Whole-rock samples from different parts of the same body generally differ in rubidium content and the 87 Sr: 86 Sr ratio of each can be plotted as a function of its 87 Rb: 86 Sr ratio in an isochron diagram. At the time of the initial crystallization different parts of the sample, regardless of rubidium concentration, would have had the same 87 Sr: 86 Sr ratio and hence plot as a horizontal line. With the passage of time 87 Rb would be lost and corresponding amounts of radiogenic 87 Sr gained. As the 87 Sr: 86 Sr ratio changes in each part of the rock, the slope of the isochron increases progressively, providing a measure of the age of the crystallization. The intercept of the isochron at the ordinate indicates the isotopic composition of common strontium at the beginning of the process.
RECONNAISSANCE Rb-Sr DATING OF THE PRECAMBRIAN ROCKS OF SOUTHERN PENINSULAR INDIA: Review
First direct radiometric dating of Archaean stromatolitic limestone | Nature
As such, precise depositional age constraints of sedimentary sequences are critical to our understanding of how these systems have evolved through time. A reaction gas is introduced between two quadropoles in the system, allowing for the online separation of 87 Sr and 87 Rb. Three case studies were investigated using this method. These time constraints are consistent with the crystallisation age of the igneous suite ca.
The alkali earth metal strontium has four stable, naturally occurring isotopes: 84 Sr 0. Only 87 Sr is radiogenic; it is produced by decay from the radioactive alkali metal 87 Rb, which has a half-life of 48,, years. Thus, there are two sources of 87 Sr in any material: that formed during primordial nucleo-synthesis along with 84 Sr, 86 Sr and 88 Sr, as well as that formed by radioactive decay of 87 Rb. Because Sr has an atomic radius similar to that of Ca, it readily substitutes for Ca in minerals. For example, consider the case of a simple igneous rock such as a granite that contains several major Sr-bearing minerals including plagioclase feldspar, K-feldspar, hornblende, biotite, and muscovite.
Meteorites are among the oldest objects we know about - formed about 4. But how do scientists know this? This article describes the principles and methods used to make that determination. There are well-known methods of finding the ages of some natural objects.