By historical geodynamics we mean that we explicitly link time-dependent
geodynamic models to the geological record.
These approaches complement those of
present day geodynamics in that we
compare the models against different kinds of the data
than traditional geophysically orientated geodynamic models.
The complementary data sets are time-dependent
plate motions, the record of stratigraphic deposits onshore and
offshore, and the record of volcanism.
The historical and present-day models each have with their strengths
On this page, we look at several studies that show the deversity of our
work and the important role they are playing in pure and applied
We will at some regional models of anomalies vertical motions.
This is followed by explicit work on global sea level change
over millions of years.
Finally, we look at the initiation of a new subduction zone.
Much of the work linking geodynamic models with plate
reconstructions has been completed by
closely working with Dietmar Müller and his
Team at the University of Sydney. We've worked closely to develop
GPlates, a open source Paleogeographic
Figure 1. Results for an inverse geodynamic model starting with scaled
seismic velocity (vs) scaled to temperature and integrated backward to
100 Ma from
Liu, Spasojevic & Gurnis.
The vertical cross sections show the scaled temperature field and
the horizontal surface maps show dynamic topography.
The cold slab (blue in cross section), and associated negative
dynamic topography (green and blue in map) are migrating from west to east.
This image was created from our data by Bernhard Steinberger
(then at the Norwegian Geological Survey)
who created this visualiztion for a Perspective
he wrote for
Regional Models and the North-America Cretaceous seaway
Inverse geodynamic models exploited the seismically resolved Farallon slab below the eastern-half of the United States and the well studied sedimentary section of the Cretaceous interior seaway that has long been recognized as forming in response to mantle flow.
The global models employed an adjoint method, which backward reverses mantle convection,
with the present-day mantle structure constrained by seismic tomography
and the time-dependent evolution by plate motions and stratigraphic data.
The application of the adjoint method to mantle convection was an important
part of Lijun Liu's Ph.D. these at Caltech and he wrote up details of the
methods in a
By synthesizing proxies for North American vertical motions from the late Cretaceous to the present (e.g. paleoshorelines and borehole tectonic subsidence curves), we reconstructed the geometry of the Farallon slab (Fig. 1).
The dynamic topography associated with the subduction of the Farallon slab is localized in western North America over the late Cretaceous, representing the primary factor controlling widespread flooding.
The dynamic model was later shown to be consistent with late Mesozoic uplift of the Colorado Plateau, and the migration of the depocenter of the hydrocarbon bearing, late Cretaceous succession across central Utah, Colorado, and southern Wyoming. While previous simplified geodynamic concepts did not predict a migrating depocenter, similar predictions are common in our dynamic models and provide an opportunity to understand such patterns commonly seen in the stratigraphic record.
Former geophysics graduate students Lijun Liu and Sonja Spasojevic
collaborated on the application of this adjoint method to North
American Cretaceous seaway. Read our People's Page
to read about the current and former graduates of the geodynamics
The models of North America are examples of regional geodynamic models.
Interestingly enough all of our regional models are within a global
domain, but we have formulated the problems so as to avoid
problems with "edge effects". Besides, application to North America,
we have applied our models to a variety of other locations,
Including Australia, New Zealand, South America and South East Asia.
Here are just some examples, with some links to the relevant papers.
There are many more examples found by going to Michael Gurnis's
Sonja completed a study of the anomalous subsidence of the
Campbell Plateau with
Rupert Sutherland of GNS Science.
As a visiting student at Caltech, Lydia DiCaprio completed a
study on the
Cenozoic tilting and subsidence of Australia.
Sydney graduate student Grace Shephard applied the adjoint models
to the reversal of the
North China Craton
Professor at China University of Geoscieces in Beijing, we are working on
linking the evolution of the North China Craton with geodynamic models.
With constraints from structural geology, sedimentology,
geochoronology, and geodynamic modeling, we are deciphering
the relations between the subduction history of paleo-Pacific plate
and the response of shallow basin and range above the
North China Craton (NCC) during its destruction process.
By combining the global tectonics,
the oceanic and continental geomagnetic fields,
regional seismic tomography, and the constraints from
the shallow geological structure, we are constructing the
3-D subduction model of western paleo-Pacific plate since 200 Ma,
including to simulate the subduction history and to
study the deep mantle convection and evolution of shallow structures.
Based on the above results, we shall be able to
explore the geodynamic explanations between the destruction of
North China Craton and the subduction of paleo-Pacific plate.
Global Sea Level
With the volume of ocean water assumed constant over millions of years,
global sea level on geologic time scales results
from a change of:
ocean bathymetry due to variations in ocean floor age,
dynamic topography in oceanic and flooded continental areas,
emplacement of oceanic plateaus, and sedimentation.
As part of her Ph.D., Sonja Spasojevic generated dynamic
earth models to better understand the origin of global and
regional sea level change.
Predicted global sea level by DEMs shows an overall decrease from the Late Cretaceous to the present, with a maximum at 80 Ma.
She used dynamic earth models are used to better understand the impact of
mantle dynamics on vertical motion of continents
and regional and global sea-level change since the Late
Her hybrid approach combined inverse and forward models of mantle
convection, and accounted for the principle contributors
to long-term sea-level change: the
evolving distribution of ocean floor age, dynamic topography in
oceanic and continental regions, and the geoid.
She inferred relative importance of dynamic versus other factors of
sea-level change, determined time-dependent patterns of dynamic subsidence
and uplift of continents, and derived a sea-level curve.
She found that both dynamic factors and the evolving distribution of
sea floor age are
important in controlling sea level.
By tracking the movement of continents over large-scale
dynamic topography by consistently mapping between mantle and plate
reference, she found that this movement resulted
in dynamic subsidence and uplift of continents.
The amplitude of dynamic topography in continental regions is larger than
global sea level in several regions and periods,
so that it controls regional sea level in
North and South America and Australia since the Late Cretaceous, North Africa and
Arabia since the Late Eocene,
and Southeast Asia in the Oligocene-Miocene period. East
and South Africa experience dynamic uplift over the last
20-30 million years, while
Siberia and Australia experience Cenozoic tilting.
The dominant factor controlling global
sea level is a changing oceanic lithosphere production that results in a large amplitude
sea-level fall since the Late Cretaceous, with dynamic topography offsetting this fall.
Components of the hydrid dynamic earth models used to compute region
and global sea level change. Both maps are at 80 Ma.
Above: age of the oceanic lithosphere from the work of
Maria Seton of
the EarthByte group, vectors of plate motion and observed marine
inundation onto the continents.
Below: Sonja Spasojevic's predicting flooding and shorelines from
the hydrid dynamic earth models.
Initiation of Subduction
Subduction initiation, although only a transient phenomenon,
is a vital phase of the plate tectonic cycle. Long-lived and well-developed subduction zones disappear and new subduction zones form.
Indeed, nearly half of all presently active subduction zones
initiated during the Cenozoic.
This record provides a rich geological history that can be used to validate dynamic models.
As such, we have an active program to try and better understand the
dynamics of subduction initiation and link such models explicitly to
the geological record. Over the years, Gurnis has worked on this problem
with a number of students and post-docs and that work cointinues
Theoretical studies, and interpretation of the Mesozoic and
later plate tectonic history of the Pacific, suggest that
subduction initiation alters the force balance on plates.
If we hope to make fundamental advances in understanding the forces driving
and resisting plate motions, then a detailed picture of
subduction initiation is needed. After a hiatus of a number of years, computational and synthesis models of subduction initiation are now being advanced.
The best examples where we know subduction started and has since evolved
into fully self-sustaining subduction zones, include the Eocene initiation
of the Izu-Bonin-Marianas (IBM) and Tonga-Kermadec.
Earlier, we have formulated models with fault or shear zone development
in a visco-elastoplastic material.
We use a simple geometry to illustrate the tectonic precursors to
the transition from forced to self-sustaining subduction.
When the plate is compressed with a weak structure, there will be uplift on one side of the shear zone; as compression continues, a paired topographic feature results, with a high ridge adjacent to a trough.
With further compression, the dip of the shear zone becomes shallower and the two sides slide past each other.
The force required to compress the system can increase during this period as the underthrust plate bends.
As more cold oceanic lithosphere is thrust below the overriding plate, the ridge subsides.
Depending on the amount of convergence, the overriding plate will uplift and subside over a period of ~5-10 Myr.
This reversal in vertical motion heralds the transition from forced to self-sustaining subduction.
Wei Leng, we have started to better understand the factors
of subduction initiation.
Changes of plate motion may have induced subduction initiation (SI),
but the tec
tonic history of SI is different from one subduction zone to another.
Izu-Bonin-Mariana (IBM) SI, accompanied by strong backarc spreading
and voluminous eruption of Boninites, contrasts with the Aleutians
which shows neither.
Using finite element models, Leng & Gurnis explored
visco-elasto-plastic parameters and driving boundary conditions for
SI evolution. With an imposed velocity, they
found three different evolutionary modes of SI:
continuous without backarc spreading,
continuous with backarc spreading and a segmented mode.
With an increase in the coefficient of friction and a decrease
in the rate of plastic weakening, the amount of convergence needed for
SI increases from ~20 to ~200 km, while the mode changes from segmented
to continuous with backarc spreading and eventually
to continuous without backarc spreading.
imposed velocity boundary condition is replaced with an
imposed stress, the amount of convergence needed for SI is reduced and
backarc spreading does not occur. These geodynamic models provide a
basis for understanding the divergent geological pathways of SI:
First, IBM evolution is consistent with subduction of an old strong
plate with imposed velocity which founders causing intense
backarc spreading and Boninitic volcanism.
Second, the New Hebrides SI is in the segmented mode due to its weak
Third, the Puysegur SI is in the continuous without backarc spreading
mode with no associated volcanic activities.
Fourth, the Aleutians SI has neither trench rollback nor backarc
spreading because the slab is regulated by constant ridge push forces.
Figure 3. A new study of subduction initiation was recently
published by Wei Leng.
Leng, W. and Gurnis. M.,
Dynamics of subduction initiation with different evolutionary pathways,
Geochemistry, Geophysics, Geosystems, 12, Q12018, doi:10.1029/2011GC003877.
Spasojevic, S., L. Liu, and M. Gurnis,
Adjoint models of mantle convection with seismic, plate motion and stratigraphic constraints: North America since the Late Cretaceous,
Geochemistry, Geophysics, Geosystems, 10,Q05W02, doi:10.1029/2008GC002345, 24 pp., 2009.
Liu, L., S. Spasojević, and M. Gurnis,
Reconstructing Farallon plate subduction beneath North America back to the Late Cretaceous,
Science, 322, 934-938, DOI:10.1126/science.1162921, 2008.
Gurnis, M., Hall, C., Lavier, L.,
Evolving force balance during inipient subduction, Geochemistry, Geophysics, Geosystems, 5, Q07001, doi:10.1029/2003GC000681, 31 pp., 2004.
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Updated November 30, 2015
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