Spaced Cleavage Development in the Metagreywackes of the Goldenville Formation, Meguma Group, Nova Scotia

The greywackes of the Goldenville Formation, Meguma Group, Nova Scotia display a well developed spaced cleavage. The cleavage is characterized by zones of mica enrichment and associated quartz depletion and forms a network of anastomosing cleavage rhombs. Parallelism between cleavage and water escape structures suggests that the cleavage was emplaced perpendicular to bedding early in the deformational history of the rocks. Subsequent passive rotation of cleavage and water escape structures reduced the bedding-cleavage angle to its present values. XRF whole rock analyses of cleavage planes and lithons from two different sample locations show that the cleavage is depleted in SiO2, CaO, Na2O and enriched in Al2O3, Fe2O3, MgO, K2O, TiO2, MnO and P2O5 relative to lithons. Mass balance calculations based on the Gresens (1967) approach indicate that the cleavage with respect to the lithon represents a 40%-60% volume loss. Using the volume loss it can be shown that the cleavage lost SiO2, Na2O, CaO, MnO, P2O5, Pb, Sr, Nb, and Y and gained MgO, K2O, Ba, Rb, and W during its formation. TiO2, Al2O3, Fe2O3 and Zr remain relatively immobile during the cleavage forming processes. The behavior of Au, Sb, As, Ce, Nd, and La can not be discerned. The cleavage was initiated by pressure solution at grain contacts. However, several of the above mentioned chemical migrations increased the solubility of quartz and therefore greatly enhanced the development of the cleavage.ThesisMaster of Science (MSc

Stepped fans and facies-equivalent phyllosilicates in Coprates Catena, Mars

Stepped fan deposits and phyllosilicate mineralogies are relatively common features on Mars but have not previously been found in association with each other. Both of these features are widely accepted to be the result of aqueous processes, but the assumed role and nature of any water varies. In this study we have investigated two stepped fan deposits in Coprates Catena, Mars, which have a genetic link to light-toned material that is rich in Fe–Mg phyllosilicate phases. Although of different sizes and in separate, but adjacent, trough-like depressions, we identify similar features at these stepped fans and phyllosilicates that are indicative of similar formation conditions and processes. Our observations of the overall geomorphology, mineralogy and chronology of these features are consistent with a two stage formation process, whereby deposition in the troughs first occurs into shallow standing water or playas, forming fluvial or alluvial fans that terminate in delta deposits and interfinger with interpreted lacustrine facies, with a later period of deposition under sub-aerial conditions, forming alluvial fan deposits. We suggest that the distinctive stepped appearance of these fans is the result of aeolian erosion, and is not a primary depositional feature. This combined formation framework for stepped fans and phyllosilicates can also explain other similar features on Mars, and adds to the growing evidence of fluvial activity in the equatorial region of Mars during the Hesperian and Amazonian