Mineral chemistry and Mossbauer spectroscopy of micas from granitic rocks of the Canadian Appalachians.
Creators: name: Tabbakh Shabani, Amir Ali.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1999
Subjects: subject: Geology.

description: This thesis represents the results of a mineral chemical and crystal chemical investigation of trioctahedral and dioctahedral micas from the Paleozoic granitic rocks of the Dunnage, Gander, Avalon and Meguma tectonic zones of the Canadian Appalachians. The objectives of the thesis were: (1) to investigate the relationships between the composition of biotite and the tectonic origin of the host granitic rock. (2) to investigate the significance of quadrupole splitting distributions in the Mossbauer spectra of these Appalachian and other biotite specimens and (3) to investigate the cis and trans-octahedral Fe2+ Mossbauer spectral contributions of dioctahedral (muscovite) micas from the granitic rocks of the Gander zone in New Brunswick. These results of the study am presented as three manuscripts intended for submission to peer-reviewed journals. In the first manuscript, the author document the mineral chemistry of biotite occurring in granitic rocks of the Canadian Appalachians. The most significant variations are changes in total Al contents and Fe/(Fe+Mg) values. Using common oxygen geobarometers, the biotite from the granitic rocks of most zones plot on or above the NNO buffer, indicating moderate oxidizing conditions, whereas biotite from the Meguma zone plots between the QFM and NNO buffers implying fairly reducing conditions during crystallization. The composition of biotite in Appalachian granitic rocks reflects primarily the nature of the host magmas and cannot be readily used for interpreting the tectonic setting of these rocks. In the second manuscript, the methodology of quadrupole splitting distribution (QSD) analysis was used to describe the room temperature 57Fe Mossbauer spectra of 71 specimens of trioctahedral micas from the Paleozoic granitic rocks of the Canadian Appalachians, the granitic rocks of the Hepburn and Bishop intrusive suites of the Early Proterozoic Wopmay orogen, Northwest Territories, and the nepheline syenite of the Cretaceous Mont Saint-Hilaire alkaline intrusion, Quebec. To the author, the details of the crystallochemical controls of the observed QSDs in biotite are not well understood because of a lack of electronic structure calculations that link local distortion environments to quadrupole splitting values. Furthermore, several key crystal chemical parameters of the synthetic phlogopite-biotite-annite solid solution (e.g., Fe/(Fe+Mg), Fe3+/Fe total) do not correlate with any of the QSD features of natural biotites. The most strongly-correlated chemical parameter is found to be Altotal . Finally, in the third manuscript, QSD analysis of specimens of muscovite from granites of the Gander zone in New Brunswick shows that the Mossbauer spectra of these dioctahedral micas fall into two distinct groups. In the first group, two well-resolved octahedral Fe2+ spectral contributions occur whereas, in the second group, a single but broader octahedral Fe 2+ contribution occurs. Furthermore, spectra from the first group clearly show bimodal QSDs for Fe2+. In the second group, the spectra show broad unimodal QSDs for Fe2+. (Abstract shortened by UMI.)