67:/Ca ratios, the minerals will have had different starting Rb/Sr ratios, and the final Sr/Sr ratio will not have increased as much in the minerals poorer in Rb. Typically, Rb/Sr increases in the order plagioclase, hornblende, K-feldspar, biotite, muscovite. Therefore, given sufficient time for significant production (ingrowth) of radiogenic Sr, measured Sr/Sr values will be different in the minerals, increasing in the same order. Comparison of different minerals in a rock sample thus allows scientists to infer the original Sr/Sr ratio and determine the age of the rock.
157:), which is low in K (and hence Rb) but high in Sr (as this substitutes for Ca), which proportionally enriches the melt in K and Rb. This then causes orthoclase and biotite, both K rich minerals into which Rb can substitute, to precipitate. The resulting Rb–Sr ratios and Rb and Sr abundances of both the whole rocks and their component minerals will be markedly different. This, thus, allows a different rate of radiogenic Sr to evolve in the separate rocks and their component minerals as time progresses.
138:. Each of these minerals has a different initial rubidium/strontium ratio dependent on their potassium content, the concentration of Rb and K in the melt and the temperature at which the minerals formed. Rubidium substitutes for potassium within the lattice of minerals at a rate proportional to its concentration within the melt.
655:
734:
The important concept in isotopic tracing is that Sr derived from any mineral through weathering reactions will have the same Sr/Sr as the mineral. Although this is a potential source of error for terrestrial rocks, it is irrelevant for lunar rocks and meteorites, as there are no chemical weathering
62:
The ratio Sr/Sr in a mineral sample can be accurately measured using a mass spectrometer. If the amount of Sr and Rb isotopes in the sample when it formed can be determined, the age can be calculated from the increase in Sr/Sr. Different minerals that crystallized from the same silicic melt will all
730:
The Rb–Sr dating method has been used extensively in dating terrestrial and lunar rocks, and meteorites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr/Sr ratio. The dates indicate the true age of the
58:
daughter, Sr, produced in this decay process is the only one of the four naturally occurring strontium isotopes that was not produced exclusively by stellar nucleosynthesis predating the formation of the Solar System. Over time, decay of Rb increases the amount of radiogenic Sr while the amount of
764:
Strontium isotope stratigraphy relies on recognised variations in the Sr/Sr ratio of seawater over time. The application of Sr isotope stratigraphy is generally limited to carbonate samples for which the Sr seawater curve is well defined. This is well known for the
Cenozoic time-scale but, due to
755:
because the Sr/Sr of a skeleton, sea shell or indeed a clay artefact is directly comparable to the source rocks upon which it was formed or upon which the organism lived. Thus, by measuring the current-day Sr/Sr ratio (and often the Nd–Nd ratios as well) the geological fingerprint of an object or
765:
poorer preservation of carbonate sequences in the
Mesozoic and earlier, it is not completely understood for older sequences. In older sequences diagenetic alteration combined with greater uncertainties in estimating absolute ages due to lack of overlap between other geochronometers (for example
716:
to a result requires studying the metasomatic and thermal history of the rock, any metamorphic events, and any evidence of fluid movement. A Rb–Sr date which is at variance with other geochronometers may not be useless, it may be providing data on an event which is not representing the age of
83:
produces similar overall chemistry. Scientists can also estimate from Sr/Sr when crust rock was first formed from magma extracted from the mantle, even if the rock is subsequently metamorphosed or even melted and recrystallized. This provides clues to the age of the Earth's continents.
74:
that, during partial melting of the mantle, prefers to join the magmatic melt rather than remain in mantle minerals. As a result, Rb is enriched in crustal rocks relative to the mantle, and Sr/Sr is higher for crust rock than mantle rock. This allows scientists to distinguish
489:
981:
Veizer, Ján; Buhl, Dieter; Diener, Andreas; Ebneth, Stefan; Podlaha, Olaf G; Bruckschen, Peter; Jasper, Torsten; Korte, Christoph; Schaaf, Michael; Ala, Davin; Azmy, Karem (August 1997). "Strontium isotope stratigraphy: potential resolution and event correlation".
426:
1114:
165:
The age of a sample is determined by analysing several minerals within multiple subsamples from different parts of the original sample. The Sr/Sr ratio for each subsample is plotted against its Rb/Sr ratio on a graph called an
295:
300:
650:{\displaystyle {\frac {^{87}{\text{Sr}}}{^{86}{\text{Sr}}}}=\left({\frac {^{87}{\text{Sr}}}{^{86}{\text{Sr}}}}\right)_{0}+{\frac {^{87}{\text{Rb}}}{^{86}{\text{Sr}}}}(e^{\lambda t}-1)}
484:
447:
665:
Rb–Sr dating relies on correctly measuring the Rb–Sr ratio of a mineral or whole rock sample, plus deriving an accurate Sr/Sr ratio for the mineral or whole rock sample.
694:
One of the major drawbacks (and, conversely, the most important use) of utilizing Rb and Sr to derive a radiometric date is their relative mobility, especially in
657:
is the isochron equation. After measurements of
Rubidum and Strontium concentration in the mineral we can easily determine the age, the t value, of the sample.
876:"Sm–Nd and Rb–Sr Chronology of Continental Crust Formation: Times of addition to continents of chemically fractionated mantle-derived materials are determined"
170:. If these form a straight line then the subsamples are consistent, and the age probably reliable. The slope of the line dictates the age of the sample.
843:"Crustal Age Domains and the Evolution of the Continental Crust in the Mozambique Belt of Tanzania: Combined Sm–Nd, Rb–Sr, and Pb–Pb Isotopic Evidence"
798:
Hawkesworth, C. J.; Vollmer, R. (1979). "Crustal contamination versus enriched mantle: 143Nd/144Nd and 87Sr/86Sr evidence from the
Italian volcanics".
184:
705:
Conversely, these fluids may metasomatically alter a rock, introducing new Rb and Sr into the rock (generally during potassic alteration or calcic (
709:) alteration. Rb–Sr can then be used on the altered mineralogy to date the time of this alteration, but not the date at which the rock formed.
668:
Several preconditions must be satisfied before a Rb–Sr date can be considered as representing the time of emplacement or formation of a rock.
1098:
1075:
938:
63:
have the same initial Sr/Sr as the parent melt. However, because Rb substitutes for K in minerals and these minerals have different
1023:
698:
fluids. Rb and Sr are relatively mobile alkaline elements and as such are relatively easily moved around by the hot, often
1129:
766:
683:
must have formed in chemical equilibrium with one another or in the case of sediments, be deposited at the same time;
672:
The system must have remained closed to Rb and Sr diffusion from the time at which the rock formed or fell below the
142:
421:{\displaystyle _{38}^{87}{\text{Sr}}(t)=~_{38}^{87}{\text{Sr}}(0)+~_{37}^{87}{\text{Rb}}(e^{\lambda t}-1)\ ,}
456:
80:
807:
71:
430:
297:, we obtain the expression which describes the growth of strontium-87 from the decay of rubidium-87:
79:
produced by melting of crust rock from magma produced by melting of mantle rock, even if subsequent
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903:
875:
823:
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39:
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50:(Sr, Sr). One of the two naturally occurring isotopes of rubidium, Rb, decays to Sr with a
680:
99:
1034:
17:
811:
146:
995:
769:) leads to greater uncertainties in the exact shape of the Sr isotope seawater curve.
1123:
1014:
967:
827:
907:
752:
695:
687:
111:
891:
290:{\displaystyle {\ce {^{87}_{37}Rb->~_{38}^{87}Sr~+e^{-}\ +{\bar {\nu }}_{e}}}}
1067:
1016:
Seawater isotope records, crustal evolution, tectonics and atmospheric evolution
930:
744:
859:
842:
178:
127:
123:
1022:. Seventh Annual V.M. Goldschmidt Conference. Tucson, AZ. pp. 103–104.
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135:
91:
64:
51:
47:
35:
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which could have disturbed the Rb–Sr system either thermally or chemically
150:
119:
43:
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skeleton can be measured, allowing migration patterns to be determined.
819:
154:
131:
115:
88:
118:
that contains several major Sr-bearing minerals including plagioclase
706:
208:
76:
954:
Elderfield, H. (October 1986). "Strontium isotope stratigraphy".
42:
of rocks and minerals from their content of specific isotopes of
731:
minerals only if the rocks have not been subsequently altered.
702:
hydrothermal fluids present during metamorphism or magmatism.
486:
as a constant, since it is stable and not radiogenic. Hence,
34:
method (Rb–Sr) is a radiometric dating technique, used by
679:
The minerals which are taken from a rock to construct an
283:
1115:
CSIRO Petroleum – Global Sr
Seawater Isotope Evolution
492:
459:
433:
303:
187:
453:
of rubidium. Furthermore, we consider the number of
1093:. Jones & Bartlett Learning. pp. 383–385.
921:Bowen, Robert (1994). "Rubidium-Strontium Dating".
874:McCulloch, M. T.; Wasserburg, G. J. (2 June 1978).
841:Moller, A.; Mezger, K.; Schenk, V. (1 April 1998).
27:
Radiometric dating technique for rocks and minerals
649:
478:
441:
420:
289:
984:Palaeogeography, Palaeoclimatology, Palaeoecology
956:Palaeogeography, Palaeoclimatology, Palaeoecology
149:assemblage of plagioclase and hornblende (i.e.;
87:Development of this process was aided by German
145:would see a granite melt begin crystallizing a
8:
1013:Jacobsen, S.B.; Wills, J.; Yin, Q. (1997).
1054:Attendorn, H.-G.; Bowen, R. N. C. (1997).
743:Initial Sr/Sr ratios are a useful tool in
858:
800:Contributions to Mineralogy and Petrology
676:(generally considered to be 650 °C);
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1060:Radioactive and Stable Isotope Geology
686:The rock must not have undergone any
110:For example, consider the case of an
59:other Sr isotopes remains unchanged.
7:
479:{\displaystyle {\ce {^{86}_{38}Sr}}}
1035:"Periodic table – strontium"
175:universal law of radioactive decay
25:
735:reactions in those environments.
1087:"Rubidium–Strontium Systematics"
1029:from the original on 2022-10-09.
141:The ideal scenario according to
98:, who later went on to discover
442:{\displaystyle {\ce {\lambda}}}
923:Isotopes in the Earth Sciences
760:Strontium isotope stratigraphy
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1:
1085:Walther, John Victor (2009).
996:10.1016/S0031-0182(97)00054-0
892:10.1126/science.200.4345.1003
968:10.1016/0031-0182(86)90007-6
70:In addition, Rb is a highly
54:of 49.23 billion years. The
1068:10.1007/978-94-011-5840-4_7
1056:"Rubidium–strontium dating"
931:10.1007/978-94-009-2611-0_4
177:and the following rubidium
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1091:Essentials of geochemistry
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202:
32:rubidium–strontium dating
18:Rubidium-strontium dating
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860:10.1093/petroj/39.4.749
717:formation of the rock.
143:Bowen's reaction series
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1039:Resources on Isotopes
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481:
444:
423:
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81:magma differentiation
1062:. pp. 159–191.
1041:. USGS. January 2004
925:. pp. 162–200.
847:Journal of Petrology
739:Isotope geochemistry
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72:incompatible element
886:(4345): 1003–1011.
812:1979CoMP...69..151H
674:closure temperature
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161:Calculating the age
1130:Radiometric dating
820:10.1007/BF00371858
779:Radiometric dating
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102:in December 1938.
1100:978-0-7637-5922-3
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962:(1): 71–90.
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1045:10 November
745:archaeology
1124:Categories
785:References
700:carbonated
449:being the
179:beta decay
173:Given the
128:hornblende
124:K-feldspar
114:such as a
56:radiogenic
36:scientists
1140:Strontium
828:128876101
749:forensics
639:−
631:λ
436:λ
404:−
396:λ
272:¯
269:ν
254:−
216:−
212:β
136:muscovite
92:Otto Hahn
52:half-life
48:strontium
46:(Rb) and
1135:Rubidium
1024:Archived
908:40675318
900:17740673
773:See also
681:isochron
206:→
168:isochron
151:tonalite
147:cumulate
120:feldspar
89:chemists
44:rubidium
880:Science
808:Bibcode
155:diorite
132:biotite
116:granite
106:Example
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134:, and
1027:(PDF)
1020:(PDF)
904:S2CID
824:S2CID
77:magma
1095:ISBN
1072:ISBN
1047:2016
935:ISBN
896:PMID
767:U–Th
751:and
721:Uses
94:and
30:The
1064:doi
992:doi
988:132
964:doi
927:doi
888:doi
884:200
855:doi
816:doi
153:or
40:age
1126::
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1058:.
1037:.
986:.
960:57
958:.
933:.
902:.
894:.
882:.
878:.
851:39
849:.
845:.
822:.
814:.
804:69
802:.
747:,
616:Sr
610:86
600:Rb
594:87
567:Sr
561:86
551:Sr
545:87
523:Sr
517:86
507:Sr
501:87
472:86
469:38
463:Sr
384:Rb
378:87
373:37
352:Sr
346:87
341:38
320:Sr
314:87
309:38
240:Sr
235:87
230:38
200:87
197:37
191:Rb
181::
130:,
126:,
122:,
1103:.
1080:.
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810::
645:)
642:1
634:t
627:e
623:(
584:+
579:0
574:)
535:(
530:=
416:,
410:)
407:1
399:t
392:e
388:(
365:+
362:)
359:0
356:(
333:=
330:)
327:t
324:(
279:e
262:+
250:e
246:+
65:K
20:)
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