The flow of surface-derived fluids through Alice Springs age middle-crustal ductile shear zones, Reynolds Range, central Australia

I. Cartwright, I. S. Buick

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Abstract

The south-east Reynolds Range, central Australia, is cut by steep north-west-trending Alice Springs age (c. 334 Ma) shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement. Amphibolite facies (550-600 °C, 500-600 M Pa) shear zones cut metapelites, while greenschist facies shear zones (420-535 °C, 400-650 M Pa) cut metagranites. The sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow. Altered granites within greenschist facies shear zones have gained Si and K but lost Ca and Na relative to their unsheared counterparts, suggesting that the fluid flowed down-temperature (and hence probably upward) through the shear zones. Time-integrated fluid fluxes calculated from silica addition are up to 2.1 x 1010 mol m-2 (c. 4.2 x 105 m3 m-2). Similar time-integrated fluid fluxes are also estimated from changes in K and Na. The sheared granitic rocks locally have δ18O values as low as 0‰ which is much lower than the δ18O values of the adjacent unsheared granites (7 to 9‰), implying that the fluid which flowed through these shear zones was derived from the surface. For the estimated time-integrated fluid fluxes, the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres. The flow of surface-derived fluids into the ductile middle crust, with subsequent expulsion upwards through the shear zones, may have been driven by seismic activity accompanying the Alice Springs deformation.

Original languageEnglish
Pages (from-to)397-414
Number of pages18
JournalJournal of Metamorphic Geology
Volume17
Issue number4
DOIs
Publication statusPublished - 1 Jul 1999

Keywords

  • Metasomatism
  • Meteoric fluids
  • Oxygen isotopes
  • Shear zones

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