Volcán Miño (21°11'S) is located on the westernmost periphery of a longlived complex of stratovolcarioes and domes called the Aucanquilcha Complex. The Aucanquilcha Complex ranges in age from 11 Ma to 1-lolocene and lies along the main N-S trending axis of Quaternary volcanoes in the Andean Central Volcanic Zone (CVZ)....
Volcan Aucanquilcha, a Pleistocene to Recent composite volcano in northern Chile, is the youngest and center-most member of the 11 m.y.-old Aucanquilcha Volcanic Cluster (AVC). The AVC has produced [approximately]350 km³ of lava over its history. Magmatism started slowly and was punctuated by high rates of eruption between 4.5 and...
We document a new model of crustal structure of the Andean front in Argentina where numerous historic earthquakes destroyed the cities of Mendoza in 1861 (M[subscript s] = ~7) and San Juan in 1944 (M[subscript w] = 7.0). The Cerro Salinas anticline is formed above the west directed Cerro Salinas...
Gravity and seismic data obtained by the geophysical group at
Oregon State University on the R/V YAQUINA during 1969, 1971, and
1973 plus other available data over the area just west of Nicaragua
and Costa Rica indicate the tectonic complexity of the region. Gravity
measurements show negative free-air anomalies over...
The interaction of magma with continental crust at convergent margins is fundamental to
understanding if and how continents grow. Isotopic and elemental data constrain the
progressive stages of development of the magmatic underpinnings of the long-lived
Aucanquilcha Volcanic Cluster (AVC), situated atop the thick continental crust of the
central Andes...
Micropaleontological data have been analyzed through mathematical
and statistical procedures, in order to: (1) establish the distribution
pattern of radiolarian assemblages in the surface sediments,
(2) establish the relationship of these assemblages with oceanographic
variables, (3) determine the faunal composition down-core with
respect to the faunal surface pattern, and (4)...
In this study, 3D finite difference and 2D finite element forward modeling were used to create an electromagnetic sensitivity analysis for the Cotopaxi volcano in Ecuador. Magnetotellurics (MT) is a natural-source electromagnetic geophysical technique that images electrical conductivity. Measuring strong contrasts in electrical conductivity in volcanic materials allows for the...
The Inmaculada Mine is located in the Miocene belt of epithermal deposits that extends from southern Peru to northern Chile and Bolivia. This belt is known for its silver-rich epithermal veins that have been worked since colonial times. The Inmaculada Mine belongs to a mining district that includes, from north...
The pressure history of a continental magmatic system can be deciphered by analyzing the composition of amphiboles in the eruptive products where the pressure of equilibration correlates with the depth of the magmatic system. This can reveal vertical evolution of the magma as amphibole composition varies significantly with temperature and...
This dissertation combines volcanological research of three convergent continental margins. Chapters
1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal
development of the Altiplano-Puna volcanic complex in the Lípez region of southwest Bolivia, a locus of a
major Neogene ignimbrite flare- up, yet the least...
Constraining the development, evolution, and timescales of large silicic magma systems is important to understanding the development of granite batholiths, the relationships between volcanoes and their plutonic underpinnings, and the development of the continental crust.
The ignimbrite flare up that produced the Altiplano-Puna Volcanic Complex of the Central Andes is...
Growth strata geometries and deformed geomorphic surfaces reflect the shorttimescale growth of Sierra de Villicum (San Juan Province, Argentina). Accumulated deformation in repeated earthquakes is recorded by the structural geometry of deformed geomorphic surfaces. Through geologic mapping and topographic surveying, six strath terraces were identified on the eastern flank of...
The 2-ka eruption of Misti volcano produced voluminous flowage deposits and a wide-spread tephra-fall deposit. The flowage deposits form large terraces within channels draining the south side of the volcano. All the channels drain into the city of Arequipa. Arequipa's city center is ~16 km from the summit of the...
A large, damaging earthquake in 1944 on a blind thrust fault caused 60 cm of surface rupture on the subsidiary La Laja fault and additional unmeasured growth of an associated backlimb fold. Both the fold and fault are components of the La Laja Fault System (LLFS) located 25 km northeast...
The ~1 Myr history of the Purico-Chascon volcanic complex (PCVC) records significant changes in the production and storage of magmas in the crust. At ~1 Ma activity at the PCVC initiated with the eruption of a large 80-100 km³ crystal-rich dacite ignimbrite with restricted whole rock ⁸⁷Sr/⁸⁶Sr isotope ratios between...
The climatic and tectonic framework of the St. Elias orogen makes it an excellent place to study the interactions between tectonic processes such as deformation and erosive processes, in particular glacial erosion. One type of link between these processes, proposed by numerical models of orogenic development, is an effect of...
This study is an effort to characterize the magma sources, plumbing system, and eruptive behavior of Mount Hood, a low-explosivity recharge-dominated volcano in the Oregon Cascades. The three manuscripts in this dissertation make use of melt inclusion data, phenocryst compositions, and whole rock petrology and geochemistry to build a schematic...
The 2008-2009 eruption of Chaitén Volcano (Chile) involved a variety of volcanic and associated hydrologic processes that damaged nearby forests. These processes included coarse (gravel) and fine (silt to sand) tephra fall, a laterally directed blast, fluvial deposition of remobilized tephra, a variety of low-temperature mass-movement processes, and a pyroclastic...
A free-air gravity anomaly map of the continental margin of
Peru between 12° and 18° S. Lat. shows a -110 to -220 mgl anomaly
associated with the Peru-Chile Trench, a -60 mgl anomaly over the
Pisco Basin on the continental shelf, and -120 mgl anomaly over the
Mollendo (or Arequipa)...
Gravity and magnetic data from cruises by the R/V Yaquina in 1973
and the R/V Wecoma in 1975 provide new data that make possible the construction of a map of the free-air gravity anomalies at sea and simple
Bouguer anomalies on lano in Panama, western Colombia, and the eastern
Panama...
Seismic refraction, reflection and gravity data obtained
across the Peru continental margin and Nazca Plate
at 9° S. permit a detailed determination of crustal structure.
Complex structures normal to the profile require the
development of a ray trace technique to analyze first and
later arrivals for eleven overlapping refraction lines....
This thesis synthesizes surficial structural data, a detailed analysis of an earthquake in 1944, and historical seismicity into a new model of crustal scale deformation in the eastern Precordillera in northwestern Argentina in the vicinity of San Juan. The eastern Precordillera was uplifted during previous thin-skinned deformation episodes, and is...
The Altiplano-Puna Volcanic Complex in the Central Andes is one of the youngest large silicic volcanic fields (LSVFs) in the world, erupting over 13,000 km³ of material during multiple supereruptions from 11 to 1 Ma. Understanding the timescales over which magma is stored in the crust prior to eruption is...
The Pastos Grandes Caldera Complex (PGCC) in southwest Bolivia has produced two large-volume (≥800 km³ DRE) dacite ignimbrites from a nested caldera source over a period of 5.5 Myr. In addition to the large-volume ignimbrites, a small-volume ignimbrite shield and post-climactic lavas define this composite system. Based on detailed field...
This dissertation is informally divided into three major sections. In the first section (Chapter 2) I use data from field mapping, isotopic geochronology, whole rock geochemistry and trace element concentrations in zircons to examine the petrology, geochemistry and ages of the Haquira East porphyry copper deposit of southern Peru. In...
Constraining the magma evolution and dynamics that lead to the eruption of large volume continental arc systems is fundamental to our understanding of continental crust formation. An investigation into the magmagenesis that results in the formation of the Central Volcanic Zone (CVZ) in the Andes of South America, situated atop...
The Pebble porphyry Cu-Au-Mo deposit in Alaska is one of the world's largest Cu-Au mineral resources. Late Cretaceous magmatic evolution in the Pebble district culminated with the intrusion of the Kaskanak Batholith and associated porphyry copper-gold-molybdenum mineralization. The Kaskanak Batholith is a multiphase granodiorite intrusion with an estimated footprint of...
Porphyry Cu-(Au-Mo) deposits are critical sources of several economically important metals. The processes governing the total metal endowment and relative proportions of ore metals at these large magmatic-hydrothermal deposits remain uncertain. The Sulphurets porphyry district, in northwestern British Columbia, Canada, contains four porphyry Au-Cu-Mo deposits that each feature distinct Cu/Au...
The San Vicente zinc lead deposit is located in the Eastern Andes of
Central Peru. The deposit is an epigenetic Mississippi Valley-type deposit
based on stratigraphic, geologic, petrographic, and geochemical evidence.
The dolomite host rocks of the Pucara Group are of Triassic-Jurassic
age. The source of metals are red sandstones...
The ~5 km3, 4.54 to 4.09 Ma Caspana Ignimbrite of the Altiplano-Puna Volcanic Complex (APVC) of the Central Andes records the eruption of an andesite and two distinct rhyolitic magmas. It provides a unique opportunity to investigate the production of silicic magmas in a continental arc flare-up, where small volumes...
The El Salvador porphyry copper deposit in the Indio Muerto district of northern Chile has been geologically investigated for more than 60 years and provides one of the best bases for understanding similar environments of ore formation elsewhere in the world. Fourteen new zircon U/Pb isotopic ages obtained via in...
To investigate the dynamic response of the outer accretionary wedge updip from the patch of greatest slip during the Mw8.8 2010 Maule earthquake, 10 Ocean Bottom Seismometers (OBS) were deployed from May 2012 to March 2013 in a small array with an inter-instrument spacing of ~10 km. Nine instruments were...
This dissertation is concerned with the behavior of sulfur in intermediate-silicic arc magmas associated with subduction at convergent margins. In particular it focusses on oxidized, sulfur-rich magmas, the conditions at which they might reach sulfate saturation, and implications of sulfate saturation. It is divided into an investigation of natural samples...
The eruptive history of the Quaternary Cascades arc has been relatively well characterized. However, much less is known about the frequency and sizes of explosive eruptions produced by earlier stages of the arc. The Late Neogene Deschutes Formation of Central Oregon preserves a remarkable record of heightened pyroclastic activity during...
This dissertation is divided into two major chapters. The first chapter covers the geologyof the Encuentro deposit with emphasis in the intrusion sequence, vein mineral assemblages and distribution, and age of mineralization. The data used for this section includes field mapping, petrography, elemental analysis of biotite, and isotopic geochronology. The...
The Clarno Formation is a series of volcanic, volcaniclastic, and related intrusive rocks located in central Oregon. It is the westernmost extent of a broader Eocene magmatic belt that covers much the western United States. The magmatic belt stretches eastward from Oregon to western South Dakota, and from the Canadian...
The imposing andesite stratovolcano is the characteristic expression of subduction zone magmatism, posing hazards to coastal populations and bearing insight into deep Earth processes. On a map of a typical volcanic arc, one can easily distinguish the approximately linear alignment and regular spacing of these major edifices that stand out...
The Cascadia subduction zone has been characterized as a typical Chilean-type
subduction zone based on qualitative comparisons of plate age and convergence rate, with
simple forearc structure. However, the discovery of unusual structural styles of
deformation, variations in the morphology of the forearc, and its absence of seismic activity
suggest...
By inverting EarthScope long-period magnetotelluric (MT) data from the southeastern United States (SEUS), we obtain electrical conductivity images that provides key insights into the geodynamics of this region. Significantly, we resolve a highly electrically resistive block that extends to mantle depths beneath the modern Piedmont and Coastal Plain physiographic provinces....
Explosively erupting volcanoes and megathrust earthquakes (Mw 8+ magnitude) occur at subduction zones and adjacent volcanic arcs. Volcanic eruptions are observed occurring close in time to megathrust earthquakes in the historical record from at least the 18th century CE to present in locations globally, including Japan in 1707 CE (Chesley...