WICHG30910a [USEMAP] The mountain chain system along the Pacific coast of the Americas begins with the Alaska Range and the Brooks Range in Alaska and runs through the Yukon into British Columbia. In the United States, the Cordillera branches include the Rocky Mountains, the Sierra Nevada, the Cascades, and various small Pacific Coastal ranges. The three main phases of the Cordilleran orogeny are the Laramide, Sevier, and Nevadan orogenies. The Rocky Mountains took shape during an intense period of plate tectonic activity of the Laramide orogeny, about 80–55 million years ago, responsible for raising the Rocky Mountains. It was the last of the three episodes of the Cordilleran orogeny. ÜBasin and Range extension-Miocene (17 Ma) - Present ÜColumbia and Yellowstone plateau North American Cordillera Fig. 105. Generalized geologic evolution of western United States from Late Precambrian time (1 billion years) to the present. MESOZOIC [USEMAP] During the Mesozoic, subduction of the Farallon Plate formed a volcanic arc and the associated compression folded and thrust-faulted the Paleozoic sediments. Note the overall thickening of the continent, which will produce the gravitational potential energy which will help extend this region once compressional forces relax. The Western Collage •Cordillera an collage of microplates and arcs –accreted during the Paleozoic and Mesozoic –terrains have different rock types and fossil assemblages that cannot be correlated –suspect terrains--fault-bounded regions that cannot be correlated –exotic terrains--clearly from somewhere else – [USEMAP] What is a Tectonostratigraphic Terrane? terrane_map_compld Terranes can be: • Native – showing shared traits with North American crust, indicating an origin adjacent to North America. • Exotic – Far-traveled, not born adjacent to North America • Superterranes – amalgamated with other terranes before accretion to the continental margin. [USEMAP] Accreted or “suspect” terranes mapsuspected.jpg copy 00047DDCTS ABA78158: Dott & Prothero [USEMAP] Coastal ranges Cascades Sierra Nevada Rocky Mountains United States Cordillera (without Alaska) KORDILERY KORDILERY 2561_1413 Antler Orogeny in Devonian-Carb. Basin and Range extension Active margin Passive margin [USEMAP] Cascacdes, Coast Ranges Laurentia passive margin Laurentia active margin Paleozoic Passive Margin • Existed in Late Precambrian and Paleozoic • Craton and cratonic basin deposits • Miogeocline continental shelf deposits Antler Orogeny (300-375 Ma) • Late Devonian - Mississippian • Collision of the arc with a passive margin • Roberts Mountain Allochton thrust over the passive margin • A series of foreland basins formed in eastern Nevada [USEMAP] [USEMAP] Orogeneze: antlerská, kolize klamathského ostrovního oblouku v devonu a spodním karbonu [USEMAP] [USEMAP] Fig. 3. Regional distribution of Antler Orogenic belt across West North America (Poole, 1974; Poole and Sanberg, 1977; Cook and Corboy, 2004). Mesozoic reactivation of the Roberts Mountains thrust is a common feature [USEMAP]Figure 1. Map showing Paleozoic and Mesozoic thrust systems of Nevada, Utah, and southeast California (modifi ed from Long, 2012). Approximate deformation fronts of Paleozoic and Mesozoic thrust systems are shown in brown and blue, respectively, and spatial extents are shaded. Location of Sierra Nevada magmatic arc is from Van Buer et al. (2009) and DeCelles (2004). Abbreviations: GT—Golconda thrust; RMT—Roberts Mountains thrust; LFTB—Luning-Fencemaker thrust belt; CNTB—central Nevada thrust belt; ESTB—Eastern Sierra thrust belt. Mesozoic https://pages.uoregon.edu/ghump/Lectures_files/_wUS_history.pdf 2561_1413 Passive margin Active margin [USEMAP] Sonoma Orogeny (200-280 Ma) • Permo -Triassic • Collision of Arc With a Passive Margin • Island Arc Terrains Were Accreted • golconda allochthon Thrust Partly Over Roberts Mountain Antler allochtone [USEMAP] sonomská, kolize dalšího ostrovníhp oblouku na konci paleozoika [USEMAP] A hick oceanic sequence of Mississippian through Permian chert, limestone, conglomerate, siltstone, shale, lava flows and pyroclastics accumulated in a trough west of the Antler orogenic belt. This tectonic assemblage was emplaced along the Golconda thrust, at least 60 miles (100 km) eastward or inboard of the new continental margin, during the Late Permian through Early Triassic Sonoma Orogeny (Speed, 1983). [USEMAP] Figure 1. Map showing Paleozoic and Mesozoic thrust systems of Nevada, Utah, and southeast California (modifi ed from Long, 2012). Approximate deformation fronts of Paleozoic and Mesozoic thrust systems are shown in brown and blue, respectively, and spatial extents are shaded. Location of Sierra Nevada magmatic arc is from Van Buer et al. (2009) and DeCelles (2004). Abbreviations: GT—Golconda thrust; RMT—Roberts Mountains thrust; LFTB—Luning-Fencemaker thrust belt; CNTB—central Nevada thrust belt; ESTB—Eastern Sierra thrust belt. Výsledek obrázku pro antler orogeny [USEMAP] Cordilleran orogeny 2561_1413 Cordilleran Orogeny components – Jurassic – Tertiary Periods Nevadan – emplacements of large granite batholiths, Sierra Nevada, Idaho, S. California, Coast Ranges. Sevier – Shallower sub-duction angle = igneous activity moves eastward. Laramide – “Rocky Mts.” – east of Sevier Orogeny –Cretaceous – Tertiary Periods Passive margin Active margin [USEMAP] [USEMAP] Fig. 6. Schematic lithospheric cross sections, shown for: A — Late Jurassic (~ 150 Ma); B — Early Cretaceous (~ 100 Ma); C — Late Cretaceous (~ 80 Ma); and D — Paleogene (~ 50 Ma) times. The Late Jurassic was marked by development of an E-dipping subduction zone, increased igneous activity along the magmatic arc, and initial shortening in the western part of the orogenic system. The Early Cretaceous included development of an accretionary complex, growth of the magmatic arc, crustal thickening in the hinterland, thin-skin shortening of the western Sevier belt, and sedimentation within a foreland basin. The Late Cretaceous included decreasing subduction angle (along with early development of a flat-slab segment to the south), a flare-up followed by shutdown of the magmatic arc, lower crustal thickening beneath a hinterland plateau, shortening in the eastern Sevier belt, and broad dynamic subsidence of the Western Interior Seaway. The Paleogene included rapid subduction and NE-underthrusting of the flat-slab segment, minor extension in the thickened hinterland, final shortening in the eastern Sevier belt, and uplift of Laramide arches that disrupted the foreland basin. The Nevadan Orogeny Marked by development of an E-dipping subduction zone, increased igneous activity along the magmatic arc, and initial shortening in the western part of the orogenic system. The Nevadan Orogeny • Several Upper Jurassic Arcs Collided •Cretaceous Franciscan Fm in the accretionary prism • Sierra Nevada was the root zone of the arc The Nevadan Orogeny was a major mountain building event that took place along the western edge of ancient North America between the Mid to Late Jurassic (between about 155 and 145 million years ago). The Sierra Nevada and the Klamath Mountains were the result of continental magmatic arc and then multiple oceanic arcs accretion. In comparison with other orogenic events, it appears that the Nevadan Orogeny occurred rather quickly (10 million years). During the early stages of orogenesis an "Andean type" continental magmatic arc developed due to subduction of the Farallon oceanic plate beneath the North American Plate. The latter stages of orogenesis, in contrast, saw multiple oceanic arc terranes accreted onto the western margin of North America in a "Cordilleran type" accretionary orogen. Deformation related to the accretion of these volcanic arc terranes is mostly limited to the western regions of the resulting mountain ranges (Klamath Mountain range and Sierra Nevada) and is absent from the eastern regions. The massive series of exposed batholiths that currently make up most of the high Sierra Nevada was formed during this event. Due to the steep angle of the subducted plate, these were located relatively close to continent's edge. [USEMAP] http://www.colorado.edu/geolsci/Resources/WUSTectonics/SierraBatholith/images/location.jpg [USEMAP] Andean" style of orogenesis involving the subduction of an oceanic plate beneath a continental plate causing partial melt of the asthenosphere wedge atop the down going plate. The partial melt then rises and causes volcanism to start to build up mountains through lava flows and deposits from eruptions. Idealized diagram showing the docking and accretion of a volcanic island at the edge of a continent. Upper diagram (1): A volcanic island (center) on oceanic crust moves toward the edge of a large continent (right). As the oceanic crust is subducted, an accretionary wedge forms at the edge of the continent and the melting oceanic crust in the subduction zone produces magma, which rises through the continental crust and forms a volcanic mountain range. Lower diagram (2): The volcanic island has docked on the edge of the continent. The active subduction zone has moved seaward, meaning that the original continental volcanic mountain range has gone extinct and an active continental volcanic mountain range has formed near the new subduction zone. The old accretionary wedge is sandwich between the extinct volcanic mountain range and the new active continental volcanic mountain range. A new accretionary wedge has formed at the active subduction zone. "Cordilleran" style of arc terrane accretion onto a continental land mass. Continued subduction transports the arc terrane to the margin of the continent where it is too buoyant to be subducted so it gets accreted to the continent [USEMAP] The Franciscan Complex is an assemblage of metamorphosed and deformed sediments and ophiolites, associated with east-dipping subduction zone. Although most of the Franciscan is Early/Late Jurassic through Cretaceous in age (150-66 Ma),[ some Franciscan rocks are as old as early Jurassic (180-190 Ma) age and as young as Miocene (15 Ma). As oceanic crust descended beneath the continent, ocean floor basalt and sediments were subducted and then tectonically underplated to the upper plate.[10] This resulted in widespread deformation with the generation of thrust faults and folding, and caused high pressure-low temperature regional metamorphism. In the Miocene, the Farallon-Pacific spreading center reached the Franciscan trench and the relative motion between Pacific-North America caused the initiation of the San Andreas Fault. [USEMAP] Fig. 1. Early Mesozoic rocks of the western US Cordillera, Cretaceous batholith belt, and location of major Mesozoic fold-and-thrust belts. The Jurassic to Cretaceous(?) Luning–Fencemaker thrust belt (LFTB) encompasses the entire basinal terrane; only frontal thrusts are shown (Oldow, 1984). Sevier fold-and-thrust belt is Cretaceous to Early Tertiary. SRR is the Santa Rosa Range. A large accretionary wedge, the Franciscan Ophiolite & Mèlange, is thrust up onto western North America Figure 1. Map of Sierra Nevada batholith naming the four Cretaceous intrusive masses (plutons) that contain giant K-feldspar crystals (block pattern), and other less porphyritic plutons (cross-hatch pattern). In addition, two late porphyry intrusions are shown: the Johnson Granite Porphyry, cutting the Cathedral Peak Granodiorite, and the Golden Bear dike, apparently fed from the Whitney Granodiorite. Modifi ed from Kistler and Fleck (1994). ~210 Ma on the east side of the batholith in a single, extensive Triassic sequence 186-155 Ma on both east and west margins of the batholith –Nevadan orogeny 125-88 Ma granitoids, which young eastward, in the axial part of the batholith [USEMAP] Sierra Nevada Mountains 23_11 Nevadan Orogeny: Subduction formed batholith cores of continental volcanic arc, once as tall as Andes [USEMAP] Mount Whitney, the highest mountain in the contiguous United States, with an elevation of 14,505 feet (4,421.2 m) The raising of Whitney (and the downdrop of the Owens Valley) is due to the same geological forces that cause the Basin and Range Province: the crust of much of the intermontane west is slowly being stretched Fig. 7. Diagram showing a timeline of events from the Middle Jurassic through Early Cretaceous of California. The apparent intrusive magma flux of the Sierra Nevada is shown as the red line (from Ducea, 2001). The light-yellow boxes represent periods during which gold mineralization is permissible. The dark-yellow boxes represent times when gold mineralization has been robustly dated (see Table 4). The age range that is permissible for gold mineralization in the Klamath Mountains (KM) ranges from the beginning of orogenic gold mineralization in California at 160 Ma until the lateral offset of the Klamath Mountains from the active arc beginning around 140 Ma. The age range that is permissible for gold mineralization in the Sierra Nevada foothills (SNF) ranges from 160 Ma to approximately 115 Ma, or even as late as 110 Ma if younger K-Ar dates are proven reliable Figure 2. Schematic diagram of major regional tectonic events in the Sierra Nevada Foothills metamorphic belt. Strictly speaking, the Mother. Lode is a narrow belt of gold-bearing quartz veins extending for about. 120 miles through the Sierra Nevada foothills from Mariposa on the south to Georgetown on the north Along with the new data from Snow et al. (2008), our ages show clearly that the bulk of the gold resource within the Mother Lode belt, centered along the Melones fault system was deposited ca. 10 m.y. This overlaps with the final 10 m.y. of ductile deformation and regional metamorphism in the Sierra Nevada foothills, post-dates the final major pulse of Jurassic foothills magmatism by about 10 m.y., and pre-dates the onset of massive batholith emplacement by about 10 m.y. (e.g., Tobisch et al., 1989; Glazner, 1991) https://www.researchgate.net/publication/292224558_New_constraints_on_the_timing_of_gold_formation_ in_the_Sierra_Foothills_province_central_California Sevier orogeny Sevier Orogen (80 Sevier Orogen (50- 130 Ma) • Fold-thrust belt behind the arc • Eastward directed thin skinned thrusts • Franciscan complex and Great Valley fore arc basins • Cretaceous • Batholithic intrusions [USEMAP] Fig. 5 Schematic Late Cretaceous cross-section of the Central Cordillera, showing the relationship between the Sevier fold-and-thrust belt and Cordilleran foreland basin on the east, metamorphic and igneous rocks of the hinterland, Sierra Nevada batholith, Great Valley forearc basin, and Franciscan accretionary complex on the west. [USEMAP] Fig. 5 Schematic Late Cretaceous cross-section of the Central Cordillera, showing the relationship between the Sevier fold-and-thrust belt and Cordilleran foreland basin on the east, metamorphic and igneous rocks of the hinterland, Sierra Nevada batholith, Great Valley forearc basin, and Franciscan accretionary complex on the west. [USEMAP] [USEMAP] The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred from approximately 160 million years (Ma) ago to around 50 Ma. This orogeny was caused by the subduction of the oceanic Farallon Plate underneath the continental North American Plate. Voluminous volcanism is also associated with the Sevier Orogeny. The Sevier orogeny partially overlapped in time and space with the Laramide orogeny. There is evidence that suggests late Sevier faults were active during the early Laramide. Sevier thrusts may have remained active until the Eocene while Laramide deformation began in the Late Cretaceous In general the Sevier orogeny defines compressional event that took advantage of weak bedding planes in overlying Paleozoic and Mesozoic sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “thin-skinned” thrust faults that generally get younger to the east. In contrast, the Laramide orogeny produced “basement-cored” uplifts that often took advantage of pre-existing faults that formed during rifting in the late Precambrian during the breakup of the supercontinent Rodinia or during the Ancestral Rocky Mountains orogeny [USEMAP] Location of the Sevier Fold and Thrust Belt (highlighted in red). After Yonkee and Weil (2015) The Sevier Fold and Thrust Belt extends from southern California near the Mexican border to Canada [USEMAP] Figure 3. (A) Generalized geologic map of the Sevier orogenic belt, approximately restored for Cenozoic extension (base map modifi ed from DeCelles, 2004). Mesozoic thrust systems: LFTB—Luning-Fencemaker thrust belt, CNTB—central Nevada thrust belt, ESTB—eastern Sierra thrust belt, WT—Windermere thrust. Structural culminations in Utah: SC— Sevier culmination, CRC—Canyon Range culmination, SAC—Santaquin culmination, WC—Wasatch culmination. Approximate eastern limit of orogenic plateau based on position of Wasatch hingeline and positions of culminations (queried where unknown) (e.g., DeCelles, 1994, 2004; DeCelles and Coogan, 2006). Line A–A′ delineates approximate crosssection line of Figure 4A. Note that exhumation magnitudes outside of the map area in this study are not quantifi ed. Luning-Fencemaker fold and thrust belt was active from the Middle or Late Jurassic through the. Early Cretaceous – Nevadan orogeny [USEMAP] Figure 4. Schematic cross sections comparing deformation geometries and exhumation patterns between the Sevier orogenic systems. Approximate cross-section lines are shown in Figure 3. (A) Schematic preextensional geometry of the Sevier orogenic system, modifi ed from Allmendinger et al. (1987) and Best et al. (2009). Placements of individual structures and plutons are largely schematic, and are meant to show only general locations. Eastern limit of high topography is placed above the Canyon Range culmination (DeCelles and Coogan, 2006). Generalized exhumation magnitudes are shown by red and orange bars. LFTB—Luning-Fencemaker thrust belt, CNTB—central Nevada thrust belt, SC—Sevier culmination, CRC—Canyon Range culmination, DWC—Delamar–Wah Wah– Canyon Range, Z–Pz—Neoproterozoic–Paleozoic.. [USEMAP] Fig. 6. Schematic lithospheric cross sections, shown for: A — Late Jurassic (~ 150 Ma); B — Early Cretaceous (~ 100 Ma); C — Late Cretaceous (~ 80 Ma); and D — Paleogene (~ 50 Ma) times. The Late Jurassic was marked by development of an E-dipping subduction zone, increased igneous activity along the magmatic arc, and initial shortening in the western part of the orogenic system. The Early Cretaceous included development of an accretionary complex, growth of the magmatic arc, crustal thickening in the hinterland, thin-skin shortening of the western Sevier belt, and sedimentation within a foreland basin. The Late Cretaceous included decreasing subduction angle (along with early development of a flat-slab segment to the south), a flare-up followed by shutdown of the magmatic arc, lower crustal thickening beneath a hinterland plateau, shortening in the eastern Sevier belt, and broad dynamic subsidence of the Western Interior Seaway. The Paleogene included rapid subduction and NE-underthrusting of the flat-slab segment, minor extension in the thickened hinterland, final shortening in the eastern Sevier belt, and uplift of Laramide arches that disrupted the foreland basin. ~210 Ma on the east side of the batholith in a single, extensive Triassic sequence 186-155 Ma on both east and west margins of the batholith –Nevadan orogeny 125-88 Ma granitoids, which young eastward, in the axial part of the batholith [USEMAP] Výsledek obrázku pro Franciscan accretionary prism [USEMAP] Fig. 8.5 Cross sections of the forearc region. Upper: general cross section of typical Cordilleran margin showing tectonic and sedimentary elements and geomorphic settings. Lower: details of forearc setting typical of the Late Jurassic through Paleocene of Central California showing tectonic and sedimentary setting of Franciscan and Great Valley sedimentary rocks. Light tan shows zones of active sedimentation. Note that most Franciscan deposits are bathyal to abyssal and that Great Valley deposits range from shoreline to abyssal. The contact between Franciscan and Great Valley rocks is everywhere tectonic – usually the Coast Range Fault zone. Queried areas have uncertain relations. Over long periods of geologic time, the entire forearc region became new continental crust added to western North America; Cenozoic sedimentary basins and associated volcanic rocks were developed across the forearc region during the ensuing compressional, transpressional, and transform tectonic regimes (Modified after Frisch et al. 2011) [USEMAP] Sevier thin-skinned deformation 23_12 b [USEMAP] http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/images/nw0300-nnc.jpg Competent (resistant to flow) [USEMAP]100 Million Years Ago ~50 Ma: End of subduction •In the Cenozoic, the slab became completely horizontal, probably due to progressive decrease in age of the subducting Farallon Plate as the ridge approached the trench. Results include end of calc-alkaline volcanism, major compressive orogeny far inland (Laramide orogeny of the Rocky Mountains) and emplacement of Pelona and related schists under Southern California 72 [USEMAP] Laramide Orogeny (50- 80 Ma) •Late Cretaceous - Early Eocene •Deformation shifted eastward following •Magmatism – Coast Range Arc •Thick-skinned tectonics The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico. Most hypotheses propose that the angle of subduction became shallow. One cause for shallow subduction may have been an increased rate of plate convergence.The Laramide Orogeny lasted about 30 million years during which the Rocky Mountain foreland ranges were pushed up. The area affected by the Laramide Orogeny includes the central and southern Rockies and the Colorado Plateau. Dynamic processes that propagate deformation across the strong and broad plateau far into the foreland and produce thick-skinned tectonics in the case of the Laramide orogeny are still largely debated [USEMAP] The Laramide orogeny was caused by subduction of a plate at a shallow angle. The Laramide Orogeny lasted about 30 million years during which the Rocky Mountain foreland ranges were pushed up. The area affected by the Laramide Orogeny includes the central and southern Rockies and the Colorado Plateau. [USEMAP] Below, an image prepared by Clair Currie, University of Alberta, showing the difference between subduction prior to Laramide time (above) and during Laramide. Buoyant Subduction Laramide Orogeny 23_14 Normal, thin-skinned Vertical block uplift Approaching Continent pushes accretionary wedge sediments into forearc sediments Now we understand weird looking Tetons [USEMAP] laramide_slab Humphreys et al., 2003 [USEMAP] deformation landward of the relatively undeformed Colo- rado Plateau [USEMAP] Mount Elbert is the highest summit of the Rocky Mountains of North America. With an elevation of 14,438 feet (4400.58 m), https://www.youtube.com/watch?v=tJk9cFz152s https://www.youtube.com/watch?v=74TEQfw6L60 Tertiary Postlaramide evolution ÜFaralon plate partly subducted. San Andreas Fault system was formed, tangential motion and expansion replaced convergent motion as the North American plate began interacting with the Pacific plate. ÜCascades orogeny – subduction of fragments of Faralon plate 42Ma-today ÜBasin and Range extension-Miocene (17 Ma) - Present ÜColumbia and Yellowstone plateau ÜCoast ranges - accretionary wedge complex formed as the Juan de Fuca and North American plates collided. Ü [USEMAP] Block diagram showing a cross section across the Coast Range,Willamette Valley, older Western Cascades, High Cascades and the High Lava Plateau of northern Oregon. [USEMAP] The Cascade Range extends from British Columbia, Canada, south to northern California where it meets the Sierra Nevada. The North Cascades span from the Canadian province of British Columbia to the U.S. state of Washington and are often officially named as the Cascades. The South Cascades in California is bounded on the west by the Sacramento Valley and the Klamath Mountains, and on the east by the Great Basin, The Cascade Region is divided, physiographically, into the Western Cascades and the High Cascades. The Western Cascades, or Ancestral Cascades encompasses volcanic rocks as old as 45 million years. The High Cascades or Modern Cascades are much younger dating from 5-7 million years to just a few hundred years The Cascades are primarily composed of volcanic igneous rock, the youngest of which is found in the active volcanoes of the High Cascades—strikingly large stratovolcanoes that rise high above the landscape of the range. The tallest of the High Cascades is Mt. Rainier, which rises to 4392 meters (14,410 feet) above sea level. The most common rock produced by these volcanoes is andesite, a fine-grained rock of intermediate silica content. Another common rock is dacite, a gray volcanic rock that lies between andesite and rhyolite in terms of its silica content. [USEMAP] Cascades Figure 1. Index map of the western US showing the Ancestral Cascade and High Cascade arcs, the southern Great Basin ignimbrite province, and outlines of the Henry and John (2013). Age contours show approximate location of the initiation of slab rollback magmatism at time indicated as inferred from locally sourced volcanic and intrusive rocks (Henry and John, 2013). East-west line labeled 15 Ma shows approximate location of the Mendocino fracture zone (southern edge of the Farallon plate, which was being subducted beneath North America) at 15 Ma (Atwater and Stock, 1998). The southern terminus of the southern segment of the ancestral Cascade arc gradually migrated north in concert with northerly migration of the Mendocino fracture zone. Accordingly, the southern limit of Farallon [USEMAP] Cascade Range, segment of the Pacific mountain system of western North America. The Cascades extend northward for more than 700 miles (1,100 km) from Lassen Peak, in northern California, U.S., through Oregon and Washington to the Fraser River in southern British Columbia, Canada. Many peaks exceed 10,000 feet (3,000 metres), including Mount Hood (11,235 feet [3,424 metres], highest point in Oregon) and Mount Rainier (14,410 feet [4,392 metres], highest in Washington and in the Cascade Range). Most of the summits are extinct volcanoes, but Lassen Peak (10,457 feet [3,187 metres]) and several others have erupted in the recent past. Mount Baker (10,778 feet [3,285 metres]) steamed heavily in 1975, and Mount St. Helens (8,365 feet [2,550 metres]) erupted in 1980 and again in 1981. [USEMAP] Mt. Rainier 4,392 metres is a steep-sided composite volcano composed of numerous andesite lava flows and volcanic mudflows and covered by glaciers. The Cascadia subduction zone is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates (segments of Faralon plate) move to the east and slide below the much larger mostly continental North American Plate. The Cascade Arc was created after accretion of the Siletzia oceanic plateau perhaps by about 42 million years ago ended a period of flat-slab subduction. The Western Cascades (Ancestral Cascades) began to form 40 million years ago with eruptions from a chain of volcanoes near the Eocene shoreline. Around 10 million years ago, the Modern (High) Cascade arc became active. This renewed period of volcanism and mountain building is believed to be related to changes in the orientation or water content of the subducting tectonic plate. Major eruption of Mount St. Helens in 1980. Tectonic processes active in the Cascadia subduction zone region include accretion, subduction, deep earthquakes, and active volcanism of the Cascades. The Juan de Fuca plate is moving at a rate of about 1.6 inches (4 cm) per year. This subduction zone is responsible for the Cascade magmatic arc. [USEMAP] Northern Cascade Range is almost entirely volcanic in origin Figure 1. Index map of the western US showing the Ancestral Cascade and High Cascade arcs, the southern Great Basin ignimbrite province, and outlines of the Henry and John (2013). Age contours show approximate location of the initiation of slab rollback magmatism at time indicated as inferred from locally sourced volcanic and intrusive rocks (Henry and John, 2013). East-west line labeled 15 Ma shows approximate location of the Mendocino fracture zone (southern edge of the Farallon plate, which was being subducted beneath North America) at 15 Ma (Atwater and Stock, 1998). The southern terminus of the southern segment of the ancestral Cascade arc gradually migrated north in concert with northerly migration of the Mendocino fracture zone. Accordingly, the southern limit of Farallon Models of how Siletzia formed are of two general types:[73] (1) Formation well offshore (possibly as seamounts, like the hotspot Hawaiian-Emperor seamount chain, or a hotspot at a spreading ridge, like Iceland) and then accretion to the continent; (2) formation inshore, on or near the continental margin (perhaps as a result of transcurrent extension, or of a slab window). Soon afterwards, Siletzia entered the preexisting, east-dipping Cordilleran subduction zone and caused it to fail, accreting to North America and causing the new east-dipping Cascadia subduction zone to form outboard of Siletzia Accounting for the observed volumes of basalt requires an enhanced magmatic source, for which most models invoke either the presence of the Yellowstone hotspot, or slab windows. The latter would have resulted from the subduction of the Kula-Farallon (or possibly Farallon—Resurrection) spreading ridge. The relation with the Kula-Farallon spreading ridge is an important element in all models, though its location through that epoch is not well determined Schematic tectonic reconstruction of the Cascadia SZI event (modified from Stern and Dumitru et al., 2019 and Wells et al., 2014). A trench jump occurred due to the accretion of the Siletzia and Yakutat large igneous province (LIP) formed by the Yellowstone plume, initiating the new Cascadia subduction zone. Shown are the new subduction zone (pink line), other active (solid purple lines) and inactive (dashed purple lines) subduction zones, and spreading ridges (solid red lines). Diagram of the northern portion of the Cascadia Subduction Zone. Siletzia is a massive formation of early to middle Eocene epoch marine basalts and interbedded sediments in the forearc of the Cascadia subduction zone, a large fragment of Farallonoceanic lithosphere Fig. 2. Suggested plate configuration map at 53 Ma. Adapted from Haeussler et al. (2003), Seton et al. (2012) and Wells et al. (2014), where the stars represent the proposed positions of the Yellowstone hotspot; 1 (O'Neill et al. (2005), 2 (Doubrovine et al., 2012) and 3 (Müller et al., 1993). Schematic tectonic reconstruction of the Cascadia SZI event (modified from Stern and Dumitru et al., 2019 and Wells et al., 2014). A trench jump occurred due to the accretion of the Siletzia and Yakutat large igneous province (LIP) formed by the Yellowstone plume, initiating the new Cascadia subduction zone. Shown are the new subduction zone (pink line), other active (solid purple lines) and inactive (dashed purple lines) subduction zones, and spreading ridges (solid red lines). The Cascadia SZI (subduction zone initiation) event formed the currently active Cascadia subduction zone at around 53 - 43 Ma (Hyndman et al., 1990; Priest, 1990; Schmandt and Humphreys, 2011; Stern and Dumitru, 2019) and induced subduction of the Farallon and Kula plates below the North America plate. The Cascadia SZI event is believed to have occurred as an episodic subduction via a trench jump after the large igneous province (LIP) Siletzia accreted at the previous trench of the Farallon/Cordilleran subduction zone (Wells et al., 2014; Stern and Dumitru, 2019). There is also an indication of the presence of the prominent Yellowstone mantle plume during the time of the onset, which might have been facilitated by the breaking of the intact subducting plate. It is worth noting that at the time of the trench jump there was ongoing subduction to the north and south of the Cascadia subduction zone. Although the accretion of the Siletzia block is likely to be the main cause of the trench jump, the nearby subduction zones in the north and south might therefore also have had a role in this SZI event. Fig. 8. Cartoon cross section illustrating the major structures inferred from our ambient-noise tomography, emphasizing the inferred distribution of Siletzia lithosphere (dark gray). Cross section location shown in Fig. 2.. The western Columbia Basin is underlain by the Columbia River ood basalts (red), deep sediment filled Eocene basins (yellow), extended Siletzia lithosphere, and magmatic underplate (dark blue). Below the northeastern Columbia Basin, Siletzia lithosphere is shown below the pre-accretion North America crust. From the body wave tomography, Siletzia lithosphere is thought to descend vertically beneath mountainous northeastern Washington. Siletzia is a massive formation of early to middle Eocene epoch marine basalts and interbedded sediments in the forearc of the Cascadia subduction zone, on the west coast of North America. Fig. 1. Map of isotopically distinguishable terranes along the Cascade volcanic arc as outlined by Schmidt et al. (2008). Dashed contours show approximate depths to the slab in km (McCrory et al., 2004). Dashed lines on oceanic plates are magnetic anomalies (Wilson, 1988). Major volcanoes are illustrated as red triangles: (LA) Lassen, (MS) Mt. Shasta, (ML) Medicine Lake, (MMc) Mt. McLaughlin, (CL) Crater Lake, (NV) Newberry Volcano, (TS) Three Sisters, (MJ) Mt. Jefferson, (MH) Mt. Hood, (SH) Mt. St. Helens, (MA) Mt. Adams, (SM) Simcoe, (MR) Mt. Rainer, (GP) Glacier Peak, (MB) Mt. Baker, (MG), Mt. Garibaldi, (MC). Mt. Cayley, (MM) Mt. Meager. Fig. 1. Map of the extent and exposed areas of the Siletz Terrane, adapted from McCrory and Wilson (2013). HR – Hurricane Ridge Fault. Figure 12. (a) Distribution of Oligocene to early Miocene volcanism in the ancestral Cascade arc and back-arc regions. They suggest that the Siletzia basalts are a product of the Yellowstone Hot Spot before the North American Plate moved on it. The relatively thin oceanic crust would have been more easily pierced by the upward-welling plume, resulting in prodigious underwater lava flows. Hence, Siletzia. This illustration, from Camp and Wells’ article, shows their idea: Palinspastic reconstruction of bimodal volcanism along the Nevada–Columbia Basin magmatic belt from ca. 17–15 Ma, with southernmost extension based solely on aeromagnetic data. See Figure 1 for definition of red and blue stars and volcanic fields HRCC, MVF, LOVF, and NNR. Orange arrows depict the orientation of mid-Miocene Basin-and-Range extension; black arrows depict the overall dilation direction of coeval mid-Miocene dikes. CJDS–Chief Joseph dike swarm, where 85% of the Columbia River Basalt Group volume erupted. Area of 17–14 Ma extension from Colgan and Henry (2009). WSRP—Western Snake River Plain. Figure 5-2. Map of the Cascade Range in the Pacific Northwest showing geographic locations, approximate extent of Western (tan) and High Cascades (purple), and the spatial relationships of some major structural features in Oregon. Note that the names Western Cascades and High Cascades are not used in Washington or south of Mount Shasta in California. Figure 1. Map showing the locations of dated Ancestral Cascade deposits along the west coast. From John et al. 2012. [USEMAP] Southern ancestral Cascades Low-angle subduction prior to ca. 52 Ma began to roll back, causing a magmatic migration across the Great Basin that culminated with Oligocene–Miocene ancestral Cascade arc activity in Nevada and southern California Subduction of the Juan de Fuca Plate results in the formation of the Coastal Ranges and Cascade Volcanoes, as well as a variety of earthquakes, in the Pacific Northwest. Olympic and Mt. Rainier national parks showcase the contrasting landscapes of the two parallel mountain ranges. . Subduction of the Juan de Fuca Plate results in the formation of the Coastal Ranges and Cascade Volcanoes, as well as a variety of earthquakes, in the Pacific Northwest. Olympic and Mt. Rainier national parks showcase the contrasting landscapes of the two parallel mountain ranges.. [USEMAP] Coast Range The Coast Range (including the Olympic Mountains) consists of sedimentary rock layers and hard crust scraped off the ocean floor where the Juan de Fuca Plate begins to dive downward. The Sierra Nevada are a remnant of volcanoes that extended southward when the ancient Farallon Plate dove beneath the edge of North America. The Coast Range (accretionary wedge), Great Valley (forearc basin), and Sierra Nevada (volcanic arc) still reflect the subduction zone topography. Rocks in Yosemite, Kings Canyon, Sequoia, and Joshua Tree national parks contain exumed magma chamber rock that formed beneath the ancient volcanoes. National Park Service sites are shown in red. Four-letter codes indicate the ancient volcanic arc parks listed near the top of this page. The mountains, part of the Pacific Coast Ranges, are not especially high – Mount Olympus is the highest summit at 7,980 ft (2,432 m) Mount Waddington in Canada 4019m The Coast Range (including the Olympic Mountains) consists of sedimentary rock layers and hard crust scraped off the ocean floor where the Juan de Fuca Plate begins to dive downward. The grinding action also produces devastating earthquakes, including some that result in giant tsunami waves. [USEMAP] Figure 3. Cross-section diagrams illustrating Cenozoic tectono-sedimentary evolution of the Cascadia forearc and the Oligocene emergence of the southern Oregon Coast Range; see text for details. ACA-Ancestral Cascades arc. [USEMAP] Block diagram showing a cross section across the Coast Range,Willamette Valley, older Western Cascades, High Cascades and the High Lava Plateau of northern Oregon. [USEMAP] Growing influence of the Pacific plate [USEMAP] M:\History.gif [USEMAP] Modern California: Strike-Slip tectonics •There is evidence of strike-slip motion across the surface rupture of the 1872 Lone Pine earthquake. This air-photo of the San Andreas Fault shows a somewhat clearer offset drainage. •On the other hand, California is also a transform plate boundary zone, which is accommodated be a series of strike-slip faults. 123 [USEMAP] Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins. The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch. [USEMAP] The Basin and Range Province began to develop about 20 million years ago. The cause of this disturbance is highly controversial amongst researchers. One possibility is that tension in the earth’s crust, potentially developed as a result in a change in tectonic activity to the west, stretched and thinned, and in some places resulted in uplift as much as twice the crusts original width. This geologic stretching and extension split the region, resulting in down-dropped basins and narrow, elongated mountain ranges. By the Neogene, the Farallon plate lay shallowly under the North American plate for hundreds of kilometers eastward of the West Coast. The Farallon plate was subjected to increasing temperatures as it subducted, causing it to expand. As heat dissipated to the overlying North American plate, that rock expanded as well. Finally, the high temperatures in the upper mantle caused the Farallon plate to melt, and the resulting magma was injected into the North American plate, destabilizing it. These processes, along with the complex crustal movements taking place along the San Andreas fault, caused the surface of the North American plate to pull apart and fault into the north-south trending mountainous blocks and valleys of the huge Basin and Range province. This province covers part of eastern California, most of Nevada, and southern Oregon, as well as parts of other states stretching from Idaho and Utah into Arizona, New Mexico, and Texas. Simple illustration of how basins and ranges are formed by faulting. Formation of the Basin and Range. Alternating basins and ranges were formed during the past 17 million years by gradual movement along faults. Arrows indicate the relative movement of rocks on either side of a fault. Image modified from original by Wade Greenberg-Brand, in turn adapted from an image by the USGS (public domain). Horsts, graben and half-grabens. Modified from University Idaho Structural Geology, online materials. Also in DeCourten 2003. Figure 5. Cross section of the Basin and Range Province. The gray rectanglar outline represents the area traversed by the Virgin River Gorge. Thin curved black lines represent faults. Modified from USGS cross section. This province is literally being split apart by tension resulting from a source of heat energy that exists below the region. Evidence for that heat is provided by numerous volcanoes and lava flows scattered throughout this province. The term “Basin and Range” comes from the generally parallel north-trending mountains (the ranges) separated by valleys (the basins). Rocks in each of these mountain ranges are tilted and bounded by faults and are thus described as fault block mountains. Our Geological Wonderland: The geology of the Virgin River Gorge can be considered to be a geological example of the rabbit hole in “Alice in Wonderland.” [USEMAP] The tectonic activity responsible for the extension in the Basin and Range is a complex and controversial The most accepted hypothesis suggests that crustal shearing associated with the San Andreas Fault caused spontaneous extensional faulting. However, plate movement alone does not account for the high elevation of the Basin and Range region. The western United States is a region of high heat flow which lowers the density of the lithosphere and stimulates isostatic uplift as a consequence. Geologic processes that elevate heat flow are varied, some researchers suggest that matle plume heat generated at a subduction zone is transferred to the overriding plate as subduction proceeds other prefer subduction of Faralon plate [USEMAP] Figure 1. The Basin and Range Province, with northern, central, and southern segments modified from Jones et al. (1992) and Wernicke (1992). The northern and central Basin and Range are bounded to the west by the Sierra Nevada batholith and to the east by the Colorado Plateau. The northern Basin and Range incorporates most of Nevada and western Utah. Its northern boundary is transitional with the Oregon High Lava Plains and the southern extension of the Columbia River Basalt Province, which containsthe initial eruptions of flood basalt in the vicinity of Steens Mountain (SM). It also extends to the northeast, south of the Snake River Plain. [USEMAP] Physiographic subdivisions of the Basin and Range region of the western United States. Greens indicate lower elevation, browns higher elevation Columbia Plateau Nestled between the Cascade and Rocky Mountain ranges, the Columbia Plateau was an inland sea for tens of millions of years, until about 15 million years ago when volcanic activity deposited layer upon layer of lava. The plateau formed between 6 million and 16 million years ago as the result of successive flows of basalt. The subsidence of the crust produced a large, slightly depressed lava plain now known as the Columbia Basin (Plateau). As the molten rock came to the surface, the earths crust gradually sank into the space left by the rising lava. A probable explanation is that a hot spot, an extremely hot plume of deep mantle material, is rising to the surface beneath the Columbia Plateau Province. The track of this hot spot starts in the west and sweeps up to Yellowstone National Park. Another theory explains migrating hotspot volcanism as the result of the fragmentation and dynamics of the subducted Farallon Plate Siletzia terrane has chemical and physical characteristics that suggest it formed due to a mantle plume, and it has a composition similar to the Columbia River Basalts, indicating that the two large lava flow provinces are related. Might the Siletzia terrane have formed due to an early version of the Yellowstone hotspot? Figure 6. Model for the evolution of Yellowstone plume (after Coble and Mahood 2012) that considers the lifting of the Juan de Fuca slab at 25 Ma (A) to have resulted in volcanic quiescence (B) between ca. 23 and 17 Ma, and the distribution of voluminous bimodal basalts and coeval rhyolites (C) to represent breakthrough of plume material at ca. 17 Ma into the upper plate to form a secondary plume head. The Columbia Plateau covers much of the Columbia River Basalt Group, shown in green on this map. The Washington cities of Spokane, Yakima and Pasco, and the Oregon city of Pendleton, lie on the Columbia Plateau. Columbia Plateau —Yellowstone Hotspot Track Volcanic rocks in the Pacific Northwest show the effects of a tectonic plate riding over a deep-mantle hotspot. The Pacific Northwest of the United States has a variety of active tectonic settings, including plate convergence at the Cascadia Subduction Zone and divergence in the Basin and Range Continental Rift Zone. But superimposed on these active tectonic features is a line of volcanic activity stretching from the Columbia Plateau of eastern Oregon and Washington all the way to the Yellowstone Plateau at the intersection of Wyoming, Idaho and Montana. [USEMAP] The volcanism of Yellowstone is believed to be linked to the somewhat older volcanism of Snake River plain. Yellowstone is thus the active part of a hotspot that has moved northeast over time.The origin of this hotspot volcanism is disputed. One theory holds that a mantle plume has caused the Yellowstone hotspot to migrate northeast, while another theory explains migrating hotspot volcanism as the result of the fragmentation and dynamics of the subducted Farallon Plate in Earth's interior [USEMAP] Yellowstone Plateau Volcanic Field The Yellowstone Plateau Volcanic Field, also known as the Yellowstone Supervolcano or the Yellowstone Volcano, is a complex volcano, volcanic plateau and volcanic field located mostly in the western U.S. state of Wyoming, but it also stretches into Idaho and Montana The volcanism of Yellowstone is believed to be linked to the somewhat older volcanism of the Snake River Plain. Yellowstone is thus the active part of a hotspot that has moved northeast over time. The origin of this hotspot volcanism is disputed. One theory holds that a mantle plume has caused the Yellowstone hotspot to migrate northeast, while another theory explains migrating hotspot volcanism as the result of the fragmentation and dynamics of the subducted Farallon Plate in Earth's interior. Yellowstone is at the northeastern end of the Snake River Plain, a great bow-shaped arc through the mountains that extends roughly 400 miles (640 km) from the park to the Idaho-Oregon border. Yellowstone National Park Grand Prismatic Spring Old Faithful Nachází se zde velké množství horkých pramenů, bublajících bahnitých jam, horských jezer, kaňonů, erodovaných lávových proudů a gejzírů. Nejznámějším gejzírem je Old Faithful, jenž tryská průměrně po 64,5 minutách do výšky 40 m, maximálně pak až do výšky 56 m. Takto vytryskuje asi 120 let. [USEMAP] The Yellowstone Plateau Volcanic Field forms the high continental divide between the northern and middle Rocky Mountains. The average elevation of the plateau is about 2,400 m (7,900 ft) and is surrounded on all sides but the southwest by mountainous terrain with peaks that reach 3,000-4,000 m (10,000 - 13,000 ft). The eastern Snake River Plain extends to the southeast as a structural depression that is about 350 km (220 mi) long. Yellowstone National Park, encompassing parts of Wyoming, Montana, and Idaho, is the location for the most recent volcanic activity. Ellesmersko– inuitská orogeneze Při severním okraji severoamerického kratonu probíhala ve spodním paleozoiku ellesmersko-inuitská orogeneze. Dostupné údaje zatím neumožňují jejich jednoznačnou interpretaci. [USEMAP] The Coast Range Arc formed as a result of subduction of the Juan de Fuca, Kula and pre-existing Farallon Plates. It is most famous for being the largest granitic outcropping in North America, which then it is usually referred to as the Coast Plutonic Complex or the Coast Mountains Batholith. Although taking its name from the Coast Mountains, this term is a geologic grouping rather than a geographic one, and the Coast Range Arc extended south into the High Cascades of the Cascade Range, past the Fraser River which is the northward limit of the Cascade Range proper. [USEMAP]