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 - 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 - Wilke, Franziska Daniela Helena A1 - Schmidt, Alexander A1 - Ziemann, Martin Andreas T1 - Subduction, peak and multi-stage exhumation metamorphism: Traces from one coesite-bearing eclogite, Tso Moran, western Himalaya JF - Lithos : an international journal of mineralogy, petrology, and geochemistry N2 - Ultrahigh-pressure (UHP), coesite-bearing edogites in the Himalaya have been documented from the Kaghan Valley in Pakistan and the Tso Morani area in northwest India. These complexes are part of the northern edge of the Indian plate that has been subducted to, and metamorphosed at, mantle depths of more than 100 km before being exhumed. Both UHP complexes are located today directly adjacent to the Indus-Tsangpo suture zone and are not separated by non-metamorphosed sequences of Tethyan sediments from the Asian margin. Herein, we present new data for one fresh coesite-bearing eclogite from the Tso Moran massif. Therein, garnets are zoned reflecting their growth during prograde and peak metamorphism and showing a thin retrograde overgrowth. Inclusions can be directly correlated to the compositional zoning and are seen as either relicts of the protolith mineral paragenesis and as "snap shots" of the mineral paragenesis during subduction and under peak conditions. Rare earth element concentrations (REE) were obtained for garnet, mineral inclusions in garnet and matrix minerals. The REE pattern in garnet reflects a sequential change in matrix minerals and their proportions due to net transfer reactions during subduction and peak metamorphism. Using conventional geothermobarometry, a peak pressure of ca. 44-48 kbar at 560-760 degrees C followed by an S-shaped exhumation curve has been deduced. Gibbs free energy minimization modelling was used to supplement our analytical findings. (C) 2015 Elsevier B.V. All rights reserved. KW - Tso Morari KW - Coesite-bearing eclogite KW - Ultra-high pressure (UHP) KW - Rare earth element (REE) distribution KW - Laser ICP-MS Y1 - 2015 U6 - https://doi.org/10.1016/j.lithos2015.06.007 SN - 0024-4937 SN - 1872-6143 VL - 231 SP - 77 EP - 91 PB - Elsevier CY - Amsterdam ER -