Stable isotope compositions of the Penninic ophiolites of the Kõszeg-Rechnitz series

Abstract

The ophiolitic rocks of the easternmost Penninic unit, the Kõszeg-Rechnitz series, were analyzed for their H, C and O stable isotope compositions. Serpentinite, gabbro, blueschist, talc deposits, ophicarbonates, as well as calcite and inclusion fluids from quartz segregation veins were analyzed in order to determine the effects of different metamorphic events on the stable isotope compositions.The oxygen isotope compositions have a wide range depending on rock type and locality. Gabbro and serpentinite of Bienenhütte (Bernstein Window) have preserved mantle-like δ 18 O values (5.9 to 6.3‰; all values are in ‰ relative to V-SMOW), whereas the serpentinite of Glashütten and Rumpersdorf (Kõszeg-Rechnitz Window) and the silicate minerals of the ophicarbonate rocks show a strong 18 O-enrichment (up to 16.2‰). The 18 O-enrichment may have been induced by lowtemperature serpentinization or interaction with 18 O-rich fluids that had been in equilibrium with sedimentary rocks. Contrary to the O isotope compositions, the H isotope compositions seem to be homogeneous in the entire series, with D values of -63 ± 7‰. Only some serpentinite rocks were depleted in D (down to -106‰), usually regarded as a result of interaction with meteoric water infiltrating during late-stage metamorphism. The meteoric water infiltration was rather limited, as even samples taken directly from slickensides within serpentinite bodies preserved isotopic compositions close to those of the bulk series. H and O isotope compositions of fluids mobilized in the metasedimentary rocks of the Penninic unit during the main metamorphic stage were determined by analyzing inclusion fluids and calcites in quartz-carbonate veins. The isotope compositions indicate interaction between these fluids and the ophiolite series, although relative deuterium enrichment has been preserved in the ophiolitic rocks.The strong D-enrichment characteristic for oceanic crust that has experienced high-temperature interaction with seawater was not detected. However, the H isotope compositions obtained for the Kõszeg-Rechnitz series indicate that subduction of the Penninic oceanic crust and the associated devolatilization may have been potentially responsible for mantle metasomatism, resulting in H Addresses: A. Demény: H-1112 Budapest, Budaörsi út 45, Hungary, e-mail: demeny@geochem.hu T. W. Vennemann: L'Anthropole, CH-1015 Lausanne, Switzerland F. Koller: Althanstr. 14, 1090 Vienna, Austria Received: January 2, , accepted: March 28, 2007 1788-2281/$ 20.00 © 2007 Akadémiai Kiadó, Budapest Central European Geology, Vol. 50/1, pp. 29-46 (2007 DOI: 10.155610. /CEuGeol.50.2007 isotope compositions of about -40‰, similar to the range determined from mantle-derived amphibole megacrysts (Demény et al. 2005). To conclude, the present dataset is discussed in the light of earlier studies on the formation of the Sopron leucophyllite.

Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

“…Whole-rock δ 18 O values for seafloor-altered oceanic crust are as high as +20‰ but most are in the range of +5 to +10‰ (Alt, 2004 Table 2). Shaded grey areas and lightly shaded grey symbols represent values from the literature for ophicalcites from the low-temperature Iberian margin and Galicia Bank (Evans and Baltuck, 1988;Milliken and Morgan, 1996;Plas, 1997;Skelton and Valley, 2000), the Alps, Apennines, and Pyrenees (Brotzu et al, 1973;Barbieri et al, 1979;Weissert and Bernoulli, 1984;Barrett and Friedrichsen, 1989;Demeny et al, 2007;Clerc et al, 2014), and from other high-temperature hydrothermal ophicalcites (Lavoie and Cousineau, 1995;Artemyev and Zaykov, 2010;Jedrysek et al, 2000). Staudigel et al (1989), , Staudigel et al (1996), andKing et al (2004), and are provided in Supplementary Table 4.…”

Ophicalcites from the northern Pyrenean belt: a field, petrographic and stable isotope study

“…Following our observations, and in accordance with phase stability of serpentine mineral (Andreani et al 2007), it appears that the variable serpentinization degree of the Pyrenean peridotites can be linked, primarily, to the thermal anomaly accompanying their exhumation. (Evans & Baltuck 1988;Plas 1997;Skelton & Valley 2000); the Alps and Apennines (Brotzu et al 1973; Barbieri et al 1979;Weissert & Bernoulli 1984;Barrett & Friedrichsen 1989;Demeny et al 2007) and from other hydrothermal ophicalcites (Lavoie & Cousineau 1995;Artemyev & Zaykov 2010). .…”