Mara Murri, MSc

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Mara Murri

Mara Murri

My research is mainly focused on geothermobarometry applied to minerals phases relevant for the Earth and planetary sciences using elastic behavior of mineral inclusions and their mineral hosts.

I am currently developing the tools for the analysis and quantification of deviatoric stresses on elastically anisotropic inclusions still entrapped in their host using micro-raman spectroscopy. Validation of the developed toold will be acheived by measuring the stress state on synthetic host inclusion pairs by single-crystal X-ray diffraction and by determining raman shifts on anisotropic minerals under deviatoric stress fields using ab-initio methods (e.g. Density Functional Theory, DFT).

The main results of this project will enable us to determine deviatoric stress components on inclusions entrapped in minerals contained in Ultra High Pressure Metamorphic (UHPM) rocks by means of micro-raman spectroscopy.

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CV

Elasticity

My bachelor degree project was focused on the determination a reliable set of thermoelastic parameters for diamond to be used in elastic geobarometry calculations. Mineral inclusions in diamond represent an extremely powerful source of information about the Earth’s mantle and they provide clues about formation depths of their carries (e.g. diamonds). Elastic behavior (i.e. Equations of State, EoS) of diamond and its inclusion can be used to infer pressure of formation of the pair, thus corresponding to their pressure of formation (depths of formation) in case of syngenetic origin under lithostatic stresses.

However in order to reliably apply elastic geobarometry, Equations of State for both host (e.g. diamond in this case) and inclusion (in principle any mineral phase) are required.

In the case of syngenesis the formation conditions of diamond can be determined from the residual pressure of inclusions trapped within the diamond, as measured at ambient conditions, and the equations of state (EoS) of the mineral inclusion and the host diamond.

Geothermometry

My master degree project was mainly focused on geothermometry applied to minerals phases relevant for the Earth and planetary sciences using elasticity and cation exchange.
Meteorites from planetary bodies and minerals from their host-rocks provide fundamental information on planet-scale geological processes (such as convection, plate tectonics and subduction). Moreover, my latest results are focused on the development of the methods used to determine the equilibrium temperature in minerals. Among these the intracrystalline Fe-Mg exchange between M1 and M2 does record the thermal history of rock. This exchange between the crystallographic sites has been successfully applied to constraint orthopyroxenes thermal history. More difficult is to apply this method to clinopyroxenes because of the presence of Ca and Na in M2 site causing the split of this position to M2 and M21. The same method has recently been applied, to cpxs from extraterrestrial sample for example to martian samples.

However, in literature a strong correlation between the total iron content and the slope of the Fe2+-Mg equilibrium distribution coefficient (kD) as a function of temperature has been observed for orthopyroxenes and pigeonites. Therefore, the main aim of my work was to determine a new geothermometric calibration for augite from a 120-m-thick lava flow from Ontario, Canada and establish a possible role of Fe content, in the range of compositions between Fs9 and Fs24, on the equilibrium behavior in augites from the same geological setting. This allwed me to evaluate the compositional effects (mainly Fe content) by comparison with the data previously obtained on augite from MIL 03346 Martian sample

This project was mainly carried out by means of single-crystal X-ray diffraction using both area and point detectors whereas the annealing and quenching procedure is carried out using large ovens.

Geobarometry

Currently I am studying host-inclusion pairs in order to determine their formation conditions by using single-crystal X-ray diffraction (SC-XRD) and micro-raman spectroscopy. X-ray diffraction experiments allow the measure of thermoelastic properties of minerals and the determination of their equations of state (i.e Volume against P-T parameters) that are the starting point to calculate the entrapment pressure of the host-inclusion system. The elastic properties of minerals are fundamental data to understand how the system behaves from such depth to Earth surface during exhumation processes.

Raman spectroscopy

Performing in-situ experiments in Diamond Anvil Cell (DAC) by using high-resolution single-crystal X-ray diffraction (HR-SC-XRD) and Raman spectroscopy in order to obtain a calibration of the Raman shifts under non-hydrostatic stresses on anisotropic minerals (i.e Quartz and Coesite that are very abundant inclusion minerals and they are also very sensitive to deviatoric stresses),it would be worthwhile because the only available data in literature are about Raman spectra of isotropic minerals under hydrostatic stress.

DFT (Density Functional Theory)

Density functional Theory allows us to calculate ab-initio raman spectra for minerals under deviatoric stresses in order to compare them with those obtained from diamond anvil cell (DAC) experiments.

RECENT PUBLICATIONS

1.  M. Murri, L. Scandolo, A. Fioretti, M.C. Domeneghetti and M. Alvaro (2016). Fe-Mg equilibrium behaviour in augite: implications for the thermal history of terrestrial and extraterrestrial rocks. American mineralogist (submitted).