Radiogenic Ingrowth
Definition
The progressive increase in a daughter isotope such as 87Sr over geological time as the parent nuclide (87Rb) decays. Materials with higher initial Rb/Sr ratios accumulate more 87Sr over time, making old, Rb-rich rocks identifiable by elevated 87Sr/86Sr.
- Parent-daughter pair
- 87Rb decays to 87Sr
- Timescale
- Geological (slow decay)
- Effect
- Higher initial Rb/Sr means more 87Sr over time
Common questions
Why does radiogenic ingrowth make old, rubidium-rich rocks identifiable by their strontium signature?+
Because 87Rb decays into 87Sr at a fixed, known rate, a rock that started with more rubidium relative to strontium accumulates a measurably higher 87Sr/86Sr ratio the longer it has existed, so the ratio becomes an age and source indicator.
How is radiogenic ingrowth applied in geoforensic provenance work?+
Investigators measure the 87Sr/86Sr ratio in a questioned sample, such as soil or bone, and compare it to reference geology from candidate regions, since the ratio reflects the age and rubidium content of the local bedrock rather than surface conditions.
Related terms
- 87Sr/86Sr Ratio
- The ratio of radiogenic strontium-87 (produced by decay of rubidium-87) to the stable reference isotope strontium-86. Values range from roughly 0.703 in...
- Isoscape
- A map of isotope ratio variation across a geographic area, derived from systematic sampling of soil, water, plant, or mineral material; used...
- Lead Isotope Triple Plot
- A graphical display of 207Pb/204Pb against 206Pb/204Pb and 208Pb/204Pb against 206Pb/204Pb. Different ore deposits fall in distinct clusters on these plots, and...
- Mixing Model
- A mathematical framework for reconstructing the proportions of two or more isotopically distinct source materials in a mixture. Required whenever a forensic...
- Strontium Isoscape
- A map of 87Sr/86Sr values across a defined geographic area, built from measurements of soil, plants, or water. Used to compare the...