Research in the petrology group

The petrology group at Göttingen has a wide range of research interests covering not only a large range of P-T-X conditions but also a variety of topics ranging from fluid-rock interaction in geothermal exploration, nuclear waste deposits and diagenesis over classical metamorphic processes at amphibolite to granulite-facies conditions in the Earth’ crust to forensics of materials such as glass in the context of archaeometry. In a very generalized way, we can classify our research in the following key areas:

1. Melt/Fluid-rock interaction / Reactive Transport
2. Early Earth processes – Archean metamorphism
3. Granulite facies metamorphism – Crustal melting and mineral textures
4. Timescales of metamorphic processes – Diffusion in minerals and melts
5. Phase equilibria and geochronology of accessory phases
6. Glass in the past – Archeometry

Our research approach is based on a set of analytical and numerical tools that complement each other and offer various links for interdisciplinary collaborations with colleagues and research groups from GZG and other national/international Universities and industry partners.

Melt/Fluid-rock interaction / Reactive Transport
In the geosphere, fluid-mediated mineral reactions are of pivotal importance in governing the redistribution of elements and isotopes. Incomplete elemental redistribution is preserved in the rock record in the form of geochemical reaction fronts, the boundaries between reacted and unreacted material. Such fronts control geochemical exchange between the hydrosphere and the geosphere, the formation of mineral deposits, and migration of aqueous fluids and melt in the lithosphere. Associated mineralogical changes can dramatically change the physicochemical properties of Earth materials affecting their flow properties (rheology), strength, porosity and permeability. Key features of such systems are a) reaction induced creation of porosity increasing permeability and further focusing of fluid into the zone of reaction; hence this results in a positive feedback between reaction, fluid ingress and further reaction, and b) recrystallization of mineral phases releasing potentially economic elements into the fluid.

Early Earth processes – Archean metamorphism
Our understanding of processes that modify the outermost shell of today’s Earth are rooted within plate tectonic theory, in which movement of this layer, i.e. the lithosphere, is dominantly horizontal. However, the transition from an initial global magma ocean to largely rigid plates necessary for plate tectonics is poorly constrained. Without clear evidence for how and when plate tectonics initiated on Earth, interactions between the solid Earth and the early atmosphere and hydrosphere remain equivocal and largely qualitative. There are two contrasting end-member models for Earth’s earliest tectonic regimes: dominantly horizontal proto-plate tectonics where one plate subducts under another vs. vertical tectonics where the crust is recycled through gravitational “dripping”. Multiple lines of evidence support proto-plate tectonics after ~3.2-3.0 Ga, whereas most studies of the Paleoarchean Barberton and Pilbara greenstone belts (3.5-3.2 Ga) advocate vertical tectonics. In contrast, studies of the Eoarchean Isua supracrustal belt (ISB) of West Greenland (~3.8-3.6 Ga) argue that plate tectonics sensu stricto had already commenced. Our research of the ISB revealed that the latter interpretation is not unequivocal and further in-depth studies are needed to pinpoint the emergence of plate tectonics as we know it today. Consequently, the timing when modern-day tectonics commenced is still to be determined.

Granulite facies metamorphism – Crustal melting and mineral textures
Granulite facies rocks provide important information about the thermal and chemical evolution of the middle–lower continental crust. They are variable in their P–T conditions and chemical composition and can be found in a variety of orogenic belts that have formed at different times in Earth’s history. The typical granulite mineral assemblage consists mainly of dry phases such as garnet or pyroxene, hydrous phases such as mica or amphibole are less common or completely absent. This means that granulite facies rocks have a relatively low H2O content and although some granulites may have formed through metamorphism of dry precursor rocks, the typical protoliths were originally water-saturated (e.g. pelites). The absence of an aqueous fluid/melt phase may also result in the preservation of local disequilibria observable through mineral reaction textures including coronae and symplectites. The complex processes of crustal melting and how this low H2O contents can be achieved during metamorphism are still controversially discussed. To better understand what happens during crustal melting, information from partially melted rocks with preserved natural melts are of great importance. They provide not only an evidence that a rock has melted but can also be used to quantitatively constrain the melt composition regarding major- and trace-elements as well as volatiles. The reconstruction of the pressure–temperature–composition–time (P–T–X–t) history of granulites using several state-of-the-art analytical and petrological techniques can give explicit implications for the geodynamic and tectonic evolution during orogenies and the processes of mineral growth and crustal melting during high-grade metamorphism.

Student education – building the skills for future experts in analytical methods and science
In our research group, we sincerely enjoy working with students in the framework of a BSc, MSc and PhD projects. Our students are an integral part and fully recognized as members of the research team. In our group, student education focuses on problem solving skills with an emphasis on hands-on experience on all our instruments which are routinely used; not only in academia but also widely in industry for material analytics and quality assurance.
We offer a wide range of topics, ideally related to one or more of our research themes – please see a list of possible topics below. This list, however, give only example project and we are happy to develop individual projects tailored to the students interests wherever possible – just come and talk to us!

BSc or MSc projects:
The gypsum enigma: why is it so difficult to hydrate anhydrite?
The dehydration reaction of gypsum to form anhydrite is well studied and often serves as model reaction for the textural evolution of reaction fronts. The opposite reaction, i.e., the hydration of anhydrite to form gypsum is in contrast almost impossible to achieve in the lab, although of great industrial interest. In this project, the student will design, perform and analyse experiments studying the parameters controlling this reaction.

Alteration of reservoir rocks: pitfalls and potential for nuclear waste deposits.
Granitic rocks are currently considered as promising candidates for nuclear waste deposits. Several studies have investigated the fluid pathways and uptake of radionuclides in fresh granitic samples to study the rates and mechanisms of granite alteration in the presence of fluid phases. Much less is known on the alteration of naturally altered granitic rocks as well as the rates and mechanisms of granite alteration as a function of varying fluid compositions.

Making early continental crust – How? How much? How long?
The formation of TTG’s in the Archean, i.e., the early Earth period, is often interpreted as the key to understand the formation of continental crust on our planet. So far, most studies have focused on the geochemical perspectives, i.e., major and trace element signatures obtained from bulk rock powders. In this project, we want to link geochemical signatures to textural processes to answer some fundamental questions on the mechanism and rates of TTG emplacement in the Archean crust.

Provenance of Ancient querns and millstones.
With the emergence of agriculture in human history, millstones were systematically used to grind cereal grains into flour. High requirements are placed on the technical properties of these stones, especially with the advent of the first hand-rotary mills, which is why only specific types of stone are suitable at all. Provenance research (origin) provides valuable information on the trade of these products in ancient cultures or even migratory movements, for example, military operations.

Analysis of historical glass: provenance, recipe and properties.
Glass is a fascinating material and has been in use throughout human history for several millennia. Glass recipes have changed over time, and the composition of the raw materials has also varied depending on their origin. With the analysis of historical glass, the age can be estimated at least roughly, as well as trade routes can be reconstructed. Today, it remains difficult to interpret the exact manufacturing processes, because recipes were rarely written down.

On the origin of the blue colour in historical metallurgical slags.
Some smelting slags solidifying as glass impress by their bright blue colors (e.g. google: "mariensteine Ahr" or "Sieberachat"). These are not produced by proportions of chromophoric elements (e.g. Fe, Cu, Co), but are the result of light scattering by segregation structures (Rayleigh-Debye or Mie scattering). Previous bachelor theses could clarify the chemism of the melting systems and characterize the particle sizes of the scattering centers.
In the following work, simple melting experiments under controlled conditions will determine the parameters (temperature, cooling rate) at which the segregation bodies are formed.

Calcareous sinter as geochemical archives.
Numerous papers deal with the chemical variation of calcareous sinter as geochemical archives for the reconstruction of extensive environmental parameters. An exciting example are calcareous deposits in Roman aqueducts, as they may store environmental parameters with very high temporal resolution. This work aims to evaluate the methodological limit of modern microchemical analysis of high spatial resolution on a Roman calcareous sinter.