whole-rock dating
whole-rock dating Igneous and metamorphic rocks that contain no minerals but have particularly high Rb:Sr ratios (see RUBIDIUM-STRONTIUM DATING), or rocks that are too fine-grained for mineral separation, can be analysed as whole-rock samples. Whole-rock samples from different parts of the same body generally differ in rubidium content and the 87Sr:86Sr ratio of each can be plotted as a function of its 87Rb: 86Sr 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 87Sr:86Sr ratio and hence plot as a horizontal line. With the passage of time 87Rb would be lost and corresponding amounts of radiogenic 87Sr gained. As the 87Sr:86Sr 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.
More From encyclopedia.com
Iron Ores , Rocks
Rocks are composed of minerals, which are natural inorganic (nonliving) substances with specific chemical compositions and structures. A rock m… Igneous Rocks , Igneous rocks are formed by the cooling and hardening of molten magma. The word igneous comes from the Latin word igneus, meaning fire, and there are… Rock , rock1 / räk/ • n. 1. the solid mineral material forming part of the surface of the earth and other similar planets, exposed on the surface or underly… Metamorphic Rocks , Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means “of changing form.” Metamorphic… Country Rock , Country rock
The term country rock refers to a body of rock that receives or hosts an intrusion of a viscous geologic material. Intrusions into count… Trachyte , trachyte Fine-grained volcanic rock of the alkaline series of intermediate rocks. Trachyte is the volcanic equivalent of syenite.
trachyte gritty vol…
You Might Also Like
NEARBY TERMS
whole-rock dating