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Dipartimento Scienze Geologiche
Università Roma TRE
Largo San Leonardo Murialdo, 1
00146 Roma, ITALY
Office: +39 06 57 33 80 24 Lab: +39 06 57 33 80 62 Fax: +39 06 57 33 82 01
flora.bajolet|at|uniroma3.it
flora bajolet's geopage - Ph.D. student at University Roma3 -
Welcome!
PROFILE
Current position: PhD. student at Roma TRE University (Italy)
Fellowship: working within the Crystal2Plate network (Marie Curie project)
Research topics
- Relationships between deep processes and their surface consequences in mountain building, especially topography: delamination, flexure of the lithosphere and isostatic rebound
- Lithosphere deformation: crustal flow inside and at the margin of high plateaux (Himalaya-Tibet, Andes...), exhumation of high grade rocks
Methods
- Analog modeling: 3D experiments, lithospheric deformation, mantle flow, topography...
- Field work: tectonics, structural geology...
Areas of interest: Himalaya-Tibet, Andes, Colombia, Sierra Nevada California
SCIENTIFIC INTERESTS
Delamination
Delamination has often been cited to explain regional uplift (usually associated with alkaline volcanism) either by "peeling" of the lithospheric mantle and in some case a part of the lower crust, or by viscous dripping (convective removal). Various geodynamic contexts such as high plateaux near a plate boundary (Tibet, Andes, Anatolia...) or smaller-scale intracontinental plateaux (Sierra Nevada California, Colorado plateau...) could be places where delamination occurs(ed).
Up to now, the analog model's set-up is built to test the "peeling model" with 3 lithospheric layers (upper crust, lower crust, lithospheric mantle) lying on an asthenospheric-like material. Record of topography and mantle flow during the experiment allow us to test the influence of several parameters (density, viscosity, geometry) on the dynamics of delamination and related topographic response.
Areas of dynamic uplift and subsidence can be traced as they move across the plate following delamination's motion and mantle flow, as well as isostatic uplift of the delaminated area. Improvements of the set-up to test different boundary conditions such as shortening or an adjacent suduction zone will be considered.
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Top view, dynamic subsidence and uplift induced by delamination |
Flexure of the lithosphere and isostatic rebound
Flexure has been the subject of numerous studies, both to develop theoritical models (elastic, visco-elastic, one or several layers...) and apply them to natural cases (glacial rebound, volcanoes, sedimentary basins loading and unloading...). It is also a crucial parameter used to estimate mantle viscosity. Computation of dynamic topography also imply to substract isostatic and flexural components. However, flexural models have not yet been tested with analogical methods.
I thus performed some simple experiments with loading and unloading of a silicone plate (visco-elastic lithosphere) with underlying asthenospheric analog material (viscous). Phases of fast elastic, then slow viscous relaxation are clearly identifiable. Exploration of various parameters, improvement of the experimental set-up involving an elastic layer, and comparison with similar numerical experiments are planed.
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Crustal flow and high plateaux
A very intriguing phenomenon highlighted in the 1980s' is the syn-convergence extension that may develop in mature mountain belts during gravitational collapse. One of the most studied examples are the Himalayas and adjacent Tibetan plateau. Mechanisms of deformation inside the plateau, lateral escape, and exhumation of high grade rocks (High Himalayan Cristallines) at the plateau's margin participating in crustal flow and mass redistribution, are still vividely debated.
In order to explore these questions, I realised gravity-scaled analog models simulating the shortening of two adjacent lithospheres: a strong one representing the Asian craton, and a weak one representing the Tibetan plateau. The model is layered with sand (brittle crust) and silicones (lower crust and lithospheric mantle) placed on a low-viscosity material (asthenosphere). In free boundary experiments, lateral escape of the model is allowed by placing a neutral (very weak) silicone at one side.
As shortening of the model proceeds, the very weak and deeper level of plateau's crust overthrusts the cratonic lithospheric mantle and injects the cratonic lower crust. This overflowing channel does not reaches the surface and its timing and shape depends on several parameters (rheology, shortening velocity,...). An important back-flow in the middle crust accompagnies this exhumation and feeds the homogeneous thickening of the plateau. Free boundary experiments allow lateral escape of the model, the plateau extruding preferentially, and delays the development of the overflowing channel. Strain partitioning and modalities of lateral escape depends on the strength of both lithospheres and resistance at the free boundary.
