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The relative permeabilities of quartzites and schists during active metamorphism at mid‐crustal levels
Author(s) -
Chamberlain C. Page,
Conrad Mark E.
Publication year - 1991
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/91gl00911
Subject(s) - schist , metamorphism , geology , quartz , metamorphic rock , geochemistry , mineralogy , paleontology
The ‘hot spot’ near Bristol, New Hampshire was an area of high fluid flow during metamorphism. In order to determine the mechanisms of fluid flow through the area, we made a detailed study of the δ 18 O values of quartz from an outcrop of interlayered quartzites and schists. Results indicate that the permeability of the quartzite was very low in comparison to that of the schist. The δ 18 qtz values from schist layers are remarkably homogenous (15.5–15.8), in contrast to the δ 18 qtz values of schist units outside of the hot spot, which vary widely. Quartz veins that cut the quartzites and pinch out in the schists have the same δ 18 O values (15.7) as quartz from the schists. In the quartzites, δ 18 qtz values immediately adjacent to the veins and schists are similar to those in the veins and schists, but decrease by ∼1 permil in the centers of the layer. We interpret these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites. The oxygen isotope exchange fronts in the quartzites prove that there was some flow from the the schists and the fractures into the quartzites. Comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system. Considering the slow rate of oxygen isotope exchange between quartz and a fluid, this implies that fluid flow from the schist and vein fracture into the quartzite was extremely limited.