Carbonates and sulfides in orogenic garnet-bearing peridotites from the Ulten Zone as witnesses for Carbon and Sulfur mobility in orogenic settings

Convergent plate boundaries are sites of sustained chemical exchanges between the Earth’s surface and deep geochemical reservoirs, playing a major role in the global cycle of carbon and sulfur. However, carbon and sulfur recycling processes continue to be hotly debated. A critical gap in the knowledge of the whole subduction factory is given by the limited accessibility to the upper mantle residing above the subducting plate, the so-called mantle wedge. This thesis investigates the carbonate and sulfide metasomatism taking place during the whole metamorphic evolution of a mantle wedge involved in the Variscan continental collision. We integrate different detailed geochemical and petrological techniques to orogenic carbonated spinel and garnet peridotites from the Ulten Zone of the Eastern Italian Alps. Our data show that the Ulten Zone peridotite experienced multiple stages of addition and removal of carbon and sulfur throughout its metamorphic evolution, as follows: (1) The Variscan lithospheric mantle was initially depleted and sulfide-poor. It subsequently inherited a sulfur and carbon component during an early metasomatic stage, when hot, H2S-CO2-bearing melts leaving a subduction-modified source percolated the overlying spinel-facies peridotite in the mantle wedge; (2) Under peak eclogite-facies P-T conditions, pervasive carbonation and sulfidation occurred. Heterogeneous melt and fluid sources variably enriched in carbon, isotopically heavy sulfur and radiogenic Sr were involved; (3) Shortly after the attainment of peak-P conditions, peridotite bodies were incorporated in a tectonic mélange with the neighboring gneisses. Here, the Ulten Zone peridotite was exposed to channelized infiltration of hybridized C-O-H fluids that promoted the formation of veinlets of carbonates locally associated with sulfide grains. (4) Upon late retrogression, infiltration of serpentinizing fluids promoted C and S remobilization at shallow crustal levels.

Microwave and millimeter-wave spectroscopy of sulfur-containing molecules

The rotational spectroscopy of several sulfur bearing molecules and their 1:1 water complex, cysteamine, cysteamine monohydrate, 1-thioglycerol and 1-propanethiol were studied in the micro-wave and (or) millimeter-wave range. Precise laboratory spectra and conformational information were obtained. For cysteamine, the conformational space (at the B3LYP-GD3(BJ)/Def2-TZVP level) and the measurement and analysis of its rotational spectra in the 6 - 18 and 59.6 - 120 GHz are reported. The hyperfine structure of the rotational spectra was observed and analyzed for the first time. Based on the measured spectra, a search of the different conformers of cysteamine was performed toward the G+0.693-0.027 molecular cloud. We computed the upper limit of the ratio of ethanolamine to cysteamine, which is >0.8−5.3. For the cysteamine monohydrate, the conformational space was explored (at the B3LYP-GD3(BJ)/Def2-TZVP level). The rotational spectra of the cysteamine monohydrate complex have been assigned in the frequency range 6 – 18.5 GHz. The global minimum, Conf A1, was the only observed one. The 34S isotopologue of Conf A1 was observed in natural abundance, while 18O isotopologue was detected by introducing the H218O. In this conformer, the water molecule plays both proton donor and acceptor roles, forming a OHw···N interaction, a SH···Ow interaction and a CH···Ow interaction. The conformational space of 1-thioglycerol has been characterized by quantum mechanical calculation and its rotational spectrum has been recorded and analyzed in the frequency range 59.6 - 78.4 GHz. The global minimum of 1-thioglycerol is gTg’Gg’ and were detected together with gTg’Tg and gGgG’g, while the two detected conformers are g’G’gGg’ and tGgGg. The high-resolution rotational spectrum of 1-propanethiol in the frequency range 59.6 – 78.4 GHz was measured. Two conformers, Gg and Tg, were observed and their spectra were analyzed. Considering the overall conformational space calculated at the B3LYP-GD3(BJ)/Def2-TZVP level they are among the lowest energy conformers.