Metamorphic and tectonic evolution of a structurally continuous blueschist-to-Barrovian terrane, Sivrihisar Massif, Turkey

Abstract

Metamorphic terranes comprised of blueschist facies and regional metamorphic (Barrovian) rocks in apparent structural continuity may represent subduction complexes that were partially overprinted during syn-to post-subduction heating or may be comprised of unrelated tectonic slices. An excellent example of a composite blueschist-to-Barrovian terrane is the southern Sivrihisar Massif, Turkey. Late Cretaceous blueschist facies rocks are dominated by marble characterized by rod-shaped calcite pseudomorphs after aragonite and interlayered with blueschist that contains eclogite and quartzite pods. Barrovian rocks, which have 40 Ar ⁄ 39 Ar white mica ages that are >20 Myr younger than those of the blueschists, are also dominated by marble, but rod-shaped calcite has been progressively recrystallized into massive marble within a 200-m transition zone. Barrovian marble is interlayered with quartzite and schist in which isograds are closely spaced and metamorphic conditions range from chlorite to sillimanite zone over 1 km present-day structural thickness. Andalusite, kyanite and prismatic sillimanite are present in muscovite-rich quartzite; in one location, all three are in the same rock. Andalusite pre-dates Barrovian metamorphism, kyanite is both pre-and syn-Barrovian and sillimanite is entirely Barrovian. Muscovite with phengitic cores and relict kyanite in quartzite below the staurolite-in isograd are evidence for pre-Barrovian subduction metamorphism preserved at the low-T end of the Barrovian domain; above the staurolite isograd, all evidence for subduction metamorphism has been erased. Some regional metamorphism may have occurred during exhumation, as indicated by synkinematic high-T minerals defining the fabric of L-tectonite. Quartz microstructures in lineated quartzite reveal a strong constrictional fabric that may have formed in a transtensional bend in the plate boundary. Transtension accounts for the closely spaced isograds and development of a strong constrictional fabric during exhumation.

Neotethyan closure history of western Anatolia: a geodynamic discussion

“…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.…”

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

“…The southern part of the massif was overprinted by regional (Barrovian) metamorphism up to sillimanite zone conditions (Whitney, 2002;Whitney et al, 2011). Here, rock layering and foliation dip generally northward, exposing a section through a sequence of increasing metamorphic temperature toward the south.…”

“…An investigation of quartz and calcite microstructures in the southern Sivrihisar Massif, Turkey (Figure 1(A) and (B)), is useful for understanding deformation microstructures, mechanisms, and conditions of naturally deformed quartz and carbonate because the massif contains abundant interlayered quartzite and marble and is comprised of a subduction complex that has been partially to completely overprinted by later metamorphism at lower pressures and a range of temperatures in a transtensional setting (Seaton, Whitney, Teyssier, Toraman, & Heizler, 2009;Whitney, 2002;Whitney, Teyssier, Toraman, Seaton, & Fayon, 2011). Recorded metamorphic conditions range from HP to LT blueschist and eclogite facies conditions (~18-22 kbar, 400°C) to low/ medium-P (~3-6 kbar) regional metamorphism at a range of T (from <400°C to >650°C) (Figure 1(C)).…”

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).…”