tion. If the subsamples are representative of the
of cosmic spherules--the Deep Sea spheres
entire size fraction, then there are 2 103 g g1 of
(Brownlee 1979) and the Greenland spherules
material in the 106250-m size fraction.
(Maurette et al. 1987)--the SPWW materials are
The types of cosmic spherules found in the
most similar to particles collected in Greenland
SPWW were assessed by mounting particles from
(Table 5). The main difference is the higher pro-
the 250425-m and 106250-m size fraction
portion of glassy spheres and the lower percent-
in epoxy, sectioning them, and examining them
age of unmelted materials in the SPWW collection.
using the Cameca SX-50 electron microprobe at
However, the fraction of unmelted micrometeor-
the University of Tennessee, Knoxville. We found
ites in the SPWW will increase as we systemati-
the full range of cosmic spherule morphologies
cally look for them. The major differences between
(Table 4).
the SPWW spherules and those found in deep-sea
Photomicrographs of SPWW particles are pre-
sediments are the increase in glass spherules found
sented in Figure 15ah. Glass spherules are com-
and the paucity of iron and G-type spherules. This
posed of mafic glass and represent particles that
is true both for magnetically and nonmagnetically
have been fully melted, devolatilized, and rapidly
collected deep-sea spheres (Taylor and Brownlee
quenched during atmospheric entry (Fig. 15a).
1991).
Cryptocrystalline spherules are predominantly
Twenty spherules from the pocket sample were
glassy particles with crystallites too small to be
analyzed using a Zeiss DSM962 at Dartmouth
individually recognized, surrounded by an iron-
College. When plotted on a MgO, SiO2, and FeO
rich glass (Fig. 15b). Barred olivine spherules are
ternary diagram (Fig. 16) or on a Ca/Si vs. Al/Si
particles that have also been fully melted but that
plot (Fig. 17), the SPWW spherules lie within the
were less rapidly quenched, allowing olivine and
field found for other collections.
magnetite crystallites to form (Fig. 15c). Relic-grain-
Although detailed examinations of non-
bearing spherules are particles that did not fully
spherical particles have not yet taken place, the
melt before quenching and retain "meteoritic"
presence of one relatively large, unmelted particle
minerals, surrounded by an iron-rich glassy rim
in one of our mounts suggests a significant
(Fig. 15d). Volatile-rich spherules are vessiculated
unmelted ET component. Unmelted particles have
particles showing regular to irregular cavities and
been found by previous studies of particles re-
lots of relic olivine, metal, or sulfide grains; they
trieved from melted Antarctic snow and ice. Fur-
ther studies will incorporate a detailed examina-
represent particles quenched quickly after initial
tion of the nonspherical particles in the sediment.
heating, before full devolatilization could occur
(Fig. 15e). The G-type are high-iron spherules and
contain magnetite dendrites in a glass matrix (Fig.
Weathering
The barred olivine spherules show various de-
15f). Iron spherules (I-type) are wholly metallic (Fig.
grees of weathering with preferential removal of
15g) and show meteoritic siderophile concentra-
Fe-rich glass interstitial to Mg-rich olivine bars.
tions. Unmelted IDP-like particles have compact,
Some stony spherules retain a glassy rim (Fig. 18),
irregular texture, with iron-rich rims around dis-
while others show 1020-m grooves at their mar-
persed voids and relic olivine grains (Fig. 15h).
gins and occasionally significant removal of glass
When compared to the other large collections
in their interiors. The one G-type spherule has a
highly weathered core (Fig. 15f), and the iron
spherule has lost the interstitial nickel-rich phase
Table 4. Types of extraterrestrial particles in the
near its periphery (Fig. 15g). The weathering is
pocket sample, 106425 m.
probably caused by the acidic water in which the
particles were immersed for up to 4 years. How
Glass
14
weathering has affected unmelted particles in not
Cryptocrystalline
11
yet known.
Barred olivine
51
Relic grain-bearing
7
Flux rates
Volatile-rich
3
A terrestrial flux rate for meteoritic material 50
High iron (G-type)
1
300 m was obtained from Greenland ice
Iron
1
IDP-like
1
(Maurette et al. 1987). To make this flux calcula-
tion, Maurette and his colleagues estimated the
Total
88
concentration of sediment in mature cryoconite
18
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