On processes taking place inside the Earth
The application of our researcher, Jacek Szczepański, PhD, from the Faculty of Earth and Environmental Management, was among those recommended for funding by the National Science Centre. The research project, worth more than PLN 1 800 000, will be carried out in cooperation with researchers from Germany and Poland.
The topic of the project is „Wpływ lepkiej relaksacji na elastotermobarometrię ramanowską: badania terenowe, mechaniczne i dyfuzyjne inkluzji mineralnych okludowanych w szerokim spektrum warunków metamorfizmu (VECTOR)” (The effect of viscous relaxation on Raman elastothermobarometry: field, mechanical and diffusion studies of mineral inclusions occluded under a wide range of metamorphism (VECTOR) conditions).
What does the project involve?
Many geological processes in the Earth’s interior occur very slowly and under conditions of high pressure and temperature. Experimental work on naturally metamorphosed rocks (i.e. rocks that have retained a record of transformations occurring at high pressures and temperatures) that has been carried out for almost 100 years contributes significantly to the understanding of the parameters controlling the physical, chemical and mechanical properties of rocks and minerals. Despite this, understanding the course of geological processes that take place in the Earth’s depths over millions of years remains a challenge for geologists. This is because of the slow rates of metamorphism processes described and the high pressures and temperatures at which they occur. This makes reproducing the phenomena associated with metamorphism in the laboratory difficult. However, instead of simulating such conditions in the laboratory, it is possible to describe the processes occurring in the Earth’s interior by studying the rocks and minerals formed during metamorphism in a natural way.
In spite of the difficulties that arise when studying the processes occurring in the Earth’s interior, the application of thermodynamic principles makes it possible to describe and interpret the record of pressure and temperature changes preserved in metamorphic rocks. In recent years, a method of estimating the conditions of metamorphism experienced by rocks during their history on the basis of measurements made with the Raman spectroscope has also begun to be developed. The method described (called elastothermobarometry Raman spectroscopy in the literature) makes use of the so called residual pressure that can be preserved in mineral inclusions.
The inclusions described are fine mineral inclusions trapped in the host mineral. Knowing the residual pressure allows us to estimate the conditions under which mechanical confinement of the inclusion in the host mineral occurred, i.e. the conditions under which metamorphism took place. However, recent studies have shown that minerals that normally behave in an elastic (resilient) manner can be affected by mechanisms that cause them to plasticise induced by a viscous creep process. This process leads to a significant deterioration of the elastic properties of the minerals and renders them unable to maintain the residual pressure originating from the period of mechanical confinement of the inclusion in the surrounding host mineral. Consequently, this phenomenon makes it seriously difficult to reconstruct the pressure and temperature conditions of metamorphism using Raman elastotemobarometry.
The aim of our project is to develop a method to quantify the effect of viscous creep on the ability of the viscous creep process to preserve residual pressures in minerals and reproduce the pressure and temperature conditions under which the inclusions formed, explains our researcher.
The effect of viscous creep on the ability of mineral inclusions trapped in a host mineral to maintain residual pressures has been recognised relatively recently. Consequently, there are no systematic studies describing this phenomenon in the available literature.
During the course of the project, we will want to create a coherent database comprising field observations, analytical measurements and numerical modelling, says prof. Szczepański. – Integration of the aforementioned data will enable quantitative description of the effects caused by viscous creep to determine the pressure and temperature of metamorphism using Raman elastothermobarometry.
The project will be carried out in collaboration with prof. Marcin Dąbrowski representing the Polish Geological Institute – National Research Institute and prof. Evangelos Moulas from the University of Mainz.
In addition to joint research (field and laboratory), the cooperation will also include the improvement of competences in the description and study of metamorphic rocks and the exchange of personnel between the three participating scientific centres.
According to our scientist, the results of the research will be usable in other material research not only directly related to geology.
In their research, the scientists will use both standard techniques such as scanning electron microscopy and electron microprobe, which will provide them with information on the chemical composition of the minerals in the micro-area, but also Raman spectroscopy, with which they will study the residual stresses retained mainly in the quartz inclusions found in garnet.
We will also use a number of less standard techniques, such as high-resolution backscattered electron diffraction and transmission electron microscopy, adds prof. Jacek Szczepański. These techniques will allow us to take a closer look at the surroundings of quartz inclusions in the host mineral in search of, for example, possible crystal lattice defects.
The research data thus obtained will be used to construct a numerical model describing the behaviour of inclusions in the host mineral during inclusion formation and during subsequent metamorphism.
Compiled by Katarzyna Górowicz-Maćkiewicz
Translated by Bartłomiej Dłubak (student of English Studies at the University of Wrocław) as part of the translation practice.
