scholarly journals An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism in the Central Andes, northern Chile (18-28°Lat.S)

2020 ◽  
Author(s):  
Gabriel Ureta ◽  
Károly Németh ◽  
Felipe Aguilera ◽  
Matias Vilches ◽  
Mauricio Aguilera ◽  
...  
Keyword(s):  
Magma Ascent ◽  
Chemical Compositions ◽  
Northern Chile ◽  
Volcanic Zone ◽  
Quaternary Volcanism ◽  
Groundwater Availability ◽  
The Andes ◽  
Magma Reservoirs ◽  
Strombolian Eruptions ◽  
Magmatic Processes

Monogenetic volcanism produces small eruptive volumes with short eruption history, different chemical compositions, and relatively simple conduit. The Central Volcanic Zone of the Andes is internationally known as a natural laboratory to study volcanism, where mafic and felsic products are present. In this contribution, the spectrum of architectures, range of eruptive styles, lithological features, and different magmatic processes of the mafic and felsic monogenetic Neogene to Quaternary volcanoes from the Central Volcanic Zone of the Andes in northern Chile (18°S-28°S) are described. The major volcanic activity occurred during the Pleistocene, where the most abundant activity corresponds to effusive and Strombolian eruptions. This volcanism is characterized by external (e.g., magma reservoirs or groundwater availability) and internal (e.g., magma ascent rate or interaction en-route to the surface) conditions, which determine the changes in eruptive style, lithofacies, and magmatic processes involved in the formation of monogenetic volcanoes.

scholarly journals Mantle Melting and Magmatic Processes Under La Picada Stratovolcano (CSVZ, Chile)

2019 ◽  
Vol 60 (5) ◽  
pp. 907-944 ◽  
Author(s):  
Jacqueline Vander Auwera ◽  
Olivier Namur ◽  
Adeline Dutrieux ◽  
Camilla Maya Wilkinson ◽  
Morgan Ganerød ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Geochemical Data ◽  
Upper Crust ◽  
Volcanic Zone ◽  
Nazca Plate ◽  
Southern Volcanic Zone ◽  
Magmatic Processes ◽  
Crystal Accumulation ◽  
Primary Magmas ◽  
Differentiation Trend

Abstract Where and how arc magmas are generated and differentiated are still debated and these questions are investigated in the context of part of the Andean arc (Chilean Southern Volcanic Zone) where the continental crust is thin. Results are presented for the La Picada stratovolcano (41°S) that belongs to the Central Southern Volcanic Zone (CSVZ) (38°S–41·5°S, Chile) which results from the subduction of the Nazca plate beneath the western margin of the South American continent. Forty-seven representative samples collected from different units of the volcano define a differentiation trend from basalt to basaltic andesite and dacite (50·9 to 65·6 wt % SiO2). This trend straddles the tholeiitic and calc-alkaline fields and displays a conspicuous compositional Daly Gap between 57·0 and 62·7 wt % SiO2. Interstitial, mostly dacitic, glass pockets extend the trend to 76·0 wt % SiO2. Mineral compositions and geochemical data indicate that differentiation from the basaltic parent magmas to the dacites occurred in the upper crust (∼0·2 GPa) with no sign of an intermediate fractionation stage in the lower crust. However, we have currently no precise constraint on the depth of differentiation from the primary magmas to the basaltic parent magmas. Stalling of the basaltic parent magmas in the upper crust could have been controlled by the occurrence of a major crustal discontinuity, by vapor saturation that induced volatile exsolution resulting in an increase of melt viscosity, or by both processes acting concomitantly. The observed Daly Gap thus results from upper crustal magmatic processes. Samples from both sides of the Daly Gap show contrasting textures: basalts and basaltic andesites, found as lavas, are rich in macrocrysts, whereas dacites, only observed in crosscutting dykes, are very poor in macrocrysts. Moreover, modelling of the fractional crystallization process indicates a total fractionation of 43% to reach the most evolved basaltic andesites. The Daly Gap is thus interpreted as resulting from critical crystallinity that was reached in the basaltic andesites within the main storage region, precluding eruption of more evolved lavas. Some interstitial dacitic melt was extracted from the crystal mush and emplaced as dykes, possibly connected to small dacitic domes, now eroded away. In addition to the overall differentiation trend, the basalts to basaltic andesites display variable MgO, Cr and Ni contents at a given SiO2. Crystal accumulation and high pressure fractionation fail to predict this geochemical variability which is interpreted as resulting from variable extents of fractional crystallization. Geothermobarometry using recalculated primary magmas indicates last equilibration at about 1·3–1·5 GPa and at a temperature higher than the anhydrous peridotite solidus, pointing to a potential role of decompression melting. However, because the basalts are enriched in slab components and H2O compared to N-MORB, wet melting is highly likely.

scholarly journals Volcanic precursors in light of eruption mechanisms at Vesuvius

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Roberto Scandone ◽  
Lisetta Giacomelli
Keyword(s):  
Structural Condition ◽  
Magma Ascent ◽  
Caldera Collapse ◽  
Parallel Increase ◽  
Strombolian Eruptions ◽  
Explosive Phase ◽  
The One ◽  
Effusive Eruptions ◽  
Quiescent Stage ◽  
Violent Strombolian Eruptions

<p>Vesuvius entered a quiescent stage after the eruption of March-April 1944. The eruption was not much different or larger than other before, like for example the one of 1906, but it occurred at the end of a long period during which it was observed a decreasing trend of explosivity of eruptions [Scandone et al. 2008]. The parallel increase in the frequency of slow effusive eruptions, with respect to violent strombolian eruptions, point out to a process of average slower rate of magma ascent possibly due to a progressive sealing of the ascent path of magma to the surface. The small caldera collapse following the 1944 explosive phase effectively sealed the upper conduit, and since then the volcano entered a quiescence stage that was unusual with respect to the pattern of activity of the previous 300 years when the maximum repose time had been of 7 years (after the eruption of 1906). Most of the uncertainty on the duration of the present stage and character of a future renewal of activity derives by the basic questions regarding the nature of the current repose: due to a diminished supply of magma, related with structural condition or a sealing of the upper ascent path to the surface? Possibly the variation of structural conditions caused average slower ascent rates of magma favoring its cooling in the upper part of the crust, and effectively sealing the ascent path.</p>

scholarly journals Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

2020 ◽  
Author(s):  
Finnigan Illsley-Kemp ◽  
Martha Savage ◽  
Colin Wilson ◽  
S Bannister
Keyword(s):  
New Zealand ◽  
Stress Field ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone ◽  
The North ◽  
Magma Reservoirs ◽  
Tectonic Forces ◽  
Subducting Slab

© 2019. American Geophysical Union. All Rights Reserved. We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW-SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep-rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench-parallel fast orientation, reflecting the pervasive presence of plate-bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E-W compression, oblique to the stress field in the subducting slab. The north-south variation in fore-arc stress is likely related to differing subduction-interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large-scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

Crustal seismicity associated to rpid surface uplift at Laguna del Maule Volcanic Complex, Southern Volcanic Zone of the Andes

2018 ◽  
Vol 353 ◽  
pp. 83-94 ◽  
Author(s):  
Carlos Cardona ◽  
Andrés Tassara ◽  
Fernando Gil-Cruz ◽  
Luis Lara ◽  
Sergio Morales ◽  
...  
Keyword(s):  
Volcanic Complex ◽  
Volcanic Zone ◽  
Surface Uplift ◽  
The Andes ◽  
Southern Volcanic Zone

Deformation driven magma ascent in stratified magma reservoirs: an experimental study

2021 ◽  
Author(s):  
Amy Ryan ◽  
Mark Zimmerman ◽  
Lars Hansen
Keyword(s):  
Pore Pressure ◽  
Seismic Waves ◽  
Soda Lime ◽  
High Viscosity ◽  
Magma Ascent ◽  
Campi Flegrei ◽  
Soda Lime Glass ◽  
Borosilicate Glasses ◽  
Magma Intrusion ◽  
Magma Reservoirs

&lt;p&gt;Mature volcanic systems (e.g., Yellowstone, USA; Campi Flegrei, Italy) are fed by stratified magma reservoirs &amp;#8211; small bodies of eruptible, crystal-poor silicic magma are suspended within a larger volume of non-eruptible, crystal-rich mush. Lavas erupted from these systems record geochemical evidence for long-term (10&lt;sup&gt;3&lt;/sup&gt; to 10&lt;sup&gt;5&lt;/sup&gt; years) deep storage followed by short (&lt;1 to 10&lt;sup&gt;3&lt;/sup&gt; years) residences in shallow chambers prior to eruption. Evidence for protracted magma ascent is frequently absent, suggesting deep-seated magmas rise quickly in reservoirs despite the high viscosity and low permeability of crystal-rich mushes. We hypothesize that deformation of a reservoir (by intrusion of new magma, passing seismic waves, tectonic stresses, etc.) allows low viscosity magmas to intrude high viscosity mush, creating mechanical instabilities that focus magma migration and facilitate rapid magma ascent through the reservoir.&lt;/p&gt;&lt;p&gt;To test this hypothesis, we are conducting high-temperature and high-pressure deformation experiments in a gas-medium, Paterson apparatus. Samples consist of a disk of soda lime glass (&amp;#8220;magma&amp;#8221;) stacked in series with a disk of a composite (&amp;#8220;mush&amp;#8221;) composed of borosilicate glass and fine quartz sand (44-106 &amp;#956;m). The mush has a crystal fraction of 80%. The stacked magma and mush disks are overlain by permeable ceramics. Sample assemblies are heated to 900&amp;#176;C (above the glass transition temperatures for soda lime and borosilicate glasses) and pressurized to 200 MPa confining pressure. At 900&amp;#176;C the magma viscosity is 10&lt;sup&gt;4&lt;/sup&gt; Pa s and the mush viscosity is ~10&lt;sup&gt;12&lt;/sup&gt;-10&lt;sup&gt;14&lt;/sup&gt; Pa s. Following heating and pressurization, samples either dwell at high P-T conditions for extended time or are subjected to axial compression (strain rates of 10&lt;sup&gt;-5&lt;/sup&gt;-10&lt;sup&gt;-3&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;; shortening up to 50% of the length of the mush disk) or pore pressure gradients (a pressure difference across the sample of 10-150 MPa, equivalent to 2-30 MPa/mm over the length of the mush disk). After dwelling or deformation, samples are rapidly quenched and decompressed, cut in longitudinal sections and polished. Polished samples are analyzed in an SEM to collect back-scatter electron images and compositional maps. BSE images can be used to look for melt structures (e.g., viscous channels, dikes) that form in the mush during deformation. The compositions of magma (soda lime) and mush (borosilicate) melts are different, therefore compositional maps can be used to look for their respective spatial distributions. In static experiments, no magma intrudes the mush. We expect deformation to facilitate magma intrusion and that the volume of intruding magma will increase with increasing strain rate, strain and pore pressure gradient. These experiments will shed light on the role deformation plays in instigating magma ascent in stratified magma reservoirs.&lt;/p&gt;

Two new scorpion species of genus Brachistosternus (Scorpiones: Bothriuridae) from northern Chile

Zootaxa ◽  
2007 ◽  
Vol 1623 (1) ◽  
pp. 55-68 ◽  
Author(s):  
ANDRÉS A. OJANGUREN-AFFILASTRO ◽  
PABLO AGUSTO ◽  
JAIME PIZARRO-ARAYA ◽  
CAMILO I. MATTONI
Keyword(s):  
Coastal Dunes ◽  
The Other ◽  
Northern Chile ◽  
High Altitudes ◽  
The Andes ◽  
Andes Mountain ◽  
Other Hand ◽  
Mountain Chain

Brachistosternus (Leptosternus) cepedai n. sp. and Brachistosternus (Leptosternus) coquimbo n. sp. are described from Coquimbo region, in northern Chile. Brachistosternus cepedai n. sp. occurs in coastal dunes and is closely related to Brachistosternus (L.) sciosciae Ojanguren-Affilastro, 2002. On the other hand, Brachistosternus coquimbo n. sp occurs at high altitudes in the Andes mountain chain and is related to Brachistosternus (L.) montanus Roig Alsina, 1977, and to several Andean species from Argentina and Chile. Adaptative characters of the psammophilous Br. (L.) cepedai n. sp. are discussed. 39 scorpion species are now known from Chile, ten of them occur in the Coquimbo Region, being the region with the more diverse scorpion fauna in the country.

Crystallization trend of titanomagnetites in an alkali basalt from Saint-Clément (Massif Central, France)

1973 ◽  
Vol 39 (304) ◽  
pp. 474-481 ◽  
Author(s):  
M. Prévot ◽  
J. Mergoil
Keyword(s):  
Magma Ascent ◽  
Chemical Compositions ◽  
Common Belief ◽  
Massif Central ◽  
X Ray ◽  
Show Evidence ◽  
Ti Content ◽  
Crystallization Stage ◽  
Temperature Crystallization ◽  
Low Temperature Process

SummaryThree generations of homogeneous titanomagnetite in a hawaiite from Saint-Clément may be defined by differences in size, habit, or reflectance, and are believed to correspond to different crystallization stages of the lava. Chemical compositions were determined by electron microprobe, and by X-ray and thermomagnetic methods.Larger crystals are of intratelluric origin and occur either as inclusions in phenocrysts of early clinopyroxene (generation 1) or separately in the groundmass (generation 2); in the latter case, they always show evidence of resorption. Post-eruptive titanomagnetite (generation 3) is smaller and so highly oxidized that it is better termed titanomaghemite. Since the maghemitization, which is a low temperature process, alters the metallic ratios (especially the Fe/Ti ratio) the metallic contents at the time of the high-temperature crystallization are exactly known only for the intratelluric titanomagnetites.As intratelluric crystallization proceeds Ti content increases greatly (5 to 14%); Mn also increases (but slightly), A1 and Mg decrease, while results for Cr are inconclusive. Apparently these changes go on until the post-eruptive crystallization stage.The titanium trend is contrary to common belief. However, it is in accordance with predictions from the Fe-Ti-O system and may be explained by a decrease in oxygen fugacity during magma ascent.

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