|
|
| Line 1: |
Line 1: |
| '''Isotope geochemistry''' is an aspect of [[geology]] based upon study of the natural variations in the relative abundances of [[isotopes]] of various elements. Variations in isotopic abundance are measured by [[isotope ratio mass spectrometry]], and can reveal information about the ages and origins of rock, air or water bodies, or processes of mixing between them.
| | Last week I woke up and realised - At the moment I have been single for some time and after much bullying from friends I today find myself signed-up for online dating. They [http://browse.deviantart.com/?qh=§ion=&global=1&q=guaranteed guaranteed] me that there are lots of pleasant, regular and enjoyable individuals to meet up, so the pitch is gone by here!<br>I try and stay as physically fit as potential coming to the gym several-times weekly. I appreciate my sports and attempt to perform or view since many a potential. I will frequently at Hawthorn suits being winter. Notice: In case that you contemplated luke bryan tour tickets 2014 ([http://lukebryantickets.flicense.com http://Lukebryantickets.flicense.com]) shopping a hobby I really do not brain, I've noticed the carnage of fumbling matches at stocktake sales.<br>My pals and fam are luke bryan concert tickets 2014 ([http://minioasis.com minioasis.com]) wonderful and spending time with them at bar gigs or dinners is definitely critical. I have never been in to clubs as I locate you can never have a nice dialog together with meet and greet luke bryan tickets - [http://www.senatorwonderling.com www.senatorwonderling.com], the sound. I also have two undoubtedly cheeky and [http://www.hotelsedinburgh.org luke bryan the today show] very adorable dogs who are consistently excited to meet up fresh people.<br><br>Also visit my weblog [http://www.banburycrossonline.com jason aldean] |
| | |
| [[Stable isotope]] geochemistry is largely concerned with isotopic variations arising from mass-dependent isotope fractionation, whereas [[radiogenic]] isotope geochemistry is concerned with the products of natural radioactivity.
| |
| | |
| ==Stable isotope geochemistry==
| |
| For most stable isotopes, the magnitude of fractionation from [[kinetic fractionation|kinetic]] and [[equilibrium fractionation]] is very small; for this reason, enrichments are typically reported in "per mil" (‰, parts per thousand).<ref name="drever_2002">{{cite book | title = The Geochemistry of Natural Waters | last = Drever | first=James | publisher = Prentice Hall | year = 2002 | location = New Jersey | isbn = 0-13-272790-0 | pages = 311–322}}</ref> These enrichments (δ) represent the ratio of heavy isotope to light isotope in the sample over the ratio of a standard. That is,
| |
| :<math>\delta ^{13}C = \Biggl( \frac{\bigl( \frac{^{13}C}{^{12}C} \bigr)_{sample}}{\bigl( \frac{^{13}C}{^{12}C} \bigr)_{standard}} -1 \Biggr) * 1000\ ^{o}\!/\!_{oo}</math>
| |
| | |
| ===Carbon===
| |
| [[Carbon]] has two [[stable isotope]]s, <sup>12</sup>C and <sup>13</sup>C, and one radioactive isotope, [[Carbon-14|<sup>14</sup>C]]. Carbon isotope ratios are measured against Vienna Pee Dee [[Belemnite]] (VPDB).<ref name="usgs_isotope_tracers">{{cite web |url= http://wwwrcamnl.wr.usgs.gov/isoig/res/funda.html |title= USGS -- Isotope Tracers -- Resources -- Isotope Geochemistry |accessdate=2009-01-18}}</ref> They have been used to track ocean circulation, among other things.
| |
| | |
| Carbon stable isotopes are fractionated primarily by [[photosynthesis]] (Faure, 2004). The <sup>13</sup>C/<sup>12</sup>C ratio is also an indicator of paleoclimate: a change in the ratio in the remains of plants indicates a change in the amount of photosynthetic activity, and thus in how favorable the environment was for the plants.
| |
| | |
| During photosynthesis, organisms using the [[C3 pathway|C<sub>3</sub> pathway]] show different enrichments compared to those using the [[C4 pathway|C<sub>4</sub> pathway]], allowing scientists not only to distinguish organic matter from abiotic carbon, but also what type of photosynthetic pathway the organic matter was using.<ref name="drever_2002"/>
| |
| | |
| ===Nitrogen===
| |
| [[Nitrogen]] has two stable isotopes, <sup>14</sup>N, and <sup>15</sup>N. The ratio between these is measured relative to nitrogen in [[air|ambient air]].<ref name="usgs_isotope_tracers"/> Nitrogen ratios are frequently linked to agricultural activities. Nitrogen isotope data has also been used to measure the amount of exchange of air between the [[stratosphere]] and [[troposphere]] using data from the greenhouse gas [[Nitrous oxide|N<sub>2</sub>O]].<ref name="boering_2004">{{cite journal | author = Park, S.; Atlas, E. L.; Boering, K. A. | title = Measurements of N<sub>2</sub>O isotopologues in the stratosphere | journal = [[Journal of Geophysical Research]] | volume = 109 | year = 2004 | issue = D1 | doi = 10.1029/2003JD003731 | pages = D01305|bibcode = 2004JGRD..10901305P }}</ref>
| |
| | |
| ===Oxygen===
| |
| [[Oxygen]] has three stable isotopes, <sup>16</sup>O, <sup>17</sup>O, and <sup>18</sup>O. Oxygen ratios are measured relative to [[Vienna Standard Mean Ocean Water]] (VSMOW) or Vienna Pee Dee Belemnite (VPDB).<ref name="usgs_isotope_tracers"/> Variations in oxygen isotope ratios are used to track both water movement, paleoclimate,<ref name="drever_2002"/> and atmospheric gases such as [[ozone]] and [[carbon dioxide]].<ref name="Brenninkmeijer_2003">{{cite journal | author = Brenninkmeijer, C. A. M.; Janssen, C.; Kaiser, J.; Röckmann, T.; Rhee, T. S.; Assonov, S. S. | title = Isotope effects in the chemistry of atmospheric trace compounds | journal = Chemical Reviews | year = 2003 | volume = 103 | pages = 5125–5161 | doi = 10.1021/cr020644k | pmid = 14664646 | issue = 12}}</ref> Typically, the VPDB oxygen reference is used for paleoclimate, while VSMOW is used for most other applications.<ref name="drever_2002"/> Oxygen isotopes appear in anomalous ratios in atmospheric ozone, resulting from [[mass-independent fractionation]].<ref name="mauersberger_1987">{{cite journal | doi = 10.1029/GL014i001p00080 | author = Mauersberger, K. | title = Ozone isotope measurements in the stratosphere | year = 1987 | volume = 14 | issue = 1 | pages = 80–83 | journal = Geophysical Review Letters|bibcode = 1987GeoRL..14...80M }}</ref> Isotope ratios in fossilized [[foraminifera]] have been used to deduce the temperature of ancient seas.<ref name="edwards_1953">{{cite journal | journal = Nature | author = Emiliani, C.; Edwards, G. | year = 1953 | volume = 171 | issue = 4359 | pages = 887–888 | title = Tertiary ocean bottom temperatures | doi = 10.1038/171887c0|bibcode = 1953Natur.171..887E }}</ref>
| |
| | |
| ===Sulfur===
| |
| [[Sulfur]] has four stable isotopes, with the following abundances: <sup>32</sup>S (0.9502), <sup>33</sup>S (0.0075), <sup>34</sup>S (0.0421) and <sup>36</sup>S (0.0002). These abundances are compared to those found in [[Canyon Diablo (meteorite)|Cañon Diablo troilite]].<ref name="Brenninkmeijer_2003"/> Variations in sulfur isotope ratios are used to study the origin of sulfur in an [[ore]]body and the temperature of formation of sulfur–bearing minerals.<ref name=Rollinson>Rollinson, H.R. (1993). ''Using Geochemical Data: Evaluation, Presentation, Interpretation'' Longman Scientific & Technical. ISBN 978-0-582-06701-1</ref>
| |
| | |
| ==Radiogenic isotope geochemistry==
| |
| | |
| Radiogenic isotopes provide powerful tracers for studying the ages and origins of Earth systems.<ref>{{cite book | author=Dickin, A.P. | year=2005 | title=Radiogenic Isotope Geology | url=http://www.onafarawayday.com/Radiogenic/ | publisher=Cambridge University Press}}</ref> They are particularly useful to understand mixing processes between different components, because (heavy) radiogenic isotope ratios are not usually fractionated by chemical processes.
| |
| | |
| Radiogenic isotope tracers are most powerful when used together with other tracers: The more tracers used, the more control on mixing processes. An example of this application is to the evolution of the [[Earth's crust]] and [[Earth's mantle]] through geological time.
| |
| | |
| ===Lead-lead isotope geochemistry===
| |
| [[Lead]] has four stable [[isotopes]] - <sup>204</sup>Pb, <sup>206</sup>Pb, <sup>207</sup>Pb, <sup>208</sup>Pb and one common radioactive isotope <sup>202</sup>Pb with a [[half-life]] of ~53,000 years.
| |
| | |
| Lead is created in the Earth via decay of [[transuranic]] [[Chemical element|elements]], primarily [[uranium]] and [[thorium]].
| |
| | |
| Lead isotope [[geochemistry]] is useful for providing [[radiometric dating|isotopic dates]] on a variety of materials. Because the lead isotopes are created by decay of different transuranic elements, the ratios of the four lead isotopes to one another can be very useful in tracking the source of melts in [[igneous rocks]], the source of [[sediments]] and even the origin of people via [[isotopic fingerprint]]ing of their teeth, skin and bones.
| |
| | |
| It has been used to date [[ice core]]s from the Arctic shelf, and provides information on the source of atmospheric lead [[air pollution|pollution]].
| |
| | |
| Lead-lead isotopes has been successfully used in [[forensic science]] to fingerprint bullets, because each batch of ammunition has its own peculiar <sup>204</sup>Pb/<sup>206</sup>Pb vs <sup>207</sup>Pb/<sup>208</sup>Pb ratio.
| |
| | |
| ===Samarium-neodymium===
| |
| {{main|Samarium-neodymium dating}}
| |
| [[Samarium]]-[[neodymium]] is an isotope system which can be utilised to provide a date as well as [[isotopic fingerprint]]s of geological materials, and various other materials including archaeological finds (pots, ceramics).
| |
| | |
| <sup>147</sup>Sm decays to produce <sup>143</sup>Nd with a half life of 1.06x10<sup>11</sup> years.
| |
| | |
| Dating is achieved usually by trying to produce an [[isochron dating|isochron]] of several minerals within a rock specimen. The initial <sup>143</sup>Nd/<sup>144</sup>Nd ratio is determined.
| |
| | |
| This initial ratio is modelled relative to CHUR - the Chondritic Uniform Reservoir - which is an approximation of the chondritic material which formed the solar system. CHUR was determined by analysing [[chondrite]] and [[achondrite]] meteorites.
| |
| | |
| The difference in the ratio of the sample relative to CHUR can give information on a model age of extraction from the mantle (for which an assumed evolution has been calculated relative to CHUR) and to whether this was extracted from a granitic source (depleted in radiogenic Nd), the mantle, or an enriched source.
| |
| | |
| ===Rhenium-osmium===
| |
| [[Rhenium]] and [[osmium]] are siderophile elements which are present at very low abundances in the crust. Rhenium undergoes [[radioactive decay]] to produce osmium. The ratio of non-radiogenic osmium to radiogenic osmium throughout time varies.
| |
| | |
| Rhenium prefers to enter [[sulfide]]s more readily than osmium. Hence, during melting of the mantle, rhenium is stripped out, and prevents the osmium-osmium ratio from changing appreciably. This ''locks in'' an initial osmium ratio of the sample at the time of the melting event. Osmium-osmium initial ratios are used to determine the source characteristic and age of mantle melting events.
| |
| | |
| ==Noble gas isotopes==
| |
| Natural isotopic variations amongst the noble gases result from both radiogenic and nucleogenic production processes. Because of their unique properties, it is useful to distinguish them from the conventional radiogenic isotope systems described above.
| |
| | |
| ===Helium-3===
| |
| [[Helium-3]] was trapped in the planet when it formed. Some <sup>3</sup>He is being added by meteoric dust, primarily collecting on the bottom of oceans (although due to [[subduction]], all oceanic [[tectonic plates]] are younger than continental plates). However, <sup>3</sup>He will be degassed from oceanic sediment during [[subduction]], so cosmogenic <sup>3</sup>He is not affecting the concentration or [[noble gas]] ratios of the [[Mantle (geology)|mantle]].
| |
| | |
| Helium-3 is created by [[cosmic ray]] bombardment, and by [[lithium]] spallation reactions which generally occur in the crust. Lithium [[spallation]] is the process by which a [[fast neutron|high-energy neutron]] bombards a [[lithium]] atom, creating a <sup>3</sup>He and a <sup>4</sup>He ion. This requires significant lithium to adversely affect the <sup>3</sup>He/<sup>4</sup>He ratio.
| |
| | |
| All degassed helium is lost to space eventually, due to the average speed of helium exceeding the [[escape velocity]] for the Earth. Thus, it is assumed the helium content and ratios of [[Earth's atmosphere]] have remained essentially stable.
| |
| | |
| It has been observed that <sup>3</sup>He is present in [[volcano]] emissions and [[oceanic ridge]] samples. How <sup>3</sup>He is stored in the planet is under investigation, but it is associated with the [[mantle (geology)|mantle]] and is used as a marker of material of deep origin.
| |
| | |
| Due to similarities in [[helium]] and [[carbon]] in [[magma]] chemistry, outgassing of helium requires the loss of [[Volatiles|volatile components]] ([[water]], [[carbon dioxide]]) from the mantle, which happens at depths of less than 60 km. However, <sup>3</sup>He is transported to the surface primarily trapped in the [[crystal]] lattice of minerals within [[fluid inclusions]].
| |
| | |
| Helium-4 is created by [[radiogenic]] production (by decay of [[uranium]]/[[thorium]]-series [[chemical element|elements]]). The [[continental crust]] has become enriched with those elements relative to the mantle and thus more He<sup>4</sup> is produced in the crust than in the mantle.
| |
| | |
| The ratio ('''R''') of <sup>3</sup>He to <sup>4</sup>He is often used to represent <sup>3</sup>He content. '''R''' usually is given as a multiple of the present atmospheric ratio ('''Ra''').
| |
| | |
| Common values for '''R/Ra''':
| |
| * Old continental crust: less than 1
| |
| * [[oceanic ridge|mid-ocean ridge]] [[basalt]] (MORB): 7 to 9
| |
| * Spreading ridge rocks: 9.1 plus or minus 3.6
| |
| * [[Hotspot (geology)|Hotspot]] rocks: 5 to 42
| |
| * Ocean and terrestrial water: 1
| |
| * Sedimentary formation water: less than 1
| |
| * Thermal spring water: 3 to 11
| |
| | |
| <sup>3</sup>He/<sup>4</sup>He isotope chemistry is being used to date [[groundwater]]s, estimate groundwater flow rates, track water pollution, and provide insights into [[hydrothermal]] processes, [[igneous]] [[geology]] and [[ore genesis]].
| |
| * [http://www.geotrack.com.au/uthhe/u-th-he-techinfo.htm (U-Th)/He dating of apatite as a thermal history tool]
| |
| * [http://lvo.wr.usgs.gov/helium.html USGS: Helium Discharge at Mammoth Mountain Fumarole (MMF)]
| |
| | |
| ==Uranium-series isotopes==
| |
| | |
| U-series isotopes are unique amongst radiogenic isotopes because, being in the U-series decay chains, they are both radiogneic and radioactive. Because their abundances are normally quoted as activity ratios rather than atomic ratios, they are best considered separately from the other radiogenic isotope systems.
| |
| | |
| ===[[Protactinium]]/[[Thorium]] - <sup>231</sup>Pa / <sup>230</sup>Th===
| |
| | |
| [[Uranium]] is well mixed in the ocean, and its decay produces <sup>231</sup>Pa and <sup>230</sup>Th at a constant activity ratio (0.093). The decay products are rapidly removed by [[adsorption]] on settling particles, but not at equal rates. <sup>231</sup>Pa has a residence equivalent to the residence time of [[abyssal zone|deep water]] in the [[Atlantic]] basin (around 1000 yrs) but <sup>230</sup>Th is removed more rapidly (centuries). [[Thermohaline circulation]] effectively exports <sup>231</sup>Pa from the Atlantic into the [[Southern Ocean]], while most of the <sup>230</sup>Th remains in Atlantic sediments. As a result, there is a relationship between <sup>231</sup>Pa/<sup>230</sup>Th in Atlantic sediments and the rate of overturning: faster overturning produces lower sediment <sup>231</sup>Pa/<sup>230</sup>Th ratio, while slower overturning increases this ratio. The combination of [[δ13C|δ<sup>13</sup>C]] and <sup>231</sup>Pa/<sup>230</sup>Th can therefore provide a more complete insight into past circulation changes.
| |
| | |
| ==Anthropogenic isotopes==
| |
| | |
| ===Tritium/helium-3===
| |
| [[Tritium]] was released to the atmosphere during atmospheric testing of nuclear bombs. Radioactive decay of tritium produces the noble gas [[helium-3]]. Comparing the ratio of tritium to helium-3 (<sup>3</sup>H/<sup>3</sup>He) allows estimation of the age of recent [[ground water]]s.
| |
| * [http://water.usgs.gov/lab/3h3he/background/ USGS Tritium/Helium-3 Dating]
| |
| * [http://wwwrcamnl.wr.usgs.gov/isoig/period/he_iig.html Hydrologic Isotope Tracers - Helium]
| |
| | |
| ==See also==
| |
| * [[Cosmogenic isotope]]s
| |
| * [[Environmental isotopes]]
| |
| * [[Geochemistry]]
| |
| * [[Isotopic signature]]
| |
| * [[Radiometric dating]]
| |
| * [[Isotope-ratio mass spectrometry]]
| |
| | |
| ==Notes==
| |
| {{reflist}}
| |
| | |
| ==References==
| |
| | |
| ===General===
| |
| | |
| *[[Claude Allègre|Allègre C.J.]], 2008. ''Isotope Geology'' ([[Cambridge University Press]]).
| |
| *Dickin A.P., 2005. ''Radiogenic Isotope Geology'' ([[Cambridge University Press]]).
| |
| *Faure G., Mensing T.M. (2004), ''Isotopes: Principles and Applications'' ([[John Wiley & Sons]]).
| |
| *Hoefs J., 2004. ''Stable Isotope Geochemistry'' ([[Springer Verlag]]).
| |
| *Sharp Z., 2006. ''Principles of Stable Isotope Geochemistry'' ([[Prentice Hall]]).
| |
| | |
| ===Stable isotopes===
| |
| * [http://www.science.uottawa.ca/~eih/ch1/ch1.htm Environmental Isotopes] ([[University of Ottawa]])
| |
| * [http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html Fundamentals of Isotope Geochemistry] (C. Kendall & E.A. Caldwell, chap.2 in ''Isotope Tracers in Catchment Hydrology'' [edited by C. Kendall & J.J. McDonnell], 1998)
| |
| * [http://pubs.usgs.gov/info/seal2/ Stable Isotopes and Mineral Resource Investigations in the United States] ([[USGS]])
| |
| | |
| ===<sup>3</sup>He/<sup>4</sup>He===
| |
| | |
| *Burnard P.G., Farley K.A., & Turner G., 1998. "Multiple fluid pulses in a Samoan [[harzburgite]]", ''Chemical Geology'', 147: 99-114.
| |
| *Kirstein L. & Timmerman M., 2000. "Evidence of the proto-Iceland lume in northwestern Ireland at 42Ma from helium isotopes", ''Journal of the Geological Society, London'', 157: 923-927.
| |
| *Porcelli D. & Halliday A.N., 2001. "The core as a possible source of mantle helium", ''Earth and Planetary Science Letters'', 192: 45-56.
| |
| | |
| ===Re-Os===
| |
| | |
| *Arne D., Bierlein F.P., Morgan J.W., & Stein H.J., 2001. "Re-Os dating of sulfides associated with gold mineralisation in central Victoria, Australia", ''Economic Geology'', 96: 1455-1459.
| |
| *Martin C., 1991. "Osmium isotopic characteristics of mantle-derived rocks", ''Geochimica et Cosmochimica Acta'', 55: 1421-1434.
| |
| | |
| ==External links==
| |
| *[http://isotopes.gov/ National Isotope Development Center] Reference information on isotopes, and coordination and management of isotope production, availability, and distribution
| |
| *[http://science.energy.gov/np/research/idpra/ Isotope Development & Production for Research and Applications (IDPRA)] U.S. Department of Energy program for isotope production and production research and development
| |
| | |
| {{Chronology}}
| |
| | |
| [[Category:Geochemistry]]
| |
| [[Category:Geophysics]]
| |
| [[Category:Geochronology]]
| |