The late growth history of the terrestrial planets, from the last giant collisions with planetary embryos to the subsequent late bombardment with smaller objects, is of critical importance for understanding the early chemical differentiation processes and the evolution of the terrestrial planets. The goal of this research program is to improve our current understanding of the late-accretion history of the Earth, its Moon, and other terrestrial planets from 4.5 to 3.8 billion years ago. A multidisciplinary approach will provide novel insights into the timing and rates, chemical budget, and geodynamic implications of late accretion and will constrain the physicochemical boundary conditions during this time interval. We will:
Important questions regarding the origin of the terrestrial planets and their building blocks are still open. Are primitive meteorites in our collections really the building blocks of Earth and other terrestrial planets? What processes are responsible for the depletion of volatile elements in the inner solar system? What do abundances of refractory elements in primitive meteorites tell us about their early history? What is the origin and budget of volatile elements in the terrestrial planets? What can the Moon tell us about the early history of the Earth? Were the terrestrial planets affected by a “late heavy bombardment” of planetesimals? Chemical and isotopic studies of meteorites and lunar samples from the Apollo missions provide new constraints. Projects ... »
Because we use highly siderophile element abundances in planetary materials to constrain planetary-scale processes in the early solar system, it is necessary to understand the processes that can change abundances of these elements in magmatic and in surface processes. Highly siderophile elements (HSE) are Re, Au and the platinum group elements Os, Ir, Ru, Rh, Pt, and Pd. These elements are characterized by very high metal-silicate partition coefficients, and thus during core formation they are preferentially extracted into the metallic core. 187Re decays to 187Os, and this decay system can be used for geochronological purposes. HSE and 187Os/188Os are used as tracers in planetary geochemistry for study of metal-silicate and solid metal-liquid metal partitioning, sulfide-silicate partitioning processes (mantle processes, ore forming processes), and crust-mantle recycling. The formation of continental crust and recycling of oceanic crust and sediments via subduction have had substantial influence on the present-day composition and chemical evolution of the Earth’s mantle. These processes can be monitored by study of the variation of radiogenic isotope ratios (87Sr/86Sr, 143Nd/144Nd, 187Os/188Os, Pb isotopes) in rocks derived from the Earth’s mantle (basalts, peridotites). We combine these tracers, with focus on the HSE, for study of the effects of partial melting and melt transport in the mantle and assimilation, fractional crystallization and mixing processes in the crust.
Radiometric dating of rocks is one of our key tools. Several projects have focused on method development for microgeochronology for sampling of rocks and minerals on the sub-mm scale, in particular from ductile shear zones and the determination of cooling and uplift rates. Other projects have used Nd model ages and U-Pb dating of zircon.
We use light stable isotopes of O, H, C, S in surface water and in shells to constrain the sources and transport paths of atmospheric precipitation in Asia and in Central Europe and to test hypotheses on changes of atmospheric transport patterns with time.
The element concentrations and isotopic composition of solutes in continental surface water and in suspended particles provide constraints on the fractionation processes and kinetics of chemical weathering. Isotopic fractionation of Li and Mg in these materials may be used as proxies of chemical weathering rate. We try to understand the fundamental processes that control these compositional variations.
The latest Neoproterozoic to Cambrian time marks the appearance of the animals and major changes in the oxygen content of the atmosphere-ocean system. In the context of the DFG research group FOR 736 (http://www.cms.fu-berlin.de/dfg-fg/fg736/), we have obtained geochronological constraints on black shale deposition using the Re-Os system. We also study the response of Neoproterozoic marine carbonates to diagenetic alteration and fluid flow in order to identify “primary” compositions in such rocks that yield information on the chemical and isotopic composition of seawater at that time.