5. December 9, 2008
5
This is the Antarctic Ice Sheet
In the Helicopter at 11,000 Ft. 5 miles west of Mt. Fleming
If we turn around and land on Mt Fleming we see……
to the south pole (800 miles)
6. December 9, 2008
6
The Edge of the Dry Valleys
-95 wind-chill on the edge
of the polar plateau and I
haven't bathed in a month
- Nice -
also called “Bad Hair Day”
8. Outline
8
• Whoa…, Location
• Magmatic End Members
• Sills/ Magmatic Slurries
• The Granular World
• Kinetic Sieving
• Silicic Segregations
• Conduit Definition
• Crystal sludge (MgO)
• Ring Structures
• Melting of host rocks
• Vertical climbing
• Lessons Learned
9. A Great Igneous Petrologist Speaks
“Igneous petrologists have long been fascinated by large basic intrusions.
Much more has been written about the structural, mineralogical, and
geochemical characteristics of these bodies than about the ways in
which they form. The reason for this imbalance is simple.
The task of interpreting what one sees in crystalline rocks in terms
of physical processes in unseen cooling magmas is formidable.”
Alexander R. McBirney (Igneous Petrology, 1984)
99
11. December 9, 2008 Dean M. Peterson
Why study geology in the Dry Valleys
• It’s an End Member Magmatic System
• Virtually 100% exposure of bedrock
– No bugs or shrubbery on 8,000 ft. slopes
• Valleys expose ~4 km vertical sections
• Original igneous textures preserved
– Sills average ~ 300m thick
12. Magmatic End Member Analogs
• Sudbury Complex
– Impact Melt Sheet (1.85 Ga.)
– Well mapped
– Superheated Magma
– Annealed
– No Phenocrysts
– No Modal Layering
• Ferrar Dolerite Sills
– Continental Rift (180 Ma)
– Virtually unmapped (no more)
– No Superheat
– No Annealing (textures preserved)
– Phenocryst-rich (Magmatic Slurry)
– Modal Layered
1212
13. Schematic Block Diagram
Continental Rifting, Intrusion of Dolerite Sills (Ferrar Sills) west of rift axis
Simplified Geology of the Dry Valleys
13
15. August 31, 2009
15
And Yes, there is 100% Exposure
Quickbird Satellite Image into Bull Pass from the South
16. August 31, 2009
16
And Yes we can Map it
Previous low-angle satellite view directionFinal Geology, Bull Pass Area
17. Magmas have Boundary Conditions !!
Simple model of the chemical, thermal, and momentum conditions
In effect, thin thermal and chemical boundary layers are embedded in wide – magma-
flow induced – shear zones where the variation in velocity is broad and gentle
1717
18. It’s a Granular World
Granular flows that occur in nature as rockslides, pyroclastic flows, dry
debris avalanches and many magmatic systems as well as those
arising from industrial processes such as mining and solids conveying,
typically contain a range of particle sizes.
A fundamental process in flows containing more than one particle size
or density is segregation; that is, sorting of the particle mixture into
regions that are uniform in size or density. Segregation can occur due
to the movement of smaller particles into the spaces beneath larger
particles during shaking, and large-scale convection within the
granular mixture, both of which result in the formation of a layer of
segregated coarse particles above fine particles, and suggest density-
independent rising times for the larger particles.
Phillips et al., 2006, Earth and Planetary Science Letters 246, p. 466–480.
18
26. Magmatic Process - Kinetic Sieving
Can get irregular ultramafic accumulations
of phenocrysts above sorted layers
Imagine a drill hole through this…………
26
39. Lessons Learned
• Magmatic systems are highly integrated physically,
chemically, and spatially
• The nature of the system at every scale is characterized by
physical processes buttressed by chemical processes
• The local size, shape, and age of the system coupled with
magma crystallinity, integrated flux, flushing frequency, and
nature of wall rock involvement determines the local and
system-wide products
• Layering is the unavoidable physical process of sorting and
ordering of entrained crystal swarms by periodic flows at
geometrically convenient locations and ends as the chemical
process of textural annealing by diffusion
