HR: 1330h
AN: V22D-0610 [PDF]
TI: Experimental Investigation of Reaction and Fluid Transport in Dolomite Rock
AU: * DeAngelis, M T
EM: mdeangel@utk.edu
AF: Dept. of Earth and Planetary Sciences -
University of Tennessee, 306 Geological Sciences Bldg., Knoxville, TN 37996 United States
AU: * DeAngelis, M T
EM: mdeangel@utk.edu
AF: Chemical Sciences Division -
Oak Ridge National Laboratory, 1 Bethel Valley Rd., Oak Ridge, TN 37831 United States
AU: Labotka, T C
EM: tlabotka@utk.edu
AF: Dept. of Earth and Planetary Sciences -
University of Tennessee, 306 Geological Sciences Bldg., Knoxville, TN 37996 United States
AU: Anovitz, L M
EM: iz9@ornl.gov
AF: Dept. of Earth and Planetary Sciences -
University of Tennessee, 306 Geological Sciences Bldg., Knoxville, TN 37996 United States
AU: Anovitz, L M
EM: iz9@ornl.gov
AF: Chemical Sciences Division -
Oak Ridge National Laboratory, 1 Bethel Valley Rd., Oak Ridge, TN 37831 United States
AU: Cole, D R
EM: coledr@ornl.gov
AF: Chemical Sciences Division -
Oak Ridge National Laboratory, 1 Bethel Valley Rd., Oak Ridge, TN 37831 United States
AU: Fayek, M
EM: mfayek@utk.edu
AF: Dept. of Earth and Planetary Sciences -
University of Tennessee, 306 Geological Sciences Bldg., Knoxville, TN 37996 United States
AU: Fayek, M
EM: mfayek@utk.edu
AF: Chemical Sciences Division -
Oak Ridge National Laboratory, 1 Bethel Valley Rd., Oak Ridge, TN 37831 United States
AB:
Metamorphism of carbonate rock is commonly the result of reaction between the minerals in the rock and an H$_2$O-rich fluid.
One example is the breakdown of dolomite, producing calcite + periclase. The reaction results in a reduction of the solid
volume of the rock and a production of CO$_2$. Both contribute to the increase in permeability during reaction, permitting
continued ingress of H$_2$O. We have attempted to determine some of the processes that occur during infiltration and reaction
experimentally. We cut 4 mm diameter cores of dolomite rocks with a variety of textures ranging from fine-grained
sedimentary dolostones to coarse-grained dolomitic marbles. Experiments are carried out using a conventional cold-seal
hydrothermal apparatus. The dolomite rock cores were sealed in gold capsules with an aliquot of isotopically enriched water
of composition HD$^{18}$O$_{0.5}\,^{16}$O$_{0.5}$. The samples were held at a $P = 100$ MPa and $T = 650$--$700\, ^{\circ}$C
for durations ranging from a few days to a few months.
After experimentation, the cores were sectioned and examined by XRD, EMP, SIMS, and CL techniques. All experiments show some
reaction, even in experiments lasting for only two days. In samples with a large water-rock ratio, complete reaction occurred
within 30 d at $700\, ^{\circ}$C. Crystallization of new mineral phases within coarse samples is concentrated along fluid
infiltration pathways, such as grain boundaries and fractures. Smaller grain size samples show more pervasive
crystallization, with original dolomite nearly completely replaced by calcite. Although periclase is the stable phase for the
conditions of these experiments, extensive brucite is observed and is believed to be the result of rapid hydration of
periclase upon quench. SIMS ion imaging shows extensive enrichment of $^{18}$O along dolomite grain boundaries and in
fractures. There is little evidence in the short-duration experiments for any exchange between fluid and the dolomite, but
the newly formed products of reaction are strongly enriched in $^{18}$O. Under the conditions of the experiments with
water--rock ratios $\ge 1$, grain-boundary transport readily occurs over the sample distances of 2--4 mm.
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting