geochronology; K decay constant; molybdenum; decay constant; rutile; K-Ar; U-Pb
Axelsson Emelie, Pape Jonas, Berndt Jasper, Corfu Fernando, Mezger Klaus, Raith Michael M. (2018), Rutile R632 - A New Natural Reference Material for U-Pb and Zr Determination, in Geostandards and Geoanalytical Research
, 42(3), 319-338.
Naumenko-Dèzes Maria O., Nägler Thomas F., Mezger Klaus, Villa Igor M. (2018), Constraining the 40K decay constant with 87Rb-87Sr – 40K-40Ca chronometer intercomparison, in Geochimica et Cosmochimica Acta
, 220, 235-247.
Naumenko M.O, Mezger K., Nägler T.F., Villa I.M. (2014), High precision determination of the terrestrial 40K abundance, in Geochimica et Cosmochimica Acta
, 122, 353-362.
This project will use natural isotope variations due radioactive decay and fractionation processes in the litho- and hydrosphere to help constrain the dynamics of geologic processes. The determination of the branching ratio of the decay of 40K to 40Ar and 40Ca will improve the quality of one of the most widely used geochronometers in the Earth Sciences. This branching ratio will be determined on natural rock samples containing K-rich minerals whose geologic history is extremely well known. The rock samples chosen contain minerals that are known to yield concordant U-Pb and Rb-Sr ages. The mineral rutile is widespread in medium to high grade rocks and is potentially a useful chronometer that provides high precision ages using the U-Pb system and metamorphic temperatures using the Zr-in-rutile thermometer. It is planned to study the behavior of the U-Pb system and the equilibration of the Zr-contents in natural rutiles from high grade rocks of the petrologically well studied Eastern Ghats belt, India. The results will provide key constraints on the geological meaning of U-Pb rutile ages and the robustness of the Zr-in-rutile thermometer. The distribution of ages in a rutile obtained by in situ spot analyses will be modeled to derive the thermal history of the minerals grains and their host rocks. The result of this project will be the development of a geochronometer for medium to high grade metamorphic rocks that can be used to reconstruct the dynamic evolution of the lithosphere. The fractionation of the stable isotopes of Mo provides key constraint on the redox-evolution of the oceans. Particularly questions related to the timing of the initial oxygen rise in Earth’s atmosphere, and extent of later ocean anoxia are targeted. However, existing models suffer from uncertainties due to a lack of constraints on Mo sources and sinks of the oceanic Mo cycle, and in particular their evolution with time. The dominant sink for isotopically light Mo are pelagic sediments, and they are largely recycled in subduction zones. As subduction zone volcanism significantly contributes to the growth of continental crust, continued recycling of Mo from pelagic sediments into the sources of subduction zone magmas should modify the Mo isotope budget of continental crust. In order to constrain the Mo cycle we will first estimate Mo isotope composition of Bulk Silicate Earth using highly metamorphosed chondrites that are considered the potential building blocks of the Earth. These isotopes then can be compared to juvenile crustal rocks to test for light (pelagic) Mo input. Second, we will study subduction zone related rock suites to evaluate the contribution to their isotope composition from a pelagic source.