John W. Shervais: Research
Projects
Metasomatism
and Magma Evolution in the Upper Mantle
Understanding the origin and evolution
of continental lithosphere is a fundamental goal of solid earth geophysics,
which seeks to characterize the material properties and physical state
of the Earth. This goal is important because continental lithosphere records
the bulk of Earth history and because a rigid lithosphere is central to
plate tectonics. Although the lithosphere is defined by its physical properties,
it must consist of real rocks with distinct petrologic origins and geochemical
characteristics. Field-based petrologic and geochemical studies are paramount
to our goal of understanding lithosphere evolution because they provide
the ultimate "ground truth" for broader scale geophysical experiments that
can only infer regional scale structures and average physical properties.
Most basalts erupted at the Earths
surface originate by partial melting of the Earth’s upper mantle. The chemical
and isotopic composition of magmas erupted in different tectonic settings
reflect differences in mantle composition, in melting process, and in subsequent
magma evolution. Understanding the roles of metasomatism (which modifies
mantle composition) and magma evolution (which modifies the resulting melts)
is crucial to our understanding of how the Earth evolves chemically and
thermally through time.
The projects listed here approach the
question of mantle compostion and evolution from two different perspectives:
first, by looking at rocks which compose the upper mantle, as exposed in
alpine peridotite massifs, and second, by looking at the partial melts
(volcanic rocks) which form from this mantle. These projects are related
in many ways to our work in the Snake River Plain of southern Idaho.
Publications Resulting From This
Project
-
Mukasa, S.B. and Shervais, J.W. (1999)
Growth of Subcontinental Lithosphere: Evidence From Repeated Dike Injections
in the Balmuccia Lherzolite Massif, Italian Alps. Lithos, in press.
-
Shervais, J.W., and Mukasa, S.B. (1991)
The Balmuccia Orogenic Lherzolite Massif, Italy. Jour. Petrology,
Special Lherzolites Issue, 155-174.
-
Mukasa, S.B., Shervais, J.W., Wilshire,
H.G., and Nielsen, J.E. (1991) Intrinsic Nd, Pb, and Sr isotopic heterogeneities
exhibited by the Lherz alpine peridotite massif, French Pyrenees. Jour.
Petrology, Special Lherzolites Issue, 117-134.
-
Wilshire, H.G., Meyer, C.E., Nakata, J.K.,
Calk, L.C., Shervais, J.W., Nielson, J.E., and Schwarzman, E.C. (1988),
Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United
States, U.S.G.S. Professional Paper 1443, 179 pp.
-
Shervais, J.W., Taylor, L.A., Lugmair,
G.W., Clayton, R.N., Mayeda, T.K. and Korotev, R.L. (1988), Early proterozoic
oceanic crust and the evolution of subcontinental mantle: eclogites and
related rocks from southern Africa, Geological Society of America Bulletin,
100,
411-423.
Master's Theses:
-
Richard A. Cooke, Compositional effects
of Mantle Metasomatism in Alpine Peridotites, M.Sc. Thesis, 1992.
-
Ilona Lawless, Petrology, Chemistry, and
Petrogenesis of alkaline volcanic and plutonic rocks from Tahiti, French
Polynesia, M.Sc. Thesis, 1990.
