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Age dating methods

In the rubidium-strontium age dating method, radioactive 87Rb isotope with a natural isotope abundance of 27.85 % and a half-life of 4.8 x 1010 a is fundamental to the 3 decay to the isobar 87 Sr. The equation for the Rb-Sr method can be derived from Equation (8.9) ... [Pg.247]

Whereas the abundance of Sr in rubidium rich rocks changes over time due to the radioactive 3 decay of Rb as a function of the primordial rubidium concentration and the age of the mineral, the abundance of the stable Sr isotope and consequently the Sr/ Sr is constant in nature. The constant Sr/ Sr isotope ratio is often used for internal standardization (mass bias correction) during strontium isotope ratio measurements of Sr/ Sr. In the rubidium-strontium age dating method, the isotope ratios Sr/ Sr and Rb/ Sr are measured mass spectrometrically (mainly by TIMS or nowadays by ICP-MS) and the primordial strontium ratio ( Sr/ Sr)o at t = 0 and the age t of the rock can be derived from the isochrone (graph of measured Sr/ Sr isotope ratios (represented on the ordinate) as a function of the Rb/ Sr ratio (on the abscissa) in several minerals with different primordial Rb concentrations). The age of the minerals will be determined from the slope of the isochrone (e — 1), and the primordial isotope ratio ( Sr/ Sr)o from the point of intersection with the ordinate (see Figure 8.9). Rb-Sr age dating is today an... [Pg.403]

Damon PE, Green WD (1963) Investigations of the helium age dating method by stable isotope dilution technique, In Radioactive Dating. Vienna, IAEA, p 55-69 Dodson MH (1973) Closure temperatures in cooling geological and petrological systems. Contrib Mineral Petrol 40 259-274... [Pg.841]

The Juan Fernandez Islands, Chile, he east of the South American mainland at approximately 33°30 S, 80°W (Fig. 6.8). The archipelago consists of two main islands, Masatierra, which lies about 660 km from the mainland, and Masafuera, which lies 150km further west. A third, small island, Santa Clara, lies off the western end of Masatierra and probably was attached to Masatierra at one time. The ages of the islands have been determined using potassium-argon dating methods to be 5.8 2.1 million years for Santa Clara 4.23 0.16 million years for Masatierra and 2.44 0.14 million years for Masafuera (Stuessy et ah, 1984). [Pg.263]

Data on mineral s arates in present day volcanic rocks. Since every dating method (including the K-Ar or C systems) can be affected by several geochemical perturbations which may lead to erroneous ages, the best test for the °Th- U mineral isochrons consists in the analysis of presently erupted lavas or historic lavas of well known eruption dates. Rather surprisingly the data obtained on such samples are not so numerous (some examples are illustrated in Fig. 10). Early data showed that, in some cases, there were interlaboratory analytical discrepancies, especially in Th isotope ratios measured on mineral separates extracted from the same lava flows (this was the case for the 1971 lava from Mt. Etna and 1944 lava from Mt. Vesuvius Capaldi and Pece 1981 Hemond and Condomines 1985 Capaldi et al. 1985). This emphasizes the fact that °Th- U mineral analyses... [Pg.140]

Th- U dating of samples from subaerial volcanoes. When several volcanic rocks covering a significant period of the eruptive activity of a volcano can be dated (either by mineral isochrons or by other dating methods), the evolution through time of the ( °Th/ Th)o or ( °Th/ U)o initial ratios will be revealed (see section 3.4). If these ratios remain nearly constant, then they may be used to calculate the ages of other lavas... [Pg.164]

Figure 22. Comparison of the ages obtained by the and dating methods on MORE... Figure 22. Comparison of the ages obtained by the and dating methods on MORE...
Agreement is found for ages determined on the same material by independent dating methods... [Pg.419]

The discovery of the decay chain, of course, started with the seminal work of Marie Curie in identifying and separating Ra. Through the work of the Curies and others, all the members of the decay chain were identified. An important milestone for geochronometrists was the discovery of °Th (called Ionium) by Bertram Boltwood, the Yale scientist who also made the first age determinations on minerals using the U-Pb dating method (Boltwood in 1906 established the antiquity of rocks and even identified a mineral from Sri Lanka-then Ceylon as having an age of 2.1 billion years )... [Pg.661]

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See also in sourсe #XX -- [ Pg.399 , Pg.400 , Pg.401 , Pg.402 , Pg.403 , Pg.404 , Pg.405 , Pg.406 ]

See also in sourсe #XX -- [ Pg.399 , Pg.400 , Pg.401 , Pg.402 , Pg.403 , Pg.404 , Pg.405 , Pg.406 ]



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