Yeshu Kolodny recognized the importance of Shulamit Grosz’ magnificent documentation of the mineralogy of the Hatrurim Formation and helped transform our understanding through studies of its carbon and oxygen composition – both during its prograde heating (decarbonation-dehydration) stages and the retrograde cooling and weathering recarbonation and hydration changes. I shall concentrate here on the prograde stages. In pioneering work showing the isotopically light C-composition of carbonates, he was able to confirm that low d13C CO2 formed by near- surface burning of organic matter in the parent sediments and decarbonation reactions were critical factors of the metamorphism. Later work by Yeshu, Shulamit and myself refined this view showing that: (i) the sequence of mineral formation could be modeled in terms of a series of decarbonation-dehydration reactions (of the type calcite + ’shale’ ->Ca-Al silicates + CO2 + H2O); (ii) depletion in 18O in the silicate mineral phases could be modeled in terms of Rayleigh isotope fractionation during vapor distillation – the first time such fractionation was clearly shown in metamorphism; (iii) heating in oxygen-deficient rocks below the air-rock surface could have generated reduced carbon gases, which in turn could have promoted higher temperature burning.
The stable isotope-petrogenetic studies are a tribute to Yeshu’s vision. With the addition of radiogenic isotope-based dating studies showing metamorphism could have occurred from Miocene to younger times, the combustion nature of the Mottled Zone metamorphic process was confirmed as a mineralogically-rich high temperature combustion event. They have led to new studies of the retrograde processes, exotic mineral veining, controls of rock chemistry on mineralogy and sometimes very high temperatures resulting in coarse-grained paralava formation, which confirm the Mottled Zone metamorphism as a world-class geological event.