Mass transfer in unmetamorphosed carbonates and during low-grade metamorphism of arenites

S U M M A R Y: Study of stylolites in Silurian carbonates of southern Ontario, and of spaced cleavage in Lower Palaeozoic meta-arenites of Nova Scotia, shows that diffusional or infiltrational mass transfer has been the dominant mechanism for dimensional change. The carbonates show a quite specific pattern of stylolite growth in, and normal to, the mean plane of the stylolite, and there is always a low-porosity halo about each stylolite. Implied shortening usually exceeds the amplitude of any teeth in stylolites and may reach 5% of the 'local' sequence. In the meta-arenites, increased inequancy, decreased long-axis fluctuation of quartz grains, lithon to cleavage, coupled with virtually constant grain dimension parallel to cleavage, suggest gross loss of volume. Modal and chemical analyses suggest that an average cleavage zone represents a dilation of - 50%, expressed as shortening normal to cleavage. Bulk loss is about 10%, almost all SiO2. In both cases, mass removal begins at zero or low levels of overall deformation. For the carbonates, total deformation is near zero; the process shuts down by self-suffocation. In the meta-arenites the process was probably partly driven by the conditions associated with greenschist-level metamorphism. In both cases, collapse across the surfaces of dissolution is nicely adjusted to keep the gross shortening approximately homogeneous.