scholarly journals Time-evolving surface and subsurface signatures of Quaternary volcanism in the Cascades arc

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1088-1093
Author(s):  
Daniel O’Hara ◽  
Leif Karlstrom ◽  
David W. Ramsey
Keyword(s):  
Cascade Range ◽  
Magma Ascent ◽  
Upper Crust ◽  
Western North America ◽  
Quaternary Volcanism ◽  
Subsurface Structures ◽  
Digital Elevation ◽  
Crustal Structures ◽  
Spatial Focusing ◽  
Scale Surface

Abstract Increased resolution of data constraining topography and crustal structures provides new quantitative ways to assess province-scale surface-subsurface connections beneath volcanoes. We used a database of mapped vents to extract edifices with known epoch ages from digital elevation models (DEMs) in the Cascades arc (western North America), deriving volumes that likely represent ∼50% of total Quaternary eruptive output. Edifice volumes and spatial vent density correlate with diverse geophysical data that fingerprint magmatic influence in the upper crust. Variations in subsurface structures consistent with volcanism are common beneath Quaternary vents throughout the arc, but they are more strongly associated with younger vents. Geophysical magmatic signatures increase in the central and southern Cascade Range (Cascades), where eruptive output is largest and vents are closely spaced. Vents and correlated crustal structures, as well as temporal transitions in the degree of spatially localized versus distributed eruptions, define centers with lateral extents of ∼100 km throughout the arc, suggesting a time-evolving spatial focusing of magma ascent.

scholarly journals A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

2019 ◽  
Author(s):  
Thomas M. Belgrano ◽  
Larryn W. Diamond ◽  
Yves Vogt ◽  
Andrea R. Biedermann ◽  
Samuel A. Gilgen ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Sedimentary Cover ◽  
Phase 1 ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Magma Ascent ◽  
Upper Crust ◽  
Vms Deposits ◽  
Geochemical Analyses ◽  
Semail Ophiolite

Abstract. Recent studies have revealed genetic similarities between Tethyan ophiolites and oceanic proto-arc sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction-initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in submarine fore-arcs. In contrast, the Semail ophiolite, in which the 3–5 km thick upper-crustal succession is exposed in an oblique cross-section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the protoarc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulphide (VMS) deposits that they host, we have re-mapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses and geophysical interpretations with pre-existing geological maps. By linking the major element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes) through to axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley) and finally boninites (Boninitic Alley). Geotimes (Phase 1) axial dykes and lavas make up ~55 vol% of the Semail upper crust, whereas post-axial (Phase 2) lavas constitute the remaining ~ 45 vol % and ubiquitously cover the underlying axial crust. The Semail boninites occur as discontinuous accumulations up to 2 km thick at the top of the sequence and constitute ~ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

Inferences of deviatoric stress in actively deforming belts from simple physical models

1991 ◽  
Vol 337 (1645) ◽  
pp. 151-164 ◽  
Keyword(s):  
Unit Length ◽  
Physical Models ◽  
Shear Stresses ◽  
Upper Crust ◽  
Western North America ◽  
The Andes ◽  
Average Shear ◽  
Tectonic Style ◽  
Relationship Of ◽  
The Relationship

Observations of temperatures and heat flux near major thrust zones indicate that in their deep levels shear stresses may exceed 50-100 MPa. Within strike-slip zones shear stresses in the lower lithosphere may also approach 50-100 MPa, though shear stresses in the upper crust of those regions are probably much lower. The relationship of tectonic style to surface elevation in the Andes and Tibet yields an estimate of about 5 x 10 12 N m -1 for the force per unit length required to deform the lithosphere of these regions. This force per unit length is equivalent to an average shear stress of about 25 MPa through a lithosphere 100 km thick. The width-to-length ratios of active belts are consistent with deformation determined by the creep of the lower lithosphere rather than by friction on faults. The patterns of rotation of crustal blocks in western North America suggest that these blocks passively follow the deformation of a continuous substrate. The observations of deformation and the estimates of stress derived from them, both suggest that the upper continental crust is weak, relative to the lower parts of the lithosphere the deformation of which it follows passively. If this is so, determinations of stress in the upper crust may have only limited relevance to the deformation of the lithosphere as a whole.

Modelling the ascent of picritic lunar magmas

2021 ◽  
Author(s):  
Marissa Lo ◽  
Giuseppe La Spina ◽  
Katherine Joy ◽  
Margherita Polacci ◽  
Mike Burton
Keyword(s):  
Thermal Evolution ◽  
Magma Ascent ◽  
Volatile Content ◽  
Major Element Composition ◽  
Analytical Instruments ◽  
Lunar Interior ◽  
Digital Elevation ◽  
Lunar Samples ◽  
Future Work ◽  
Compare And Contrast

<p>Quantifying the volatile content of the lunar interior is valuable for understanding the formation, thermal evolution, and magmatic evolution of the Earth and Moon. Petrological modelling and geochemical measurements have been used to study the volatile composition of the lunar interior. Improvements to analytical instruments have facilitated more precise measurements of the volatile content of lunar samples and meteorites, however, several problems remain with these measurements, hence, the volatile content of lunar magmas has yet to be constrained with certainty. We propose a volcanological approach for inferring the volatile contents of different lunar magmas.</p><p>            A terrestrial magma ascent model has been modified for lunar applications. Numerous parameters were adjusted for lunar conditions, including: magma major element composition, from low-Ti (green and yellow glasses) to high-Ti (orange, red, and black glasses); H<sub>2</sub>O content; CO content; gravity; and pressure. The model calculated values for gas exsolution, viscosity, mass flow rate, and several other ascent processes, from a depth of 10 km to the surface. Using these results, we will assess the effect of varying magmatic volatile content on lunar magma ascent processes. We will also compare and contrast our results with existing models for lunar magma ascent, as well as models for magma ascent on other planetary bodies. Future work will involve modelling eruptions, using results from the magma ascent model, and verifying the results of the models using images and digital elevation models of the lunar surface.</p>

Relationships between inherited crustal structures and seismicity in the western Alps inferred from 3D structural modeling

2010 ◽  
Vol 181 (6) ◽  
pp. 583-590 ◽  
Author(s):  
Christian Sue ◽  
Philippe Calcagno ◽  
Gabriel Courrioux ◽  
Pierre Tricart ◽  
Julien Frechet ◽  
...  
Keyword(s):  
Cross Sections ◽  
Seismic Activity ◽  
Structural Model ◽  
Sedimentary Cover ◽  
Field Method ◽  
Western Alps ◽  
Geological Body ◽  
Digital Elevation ◽  
Crustal Structures ◽  
Elevation Model

Abstract We developed a 3-D structural model of a key area in the southwestern Alps, at the boundary between the external and internal zones. Six geological bodies are analyzed: internal and external basements, Briançonnais and Piemontais zones (internal sedimentary cover nappes), exotic flyschs, and external sedimentary cover. 3D volumes of each geological body are modeled using the structural map of the area projected on the Digital Elevation Model (DEM) and 5 cross-sections. The global model is interpolated from the map, DEM, and cross sections, using the potential field method, and represented by a Voronoï diagram. The final 3D-model is used as a structural frame to plot the earthquakes of the GéoFrance3D database, allowing to precisely and quantitatively investigate the relationships between crustal structures and current seismic activity of the belt. The boundary between external and internal zones corresponds to the so-called Crustal Penninic Thrust (CPT), which is a former Oligocene major thrust. Our model establishes that this former thrust represents the western limit of the seismic activity along the Briançonnais seismic arc, currently undergoing extensional tectonics.

scholarly journals Seismic velocity structure of Unzen Volcano, Japan, and relationship to the magma ascent route during eruptions in 1990–1995

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kanta Miyano ◽  
Koki Aizawa ◽  
Takeshi Matsushima ◽  
Azusa Shito ◽  
Hiroshi Shimizu
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
P Wave ◽  
Pyroclastic Flows ◽  
Magma Ascent ◽  
Unzen Volcano ◽  
Subsurface Structures ◽  
Brittle Ductile Transition ◽  
P Wave Velocity ◽  
Tectonic Earthquakes

AbstractSubsurface structures may control the migration of magma beneath a volcano. We used high-resolution seismic tomography to image a low- P-wave velocity (Vp) zone beneath Unzen Volcano, Japan, at depths of 3–16 km beneath sea level. The top of this low-Vp zone is located beneath Mt. Fugendake of Unzen volcano, which emitted 0.21 km3 of dacitic magma as lava domes and pyroclastic flows during eruptions in 1990–1995. Based on hypocenter migrations prior to the 1990–1995 eruptions and modeled pressure source locations for recorded crustal deformation, we conclude that the magma for the 1990–1995 eruptions migrated obliquely upward along the top of the low-Vp zone. As tectonic earthquakes occurred above the deeper part of the low-Vp zone, the deep low-Vp zone is interpreted to be a high-temperature region (> 400 °C) overlying the brittle–ductile transition. By further considering Vs and Vp/Vs structures, we suggest that the deeper part of the low-Vp zone constitutes a highly crystalized magma-mush reservoir, and the shallower part a volatile-rich zone.

scholarly journals Magmatic Epidote and Amphibole from the Rio Espinharas Hybrid Complex, Northeastern Brazil

2005 ◽  
Vol 32 (2) ◽  
pp. 41 ◽  
Author(s):  
THOMAS CAMPOS ◽  
ANA MARGARIDA NEIVA ◽  
LAURO VALENTIM STOLL NARDI ◽  
LUCIANO SCHAEFFER PEREIRA ◽  
LEONARDO FRAGA BONZANINI ◽  
...  
Keyword(s):  
Northeastern Brazil ◽  
Granitic Rocks ◽  
Magma Ascent ◽  
Upper Crust ◽  
Whole Grain ◽  
Hybrid Complex ◽  
Intimate Association ◽  
Quartz Monzonite ◽  
Upward Transport ◽  
Transcurrent Faults

The petrography and chemistry of epidote and amphibole from the Rio Espinharas hybrid complex (REHC), northeastern Brazil are reported. The Rio Espinharas complex is composed of an intimate association of diorite to shoshonitic metaluminous quartzmonzonite to slightly peraluminous syenogranite. The epidote shows four textural relationships: three are primary and one is resulting from sub-solidus reaction. Euhedral epidote is dispersed and associated mainly with biotite and amphibole. In some cases euhedral crystals of the epidote contain allanite cores, which are subhedral to anhedral and constitute in average less than 20% of the whole grain. The contact between primary epidote and plagioclase is corroded, suggesting reaction with the host-magma. Secondary anhedral epidote is rare and results from plagioclase alteration. The preservation of magmatic epidote in granitic rocks emplaced in the upper crust is attributed to rapid magma ascent, which implies fast upward transport probably by dyking associated to shear zone. The REHC occurs between two transcurrent faults that impose an elongated shape, suggesting that magma filled fractures. The time of 14 years required for dissolution zones of 0.15 mm width of epidote on porphyritic quartz monzonite, corresponds to an average ascent rate of ≥ 700 m year-1 from 7.1 to 2.9 kbar.

scholarly journals A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Solid Earth ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 1181-1217
Author(s):  
Thomas M. Belgrano ◽  
Larryn W. Diamond ◽  
Yves Vogt ◽  
Andrea R. Biedermann ◽  
Samuel A. Gilgen ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Sedimentary Cover ◽  
Phase 1 ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Massive Sulfide ◽  
Magma Ascent ◽  
Upper Crust ◽  
Vms Deposits ◽  
Semail Ophiolite

Abstract. Numerous studies have revealed genetic similarities between Tethyan ophiolites and oceanic “proto-arc” sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in marine settings. In contrast, the 3–5 km thick upper-crustal succession of the Semail ophiolite, which is exposed in an oblique cross section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the proto-arc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulfide (VMS) deposits that they host, we have remapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses, and geophysical interpretations with pre-existing geological maps. By linking the major-element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes), through axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley), and finally boninites (Boninitic Alley). Geotimes (“Phase 1”) axial dykes and lavas make up ∼55 vol % of the Semail upper crust, whereas post-axial (“Phase 2”) lavas constitute the remaining ∼45 vol % and ubiquitously cover the underlying axial crust. Highly depleted boninitic members of the Lasail unit locally occur within and directly atop the axial sequence, marking an earlier onset of boninitic magmatism than previously known for the ophiolite. The vast majority of the Semail boninites, however, belong to the Boninitic Alley unit and occur as discontinuous accumulations up to 2 km thick at the top of the ophiolite sequence and constitute ∼15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

Fire-related landform associations of remnant old-growth trees in the southern Washington Cascade Range

2004 ◽  
Vol 34 (11) ◽  
pp. 2371-2381 ◽  
Author(s):  
William S Keeton ◽  
Jerry F Franklin
Keyword(s):  
Forest Cover ◽  
Fire Behavior ◽  
Douglas Fir ◽  
Cascade Range ◽  
Fire Intensity ◽  
Old Growth ◽  
Biological Legacies ◽  
Digital Elevation ◽  
Biological Legacy ◽  
Topographic Heterogeneity

The spatial distribution of biological legacies left by natural disturbances is an important source of variability in forest development. We investigated one type of biological legacy: remnant old-growth trees persisting in mature Douglas-fir forests. We hypothesized that persistence varies with topographic heterogeneity influencing fire behavior. Our two study areas are located in the southern Washington Cascade Range, USA. They have an unfragmented, mature forest cover that regenerated following wildfire. We mapped all remnant old-growth trees (live and dead) within 4.2–6.4 km long belt transects. Digital elevation models were used to generate convergent and divergent landform classes. Frequency analysis was used to test for landform associations. Live remnant western hemlock and western redcedar were strongly associated with convergent landforms and aspects that had greater availability of soil moisture. Live remnant Douglas-fir were most abundant, but were not correlated with convergence or divergence, although certain landforms had higher concentrations. Remnant snags were abundant across convergent and divergent landforms. We conclude that species with low fire resistance survive most frequently on landforms that have a dampening effect on fire intensity. Topographic variability may indirectly influence ecological functions associated with biological legacies by affecting the spatial distributions of remnant old-growth trees.

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.

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