The northwestern corner of the Basin and Range Province (NWBR) lies in southeast Oregon where extensive Late Miocene, mafic to bimodal basalt-rhyolite volcanism and extensional faults dominate a stark and arid landscape. Near Lake Abert, the Late Miocene volcanic section abuts Early Miocene, dominantly intermediate composition volcanoes at the Coleman...
Normal faults characterizing extensional provinces may terminate along-strike at regions of zero extension, at zones of transform faults, or at triple junctions. Termination of the Basin and Range extensional province in southeastern Oregon is thought to occur by right-lateral transform motion distributed across the Brothers Fault zone (BFZ) in central...
New data are presented that provide evidence for the onset of extensional deformation in the Northwestern Basin and Range within 1 million years after the eruption of the Steens Basalt at 16.5 Ma. New geologic mapping (1:24,000), stratigraphic sections, and ⁴⁰Ar/³⁹Ar dating of the Crane Basin rocks provide a control...
Plate boundaries are commonly regions of complex, diffuse deformation with
the motion across the boundary accommodated by numerous structural systems, rather
than being narrow, discrete zones of deformation. One such boundary occurs where
the North American plate makes contact with Juan de Fuca, Gorda, and Pacific plates
along the west...
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...
The Botija Cu-Mo-Au porphyry deposit is located in the Cobre Panamá mining district, which contains several deposits with a global measure and indicated and inferred resource of 14.8 MT of Cu. These deposits are associated with the Cerro Petaquilla batholith, which has U/Pb zircon ages of 26-33 Ma (Whattam et...
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...
Near-surface advanced argillic hydrothermal alteration zones, also referred to as lithocaps, are characterized by quartz, alunite, clays (pyrophyllite and kaolinite group minerals), and minor F-bearing aluminosilicates (i.e., topaz, zunyite, diaspore, and APS) that form where water-, SO2-, and HF-rich gas condenses into shallow groundwater, acidifies, and reacts with rocks. The...
Three broadly interrelated problems of critical significance to the proper interpretation of melt inclusion (MI) data are addressed in this thesis. The first issue, the petrogenesis of anorthitic plagioclase phenocrysts in MORB lavas, has relevance due to the presence of numerous MI in many high-An feldspars. This problem was addressed...