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

Abstract

<p> 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.</p> <p> 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.</p> <p> 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.</p>