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hornbeastdanishMechanics

Nov 14, 2013 (3 years and 11 months ago)

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The Earth’s Paleozoic/Mesozoic tectonic and paleogeographic evolution

Kara Matthews, Nicolas Flament, Dietmar Müller

Continents and sedimentary basins through time have recorded fundamental Earth
system cycles, reflecting environmental change, migration
of fauna and flora and
shifting coastlines. It was originally thought that successive advances and retreats of
shallow inland seas mainly reflect global sea level variations (eustasy). However, it is
now well established that large
-
scale surface morphology

such as the high
topography of the East African Rift, the low
-
lying Amazon River Basin and the
southwest to northeast tilt of the Australian continent are strongly controlled by
processes deep within the Earth. Quantifying the magnitude and time
-
dependen
ce
of mantle
-
driven topography requires integrating geological data with coupled
models of the plate
-
mantle system. In turn, these models need to be validated with
observational data, such as published paleogeographic maps and paleobiology data.




The ov
erarching aim of these projects is to understand the deep
-
seated driving
forces of large
-
scale topographic change, providing dynamic models of the Earth’s
subduction history, deep plume sources and dynamic topography for the Paleozoic
-
Mesozoic periods. Th
e Paleozoic follows the breakup of the supercontinent Rodinia
after the end of the so
-
called Snowball Earth period. Throughout the early Paleozoic,
the Earth's landmass was broken up into a substantial number of continents.
Towards the end of the era, cont
inents gathered together into the supercontinent
Pangaea. We offer two Honours projects focussed on building models for the
Paleozoic/Mesozoic Earth using the software
GPlates
, and using geological
observations to test geodynamic models, which predict man
tle convection patterns
and surface uplift/subsidence through time:

Project 1: The evolution of proto
-
Atlantic/Indian ocean basins and marginal seas
in the Cambrian to Devonian

Project 2: The evolution of proto
-
Atlantic/Indian ocean basins and marginal s
eas
in the Carboniferous to Jurassic


These projects
will address the following questions:



How were ocean basins, including back
-
arc basins, created and destroyed
between the Cambrian and Jurassic periods?



How have the fundamentally different plate tectoni
c configurations before and
during/after the assembly of the supercontinent Pangea affected subduction
history, the history of mid
-
ocean ridge system evolution, mantle convection
patterns and ultimately regional sea level fluctuations?


The projects will
involve acquiring various software an
d database skills, including
GPlates
, including s
patio
-
temporal data mining, Arc
GIS, the Generic Mapping Tools,
shell scripting, dealing with the paleobiology database, as well as learning the b
asics
of geodynamic model
ling. These
projects will prepare students both for working in
the exploration industry as well as for a research
-
oriented career in government
agencies or universities.


Constructing a revised plate tectonic history for the Caribbean

Supervisors:
Prof Dietmar Müller,
Dr

Simon Williams

The Caribbean has witnessed a complex geological evolution during the last 150 Ma.
Understanding this history, in particular tracking the locations and polarity of
subduction zones within this region, has important im
plications for geodynamic
modeling of the area. However, there remains much debate amongst geoscience
researchers over some of the fundamental details of this area’s plate tectonic history


for example the polarity of subduction along the so
-
called ‘Great

Arc’ of the
Antilles during the Cretaceous, and whether or not a large Oceanic Plateau collided
with this arc.

The model of Ross and Scotese (1988) provides a quantitative
framework

of how the
different plates and magmatic arc fragments evolved within thi
s region. However, a
wealth of new geological and geophysical data have been collected during this time,
and there is a clear need to reassess these earlier models in the context of these new
data. Numerous authors propose alternative reconstruction histor
ies in terms of
simple cartoons for small regions of study. In our case
you

will use
GPlates

(plate
tectonic analysis software developed by the Earthbyte group) to test and generate
truly quantitative models that fit within
a

globally consistent plate mode
l.

The central aim of this project will be to derive revised plate reconstructions for the
Caribbean. The project will be multidisciplinary in nature


collating data from online
sources and the scientific literature that tell us about the nature and timin
g of
geodynamic processes occurring throughout the Caribbean


for example
magmatism, subduction, phases of extensional and compressional deformation. You
will then assimilate all these data within
GPlates
, and use these constraints to test
existing models

of Caribbean geodynamics and generate a new set of plate
reconstructions including plate boundary locations and plate velocities. This project
will also involve the analysis of seismic tomography and geodynamic modeling
output to help validate the chosen
locations of subduction
.



Tilting continents: influence of dynamic topography on relative sea level

Supervisors
: Nicolas Flament, Dietmar Müller

It has long been identified that continents tilt as they drift over the convecting
mantle. Recent work has
shown that mantle convection makes it impossible to
determine global sea level at a single passive margin. The aim of this project is to
estimate the relative contributions of mantle convection and global sea level change
to the waxing and waning of conti
nental interiors by shallow seas observed in the
geological record.


Continental dynamic topography at 101 Ma (left), and its rate of change (right)
between 111 and 101

Ma, both shown in the present
-
day frame of reference

The project will involve analysin
g the dynamic topography and its rate of change
predicted by global mantle flow models (example shown on figure) and comparing
them to geological constraints. This will require the use of analytical skills, basic
scripting (in shell, python or other) and
the use of various software skills, including
GPLates
, the Generic Mapping Tools.
Part of a large industry collaboration, this
project will prepare students both for working in the exploration industry as well as
for a research
-
oriented career in governmen
t agencies or universities.

Tectonic evolution of the eastern Tethys

Supervisors: Dr S
imon Williams, Dr Kara Matthews

The continental margins of the Tethys Ocean have undergone a largely
uninterrupted history of sedimentation and carbonate platform build
-
up over the
last 500 Myr, accentuated by episodes of rift basin formation, broad subsidence and
major transgressions in

the mid
-
late Cretaceous. While the contribution of mantle
flow to the flooding of other continents (e.g. Cretaceous North America) has long
been established, it is still unknown to what extent
f
looding

in Eurasia

at this time, or
any other time, is due to

dynamic topography. Part of the problem is a lack of
detailed plate reconstructions within a deforming plate framework for the area to
use as surface boundary conditions into numerical models. In this project, you will
construct an end
-
member plate kine
matic model for the opening and closure of the
Eastern Tethys Ocean, which will include a detailed history of microcontinent
accretion and back
-
arc basin formation along the southern Eurasian margin and
rifting and basin formation along the western Austral
ian margin
. These
reconstructions will be examined in the context of paleo
-
geographic maps and
compared to geodynamic model output to better resolve the continental flooding
history along the northern Tethyan margin.

3D Numerical Experiments of Salt Tecton
ics

Supervisors:

A/Prof
Patrice Rey, Luke Mondy and
Dr

Sascha Brune

Evaporite deposits exert a very strong control on the structural evolution of rift
basins. Because of its capacity to flow at upper crustal temperatures and under small
deviatoric

stresses, salt allows for the mechanical decoupling of the post
-
salt
sedimentary sequences, which can slide above pre
-
salt strata. These gravitational
décollements produce significant extensional and contractional structures, as well as
salt diapirs and
salt canopies often closely related to hydrocarbon traps. Through a
series of 3D numerical experiments, the project aims to understand how the
thickness, depth and viscosity of the salt layers control the style, distribution and
magnitude of deformation.
This project doesn’t require any particular computational
skills and can suit an astute student interested to develop computational skills.


Landscape connectivity through the Wilson cycle: Implication for biodiversity

Supervisors:

A/Prof
Patrice Rey,
Guil
laume Duclaux and Luke Mondy

We know that plate tectonics, through continental break
-
up, is a major driver for the
evolution of species. At the scale of each continent, landscape connectivity favour
natural selection processes, which impediment to biodive
rsity. In the contrary,
during orogenic periods, the fragmentation of landscape favour the multiplication of
ecological niche driving species differentiation and favouring biodiversity. This
pioneering project aims at investigating how tectonic processes
coupled to surface
processes interplay to control landscape connectivity. The project will involve
studying how a fragmented landscape, made of multiple drainage basins, high
mountain ranges, elevated plateaux and deep valley, evolves under the action of
erosion, sediments transport and accumulation. If time permit, the project will also
investigate the evolution of a highly connected landscape during orogenesis.


What Happens to the Continental Crust Once it Has Been S
ubducted?

Supervisors:
Patrice Rey,
Christian Teyssier

(
Univ. of Minneapolis
)

and Donna
Whitney (Univ. of Minneapolis)

Continental subduction is the process through which the continental crust gets
dragged into a subduction

zone burying the continental crust deep into the diamond
stability field (>150km). The subduction of the continental crust is however limited
by the buoyancy of the crust. It is not clear what happens to the continental crust
once the maximum depth is rea
ched. Does the crustal slab melt and rise through the
overriding mantle wedge as a large crustal diaper that flattens out at the base of the
overriding crust, or does the slab get exhumed back to the surface as a rigid buoyant
slab? Also important is the q
uestion of how the growing gravitational force related
to the subducting continental crust impacts on the converging continents.

This project aims at exploring the processes controlling the relaxation of subducted
continental crusts. The project involves 2
D and 3D thermo
-
mechanical experiments

using
Underworld
.

The subduction of Baltica under Laurentia (440
-
390 Ma) will be
used as a prime example providing first order constraints on the timing of
continental subduction as well as the PTt paths followed by e
xhumed high
-
pressure
crustal eclogites.


The role of gravitational forces in the opening of back
-
arc basins: application of the
opening of the Aegean Sea

Supervisors: Patrice Rey

Slab rollback, the oceanward motion of the subducting oceanic lithosphere, is

a
favourite amongst the processes leading to back
-
arc extension and detachment of
micro
-
continents from continental mainlands. A different way to interpret the
dynamic of back
-
arc extension involves gravitational forces that arise from the
thinning of the

lithospheric mantle. A recent set of numerical experiments show that
gravitational forces can drive back
-
arc extension forcing slab rollback. Coeval
extensional and contractional tectonics in the overriding plate is a key observable
that can help to decip
her between rollback
-
driven back
-
arc extension and back
-
arc
driven slab rollback.

This project aims at exploring further the link between gravitational forces and back
-
arc extension and to apply this new concept t
o the opening of the Tasman Sea,
the
Aegean

Sea

and the evolution of the Appennines
.

How far can the lower crust flow?

Supervisor: Patrice Rey

Gravitational potential energy stored in an orogenic

plateau can be strong enough to
deform the surrounding region (foreland), hence contributing to both plateau
growth and collapse. Gravity
-
driven channel flow from the plateau lower crust into
the foreland lower crust, called channel extrusion, has been pr
oposed as a main
contributor to the eastward growth of the Tibetan plateau, possibly driving the
lower crustal channel as far as 2000 km in 15 myr, at an average flow velocity over
10 cm/yr. However, isostasy
-
driven upward flow in response to either erosio
n
focused on the plateau steep
margins, or stretching of the plateau upper crust to
produce domical structures (metamorphic core complexes), compete with horizontal
channel flow extrusion. Using 2D and 3D thermal
-
mechanical modelling, this project
aims at

exploring the dynamic coupling among the various flow processes that take
place during gravitational collapse and the assess the magnitude of channel
extrusion in southeast Tibet.


Multispectral
Mapping the Opalized Redox Front

in the Great Artesian

Basin

Supervisor: Patrice Rey, Gemma Roberts

The vast majority of precious opal is hosted in the Great Artesian Basin (GAB) in
central Australia, one of the largest intra
-
continental basins on Earth.
O
pal formed
via acidic oxidative weathering
following

the reg
ression of the
Eromanga Sea that
flooded c
entral Australia between 125 and 95 Ma.
This opalized horizon is now
preserved

below the Tertiary unconformity. Using multispectral satellite images
this
project

aims

i/ to construct at the scale of the Great Art
esian Basin a 3D map of the
unconformity between Tertiary sedimentary rocks and the Lower
-
Cretaceous
formations
, and ii/

to map
where the

opalized redox front
has been preserved and
where it has been eroded
. This project will be appropriate for a student
willing to
become an expert in satellite image processing,
and
3D surface modelling.


C
ontrol of
inherited
fault patterns on rift
evolution

Supervisors:

Sascha Brune and

Patrice Rey

The architecture of continental rift systems (e.g

East Africa), and passive margins
(e.g. Africa
-
South America, Australia
-
Antarctica) is controlled by plate kinematics,
rock rheology, and volcanism.
This
research field

is
of special importance

to the
hydrocarbon industry, since
rift basins

are primary ta
rget for exploration.

H
ere
you have the opportunity to evaluate the impact of inherited fault networks on
the evolution of rift systems and subsequent passive margin formation. Using an
established geodynamic model setup, you will study the effect of rand
om initial fault
patterns on key rift properties: symmetry, basin depth, and margin width.

This will
require

basic analytical skills and some computational competence for
scripting

and
model visualization.


Rate of deformation for two rift models with di
fferent random initial fault patterns
but otherwise identical properties.
This illustrates the impact of the initial fault
configuration on overall rift dynamics.


Sinking slabs: Deciphering the 200 My memory of Earth’s mantle

Supervisors:

Sascha Brune,
Nicolas Flament,

and

Dietmar Müller

At subduction zones, dense lithospheric slabs are pulled into the inside of the
Earth where they sink for hundreds of millions of years towards the core mantle
boundary. The present day structure

of

Earth
’s mantle

as it
is imaged through
seismic tomography contains information on the locations of ancient subduction
zones and past plate motion. When deciphering this information, the movement of
slabs within the convecting mantle of the Earth must be taken into account.

How
ever, fundamental physical properties of the deep Earth (e.g. the viscosity
distribution) are not easily accessible.

Within this project you will apply an established numerical model of mantle
convection. The aim is to evaluate the vertical and lateral vel
ocities of subducted
slabs for different viscosity distributions of Earth’s mantle

which will give new insight
into the viscosity distribution

of the deep Earth.
By comparing the numerical results
to seismic tomography images (see Figure below), you will e
stablish a link between
past plate motions and present
-
day mantle structure.

This will be important in order
to enhance absolute plate motion models before 100 My.

You will be trained in using the plate tectonics software GPlates, th
e mantle
convection mod
el Terra, standard

visualization tool
s

(GMT and
Paraview
) and basic
scripting. You will acquire valuable insight into geodynamic processes that are
ultimately responsible for the formation of georesources. This knowledge base might
make the difference when

you apply for positions in exploration industry or if you
start a research

career
at a university.



Comparing predictions of different numerical model setups (red, blue, black contours)
to present
-
day mantle structure from seismic tomography (in
background).