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32-702: It is located near the eastern contact of the Coast Plutonic Complex and the Whitehorse Trough . There are thick series of pyroclastic and epiclastic rocks at the caldera. Remnants of this huge caldera complex are preserved near Bennett Lake in the Coast Mountains . The complex compose the Skukum Group . The Bennett Lake Volcanic Complex was formed when the ancient Kula Plate was subducting under North America during

64-595: A layered metamorphic rock known as gneiss . In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite , appearing to have been nearly melted in the procedure. The remarkable migmatite of the Chelan and Skagit areas in Washington are well known in geologic circles. During construction of intrusions 70 and 57 million years ago,

96-569: A location in the Interior of British Columbia , Canada is a stub . You can help Misplaced Pages by expanding it . This article about a Yukon location is a stub . You can help Misplaced Pages by expanding it . Coast Plutonic Complex The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon . The Coast Range Arc lies along

128-653: A northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated

160-647: A result of subduction of the Kula and pre-existing Farallon Plates . It is most famous for being the largest single body of granitic rock in North America, which is usually referred to as the Coast Plutonic Complex or the Coast Mountains Batholith . It is a coast-parallel continental volcanic arc similar to the Andes of South America and the largest continental volcanic arc fossil in

192-536: A very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

224-479: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

256-590: Is unknown why such a large rupture of the Farallon Plate occurred. Some geologists believe some fundamental change in convection within the Earth's mantle caused the rifting event, while others believe the huge oceanic plate became mechanically unstable as it continued to subduct beneath the Pacific Northwest. The Kula Plate once again continued to subduct beneath the continental margin, supporting

288-754: The Anahim Volcanic Belt , lie in the middle of the Coast Range Arc. Volcanics that form the Anahim Volcanic Belt are not strictly related to Coast Range Arc subduction, but might have formed as a result of the North American Plate sliding over a place that has experienced active volcanism for a long period of time which is described as the Anahim hotspot . During its formation, it lay beneath granitic intrusions of

320-694: The Cretaceous Period is divided in the geologic time scale . Rock strata from this epoch form the Upper Cretaceous Series . The Cretaceous is named after creta , the Latin word for the white limestone known as chalk . The chalk of northern France and the white cliffs of south-eastern England date from the Cretaceous Period. During the Late Cretaceous, the climate was warmer than present, although throughout

352-644: The Coast Range Arc. Volcanism began to decline along the length of the arc about 60 million years ago during the early Paleogene period of the Cenozoic era as the rapid northern movement of the Kula Plate became parallel with the Pacific Northwest, creating a transform fault plate boundary similar to the Queen Charlotte Fault . During this passive plate boundary, the Kula Plate began subducting underneath Alaska and southwestern Yukon at

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384-470: The Coast Range Arc. The approximately 20-kilometre (12 mi) long Bella Bella and approximately 6-kilometre (4 mi) long Gale Passage dike swarms lie in granitic intrusions of the Coast Range Arc and are used to calculate the first appearance of the Anahim hotspot about 13 and 12 million years ago. Late Cretaceous The Late Cretaceous (100.5–66 Ma ) is the younger of two epochs into which

416-859: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

448-850: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

480-400: The ancient Bridge River Ocean which lay between North America and the pre-existing Insular Islands . Massive amounts of molten granite injected over this period, burning the old oceanic sediments into a glittering medium-grade metamorphic rock called schist . The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into

512-458: The arc suggest that the Coast Range Arc was created on Stikinia , a geologic feature that formed in an older volcanic arc environment during the Paleozoic and Mesozoic periods. One of the major events during the Coast Range Arc was about 85 million years ago when a huge rift developed near the center of the oceanic Farallon Plate . This rifting event created the oceanic Kula Plate . It

544-524: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

576-570: The caldera collapse. High level andesite and rhyolite dikes and intrusive bodies crosscut volcanic flows and tuffs at all levels. Dike swarms are emplaced along ring fractures and fault zones at the southwest edge of the caldera. Near the dying stages of the volcano , magma surged upward and arched the roof of the magma chamber into a broad dome with relief of about 1,500 m (4,921 ft) . 60°01′29.04″N 135°19′33.14″W  /  60.0247333°N 135.3258722°W  / 60.0247333; -135.3258722 This article about

608-513: The caldera, which discharged about 850 cubic kilometres (200 cu mi) of pyroclastic material. This volcanic event occurred shortly before nearly all the Kula Plate had been subducted beneath the North American Plate about 40 million years ago. Since the end of the Coast Range Arc about 50 million years ago, many volcanoes have disappeared from erosion . What remains of the Coast Range Arc to this day are granitic intrusions , which were formed when magma intruded and cooled at depth beneath

640-722: The early Eocene period. Cataclysmic eruptions from the Bennett Lake Volcanic Complex were from vents along arcuate fracture systems that ejected out about 850 km (200 cu mi) of glowing avalanches of pyroclastic rock called pyroclastic flows . Evacuation of the underlying magma chamber was followed by several stages of collapse to form two calderas, one nested inside the other, that produced an elliptical depression 19 km (12 mi) by 30 km (19 mi) across. The calderas were from 200 m (656 ft) to 2,700 m (8,858 ft) deep. Volcanism continued for some time after

672-601: The large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held

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704-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

736-577: The northern end of the arc during the early Eocene period. The Coast Range Arc was home to some of the world's most dangerous and explosive volcanoes. Cataclysmic eruptions at the British Columbia–Yukon border created a huge nested caldera called the Bennett Lake Volcanic Complex about 50 million years ago during the early Eocene period. These eruptions were from vents along arcuate fracture systems associated with

768-533: The northern motion of the Kula Plate might have been between 140 and 110 millimetres (5.5–4.3 in) per year. However, other geologic studies determined the Kula Plate moved at a rate as fast as 200 millimetres (7.9 in) per year. Intrusions of the Coast Range Arc are intruded by widespread basaltic dikes . These dikes, although not voluminous, provide an important sampling of the post-arc lithosphere . Additionally, widespread volcanic belts , such as

800-540: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

832-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

864-539: The period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics , the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained

896-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

928-674: The volcanoes. However, remnants of some volcanoes exist in southwestern Yukon, including Montana Mountain , Mount Nansen , and the Bennett Lake , Mount Skukum and Sifton Range volcanic complexes . Many granitic rocks of the Coast Range Arc are plentiful in the North Cascades of the Cascade Range, which is the southernmost boundary of the arc. Here, these granites intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of

960-743: The western margin of the North American Plate in the Pacific Northwest of western North America . 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. The Coast Range Arc formed as

992-585: The world. Volcanism in the arc began during the Late Cretaceous period 100 million years ago based on andesitic composition of the Early Cretaceous volcanic sections and their close temporal and spatial association with masses of felsic intrusive igneous rock with phaneritic texture called tonalite . The basement of the Coast Range Arc was likely Early Cretaceous and Late Jurassic intrusions. Stratigraphic and field relations in

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1024-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

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