TY - JOUR A1 - Schmidt, Alexander A1 - Pourteau, Amaury A1 - Candan, Osman A1 - Oberhänsli, Roland T1 - Lu-Hf geochronology on cm-sized garnets using microsampling: New constraints on garnet growth rates and duration of metamorphism during continental collision (Menderes Massif, Turkey) JF - Earth & planetary science letters N2 - This study shows Lu-Hf geochronology of zoned garnet crystals contained in mica schists from the southern Menderes Massif, Turkey. Selected samples are four 3-5 cm large garnet megacrysts of which several consecutive garnet shells have been sampled with a micro-saw and analyzed for dating. The results are used to extract growth rates of garnet, and also to improve the time constraint for Alpine-aged overprint of the Pan-African basement in the Menderes Massif. The new data provides a precise age determination for prograde Barrovian metamorphism in the southern Menderes Massif, which so far was placed between 63 and 27 Ma on the basis of mica Rb-Sr and Ar-Ar dating. This study provides new constraints crucial to the understanding of the tectonic evolution of southwest Anatolia and the Aegean realm, as it yields a shorter outline for Alpine aged continental collision. KW - Lu-Hf geochronology KW - garnet KW - Alpine metamorphism KW - Menderes Massif Y1 - 2015 U6 - https://doi.org/10.1016/j.epsl.2015.09.015 SN - 0012-821X SN - 1385-013X VL - 432 SP - 24 EP - 35 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Aygül, Mesut A1 - Okay, Aral I. A1 - Oberhänsli, Roland A1 - Ziemann, Martin Andreas T1 - Thermal structure of low-grade accreted Lower Cretaceous distal turbidites, the Central Pontides, Turkey: insights for tectonic thickening of an accretionary wedge JF - Turkish journal of earth sciences = Türk yerbilimleri dergisi N2 - Albian-Turonian subduction-accretionary complexes are exposed widely in the Central Pontides. A major portion of the accretionary complexes is made up of a metaflysch sequence consisting of slate/phyllite and metasandstone intercalation with blocks of marble, Na-amphibole bearing metabasite, and serpentinite. The metaflysch sequence represents distal parts of a large Lower Cretaceous submarine turbidite fan deposited on the Laurasian active continental margin that was subsequently accreted and metamorphosed during the Albian. Raman spectra of carbonaceous material of the metapelitic rocks revealed that the metaflysch consists of metamorphic packets with distinct peak metamorphic temperatures. The majority of the metapelites are low-temperature (ca. 330 degrees C) slates characterized by lack of differentiation of the graphite (G) and D2 defect bands. They possibly represent offscraped distal turbidites along the toe of the Albian accretionary wedge. Other phyllites are characterized by a slightly pronounced G band with a D2 defect band occurring on its shoulder. Peak metamorphic temperatures of these phyllites are constrained to 370-385 degrees C. The phyllites are associated with a strip of incipient blueschist facies metabasites and are found as a sliver within the offscraped distal turbidites. We interpret the phyllites as underplated continental sediments together with oceanic crustal basalt along the basal decollement. Tectonic emplacement of the underplated rocks into the offscraped distal turbidites was possibly achieved by out-of-sequence thrusting causing tectonic thickening and uplift of the wedge. KW - Pontides KW - distal turbidites KW - offscraping KW - underplating KW - low-grade metamorphism KW - graphitization KW - Raman microspectroscopy Y1 - 2015 U6 - https://doi.org/10.3906/yer-1504-4 SN - 1300-0985 VL - 24 IS - 5 SP - 461 EP - 474 PB - Tübitak CY - Ankara ER - TY - JOUR A1 - Aygül, Mesut A1 - Okay, Aral I. A1 - Oberhänsli, Roland A1 - Schmidt, Alexander A1 - Sudo, Masafumi T1 - Late Cretaceous infant intra-oceanic arc volcanism, the Central Pontides, Turkey: Petrogenetic and tectonic implications JF - Journal of Asian earth sciences N2 - A tectonic slice of an arc sequence consisting of low-grade metavolcanic rocks and overlying metasedimentary succession is exposed in the Central Pontides north of the Izmir-Ankara-Erzincan suture separating Laurasia from Gondwana-derived terranes. The metavolcanic rocks mainly consist of basaltic andesite/andesite and mafic cognate xenolith-bearing rhyolite with their pyroclastic equivalents, which are interbedded with recrystallized pelagic limestone and chert. The metasedimentary succession comprises recrystallized micritic limestone with rare volcanogenic metaclastic rocks and stratigraphically overlies the metavolcanic rocks. The geochemistry of the metavolcanic rocks indicates an arc setting evidenced by depletion of HFSE (Ti, P and Nb) and enrichment of fluid mobile LILE. Identical trace and rare earth elements compositions of basaltic andesites/andesites and rhyolites suggest that they are cogenetic and derived from a common parental magma. The arc sequence crops out between an Albian-Turonian subduction-accretionary complex representing the Laurasian active margin and an ophiolitic melange. Absence of continent derived detritus in the arc sequence and its tectonic setting in a wide Cretaceous accretionary complex suggest that the Kosdag Arc was intra-oceanic. Zircons from two metarhyolite samples give Late Cretaceous (93.8 +/- 1.9 and 94.4 +/- 1.9 Ma) U/Pb ages. These ages are the same as the age of the supra-subduction ophiolites in western Turkey, which implies that that the Kosdag Arc may represent part of the incipient arc formed during the generation of the supra-subduction ophiolites. The low-grade regional metamorphism in the Kosdag Arc is constrained to 69.9 +/- 0.4 Ma by Ar-40/Ar-39 muscovite dating indicating that the arc sequence became part of a wide Tethyan Cretaceous accretionary complex by the latest Cretaceous. Non-collisional cessation of the arc volcanism is possibly associated with southward migration of the magmatism as in the Izu-Bonin-Mariana arc system. (c) 2015 Elsevier Ltd. All rights reserved. KW - Intra-oceanic subduction KW - Felsic volcanism KW - Arc accretion KW - Ophiolite obduction Y1 - 2015 U6 - https://doi.org/10.1016/j.jseaes.2015.07.005 SN - 1367-9120 SN - 1878-5786 VL - 111 SP - 312 EP - 327 PB - Elsevier CY - Oxford ER -