P-Wave
• Compression
wave
• Only through solids
• fast-moving first arriving
S-Wave
Van der Hilst, RD et al. 1997. Nature 386: 578-584
Svensen, H et al 2004. Nature 429: 542-545
Justin Liefer
MAS 603
• waves passing through
different substances
• light and tranparent
Reflection Sesimologyliquids – refractive index
• with seismic waves –
impedence
Seismic
tomography
• Large
•Impedence depends on
wave velocity and density
of substance
Surface Waves
• Rayleigh
waves
• long wave,
slow
Convective Mantle
• Mineral phase changes to weak
for stratification
• Deep anomalies = slabs in lower
mantle
•Shear wave
•Solids and
liquids
• slower
•longitudinal
Stratified Mantle
• Some slabs stuck in upper mantle
•
•Really old reservoirs = poorly
mixed
•Global Tomography and gravity
data explained better
database over 30
years
• Model by inversion
•Comparison to other
on-going models
• P-wave data for Lower
Mantle
• High Resolution
Great deal of similarity
with model based on Swaves
Slab model for 1800-2000
kmExcellent recovery
• Transition zone and
boundary at 660km not a
barrier
• Other structures
(Tonga) like the Farralon
anomaly
• subducted oceanic
lithosphere – down CMB
• Distance to big for
simple conduction
• Slabs bounce off
transition zone, some
don’t
• Stratification is local,
short time-scale
• Stratification may
occur in deep lower
mantle, sinking without
re-surfacing
•Sinking and ref i i t
• Intensive exploration
of More and Voring
Basin- 735 Vents
• Seismic Reflection
• Gravity Data
• Seismic mapping with
cores
• Core analysis
•80,000 sq. Km
• About 1/5 of North
Atlantic Volcanic
Province
• Sills can be difficult to
measure- poor imaging
• Good cores and local
high concentration of
hydrothermal vents
Vents are usually eye-shaped or
domed
Ka-Boom
• Extreme warm temperatures for 200,000 years (Arctic palm
trees!)
• Increase of 6-8 degrees in global temp over short period of
time
Sill
The Recipe
• Large lava flow area
• Organic carbon rich
sediment to make methane
• Conduit to methane
deposits and sudden lava
flow
• Sill
complex was
formed with fast lava
flow
• Organic
rich sediments
placed in
Paleocence/Cretaceous
mud stones
• Sill intruded there, high
potential for methane
production
• 3 x amount need for
i
• CO2 release could cause warming
• van der Hilst
• Large surface degassing potential in
More and Voring Basins, Himalayas
also.
• Seisimic tomography greatly
improved by better models and
more data
• CO2 release due to degassing –
3.6kg/cu. m
• CO2 release due to intrusion – 25-100
kg
• Svensen
• More and Voring sill complex has
the right recipe for large methane
hydrate release in Eocene
• Methane release is potent enough
to explain rapid changes observed
• Global mantle processes are
convective, but locally, stratification
can occur