Newly obtained ratios among C16O, C17O and C18O from young stellar objects
(YSOs) suggest that the solar system is indeed unusual in its 18O/17O
compared with the present-day Galaxy.  Galactic chemical evolution (GCE)
models suggest that 18O/17O is independent of time.  The disparity between
present-day Galactic and solar 18O/17O requires that either our
understanding of the GCE of oxygen is incorrect or that the solar system
was born in an environment enriched by low-mass supernovae.  Enrichment
from low-mass type II supernovae (exploding B stars) on the order of 1 % by
mass can account for the enhancement in 18O/17O of the birth environment of
the solar system compared with normal Galactic values.  Statistical
analysis shows that pollution by low-mass SNe II progenitors requires that
the parental molecular cloud of the solar system was proximal to a cluster
composed of order 500 stars.  This cluster predated the solar system by
~10 to 30 million years.  B star enrichment explains the anomalous Si
isotopic composition of the solar system and the presence of 60Fe.  It
cannot explain the presence of 26Al and 41Ca in the young solar system.

Luminescence is the name for light emitted by crystalline materials as
electrons recombine with holes in the lattice. The emission can be prompt
(e.g. cathodoluminescence) or delayed (e.g. fluorescence,
thermoluminescence), and the magnitude of the observed signal may be used
to infer past events. Signals from quartz and feldspars have been used to
determine the time since grains were heated or exposed to daylight. Recent
advances have helped widen the range of applications of luminescence
dating, including recent attempts to apply it to short timescale
thermochronology.

However, the details of the underlying physical basis remains somewhat
enigmatic. In quartz, many different electron traps and hole centers have
been described, but it is difficult to relate these to the observed
luminescence signals of geologic materials. Establishing the most important
of these represents a significant goal, as these signals have the potential
to provide a very wide range of geologic and environmental events. I aim to
stimulate discussion of the experimental methods which might be adopted to
make progress to achieve this goal.

The spatial relationship between Au-Cu-rich sulfide deposits and convergent
margin magmatism is well established, however the reason for this
association is unclear. The study of Au ores themselves has given little
clue to the earliest stages of the concentration process. Previous studies
have shown that during melt evolution in a crustal magma chamber, the
concentrations of Cu and Au increase with increasing SiO2 until 60 wt. %
SiO2, at which point they suddenly decrease (Sun et. al., 2004). The cause
was suggested to be Au loss in a fugitive volatile phase triggered by
magnetite saturation and accompanying redox changes in an evolving crustal
magma chamber, but this hypothesis remained untested by other observations.
We present a more comprehensive geochemical data set for volcanic glasses
from the Eastern Manus back-arc basin, including Ag, Pt, and the key
element Se and compare this information with our data base of MORB
analyses.


Se, a proxy for S, whose magmatic concentrations are not disguised by
syn-eruption, late-stage degassing, shares the abrupt decrease with Au, Cu,
and Ag. Petrologic modelling reveals the amount of magnetite fractionation
is sufficient to convert most of the S originally dissolved in the magma as
sulfate to sulfide, triggering saturation in a Cu-rich crystalline sulfide
mineral, probably bornite (ideally, Cu5FeS4). The Cu-rich sulfide mineral
sequesters Au and Ag, elements with the same valence as Cu in sulfides, but
not other traditionally chalcophile elements such as Ni, Re and Pt. This
mechanism of Au concentration requires specific conditions, the occurrence
of which provides a pre-enrichment step to the formation of economic
Au-Ag-Cu provinces. The ore-metal abundances in the mantle source of the
parental Eastern Manus basalts are similar to the sources of mid-ocean
ridge basalt (MORB), so the Cu-Au-rich characteristics of the province
requires no enrichment from subducted material. Instead, the association of
major Cu-Au deposits with convergent-margin magmatism results from a
specific enrichment event during magmatic evolution under oxidizing
conditions.


Sun, W, Arculus, RJ, Kamenetsky, VS and  Binns, RA, 2004, Release of
gold-bearing fluids in convergent margin magmas prompted by magnetite
crystallisation. Nature, v. 431, p. 975-978.

The magmatic iron meteorite groups formed by the fractional crystallization
of metallic magmas.  The IIAB magma had the highest initial content of S
and P.  The higher the S content, the larger the solid/liquid distribution
coefficients (D values) for trace elements.  The D values for refractory
PGEs in the IIAB magma reached values >10 leading to a high degree of
fractionation of Ir, Os and Re.  The highest IIAB Os is 10000 that of the
lowest Os content.

The D values for S is <0.02 and for P is <0.1 thus continuing
crystallization leads to strong enrichments of these elements in the
residual magma.  Relatively early in the crystallization of the IIAB core S
and P contents become high enough to cause the magma to enter the
two-liquid field, i.e., to form immiscible S-rich and P-rich magmas.
Because the solubilitiy of S in the P rich magma is relatively high, the
P-rich magma is dominant.  As crystallization continues the less-dense
S-rich magma separates and concentrates at the core-mantle interface; its
composition is close to that of the Fe-FeS eutectic.

As crystallization of the IIAB core continues, the fraction of trapped
melt increases, perhaps because of increases in the viscosity of the
relatively low temperature magma.  When these meteorites solidified massive
FeS and Fe2NiP precipitated from the last dregs of the melt.

IIG is the newest and smallest iron meteorite group; it has the highest P
contents known in iron meteorites. Because it differed in its contents of
key taxonomic elements such as Ge, Ni, As and Au differed from those of the
nearest IIAB relatives, past researchers concluded that it formed on a
separate parent asteroid.  We now show that these irons could be formed
during the crystallization of trapped P-rich melt in the IIAB core.

Reference: J. Wasson and W.-H. Choe, Geochim. Cosmochim. Acta 73, 4879
(2009)

Calcium is a major element in the Earth, and plays significant roles in
igneous, metamorphic, sedimentary and biological processes. It is also
unique among the heavier elements (here meaning those past sulfur in the
periodic table) in the 20% range of mass spanned by stable nuclei, from
40Ca through 48Ca. These two properties have generated wide interest in
potential uses of calcium-isotopic signatures. However, despite a growing
set of high-precision studies, relatively little is known about the
fundamental processes that might generate useful isotopic signatures. This
talk will describe a theoretical study of equilibrium calcium-isotope
(44Ca/40Ca) fractionation in crystals, focusing on low-temperature
precipitates (e.g., calcite, aragonite) and possible crystalline analogues
of dissolved Ca2+. At equilibrium, 44Ca/40Ca appears to be inversely
correlated with the coordination number of calcium (i.e., the number of
nearest-neighbor oxygen anions in a crystal structure). As was found in an
earlier study of magnesium isotope fractionation, calcite is a bit lower in
44Ca/40Ca than might be expected for its coordination number, this mineral
appears to be intermediate between crystals containing Ca(H2O)72+ and
Ca(H2O)82+ groups – the most likely coordination numbers for Ca2+ in
aqueous solution. This result is consistent with little-or-no equilibrium
Ca-isotope fractionation between calcite and seawater, but also suggests
that the magnitude (and even direction) of fractionation will be sensitive
to speciation changes in solution.