Rocks are the materials large volumes of the earth and other planetary bodies are made of. Understanding the properties and behavior of rocks over a wide range of conditions varying from the extreme pressures and temperatures of the Earth’s deep interior to the conditions of solar nebula condensation out in space is fundamental for the comprehension of planet formation, the geodynamic processes that shape the Earth and the functionality of geological materials in technical applications. Petrology is the scientific study of rocks. It aims at “reading the petrogenetic memory” engraved in the mineral contents, major and trace element compositions, microstructures and textures of rocks. Petrological research builds on sampling of rocks in the field, their characterization using instrumental analysis such as optical and electron microscopy, X-ray and electron diffraction, x-ray fluorescence and various techniques of mass spectrometry. This is complemented by synthesis of rock analogues and experimentation in the lab, and by theoretical analysis including thermodynamic and kinetic modeling. Petrological tools help to quantitatively reconstruct the rock’s petrogenetic history and to predict bulk material properties and behavior under the physical and chemical conditions of the Earth’s interior. Through petrological research key constraints are established for tectonic, geodynamic and geophysical models. In addition, petrology may be regarded as a „geo-materials science” dealing with technical applications of complex (geological) materials, which may be functional in many respects.
The petrology division of the Department of Lithosphere Research has major activities in
- Theoretical and experimental petrology
- Igneous petrology/geochemistry
- Metamorphic petrology
Theoretical and experimental petrology
In our geo-materials research we focus on small scale structures and micro-chemical patterns. Crystal defects, grain- and phase boundaries, and micro-chemical zoning provide insight into the processes, which occur on the atomic or molecular level and control the kinetics of mineral reactions and bulk behavior of geological materials. These processes govern the development of microstructures and textures and this way coin the geodynamic record of rocks. In addition, they determine how and at what rate bulk rock properties change in response to external forcing and possibly feed back into geodynamic processes. Both, reading the petrogenetic information stored in rocks as well as understanding the feedback between bulk material properties and geodynamics is the target area of theoretical and experimental petrology. Experiments are done to simulate in the laboratory mineral reactions at relevant pressures and temperatures. Experimental run products are characterized using state of the art instrumental analysis with a focus on techniques with high spatial resolution such as electron- and ion-beam techniques. Micro-chemical patterns, microstructures and textures are interpreted based on quantitative thermodynamic and kinetic models and numerical simulations. Much of this research is embedded in a program of coordinated research: DFG Forschergruppe FOR 741: “Nanoscale processes and geomaterials properties”.
Igneous petrology is concerned with the identification, classification, origin and evolution, of igneous rocks. By far the largest part of the Earth is inaccessible. Even the deepest research borehole into the continental crust reaches a depth of not more than 12.3 km. Besides using geophysical methods, the only way to understand the composition and evolution of the Earth and the physico-chemical processes that occur in its interior, is by studying the rocks that originated in the Earth’s deep interior. Such rocks can reach the Earth’s surface as a consequence of tectonic- and/or of magmatic processes such as volcanism. The processes that are involved in magma formation and in the crystallization of igneous rocks are investigated to constrain the composition and evolution of the continental crust and the upper mantle of the Earth.Major research interests of our group are in the study of primitive magma generation at depth, the origin of continental flood basalts (CFB), ocean island basalts (OIB), mantle xenoliths, orogenic peridotite, and ophiolites that are fragments of an ancient oceanic crust. Therefrom details of the evolution of the oceanic crust are derived. Further studies concern igneous intrusions into the continental crust, including gabbros, diorites, and a broad variety of granitoid rocks that represent the source material for continental crustal growth.
Metamorphic petrology focuses on the composition, microstructure, and texture of metamorphic rocks such as slate, marble, gneiss, or schist. Such rocks started out as sedimentary or igneous rocks but have undergone chemical, mineralogical or microstructural changes at elevated pressure and temperature.
An example of a research topic is the investigation of the polymetamorphic evolution of crystalline basement units in the Alpine orogen. One focus area is the evolution of the Penninic ophiolites during the Tertiary low T-high P metamorphism within the framework of the Alpine orogenesis and the history of the ancient Piemont and Valais oceanic domains. Another topic in our Alpine studies focuses on the tectonometamorphic evolution of Austroalpine basement units affected by Carboniferous, Permian-Triassic and Cretaceous metamorphism at different metamorphic grades. We investigate the mechanisms of chemical re-equilibration during metamorphic overprinting with special focus to host mineral - inclusion relationships and to the interaction of chemical reactions and deformation. We also involved in petrological studies on samples from granulites from all over the world, where the focus is on understanding the preservation and modification of high-grade phase relations.
Unravelling the petrogenetic history of metamorphic rocks helps to establish and test geodynamic models for orogen evolution. The polymetamorphic nature of the investigated rocks demands for a thorough understanding of the interplay between major and trace element equilibration and deformation. In this context strong links are maintained to structural geology and geochronology.