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Project Goals and Objectives:
(for a more complete project summary, click
here)
The primary objective of this study is to use volcanic
and glacial records at Minna Bluff in the western Ross Embayment of Antarctica
to interpret Antarctic cryosphere history. Minna Bluff is a significant
topographic barrier that has effectively blocked the Ross Ice Shelf and the
former Ross Sea Ice Sheet from flowing southward into McMurdo Sound.
Documenting the timing of blockage of ice flow is critical for reconstructing
past behavior of the Ross Ice Shelf/Ice Sheet and for interpreting the ANDRILL
cores. In addition to providing a record of the emergence of the topographic
barrier, the Minna Bluff study yields a discontinuous but reliable record of
synvolcanic expansions of the Ross Sea Ice Sheet and local ice caps..
Distinctive volcanic lithofacies are produced when erupting magmas interact with
glacial ice; documenting and dating these deposits will constitute a proxy
record of paleoelevation of grounded ice adjacent to Minna Bluff, which in turn
can be used as ground truth for models of ice sheet behavior. Because of the
unique ability of glaciovolcanic sequences to preserve evidence of several
critical ice sheet parameters, the lithofacies analysis will provide reliable
raw data to infer past ice-sheet conditions, including ice thickness, hydrology,
and basal thermal regime.
 Left:
Modis image of McMurdo Sound area. Major volcanic are centers are
labeled. Ross Island is capped by the active volcano Mt. Erebus.
BI is Black Island and WI is White Island. The Andrill MIS site is
the McMurdo Ice Shelf site of the ocean sediment/rock core that was drilled in
2006-7 season.
Minna
Bluff forms the southeast arm of the Mt. Discovery volcanic system.
Today the Ross Ice Shelf is pinned on Ross Island. Prior to the Plio-Pleistocene
growth of Ross Island, Minna Bluff probably acted as a pinning point for the ice
shelf front.
A
secondary goal of this study is to characterize the mineralogy and geochemistry
of lava samples in order to determine the compositional spectrum and evaluate
the evolutionary history of magmas erupted at Minna Bluff. The late Miocene
age of Minna Bluff corresponds to a major shift in magma composition and focus
of volcanic activity in the region; documenting the chemical variations is
significantly important to our understanding of the fundamental cause of
volcanism in this portion of the West Antarctic rift system.
Project Activities:
The project has both field and
laboratory components. The major completed activity of year 1 was the field
season at Minna Bluff from late December 2006 to early February 2007. In total
there were 11 participants in the field season: 3 PIs/CoPIs (Wilch, McIntosh,
Panter), 2 other senior personnel (Dunbar, Smellie), 2 graduate students (Scanlan,
Fargo), 1 undergraduate (Roberts), and 3 mountaineers (Burton, Smith, Detwieler,
latter two provided by Raytheon Polar Services Company). All of the field party
members participated in two training courses from by the field safety training
program at McMurdo Station, Snowcraft I and II.
We focused our 32-day
field season on the east end of Minna Bluff, locally referred to as Minna Hook,
where we mapped and described the geology along the eroded bluff faces just
above the sheared Ross Ice Shelf. In the field we did mapping on foot but were
transported to distant sites by helicopter.
In
total we collected more than 300 samples for geochronology, geochemistry, and
lithofacies analysis. Sample locations were recorded on GPS. The samples
arrived at the PIs’ respective institutions in late April or early May. Two
additional undergraduates from Albion College have begun lithofacies analysis
under the supervision of Thom Wilch. Samples are currently being
processed and initial results will be presented at the International Symposium
for Antarctic Earth Science in Santa Barbara CA in late August 2007.
Publications:
Wilch, T.I.; McIntosh, W.C.; Smellie, J.L.; Dunbar, N.W.; Fargo, A.; Scanlan,
M.K.; Roberts, P.D.; Panter, K.S., 2007, Late Miocene volcanism and glaciation
at Minna Bluff, Antarctica, Online Proceedings of the 10th International
Symposium on Antarctic Earth Science, Santa Barbara CA, August 2007.
Scanlan, M., Panter, K.S., and Dunbar, N.W., 2007, Evidence for magma
mixing/mingling in lavas from Minna Bluff, South Victoria Land, Online
Proceedings of the 10th International Symposium on Antarctic Earth Science,
Santa Barbara CA, August 2007.
Photo Gallery:
Most of the 2006-7 field party at Minna Bluff.
Left to right: Bill McIntosh (NMT), Paul Roberts (Albion undergraduate
student), Andrew Fargo (NMT, graduate student), Mary Scanlan (BGSU. graduate
student), John Smellie (BAS), Nelia Dunbar (NMT), Tim Burton (BAS mountaineer),
Thom Wilch (Albion), Matt Smith (RPSC). Other participants not pictured:
Kurt Panter (BGSU), Susan Detweiler (RPSC mountaineer). Photo by Tim
Burton.
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