Quartz and calcite microfabric transitions in a pressure and temperature gradient, Sivrihisar, Turkey

Abstract

Interlayered quartzite and marble in the southern Sivrihisar Massif, Turkey, record metamorphic conditions ranging from high-pressure/low-temperature through a Barrovian overprint from chlorite-to sillimanite-zone conditions. This sequence was exhumed under transtension, producing macroscopic constrictional fabrics (L-tectonites) during crustal thinning. Quartz microstructures consist of dynamically recrystallized aggregates in the dislocation creep regime dominated by grain boundary migration. Quartz microstructures are relatively constant across the high metamorphic gradient, and crystallographic fabric patterns transition from plane strain to constriction strain. Calcite fabrics are characterized by progressive overprinting of a columnar texture inherited from the high-pressure polymorph aragonite. In the low-temperature Barrovian domain (<400°C), shearing of calcite rods produced a very strong c-axis point maximum. At moderate temperature, calcite rods were partially to totally recrystallized and the strong preferred orientation maintained. At temperature >500°C and high constriction strain, marble has no crystallographic fabric, likely reflecting a transition from dislocation creep to diffusion creep. Phengite in high-pressure/low-temperature marble and quartzite yields relatively simple age spectra with Late Cretaceous 40 Ar/ 39 Ar ages. Barrovian muscovite records significantly younger ages (63-55 Ma). The transtension system and associated metamorphism may have occurred above a subduction zone in Paleocene-Eocene time as a precursor to intrusion of Eocene (~53 Ma) arc plutons.

Neotethyan closure history of western Anatolia: a geodynamic discussion

“…3), as demonstrated by geochronologic studies (e.g. Sherlock et al 1999;Seaton et al 2009Seaton et al , 2014Budde and Scherer 2013;Mulcahy et al 2014;Pourteau et al 2015). This is consistent with the Turonian age of the youngest SSZ-type basalt in accretionary complexes (Göncüoğlu et al 2006).…”

“…3) (Okay et al 1998;Sherlock et al 1999;Seaton et al 2009;Budde and Scherer 2013;Mulcahy et al 2014;Seaton et al 2014;Plunder et al 2015) and was followed by blueschist-facies retrogression at ~83-60 Ma (Sherlock et al 1999). Near Sivrihisar, a Barrovian-type overprint at 63-57 Ma has been documented (Seaton et al 2009;Whitney et al 2011;Seaton et al 2014). Clasts of lawsonite-bearing blueschist reported from Upper Campanian-Lower Maastrichtian levels of the Haymana fore-arc basin ( Fig.…”

Sedimentologic to metamorphic processes recorded in the high-pressure/low-temperature Mesozoic Rosetta Marble of Anatolia

“…Similar calcite fibres were described in several HP-LT marble units of Anatolia (Rimmelé et al 2003;Candan et al 2005;Seaton et al 2009Seaton et al , 2014Pourteau et al 2010;Davis and Whitney 2006;Okay and Whitney 2010;Whitney et al 2014). The long axes of fibres within one calcite rod are oriented parallel in space, and this suggests crystallization perpendicular to the main stress due to dislocation creep processes during metamorphism (Brady et al 2004).…”

“…Fibrous calcites are commonly observed in HP-LT units and have been interpreted as topotactic pseudomorphs after aragonite (Gillet and Goffé 1988;Rimmelé et al 2003;Brady et al 2004;Seaton et al 2009Seaton et al , 2014. Similar calcite fibres were described in several HP-LT marble units of Anatolia (Rimmelé et al 2003;Candan et al 2005;Seaton et al 2009Seaton et al , 2014Pourteau et al 2010;Davis and Whitney 2006;Okay and Whitney 2010;Whitney et al 2014).…”

“…11). Calcite fibres are often interpreted as topotactic pseudomorphs after aragonite (Brady et al 2004;Gillet and Goffé 1988;Rimmelé et al 2003;Seaton et al 2009Seaton et al , 2014. Fibres in calcite rods of Rosetta Marble are mostly oriented oblique to the bedding and often strictly parallel to each other.…”