Cumulate fragments in silicic ignimbrites: The case of the Snake River Plain Ben S. Ellis et al., Institute for Geochemistry and Petrology, ETH Zurich, NW Clausiusstrasse 25, 8092 Zurich, Switzerland. Published online 31 Mar. 2014; http://dx.doi.org/10.1130/G35399.1.
The Snake River Plain of southern Idaho contains a record of the early volcanism from the Yellowstone province in the form of voluminous rhyolitic ignimbrites and lavas. Within these deposits, crystals occur both as single, discrete grains ("phenocrysts") surrounded by melt and as aggregates of many individual crystals. Mineral chemistry indicates the presence of several populations, found both in phenocrysts and in the crystal aggregates. Hence, it appears that these large volcanic eruptions are the results of the amalgamation of multiple melt lenses during eruption. In order to effectively segregate melt batches prior to eruption and insulate them, rheologically strong and warm barriers are necessary. Ben S. Ellis and colleagues suggest that these "hot walls" are generated by melt removal from crystal-rich regions of the reservoirs. The melt then pools in individual, but nearby lenses, which co-erupt. The crystal aggregates represent fragments torn from the walls during eruption.
Neoproterozoic oceanic crust remnants in northeast Brazil
Fabrcio Caxito et al., Instituto de Geocincias, Universidade Federal de Minas Gerais, Belo Horizonte 31270-901, Brazil; and Geotop, Universit du Qubec Montral, Montral H3C 3P8, Canada. Published online 31 Mar. 2014;
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Geological Society of America