High grade blueschist metamorphism on the Aegean island of Syros involves the widespread growth of the calc-silicate minerals lowsonite, zoisite and epidote/clinozoisite in a wide range lithologies. In calcareous metasediments the only realistic lawsonite-generating reaction appeared to be one involving calcite-breakdown and thus for significant reaction CO<SUB>2</SUB> would have to have been flushed from the rock by the infiltration of a water-rich fluid. The distribution of lawsonite was mapped in the metasediments. Structural mapping was used to elucidate the strain history of the syn-blueschist deformation. Detailed petrographic and microfabric analysis of relevant samples was undertaken to document their petrologic and microstructural development and to identify lawsonite forming reactions. Changes in bulk rock composition accompanying the growth of lawsonite were assessed. The results show that in the greyschist units of northern Syros lawsonite growth is controlled by a syn-deformational, fracture-controlled fluid infiltration event traces of which are visible as quartz veins. Ca-bearing, water-rich fluid pervasively infiltrated the schists adjacent to the fractures resulting in the growth of large amounts of lawsonite by metasomatic reactions involved the breakdown of mica. The scale of fluid transport and therefore the extent of metasomatic alteration is controlled by the deformation and compositional variation. These observations confirm the suggestion in the previous studies that lawsonite growth is at least partially controlled by the infiltration of an externally-derived fluid. The preservation of small scale variation in fluid composition within significant parts of the metasediments is explained by the channelized nature of the event.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641732 |
| Date | January 1998 |
| Creators | Bloor, Philip Martin |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10830 |
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