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James Day
Assistant Professor
Email address: [email protected]
Phone extension: 45431
Web: http://scrippsscholars.ucsd.edu/jmdday
Research Interests: Planetary accretion and differentiation processes; cosmochemistry; mantle
geochemistry; igneous and metamorphic petrology; volcanology
Heat lost from Earth’s interior drives convective motion within the rocky mantle. This
process is ultimately responsible for volcanism on our planet and for the tectonic upheavals
that shapes the continents on which we live. Research at the Scripps Isotope Geochemistry
Laboratory (SIGL) focusses on better understanding mantle convection by using elements and
their isotopes as tracers and employing field observations and direct studies of rocks to
understand the history of mantle convection. Mantle convection is also ultimately responsible
for creating some economically important precious metal ore deposits, and studies are ongoing at the SIGL to better understand how such ore deposits are created.
We use a number of means for studying mantle convection. First, we directly study
mantle rocks exposed at the Earth’s surface. For example, we are currently studying ophiolites
which are slivers of oceanic crust and mantle that were forced onto continents during oceanclosing and mountain-forming events. Our recent study of the Shetland ophiolite complex in
northern Scotland highlights how the mantle carries geochemical evidence for melting events
that have occurred across billions of years of Earth history (O’Driscoll et al., 2012). We also
examine how the Earth’s mantle evolves through the study of volcanism preserved in ocean
islands likes the Canary Islands. These types of study provide compelling evidence for the
return of oceanic and continental crust that has been taken down into the mantle at subduction
zones (e.g., Day et al., 2012a).
Our studies of terrestrial mantle and crustal processes are complemented by research in
planetary science. Significant strides have been made in the last year to understand how
precious metals such as gold, platinum and palladium were brought to planets (Brandon et al.,
2012; Day et al., 2012b; Riches et al., 2012). The abundances of these elements are higher than
expected in most planetary bodies, where formation of metallic cores should have stripped
precious metals almost completely from the silicate mantles and crusts. That there are jewelry
items made of gold and platinum argue that this could not have been the case and our recent
work shows that the addition of precious-metal-rich impactors led to re-enrichment of these
important elements to planetary mantles and crusts after core formation was complete.
Furthermore, the timing of these events was extremely soon after the formation of some
planets (Day et al., 2012b). This rapid addition of precious metals is surprising and the process
is likely a natural consequence or continuum of the growth of planets.
Work at the SIGL to understand planet formation includes understanding how volatiles
were brought to, and retained - or lost - within planets. To do this, we recently published an
extensive study of strontium isotopes in planetary materials in order to show that isotopic
variations of this element likely reflect heterogeneity imparted from the creation of the Solar
nebula (Moynier et al. 2012). We have also begun a major campaign to directly measure
volatile enrichment and depletion in planets through the study of moderately volatile elements,
such as zinc (Paniello et al., 2012). Our recent work on lunar rocks shows clear enrichment of
the heavy isotopes of Zn in the Moon (positive 66Zn in Figure 1), indicating extreme volatile
depletion of the Moon relative to Earth and Mars. This exciting result, along with evidence for
early accretion of precious metals to planetary bodies (Day et al., 2012b) offers tantalizing
glimpses into how volatiles and other elements were ultimately set within the planets.
Recent Publications
Brandon, A.D., Puchtel, I.S., Walker, R.J., Day, J.M.D., Irving, A.J., Taylor, L.A. (2012)
Evolution of the martian mantle inferred from the 187Re-187Os isotope and highly siderophile
element abundance systematics of shergottite meteorites. Geochimica et Cosmochimica Acta,
76, 206-235.
Day, J.M.D., Macpherson, C.G., Lowry, D., Pearson, D.G. (2012a) Oxygen isotope heterogeneity
of the mantle beneath Canary Islands: a discussion of the paper of Gurenko et al. Contributions
to Mineralogy and Petrology, 164, 177-183.
Day, J.M.D., Walker, R.J., Qin, L., Rumble, D. (2012b) Late accretion as a natural consequence
of planetary growth. Nature Geoscience, 5, 614-617.
Day, J.M.D., Walker, R.J., Ash, R.D., Liu, Y., Rumble, D., Irving, A.J., Goodrich, C.A., Tait, K.,
McDonough, W.F., Taylor, L.A. (2012c) Origin of felsic achondrites Graves Nunataks 06128
and 06129 and ultramafic brachinites and brachinite-like achondrites by partial melting of
volatile-rich primitive parent bodies. Geochimica et Cosmochimica Acta, 81, 94-128.
Filiberto, J., Chin, E., Day, J.M.D., Franchi, I.A., Gross, J., Greenwood, R.C., Penniston-Dorland,
S., Schwenzer, S., Treiman, A. (2012) Geochemistry of intermediate olivine-phyric shergottite
northwest Africa 6234, with similarities to basaltic shergottite northwest Africa 480 and
olivine-phyric shergottite northwest Africa 2990. Meteoritics and Planetary Science, 47, 12561273.
Moynier, F., Day, J.M.D., Okui, W., Yokoyama, T., Bouvier, A., Walker, R.J., Podosek, F.A.
(2012) Planetary-scale strontium isotopic heterogeneity and the age of volatile-depletion of
early Solar System materials. Astrophysical Journal, 758:45 (7 pp.) doi:10.1088/0004637X/757/1/1
O’Driscoll, B., Day, J.M.D., Walker, R.J., Daly, J.S., McDonough, W.F., Piccoli, P.M. (2012)
Chemical heterogeneity in the upper mantle recorded by peridotites and chromitites from the
Shetland Ophiolite Complex, Scotland. Earth and Planetary Science Letters, 333-334, 226-237.
Paniello, R.C., Day, J.M.D., Moynier, F. (2012) Zinc isotopic evidence for the origin of the
Moon. Nature, doi:10.1038/nature11507
Riches, A.J.V., Day, J.M.D., Walker, R.J., Simonetti, A., Liu, Y., Neal, C.R., Taylor, L.A. (2012)
Rhenium-osmium isotope and highly siderophile element abundance systematics of angrite
meteorites. Earth and Planetary Science Letters, 353-354, 208-218.