3   The Rb)Sr method


Rubidium, a group 1 alkali metal, has two naturally occurring isotopes, 85Rb and 87Rb, whose abundances are 72.17% and 27.83% respectively. These figures yield an atomic abundance ratio of 85Rb/87Rb = 2.593 (Catanzaro et al., 1969), which is a constant throughout the Earth, Moon and most meteorites due to isotopic homogenisation in the solar nebula. 87Rb is radioactive, and decays to the stable isotope 87Sr by emission of a $ particle and antineutrino (<). The decay energy (Q) is shared as kinetic energy by these two particles.


           8737Rb  6   8738Sr  +  $!  +  <  +  Q



3.1       The Rb decay constant


            The low decay energy for this transformation (275 keV) has always caused problems in the accurate determination of the Rb decay constant. Because the decay energy is divided between the $ particle and anti-neutrino, the $ particles have a smooth distribution of kinetic energy from the total energy down to zero. When attempting to accurately determine the decay constant by direct counting, the low energy $ particles cause great problems because they may be absorbed by surrounding Rb atoms before they ever reach the detector. For example, in a thick (>1:m deep) solid Rb sample, attenuation is so severe that a false frequency maximum is generated at ca. 10 keV (Fig. 3.1).

Fig. 3.1. Plot of activity against kinetic energy for $ particles generated by 87Rb decay. Solid lines =  solid Rb sources; dashed lines = liquid scintillator measurements. After Neumann and Huster (1976).


            One way to avoid the attenuation problem is to use a photo- multiplier with a liquid scintillator solution doped with Rb. The $ particles will be absorbed by molecules of the scintillator (emitting light flashes) before they can be absorbed by other Rb atoms. The major problem with this method is that a low-energy cut-off at ca. 10 keV must be applied to avoid the high background noise associated with liquid scintillation. The consequent extrapolation of count-rate curves down to zero energy leads to a large uncertainty in the result (Fig. 3.1). Hence this method has given values for the 87Rb half-life from 47.0 " 1.0 Byr (Flynn and Glendenin, 1959) to 52.1 " 1.5 Byr (Brinkman et al., 1965).


            Another approach to direct counting is to make measurements with progressively thinner solid Rb sources using a proportional counter. The results are then extrapolated to a theoretical source of zero thickness to remove the effect of self-absorption. The proportional counter has a much lower noise level, so the energy cut-off can be set as low as 0.185 keV. Rb films with thicknesses down to 1 :m were measured by Neumann and Huster (1974), and extrapolated to zero thickness by Neumann and Huster (1976) to derive an 87Rb half-life of 48.8 " 0.8 Byr (equivalent to a decay constant of 1.42 H 10!11 yr!1).


            An alternative approach to determining the Rb decay constant is to measure the amount of 87Sr produced by decay of a known quantity of 87Rb in the laboratory over a known period of time. This method was first attempted by McMullen et al. (1966) on a rubidium sample they had purified in 1956, and was repeated on the same sample batch by Davis et al. (1977). Unfortunately, McMullen et al. omitted to measure the small but significant level of residual 87Sr present in their rubidium before they put it away on the shelf. Hence, the accuracy of their determination was compromised. However, this problem contributes less than 1% uncertainty to the later determination of Davis et al. (1977). Their proposed value for the 87Rb half-life (48.9 " 0.4 Byr, equivalent to a decay constant of 1.42 H 10!11 yr!1) can therefore be taken to support the value of Neumann and Huster (1976).


            A third approach to the determination of the Rb decay constant is to date geological samples whose ages have also been measured by other methods with more reliable decay constants. This method has the disadvantage that it involves geological uncertainties, such as whether all isotopic systems closed at the same time and remained closed. However, it provides a useful check on the direct laboratory determinations. In this respect it is worth noting that Pinson et al. (1963) proposed a rubidium half-life of 48.8 Byr on the basis of Rb)Sr dating of stony meteorites.


            During the last 30 years, values of the decay constant used in geological age calculations have varied between 1.47 and 1.39 H 10!11 yr!1 (t1/2 = 46.8 to 50.0 Byr). The most commonly used value of 1.42 H 10!11 yr!1 (t1/2 = 48.8 Byr) was adopted by international convention (Steiger and Jager, 1977), but probably needs to be revised. For example, very precise U)Pb and Rb)Sr isochrons for chondritic meteorites can only be made to agree if the 87Rb decay constant is reduced to 1.402 (" 0.008) H 10!11 yr!1, equivalent to a half-life of 49.4 " 0.3 Byr (Minster et al., 1982).





Albarede, F., Michard, A., Minster, J. F. and Michard, G. (1981). 87Sr/86Sr ratios in hydrothermal waters and deposits from the East Pacific Rise at 21 oN. Earth Planet. Sci. Lett. 55, 229)36.

Armstrong, R. L. (1971). Glacial erosion and the variable isotopic composition of strontium in sea water. Nature Phys. Sci. 230, 132)33.


Asmerom, Y., Jacobsen, S. B., Knoll, A. H., Butterfield, N. J. and Swett, K. (1991). Strontium isotopic variations of Neoproterozoic seawater: implications for crustal evolution. Geochim. Cosmochim. Acta 55, 2883)94.


Basu, A. R., Jacobsen, S. B., Poreda, R. J., Dowling, C. B. and Aggarwal, P. K. (2001). Large groundwater strontium flux to the oceans from the Bengal Basin and the marine strontium isotope record. Science 293, 1470–3.


Beckinsale, R. D., Pankhurst, R. J., Skelhorn, R. R. and Walsh, J. N. (1978). Geochemistry and petrogenesis of the early Tertiary lava pile of the Isle of Mull, Scotland. Contrib. Mineral. Petrol. 66, 415)27.


Birck, J. L. and Allegre, C. J. (1978). Chronology and chemical history of the parent body of basaltic achondrites studied by the 87Rb)87Sr method. Earth Planet. Sci. Lett. 39, 37)51.


Blum, J. D. and Erel, Y. (1995). A silicate weathering mechanism linking increases in marine 87Sr/86Sr with global glaciation. Nature 373, 415–8.


Blum, J. D., Gazis, C. A., Jacobson, A. D. and Chamberlain, C. P. (1998). Carbonate versus silicate weathering in the Raikhot watershed within the High Himalayan Crystalline Series. Geology 26, 411–4.


Bowring, S. A., Grotzinger, J. P., Isachsen, C. E., Knoll, A. H., Pelechaty, S. M. and Kolosov, P. (1993). Calibrating rates of Early Cambrian evolution. Science 261, 1293)8.


Brand, U. and Veizer, J. (1980). Chemical diagenesis of a multicomponent carbonate system ) 1: Trace elements. J. Sed. Petrol. 50, 1219)36.


Brannon, J. C., Podosek, F. A. and McLimans, R. K. (1992). Alleghenian age of the Upper Mississippi Valley zinc-lead deposit determined by Rb–Sr dating of sphalerite. Nature 356, 509–11.


Brass, G. W. (1976). The variation of the marine 87Sr/86Sr ratio during Phanerozoic time: interpretation using a flux model. Geochim. Cosmochim. Acta 40, 721)30.


Brinkman, G. A., Aten, A. H. W. and Veenboer, J. T. (1965). Natural radioactivity of K-40, Rb-87 and Lu-176. Physica 31, 1305)19.


Brooks, C., Hart, S. R., Hofmann, A. and James, D. E. (1976a). Rb)Sr mantle isochrons from oceanic regions. Earth Planet. Sci. Lett. 32, 51-61.


Brooks, C., James, D. E. and Hart, S. R. (1976b). Ancient lithosphere: its role in young continental volcanism. Science 193, 1086)94.


Brown, E. H. (1971). Phase relations of biotite and stilpnomelane in the green-schist facies. Contrib. Mineral. Petrol. 31, 275)99.


Burke, W. H., Denison, R. E., Hetherington, E. A., Koepnick, R. B., Nelson, H. F. and Otto, J. B. (1982). Variations of seawater 87Sr/86Sr throughout Phanerozoic time. Geology 10, 516)19.


Catanzaro, E. J., Murphy, T. J., Garner, E. L. and Shields, W. R. (1969). Absolute isotopic abundance ratio and atomic weight of terrestrial rubidium. J. Res. NBS 73A, 511)16.


Chaudhuri, S. and Clauer, N. (1986). Fluctuations of isotopic composition of strontium in seawater during the Phanerozoic eon. Chem. Geol. (Isot. Geosci. Section) 59, 293–303.


Christensen, J. N., Halliday, A. N., Leigh, K. E., Randell, R. N. and Kesler, S. E. (1995a). Direct dating of sulfides by Rb–Sr: a critical test using the Polaris Mississippi Valley-type Zn–Pb deposit. Geochim. Cosmochim. Acta 59, 5191)7.


Christensen, J. N., Halliday, A. N., Vearncombe, J. R. and Kesler, S. E. (1995b). Testing models of large-scale crustal fluid flow using direct dating of sulfides: Rb–Sr evidence for early dewatering and formation of Mississippi Valley-type deposits, Canning Basin, Australia. Econ. Geol. 90, 877)84.


Clark, S. P. and Jager, E. (1969). Denudation rate in the Alps from geochronologic and heat flow data. Amer. J. Sci. 267, 1143)60.


Clauer, N. (1979). A new approach to Rb)Sr dating of sedimentary rocks. In: Jager, E. and Hunziker, J. C. (Eds) Lectures in Isotope Geology. Springer, pp. 30)51.


Clauer, N., Keppens, E. and Stille, P. (1992). Sr isotopic constraints on the process of glauconitization. Geology 20, 133)6.


Clemens, S. C., Farrell, J. W. and Gromet, L. P. (1993). Synchronous changes in seawater strontium isotope composition and global climate. Nature 363, 607)10.


Clemens, S. C., Gromet, L. P. and Farrell, J. W. (1995). Artefacts in Sr isotope records. Nature 373, 201.


Cliff, R. A. (1985). Isotope dating in metamorphic belts. J. Geol. Soc. Lond. 142, 97)110.


Compston, W. and Jeffery, P. M. (1959). Anomalous common strontium in granite. Nature 184, 1792)3.


Compston, W., McDougall, I. and Wyborn, D. (1982). Possible two-stage 87Sr evolution in the Stockdale rhyolite. Earth Planet. Sci. Lett. 61, 297)302.

Compston, W. and Pidgeon, R. T. (1962). Rubidium)strontium dating of shales by the total-rock method. J. Geophys. Res. 67, 3493)502.


Compston, W., Williams, I. S., Kirschvink, J. and Zhang, Z. (1990). Zircon U)Pb ages relevant to the Cambrian numerical timescale. Geol. Soc. Australia 27, 21 (abstract).


Cowie, J. W. and Johnson, M. R. W. (1985). Late Precambrian and Cambrian geological time-scale. In: Snelling, N. J. (Ed.) The Chronology of the Geological Record. Mem. Geol. Soc. Lond. 10, 47)64.


Dasch, E. J. and Biscaye, P. E. (1971). Isotopic composition of strontium in Cretaceous-to-Recent, pelagic foraminifera. Earth Planet. Sci. Lett. 11, 201)4.


Davis, D. W., Gray, J. and Cumming, G. L. (1977). Determination of the 87Rb decay constant. Geochim. Cosmochim. Acta 41, 1745)9.


Del Moro, A., Puxeddu, M. Radicati de Brozolo, F. and Villa, I. M. (1982). Rb)Sr and K)Ar ages on minerals at temperatures of 300 ) 400 oC from deep wells in the Larderello geothermal field (Italy). Contrib. Mineral. Petrol. 81, 340)9.


DePaolo, D. J. (1986). Detailed record of the Neogene Sr isotopic evolution of seawater from DSDP Site 590B. Geology 14, 103)6.


DePaolo, D. J. (1987). Correlating rocks with strontium isotopes. Geotimes (Dec. 1987), 16––18.

Derry, L. A., Keto, L. S., Jacobsen, S. B., Knoll, A. H. and Swett, K. (1989). Sr isotopic variations in Upper Proterozoic carbonates from Svalbard and East Greenland. Geochim. Cosmochim. Acta 53, 2331)9.


Dia, A. N., Cohen, A. S., O’Nions, R. K. and Shackleton, N. J. (1992). Seawater Sr isotope variation over the past 300 kyr and influence of global climate cycles. Nature 356, 786)8.


Dodson, M. H. (1973). Closure temperature in cooling geochronological and petrological systems. Contrib. Mineral. Petrol. 40, 259)74.


Dodson M. H. (1979). Theory of cooling ages. In: Jager, E. and Hunziker, J. C. (Eds) Lectures in Isotope Geology. Springer, pp. 194)202.


Dunoyer de Segonzac, G. (1969). Les mineraux argileux dans la diagenese. Passage au metamorphisme. Mem. Serv. Carte Geol. Alsace Lorraine 29, 320 p.


Elderfield, H. and Gieskes, J. M. (1982). Sr isotopes in interstitial waters of marine sediments from Deep Sea Drilling Project cores. Nature 300, 493–7.


English, N. B., Quade, J., DeCelles, P. G. and Garzione, C. N. (2000). Geologic control of Sr and major element chemistry in Himalayan rivers, Nepal.  Geochim. Cosmochim. Acta 64, 2549)66.


Fairbairn, H. W., Hurley, P. M. and Pinson, W. H. (1961). The relation of discordant Rb)Sr mineral and rock ages in an igneous rock to its time of crystallization and subsequent Sr87/Sr86 metamorphism. Geochim. Cosmochim. Acta 23, 135)44.


Farrell, J. W., Clemens, S. C. and Gromet, L. P. (1995). Improved chronostratigraphic reference curve of late Neogene seawater 87Sr/86Sr. Geology 23, 403–6.


Faure, G., Hurley, P. M. and Powell, J. L. (1965). The isotopic composition of strontium in surface water from the North Atlantic Ocean. Geochim. Cosmochim. Acta 29, 209)20.


Field D. and Raheim, A. (1979a). Rb)Sr total rock isotope studies on Precambrian charnockitic gneisses from South Norway: evidence for isochron resetting during a low-grade metamorphic-deformational event. Earth Planet. Sci. Lett. 45, 32)44.


Field D. and Raheim, A. (1979b). A geologically meaningless Rb)Sr total rock isochron. Nature 282, 497)9.


Flynn, K. F. and Glendenin, L. E. (1959). Half-life and $ spectrum of Rb87. Phys. Rev. 116, 744)8.


Gale, N. H., Beckinsale, R. D. and Wadge, A. J. (1979). A Rb)Sr whole rock isochron for the Stockdale Rhyolite of the English Lake District and a revised mid-Paleozoic time-scale. J. Geol. Soc. Lond. 136, 235)42.


Gast, P. W. (1955). Abundance of Sr87 during geologic time. Bull. Geol. Soc. Amer. 66, 1449)64.


Grant, N. K., Laskowski, T. E. and Foland, K. A. (1984). Rb)Sr and K)Ar ages of Paleozoic glauconites from Ohio)Indiana and Missouri, USA. Isot. Geosci. 2, 217)39.


Gray, C. M., Papanastassiou, D. A. and Wasserburg, G. J. (1973). The identification of early condensates from the solar nebula. Icarus 20, 213)39.


Halliday, A. N. and Porcelli, D. (2001). In search of lost planets– the paleocosmochronology of the inner solar system. Earth Planet. Sci. Lett. 192, 545–559.


Harris, N. (1995). Significance of weathering Himalayan metasedimentary rocks and leucogranites for the Sr isotope evolution of seawater during the early Miocene. Geology 23, 795–8.


Harris, W. B. (1976). Rb)Sr glauconite isochron, Maestrichtian unit of Peedee Formation, North Carolina. Geology 4, 761)2.


Henderson, G. M., Martel, D. J., O’Nions, R. K. Shackleton, N. J. (1994). Evolution of seawater  87Sr/86Sr over the last 400 ka: the absence of glacial/interglacial cycles. Earth Planet. Sci. Lett. 128, 643–51.


Hess, J., Bender, M. L. and Schilling, J. G. (1986). Evolution of the ratio of strontium-87 to strontium-86 in seawater from Cretaceous to present. Science 231, 979)84.


Hodell, D. A., Mead, G. A. and Mueller, P. A. (1990). Variation in the strontium isotopic composition of seawater (8 Ma to present): implications for chemical weathering rates and dissolved fluxes to the oceans. Chem. Geol. (Isot. Geosci. Section) 80, 291–307.


Hofmann, A. W. and Giletti, B. J. (1970). Diffusion of geochronologically important nuclides under hydrothermal conditions. Eclogae Geol. Helv. 63, 141)50.


Hunziker, J. C. (1974). Rb)Sr and K)Ar age determination and the Alpine tectonic history of the Western Alps. Mem. Inst. Geol. Min. Univ. Padova 31, 1)54.


Hurley, P. M., Cormier, R. F., Hower, J., Fairbairn, H. W. and Pinson, W. H. (1960). Reliability of glauconite for age measurement by K)Ar and Rb)Sr methods. Amer. Assoc. Pet. Geol. Bull. 44, 1793)808.


Jacobson, A. D. and Blum, J. D. (2000). Ca/Sr and 87Sr/86Sr geochemistry of disseminated calcite in Himalayan silicate rocks from Nanga Parbat: influence on river-water chemistry. Geology 28, 463–6.


Jacobson, A. D., Blum, J. D., Chamberlain, C. P., Poage, M. A. and Sloan, V. F. (2002). Ca/Sr and Sr isotope systematics of a Himalayan glacial chronosequence: carbonate versus silicate weathering rates as a function of landscape surface age. Geochim. Cosmochim. Acta 66, 13–27.


Jager, E. (1973). Die Alpine orogenese im lichte der radiometrischen altersbestimmung. Eclogae Geol. Helv. 66, 11)21.


Jager, E. Niggli, E. and Wenk, E. (1967). Rb)Sr altersbestimmungen an glimmern der Zentralalpen. Beitr. Geol. Karte Schweiz N. F. 134, 1)67.


Kaufman, A. J., Jacobsen, S. B. and Knoll, A. H. (1993). The Vendian record of Sr and C isotopic variations in seawater: implications for tectonics and paleoclimate. Earth Planet. Sci. Lett. 120, 409)30.


Kubler, B. (1966). La cristallinite d’illite et les zones tout a fait superieures du metamorphisme. Colloque. sur les Etages Tectoniques. Univ. Neuchatel. A la Baconniere Neuchatel, Suisse, pp. 105)22.


Lanphere, M. A., Wasserburg, G. J., Albee, A. L. and Tilton, G. R. (1964). Redistribution of strontium and rubidium isotopes during metamorphism, World Beater complex, Panamint Range, California. In: Craig, H., Miller, S. L. and Wasserburg, G. J. (Eds) Isotopic and Cosmic Chemistry. North Holland Pub., pp. 269)320.


MacLeod, K. G., Huber, B. T. and Fullagar, P. D. (2001). Evidence for a small (~0.000 030) but resolvable increase in seawater 87Sr/86Sr ratios across the Cretaceous–Tertiary boundary. Geology 29, 303–6.


Martin, E. E. and Macdougall, J. D. (1991). Seawater Sr isotopes at the Cretaceous/Tertiary boundary. Earth Planet. Sci. Lett. 104, 166)80.


McArthur, J. M., Howarth, R. J. and Bailey, T. R. (2001). Strontium isotope stratigraphy: LOWESS Version 3: best fit to the marine Sr-isotope curve for 0-509 Ma, and accompanying look-up table for deriving numerical age. J. Geol. 109, 155–7.


McArthur, J. M., Thirlwall, M. F., Engkilde, M., Zinsmeister, W. J. and Howarth, R. J. (1998). Strontium isotope profiles across K/T boundary sequences in Denmark and Antarctica. Earth Planet. Sci. Lett. 160, 179–192.


McKerrow, W. S., Lambert, R. St J. and Chamberlain V. E. (1980). The Ordovician, Silurian and Devonian time scales. Earth Planet. Sci. Lett. 51, 1-8.


McMullen, C. C., Fritze, K. and Tomlinson, R. H. (1966). The half-life of rubidium-87. Can. J. Phys. 44, 3033)8.


Minster, J-F., Birck, J-L. and Allegre, C. J. (1982). Absolute age of formation of chondrites studied by the 87Rb)87Sr method. Nature 300, 414)9.


Morton, J. P. and Long, L. E. (1980). Rb)Sr dating of Palaeozoic glauconite from the Llano region, central Texas. Geochim. Cosmochim. Acta 44, 663)72.


Nakai, S., Halliday, A. N., Kesler, S. E. and Jones, H. D. (1990). Rb–Sr dating of sphalerites from Tennessee and the genesis of Mississippi Valley type ore deposits. Nature 346, 354)7.


Nakai, S., Halliday, A. N., Kesler, S. E., Jones, H. D., Kyle, J. R. and Lane, T. E. (1993). Rb–Sr dating of sphalerites from Mississippi Valley-type (MVT) ore deposits. Geochim. Cosmochim. Acta 57, 417)27.


Neumann, W. and Huster, E. (1974). The half-life of 87Rb measured as a difference between the isotopes of 87Rb and 85Rb. Z. Physik 270, 121)7.


Neumann, W. and Huster, E. (1976). Discussion of the 87Rb half-life determined by absolute counting. Earth Planet. Sci. Lett. 33, 277)88.


Nicolaysen. L. O. (1961). Graphic interpretation of discordant age measurements on metamorphic rocks. Ann. N. Y. Acad. Sci. 91, 198)206.


Odin, G. S. and Dodson, M. H. (1982). Zero isotopic age of glauconies. In: Odin, G. S. (Ed.) Numerical Dating in Stratigraphy. Wiley, pp. 277)305.


Odin, G. S., Gale, N. H. and Dore, F. (1985). Radiometric dating of Late Precambrian times. In: Snelling, N. J. (Ed.) The Chronology of the Geological Record. Mem. Geol. Soc. Lond. 10, 65)72.


Palmer, M. R. and Edmond, J. M. (1989). The strontium isotope budget of the modern ocean. Earth Planet. Sci. Lett. 92, 11)26.


Palmer, M. R. and Edmond, J. M. (1992). Controls over the strontium isotope composition of river water. Geochim. Cosmochim. Acta 56, 2099)2111.


Papanastassiou, D. A., Wasserburg, G. J. and Burnett, D. S. (1969). Initial strontium isotopic abundances and the resolution of small time differences in the formation of planetary objects. Earth Planet. Sci. Lett. 5, 361)76.


Papanastassiou, D. A. and Wasserburg, G. J. (1970). Rb)Sr ages of lunar rocks from the Sea of Tranquillity. Earth Planet. Sci. Lett. 8, 1)19.


Peterman, Z. E., Hedge, C. E. and Tourtelot, H. A. (1970). Isotopic composition of strontium in sea water throughout Phanerozoic time. Geochim. Cosmochim. Acta 34, 105)20.


Pettke, T. and Diamond, L. W. (1996). Rb–Sr dating of sphalerite based on fluid inclusion–host mineral isochrons: a clarification of why it works. Econ. Geol. 91, 951)6.


Pierson-Wickmann, A.-C., Reisberg, L. and France-Lanord, C. (2002). Impure marbles of the Lesser Himalaya: another source of continental radiogenic osmium. Earth Planet. Sci. Lett. 204, 203–14.


Pinson, W. H., Schnetzler, C. C., Beiser, E., Fairbairn, H. W. and Hurley, P. M. (1963). Rb)Sr age of stony meteorites. MIT Geochron. Lab. 11th Ann. Rep. NYO-10, 517.


Popp, B. N., Podosek, F. A., Brannon, J. C., Anderson, T. F. and Pier, J. (1986). 87Sr/86Sr ratios in Permo-Carboniferous sea water from the analyses of well-preserved brachiopod shells. Geochim. Cosmochim. Acta 50, 1321)8.


Provost, A. (1990). An improved diagram for isochron data. Chem. Geol. (Isot. Geosci. Section) 80, 85)99.


Purdy, J. W. and Jager, E. (1976). K)Ar ages on rock-forming minerals from the Central Alps. Mem. Inst. Geol. Mineral. Univ. Padova 30, 3)31.


Raymo, M. E., Ruddiman, W. F. and Froelich, P. N. (1988). Influence of late Cenozoic mountain building on ocean geochemical cycles. Geology 16, 649)53.


Richter, F. M. and DePaolo, D. J. (1987). Numerical models for diagenesis and the Neogene Sr isotope evolution of seawater from DSDP Site 590B. Earth Planet. Sci. Lett. 83, 27)38.

Richter, F. M., Rowley, D. B. and DePaolo, D. J. (1992). Sr isotope evolution of seawater: the role of tectonics. Earth Planet. Sci. Lett. 109, 11)23.


Rundberg, Y. and Smalley, P. C. (1989). High-resolution dating of Cenozoic sediments from northern North Sea using 87Sr/86Sr stratigraphy. AAPG Bull. 73, 298)308.


Schreiner, G. D. L. (1958). Comparison of the Rb-87/Sr-87 ages of the Red granite of the Bushveld complex from measurements on the total rock and separated mineral fractions. Proc. Roy. Soc. Lond. A. 245, 112)7.


Sheppard, T. J. and Darbyshire, D. P. F. (1981). Fluid inclusion Rb–Sr isochrons for dating mineral deposits. Nature 290, 578–9.


Spooner, E. T. C. (1976). The strontium isotopic composition of seawater, and seawater)oceanic crust interaction. Earth Planet. Sci. Lett. 31, 167)74.


Steiger, R. H. and Jager, E. (1977). Subcommission on geochronology: convention on the use of decay constants in geo- and cosmo-chronology. Earth Planet. Sci. Lett. 36, 359)62.


Sun, S. S. and Hanson, G. N. (1975). Evolution of the mantle: geochemical evidence from alkali basalt. Geology 3, 297)302.


Tatsumoto, M. (1966). Genetic relations of oceanic basalts as indicated by lead isotopes. Science 153, 1094)101.


Tilton, G. R. (1988). Age of the Solar system. In: Kerridge, J. F. and Matthews, M. S. (Eds), Meteorites and the Early Solar System, Univ. Arizona Press, pp. 259–75.


Tretbar, D. R., Arehart, G. B. and Christensen, J. N. (2000). Dating gold deposition in a Carlin-type gold deposit using Rb/Sr methods on the mineral galkhaite. Geology 28, 947)50.


Veizer, J. and Compston, W. (1974). 87Sr/86Sr composition of seawater during the Phanerozoic. Geochim. Cosmochim. Acta 38, 1461)84.


Veizer, J. and Compston, W. (1976). 87Sr/86Sr in Precambrian carbonates as an index of crustal evolution. Geochim. Cosmochim. Acta 40, 905)14.


Veizer, J. and 14 others. (1999). 87Sr/86Sr, d 13C and d 18O evolution of Phanerozoic seawater. Chem. Geol. 161, 59)88.


Verschure, R. H. Andriessen, P. A. M., Boelrijk, N. A. I. M., Hebeda, E. H., Maijer, C. Prien, H. N. A. and Verdurmen, E. A. T. (1980). On the thermal stability of Rb)Sr and K)Ar biotite systems : evidence from co-existing Sveconorwegian (ca. 870 Ma) and Caledonian (ca. 400 Ma) biotites in S. W. Norway. Contrib. Mineral. Petrol. 74, 245)52.


Wasserburg, G. J., Papanastassiou, D. A. and Sanz, H. G. (1969). Initial strontium for a chondrite and the determination of a metamorphism or formation interval. Earth Planet. Sci. Lett. 7, 33)43.


Wetherill, G. W., Davis, G. L. and Lee-Hu, C. (1968). Rb)Sr measurements on whole rocks and separated minerals from the Baltimore Gneiss, Maryland. Geol. Soc. Amer. Bull. 79, 757)62.


Wickman, F. E. (1948). Isotope ratios: a clue to the age of certain marine sediments. J. Geol. 56, 61)6.