RICERCA ITALIANA     

Effect of petrological variables on mica crystal chemistry.

Università degli Studi di Modena e Reggio Emilia

Abstract

The main objectives of this research project are:
a) To increase the crystal chemical and crystal physical knowledge on natural micas to understand and predict their behaviour and role in well defined petrogenetic environments;
b) To work out or improve criteria, based on micas, describing the petrogenetic or geological processes either generating or re-equilibrating the phases.

Natural processes involving micas can be better described if thermodynamic, crystal chemical and crystal physical aspects are considered together as also evidenced by the significant added value that such information as the crystal chemical determination of each phase, as order-disorder pattern and as polytypic zoning can provide over the definition of reactions involving micas. The following research lines will be endeavoured:
i)determination of the crystal chemistry of individual phases;
ii)determination of order-disorder reaction especially for iso-electronic atom species;
iii)study of zoning in polytypes;
iv)modelling of crystal-chemical, geometrical and thermodynamic relations;
v)experiments on micas under non-ambient consitions;
vi)analysis of the short-range order mechanisms;
vii)determination of the redox state of the transition atoms.

Different experimental techniques will thus be used, such as ionic and electron microprobe, X-ray and neutron diffraction (on powder and crystals), electron (e.g >>>

Principal Investigator

Maria Franca BRIGATTI Università degli Studi di MODENA e REGGIO EMILIA

Research Objectives

SYNTETIC LIST OF THE OBJECTIVES. i) To increase the crystal chemical and crystal physical knowledge on natural micas, understand and predict their behaviour and role in well defined petrogenetic environments; ii) To work out or improve criteria, based on micas, describing the petrogenetic or geological processes either generating or re-equilibrating the phases.

THE OBJECTIVES. During the last two decades, studies on micas drew the attention of several researchers and provided significant results towards a better structural definition, a deeper crystal chemical insight and an increased knowledge on the complex relationships between chemical, physical and topological properties of micas and their petrological environment. The Research Units (RU) joining this program led many of these studies.
Despite these significant progresses, much work on micas is still required both to validate the characterization of the phases, according also to the new IMA nomenclature (Rieder et al., 1998), and to better clarify the relationships between mica structure and crystal chemical composition, and their relationships with the petrological environments or processes.
The objectives of this project are thus both actual and completely matching the various competences of the RU here integrated. The high scientific profile of the RU, as well as their potential to implement cross-disciplinary researches and their ability to cooperate to reach common scientific goals >>>

First Results

The scientific objectives of the project are described in A form, and in greater detail in the B form by local RU. Also considering a coherent scientific approach and the overall project layout, results will be obtained step by step.

At the end of PHASE I: samples to be studied will be available; an early analytical characterization will be performed to identify samples promising for further analyses; the program for jointly executed researches will be detailed, agreed and implemented.At the end of PHASE II: the greatest part of experimental data will be available; a mid-term project meeting will be organized to discuss results and provide early interpretations; weak points deserving future attention will be identified; sampling, experimental, strategic and conceptual approaches will be discussed and optimised.At the end of PHASE III: all the experimental data will be available; data will be formatted and arranged into data-bases; statistical analyses will be performed; the interpretation of result will start.At the end of PHASE IV: the interpretation of results will be concluded; the documentation of results via scientific papers and communications at meetings will be on progress; a significant number of scientific papers will be rendered available to the scientific community before the end of the project time.

Timescale

24 months

National and international background

A recent review on micas is reported in the volume "Micas: Crystal Chemistry and Metamorphic Petrology" (Mottana et al., Eds. 2002). This volume, also reporting an interesting "History" of micas by Cipriani (2002), was one of the results of the previous project on micas, financed by MURST. This review underlines that, in these last 20 years (i.e. after the printing of the previous review volume edited by Bailey in 1984), a great progress has been carried out on micas, by using many different experimental techniques, such as: 1) Powder X-ray diffraction, both considering or not the entire spectrum and single crystal X-ray powder diffraction both at room and high temperature and pressure (Brigatti & Guggenheim 2002, Ferraris & Ivaldi 2002, Zanazzi & Pavese 2002); 2) Neutron diffraction (Zanazzi & Pavese 2002); 3) Different spectroscopies (Mössbauer: Dyar 2002; Infrared: Beran 2002; XAS: Mottana et al. 2002); 4) Transmission electron microscopy (Kogure 2002). Moreover investigations on polytypes (Nespolo & Durovic 2002), on compositional variation of dioctahedral micas from different metamorphic environments (Guidotti & Sassi 2002) and on illites in low metamorphic environments (Arkai 2002) attracted significant interest too.
Literature also numbers a lot of extremely interesting approaches on Experimental Mineralogy (Massonne & Schreyer 1986, Robert et al. 1993, Icenhover & London 1995; Fechtelkord et al. 2003) which, being affected by metastability problems, are >>>