http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
xiv, 169 leaves : illustrations, maps ; 28 cm.
Calcite is commonly found as a vein-filling mineral in rocks.
However, the factors controlling its deposition are complex
and not well understood in quantitative terms. In order to
advance our understanding of the processes involved, a model
for calcite precipitation simulating calcium carbonate mass
transport in open spaces has been developed. The model was
tested by a new experimental technique that uses a follow-
through reactor simulating a vein opening. Agreement was
observed between model predictions and experimental
observations for the deposition of calcite in synthetic
veins. The influences of solution saturation state with
respect to calcite and flow velocity on both amount and
distribution of calcite precipitate were well predicted by
the model. The model predicts that the solution slightly
supersaturated with respect to calcite can produce a uniform
deposition of calcite within a vein. This condition demands
what may be unreasonably large volumes of solution flow and
long periods of time to achieve vein fillings. To test some
of these results, I studied a set of veins in the Cretaceous
Austin Chalk. Multi-layered crack-seal calcite veins in
the Austin Chalk Formation near San Antonio, Texas are
composed of alternating millimeter- to submillimeter-thick
calcite veinlets and host lithons, occasionally crosscut by
coarse, equant-grained secondary calcite veins. The grain
fabrics in calcite veinlets are mostly equant or irregular,
suggesting face-controlled grain growth in a fluid-filled
cavity. Linear changes in 8180 (e.g. -2.6 to -5.6%o, PDB) of
the calcite veinlets along the length of veins suggest that
the individual calcite veinlets were sequentially developed.
A systematic 8 18 0 decrease in the vein opening direction
primarily resulted from a continuous increase in temperature
of the ascending fluids delivered to the Austin Chalk.
Relatively constant 8 13C (approximately +1.4 ︢0.4%o, PDB)
for the multi-layered veins and most secondary veins
indicates that the composition of fluids from which the
calcite veins precipitated was initially buffered by the bulk
chalk. The relatively thick veinlets can be developed by
progressive opening simultaneous with calcite precipitation
under a low fluid pressure. Multi-layered crack-seal veins
presumably occur in sequentially developed so called
66releasing bend" geometries related to episodic fault slip.
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Includes bibliographical references: pages 144-157.