10 research outputs found
Labelle en quête d'identité. Aménager un noyau villageois attractif
Affiche de projet terminal, baccalauréat en Urbanisme. Institut d'urbanisme, Université de Montréal
Spatial Visualization of Geochemical Data: Application to the Chichinautzin Volcanic Field, Mexico
The presence of spatial magma heterogeneities in volcanic monogenetic fields is a major observation discussed as well synthesized for worldwide volcanic fields. Magma heterogeneities still have not been visualized in the form of detailed spatial analyst tools, which could further help structuring works of geological mapping, volcanic hazard, and geoheritage evaluations. Here we synthetized 32 published datasets with a novel geochemical mapping model inspired by sub-disciplines of geomatic in one of the most documented monogenetic fields on earth: the Chichinautzin Volcanic Field (CVF) in Mexico. The volcanic units from CVF are covering the 2500Â km2 area, and its neighbor stratovolcanoes are bordering the limit of most volcanic centers (Popocatepetl, Iztaccihuatl, and Nevado de Toluca). The results illustrate polygons and point map symbols from geochemical markers such as Alkalis vs SiO2, Sr/Y, and Ba/Nb. The geochemical heterogeneity of the CVF monogenetic bodies decreases as it approaches the Popocatepetl-Iztaccihuatl stratovolcanoes. This alignment is not observed in the occidental CVF portion near the flank of Nevado de Toluca, but geochemical anomalies associated to markers of continental crust interaction such as Sr/Y follow elongated patterns that are not strictly following structural lines and faults mapped on surface
Crustal controls on light noble gas isotope variability along the Andean Volcanic Arc
This study combines new noble gas data from fluid inclusions in minerals from Sabancaya, Ubinas, and El Misti (CVZ, Peru) and Villarica (South Chile, SVZ) with a revised noble gas compilation in the Andes, to identify systematic along arc variations in helium isotope compositions. We find 3He/4He ratios varying from 8.8 RA (Colombia) to 7.4 RA (Ecuador) within the NVZ, and only as high as 6.4 RA in the CVZ (RA is the atmospheric 3He/4He ratio of 1.39 × 10–6). These distinct isotope compositions cannot be explained by variable radiogenic 4He production via slab fluid transport of U and Th in the mantle wedge, since both NVZ and CVZ share similar slab sediment inputs (Th/La ≈ 0.08–0.13). Instead, the progressively more radiogenic 3He/4He signatures in Ecuador and Peru reflect 4He addition upon magma ascent/storage in the crust, this being especially thick in Peru (>70 km) and Ecuador (>50 km) relative to Colombia (∼30–45 km). The intermediate compositions in the North (8.0 RA) and South (7.9 RA) Chile, both high sediment flux margins, mostly reflect a more efficient delivery of radiogenic He in the wedge from the subducted (U-Th-rich) terrigenous sediments. Our results bring strong evidence for the major role played by crustal processes in governing noble gas compositions along continental arcs
Geochemistry and volatile content of magmas feeding explosive eruptions at Telica volcano (Nicaragua)
Telica volcano, in north-west Nicaragua, is a young stratovolcano of intermediate magma composition producing
frequent Vulcanian to phreatic explosive eruptions. The Telica stratigraphic record also includes examples of
(pre)historic sub-Plinian activity. To refine our knowledge of this very active volcano, weanalyzedmajor element
composition and volatile content of melt inclusions fromsomestratigraphically significant Telica tephra deposits.
These include: (1) the Scoria Telica Superior (STS) deposit (2000 to 200 years Before Present; Volcanic Explosive
Index, VEI, of 2–3) and (2) pyroclasts from the post-1970s eruptive cycle (1982; 2011). Based on measurements
with nanoscale secondary ion mass spectrometry, olivine-hosted (forsterite [Fo] N 80) glass inclusions fall into 2
distinct clusters: a group of H2O-rich (1.8–5.2 wt%) inclusions, similar to those of nearby Cerro Negro volcano,
and a second group of CO2-rich (360–1700 μg/g CO2) inclusions (Nejapa, Granada). Model calculations show
that CO2 dominates the equilibrium magmatic vapor phase in the majority of the primitive inclusions (XCO2 N
0.62–0.95). CO2, sulfur (generally b2000 μg/g) and H2O are lost to the vapor phase during deep decompression
(P N 400 MPa) and early crystallization of magmas. Chlorine exhibits a wide concentration range (400–2300
μg/g) in primitive olivine-entrapped melts (likely suggesting variable source heterogeneity) and is typically
enriched in the most differentiated melts (1000–3000 μg/g). Primitive, volatile-rich olivine-hosted melt inclusions
(entrapment pressures, 5–15 km depth) are exclusively found in the largest-scale Telica eruptions (exemplified
by STS in our study). These eruptions are thus tentatively explained as due to injection of deep CO2-rich
mafic magma into the shallow crustal plumbing system. More recent (post-1970), milder (VEI 1–2) eruptions,
instead, do only exhibit evidence for low-pressure (P b 50–60 MPa), volatile-poor (H2O b 0.3–1.7 wt%; CO2
b 23–308 μg/g) magmatic conditions. These are manifested as andesitic magmas, recording multiple magma
mixing events, in pyroxene inclusions.Wepropose that post-1970s eruptions are possibly related to the high viscosity
of resident magma in shallow plumbing system (b2.4 km), due to crystallization and degassing
Volatile contents of mafic-to-intermediate magmas at San Cristóbal volcano in Nicaragua
San Cristóbal volcano in northwest Nicaragua is one of the most active basaltic–andesitic stratovolcanoes of the
Central American Volcanic Arc (CAVA). Here we provide novel constraints on the volcano's magmatic plumbing
system, by presenting the first direct measurements of major volatile contents in mafic-to-intermediate glass
inclusions from Holocene and historic-present volcanic activity. Olivine-hosted (forsterite [Fo] b80; Fob80)
glass inclusions from Holocene tephra layers contain moderate amounts of H2O (0.1–3.3 wt%) and S and Cl up
to 2500 μg/g, and define the mafic (basaltic) endmember component. Historic-present scoriae and tephra layers
exhibit more-evolved olivines (Fo69–72) that contain distinctly lower volatile contents (0.1–2.2 wt% H2O,
760–1675 μg/g S, and 1021–1970 μg/g Cl), and represent a more-evolved basaltic–andesitic magma. All glass
inclusions are relatively poor in CO2, with contents reaching 527 μg/g (as measured by nanoscale secondary
ion mass spectrometry), suggesting pre- to postentrapment CO2 loss to a magmatic vapor. We use results of
Raman spectroscopy obtained in a population of small (b50 μm) inclusions with CO2-bearing shrinkage bubbles
(3–12 μm) to correct for postentrapment CO2 loss to bubbles, and to estimate the original minimumCO2 content
in San Cristóbal parental melts at ~1889 μg/g, which is consistent with the less-CO2-degassed melt inclusions
(MI) (N1500 μg/g) found in Nicaragua at Cerro Negro, Nejapa, and Granada. Models of H2O and CO2 solubilities
constrain the degassing pathway of magmas up to 425 MPa (~16 km depth), which includes a deep CO2
degassing step (only partially preserved in the MI record), followed by coupled degassing of H2O and S plus
crystal fractionation at magma volatile saturation pressures from ∼195 to b10 MPa. The variation in volatile
contents from San Cristóbal MI is interpreted to reflect (1) Holocene eruptive cycles characterized by the rapid
emplacement of basaltic magma batches, saturated in volatiles, at depths of 3.8–7.4 km, and (2) the ascent of
more-differentiated and cogenetic volatile-poor basaltic andesites during historic-present eruptions, having
longer residence times in the shallowest (b3.4 km) and hence coolest regions of the magmatic plumbing system.
We also report the first measurements of the compositions of noble-gas isotopes (He, Ne, and Ar) in fluid inclusions
in olivine and pyroxene crystals. While the measured 40Ar/36Ar ratios (300–304) and 4He/20Ne ratios
(9–373) indicate some degree of air contamination, the 3He/4He ratios (7.01–7.20 Ra) support a common mantle
source for Holocene basalts and historic-present basaltic andesites. The magmatic source is interpreted as generated
by a primitive MORB-like mantle, that is influenced to variable extents by distinct slab fluid components for
basalts (Ba/La ~ 76 and U/Th ~ 0.8) and basaltic andesites (Ba/La ~ 86 and U/Th ~ 1.0) in addition to effects of
magma differentiation. These values for the geochemical markers are particularly high, and their correlation
with strong plume CO2/S ratios from San Cristóbal is highly consistent with volatile recycling at the CAVA
subduction zone, where sediment involvement in mantle fluids influences the typical relatively C-rich signature
of volcanic gases in Nicaragua.Published131-1481V. Storia eruttivaJCR Journa
Cost Analysis of Noninvasive Helmet Ventilation Compared with Use of Noninvasive Face Mask in ARDS
Intensive care unit (ICU) costs have doubled since 2000, totalling 108 billion dollars per year. Acute respiratory distress syndrome (ARDS) has a prevalence of 10.4% and a 28-day mortality of 34.8%. Noninvasive ventilation (NIV) is used in up to 30% of cases. A recent randomized controlled trial by Patel et al. (2016) showed lower intubation rates and 90-day mortality when comparing helmet to face mask NIV in ARDS. The population in the Patel et al. trial was used for cost analysis in this study. Projections of cost savings showed a decrease in ICU costs by 3103 per patient, along with a 43.3% absolute reduction in intubation rates. Sensitivity analysis showed consistent cost reductions. Projected annual cost savings, assuming the current prevalence of ARDS, were 291682 in hospital costs. At a national level, using yearly incidence of ARDS cases in American ICUs, this represents $449 million in savings. Helmet NIV, compared to face mask NIV, in nonintubated patients with ARDS, reduces ICU and hospital direct-variable costs along with intubation rates, LOS, and mortality. A large-scale cost-effectiveness analysis is needed to validate the findings