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107-762: Isotopic dating indicates the most active magmatic phase of the NAIP was between c.  60.5 and c. 54.5 Ma (million years ago) (mid-Paleocene to early Eocene) – further divided into Phase 1 (pre-break-up phase) dated to c. 62–58 Ma and Phase 2 (syn-break-up phase) dated to c. 56–54 Ma. Continuing research also indicates that tectonic plate movement (of the Eurasian , Greenland , and North American plates), regional rifting events, and seafloor spreading between Labrador and Greenland may have begun as early as c. 95–80 Ma, c. 81 Ma, and c. 63–61 Ma respectively (late Cretaceous to early Paleocene). Studies have suggested that

214-405: A mass spectrometer . The mass spectrometer was invented in the 1940s and began to be used in radiometric dating in the 1950s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ," depending on their mass and level of ionization. On impact in the cups,

321-466: A July 2022 paper in the journal Applied Geochemistry , the authors proposed that the terms "parent isotope" and "daughter isotope" be avoided in favor of the more descriptive "precursor isotope" and "product isotope", analogous to "precursor ion" and "product ion" in mass spectrometry . Flood basalt A flood basalt (or plateau basalt ) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or

428-510: A better time resolution than that available from long-lived isotopes, short-lived isotopes that are no longer present in the rock can be used. At the beginning of the solar system, there were several relatively short-lived radionuclides like Al, Fe, Mn, and I present within the solar nebula. These radionuclides—possibly produced by the explosion of a supernova—are extinct today, but their decay products can be detected in very old material, such as that which constitutes meteorites . By measuring

535-408: A consequence of background radiation on certain minerals. Over time, ionizing radiation is absorbed by mineral grains in sediments and archaeological materials such as quartz and potassium feldspar . The radiation causes charge to remain within the grains in structurally unstable "electron traps". Exposure to sunlight or heat releases these charges, effectively "bleaching" the sample and resetting

642-450: A cubic km per day per km of fissure length ) and the relatively low viscosity of basaltic lava. However, the lateral extent of individual flood basalt flows is astonishing even for so fluid a lava in such quantities. It is likely that the lava spreads by a process of inflation in which the lava moves beneath a solid insulating crust, which keeps it hot and mobile. Studies of the Ginkgo flow of

749-476: A dead zone. However, not all large igneous provinces are connected with extinction events. The formation and effects of a flood basalt depend on a range of factors, such as continental configuration, latitude, volume, rate, duration of eruption, style and setting (continental vs. oceanic), the preexisting climate , and the biota resilience to change. Representative continental flood basalts and oceanic plateaus, arranged by chronological order, together forming

856-411: A different nuclide. This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles ) and beta decay ( electron emission, positron emission, or electron capture ). Another possibility is spontaneous fission into two or more nuclides. While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of

963-402: A half-life of 1.3 billion years, so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas , feldspars , and hornblendes , though the closure temperature is fairly low in these materials, about 350 °C (mica) to 500 °C (hornblende). This is based on the beta decay of rubidium-87 to strontium-87 , with a half-life of 50 billion years. This scheme

1070-479: A higher time resolution at the expense of timescale. I beta-decays to Xe with a half-life of 16.14 ± 0.12 million years . The iodine-xenon chronometer is an isochron technique. Samples are exposed to neutrons in a nuclear reactor. This converts the only stable isotope of iodine ( I ) into Xe via neutron capture followed by beta decay (of I ). After irradiation, samples are heated in

1177-399: A kiln. Other methods include: Absolute radiometric dating requires a measurable fraction of parent nucleus to remain in the sample rock. For rocks dating back to the beginning of the solar system, this requires extremely long-lived parent isotopes, making measurement of such rocks' exact ages imprecise. To be able to distinguish the relative ages of rocks from such old material, and to get

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1284-546: A line from Ireland to the Hebrides and plutonic complexes were formed. Hot magma over 1000 °C surfaced as multiple, successive and extensive lava flows covered over the original landscape, burning forests, filling river valleys, burying hills, to eventually form the Thulean Plateau, which contained various volcanic landforms such as lava fields and volcanoes . There was more than one period of volcanic activity during

1391-592: A listing of large igneous provinces : Flood basalts are the dominant form of magmatism on the other planets and moons of the Solar System. The maria on the Moon have been described as flood basalts composed of picritic basalt. Individual eruptive episodes were likely similar in volume to flood basalts of Earth, but were separated by much longer quiescent intervals and were likely produced by different mechanisms. Extensive flood basalts are present on Mars. Trap rock

1498-464: A million years, with individual events each erupting hundreds of cubic kilometers of basalt. This highly fluid basalt lava can spread laterally for hundreds of kilometers from its source vents, covering areas of tens of thousands of square kilometers. Successive eruptions form thick accumulations of nearly horizontal flows, erupted in rapid succession over vast areas, flooding the Earth's surface with lava on

1605-467: A polished slice of a material to determine the density of "track" markings left in it by the spontaneous fission of uranium-238 impurities. The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons . This causes induced fission of U, as opposed to the spontaneous fission of U. The fission tracks produced by this process are recorded in

1712-430: A radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life , usually given in units of years when discussing dating techniques. After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide or decay product . In many cases, the daughter nuclide itself is radioactive, resulting in a decay chain , eventually ending with

1819-438: A range of several hundred thousand years. A related method is ionium–thorium dating , which measures the ratio of ionium (thorium-230) to thorium-232 in ocean sediment . Radiocarbon dating is also simply called carbon-14 dating. Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years (which is very short compared with the above isotopes), and decays into nitrogen. In other radiometric dating methods,

1926-612: A regional scale. These vast accumulations of flood basalt constitute large igneous provinces . These are characterized by plateau landforms, so that flood basalts are also described as plateau basalts . Canyons cut into the flood basalts by erosion display stair-like slopes, with the lower parts of flows forming cliffs and the upper part of flows or interbedded layers of sediments forming slopes. These are known in Dutch as trap or in Swedish as trappa , which has come into English as trap rock ,

2033-406: A series of steps and the xenon isotopic signature of the gas evolved in each step is analysed. When a consistent Xe / Xe ratio is observed across several consecutive temperature steps, it can be interpreted as corresponding to a time at which the sample stopped losing xenon. Samples of a meteorite called Shallowater are usually included in the irradiation to monitor

2140-470: A significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied. All ordinary matter is made up of combinations of chemical elements , each with its own atomic number , indicating

2247-559: A silica content of around 52%. The magnesium number (the mol% of magnesium out of the total iron and magnesium content) is around 55, versus 60 for a typical MORB. The rare earth elements show abundance patterns suggesting that the original (primitive) magma formed from rock of the Earth's mantle that was nearly undepleted ; that is, it was mantle rock rich in garnet and from which little magma had previously been extracted. The chemistry of plagioclase and olivine in flood basalts suggests that

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2354-511: A single province. For example, the flood basalts of the Parana Basin can be divided into a low phosphorus and titanium group (LPT) and a high phosphorus and titanium group (HPT). The difference has been attributed to inhomogeneity in the upper mantle, but strontium isotope ratios suggest the difference may arise from the LPT magma being contaminated with a greater amount of melted crust. Theories of

2461-467: A term particularly used in the quarry industry. The great thickness of the basalt accumulations, often in excess of 1,000 meters (3,000 ft), usually reflects a very large number of thin flows, varying in thickness from meters to tens of meters, or more rarely to 100 meters (330 ft). There are occasionally very thick individual flows. The world's thickest basalt flow may be the Greenstone flow of

2568-460: A variable amount of uranium content. Because the fission tracks are healed by temperatures over about 200 °C the technique has limitations as well as benefits. The technique has potential applications for detailing the thermal history of a deposit. Large amounts of otherwise rare Cl (half-life ~300ky) were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of Cl in

2675-496: Is comparable with the rate of extrusion of lava at mid-ocean ridges and much higher than the rate of extrusion by hotspots. However, extrusion at mid-ocean ridges is relatively steady, while extrusion of flood basalts is highly episodic. Flood basalts create new continental crust at a rate of 0.1 to 8 cubic kilometers (0.02 to 2 cu mi) per year, while the eruptions that form oceanic plateaus produce 2 to 20 cubic kilometers (0.5 to 5 cu mi) of crust per year. Much of

2782-416: Is enhanced if measurements are taken on multiple samples from different locations of the rock body. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron . This can reduce the problem of contamination . In uranium–lead dating , the concordia diagram

2889-561: Is episodic, and each episode has its own chemical signature. There is some tendency for lava within a single eruptive episode to become more silica-rich with time, but there is no consistent trend across episodes. Large Igneous Provinces (LIPs) were originally defined as voluminous outpourings, predominantly of basalt, over geologically very short durations. This definition did not specify minimum size, duration, petrogenesis, or setting. A new attempt to refine classification focuses on size and setting. LIPs characteristically cover large areas, and

2996-533: Is often performed on the mineral zircon (ZrSiO 4 ), though it can be used on other materials, such as baddeleyite and monazite (see: monazite geochronology ). Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for zirconium , but strongly reject lead. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of

3103-449: Is one way of measuring the decay constant of a system, which involves accumulating daughter nuclides. Unfortunately for nuclides with high decay constants (which are useful for dating very old samples), long periods of time (decades) are required to accumulate enough decay products in a single sample to accurately measure them. A faster method involves using particle counters to determine alpha, beta or gamma activity, and then dividing that by

3210-419: Is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral. These methods can be used to date the age of a sediment layer, as layers deposited on top would prevent the grains from being "bleached" and reset by sunlight. Pottery shards can be dated to the last time they experienced significant heat, generally when they were fired in

3317-419: Is required for so much magma to be generated in so short a time. This is widely believed to have been supplied by a mantle plume impinging on the base of the Earth's lithosphere , its rigid outermost shell. The plume consists of unusually hot mantle rock of the asthenosphere , the ductile layer just below the lithosphere, that creeps upwards from deeper in the Earth's interior. The hot asthenosphere rifts

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3424-435: Is the Al – Mg chronometer, which can be used to estimate the relative ages of chondrules . Al decays to Mg with a half-life of 720 000 years. The dating is simply a question of finding the deviation from the natural abundance of Mg (the product of Al decay) in comparison with the ratio of

3531-421: Is thus the time at which the rock or mineral cooled to closure temperature. This temperature varies for every mineral and isotopic system, so a system can be closed for one mineral but open for another. Dating of different minerals and/or isotope systems (with differing closure temperatures) within the same rock can therefore enable the tracking of the thermal history of the rock in question with time, and thus

3638-473: Is uncommon in flood basalt provinces. One possibility is that a primitive melt stagnates when it reaches the mantle-crust boundary, where it is not buoyant enough to penetrate the lower-density crust rock. As a tholeiitic magma differentiates (changes in composition as high-temperature minerals crystallize and settle out of the magma) its density reaches a minimum at a magnesium number of about 60, similar to that of flood basalts. This restores buoyancy and permits

3745-418: Is used to date old igneous and metamorphic rocks , and has also been used to date lunar samples . Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium–lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Application of in situ analysis (Laser-Ablation ICP-MS) within single mineral grains in faults have shown that

3852-535: Is used which also decreases the problem of nuclide loss. Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3.60 ± 0.05 Ga (billion years ago) using uranium–lead dating and 3.56 ± 0.10 Ga (billion years ago) using lead–lead dating, results that are consistent with each other. Accurate radiometric dating generally requires that

3959-592: The Hebridean Igneous Province . Other notable NAIP landform locations in the United Kingdom include: Carlingford, County Louth is the only location of a major intrusion complex within the Republic of Ireland 's part of the NAIP. The intensity of scientific investigation within the NAIP has made it one of the most historically important and deeply studied igneous provinces in the world. Basalt petrology

4066-635: The Keweenaw Peninsula of Michigan , US, which is 600 meters (2,000 ft) thick. This flow may have been part of a lava lake the size of Lake Superior . Deep erosion of flood basalts exposes vast numbers of parallel dikes that fed the eruptions. Some individual dikes in the Columbia River Plateau are over 100 kilometers (60 mi) long. In some cases, erosion exposes radial sets of dikes with diameters of several thousand kilometers. Sills may also be present beneath flood basalts, such as

4173-471: The Palisades Sill of New Jersey , US. The sheet intrusions (dikes and sills) beneath flood basalts are typically diabase that closely matches the composition of the overlying flood basalts. In some cases, the chemical signature allows individual dikes to be connected with individual flows. Flood basalt commonly displays columnar jointing , formed as the rock cooled and contracted after solidifying from

4280-809: The Permian-Triassic boundary, the Triassic-Jurassic boundary, and in the Toarcian Age of the Jurassic correspond to the ages of large igneous provinces in Siberia, the Central Atlantic Magmatic Province, and the Karoo-Ferrar flood basalt. Some idea of the impact of flood basalts can be given by comparison with historical large eruptions. The 1783 eruption of Lakagígar was the largest in

4387-423: The age of Earth itself, and can also be used to date a wide range of natural and man-made materials . Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale . Among the best-known techniques are radiocarbon dating , potassium–argon dating and uranium–lead dating . By allowing the establishment of geological timescales, it provides

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4494-441: The biosphere as a consequence of industrialization have also depressed the proportion of carbon-14 by a few percent; in contrast, the amount of carbon-14 was increased by above-ground nuclear bomb tests that were conducted into the early 1960s. Also, an increase in the solar wind or the Earth's magnetic field above the current value would depress the amount of carbon-14 created in the atmosphere. This involves inspection of

4601-555: The ocean floor with basalt lava . Many flood basalts have been attributed to the onset of a hotspot reaching the surface of the Earth via a mantle plume . Flood basalt provinces such as the Deccan Traps of India are often called traps , after the Swedish word trappa (meaning "staircase"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in

4708-743: The Atlantic Ocean, formed around 125 million years ago as the South Atlantic opened, while a second set of smaller flood basalts formed near the Triassic-Jurassic boundary in eastern North America as the North Atlantic opened. However, the North Atlantic flood basalts are not connected with any hot spot traces, but seem to have been evenly distributed along the entire divergent boundary. Flood basalts are often interbedded with sediments, typically red beds . The deposition of sediments begins before

4815-467: The Caribbean, Nauru, East Mariana, and Pigafetta provinces. Continental flood basalts (CFBs) or plateau basalts are the continental expressions of large igneous provinces. Flood basalts contribute significantly to the growth of continental crust. They are also catastrophic events, which likely contributed to many mass extinctions in the geologic record. The extrusion of flood basalts, averaged over time,

4922-475: The Columbia River Plateau, which is 30 to 70 meters (98 to 230 ft) thick, show that the temperature of the lava dropped by just 20 °C (68 °F) over a distance of 500 kilometers (310 mi). This demonstrates that the lava must have been insulated by a surface crust and that the flow was laminar , reducing heat exchange with the upper crust and base of the flow. It has been estimated that

5029-452: The Ginkgo flow advanced 500 km in six days (a rate of advance of about 3.5 km per hour). The lateral extent of a flood basalt flow is roughly proportional to the cube of the thickness of the flow near its source. Thus, a flow that is double in thickness at its source can travel roughly eight times as far. Flood basalt flows are predominantly pāhoehoe flows, with ʻaʻā flows much less common. Eruption in flood basalt provinces

5136-449: The NAIP include: The British portion of the NAIP, particularly West Scotland, provides relatively easy access, compared to the largely inaccessible basalt fields of West Greenland, to deeply eroded relics of the central volcanic complexes. Locations of major intrusion complexes within the British part of the NAIP include: Those occurrences within the Hebrides are sometimes referred to as

5243-424: The NAIP, and in doing so have advanced knowledge in geology, mineralogy and in more recent decades geochemistry and geophysics. Radiometric dating Radiometric dating , radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares

5350-561: The NAIP, in between which sea levels rose and fell and erosion took place. Volcanic activity would have started with volcaniclastic accumulations, like volcanic ash , quickly followed by vast outpourings of highly fluid basaltic lava during successive eruptions through multiple volcanic vents or in linear fissures. As mafic low viscosity lava reached the surface it rapidly cooled and solidified, successive flows built up layer upon layer, each time filling and covering existing landscapes. Hyaloclastites and pillow lavas were formed when

5457-596: The Rb-Sr method can be used to decipher episodes of fault movement. A relatively short-range dating technique is based on the decay of uranium-234 into thorium-230, a substance with a half-life of about 80,000 years. It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 32,760 years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sediments , from which their ratios are measured. The scheme has

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5564-412: The abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features , including the age of fossilized life forms or

5671-410: The age equation graphically and calculate the age of the sample and the original composition. Radiometric dating has been carried out since 1905 when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth . In the century since then the techniques have been greatly improved and expanded. Dating can now be performed on samples as small as a nanogram using

5778-520: The age of the sample even if some of the lead has been lost. This can be seen in the concordia diagram, where the samples plot along an errorchron (straight line) which intersects the concordia curve at the age of the sample. This involves the alpha decay of Sm to Nd with a half-life of 1.06 x 10 years. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. This involves electron capture or positron decay of potassium-40 to argon-40. Potassium-40 has

5885-422: The atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, Cl is also useful for dating waters less than 50 years before the present. Cl has seen use in other areas of the geological sciences, including dating ice and sediments. Luminescence dating methods are not radiometric dating methods in that they do not rely on abundances of isotopes to calculate age. Instead, they are

5992-477: The atmosphere. The NAIP is made up of both onshore and offshore basalt floods , sills , dykes , and plateaus. Dependent upon various regional locations, the NAIP is made up of MORB (Mid Ocean Ridge Basalt), alkali basalt, tholeiitic basalt , and picrite basalt . Basaltic volcanic rocks up to 2.5 kilometres (1.6 mi) thick cover 65,000 square kilometres (25,000 sq mi) in east Greenland. Numerous intrusions related to hot-spot magmatism are exposed in

6099-404: The bottom third of the flow. The greater hydrostatic pressure, due to the weight of overlying rock, also contributes to making the lower columns larger. By analogy with Greek temple architecture, the more regular lower columns are described as the colonnade and the more irregular upper fractures as the entablature of the individual flow. Columns tend to be larger in thicker flows, with columns of

6206-416: The clock to zero. The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried. Stimulating these mineral grains using either light ( optically stimulated luminescence or infrared stimulated luminescence dating) or heat ( thermoluminescence dating ) causes a luminescence signal to be emitted as the stored unstable electron energy

6313-511: The coastal region of east Greenland. The intrusions show a wide range of compositions. The Skaergaard intrusion ( Early Cenozoic or about 55 million year age) is a layered gabbro ( mafic ) intrusion that has mineralized rock units enriched in palladium and gold . In contrast, the Werner Bjerge complex is made up of potassium- and sodium-rich (alkaline) granitic rock, containing molybdenum . Locations of submarine central complexes within

6420-402: The composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature . This is well established for most isotopic systems. However, construction of an isochron does not require information on the original compositions, using merely the present ratios of the parent and daughter isotopes to a standard isotope. An isochron plot is used to solve

6527-453: The conversion efficiency from I to Xe . The difference between the measured Xe / Xe ratios of the sample and Shallowater then corresponds to the different ratios of I / I when they each stopped losing xenon. This in turn corresponds to a difference in age of closure in the early solar system. Another example of short-lived extinct radionuclide dating

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6634-787: The crust, covering an area of 5 million square kilometres (1.9 million square miles), equal to 62% of the area of the contiguous states of the United States. The hot magma contained vast quantities of carbon dioxide and sulfur oxides , and released additional carbon dioxide and methane from deep petroleum reservoirs and younger coal beds in the region. The released gases created over 6400 diatreme -like pipes , each typically over 1.6 kilometres (1 mi) in diameter. The pipes emitted up to 160 trillion tons of carbon dioxide and 46 trillion tons of methane. Coal ash from burning coal beds spread toxic chromium , arsenic , mercury , and lead across northern Canada. Evaporite beds heated by

6741-472: The decay products of extinct radionuclides with a mass spectrometer and using isochronplots, it is possible to determine relative ages of different events in the early history of the solar system. Dating methods based on extinct radionuclides can also be calibrated with the U–Pb method to give absolute ages. Thus both the approximate age and a high time resolution can be obtained. Generally a shorter half-life leads to

6848-444: The development of a large igneous province and marks a shift to more centralized volcanism. Flood basalts show a considerable degree of chemical uniformity across geologic time, being mostly iron-rich tholeiitic basalts. Their major element chemistry is similar to mid-ocean ridge basalts (MORBs), while their trace element chemistry, particularly of the rare earth elements , resembles that of ocean island basalt . They typically have

6955-422: The event. In situ micro-beam analysis can be achieved via laser ICP-MS or SIMS techniques. One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of

7062-750: The existing isotope decays with a characteristic half-life (5730 years). The proportion of carbon-14 left when the remains of the organism are examined provides an indication of the time elapsed since its death. This makes carbon-14 an ideal dating method to date the age of bones or the remains of an organism. The carbon-14 dating limit lies around 58,000 to 62,000 years. The rate of creation of carbon-14 appears to be roughly constant, as cross-checks of carbon-14 dating with other dating methods show it gives consistent results. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. The releases of carbon dioxide into

7169-418: The first flood basalt eruptions, so that subsidence and crustal thinning are precursors to flood basalt activity. The surface continues to subside as basalt erupt, so that the older beds are often found below sea level. Basalt strata at depth ( dipping reflectors ) have been found by reflection seismology along passive continental margins. The composition of flood basalts may reflect the mechanisms by which

7276-501: The flows altering the basalts and deposited distinctive suites of zeolite minerals. Activity of the NAIP 55 million years ago may have caused the Paleocene–Eocene Thermal Maximum , where a large amount of carbon was released into the atmosphere and the Earth substantially warmed. One hypothesis is that the uplift caused by the NAIP hotspot caused methane clathrates to dissociate and dump 2000 gigatons of carbon into

7383-487: The flows are very homogeneous and rarely contain xenoliths , fragments of the surrounding rock ( country rock ) that have been entrained in the lava. Because the lavas are low in dissolved gases, pyroclastic rock is extremely rare. Except where the flows entered lakes and became pillow lava , the flows are massive (featureless). Occasionally, flood basalts are associated with very small volumes of dacite or rhyolite (much more silica-rich volcanic rock), which forms late in

7490-567: The formation of a stable (nonradioactive) daughter nuclide; each step in such a chain is characterized by a distinct half-life. In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter. Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years (e.g., tritium ) to over 100 billion years (e.g., samarium-147 ). For most radioactive nuclides,

7597-407: The formation of flood basalts must explain how such vast amounts of magma could be generated and erupted as lava in such short intervals of time. They must also explain the similar compositions and tectonic settings of flood basalts erupted across geologic time and the ability of flood basalt lava to travel such great distances from the eruptive fissures before solidifying. A tremendous amount of heat

7704-410: The great bulk of the magmatism occurs in less than 1 Ma. Principal LIPs in the ocean basins include Oceanic Volcanic Plateaus (OPs) and Volcanic Passive Continental Margins . Oceanic flood basalts are LIPs distinguished from oceanic plateaus by some investigators because they do not form morphologic plateaus, being neither flat-topped nor elevated more than 200 m above the seafloor. Examples include

7811-472: The half-life depends solely on nuclear properties and is essentially constant. This is known because decay constants measured by different techniques give consistent values within analytical errors and the ages of the same materials are consistent from one method to another. It is not affected by external factors such as temperature , pressure , chemical environment, or presence of a magnetic or electric field . The only exceptions are nuclides that decay by

7918-676: The heavy parent isotopes were produced by nucleosynthesis in supernovas, meaning that any parent isotope with a short half-life should be extinct by now. Carbon-14, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon-14 ends up as a trace component in atmospheric carbon dioxide (CO 2 ). A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesis , and animals acquire it from consumption of plants and other animals. When an organism dies, it ceases to take in new carbon-14, and

8025-627: The historical record, killing 75% of the livestock and a quarter of the population of Iceland. However, the eruption produced just 14 cubic kilometers (3.4 cu mi) of lava, which is tiny compared with the Roza Member of the Columbia River Plateau, erupted in the mid- Miocene , which contained at least 1,500 cubic kilometers (360 cu mi) of lava. During the eruption of the Siberian Traps , some 5 to 16 million cubic kilometers (1.2 to 3.8 million cubic miles) of magma penetrated

8132-413: The history of metamorphic events may become known in detail. These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace. This field is known as thermochronology or thermochronometry. The mathematical expression that relates radioactive decay to geologic time is where The equation is most conveniently expressed in terms of

8239-525: The ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams. Uranium–lead radiometric dating involves using uranium-235 or uranium-238 to date a substance's absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. An error margin of 2–5% has been achieved on younger Mesozoic rocks. Uranium–lead dating

8346-458: The isotopic "clock" to zero. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature. The age that can be calculated by radiometric dating

8453-677: The lava flowed into lakes, rivers and seas. Magma that did not make it to the surface as flows froze in conduits as dikes and volcanic plugs and large amounts spread laterally to form sills . Dike swarms extended across the British Isles throughout the Cenozoic . Individual central complexes developed with arcuate intrusions (cone sheets, ring dikes and stocks ), the intrusions of one centre cut through earlier centres recording magmatic activity with time. During intermittent periods of erosion and change in sea levels, heated waters circulated through

8560-403: The lava prior to its being erupted to the surface, which are often present in other extrusive igneous rocks. Phenocrysts are more abundant in the dikes that fed lava to the surface. Flood basalts are most often quartz tholeiites . Olivine tholeiite (the characteristic rock of mid-ocean ridges ) occurs less commonly, and there are rare cases of alkali basalts . Regardless of composition,

8667-419: The lava. The rock fractures into columns, typically with five to six sides, parallel to the direction of heat flow out of the rock. This is generally perpendicular to the upper and lower surfaces, but rainwater infiltrating the rock unevenly can produce "cold fingers" of distorted columns. Because heat flow out of the base of the flow is slower than from its upper surface, the columns are more regular and larger in

8774-777: The lithosphere above the plume, allowing magma produced by decompressional melting of the plume head to find pathways to the surface. The swarms of parallel dikes exposed by deep erosion of flood basalts show that considerable crustal extension has taken place. The dike swarms of west Scotland and Iceland show extension of up to 5%. Many flood basalts are associated with rift valleys, are located on passive continental plate margins, or extend into aulacogens (failed arms of triple junctions where continental rifting begins.) Flood basalts on continents are often aligned with hotspot volcanism in ocean basins. The Paraná and Etendeka traps , located in South America and Africa on opposite sides of

8881-436: The magma reaches the surface. The original melt formed in the upper mantle (the primitive melt ) cannot have the composition of quartz tholeiite, the most common and typically least evolved volcanic rock of flood basalts, because quartz tholeiites are too rich in iron relative to magnesium to have formed in equilibrium with typical mantle rock. The primitive melt may have had the composition of picrite basalt , but picrite basalt

8988-694: The magma released hydrochloric acid , methyl chloride , methyl bromide , which damaged the ozone layer and reduced ultraviolet shielding by as much as 85%. Over 5 trillion tons of sulfur dioxide was also released. The carbon dioxide produced extreme greenhouse conditions, with global average sea water temperatures peaking at 38 °C (100 °F), the highest ever seen in the geologic record. Temperatures did not drop to 32 °C (90 °F) for another 5.1 million years. Temperatures this high are lethal to most marine organisms, and land plants have difficulty continuing to photosynthesize at temperatures above 35 °C (95 °F). The Earth's equatorial zone became

9095-460: The magma to complete its journey to the surface, and also explains why flood basalts are predominantly quartz tholeiites. Over half the original magma remains in the lower crust as cumulates in a system of dikes and sills. As the magma rises, the drop in pressure also lowers the liquidus , the temperature at which the magma is fully liquid. This likely explains the lack of phenocrysts in erupted flood basalt. The resorption (dissolution back into

9202-471: The magma was only slightly contaminated with melted rock of the Earth's crust , but some high-temperature minerals had already crystallized out of the rock before it reached the surface. In other words, the flood basalt is moderately evolved . However, only small amounts of plagioclase appear to have crystallized out of the melt. Though regarded as forming a chemically homogeneous group, flood basalts sometimes show significant chemical diversity even with in

9309-428: The measured quantity N ( t ) rather than the constant initial value N o . To calculate the age, it is assumed that the system is closed (neither parent nor daughter isotopes have been lost from system), D 0 either must be negligible or can be accurately estimated, λ is known to high precision, and one has accurate and precise measurements of D* and N ( t ). The above equation makes use of information on

9416-408: The melt) of a mixture of solid olivine, augite, and plagioclase—the high-temperature minerals likely to form as phenocrysts—may also tend to drive the composition closer to quartz tholeiite and help maintain buoyancy. Once the magma reaches the surface, it flows rapidly across the landscape, literally flooding the local topography. This is possible in part because of the rapid rate of extrusion (over

9523-506: The modern day Iceland hotspot corresponds to the earlier 'North Atlantic mantle plume' that would have created the NAIP. Through both geochemical observations and reconstructions of paleogeography , it is speculated that the present day Iceland hotspot originated as a mantle plume on the Alpha Ridge ( Arctic Ocean ) c. 130–120 Ma, migrated down Ellesmere Island , through Baffin Island , onto

9630-438: The more rapidly cooling lava close to the base of the flow forms a thin chilled margin of glassy rock, and the more rapidly crystallized rock just above the glassy margin contains vesicles trapped as the rock was rapidly crystallizing. These have a distinctive appearance likened to a clay tobacco pipe stem, particularly as the vesicle is usually subsequently filled with calcite or other light-colored minerals that contrast with

9737-440: The most voluminous of all extrusive igneous rocks , forming enormous deposits of basaltic rock found throughout the geologic record. They are a highly distinctive form of intraplate volcanism , set apart from all other forms of volcanism by the huge volumes of lava erupted in geologically short time intervals. A single flood basalt province may contain hundreds of thousands of cubic kilometers of basalt erupted over less than

9844-496: The new crust formed during flood basalt episodes takes the form of underplating , with over half the original magma crystallizing out as cumulates in sills at the base of the crust. The eruption of flood basalts has been linked with mass extinctions. For example, the Deccan Traps , erupted at the Cretaceous-Paleogene boundary , may have contributed to the extinction of the non-avian dinosaurs. Likewise, mass extinctions at

9951-423: The number of protons in the atomic nucleus . Additionally, elements may exist in different isotopes , with each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of a particular element is called a nuclide . Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into

10058-466: The number of radioactive nuclides. However, it is challenging and expensive to accurately determine the number of radioactive nuclides. Alternatively, decay constants can be determined by comparing isotope data for rocks of known age. This method requires at least one of the isotope systems to be very precisely calibrated, such as the Pb–Pb system . The basic equation of radiometric dating requires that neither

10165-505: The other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. The closure temperature or blocking temperature represents the temperature below which the mineral is a closed system for the studied isotopes. If a material that selectively rejects the daughter nuclide is heated above this temperature, any daughter nuclides that have been accumulated over time will be lost through diffusion , resetting

10272-407: The parent and daughter nuclides must be precise and accurate. This normally involves isotope-ratio mass spectrometry . The precision of a dating method depends in part on the half-life of the radioactive isotope involved. For instance, carbon-14 has a half-life of 5,730 years. After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating cannot be established. On

10379-443: The parent has a long enough half-life that it will be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material. The procedures used to isolate and analyze

10486-443: The parent nuclide nor the daughter product can enter or leave the material after its formation. The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created. It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration . Precision

10593-551: The past 250 million years, creating large igneous provinces , lava plateaus , and mountain ranges . However, more have been recognized such as the large Ontong Java Plateau , and the Chilcotin Group , though the latter may be linked to the Columbia River Basalt Group . Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts. Flood basalts are

10700-425: The plastic film. The uranium content of the material can then be calculated from the number of tracks and the neutron flux . This scheme has application over a wide range of geologic dates. For dates up to a few million years micas , tektites (glass fragments from volcanic eruptions), and meteorites are best used. Older materials can be dated using zircon , apatite , titanite , epidote and garnet which have

10807-414: The process of electron capture, such as beryllium-7 , strontium-85 , and zirconium-89 , whose decay rate may be affected by local electron density. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock to measure

10914-502: The stable isotopes Al / Mg . The excess of Mg (often designated Mg *) is found by comparing the Mg / Mg ratio to that of other Solar System materials. The Al – Mg chronometer gives an estimate of the time period for formation of primitive meteorites of only a few million years (1.4 million years for Chondrule formation). In

11021-534: The surrounding dark basalt. At still smaller scales, the texture of flood basalts is aphanitic , consisting of tiny interlocking crystals. These interlocking crystals give trap rock its tremendous toughness and durability. Crystals of plagioclase are embedded in or wrapped around crystals of pyroxene and are randomly oriented. This indicates rapid emplacement so that the lava is no longer flowing rapidly when it begins to crystallize. Flood basalts are almost devoid of large phenocrysts , larger crystals present in

11128-421: The time from the incorporation of the original nuclides into a material to the present. The radioactive decay constant, the probability that an atom will decay per year, is the solid foundation of the common measurement of radioactivity. The accuracy and precision of the determination of an age (and a nuclide's half-life) depends on the accuracy and precision of the decay constant measurement. The in-growth method

11235-409: The very thick Greenstone flow, mentioned earlier, being around 10 meters (30 ft) thick. Another common small-scale feature of flood basalts is pipe-stem vesicles . Flood basalt lava cools quite slowly, so that dissolved gases in the lava have time to come out of solution as bubbles (vesicles) that float to the top of the flow. Most of the rest of the flow is massive and free of vesicles. However,

11342-558: The west coast of Greenland, and finally arrived on the east coast of Greenland by c. 60 Ma. Extensive outpourings of lava occurred, particularly in East Greenland, which during the Paleogene was then adjacent to Britain. Little is known of the geodynamics of the opening of the North Atlantic between Greenland and Europe. As the Earth's crust was stretched above the mantle hotspot under stress from plate rifting, fissures opened up along

11449-533: Was born in the Scottish Hebrides in 1903 led by the eminent British geologist Sir Archibald Geikie . From the outset Geikie studied the geology of Skye and other Western Isles taking a keen interest in volcanic geology and in 1871 he presented the Geological Society of London with an outline of the 'Tertiary Volcanic History of Britain'. Following Geikie many have tried, and continue to study and understand

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