TECTONOPHYSICS I ELSEVIER Tectonophysics 255(1996) 163-174 Fluid inclusions in "Marmarosh Diamonds" " evidence for tectonic history of the Folded Carpathian Mountains, Ukraine

Fissures in the nappes of the Folded Carpathians contain euhedral quartz crystals known as Marmarosh Diamonds. Study of Marmarosh Diamonds collected from the nappes in the Ukrainian part of the Carpathians howed that these quartz crystals contain abundant primary syngenetic methane-rich and aqueous inclusions. Many of the early inclusions how evidence of "explosion " (decrepitation u der conditions of internal overpressure), caused by tectonic uplift of the enclosing sediments during Miocene times. Regional mapping of morphologic and microthermometric characteristics of inclusions indicates that the decrepitated inclusions display characteristic textural features and homogenization temperature patterns within the different nappes, suggesting that the various nappes have experienced significantly different burial-uplift histories. Thus, inclusions reveal an increase in depth of burial from the inner regions of the Folded Flysch Carpathians towards the outer regions: about 2 km for the Marmarosh nappe, 5 km for the Rahiv nappe, 7 km for the Porculec and Chornogora nappes and 10 km for the Krosno zone. The corresponding average geothermal gradients decreased from about 40-45°C/km for the Mannarosh nappe to about 20-25°C/km the Krosno zone. It is also concluded that the Marmarosh nappe followed a P-T path close to the original inclusion isochore, because inclusions from quartz crystals collected within this nappe show no evidence of decrepitation. On the other hand, inclusions in quartz from the Krosno zone show very intense xplosion features and the highest fluid densities that have been recorded for the region, suggesting that the Krosno zone was the most buried part of the Ukrainian Folded Carpathians during formation of the inclusions. 1