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 ?
Initial extension resulted in a series of depocenters orthogonally and obliquely oriented respect to the margin, filled with volcanoclastic and pyroclastic deposits associated with lava flows, ignimbrites and other related products (Franzese and Spalletti, 2001).
and Furuya, T.: 2004, Using an airborne laser scanner for the identification of shallow landslides and susceptibility assessment in an area of ignimbrite overlain by permeable pyroclastics.
OLDER RUIZ RIO CLARO IGNIMBRITE 0.089 +/- (0.8-0.2 Ma) 0.007 Ma DESTRUCTIVE PHASE (PF) EL CISNE LAVAS PIRANA STAGE 0.24-0.15 Ma EARLY CONES LAVAS, LOW K SUITE EARLY CONE LAVAS 0.4+/-0,1 Ma SANTA ISABEL LAVAS 0.76 +/-0.0S Ma CONSTRUCTIVE PHASE (LAVA FLOWS) 0.76+/-0.2 Ma ANCESTRAL RUIZ DESTRUCTIVE PHASE (PF?) 0.97-0.77 Ma (1,8-0.8 Ma) CONSTRUCTIVE PHASE 1.8-0.97 Ma (LAVA FLOWS AND DOMES) PRL VOLCAN ICLASTIC BASAME NT: PRE-RUIZ LAVAS DESTRUCTIVE PHASE 5 1.5 Ma {L8 +/- 0.1 Ma)
The 322 Ka Tirito Tuff: Stratigraphy, Geochronology and Mechanism of Deposition of the Largest and Most Recent Ignimbrite in the Valley Central, Costa Rica.--Bull.
Volcanic centres have not been widely recognised, with the exception of the Glendinning Ignimbrite, which contains abundant large locally derived clasts near the base (Simpson 1998).
B., 2006: The 322 ka Tiribi Tuff: stratigraphy, geochronology and mechanisms of deposition of the largest and most recent ignimbrite in Valle Central, Costa Rica.--Bull.
In the upper part of the old pallid zone, which can be brilliantly white, there remain only some quartz crystals from the original ignimbrite parent material.
PEREZ, W., ALVARADO, G.E.& GANS, P.B., 2006: The 322 kaTiribi Tuff: stratigraphy, geochrology and mechanisms of deposition of the largest and most recent ignimbrite in the Valle Central, Costa Rica.--Bull.
Key words: caldera, eruption unit, ignimbrite, domes, magmatic eruption, phreatomagmatic eruption, pyroclastic flow, pyroclastic surge.
The last known eruption in Panama occurred 400500 years ago from Volcan Baru (Sherrod et al., 2007), while the most recent eruption from La Yeguada occurred approximately 32,000 years ago, and at El Valle the El Hato Ignimbrite Flow is known to be younger than 56,000 years based on stratigraphy, but likely is Holocene (<10,000 years) based on the fresh morphology in a tropical area.
COOK, E.F., 1959: Ignimbrite bibliography.--30 pags., Idaho Bur.