TY - JOUR A1 - Harlov, Daniel E. A1 - Tropper, Peter A1 - Seifert, Wolfgang A1 - Nijland, Timo A1 - Förster, Hans-Jürgen T1 - Formation of Al-rich titanite (CaTiSiO4O-CaAlSiO4OH) reaction rims on ilmenite in metamorphic rocks as a function of fH(2)O and fO(2) N2 - Reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona, area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Otztal Complex. The titanite rims, and hence the stability of titanite (CaTiSiO4O) and Al-OH titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH(2)O- and fO(2)-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO-FeO/Fe2O3-TiO2-SiO2-H2O-O-2 (CFTSH) and CaO-FeO/Fe2O3-Al2O3- SiO2-H2O-O-2 (CFASH) present in each of the examples. Textural evidence suggests that titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite +quartz+ H2O = amphibole +titanite and oxidation reactions such as amphibole + ilmenite + O-2 = titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Otztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH(2)O and fO(2) to be high for titanite formation, which is also in accordance with equilibria involving Al-OH titanite. This study shows that, in addition to P, T, bulk-rock composition and composition of the coexisting fluid, fO(2) and fH(2)O also play an important role in the formation of Al-bearing titanite during amphibolite- and greenschist-facies metamorphism. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00244937 U6 - https://doi.org/10.1016/j.lithos.2005.08.005 SN - 0024-4937 ER - TY - JOUR A1 - Seifert, Wolfgang A1 - Rhede, Dieter A1 - Förster, Hans-Jürgen A1 - Thomas, Rainer T1 - Accessory minerals as fingerprints for the thermal history and geochronology of the Caledonian Rumburk granite N2 - Accessory minerals of the Caledonian Rumburk granite are investigated to gain insight into its magmatic and post-magmatic evolution history. Recent geothermometers calibrated for trace elements in rutile (Zr), zircon (Ti), and quartz (Ti) were used to determine mineral-formation temperatures, which are compared with T data obtained from melt and fluid-inclusion Studies on quartz. Improved electron-microprobe analytical conditions allowed distinguishing several generations of rutile. Submicron-sized rutile needles included in quartz crystallized at around 739 +/- 13 degrees C and, thus, are evidently magmatic. Simultaneous crystallization of the high-T rutile and quartz is the favoured concept compared with an exsolution model for the needles. Th-U-total Pb dating of xenotime-(Y) by electron microprobe yielded a bimodal age distribution of 494 +/- 8 Ma (2 sigma; n = 44) and 311 +/- 8 Ma (2 sigma; n = 48), which is missing in monazite-(Ce). The older age correlates with the early Ordovician granite emplacement age Suggested by earlier isotopic Studies. The younger Carboniferous age also may be geologically reasonable, because the granite experienced a minor tectonothermal overprint during the Variscan orogenesis. However, whether this event has caused the resetting of the isotopic system in the xenotime is uncertain. This also holds for the age of the partial breakdown of monazite and xenotime into reaction coronas composed of fluorapatite, allanite-(Ce), epidote +/- clinozoisite. This alteration assemblage was likely produced already during autometasomatic reworking of the solidifying magma in Ordovician time, but it cannot be excluded that it relates to a Carboniferous fluid imprint connected with late-Variscan processes. Y1 - 2009 UR - http://www.ingentaconnect.com/content/schweiz/njma U6 - https://doi.org/10.1127/0077-7757/2009/0147 SN - 0077-7757 ER - TY - JOUR A1 - Bachmann, Raik A1 - Oncken, Onno A1 - Glodny, Johannes A1 - Seifert, Wolfgang A1 - Georgieva, Viktoria A1 - Sudo, Masafumi T1 - Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone N2 - We present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central Alps of Europe related to Late Cretaceous-early Tertiary subduction and accretion of the South Penninic lower plate underneath the Adriatic upper plate. The material forming the exposed plate interface zone has experienced flow and fracturing over an extended period of time followed by syncollisional exhumation, thus reflecting a multistage evolution. Fabric formation and metamorphism, however, chiefly record the deformation conditions of the precollisional setting along the plate interface. We identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200 and 300 degrees C. This zone coincides with a domain of intense veining in the subduction melange with mineral growth into open cavities, indicating fast, possibly seismic, rupture. Evidence for transient near-lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear zones continues into the region below the occurrence of pseudotachylytes, possibly reflecting a zone of conditionally stable slip. The zone above the unstable slip area is devoid of veins but displays ample evidence of fluid-assisted processes similar to the deeper zone: solution-precipitation creep and dehydration reactions in the melange matrix, hydration, and sealing of the base of the upper plate. Seismic rupture here is possibly expressed by ubiquitous localized deformation zones. We hypothesize that trenchward sealing of parts of the plate interface as well as reaction-enhanced destruction of upper plate permeability is an important component, localizing the unstable slip zone. This relation may result from the competition of the pervasive, presumably interseismic, pressure solution creep destroying permeability and building elevated fluid pressure until the strength threshold is reached with seismic failure. Y1 - 2009 UR - http://www.agu.org/journals/jb/ U6 - https://doi.org/10.1029/2008jb005927 SN - 0148-0227 ER -