Fluid-rock interaction and thermal evolution during thrusting of an Alpinemetamorphic complex (Tinos island, Greece)

This study examines the fluid-rock interaction and thermal evolution along a thrust that juxtaposes calcite-rich marbles of high P-T metamorphic unit of the Attic-Cycladic Massif (Greece) on top of a lower-grade dolomite marb le unit. The Tertiary thrust represents a major phase of tectonic movement related to the decompression of the Alpine orogen in the Hellenides. The st able isotope signatures of the thrust plane and adjacent sections of the fo otwall and hanging wall rocks are characterized by significant carbon and o xygen isotope depletions. The depletion is most pronounced in calcite, but is almost entirely missing in coexisting dolomite. The isotopic patterns in the thrust zone can be explained by the infiltration of an externally deri ved water-rich H2O-CO2-CH4 fluid [X-C (= X-CO2 + X-CH4) < 0.05] at water-ro ck ratios on the order of 0.1 to 0.5 by weight. The fluid-induced calcite r ecrystallization is viewed as an important rheological control during thrus ting. The temperature evolution of the footwall, hanging wall and mylonitic tectonic contact was determined by calcite-dolomite solvus thermometry. Hi stograms of calcite-dolomite temperatures are interpreted as indicating a h eating of the footwall dolomite marble during the thrusting of the hotter u pper plate. Conversely, the hanging wall marble unit was cooled during the thrusting. The calcite-dolomite thermometry of the thrust plane gives tempe ratures intermediate between the initial temperatures of the lower and uppe r marble units, and this leads to the conclusion that conductive heat trans fer rather than fluid infiltration controlled the thermal evolution during thrusting.