Coordinate time: Difference between revisions

Revision as of 01:11, 15 March 2013

Samarium-neodymium dating is useful for determining the age relationships of rocks and meteorites, based on decay of a long-lived samarium (Sm) isotope to a radiogenic neodymium (Nd) isotope. Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data. The various reservoirs within the solid earth will have different values of initial ¹⁴³Nd/¹⁴⁴Nd ratios, especially with reference to the mantle.

The usefulness of Sm-Nd dating is the fact that these two elements are rare earths. They are thus, theoretically, not particularly susceptible to partitioning during melting of silicate rocks. The fractionation effects of crystallisation of felsic minerals (see above) changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the ¹⁴³Nd/¹⁴⁴Nd ratios with ingrowth of radiogenic ¹⁴³Nd.

The mantle is assumed to have undergone chondritic evolution, and thus deviations in initial ¹⁴³Nd/¹⁴⁴Nd ratios can provide information as to when a particular rock or reservoir was separated from the mantle within the Earth's past.

In many cases, Sm-Nd and Rb-Sr isotope data are used together.

Sm-Nd radiometric dating

Samarium has five naturally occurring isotopes and neodymium has seven.
The two elements are joined in a parent-daughter relationship by the alpha-decay of ¹⁴⁷Sm to ¹⁴³Nd with a half life of 1.06Template:E years.

¹⁴⁶Sm is an almost-extinct nuclide which decays via alpha emission to produce ¹⁴²Nd, with a half-life of 1.08Template:E years.

¹⁴⁶Sm is itself produced by the decay of ¹⁵⁰Gd via alpha-decay with a half-life of 1.79Template:E years.

An isochron is calculated normally. As with Rb-Sr and Pb-Pb isotope geochemistry, the initial ¹⁴³Nd/¹⁴⁴Nd ratio of the isotope system provides important information on crustal formation and the isotopic evolution of the solar system.

Sm and Nd geochemistry

The concentration of Sm and Nd in silicate minerals increase with the order in which they crystallise from a magma according to Bowen's reaction series. Samarium is accommodated more easily into mafic minerals, so a mafic rock which crystallises mafic minerals will concentrate neodymium in the melt phase faster relative to samarium. Thus, as a melt undergoes fractional crystallization from a mafic to a more felsic composition, the abundance of Sm and Nd changes, as does the ratio between Sm and Nd.

Thus, ultramafic rocks have low Sm and Nd and high Sm/Nd ratios. Felsic rocks have high concentrations of Sm and Nd but low Sm/Nd ratios (komatiite has 1.14 parts per million (ppm) Sm and 3.59 ppm Nd versus 4.65 ppm Sm and 21.6 ppm Nd in rhyolite).

The importance of this process is apparent in modeling the age of continental crust formation.

The CHUR model

Through the analysis of isotopic compositions of neodymium, DePaolo and Wasserburg ^[1] discovered that terrestrial igneous rocks closely followed the Chondritic Uniform Reservoir (CHUR) line.

Chondritic meteorites are thought to represent the earliest (unsorted) material that formed in the solar system before planets formed. They have relatively homogeneous trace element signatures and therefore their isotopic evolution can model the evolution of the whole solar system and of the ‘Bulk Earth’.

After plotting the ages and initial ¹⁴³Nd/¹⁴⁴Nd ratios of terrestrial igneous rocks on a Nd evolution vs. time diagram, DePaolo and Wasserburg determined that Archean rocks had initial Nd isotope ratios very similar to that defined by the CHUR evolution line.

Epsilon notation

Since ¹⁴³Nd/¹⁴⁴Nd departures from the CHUR evolution line are very small, DePaolo and Wasserburg argued that it would be useful to create a form of notation that described ¹⁴³Nd/¹⁴⁴Nd in terms of their deviations from the CHUR evolution line. This is called the epsilon notation whereby one epsilon unit represents a one part per 10,000 deviation from the CHUR composition.^[2] Algebraically, epsilon units can be defined by the equation:

ε_{N d (t)} = [\frac{{(\frac{^{143} N d}{^{144} N d})}_{s a m p l e (t)}}{{(\frac{^{143} N d}{^{144} N d})}_{C H U R (t)}} - 1] * 10000

Since epsilon units are larger and therefore a more tangible representation of the initial Nd isotope ratio, by using these instead of the initial isotopic ratios, it is easier to comprehend and therefore compare initial ratios of crust with different ages. In addition, epsilon units will normalize the initial ratios to CHUR, thus eliminating any effects caused by various analytical mass fractionation correction methods applied.^[2]

Nd Model Ages

Since CHUR defines initial ratios of continental rocks through time, it was deduced that measurements of ¹⁴³Nd/¹⁴⁴Nd and ¹⁴⁷Sm/¹⁴⁴Nd, with the use of CHUR, could produce model ages for the segregation from the mantle of the melt which formed any crustal rock. This has been termed ‘t-CHUR’.^[3] In order for a T_CHUR age to be calculated, fractionation between Nd/Sm would have to have occurred during magma extraction from the mantle to produce a continental rock. This fractionation would then cause a deviation between the crustal and mantle isotopic evolution lines. The intersection between these two evolution lines then indicates the crustal formation age. The T_CHUR age is defined by the following equation:

T_{C H U R} = (\frac{1}{λ}) l n [1 + \frac{{(\frac{^{143} N d}{^{144} N d})}_{s a m p l e} - {(\frac{^{143} N d}{^{144} N d})}_{C H U R}}{{(\frac{^{147} S m}{^{144} N d})}_{s a m p l e} - {(\frac{^{147} S m}{^{144} N d})}_{C H U R}}]

The T_CHUR age of a rock, can yield a formation age for the crust as a whole if the sample has not suffered disturbance after its formation. Since Sm/Nd are rare-earth elements (REE), their characteristic immobility enables their ratios to resist partitioning during metamorphism and melting of silicate rocks. This therefore allows for crustal formation ages to be calculated, despite any metamorphism the sample has undergone.

References

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.

Template:Chronology

↑ One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
↑ ^2.0 ^2.1 Dickin, A.P., 2005. Radiogenic Isotope Geology, 2nd ed. Cambridge: Cambridge University Press. ISBN 0-521-82316-1 pp. 76–77
↑ One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang

[1] One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang

[Dickin-2] 2.0 ^2.1 Dickin, A.P., 2005. Radiogenic Isotope Geology, 2nd ed. Cambridge: Cambridge University Press. ISBN 0-521-82316-1 pp. 76–77

[3] One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang

[1]

[2]

[3]

@@ Line 1: / Line 1: @@
-Irwin Butts is what my spouse loves to call me though I don't truly like becoming called like that. Puerto Rico is exactly where he's been residing for many years and he will never move. Body developing is what my family and I enjoy. I am a meter reader but I strategy on altering it.<br><br>Check out my site :: over the counter std test ([http://chatbook.biz/blogs/post/922 navigate here])
+'''Samarium-neodymium dating''' is useful for determining the age relationships of rocks and meteorites, based on decay of a long-lived [[samarium]] (Sm) isotope to a [[radiogenic]] [[neodymium]] (Nd) isotope. Nd isotope ratios are used to provide information on the source of [[igneous]] melts as well as to provide age data. The various reservoirs within the solid earth will have different values of initial <sup>143</sup>Nd/<sup>144</sup>Nd ratios, especially with reference to the [[mantle (geology)|mantle]].
+The usefulness of Sm-Nd dating is the fact that these two elements are [[Rare earth element|rare earths]]. They are thus, theoretically, not particularly susceptible to partitioning during melting of [[silicate minerals|silicate rocks]]. The [[Fractional crystallization (geology)|fractionation]] effects of crystallisation of [[felsic]] minerals (see above) changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the <sup>143</sup>Nd/<sup>144</sup>Nd ratios with ingrowth of radiogenic <sup>143</sup>Nd.
+The mantle is assumed to have undergone [[chondritic evolution]], and thus deviations in initial <sup>143</sup>Nd/<sup>144</sup>Nd ratios can provide information as to when a particular rock or reservoir was separated from the mantle within the Earth's past.
+In many cases, Sm-Nd and [[rubidium-strontium dating|Rb-Sr]] isotope data are used together.
+==Sm-Nd radiometric dating==
+Samarium has five naturally occurring isotopes and neodymium has seven.<br>
+The two elements are joined in a parent-daughter relationship by the [[alpha-decay]] of <sup>147</sup>Sm to <sup>143</sup>Nd with a [[half life]] of 1.06{{e|11}} years.
+<sup>146</sup>Sm is an almost-extinct nuclide which decays via alpha emission to produce <sup>142</sup>Nd, with a half-life of 1.08{{e|8}} years.
+<sup>146</sup>Sm is itself produced by the decay of <sup>150</sup>[[Gadolinium|Gd]] via alpha-decay with a half-life of 1.79{{e|6}} years.
+An [[isochron dating|isochron]] is calculated normally. As with Rb-Sr and Pb-Pb [[isotope geochemistry]], the initial <sup>143</sup>Nd/<sup>144</sup>Nd ratio of the isotope system provides important information on [[Crust (geology)|crustal]] formation and the isotopic evolution of the solar system.
+==Sm and Nd geochemistry==
+The concentration of Sm and Nd in [[silicate]] minerals increase with the order in which they crystallise from a magma according to [[Bowen's reaction series]]. Samarium is accommodated more easily into [[mafic]] minerals, so a mafic rock which crystallises mafic minerals will concentrate neodymium in the melt phase faster relative to samarium. Thus, as a melt undergoes fractional crystallization from a mafic to a more felsic composition, the abundance of Sm and Nd changes, as does the ratio between Sm and Nd.
+Thus, [[ultramafic]] rocks have low Sm and Nd and ''high'' Sm/Nd ratios. [[Felsic]] rocks have high concentrations of Sm and Nd but ''low'' Sm/Nd ratios ([[komatiite]] has 1.14 parts per million (ppm) Sm and 3.59 ppm Nd versus 4.65 ppm Sm and 21.6 ppm Nd in [[rhyolite]]).
+The importance of this process is apparent in modeling the age of [[continental crust]] formation.
+==The CHUR model==
+Through the analysis of isotopic compositions of neodymium, DePaolo and [[Gerald J. Wasserburg|Wasserburg]] <ref>{{cite journal|last1=Depaolo|first1=D. J.|last2=Wasserburg|first2=G. J.|title=Nd isotopic variations and petrogenetic models|journal=Geophysical Research Letters|volume=3|pages=249|year=1976|doi=10.1029/GL003i005p00249|bibcode=1976GeoRL...3..249D|issue=5}}</ref> discovered that terrestrial igneous rocks closely followed the [[Chondritic unfractionated reservoir|Chondritic Uniform Reservoir]] (CHUR) line.
+Chondritic meteorites are thought to represent the earliest (unsorted) material that formed in the solar system before planets formed. They have relatively homogeneous trace element signatures and therefore their isotopic evolution can model the evolution of the whole solar system and of the ‘Bulk Earth’.
+After plotting the ages and initial <sup>143</sup>Nd/<sup>144</sup>Nd ratios of terrestrial igneous rocks on a Nd evolution vs. time diagram, DePaolo and Wasserburg determined that Archean rocks had initial Nd isotope ratios very similar to that defined by the CHUR evolution line.
+===Epsilon notation===
+Since <sup>143</sup>Nd/<sup>144</sup>Nd departures from the CHUR evolution line are very small, DePaolo and Wasserburg argued that it would be useful to create a form of notation that described <sup>143</sup>Nd/<sup>144</sup>Nd in terms of their deviations from the CHUR evolution line. This is called the epsilon notation whereby one epsilon unit represents a one part per 10,000 deviation from the CHUR composition.<ref name=Dickin>Dickin, A.P., 2005. [http://books.google.com/books?id=z8ZCg2HRvWsC&pg=PA76 Radiogenic Isotope Geology], 2nd ed. Cambridge: Cambridge University Press. ISBN 0-521-82316-1 pp. 76–77</ref> Algebraically, epsilon units can be defined by the equation:
+<br>
+::<math> \varepsilon_{Nd(t)} = \left[\frac{\left(\frac{^{143}Nd}{^{144}Nd}\right)_{sample(t)}}{\left(\frac{^{143}Nd}{^{144}Nd}\right)_{CHUR(t)}}-1\right]* 10000 </math>
+Since epsilon units are larger and therefore a more tangible representation of the initial Nd isotope ratio, by using these instead of the initial isotopic ratios, it is easier to comprehend and therefore compare initial ratios of crust with different ages. In addition, epsilon units will normalize the initial ratios to CHUR, thus eliminating any effects caused by various analytical mass fractionation correction methods applied.<ref name=Dickin/>
+===Nd Model Ages===
+Since CHUR defines initial ratios of continental rocks through time, it was deduced that measurements of <sup>143</sup>Nd/<sup>144</sup>Nd and <sup>147</sup>Sm/<sup>144</sup>Nd, with the use of CHUR, could produce model ages for the segregation from the mantle of the melt which formed any crustal rock. This has been termed ‘t-CHUR’.<ref>{{cite journal|last1=McCulloch|first1=M. T.|last2=Wasserburg|first2=G. J.|title=Sm-Nd and Rb-Sr Chronology of Continental Crust Formation|journal=Science|volume=200|pages=1003–11|year=1978|doi=10.1126/science.200.4345.1003|issue=4345|pmid=17740673|bibcode = 1978Sci...200.1003M }}</ref>
+In order for a T<sub>CHUR</sub> age to be calculated, fractionation between Nd/Sm would have to have occurred during magma extraction from the mantle to produce a continental rock. This fractionation would then cause a deviation between the crustal and mantle isotopic evolution lines. The intersection between these two evolution lines then indicates the crustal formation age. The T<sub>CHUR</sub> age is defined by the following equation:
+<br>
+::<math> T_{CHUR}=(\frac{1}{\lambda})ln \left[1+ \frac{\left(\frac{^{143}Nd}{^{144}Nd}\right)_{sample}-\left(\frac{^{143}Nd}{^{144}Nd}\right)_{CHUR}}{\left(\frac{^{147}Sm}{^{144}Nd}\right)_{sample}-\left(\frac{^{147}Sm}{^{144}Nd}\right)_{CHUR}}\right]</math>
+<br>
+The T<sub>CHUR</sub> age of a rock, can yield a formation age for the crust as a whole if the sample has not suffered disturbance after its formation. Since Sm/Nd are rare-earth elements (REE), their characteristic immobility enables their ratios to resist partitioning during metamorphism and melting of silicate rocks. This therefore allows for crustal formation ages to be calculated, despite any metamorphism the sample has undergone.
+==References==
+{{reflist}}
+{{Chronology}}
+[[Category:Radiometric dating]]

Coordinate time: Difference between revisions

Revision as of 01:11, 15 March 2013

Contents

Sm-Nd radiometric dating

Sm and Nd geochemistry

The CHUR model

Epsilon notation

Nd Model Ages

References

Navigation menu

Coordinate time: Difference between revisions

Revision as of 01:11, 15 March 2013

Sm-Nd radiometric dating

Sm and Nd geochemistry

The CHUR model

Epsilon notation

Nd Model Ages

References

Navigation menu

Search