geological data, geophysics and modelling of the mantle yanick ricard & joerg schmalzl "...
TRANSCRIPT
Geological data, geophysics and modelling of the mantle
Yanick Ricard & Joerg Schmalzl
Geophysical observations; Introduction Geochemical measurements Physics of convection Modeling of the mantle; mixing properties Connecting chemical and physical observation
Introduction & Motivation
Dynamic Earth
- most prominent observations:
-Earth quakes
-Volcanos
Very hard to get any data
Geochemical/geological observations
- collect samples at mid-ocean ridges & volcanos
--> compare with:
- composition of chondrites
- each other
-> strength is the temporal resolution
-> weakness in the spatial domain
Being treated in separate lecture.
Geophysical Observations- Seismic waves- Heat flow measurments- Post glacial rebound- Gravimetrie
=> Problem: Snapshot of present situation But .. spatial information
Mixing is THE link between the two fields !
How to proceed:
Gather information about the convective regime i.e. material properties, boundary conditions, e.t.c.
=> have a model of convection in the Earth mantle and understand the mixing properties
=> feed information derived from the geochemical investigations back into the model and try to refine it until it fullfills geochemical constrains
=> the SUPER-MODEL
But....
parameters are only poorly constrained
convection & convective mixing are very non-linear processes
Therefore a fundamental understanding of the physical processes is required to isolate robust features of convective mixing. (seperate lecture)
Deviation from the spherical shape:
- different wave forms- non uniform
distribution of sender/receiver
- agreements on hot anomaly under Africa and Pacific
- herterogeneity near CMB
Hotspots:
seem too:
- exist over long time- being stationary- independent of the
plate motion- are geochemically
distinced
Concluding from seismology:
Solid mantle and liquid outer core velocity change at 670km defining upper and lower
mantle Global tomography showing large warm regions
under Pacific & Africa Large variations in seismic velocity near core
mantle boundary Subducting plates are penetrating into lower mantle Origin of Hotspots still unclear (670km ??, D´´, ..)
Estimating the parameters for convection:
The vigor of convection is determined by the Rayleigh number Ra:
Surface heatflux :
Heat flux at the core-mantle boundary Rate of internal heating due to radioactive decay
(20-80%)
Concluding
Plate motion indicates that there is convection in the Earth mantle
Estimates of the parameters reveals that convection in the Earth mantle is vigorous
But material parameters are poorly constrained and also functions of P,T
By understanding the connection to geochemical observations the parameters could be much better constrained