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Exhumation Paths (exhumation + paths)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Exhumation paths of high-pressure metapelites obtained from local equilibria for chlorite,phengite assemblages

GEOLOGICAL JOURNAL, Issue 3-4 2000
O. Vidal
Abstract The compositional variation of phengite and chlorite pairs in rocks sampled across the metamorphic zonation of three different blueschist belts (Cycladic, Sambagawa and Schistes Lustrés) is characterized from the regional to the thin-section scale. The different sample suites show different compositional trends, but similar trends are observed at the regional and thin-section scale in the same unit. At the thin-section scale, several local chlorite,phengite equilibria involving minerals of different compositions can be identified. These observations suggest that at temperature T <,,550°C, equilibration of chlorite and phengite compositions with varying pressure and temperature is controlled by crystallization/recrystallization processes rather than by changing the composition of older grains by lattice diffusion. In some instances, the relative time of growth of the different phyllosilicate generations can be determined using microstructural criteria. The observed compositional variations are interpreted and quantified in terms of pressure (P) and temperature (T) variations using new thermodynamic solution models accounting for the Tschermak, di/trioctahedral, and pyrophyllitic substitutions. Chlorite,phengite local equilibria constrain the shape of the exhumation P,T paths of the rocks under consideration. The assemblage chlorite,phengite,paragonite,albite,quartz,H2O can be used to constrain different P,T paths for Tinos and Sambagawa blueschists. Copyright © 2000 John Wiley & Sons, Ltd. [source]

Silica precipitates in omphacite from eclogite at Alpe Arami, Switzerland: evidence of deep subduction

JOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2002
L. F. Dobrzhinetskaya
Abstract Observations of oriented SiO2 precipitates in omphacite from eclogite with tholeiitic basalt protolith bordering the Alpe Arami garnet peridotite massif, Ticino, Switzerland, and petrological studies of the eclogitic mineral assemblages, suggest that this rock was subjected to higher-pressure metamorphism than previously realized. We employed various calibrations of the Fe2+ , Mg exchange thermometer and calculations of equilibria with thermodynamic data, considering the calcium,Tschermak's component (CaAl2SiO6), of garnet-pyroxene pairs. From these calculations, it is concluded that the eclogitic lenses have recorded at least four stages of mineral growth corresponding to the following: Stage I (prograde) c. 2.4 GPa; 700 °C; Stage IIa (maximum recorded grade) c. 7.0 GPa; 1100 °C; Stage IIb (retrograde) c. 3.7 GPa; 900 °C; Stage III (retrograde) c. 2.1 GPa; 750 °C. Because of the preservation of Stage I, a relatively rapid subduction and exhumation of Alpe Arami eclogite is suggested. The exhumation path of the eclogitic rock is in good agreement with most exhumation paths inferred for the Alpe Arami garnet lherzolite proposed previously by several authors based upon a variety of different observations, although the eclogite and peridotite exhumation paths may diverge at depths greater than 120 km. [source]

Modelling interactions between fold,thrust belt deformation, foreland flexure and surface mass transport

BASIN RESEARCH, Issue 2 2006
Guy D. H. Simpson
ABSTRACT Interactions between fold and thrust belt deformation, foreland flexure and surface mass transport are investigated using a newly developed mathematical model incorporating fully dynamic coupling between mechanics and surface processes. The mechanical model is two dimensional (plane strain) and includes an elasto-visco-plastic rheology. The evolving model is flexurally compensated using an elastic beam formulation. Erosion and deposition at the surface are treated in a simple manner using a linear diffusion equation. The model is solved with the finite element method using a Lagrangian scheme with marker particles. Because the model is particle based, it enables straightforward tracking of stratigraphy and exhumation paths and it can sustain very large strain. It is thus ideally suited to study deformation, erosion and sedimentation in fold,thrust belts and foreland basins. The model is used to investigate how fold,thrust deformation and foreland basin development is influenced by the non-dimensional parameter , which can be interpreted as the ratio of the deformation time scale to the time scale for surface processes. Large values of imply that the rate of surface mass transport is significantly greater than the rate of deformation. When , the rates of surface processes are so slow that one observes a classic propagating fold,thrust belt with well-developed wedge top basins and a largely underfilled foreland flexural depression. Increasing causes (1) deposition to shift progressively from the wedge top into the foredeep, which deepens and may eventually become filled, (2) widespread exhumation of the fold,thrust belt, (3) reduced rates of frontal thrust propagation and possible attainment of a steady-state orogen width and (4) change in the style and dynamics of deformation. Together, these effects indicate that erosion and sedimentation, rather than passively responding to tectonics, play an active and dynamic role in the development of fold,thrust belts and foreland basins. Results demonstrate that regional differences in the relative rates of surface processes (e.g. because of different climatic settings) may lead to fold,thrust belts and foreland basins with markedly different characteristics. Results also imply that variations in the efficiency of surface processes through time (e.g., because of climate change or the emergence of orogens above sea level) may cause major temporal changes in orogen and basin dynamics. [source]