Thermal structure of old continental lithosphere from the inversion of surface-wave dispersion with ...
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Thermal structure of old continental lithosphere from the inversion of surface-wave dispersion with thermodynamic a-priori constraints. N. Shapiro, M. Ritzwoller, University of Colorado at Boulder. J.-C. Mareschal, Université du Québec à Montréal.

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N. Shapiro, M. Ritzwoller, University of Colorado at Boulder

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N shapiro m ritzwoller university of colorado at boulder

Thermal structure of old continental lithosphere from the inversion of surface-wave dispersion with thermodynamic a-priori constraints

N. Shapiro, M. Ritzwoller, University of Colorado at Boulder

J.-C. Mareschal, Université du Québec à Montréal

C. Jaupart, Institut de Physique du Globe de Paris


Objectives

Objectives

to reconcile thermal and seismic models of the old continental lithosphere

2.to develop methods for joint inversion of the seismic and the thermal data


Thermal models of the old continental lithosphere

Thermal models of the old continental lithosphere

from Jaupart and Mareschal (1999)

from Poupinet et al. (2003)

Constrained by thermal data: heat flow, xenoliths

Derived from simple thermal equations

Lithosphere is defined as an outer conductive layer

Estimates of thermal lithospheric thickness are highly variable


Seismic models of the old continental lithosphere

Seismic models of the old continental lithosphere

Based on ad-hoc choice of reference 1D models and parameterization

Complex vertical profiles that do not agree with simple thermal models

Seismic lithospheric thickness is not uniquely defined

Additional physical constraints are required to eliminate non-physical vertical oscillations in seismic profiles and to improve estimates of seismic velocities at each particular depth


Inversion of seismic surface waves

Inversion of seismic surface-waves

1. Data

2. Two-step inversion

procedure

global set of broadband fundamental-mode Rayleigh and Love wave dispersion measurements (more than 200,000 paths worldwide)

Surface-wave tomography: construction of 2D dispersion maps

Inversion of dispersion curves for the shear-velocity model

Group velocities 18-200 s.

Measured at Boulder.

Phase velocities 40-150 s.

Provided by Harvard and Utrecht groups


Dispersion maps

Dispersion maps

100 s Rayleigh wave group velocity


Local dispersion curves

Local dispersion curves

All dispersion maps: Rayleigh and Love wave group and phase velocities at all periods


Inversion of dispersion curves

Inversion of dispersion curves

All dispersion maps: Rayleigh and Love wave group and phase velocities at all periods

Monte-Carlo sampling of model space to find an ensemble of acceptable models


Details of the inversion seismic parameterization

Details of the inversion: seismic parameterization

Ad-hoc combination of layers and B-splines

Seismic model is slightly over-parameterized

Non-physical vertical oscillations

Physically motivated parameterization is required


Details of the inversion monte carlo approach

Monte-Carlo inversion: random sampling of the model space

Details of the inversion: Monte-Carlo approach

Linearized iterative inversion

Finds only one best-fit model. Does not provide reliable uncertainty estimates

Linearization can be numerically sophisticated


Details of the inversion monte carlo approach1

Details of the inversion: Monte-Carlo approach

Monte-Carlo inversion: random sampling of the model space

Linearized iterative inversion

Finds only one best-fit model. Do not provide reliable uncertainty estimations

Linearization can be numerically sophisticated

Finds an ensemble of acceptable models that can be used to estimate uncertainties

Does not require linearization. Easy transformation between seismic and temperature spaces


Conversion between seismic velocity and temperature

conversion between seismic velocity and temperature

computed with the method of Geos et al. (2000) using laboratory-measured thermo-elastic properties of main mantle minerals and cratonic mantle composition

non-linear relation


Monte carlo inversion of the seismic data based on the thermal description of model

Monte-Carlo inversion of the seismic data based on the thermal description of model


Monte carlo inversion of the seismic data based on the thermal description of model1

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models


Monte carlo inversion of the seismic data based on the thermal description of model2

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models

constraints from thermal data (heat flow)


Monte carlo inversion of the seismic data based on the thermal description of model3

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models

constraints from thermal data (heat flow)

randomly generated thermal models


Monte carlo inversion of the seismic data based on the thermal description of model4

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models

constraints from thermal data (heat flow)

randomly generated thermal models

converting thermal models into seismic models


Monte carlo inversion of the seismic data based on the thermal description of model5

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models

constraints from thermal data (heat flow)

randomly generated thermal models

converting thermal models into seismic models

finding the ensemble of acceptable seismic models


Monte carlo inversion of the seismic data based on the thermal description of model6

Monte-Carlo inversion of the seismic data based on the thermal description of model

a-priori range of physically plausible thermal models

constraints from thermal data (heat flow)

randomly generated thermal models

converting thermal models into seismic models

finding the ensemble of acceptable seismic models

converting into ensemble of acceptable thermal models


Lithospheric structure of the canadian shield

Lithospheric structure of the Canadian shield

Thermal data: heat flow

  • Computation of end-member crustal geotherms

  • Extrapolation of temperature bounds over a large area

  • Conversion into seismic velocity bounds


Inversion with the seismic parameterization

Inversion with the seismic parameterization

seismically

acceptable models


Inversion with the seismic parameterization1

Inversion with the seismic parameterization

seismically

acceptable models


Inversion with the seismic parameterization2

Inversion with the seismic parameterization

seismically

acceptable models


Thermal parameterization of the old continental uppermost mantle

Thermal parameterization of the old continental uppermost mantle


3d temperature model of the uppermost mantle

3D temperature model of the uppermost mantle


3d temperature model of the uppermost mantle1

3D temperature model of the uppermost mantle


Lithospheric thickness and mantle heat flow

Lithospheric thickness and mantle heat flow

Power-law relation between lithospheric thickness and mantle heat flow is consistent with the model of Jaupart et al. (1998) who postulated that the steady heat flux at the base of the lithosphere is supplied by small-scale convection.


Conclusions

Conclusions

Seismic surface-waves and surface heat flow data can be reconciled over broad continental areas, i.e., both types of observations can be fit with a simple steady-state thermal model of the upper mantle.

Seismic inversions can be reformulated in terms of an underlying thermal model.

The estimated lithospheric structure is not well correlated with surface tectonic history.

The inferred relation between lithospheric thickness and mantle heat flow is consistent with geodynamical models of stabilization of the continental lithosphere (Jaupart et al., 1998).


3d seismic model

3D seismic model


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