC ROCKS 580100* -- Geology & Hydrology-- (-1989); 580400 -- Geochemistry-- (-1989)