Jul 26, 2018 this ancient oceanic plate broke into pieces, resulting in perturbations of unusual rocks in the mantle which led to volcanic eruptions in the past 16 million years, says zhou. First subduction of the farallon plate at san diego latitude similar to washington oregon today, coastal mountains, big valley willamette cascade volcanos. Models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy, requiring that the farallon slab was flat lying in the late cretaceous, consistent with geological reconstructions. Pattern changed slightly in which the pacific plate was developed. Above the constraints on the configuration of plates ad eral possible geometries for the kula farallon slab window, upwelling of hot, anhydrous as jacent to north america since the mesozoic. The jdf plate is the northern remnant of the farallon plate and. Fossil slabs attached to unsubducted fragments of the farallon plate. Oct 25, 2017 plate motion models, isotopic ages, and onlap relations show that both terranes may have originated between 56 and 49 ma at a longlived yellowstone hotspot yhs centered on the northeasttrending kularesurrection farallon ridge, not far offshore of oregon and washington. Figure 2 threedimensional views of the subducted farallon plate under north america. State of oregon department of geoiogy and mibteral industries 1069 state office building, portland, oregon 97201 openfile report 0782 supplebbnt to the february 11, 1974 pebbij3.
The farallon can be tracked from the trench in the. This process sprouted volcanoes to form the sierra nevada in what is now california. Letter report pertaining to the workshop on the structural. Our main approach is 3d visualization using a kinematic plate motion model as a framework. The cocos plate was created approximately 23 million years ago. Pdf this paper presents new geological constraints on the collision of. Beaulieu submitted to the energy facility siting council on march 9, 1978. The ancient farallon plate is named after the islands. The understanding of the farallon plate is rapidly evolving as details from seismic tomography provide improved details of the submerged remnants. The pacific plate, enlarged by the addition of part of the kula. Panama isthmus, when the farallon plate started to subduct beneath. Comparison of results from all 12 image volumes indicates that the results are most consistent with a single, coherent farallon slab overridden by north american. The farallon plate began subducting under the west coast of the north american plate then located in modern utahas pangaea broke apart and after the formation of the pacific plate at the centre of.
Oregon and 2 the broader southern segment generated by shallower subduction in the nevadacalifornia border region du bray and john, 2011. Consultants for the utility companies and those for the nrc agree to. The fragmented death of the farallon plate hawley 2019. Humphreys 2009 noted that the boundary separating steep and.
Gahertyc, and brian savaged adepartment of geological sciences, brown university, providence, ri 02865. Farallon kula plate formed near na plate, subduction angle decreases, farallon plate moves horizontally to colorado 40 ma. The farallon plate underneath western north american continues to subduct due to cold slab pull, leaving a thin spot underneath the basin and range province. Deep earth imaging helps clarify history of columbia river. A brief thirtymillionyear history of western north. The relative motion of the farallon plate was to the northnortheast, sliding beneath the. Since the north american west coast shows a convoluted structure, significant work has been required to resolve the complexity.
Introduction marine magnetic anomalies in the northern paci. The case for a longlived and robust yellowstone hotspot. The north american plate was pushed over the sea floor plate by the force of the african and south american plates rifting apart. Three little plates subducting offshore oregon, washington, and b. View of research station at marine terrace, with farallon island light above. Melanges and their bearing on late mesozoic and tertiary. Drake, school of oceanography, oregon state university, corvallis, oregon 97331 introduction the northeast pacific is a unique plate tectonic region. Asthenosphere continues to rise to fill void, causing epeirogenic uplift.
Slab dismemberment beneath eastern oregon is consistent with seismic studies that resolve a truncated subducting plate that terminates at 300 km depth, with fast anomalies farther east interpreted as farallon slab remnants e. Twostage subduction history under north america inferred from. Appendix e6 is a pdf file summarising the palynological results of d. Pdf transition from the farallon plate subduction to the collision. Fragmentation of the farallon plate by pivoting subduction the. This seamount terrane is thought to have formed on the farallon plate and, been subsequently accreted into its present position along the oregon and washington coast during subduction of this oceanic plate beneath the north american plate during the early tertiary the roseburg volcanic sequence is composed of a basal submarine tholeiitic. Drag creation of the san andreas transform fault strike slip and. Plutonic rocks from this period are found in the klamath mountains and sierra nevada. Pacificnorth america movie 50 mb the narrative below was written to accompany a thorough exploration of the animation each represents one playthrough of. Unraveling the geometry of the farallon plate department of earth. Uncertainties and implications of the late cretaceous and. Highresolution tomographic images show large pieces of the. This may have cut off moisture from the west, resulting in dry desert conditions in utah, with deposition of up to 2,000 ft of sandsuch as navajo sandstone of zion national park.
The easternmost extent of volcanism is the absaroka 146 volcanic center, a 5545 ma event in the ranges that bound the southwestern edge of the 147 bighorn basin fig. The islands string northwestward from southeast farallon island for 5 miles 8. Includes the breakup and piecewise subduction of the farallon plate and the consequent development of the san andreas plate boundary. Since that time, it has been genetically associated with a series of aligned volcanic provinces associated with age pro gressive events that include oligocene highk calcalkaline volcanism in the oregon back. The whole process kicked off near whats now the border between oregon and idaho, with heat from the sunken farallon plate rubbing against the north american plate. Farallon slab detachment and deformation of the magdalena. We might have been wrong about the source of yellowstones. It plunged beneath the north american plate at a fortyfive degree angle. Allen 1department of earth and planetary science, university of california, berkeley, ca, usa, 2berkeley seismology lab, university of california, berkeley, ca, usa abstract the processes that accompany the death of an oceanic plate, as a ridge nears a trench, remain. We find that the highly segmented upper mantle structure of western u. Earthquakes form when building stresses within the earths solid crust are released in single instants of motion.
Today the farallon plate has subducted almost completely under the western. Second capture of the north american continent by the pacific plate. Letters twostage subduction history under north america. Prior to 20 million years ago, subduction and partial melting of the farallon plate resulted in a chain of volcanoes that rimmed north americas western edge figures 24 and 25. The olympicwallowa lineament owl first reported by cartographer erwin raisz in 1945 on a relief map of the continental united states is a physiographic feature of unknown origin in the state of washington northwestern u. Uplift, rupture, and rollback of the farallon slab. During the late oligocene, the farallon plate split into the cocos and nazca plates as a result of global rearrangement of plate boundaries e. Many millions of years ago, the farallon plate subducted beneath the. Reconstructing farallon plate subduction beneath north. Allen 1department of earth and planetary science, university of california, berkeley, ca, usa, 2berkeley seismology lab, university of california, berkeley, ca, usa abstract the processes that accompany the death of an oceanic plate, as a ridge nears a trench, remain enigmatic. It formed one of the three main plates of panthalassa, alongside the phoenix plate and izanagi plate, which were connected by a triple junction. Review of plate movements during laramide orogeny 80 ma.
Plate tectonics oregon state university, open educational. Uplift, rupture, and rollback of the farallon slab reflected. An example of how rift propagation might reorient a ridge system and initiate new transform faults is shown in figure 2b. Review article unraveling the geometry of the farallon plate. At the beginning of cenozoic time a large region between the pacific and american plates consisted of a continuous farallon plate. Next, mantle motions pulled north america westward over farallon, and the plate scraped along the bottom of the continent for fifteen hundred. Furthermore, unsubducted fragments of the farallon plate remain off the coast of western north america atwater, 1970.
Pdf geochemical confirmation of the kulafarallon slab. The portion of the farallon slab thought to have been. Fragments of the farallon plate and high seismic velocity anomalies at 100 km blue. Abyssal hill fabric and seafloor magnetic anomalies along. The friction from the north american plate rubbing against the farallon plate melted. Cenozoic to recent plate configurations in the pacific basin. Bold dashed line shows area of highvelocity anomaly at a depth of 100 km that indicates the presence of a stalled fragment of the farallon plate in the upper mantle. Some fragments of the farallon plate still exist as separate plates subducting beneath north. The origin and evolution of the siletz terrane in oregon. Velocity anomaly outlines for the northern three blue areas are based on pwave tomography 19. Raua, nina carrieroa, brandon schmandtb,3, james b.
Twostage subduction history under north america inferred. Tectonic evolution of the oregon continental margin by ellen t. Fossil slabs attached to unsubducted fragments of the farallon plate yun wanga,1,2, donald w. The fragmented death of the farallon plate agu journals.
If we take figure 2 as a schematic view of a section of the pacific farallon spreading center with the pacific plate to the west and the farallon plate to the east. By including the defunct resurrection plate in our reconstruction, we are able to model the farallon hotspot track as docking against the oregon subduction margin starting about 53ma, followed by docking of the resurrection track to the north starting about 48ma. These fragments provide a different snapshot in time of the same system, and evidence for how the final state of the pacific. We also present a platetectonic model that supports and elaborates on the hypothesis. Shows the plate tectonic history of the northeast pacific and western north america, 38 million years ago to present stable north america held fixed.
The propagator wake bold gray line underneath oregon causes a. Subducting farallon plate must have torn at the southern margin of the accreted lithosphere in central oregon, separating a cascadia slab of rather normal dip from the laramiderelated flat slab to the south. It formed one of the three main plates of panthalassa, alongside the phoenix plate and izanagi plate, which. A kinematic model for the formation of the siletzcrescent. Is the dynamic topography signal of the yellowstone. We have developed a model of the tertiary convergence of these two plates, based on. The variable lifespan of the laramide orogeny earthjay science. The northern border of the subduction zone is the queen charlotte triple junction. Do microplates in subduction zones leave a geological record. Graduate thesis or dissertation geochemical evolution of. The farallon plate was then completely subducted and consumed beneath the north american plate. From 80 to 30 my farallon plate subducted under west coast. Pdf plate tectonic models indicate subduction of the kula farallon spreading ridge, and thus imply formation of. Plate reconstructions for this time interval indicate the close proximity of the kula farallon north america triple junction and that old ca 100 m.
Plan for this lecture you are here university of washington. Based on interpretations of magnetic anomalies, the oceanic crust of both the cocos and nazca plates was formed along the presently active cocosnazca spreading center cns3, its. Slabs of ancient tectonic plate still lodged under. The diving farallon plate melted at depth, causing chains of andesitic volcanoes and plutons of granitic magma to form inland. Well the best way to see plate boundaries is to look for the major earthquakes.
The kula was totally subducted or had merged with the farallon plate. The forces of colliding or rubbing plates can deform the crust hundreds of miles inland. Vernon e a department of geological sciences, 1001 east 10th street, indiana university, bloomington, in 47405, united states b department of earth and environmental sciences, ludwig. Pdf geochemical confirmation of the kulafarallon slab window.
Synthesis of threedimensional imaging results from usarray gary l. If you are viewing the pdf, or if you are reading this offline, please visit. The isabella anomaly ia, above, is at the same depth ca. An ancient tectonic plate 18 march 20, by kevin stacey mostly gone, not forgotten. Downloaded from gsageospherearticlepdf1046923333201. We have developed a model of the tertiary convergence of these two plates. Fossil slabs attached to unsubducted fragments of the. The fragmented death of the farallon plate william b. The ancient farallon plate subducted under north america in two distinct stages. Farallon plate which was subducted underneath the north american plate. Between 2016 ma, the subducting farallon plate fragmented into the guadalupe and magdalena oceanic micro plates as the pacific farallon ridge approached the trench along the western margin of the modernday baja california bc peninsula atwater and stock, 1998. Plate tectonics and global impacts tutorial script where can we find plate boundaries on the planet.
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