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Physicochemical properties of crustal fluids in fluid inclusions

English title Physicochemical properties of crustal fluids in fluid inclusions
Applicant Diamond Larryn W.
Number 122131
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geochemistry
Start/End 01.10.2008 - 31.03.2009
Approved amount 55'562.00
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Keywords (8)

Fluid inclusions; hydrothermal; experimental; synthesis; fluid; plastic deformation; paleo-fluids; systematics

Lay Summary (English)

Lead
Lay summary
Geochemical and petrographic analyses of fluid inclusions in minerals show that pore-fluids dominated by CO2, H2O and NaCl play important roles in hydrothermal ore deposition, metamorphism, igneous petrogenesis and rock deformation. Progress in understanding fluid-rock interaction in the above processes is hindered by a lack of criteria to assess whether specific fluid inclusion samples have preserved their original properties during post-entrapment evolution of rock stresses and pore-fluid compositions. For example, it is not clear which combinations of gradients in pressure and chemical-potential may drive post-entrapment loss or gain of H2O (or other species) from the inclusions, via diffusion through the host mineral to the surrounding pore-fluid. Similarly, the fluid inclusion textures that result from post-entrapment changes in external overpressures or underpressures are not well enough characterised to be diagnostic. Nothing is known about the effects of moderate amounts of plastic deformation on fluid inclusions in minerals. To redress these deficiencies we are carrying out two kinds of "reequilibration" experiments at pressures up to 700 MPa and temperatures up to 600 °C. In the first, we subject synthetic fluid inclusions to gradients in pressure and chemical potentials under hydrostatic conditions in hydrothermal autoclaves, then we analyse the resulting changes in inclusion textures, composition and molar volume. These experiments simulate the changes in pressure and pore-fluid chemistry that may affect inclusion-bearing rocks when they are driven through tectonic cycles. In the second type of experiment, we subject natural inclusion-bearing quartz to differential (non-hydrostatic) stresses in a Griggs-type piston cylinder apparatus, and thereby strain the host crystal plastically. We then analyse the resulting changes in inclusion textures, composition and molar volume, and compare them to naturally deformed samples from quartz veins in Alpine shear zones. The results will provide a set of petrographic and microthermometric criteria so that geologists will be able interpret the significance and reliability of inclusion samples that have experienced elevated pressures, elevated temperatures and ductile deformation following their entrapment.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
111834 Physicochemical properties of crustal fluids in fluid inclusions 01.07.2006 Project funding (Div. I-III)

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