Geology topics

James E. Wright

Publications and source records attributed to James E. Wright.

4 recordsLinked to original sources

USGS2015

Composite Sunrise Butte pluton: Insights into Jurassic–Cretaceous collisional tectonics and magmatism in the Blue Mountains Province, northeastern Oregon

The composite Sunrise Butte pluton , in the central part of the Blue Mountains Province, northeastern Oregon, preserves a record of subduction-related magmatism, arc-arc collision, crustal thickening, and deep-crustal anatexis. The earliest phase of the pluton (Desolation Creek unit) was generated in a subduction zone environment, as the oceanic lithosphere between the Wallowa and Olds Ferry island arcs was consumed. Zircons from this unit yielded a 206 Pb/ 238 U age of 160.2 ± 2.1 Ma. A magmatic lull ensued during arc-arc collision, after which partial melting at the base of the thickened Wallowa arc crust produced siliceous magma that was emplaced into metasedimentary rocks and serpentinite of the overthrust forearc complex. This magma crystallized to form the bulk of the Sunrise Butte composite pluton (the Sunrise Butte unit; 145.8 ± 2.2 Ma). The heat necessary for crustal anatexis was supplied by coeval mantle-derived magma (the Onion Gulch unit; 147.9 ± 1.8 Ma). The lull in magmatic activity between 160 and 148 Ma encompasses the timing of arc-arc collision (159-154 Ma), and it is similar to those lulls observed in adjacent areas of the Blue Mountains Province related to the same shortening event. Previous researchers have proposed a tectonic link between the Blue Mountains Province and the Klamath Mountains and northern Sierra Nevada Provinces farther to the south; however, timing of Late Jurassic deformation in the Blue Mountains Province predates the timing of the so-called Nevadan orogeny in the Klamath Mountains. In both the Blue Mountains Province and Klamath Mountains, the onset of deep-crustal partial melting initiated at ca. 148 Ma, suggesting a possible geodynamic link. One possibility is that the Late Jurassic shortening event recorded in the Blue Mountains Province may be a northerly extension of the Nevadan orogeny. Differences in the timing of these events in the Blue Mountains Province and the Klamath-Sierra Nevada Provinces suggest that shortening and deformation were diachronous, progressing from north to south. We envision that Late Jurassic deformation may have collapsed a Gulf of California-style oceanic extensional basin that extended from the Klamath Mountains (e.g., Josephine ophiolite) to the central Blue Mountains Province, and possibly as far north as the North Cascades (i.e., the coeval Ingalls ophiolite). The lull in magmatic activity between 160 and 148 Ma encompasses the timing of arc-arc collision (159–154 Ma), and it is similar to those lulls observed in adjacent areas of the Blue Mountains Province related to the same shortening event. Previous researchers have proposed a tectonic link between the Blue Mountains Province and the Klamath Mountains and northern Sierra Nevada Provinces farther to the south; however, timing of Late Jurassic deformation in the Blue Mountains Province predates the timing of the so-called Nevadan orogeny in the Klamath Mountains. In both the Blue Mountains Province and Klamath Mountains, the onset of deep-crustal partial melting initiated at ca. 148 Ma, suggesting a possible geodynamic link. One possibility is that the Late Jurassic shortening event recorded in the Blue Mountains Province may be a northerly extension of the Nevadan orogeny. Differences in the timing of these events in the Blue Mountains Province and the Klamath–Sierra Nevada Provinces suggest that shortening and deformation were diachronous, progressing from north to south. We envision that Late Jurassic deformation may have collapsed a Gulf of California–style oceanic extensional basin that extended from the Klamath Mountains (e.g., Josephine ophiolite) to the central Blue Mountains Province, and possibly as far north as the North Cascades (i.e., the coeval Ingalls ophiolite).

Idaho, Oregon↗

USGS2013

Eocene extension in Idaho generated massive sediment floods into Franciscan trench and into Tyee, Great Valley, and Green River basins

The Franciscan Complex accretionary prism was assembled during an ∼165-m.y.-long period of subduction of Pacific Ocean plates beneath the western margin of the North American plate. In such fossil subduction complexes, it is generally difficult to reconstruct details of the accretion of continent-derived sediments and to evaluate the factors that controlled accretion. New detrital zircon U-Pb ages indicate that much of the major Coastal belt subunit of the Franciscan Complex represents a massive, relatively brief, surge of near-trench deposition and accretion during Eocene time (ca. 53–49 Ma). Sediments were sourced mainly from the distant Idaho Batholith region rather than the nearby Sierra Nevada. Idaho detritus also fed the Great Valley forearc basin of California (ca. 53–37 Ma), the Tyee forearc basin of coastal Oregon (49 to ca. 36 Ma), and the greater Green River lake basin of Wyoming (50–47 Ma). Plutonism in the Idaho Batholith spanned 98–53 Ma in a contractional setting; it was abruptly superseded by major extension in the Bitterroot, Anaconda, Clearwater, and Priest River metamorphic core complexes (53–40 Ma) and by major volcanism in the Challis volcanic field (51–43 Ma). This extensional tectonism apparently deformed and uplifted a broad region, shedding voluminous sediments toward depocenters to the west and southeast. In the Franciscan Coastal belt, the major increase in sediment input apparently triggered a pulse of massive accretion, a pulse ultimately controlled by continental tectonism far within the interior of the North American plate, rather than by some tectonic event along the plate boundary itself.

California, Idaho, Oregon, Wyoming↗

USGS2008

Late Jurassic igneous rocks in south-central Arizona and north-central Sonora: Magmatic accompaniment of crustal extension

In Middle Jurassic time, the region of south-central Arizona and north-central Sonora was part of a continental magmatic arc. In early Late Jurassic time, this magmatic arc gradually gave way to a extensional regime. Late Jurassic rifting was accompanied by magmatism, typically small in volume relative to the preceding arc phase, and with mildly alkaline compositions. These igneous rocks, the 158- to 146-Ma Ko Vaya Suite, make up much or most of the Comobabi, Artesa, Quijotoa, and Brownell Mountains and Sierra del Cobre. The bimodal Ko Vaya Suite constitutes volcanic to shallow plutonic complexes comprising chiefly trachyandesite and volcanic wacke; monzodiorite; rhyolite porphyry; distinctive, compositionally and texturally heterogeneous, quartzpoor granite (the Ko Vaya Granite); A-type perthite granite and quartz syenite; aphyric intrusive rhyolite; and locally abundant hematite veins. Alteration, particularly potassic alteration, is widespread. Minimally altered samples of granite and quartz syenite have the composition of trachyte or trachydacite and alkali rhyolite. The Ko Vaya Suite is nonconformably overlain by the latest Jurassic Sand Wells Formation, approximately correlative with the Glance Conglomerate, the basal unit of the Bisbee Group. The Ko Vaya Suite is in some ways analogous to the coeval Independence dike swarm of eastern California, but less diffuse. We infer that the Ko Vaya Suite represents especially intense or focused Late Jurassic extensional magmatism.

Arizona, Sonora↗

USGS1990

Chapter 6: Petrogenesis of the composite peraluminous-metaluminous Old Woman-Piute Range batholith, southeastern California; isotopic constraints

The Late Cretaceous Old Woman–Piute Range batholith includes both metaluminous and strongly peraluminous granitoid series that intruded the reactivated craton of southeastern California shortly after the orogenic peak. Whole-rock Sr, Nd, and O, feldspar Pb, and zircon U-Pb isotopic compositions, in combination with major- and trace-element and petrographic data, indicate that although these series are not comagmatic, they both were generated primarily by anatexis of Proterozoic crust. Differences between the two rock types are functions of source compositions: peraluminous granitoids were apparently generated from an intermediate to felsic source, metaluminous granitoids from more mafic igneous material with a possible modest subcrustal contribution. No sedimentary input is required in production of the peraluminous granites, and in fact, chemically mature sedimentary material is ruled out as an important contributor— that is, these are not S-type granites. Lead-isotope data reveal that the crust that yielded both magma series had undergone an ancient high-grade uranium depletion event, but independent evidence indicates that at the time of anatexis this crust was by no means anhydrous.

California↗