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 - Keyser, William A1 - Tsai, Chin-Ho A1 - Iizuka, Yoshiyuki A1 - Oberhänsli, Roland A1 - Ernst, W. G. T1 - High-pressure metamorphism in the Chinshuichi area, Yuli belt, eastern Taiwan JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - Tectonic blocks and slabs of mafic-ultramafic rocks are distributed discontinuously in the Yuli metamorphic belt of Taiwan. The blocks include rare omphacite metagabbros and gamet-epidote blueschists in the Wanjung and Juisui (Tamayen) areas, respectively. Such high-pressure (HP) mineral assemblages have been attributed to a mid-Miocene subduction event. However, the surrounding psammitic, pelitic and chloritic schists are the dominant greenschist-facies lithologies of the Yuli belt. In the Chinshuichi area, tectonic blocks are enclosed in garnet-bearing metapelites, suggesting elevated pressures. In this area, we recently discovered meta-plagiogranite containing the assemblage glaucophane + omphacite (X-Jd up to 039) + rutile + quartz, indicating P-T conditions near 13 kbar/550 degrees C. New equilibrium phase modeling of a garnet-paragonite mica schist and compositional isopleths for peak assemblage minerals garnet and phengite (Si = 3.33-3.37 pfu) indicate metamorphic conditions of 15.5-17 kbar/530-550 degrees C. These P-T estimates are higher than previously reported in the Yuli belt and suggest that both tectonic blocks and host metapelites underwent HP metamorphism. The juxtaposition of tectonic blocks and metapelites apparently occurred during the formation of a subduction-accretionary complex, followed by exhumation facilitated by a collisional event. These new findings imply that HP metamorphism was not limited to tectonic blocks, and instead played a significant role attending orogenesis in eastern Taiwan. (C) 2015 Elsevier B.V. All rights reserved. KW - Equilibrium phase modeling KW - Omphacite KW - Glaucophane KW - Meta-plagiogranite KW - High-pressure metamorphism KW - Yuli belt KW - Tananao Complex Y1 - 2016 U6 - https://doi.org/10.1016/j.tecto.2015.09.012 SN - 0040-1951 SN - 1879-3266 VL - 692 SP - 191 EP - 202 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Candan, O. A1 - Akal, C. A1 - Koralay, O. E. A1 - Okay, A. I. A1 - Oberhänsli, Roland A1 - Prelevic, D. A1 - Mertz-Kraus, R. T1 - Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey - Evidence for southward subduction of Paleotethys JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recrystallized limestones. The low-grade metamorphism and deformation occurred at the Cretaceous-Tertiary boundary. There is no evidence for Carboniferous deformation and metamorphism in the region. Carboniferous arc-type granites and previously described Carboniferous subduction-accretion complexes on the northern margin of the Anatolide-Tauride Block suggest southward subduction of Paleotethys under Gondwana during the Carboniferous. Considering the Variscan-related arc granites in Pelagonian and Sakarya zones on the active southern margin of Laurasia, a dual subduction of Paleotethys can be envisaged between Early Carboniferous and Late Permian. However, the southward subduction was short-lived and by the Late Permian the Gondwana margin became passive. (C) 2016 Elsevier B.V. All rights reserved. KW - Carboniferous magmatism KW - Paleotethys KW - Gondwana KW - Afyon zone KW - Anatolide-Tauride Block Y1 - 2016 U6 - https://doi.org/10.1016/j.tecto.2016.06.030 SN - 0040-1951 SN - 1879-3266 VL - 683 SP - 349 EP - 366 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Candan, O. A1 - Koralay, O. E. A1 - Topuz, G. A1 - Oberhänsli, Roland A1 - Fritz, H. A1 - Collins, A. S. A1 - Chen, F. T1 - Late Neoproterozoic gabbro emplacement followed by early Cambrian eclogite-facies metamorphism in the Menderes Massif (W. Turkey): Implications on the final assembly of Gondwana JF - Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research N2 - Numerous (meta-)gabbroic dikes or stocks occur within the latest Neoproterozoic-early Cambrian series of the Menderes Massif (Anatolide-Tauride Block, western Turkey). These well-preserved rocks were locally converted into eclogitic metagabbros and garnet amphibolites along the contacts or shear zones. Both bulk-rock composition and compositions of igneous clinopyroxenes suggest continental tholeiitic affinity. U-Pb dating of igneous zircons from gabbroic rocks yielded a mean age of 563 +/- 1 Ma (2 sigma), indicating emplacement during the latest Neoproterozoic (Ediacaran). On the other hand, rims of zircons from eclogitic metagabbro gave 535 +/- 3 Ma (2 sigma) (early Cambrian), in addition to 558 +/- 3 Ma (2 sigma) obtained from the igneous core of zircons. These ages are interpreted as the time of high-P metamorphism and crystallization age of gabbroic protolith, respectively. Given the estimated paleogeographic position of the Anatolide-Tauride Block during the late Neoproterozoic and early Cambrian, this orogenic event can be spatially and temporally related to the northward continuity of 600-500 Ma orogenic event (Malagasy/Kuunga orogeny) extending from western margin of India, Madagascar, via Arabia up to northern margin of Gondwana beneath thick Phanerozoic cover series in Arabian Peninsula. Therefore, the high-P evolution of the basement of the Menderes Massif and associated basic intrusions can be interpreted to mark the latest stages of consumption of the basin/oceanic branches and final amalgamation of the Gondwana during the late Neoproterozoic-early Cambrian around the Arabian region. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. KW - Gabbro KW - Eclogite KW - Malagasy/Kuunga orogeny KW - Menderes Massif KW - Turkey Y1 - 2016 U6 - https://doi.org/10.1016/j.gr.2015.02.015 SN - 1342-937X SN - 1878-0571 VL - 34 SP - 158 EP - 173 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Cetinkaplan, Mete A1 - Pourteau, Amaury A1 - Candan, Osman A1 - Koralay, O. Ersin A1 - Oberhänsli, Roland A1 - Okay, Aral I. A1 - Chen, Fukun A1 - Kozlu, Huseyin A1 - Sengun, Firat T1 - P-T-t evolution of eclogite/blueschist facies metamorphism in Alanya Massif: time and space relations with HP event in Bitlis Massif, Turkey JF - International journal of earth sciences N2 - The Alanya Massif, which is located to the south of central Taurides in Turkey, presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. In two thrust sheets, Sugozu and GundogmuAY nappes, HP metamorphism under eclogite (550-567 A degrees C/14-18 kbar) and blueschist facies (435-480 A degrees C/11-13 kbar) conditions have been recognized, respectively. Whereas the rest of the Massif underwent MP metamorphism under greenschist to amphibolite facies (525-555 A degrees C/6.5-7.5 kbar) conditions. Eclogite facies metamorphism in Sugozu nappe, which consists of homogeneous garnet-glaucophane-phengite schists with eclogite lenses is dated at 84.8 +/- A 0.8, 84.7 +/- A 1.5 and 82 +/- A 3 Ma (Santonian-Campanian) by Ar-40/Ar-39 phengite, U/Pb zircon and rutile dating methods, respectively. Similarly, phengites in GundogmuAY nappe representing an accretionary complex yield 82-80 Ma (Campanian) ages for blueschist facies metamorphism. During the exhumation, the retrograde overprint of the HP units under greenschist-amphibolite facies conditions and tectonic juxtaposition with the Barrovian units occurred during Campanian (75-78 Ma). Petrological and geochronological data clearly indicate a similar Late Cretaceous tectonometamorphic evolution for both Alanya (84-75 Ma) and Bitlis (84-72 Ma) Massifs. They form part of a single continental sliver (Alanya-Bitlis microcontinent), which was rifted from the southern part of the Anatolide-Tauride platform. The P-T-t coherence between two Massifs suggests that both Massifs have been derived from the closure of the same ocean (Alanya-Bitlis Ocean) located to the south of the Anatolide-Tauride block by a northward subduction. The boundary separating the autochthonous Tauride platform to the north from both the Alanya and Bitlis Massifs to the south represents a suture zone, the Pamphylian-Alanya-Bitlis suture. KW - Tauride KW - Eclogite KW - Alanya KW - Blueschist KW - Metamorphism Y1 - 2016 U6 - https://doi.org/10.1007/s00531-014-1092-8 SN - 1437-3254 SN - 1437-3262 VL - 105 SP - 247 EP - 281 PB - Springer CY - New York ER - TY - JOUR A1 - Scheffler, Franziska A1 - Oberhänsli, Roland A1 - Pourteau, Amaury A1 - Immenhauser, A. A1 - Candan, O. T1 - Sedimentologic to metamorphic processes recorded in the high-pressure/low-temperature Mesozoic Rosetta Marble of Anatolia JF - International journal of earth sciences N2 - Anatolia’s high-pressure metamorphic belts are characterized in part by a Neotethyan stratigraphic succession that includes a mid-Cretaceous hemi-pelagic marble sequence. This unit contains, towards its stratigraphic top, dm-to-m-long radiating calcitic rods forming rosette-like textures. Here, we refer to these features as “Rosetta Marble”. The remarkable textural similarity of non-metamorphic selenite crystals and radiating calcite rods in the Rosetta Marble strongly suggests that these textures represent pseudomorphs after selenites. Metamorphosed hemi-pelagic limestones, dominated by Rosetta selenite pseudomorphs, are alternating with siliceous meta-sediments containing relictic radiolaria tests. This stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non-evaporative hemi-pelagic deposition from normal-marine seawater. The regional distribution of Rosetta Marble exposures over 600 km is indicative of basin-scale evaporitic intervals. High-pressure, low-temperature metamorphism of these rocks is witnessed by Sr-rich (up to 3500 ppm), fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz. Peak metamorphic conditions of 1.2 GPa and 300–350 °C are attested by high-Si white mica thermobarometry. The Rosetta Marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta-sedimentary rocks. KW - Gypsum KW - High-pressure metamorphism KW - Neotethys KW - Anatolia Y1 - 2016 U6 - https://doi.org/10.1007/s00531-015-1214-y SN - 1437-3254 SN - 1437-3262 VL - 105 SP - 225 EP - 246 PB - Springer CY - New York 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 - Altenberger, Uwe A1 - Oberhänsli, Roland A1 - Stein, Eckehard A1 - Moghni, Mohsen T1 - Geochemistry, tectonic setting and geodynamic position of late orogenic dikes in the Melibocus Massiv, Bergstraesser Odenwald Y1 - 2001 ER - TY - JOUR A1 - Wilhelm, Stefan A1 - Altenberger, Uwe A1 - Oberhänsli, Roland T1 - Intrusive marbles in the Ivrea Zone (Italy) : evidence for melting of metacarbonates Y1 - 2001 ER - TY - JOUR A1 - Candan, O. A1 - Dora, O. A1 - Oberhänsli, Roland A1 - Cetinkaplan, Mete A1 - Partzsch, Julius A1 - Warkus, Friederike C. A1 - Dürr, S. T1 - Pan-African high-pressure metamorphism in the Precambrian basement of the Menderes massif, Western Anatolia, Turkey Y1 - 2000 ER - TY - JOUR A1 - Oberhänsli, Roland A1 - Partzsch, Julius A1 - Candan, O. A1 - Cetinkaplan, Mete T1 - First occurrence of Fe-Mg-carpholite documenting a high pressure metamorphism in the metasediments of the Lycian nappes, SW Turkey Y1 - 2000 ER - TY - JOUR A1 - Wenzel, T. A1 - Oberhänsli, Roland A1 - Mezger, Klaus T1 - K-rich plutonic rocks and lamprophyres from the Meissen Massif (northern Bohemian Massif) : Geochemical evidence for variably enriched lithospheric mantle sources Y1 - 2000 ER - TY - JOUR A1 - Oberhänsli, Roland A1 - Wendt, A. S. A1 - Goffe, B. A1 - Michard, Andre T1 - Detrital chromites in metasediments of East-Arabian continental margin in te Saih Hatat area : constraints for the palaeogeographic setting of the Hawasina and Semail basins (Oman Mountains) Y1 - 1999 ER - TY - JOUR A1 - Bazylev, B. A. A1 - Zakariadze, G. S. A1 - Zhelyazkova-Panayotova, M. D. A1 - Kolcheva, K. A1 - Oberhänsli, Roland A1 - Solov'eva, N. V. T1 - Petrology of ultramafic rocks from the ophiolithe association in the crystalline basement of the Rhodope massif Y1 - 1999 ER - TY - JOUR A1 - Omrani, Hadi A1 - Moazzen, Mohssen A1 - Oberhänsli, Roland A1 - Moslempour, Mohammad Elyas T1 - Iranshahr blueschist: subduction of the inner Makran oceanic crust JF - Journal of metamorphic geology N2 - The Makran accretionary prism in SE Iran and SW Pakistan is one of the most extensive subduction accretions on Earth. It is characterized by intense folding, thrust faulting and dislocation of the Cenozoic units that consist of sedimentary, igneous and metamorphic rocks. Rock units forming the northern Makran ophiolites are amalgamated as a melange. Metamorphic rocks, including greenschist, amphibolite and blueschist, resulted from metamorphism of mafic rocks and serpentinites. In spite of the geodynamic significance of blueschist in this area, it has been rarely studied. Peak metamorphic phases of the northern Makran mafic blueschist in the Iranshahr area are glaucophane, phengite, quartz +/- omphacite+epidote. Post peak minerals are chlorite, albite and calcic amphibole. Blueschist facies metasedimentary rocks contain garnet, phengite, albite and epidote in the matrix and as inclusions in glaucophane. The calculated P-T pseudosection for a representative metabasic glaucophane schist yields peak pressure and temperature of 11.5-15kbar at 400-510 degrees C. These rocks experienced retrograde metamorphism from blueschist to greenschist facies (350-450 degrees C and 7-8kbar) during exhumation. A back arc basin was formed due to northward subduction of Neotethys under Eurasia (Lut block). Exhumation of the high-pressure metamorphic rocks in northern Makran occurred contemporarily with subduction. Several reverse faults played an important role in exhumation of the ophiolitic and HP-LT rocks. The presence of serpentinite shows the possible role of a serpentinite diapir for exhumation of the blueschist. A tectonic model is proposed here for metamorphism and exhumation of oceanic crust and accretionary sedimentary rocks of the Makran area. Vast accretion of subducted materials caused southward migration of the shore. KW - back arc basin KW - Bajgan/Durkan KW - HP-LT metamorphic rocks KW - Iran KW - Lut Blocks KW - Northern Makran KW - subduction and exhumation Y1 - 2017 U6 - https://doi.org/10.1111/jmg.12236 SN - 0263-4929 SN - 1525-1314 VL - 35 SP - 373 EP - 392 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Aygül, Mesut A1 - Oberhänsli, Roland T1 - Tectonic Stacking of HP/LT Metamorphic Rocks in Accretionary Wedges and the Role of Shallowing Slab-Mantle Decoupling JF - Tectonics N2 - High-pressure/low-temperature (HP/LT) chloritoid-bearing micaschists crop out widely in the central part of northern Turkey and represent deep-seated subduction-accretionary complexes. Three peak metamorphic assemblages are identified in the area studied: (1) garnet-chloritoid-glaucophane with pseudomorphs after lawsonite; (2) chloritoid with pseudomorphs after glaucophane; and (3) chloritoid with pseudomorphs after jadeite in addition to phengite, paragonite, quartz, chlorite, rutile, and apatite. The latter is interpreted as transformation of a chloritoid + glaucophane assemblage to chloritoid + jadeite with increasing pressure; PT modeling indicates similar to 17 and 22-25 kbars for the two peak parageneses. The diversity of peak metamorphic assemblages and the PT estimates suggest that basal accretion occurred at different depths within the wedge. The depth of the basal accretion is possibly controlled by the slab-mantle decoupling depth. Stretching and thinning of the lithospheric fore arc induced by the slab rollback possibly caused shallowing of the slab-mantle decoupling depth which limited depth of the basal accretion from 70-80km to similar to 55km within the subduction channel. A slab-mantle coupling depth-controlled basal accretion may also explain the scarcity of eclogite and high-grade blueschist facies metamorphic rocks in active intraoceanic subduction zones. Because the overriding plate is young and hot in intraoceanic subductions, the slab and mantle are coupled at a relatively shallow depth before eclogitization of the oceanic crust. This prevents accretion and exhumation of eclogite along the subduction channel. KW - chloritoid micaschist KW - accretionary complex KW - slab-mantle decoupling KW - basal accretion Y1 - 2017 U6 - https://doi.org/10.1002/2017TC004689 SN - 0278-7407 SN - 1944-9194 VL - 36 SP - 2332 EP - 2346 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Weber, Michael H. A1 - Abu-Ayyash, Khalil A1 - Abueladas, Abdel-Rahman A1 - Agnon, Amotz A1 - Al-Amoush, H. A1 - Babeyko, Andrey A1 - Bartov, Yosef A1 - Baumann, M. A1 - Ben-Avraham, Zvi A1 - Bock, Günter A1 - Bribach, Jens A1 - El-Kelani, R. A1 - Forster, A. A1 - Förster, Hans-Jürgen A1 - Frieslander, U. A1 - Garfunkel, Zvi A1 - Grunewald, Steffen A1 - Gotze, Hans-Jürgen A1 - Haak, Volker A1 - Haberland, Christian A1 - Hassouneh, Mohammed A1 - Helwig, S. A1 - Hofstetter, Alfons A1 - Jackel, K. H. A1 - Kesten, Dagmar A1 - Kind, Rainer A1 - Maercklin, Nils A1 - Mechie, James A1 - Mohsen, Amjad A1 - Neubauer, F. M. A1 - Oberhänsli, Roland A1 - Qabbani, I. A1 - Ritter, O. A1 - Rumpker, G. A1 - Rybakov, M. A1 - Ryberg, Trond A1 - Scherbaum, Frank A1 - Schmidt, J. A1 - Schulze, A. A1 - Sobolev, Stephan Vladimir A1 - Stiller, M. A1 - Th, T1 - The crustal structure of the Dead Sea Transform N2 - To address one of the central questions of plate tectonics-How do large transform systems work and what are their typical features?-seismic investigations across the Dead Sea Transform (DST), the boundary between the African and Arabian plates in the Middle East, were conducted for the first time. A major component of these investigations was a combined reflection/ refraction survey across the territories of Palestine, Israel and Jordan. The main results of this study are: (1) The seismic basement is offset by 3-5 km under the DST, (2) The DST cuts through the entire crust, broadening in the lower crust, (3) Strong lower crustal reflectors are imaged only on one side of the DST, (4) The seismic velocity sections show a steady increase in the depth of the crust-mantle transition (Moho) from 26 km at the Mediterranean to 39 km under the Jordan highlands, with only a small but visible, asymmetric topography of the Moho under the DST. These observations can be linked to the left-lateral movement of 105 km of the two plates in the last 17 Myr, accompanied by strong deformation within a narrow zone cutting through the entire crust. Comparing the DST and the San Andreas Fault (SAF) system, a strong asymmetry in subhorizontal lower crustal reflectors and a deep reaching deformation zone both occur around the DST and the SAF. The fact that such lower crustal reflectors and deep deformation zones are observed in such different transform systems suggests that these structures are possibly fundamental features of large transform plate boundaries Y1 - 2004 ER - TY - JOUR A1 - Karo, Nihad M. A1 - Oberhänsli, Roland A1 - Aqrawi, Ahmed M. A1 - Elias, Elias M. A1 - Aswad, Khalid J. A1 - Sudo, Masafumi T1 - New Ar-40/Ar-39 age constraints on cooling and unroofing history of the metamorphic host rocks (and igneous intrusion associates) from the Bulfat Complex (Bulfat area), NE-Iraq JF - Arabian journal of geosciences N2 - The Northern Zagros Suture Zone (NZSZ), formed as a result of the collision between Arabian and Sanandaj-Sirjan microplate, is considered as part of the Zagros orogenic belt. NZSZ is marked by two allochthonous thrust sheets in upward stacking order: lower and upper allochthon. The Bulfat complex is a part of the upper allochthon or "Ophiolite-bearing terrane" of Albian-Cenomenion age (97-105 Ma). Voluminous highly sheared serpentinites associated with ophiolites occur within this upper allochthon. In addition, the Gemo-Qandil Group is characterized by gabbroic to dioritic Bulfat intrusion with a crystallization age spanning from similar to 45 to similar to 40 Ma, as well as extensive metapelites with contact to the Walash-Naupurdam metavolcanic rocks. Due to the deformation in the Sanandaj-Sirjan Zone along the eastern side of the Iraqi segment of NZSZ, the Gemo-Qandil Group was regionally metamorphosed during late Cretaceous (similar to 80 Ma). This tectono-compressional dynamics ultimately caused an oscillatory deformation against Arabian continental margin deposits as well. During these events, gabbro-diorite intrusion with high-grade contact metamorphic aureoles occurred near Bulfat. Thus, there is an overlap between regional and contact metamorphic conditions in the area. The earlier metamorphic characteristic can be seen only in places where the latter contact influence was insignificant. Generally, this can only observed at a distance of more than 2.5 km from the contact. According to petrographic details and field observations, the thermally metamorphosed metapelitic units of the metasediment have been completely assimilated, with only some streaks of biotite and relicts of initial foliation. They strongly resemble amphibolite-grade slices from the regional metamorphic rocks in the region. Metapelitic samples far from the intrusion give similar biotite cooling ages as the intrusive rocks. Thus, they may be affected by the same thermal event. Ar-40/Ar-39 dating of biotite in metapelite rocks of Bulfat by step-wise heating with laser gave average weighted isotopic ages of 34.78 +/- 0.06 Ma. This is interpreted as crystallization/recrystallization age of biotite possibly representing the time of cooling and uplift history of the Bulfat intrusion. Cooling and exhumation rates for the Bulfat gabbro-diorite rocks were estimated as similar to 400 A degrees C/Ma and similar to 3.3 mm/year respectively. According to petrographic details, field observations and Ar/Ar dating concerning the contact metamorphism near Bulfat due to the gabbro-diorite intrusion, no significant deformation is visible during exhumation processes after the Paleogene tectono-thermal event, indicating that isotopic ages of 34.78 +/- 0.06 Ma could mark the timing of termination of the island arc activity in the Ophiolite-bearing terrane (upper allochthon). KW - Iraq KW - Bulfat KW - Metapelites KW - Northern Zagros Suture Zone (NZSZ) KW - Ar-40/Ar-39 KW - Cooling and unroofing history Y1 - 2018 U6 - https://doi.org/10.1007/s12517-018-3571-x SN - 1866-7511 SN - 1866-7538 VL - 11 IS - 10 PB - Springer CY - Heidelberg 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 - TY - JOUR A1 - Wichura, Henry A1 - Bousquet, Romain A1 - Oberhänsli, Roland A1 - Strecker, Manfred A1 - Trauth, Martin H. T1 - Evidence for middleUocene uplift of the East African Plateau N2 - Cenozoic uplift of the East African Plateau has been associated with fundamental climatic and environmental changes in East Africa and adjacent regions. While this influence is widely accepted, the timing and the magnitude of plateau uplift have remained unclear. This uncertainty stems from the lack of datable, geomorphically meaningful reference horizons that could record surface uplift. Here, we document the existence of significant relief along the East African Plateau prior to rifting, as inferred from modeling the emplacement history of one of the longest terrestrial lava flows, the similar to 300-km-long Yatta phonolite flow in Kenya. This 13.5 Ma lava flow originated on the present-day eastern Kenya Rift flank, and utilized a riverbed that once routed runoff from the eastern rim of the plateau. Combining an empirical viscosity model with subsequent cooling and using the Yatta lava flow geometry and underlying paleotopography (slope angle), we found that the prerift slope was at least 0.2 degrees, suggesting that the lava flow originated at a minimum elevation of 1400 m. Hence, high paleotopography in the Kenya Rift region must have existed by at least 13.5 Ma. We infer from this that middle Miocene uplift occurred, which coincides with the two-step expansion of grasslands, as well as important radiation and speciation events in tropical Africa. Y1 - 2010 UR - http://geology.gsapubs.org/ U6 - https://doi.org/10.1130/G31022.1 SN - 0091-7613 ER -