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Academic Background | Research Interests | Publications
Mailing Address:
330 Olin Hall
34th and North Charles Streets
Johns Hopkins University
Baltimore, Maryland 21218
U.S.A.
Academic
Background
1975 Ph.D. Harvard
1971
B.S. Stanford
Metamorphic Geology
The goal of research in metamorphic
petrology at Johns Hopkins is to develop an understanding of contact and
regional metamorphism that integrates mineralogy and mineral chemistry,
whole-rock chemistry, and isotope geochemistry with models for heat flow, mass
transfer, and tectonics.
Specific interests include thermodynamic analysis of phase equilibria,
mineral thermometry and barometry, geochronology, and fluid and heat transport.
The general strategy of our group is to identify individual field areas
in Europe and North America that serve as natural laboratories for the study of
metamorphism. Fieldwork
is followed by various kinds of quantitative analysis in the laboratory
(electron and ion microprobe analysis of minerals, whole-rock analysis by XRF,
and stable isotope analysis of rocks and minerals).
Analytical data are then interpreted with thermodynamics and transport
theory to develop an understanding of the process of metamorphism.
The research on regional
metamorphism in New England and the Alps is aimed at better understanding the
amount, geometry, and geochemical effects of fluid flow in two classic areas of
mid-crustal regional metamorphism.
Current studies in Maine and Vermont build on earlier work in northern
New England that demonstrates prograde mineral reactions in many rock types were
driven by pervasive infiltration of chemically reactive fluids, primarily along
lithologic layering.
Further work will assess whether an additional fracture-controlled
component of reactive fluid flow caused measurable major-element mobility and,
if so, the elements and scale of mass transport involved, by examining quartz
veins and their metasomatic halos in eastern Vermont.
Both the scale of equilibration between different layers by diffusion and
whether there was significant flow of reactive fluids across the layers are
being evaluated from measurements of the progress of prograde decarbonation
reactions in large exposures of thinly bedded micaceous carbonate rocks in
Vermont and Maine.
If there was cross-layer flow, results will constrain the relative
importance of flow parallel to and perpendicular to layers.
The goal of a new investigation of carbonated metaperidotite in the Swiss
Alps is to determine how regional metamorphic fluid flow drives prograde
carbonation reactions in certain rock types.
The occurrence we are studying represents a natural example of how carbon
dioxide can be sequestered in the crust by reaction between fluids and ultramafic rocks
at elevated temperature.
Studies in contact metamorphism are
split between the Sierra Nevada, California, and the Dolomites, northern Italy.
Tectonic models have been proposed for the amount and timing of uplift of
the Sierra Nevada.
Current research is aimed at developing a regional depth-time
relationship for emplacement of the batholith that will confirm or refute those
models for differential uplift of the southern Sierra Nevada relative to
northern and central portions and the timing of the differential uplift, should
it have occurred.
We have collected a suite of contact metamorphosed pelitic hornfelses in
pendants along the length of the Sierra Nevada batholith from north of Yosemite
Park south to the Garlock Fault.
Pressure of contact metamorphism at each locality will be estimated from
well-calibrated mineral equilibria, and the age of the pressure estimate will be
determined from Th-Pb dates for monazite measured in
situ with the ion microprobe.
New work in the Dolomites focuses on the role that flow of heated
seawater, driven by Triassic plutonism in the area, played in the formation of
dolomite from limestone in the Latemar buildup.
The buildup will be contoured with progress of the calcite-dolomite
reaction and with oxygen and carbon isotope composition.
Results will determine both the thermal structure of the flow system in
three dimensions and the direction and amount of fluid flow.
Any correlation between areas with enhanced reaction progress and the
distribution of dikes, faults, and lithologic contacts will reveal the degree to
which each of these pre-metamorphic structures controlled the geometry of the
flow of heated seawater.
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