The platinum group element systematics of the upper continental crust
|Samples from Xifeng, Chinese loess plateau, were part of the sample collection analyzed in our lab for platinum group element concentrations and Re-Os isotope systematics. Other loess deposits studied by us are located in Europe (incl. Svalbard), North America, and Argentina. (B-m Jahn)|
Prof. Bor-ming Jahn
This collaborative research project investigated the use of loess as a proxy for the chemical composition of the upper (eroding) continental crust. We have analyzed loess samples from Europe, China, Argentina, North America and Svalbard for their platinum group element (PGE) and rhenium-osmium isotope systematics. The results of our study (Peucker-Ehrenbrink & Jahn, 2001, G-cubed 2, doi: 10.1029/2001GC000172) indicate that geochemistry of loess can be used as a proxy for the chemical composition of upper continental crust.
Average PGE concentrations in the upper continental crust are
Os: 31 pg/g
Ir: 22 pg/g
Ru: 210 pg/g
Pt: 510 pg/g
Pd: 520 pg/g
Re: at least 200 pg/g, probably significantly higher.
The average 187Os/188Os of the eroding continental crust is 1.05 (+- 0.23, s.d., n=16), whereas the ratio for the upper continental crust, corrected assuming an average age of 2.3 billion years, is 1.40 (+-0.3, s.d., n=16).
The 186Os/188Os of the upper continental crust, infered from Pt/Os and an average crustal age of 2.2 billion years, is 0.119871.