Fractionation dating technique Nairobi quick sex hookup sites
At the time of crystallization, this produces a wide range in the Rb/Sr ratio in rocks that have identical − 1).
In practice, rock samples weighing several kilograms each are collected from a suite of rocks that are believed to have been part of a single homogeneous liquid prior to solidification.
For an isochron to be valid, each sample tested must (1) have had the same initial ratio, (2) have been a closed system over geologic time, and (3) have the same age.
Well-preserved, unweathered rocks that crystallized rapidly and have not been subjected to major reheating events are most likely to give valid isochrons.
The samples are crushed and homogenized to produce a fine representative rock powder from which a fraction of a gram is withdrawn and dissolved in the presence of appropriate isotopic traces, or spikes.
Strontium and rubidium are extracted and loaded into the mass spectrometer, and the values appropriate to the , the data are examined to assess how well they fit the required straight line.
As discussed above, rubidium–strontium mineral ages need not be identical in a rock with a complex thermal history, so that results may be meaningful in terms of dating the last heating event but not in terms of the actual age of a rock.
Should a simple igneous body be subjected to an episode of heating or of deformation or of a combination of both, a well-documented special data pattern develops.
When minerals with a low-rubidium or a high-strontium content are analyzed, the isochron-diagram approach can be used to provide an evaluation of the data.In contrast, Earth’s most abundant lava rocks, which represent the mantle and make up the major oceanic ridges, have values between 0.703 and 0.705.This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70,000, it is quite significant.On the other hand, meteorites that have spent most of their time in the deep freeze of outer space can provide ideal samples.Potassium-bearing minerals including several varieties of mica, are ideal for rubidium–strontium dating as they have abundant parent rubidium and a low abundance of initial strontium.
With heat, daughter isotopes diffuse out of their host minerals but are incorporated into other minerals in the rock.