Laf-105
Item
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Title
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Laf-105
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Description
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This is a pyroclastic rock from violent eruptions causing fragments to become welded within the rock. It contains xenoliths inclusions of country rock. The black material contained within the rock is compressed pumice, called fiamme. Pumice forms from rapid cooling of explosive volcanic eruptions and the xenoliths also contained within the rock are due to continued increased temperature and overlying pressure. The black material in thin section represents volcanic glass from the compacted pumice. This is typical to violent eruptions and quick cooling of generally silicic rich magmas. There are visible grains in thin section of plagioclase that displays cracks due to abrupt release of overlying pressure and rapid decrease in temperature, something characteristic to a quick eruption on a continental margin. This rock is called a welded tuff and occurs close to the eruption vent of a volcano where overlying sediment can cause pressure to increase and compress the fragments. This makes sense because as the oceanic plate subducted and volcanoes emerged on the continental plate volcanic eruptions occur and this welded tuff would be located close to the slope of one of these continental volcanoes.
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Subject
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Rocks from Convergent Continental-Oceanic Tectonic Margins
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Creator
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Ryan Sanders
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Source
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Lafayette College Geology Department
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Date
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4/9/15
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Rights
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Lafayette College Geology Department
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Identifier
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Laf-105
