Part 5- Rb-Sr Decay System Flashcards
What does the fact that Sr and Rb are fluid-mobile mean for the decay system?
The closed system is easily violated by weathering and metamorphism.
How long is the half life of the 87Rb-87Sr decay system?
48 Gyr
What type of rocks are well dated using this system?
Acidic rocks and their metamorphic equivalents.
Which two techniques can be used to date igneous rocks with the Rb-Sr isochron method?
Mineral isochron.
Whole rock isochron (preferred- less easy to be altered by fluids).
If a metamorphic event were to affect a rock what would the whole rock and the mineral isochrons show?
The whole rock isochron would give the age of crystallisation.
The mineral isochron would date the metamorphic event.
What is the distribution of Sr and Rb in the BSE?
Sr is enriched.
Rb is depleted (it’s a volatile).
What category of Goldschmidt’s classification do both Sr and Rb fit into?
Lithophile
How does the Rb/Sr ratio of the BSE compare to CI carbonaceous chondrites?
Why?
An order of magnitude lower.
Due to depletion of Rb in the BSE.
Due to the lithophile nature of Rb and Sr, what impact will core formation have on their concentrations in the BSE vs. the BE?
Concentrations higher in BSE relative to BE.
Are Rb and Sr compatible or incompatible?
They’re incompatible.
Which reservoirs have particularly high concs of Rb and Sr? Why?
OIBs and the CC.
They’re formed by small degree partial melts in general therefore the elements partition well into these.
What are the Rb/Sr ratios of OIBs and the CC like?
Relatively high because Rb is more incompatible than Sr.
What type of decay does the Rb-Sr decay system undergo?
Beta/Negatron (B-)
