Kamafugitic diatremes: their textures and field relationships with examples from the Goiás alkaline province, Brazil

Junqueira-Brod, Tereza Cristina; Gaspar, José Carlos; Brod, José Affonso; Kafino, Camilla Vasconcelos

doi:10.1016/j.jsames.2004.11.002

Cited by 28 publications

(10 citation statements)

References 45 publications

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“…The occurrence of enough water at specific temperatures in the cloud can promote ash aggregation and the formation of accretionary lapilli. The term accretionary lapilli has been used to describe several lithologies over the past decades such as: unstructured aggregates [e.g., Hayakawa, 1990;Rosi, 1992;Sisson, 1995;Watanabe et al, 1999;Trusdell et al, 2005], multiple concentriclaminated aggregates [e.g., Cole and Scarpati, 1993;Junqueira-Brod et al, 2005;Edgar et al, 2007], aggregates with a single fine-grained coating around a massive ash core [Branney, 1991] and ash-coated lithic clasts [Bednarz and Schmincke, 1990;Palladino et al, 2001]. Schumacher and Schmincke [1991] and [1995] distinguish two different types of lapilli, based upon their internal structure: rim-type and core-type.…”

Section: Introductionmentioning

confidence: 99%

Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli)

Morgavi

Valentini²,

Porreca³

et al. 2019

Annals of Geophysics

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The Secche di Lazzaro formation (ca. 6.2-7 kys BP) is a phreatomagmatic deposit situated in the southwestern part of the island of Stromboli (Aeolian Archipelago, Italy). The volcanic sequence is comprised of three main units. In the lower unit accretionary lapilli are particularly abundant and are characterized by strong cementation between the particles and an uncommon resistance to breakage. To understand the processes behind the formation of the Secche di Lazzaro (SdL) accretionary lapilli a multi-analytical approach was used on the lapilli Aggregate Tuff (AT), and on single Accretionary Lapilli (AL). We carried out granulometric analysis, Field Emission-Scanning Electron Microscopy (FE-SEM), Electron Microprobe Analysis (EMPA), X-ray powder diffraction (XRPD) and 3D imaging by X-ray micro-tomography (X-mCT). The granulometric data show that most particles in the AT have a diameter equal to Φ-1 corresponding to 2 mm. The EMPA, FE-SEM and XRPD analyses reveal the presence of different mineral phases, mainly plagioclase, K-feldspar, halite, and clinopyroxene, together with volcanic glass. From the X-mCT analysis, we constrained the particle distribution and estimated the porosity of AL. The results of the FE-SEM images provided the chemical distribution within individual lapilli allowing the identification of rim and core zoning as well as the presence of halite located both on the border of single lapilli and on the juncture between different lapilli. Moreover, halite occurs among different aggregates in single AL, thus acting as a binding agent, as well as within rim pores. The results of this work shed new light into the formation of accretionary lapilli in phreatomagmatic eruption a t volcanic island involving marine water.

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Section: Introductionmentioning

confidence: 99%

Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli)

Morgavi

Valentini²,

Porreca³

et al. 2019

Annals of Geophysics

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“…In some cases, it has been observed that the rim is a dense mass of microphenocrysts with a concentric flow texture set in devitrified glassy matrix, almost entirely transformed into a mixture of clay minerals (Junqueira-Brod et al, 2005). But, the original character (coherent or originated by agglutination/coalescence of magma droplets) of this devitrified matrix remains unknown.…”

Section: Introductionmentioning

confidence: 99%

Silicate glass micro and nanospherules generated in explosive eruptions of ultrabasic magmas: Implications for the origin of pelletal lapilli

Sánchez

Sarrionandia

Aróstegui

et al. 2015

Journal of Volcanology and Geothermal Research

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“…Some accounts of ash aggregates discriminate between structureless and concentriclaminated aggregates, but others have used the term "accretionary lapilli" to describe variously, massive ash pellets (e.g., Hayakawa, 1990;Rosi, 1992;Sisson, 1995;Watanabe et al, 1999;Trusdell et al, 2005), concentriclaminated aggregates (e.g., Cole and Scarpati, 1993;Edgar et al, 2002;Junqueira-Brod et al, 2005), aggregates with a single fi ne-grained coating around a massive core (Branney, 1991), and ash-coated clasts (Bednarz and Schmincke, 1990;Palladino et al, 2001). Although classifi cations have been proposed (e.g., Reimer, 1983;Schumacher and Schmincke, 1991;Thordarson, 2004), terminological usage remains inconsistent.…”

Section: Introductionmentioning

confidence: 99%

Origin of accretionary lapilli within ground-hugging density currents: Evidence from pyroclastic couplets on Tenerife

Brown

Branney

Maher

et al. 2009

Geological Society of America Bulletin

121

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Aggregation of airborne particles is an important way in which the atmosphere is cleansed of fi ne dust particles, such as following explosive eruptions and meteorite impacts. We identify successive stages in the growth history of particle aggregates based upon well-preserved ash aggregate-bearing pyroclastic layers on Tenerife. The layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper , widespread coignimbrite ash-fall layer. The upper part of each ignimbrite contains whole and fragmented concentric-laminated accretionary lapilli, whereas the overlying coignimbrite ash-fall layer lacks accretionary lapilli and is composed of frameworksupported smaller and nonlaminated ash pellets , sometimes slightly deformed or partly disaggregated. The pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer. These fi eld relations are repeated numerous times in several different successions, and they indicate that ash pellets, not accretionary lapilli, form within the coignimbrite ash plumes. Some pellets fell directly to the ground, producing coignimbrite ash-fall layers, but others settled into pyroclastic density currents, where they accreted successive concentric laminations of fi ne ash as they circulated through the variously turbulent levels of the stratifi ed current, and heat of the lower part of the current dried and partly lithifi ed them into brittle accretionary lapilli. The fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli. Numerous ignimbrite veneers on Tenerife have the form of ash layers, a few centimeters thick, that drape topography and locally contain matrix-supported accretionary lapilli. Most volcanoes lack laterally continuous fi eld exposure, and such accretionary lapilli-bearing layers might be mistaken for ash-fall deposits. We highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits, for example , during hazard assessments.

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Kamafugitic diatremes: their textures and field relationships with examples from the Goiás alkaline province, Brazil

Cited by 28 publications

References 45 publications

Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli)

Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli)

Silicate glass micro and nanospherules generated in explosive eruptions of ultrabasic magmas: Implications for the origin of pelletal lapilli

Origin of accretionary lapilli within ground-hugging density currents: Evidence from pyroclastic couplets on Tenerife

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