On the Aegean island of Naxos, four major fluid flow events (lp, 2r, 3r and 4r) occurred during Miocene greenschist- to amphibolite-facies metamorphism. I have made a study of grain-scale fluid pathways and the extent of isotopic equilibration at a number of localities across the island. I have combined ion microprobe analyses of <sup>18</sup>O/<sup>16</sup>O,<sup>13</sup>C/<sup>12</sup>C,<i> </i>Mn and Fe with detailed cathodoluminescence imaging to obtain direct evidence of grain-scale infiltration mechanisms, the timing of different fluid flow events and subsequent isotopic modification, fluid compositions, and the time scales of fluid infiltration. On Naxos, fluid flow was channelled and heterogeneous at all scales of observation. At the km-scale, the isotopic and petrological record of fluid flow is very variable. The metamorphic fluids (lp and 2r) were chemically and isotopically heterogeneous. Fluid pathways were probably controlled by deformation and lithological contrasts. A detailed study of a marble band was made at one locality. At the m-scale, the pattern of infiltration (resulting from buoyancy-driven flow) was controlled by the structure and permeability contrast of the lithological layering. An isotopic front formed at the bottom contact of the band as a result of advection of fluid along a network of cracks and grain boundaries, combined with volume diffusion into grains. The front represents the final product of at least two fluid flow events. Cm- to m-scale δ<sup>18</sup>O data provide only limited information about fluid flow events: multiple events cannot be distinguished. Modelling of bulk data may give misleading results as some of the assumptions made in applying chromatographic theory to metamorphic fluid flow are not valid. In summary, metamorphic fluid flow on Naxos was spatially and chemically heterogeneous at all scales of observation. Permeability was dynamically created and maintained: fluid pathways were controlled by deformation and lithological contrasts. Grain-scale fluid networks are transient: time scales of fluid flow are extremely short compared with time scales of metamorphism.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653852 |
| Date | January 1999 |
| Creators | Lewis, Stephanie |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15207 |
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