Project Details
Projekt
New constraints on the bulk composition and compositional evolution of the Earth from La-Ce isotope measurements
Applicant
Professor Andreas Stracke, Ph.D.
Subject Area
Mineralogy, Petrology and Geochemistry
Term
from 2014 to 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 255952258
This study aims to provide novel constraints on Earths bulk refractory element composition and the geochemical cycles that govern silicate Earth differentiation by exploiting the La-Ce isotope system. High-precision 138La-138Ce isotope data may provide novel constraints on several fundamental questions to which the conventional isotope systems have not yet provided definite answers. The inherent ambiguity in the observed difference between the 142Nd isotope composition of bulk Earth and chondritic meteorites, for example, could be resolved by comparing high-precision 138La-138Ce and 147Sm-143Nd isotope data in a variety of chondritic meteorites and mantle-derived rocks. About four times more precise Ce isotope measurements have become possible on a new generation of thermal ionization mass spectrometers (TIMS). Such high-precision Ce isotope data will allow investigating Earths bulk composition and its subsequent chemical differentiation from a novel perspective. The latter is the main objective of the proposed study. In addition, the combined La-Ce and Sm-Nd isotope systems can potentially distinguish between different hypotheses proposed for geochemical cycling between the continental crust and mantle, such as recycling different types of marine sediment versus erosion and subduction of lower continental crust. Further constraints will also be possible on the extent of depletion of the Earths mantle, which is a crucial parameter for estimating global mass balances and has important ramifications on the putative existence of an isolated reservoir in the deep Earth. Hence, it is proposed to determine the Ce-Nd isotope composition of a representative number and variety of pristine meteorites and mantle-derived rocks, i.e., basalts from mid ocean ridges (MORB), peridotites from the subcontinental lithospheric mantle, and ocean islands (OIB). The MORB and OIB data set will be complemented by existing high-precision Sr-Pb-Hf isotope and trace element data. The comparison of Ce-Nd isotope data in meteorites and MORB-OIB will provide novel constraints on Earths bulk refractory element composition. The MORB, peridotite and OIB data will reveal the extent of mantle depletion, and the processes leading to compositional heterogeneity in the Earths mantle. The proposed study could thus fundamentally improve our understanding of key parameters and processes that shape the system earth.
DFG Programme
Research Grants
International Connection
France, USA
