thermodynamics; halogen; chlorine isotope; contact metamorphism; SIMS; fluid-rock
Siron Guillaume, Baumgartner Lukas P., Bouvier Anne-Sophie, Putlitz Benita, Vennemann Torsten (2017), Biotite Reference Materials for Secondary Ion Mass Spectrometry 18O/16O Measurements, in Geostandard and Geoanalytical Reserarch
, 41(2), 243-253.
Didier Amélie, Putlitz Benita, Baumgartner Lukas P., Bouvier Anne-Sophie, Vennemann Torsten (2017), Evaluation of potential monazite reference materials for oxygen isotope analyses by SIMS and laser assisted fluorination, in Chemical Geology
, 450, 199-209.
Manzini Melina, Barnes J.D., Bonifacie M, Rose-Koga E.F., Ulmer P., Métrich N., Bardoux G., Layne G.D., Straub S., Baumgartner L.P., John T (2017), SIMS chlorine isotope analyses in melt inclusions from arc settings, in Chemical Geology
, 449, 112-122.
Seitz Susanne, Putlitz Benita, Baumgartner Lukas P., Escrig Stefan, Bouvier Anne-Sophie (2016), Calculating Titanium Diffusion in Quartz-Phenocrysts from Nano Scale Profiles: An Example from a Jurassic rhyolite, Chon Aike Province (Fitz Roy, Patagonia)., in Geology
, 44, 67-70.
Fekete Szandra, Weis P., Driesner T., Bouvier A.-S., Baumgartner L.P., Heinrich C.A. (2016), Contrasting hydrological processes of meteoric water incursion during magmatic–hydrothermal ore deposition: An oxygen isotope study by ion microprobe, in Earth and Planetary Science Letters
, 451, 263-271.
Seitz Susanne, Baumgartner Lukas P., Bouvier Anne-Sophie, Putlitz Benita, Vennemann Torsten (2016), Quartz reference materials for oxygen isotope analysis by SIMS, in Geostandards and Geoanalytical
I propose to study the halogen and hydrogen content (F, Cl, H) a of OH-bearing minerals (biotite muscovite/phengite, and apatite) in meta-pelites of two contact aureoles to deduce metamorphic fluid compositions. Stable isotope compositions of chlorine, oxygen, and hydrogen will be measured in the same minerals to track dehydration and hydration reactions, identify potential fluid infiltration, and fluid un-mixing (if present). The aim is to establish 1) a comprehensive inventory of halogens in contact metamorphic pelites; 2) identify the effect of dehydration reactions; 3) study the effect of partial melting on the composition of fluids present; and to identify the signature of retrograde hydration of pelitic rocks surrounding upper crustal and upper-middle crustal intrusive rocks.Two case studies are proposed: I) The 12.5 Ma old Torres del Paine granite laccolith (Patagonia, Chile) intruded in the upper most crust (˜ 3km deep) into a series of anchi- to lower greenschist facies, immature Cretaceous turbidites. During metamorphism, the clastic mineralogy is re-equilibrated, and mostly hydrated in the outermost aureole. The highest metamorphic grade is cordierite-biotite-K-feldspar hornfels. Very limited fluid infiltration and nearly no retrograde reactions occurred. II) The Little Cottonwood granodiorite stock (Utah, USA) intruded into a thick sequence of late Proterozoic (lower) anchizone metamorphic quartzites and pelites. The highest grade rocks are magnetite-cordierite-sillimanite-biotite rocks showing abundant partial melting. Intrusion depth is estimated at ca. 10-12km. Crystallization of partial melts resulted in locally abundant retrograde muscovite. These contact aureoles were selected to contrast the effect of a) “wet” prograde metamorphism of non-metamorphic rocks undergoing dehydration (case II) versus partially “dry”, since host rocks in the far-field of the Paine aureole (case I) had to be hydrated (immature clastic mineralogy of high-grade metamorphic or igneous origin); b) upper middle crustal (II) versus upper crustal intrusions and contact metamorphism (I) and c) the effect of partial melting (case II) versus no melting (I). Finally, the Torres del Paine shows abundant effect of igneous water saturation upon crystallization (miarolitic cavities), and preliminary data shows small amount of igneous fluids infiltrated the host rocks, whereas no cavities are present in the Little Cottonwood.Major element, fluorine, and chlorine analysis will be obtained by electron microprobe (EMP). Our secondary ion microprobe (IMS1280HR SwissSIMS) will be used where concentrations are too low (e.g. <50-100ppm F, Cl), for hydrogen analysis and isotope (O,H,Cl) analysis of minerals. Traditional isotope analysis (O,H) will be used for mineral separates. The OH-/Cl- and OH-/F- ratios in minerals will be used to calculate the HF°/H2O and HCl°/H2O activity ratios for metamorphic fluids using available experimental calibrations. Thermodynamic data for aqueous species and minerals permit to calculate total halogen concentrations in the fluid phase and mass balances for halogens.Contact aureoles were selected in this proposal, because their geology is relatively simple, and rapid cooling optimizes the chances to prevent resetting of halogen concentrations during retrogression