P-T-X-controlled element transport through granulite-facies ternary feldspar from Lofoten,Norway |
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| Authors: | Katharina Hartmann Richard Wirth Gregor Markl |
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| Institution: | 1.GeoForschungsZentrum Potsdam,Potsdam,Germany;2.Eberhard-Karls Universit?t Tübingen, Institut für Geowissenschaften,Tübingen,Germany |
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| Abstract: | Fluid transport on the grain-scale controls many rock properties and governs chemical exchange. Charnockites from Lofoten
indicate fluid penetration into ternary alkali feldspars controlled by their microtextures. In a process of fluid infiltration
at granulite-facies conditions (∼600°C and 8–11 kbar), tiny pyroxenes enclosed in alkali feldspar reacted to amphiboles, which
are always spatially connected to perthitic albite. Investigation of these microtextures by TEM imaging of Focused Ion Beam
(FIB) prepared foils revealed that pyroxenes in contact with albite lamellae show dissolution features. An amorphous Fe- and
Cl-bearing material interpreted to be a residuum of the percolating fluid was found within albite lamellae. Textures and mineral
compositions indicate that a Cl-rich aqueous fluid attacked the lamellae, which then provided pathways for further fluid flow.
A correspondence was found between feldspar compositions, their microtexture and their degree of alteration as a result of
their permeability for fluids at specific temperatures. Hence, in addition to pressure and temperature, small variations of
feldspar composition can strongly influence the fluid permeability of feldspathic rocks under lower crustal conditions. |
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| Keywords: | Feldspar Exsolution Pyroxene Amphibole Nanotunnel Fluid pathways Fluid alteration |
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