Ignimbrite


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ignimbrite

[′ig·nəm‚brīt]
(petrology)
A rock deposit (welded or not) resulting from one or more ground-hugging flows of hot volcanic fragments and particles commonly produced during explosive eruptions (pyroclastic flows and tephra fall). Most ignimbrites have a sheet-like shape, cover many thousands of square kilometers, and have chemical compositions that span the range commonly exhibited by igneous rocks (basaltic to rhyolitic). Also known as ash-flow tuff; pyroclastic-flow deposit; welded tuff.

Ignimbrite

 

(or welded tuff), fragmental volcanic rocks with a tuff body consisting of lava and ash, with comparatively large inclusions of dark glass embedded in the body. In the marginal zones the glass and tuff usually merge so that the rocks appear to be welded. Against the gray background of the rock the glass inclusions appear either as irregular flakes and sparks or as lenses arranged in a subparallel manner which by their shape resemble tongues of flame. For this reason they are frequently called fiamme from the Italian word for flame. The formation of ignim-brite is explained by deposition from glowing ash clouds that occur during Katmai-type eruptions. Ignimbrite is most often found among persilicic volcanic rocks (rhyolites, trachytes, da-cites, and more rarely andesites) and occurs in the form of horizontal beds in volcanogenic masses. Ignimbrites are characteristic for many of the world’s volcanic regions.

References in periodicals archive ?
2 m depth, two of these AETLs (11 and 12) are installed in the base of the Taupo Ignimbrite, whereas AETL 10 is installed into Palaeosol layer 1 (Fig.
Both anomalies are beneath ignimbrite rocks which blanket this area and mask any geochemical signature at surface.
So to ignimbrite, a word of apparently Latin origin that means "fiery rock dust cloud.
Both factors shape the landscape into two main morphological units: high relief zone with steep slopes (made up of trachy-rhyolitic suite) and the ignimbrite escarpment forming the shelf zone.
Radiometric dating of ignimbrite from Inner Mongolia provides no indication of a post-Middle Jurassic age for the Daohugou beds.
Alkali-ion exchange during devitrification and hydration of glasses in ignimbrite cooling-units.
Ignimbrite sheets of similar composition above the sill suggest that the granite was emplaced beneath cover rocks no more than 1 km thick.
The Western Islands is also the likely source of four of the ignimbrite and andesite gabagaba from Erub.
Importance: At Tombstone, the large magnetic high revealed by the newly retrieved magnetic map represents the large body of solidified (but previously molten) granite (magma), which is the subsurface continuation of the exposed Schieffelin granodiorite (granite body named for the discoverer of the district, Ed Schieffelin), and other associated intrusives, which fed the explosive caldera and the surface (sub aerial) deposition of the Uncle Sam ignimbrite (welded tuff).
Between 2008 and 2010, we carried out survey and excavations along the course of the Sora River (a narrow valley defined by two parallel outcrops of ignimbrite rocks) with the goal of identifying locations with stratified deposits for reconstructing the regional sequence of human occupation (Albarracin-Jordan & Cap riles 2011; Capriles & Albarracin-Jordan 2013).