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63-508: The HALIP event lasted from 130 million years ago to approximately 60 million years ago. During its active period, there were two distinct phases of volcanism. The first phase lasted from 130 million years ago to 80 million years ago and was characterized by tholeiitic igneous activity. During this time, numerous dikes and sills formed, and there were eruptions of basaltic flow. The basalts formed at this time are relatively rich in TiO 2 and have

126-416: A ternary diagram showing the relative proportions of the oxides Na 2 O + K 2 O (A), FeO + Fe 2 O 3 (F), and MgO (M). As magmas cool, they precipitate out significantly more iron and magnesium than alkali, causing the magmas to move towards the alkali corner as they cool. In the tholeiitic magma, magnesium-rich crystals are produced preferentially, the magnesium content of the magma plummets, causing

189-473: A 10–15 million-year period, lava flow after lava flow poured out of multiple dikes which trace along an old fault line running from south-eastern Oregon through to western British Columbia. The many layers of lava eventually reached a thickness of more than 1.8 km (5,900 ft). As the molten rock came to the surface, the Earth's crust gradually sank into the space left by the rising lava. This subsidence of

252-474: A fine, glassy groundmass , as may other types of basalt. Tholeiitic rocks are the most common igneous rocks in Earth's crust , produced by submarine volcanism at mid-ocean ridges and make up much of the ocean crust. Tholeiitic basaltic magmas are initially generated as partial melts of peridotite ( olivine and pyroxene ) produced by decompression melting of the Earth's mantle . Tholeiitic basalt constituting

315-643: A maximum Pomona flow emplacement duration of several months based on the time required for rivers to be reestablished in their canyons following a basalt flow interruption. Three major tools are used to date the CRBG flows: Stratigraphy, radiometric dating, and magnetostratigraphy. These techniques have been key to correlating data from disparate basalt exposures and boring samples over five states. Major eruptive pulses of flood basalt lavas are laid down stratigraphically . The layers can be distinguished by physical characteristics and chemical composition. Each distinct layer

378-418: A similar composition to continental flood basalts . The second phase lasted from approximately 85 million years ago to 60 million years ago and was characterized by mildly alkaline igneous activity and the eruption of flood basalts. The igneous rocks formed during the second phase have a similar geochemical makeup as the intra-plate composition. The Arctic Ocean is a few hundred million years old, making it

441-654: A source near the Alpha Ridge . The Svalbard province is also closely associated with the Franz Josef Land province (discussed below). The two provinces combined cover an area of approximately 750,000 km (290,000 sq mi). The Franz Josef Land province is closely associated with the Svalbard province. Franz Josef Land is located approximately 300 km (190 mi) east of Svalbard and contains igneous rocks of very similar composition to those of Svalbard. However,

504-465: A stratum was deposited. This is possible because, as magnetic minerals precipitate in the melt (crystallize), they align themselves with Earth's current magnetic field. The Steens Basalt captured a highly detailed record of the Earth's magnetic reversal that occurred roughly 15 million years ago. Over a 10,000-year period, more than 130 flows solidified – roughly one flow every 75 years. As each flow cooled below about 500 °C (932 °F), it captured

567-675: Is 17.67±0.32 Ma with younger lava flows ranging to 15.50±0.40 Ma. Although the Imnaha Basalt overlies Lower Steens Basalt, it has been suggested that it is interfingered with Upper Steens Basalt. The next oldest of the flows, from 17 million to 15.6 million years ago, make up the Grande Ronde Basalt. Units (flow zones) within the Grande Ronde Basalt include the Meyer Ridge and the Sentinel Bluffs units. Geologists estimate that

630-792: Is believed the Yellowstone Hotspot created features like Smith Rock in Central Oregon and perhaps another flood basalt event known as Siletzia which underlies much of the Pacific Northwest coast with exposures in the Oregon Coast Range . There is additional confirmation that Yellowstone is associated with a deep hot spot. Using tomographic images based on seismic waves, relatively narrow, deeply seated, active convective plumes have been detected under Yellowstone and several other hot spots. These plumes are much more focused than

693-997: Is made up of the Umatilla Member flows, the Wilbur Creek Member flows, the Asotin Member flows (13 million years ago), the Weissenfels Ridge Member flows, the Esquatzel Member flows, the Elephant Mountain Member flows (10.5 million years ago), the Bujford Member flows, the Ice Harbor Member flows (8.5 million years ago) and the Lower Monumental Member flows (6 million years ago). Camp & Ross (2004) observed that

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756-450: Is named for its type locality near the municipality of Tholey , Saarland , Germany . Columbia River Basalt Group The Columbia River Basalt Group (CRBG) is the youngest, smallest and one of the best-preserved continental flood basalt provinces on Earth, covering over 210,000 km (81,000 sq mi) mainly eastern Oregon and Washington , western Idaho , and part of northern Nevada . The basalt group includes

819-671: Is thought to have caused global warming that led to the Cenomanian-Turonian extinction event . Late Cretaceous (92–86 Ma) vertebrates, including 2.4 m (7.9 ft) long champsosaurs , a crocodile-like reptile, found in the Canadian Arctic suggests that polar climate was much warmer during the Cretaceous when average annual temperature must have exceeded 14 °C. The BLIP intrusions could have released perhaps 9,000 Gt (8.9 × 10 long tons; 9.9 × 10 short tons) of carbon from

882-429: Is typically assigned a name usually based on area (valley, mountain, or region) where that formation is exposed and available for study. Stratigraphy provides a relative ordering (ordinal ranking) of the CRBG layers. Absolute dates, subject to a statistical uncertainty, are determined through radiometric dating using isotope ratios such as Ar/ Ar dating, which can be used to identify the date of solidifying basalt. In

945-784: The Amerasian Basin and the Arctic Ocean. HALIP dispersed the components of this second continent around the margins of the Arctic Ocean where they are now terranes and microplates embedded into fold belts or overlain by sediments. As the Atlantic and Arctic oceans opened during the Mesozoic and into the Cenozoic , the Arctic Region underwent several stages of rifting, sedimentation, and magmatism. Dolerites collected from Svalbard and elsewhere in

1008-584: The Canadian Arctic Islands . The region is characterized by the presence of a radiating dike swarm across the Queen Elizabeth Islands that seems to suggest the presence of a mantle plume beneath the Alpha Ridge. This province contains igneous rocks of both tholeiitic and alkaline composition. There are also a respectable number of sills and flood basalts in the province. The flood basalts in

1071-532: The Chilcotin Group in south-central British Columbia , Canada . The Latah Formation sediments of Washington and Idaho are interbedded with a number of the Columbia River Basalt Group flows, and outcrop across the region. Absolute dates, subject to a statistical uncertainty, are determined through radiometric dating using isotope ratios such as Ar/ Ar dating, which can be used to identify

1134-669: The Icelandic hotspot . The HALIP is divided into several magmatic provinces. These provinces are divided by location, igneous rock composition, and the formations present. In the Svalbard province, the HALIP is expressed as an extensive system of alkaline intrusive doleritic rocks. The intrusions largely appear in the form of sills that can reach thicknesses of 100 m (330 ft) and continuously extend for up to 30 km (19 mi) laterally. The basaltic rocks found in Svalbard have an intra-plate composition and are thought to originate from

1197-484: The International Union of Geological Sciences recommends that tholeiitic basalt be used in preference to that term. Tholeiitic rock types tend to be more enriched in iron and less enriched in aluminium than calc-alkaline rock types. They are thought to form in a less oxidized environment than calc-alkaline rocks. Tholeiitic basalt is formed at mid-ocean ridges and makes up much of the oceanic crust. Almost all

1260-549: The Tualatin Mountains on the west side of Portland. Individual flows included large quantities of basalt. The McCoy Canyon flow of the Sentinel Bluffs Member released 4,278 km (1,026 cu mi) of basalt in layers of 10 to 60 m (33 to 197 ft) in thickness. The Umtanum flow has been estimated at 2,750 km (660 cu mi) in layers 50 m (160 ft) deep. The Pruitt Draw flow of

1323-678: The Yellowstone hotspot 's initial flood-basalt event occurred near Steens Mountain when the Imnaha and Steens eruptions began. As the North American Plate moved several centimeters per year westward, the eruptions progressed through the Snake River Plain across Idaho and into Wyoming . Consistent with the hot spot hypothesis, the lava flows are progressively younger as one proceeds east along this path. Previous to this eruptive period, it

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1386-428: The calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. Rock types of the tholeiitic magma series include tholeiitic basalt , ferro-basalt, tholeiitic basaltic andesite , tholeiitic andesite , dacite and rhyolite . The variety of basalt in the series was originally called tholeiite but

1449-457: The contact aureoles which could have triggered the Aptian oceanic anoxic event (OAE1a) at 120 Ma. 79°26′56″N 11°23′44″E  /  79.4488°N 11.3955°E  / 79.4488; 11.3955 Tholeiitic magma series The tholeiitic magma series ( / ˌ θ oʊ l i ˈ aɪ t ɪ k / ) is one of two main magma series in subalkaline igneous rocks , the other being

1512-492: The 500 km (310 mi)-long Ginkgo flow of the Frenchman Springs Member, determining that it had been formed in roughly a week, based on the measured melting temperature along the flow from the origin to the most distant point of the flow, combined with hydraulics considerations. The Ginkgo basalt was examined over its 500 km (310 mi) flow path from a Ginkgo flow feeder dike near Kahlotus, Washington to

1575-496: The Arctic are mafic intra-plate tholeiites characteristic of HALIP, which indicated that the LIP formed during the opening of the Arctic Ocean around 148–70 Ma. Seismic and magnetic analyses of the seafloor produced ages of 118–83 Ma. The HALIP is widely thought to have originated from a mantle plume , and the igneous activity of the province often tracked along a similar path as

1638-403: The CRBG deposits Ar, which is produced by K decay, only accumulates after the melt solidifies. Magnetostratigraphy is also used to determine age. This technique uses the pattern of magnetic polarity zones of CRBG layers by comparison to the magnetic polarity timescale. The samples are analyzed to determine their characteristic remanent magnetization from the Earth's magnetic field at the time

1701-738: The Canadian Arctic Islands are similar to those of the Columbia River flood basalts in the Pacific Northwest of the United States. The Sverdrup Basin Magmatic Province covers an area of 550,000 km (210,000 sq mi). The Amerasian Basin's most prominent feature is the Alpha Ridge – which is thought to be the location of the mantle plume that fed the HALIP. The ridge reaches a height of 2,700 m (8,900 ft) from

1764-428: The Columbia River Basalt Group (CRBG), similar to other large igneous provinces , was also marked by atmospheric loading through the mass exsolution and emission of volatiles, via the process of volcanic degassing. Comparative analysis of volatile concentrations in source feeder dikes to associated extruded flow units have been quantitatively measured to determine the magnitude of degassing exhibited in CRBG eruptions. Of

1827-448: The Ginkgo flow occurred in less than a week. The cooling/hydraulics analyses are supported by an independent indicator; if longer periods were required, external water from temporarily dammed rivers would intrude, resulting in both more dramatic cooling rates and increased volumes of pillow lava . Ho's analysis is consistent with the analysis by Reidel, Tolan, & Beeson (1994), who proposed

1890-538: The Grande Ronde Basalt comprises about 85 percent of the total flow volume. It is characterized by a number of dikes called the Chief Joseph Dike Swarm near Joseph , Enterprise , Troy and Walla Walla through which the lava upwelling occurred (estimates range to up to 20,000 such dikes). Many of the dikes were fissures 5 to 10 m (16 to 33 ft) wide and up to 10 miles (16 km) in length, allowing for huge quantities of magma upwelling. Much of

1953-621: The Grande Ronde basalts, but can be identified by different chemical characteristics. It flowed west to the Pacific, and can be found in the Columbia Gorge, along the upper Clackamas River, the hills south of Oregon City . and as far west as Yaquina Head near Newport, Oregon – a distance of 750 km (470 mi). The Saddle Mountains Basalt, seen prominently at the Saddle Mountains ,

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2016-537: The Oregon Plateau in sections up to 1 km (3,300 ft) thick. It contains the earliest identified eruption of the CRBG large igneous province. The type locality for the Steens basalt, which covers a large portion of the Oregon Plateau, is an approximately 1,000 m (3,300 ft) face of Steens Mountain showing multiple layers of basalt. The oldest of the flows considered part of the Columbia River Basalt Group,

2079-521: The Roza flow. Sulfuric acid , a by-product of emitted sulfur dioxide and atmospheric interactions, has been calculated to be 1.7Gt annually for the Roza flow and 17Gt in total. Analysis of glass inclusions within phenocrysts of the basaltic deposits have yielded emission volumes on the magnitude of 310 Mt of hydrochloric acid , and 1.78 Gt of hydrofluoric acid , additionally. Major hotspots have often been tracked back to flood-basalt events. In this case

2142-602: The Steens Basalt flow are considered to be atypical of other dike swarm trends associated with the CRBG. These swarms, characterized by a maintained trend of N20°E, trace the northward continuation of the Nevada shear zone and have been attributed to magmatic rise through this zone on a regional scale. Virtually coeval with the oldest of the flows, the Imnaha basalt flows welled up across northeastern Oregon. There were 26 major flows over

2205-465: The Steens and Picture Gorge basalt formations. During the middle to late Miocene epoch , the Columbia River flood basalts engulfed about 163,700 km (63,200 sq mi) of the Pacific Northwest , forming a large igneous province with an estimated volume of 174,300 km (41,800 cu mi). Eruptions were most vigorous 17–14 million years ago, when over 99 percent of

2268-448: The Steens basalt, includes flows geographically separated but roughly concurrent with the Imnaha flows. Older Imnaha basalt north of Steens Mountain overlies the chemically distinct lowermost flows of Steens basalt; hence some flows of the Imnaha are stratigraphically younger than the lowermost Steens basalt. One geomagnetic field reversal occurred during the Steens Basalt eruptions at approximately 16.7 Ma, as dated using Ar/ Ar ages and

2331-783: The Teepee Butte Member released about 2,350 km (560 cu mi) with layers of basalt up to 100 m (330 ft) thick. The Wanapum Basalt is made up of the Eckler Mountain Member (15.6 million years ago), the Frenchman Springs Member (15.5 million years ago), the Roza Member (14.9 million years ago) and the Priest Rapids Member (14.5 million years ago). They originated from vents between Pendleton, Oregon and Hanford, Washington . The Frenchman Springs Member flowed along similar paths as

2394-418: The archipelago is scattered with a prominent swarm of southeast trending dikes. Extensive sills and volcanic flows can also be found in the region, as well as a few dikes of other trends. The timing of the Franz Josef Land formations and the Svalbard formations is thought to be nearly identical, furthering the evidence for a large initial plume head model for the HALIP. The Sverdrup Basin province spreads across

2457-497: The basalt found on the Moon is tholeiitic basalt. Rocks in the tholeiitic magma series are classified as subalkaline (they contain less sodium than some other basalts) and are distinguished from rocks in the calc-alkaline magma series by the redox state of the magma they crystallized from (tholeiitic magmas are reduced; calc-alkaline magmas are oxidized ). When the parent magmas of basalts crystallize, they preferentially crystallize

2520-587: The basalt was released. Less extensive eruptions continued 14–6 million years ago. Erosion resulting from the Missoula Floods has extensively exposed these lava flows, laying bare many layers of the basalt flows at Wallula Gap , the lower Palouse River , the Columbia River Gorge and throughout the Channeled Scablands . The Columbia River Basalt Group is thought to be a potential link to

2583-534: The crust produced a large, slightly depressed lava plain now known as the Columbia Basin or Columbia River Plateau . The northwesterly advancing lava forced the ancient Columbia River into its present course. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. In these ancient lake beds are found fossil leaf impressions, petrified wood , fossil insects, and bones of vertebrate animals. In

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2646-689: The date of solidifying basalt. In the CRBG deposits Ar, which is produced by K decay, only accumulates after the melt solidifies. Other flood basalts include the Deccan Traps (late Cretaceous period ), that cover an area of 500,000 km (190,000 sq mi) in west-central India ; the Emeishan Traps ( Permian ), which cover more than 250,000 square kilometers in southwestern China ; and Siberian Traps (late Permian ) that cover 2 million km (800,000 sq mi) in Russia . Some time during

2709-434: The emission of sulphur for the Roza flow is calculated to be on the order of 12Gt (12,000 million tonnes) at a rate of 1.2Gt (1,200 million tonnes) annually, in the form of sulphur dioxide (SO2). However, other research through petrologic analysis has yielded SO2 mass degassing values at 0.12% - 0.28% of the total erupted mass of the magma, translating to lower emission estimates in the range of 9.2Gt of sulfur dioxide for

2772-520: The exposed 2,000-foot (610 m) walls of Joseph Canyon along Oregon Route 3 . The Grande Ronde basalt flows flooded down the ancestral Columbia River channel to the west of the Cascade Mountains . It can be found exposed along the Clackamas River and at Silver Falls State Park where the falls plunge over multiple layers of the Grande Ronde basalt. Evidence of eight flows can be found in

2835-667: The flow terminus in the Pacific Ocean at Yaquina Head , Oregon . The basalt had an upper melting temperature of 1 095 ± 5 °C and a lower temperature to 1 085 ± 5 °C; this indicates that the maximum temperature drop along the Ginkgo flow was 20 °C. The lava must have spread quickly to achieve this uniformity. Analyses indicate that the flow must remain laminar , as turbulent flow would cool more quickly. This could be accomplished by sheet flow, which can travel at velocities of 1 to 8 metres per second (2.2 to 17.9 mph) without turbulence and minimal cooling, suggesting that

2898-410: The geomagnetic polarity timescale. Steens Mountain and related sections of Oregon Plateau flood basalts at Catlow Peak and Poker Jim Ridge 70 to 90 km (43 to 56 mi) to the southeast and west of Steens Mountain, provide the most detailed magnetic field reversal data (reversed-to-normal polarity transition) yet reported in volcanic rocks. The observed trend in feeder dike swarms associated with

2961-443: The intermediate members of the tholeiitic and calc-alkali magma series quite well. However, the felsic end members of the two series are nearly indistinguishable, so granitic rocks are generally assigned to the calc-alkali magma series. The mafic end members may be distinguished by the aluminium content, with tholeiitic basalts containing 12% to 16% Al 2 O 3 versus 16% to 20% Al 2 O 3 for calc-alkali basalts. Like all basalt,

3024-693: The lava flowed north into Washington as well as down the Columbia River channel to the Pacific Ocean ; the tremendous flows created the Columbia River Plateau . The weight of this flow (and the emptying of the underlying magma chamber) caused central Washington to sink, creating the broad Columbia Basin in Washington. The type locality for the formation is the canyon of the Grande Ronde River . Grande Ronde basalt flows and dikes can also be seen in

3087-463: The magma to move away from the magnesium corner until it runs low on magnesium and simply moves towards the alkali corner as it loses iron and any remaining magnesium. With the calc-alkaline series, however, the precipitation of magnetite causes the iron-magnesium ratio to remain relatively constant, so the magma moves in a straight line towards the alkali corner on the AFM diagram. The AFM plot distinguishes

3150-499: The magnetic field's orientation-normal, reversed, or in one of several intermediate positions. Most of the flows froze with a single magnetic orientation. However, several of the flows, which freeze from both the upper and lower surfaces, progressively toward the center, captured substantial variations in magnetic field direction as they froze. The observed change in direction was reported as 50⁰ over 15 days. The Steens Basalt flows covered about 50,000 km (19,000 sq mi) of

3213-667: The mid-Miocene. The flows can be divided into four major categories: The Steens Basalt, Grande Ronde Basalt, the Wanapum Basalt, and the Saddle Mountains Basalt. The various lava flows have been dated by radiometric dating—particularly through measurement of the ratios of isotopes of potassium to argon . The Columbia River flood basalt province comprises more than 300 individual basalt lava flows that have an average volume of 500 to 600 cubic kilometres (120 to 140 cu mi). The transition to flood volcanism in

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3276-574: The middle Miocene, 17 to 15 Ma, the Columbia Plateau and the Oregon Basin and Range of the Pacific Northwest were flooded with lava flows. Both flows are similar in composition and age, and have been attributed to a common source, the Yellowstone hotspot . The ultimate cause of the volcanism is still up for debate, but the most widely accepted idea is that the mantle plume or upwelling (similar to that associated with present-day Hawaii) initiated

3339-497: The more magnesium-rich and iron-poor forms of the silicate minerals olivine and pyroxene , causing the iron content of tholeiitic magmas to increase as the melt is depleted of iron-poor crystals. However, a calc-alkaline magma is oxidized enough to precipitate significant amounts of the iron oxide magnetite , causing the iron content of the magma to remain more steady as it cools than with a tholeiitic magma. The difference between these two magma series can be seen on an AFM diagram,

3402-489: The more than 300 individual flows associated with the CRBG, the Roza flow contains some of the most chemically well preserved basalts for volatile analysis. Contained within the Wanapum formation, Roza is one of the most extensive members of the CRBG with an area of 40,300 square kilometres and a volume of 1,300 cubic kilometres. With magmatic volatile values assumed at 1 - 1.5 percent by weight concentration for source feeder dikes,

3465-488: The oceanic crust is termed MORB: m id- o cean- r idge b asalt. Throughout the process of igneous differentiation , the oceanic crust acts to reduce the magma, producing the tholeiitic trend. In contrast, alkali basalts are not typical of ocean ridges, but are erupted on some oceanic islands and on continents, as also is tholeiitic basalt. Because the Moon is extremely reduced , all of its basalts are tholeiitic. Tholeiite

3528-556: The period, one roughly every 15,000 years. Although estimates are that this amounts to about 10% of the total flows, they have been buried under more recent flows, and are visible in few locations. They can be seen along the lower benches of the Imnaha River and Snake River in Wallowa county. The Imnaha lavas have been dated using the K–Ar technique, and show a broad range of dates. The oldest

3591-455: The plume at 650 and 400 km (400 and 250 mi), which may correspond to phase changes or may reflect still-to-be-understood viscosity effects. Additional data collection and further modeling will be required to achieve a consensus on the actual mechanism. The Columbia River Basalt Group flows exhibit essentially uniform chemical properties through the bulk of individual flows, suggesting rapid placement. Ho and Cashman (1997) characterized

3654-416: The rock type is dominated by olivine , clinopyroxene and plagioclase , with minor iron- titanium oxides. Orthopyroxene or pigeonite may also be present in tholeiitic basalt, and olivine, if present, may be rimmed by either of these calcium-poor pyroxenes. Tridymite or quartz may be present in the fine-grained groundmass of tholeiitic basalt, and feldspathoids are absent. Tholeiitic rocks may have

3717-462: The seafloor. Also in the region are a few basaltic dikes. The Amerasian Basin extends over 200,000 km (77,000 sq mi). The northern Greenland province, also known as Peary Land, contains three dike swarms. The Nansen Land swarm trends SSE-SE and is the oldest of the swarms. The middle-aged swarm is known as the Erlandsen Swarm and trends SE-ESE. The J. P. Koch Swarm is the youngest of

3780-648: The three and trends eastward. The two younger swarms tend to have igneous rocks of alkaline composition, while the Nansen Land swarm tends to have more tholeiitic composition. The Peary Land province covers an area of over 80,000 km (31,000 sq mi). The Barents Sea province is characterized by igneous intrusions with much similarity to Svalbard and Franz-Josef Land. This region is well known for being petroleum-rich. The Barents Sea province covers an area of 15,000 to 20,000 km (5,800 to 7,700 sq mi). The HALIP, along with other large igneous provinces,

3843-399: The upwelling observed with large-scale plate-tectonics circulation. The hot spot hypothesis is not universally accepted as it has not resolved several questions. The Yellowstone hot spot volcanism track shows a large apparent bow in the hot-spot track that does not correspond to changes in plate motion if the northern CRBG floods are considered. Further, the Yellowstone images show necking of

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3906-561: The widespread and voluminous basaltic volcanism about 17 million years ago. As hot mantle plume materials rise and reach lower pressures, the hot materials melt and interact with the materials in the upper mantle , creating magma . Once that magma breaches the surface, it flows as lava and then solidifies into basalt. Prior to 17.5 million years ago, the Western Cascade stratovolcanoes erupted with periodic regularity for over 20 million years, even as they do today. An abrupt transition to shield volcanic flooding took place in

3969-454: The youngest ocean on Earth. In the Precambrian , when the Arctic was located south of the Equator, the continent Arctica (or Arctida) filled the gap between the cratons that today surround the Arctic region. Arctica rifted apart in the Late Precambrian (950 Ma) and was reassembled in a new configuration in the Late Paleozoic (255 Ma). During the Jurassic -Cretaceous this second continent, known as Pangea , broke apart, opening

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