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· Web view Coeval extensional and contractional tectonics in the overriding plate is a key observable that can help to decipher between rollback-driven back-arc extension and back-arc

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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-dependence 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 overarching 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. The 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, continents 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 mantle 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 seas 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 tectonic 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 and database skills, including GPlates, including spatio-temporal data mining, ArcGIS, the Generic Mapping Tools, shell scripting, dealing with the paleobiology database, as well as learning the basics of geodynamic modelling. 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 implications 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 this 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 histories 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 model.

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 timing 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 continental 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 analysing 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 government agencies or universities.

Tectonic evolution of the eastern Tethys

Supervisors: Dr Simon 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 flooding 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 kinematic 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 Australian 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 Tectonics

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, Guillaume 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 biodiversity. 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 Continen

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