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Geochemical and stable isotope resetting in shear zones from Täschalp: constraints on fluid flow during exhumation in the Western Alps
Author(s) -
Cartwright I.,
Barnicoat A. C.
Publication year - 2003
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1046/j.1525-1314.2003.00423.x
Subject(s) - geology , shear zone , greenschist , schist , geochemistry , ophiolite , metamorphic facies , fluid dynamics , shear (geology) , metamorphism , petrology , mineralogy , metamorphic rock , geomorphology , facies , tectonics , seismology , structural basin , physics , mechanics
Fluid flow at greenschist facies conditions during exhumation of the western Alps occurred in several penecontemporaneous systems, including shear zones at lithological contacts, deformed contacts between serpentinite bodies and metabasalts, albite veins within metabasalts, and calcite + quartz veins within calcareous schists. Fluid flow in shear zones that juxtapose metasediments and ophiolitic rocks within the Piemonte Unit reset O and H isotope ratios. δ 18 O values are buffered by the wall rocks; however, calculated fluid δ 2 H values are similar within all the shear zones suggesting that they formed an interconnected network. The similarity of δ 2 H values of the sheared rocks and those of unsheared calcareous schists suggests that the fluids were derived from, or had equilibrated with, the schists that envelop the ophiolite rocks. Time‐integrated fluid fluxes at the sheared contacts estimated from changes in Si in metabasalts were up to 10 5 m 3 m −2 , with the fluid flowing up temperature driven either by topography or seismic pumping. Individual shear zones were active for c. 2–3 Myr, implying average fluid fluxes of up to 10 −9 m 3 m −2 s −1 . Rocks in shear zones within the ophiolite away from contacts with the metasediments show much less marked isotopic and geochemical changes, implying that fluid volumes decreased into the ophiolite unit, consistent with the source of fluids being the metasediments. Fluids were generated by dehydration reactions that were intersected during exhumation and, while many rocks show the affects of fluid–rock interaction, large‐scale fluid flow between major units was not common.