TY - JOUR A1 - Akal, Cüneyt A1 - Candan, Osman A1 - Koralay, O. Ersin A1 - Oberhänsli, Roland A1 - Chen, Fukun A1 - Prelevic, Dejan T1 - Early Triassic potassic volcanism in the Afyon Zone of the Anatolides/Turkey - implications for the rifting of the Neo-Tethys JF - International journal of earth sciences N2 - Afyon Zone, which was derived from the Anatolide-Tauride platform during closure of the Neo-Tethys, is made up of pre-Mesozoic basement and unconformably overlying Triassic-Early Tertiary cover series. The Afyon Zone contains widespread metavolcanic rocks, which are dominated by rhyolite, dacite, and trachyandesite. They form a distinct volcanic succession, which is separated from the underlying Silurian-Lower Carboniferous metacarbonates and meta-siliciclastics by a regional unconformity. Trachyandesitic metavolcanics are made up of massive lava flows, pyroclastics and epiclastics, less frequently, domes and dikes, which were developed on a deeply eroded subaerial landmass. U/Pb and Pb/Pb zircon geochronology yielded Lower Triassic (similar to 250 Ma) ages, which are interpreted as extrusion age of trachyandesitic volcanics. Based on the stratigraphic, geochronological, and geochemical data, we suggest that these Lower Triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the Gondwana, which led to the development of the northern branch of the Neo-Tethys. KW - Meta-trachyandesite KW - Afyon Zone KW - Turkey KW - Neo-Tethys KW - Paleo-tethys Y1 - 2012 U6 - https://doi.org/10.1007/s00531-011-0654-2 SN - 1437-3254 VL - 101 IS - 1 SP - 177 EP - 194 PB - Springer CY - New York ER - TY - JOUR A1 - Altenberger, Uwe A1 - Mejia Jimenez, D. M. A1 - Günter, C. A1 - Sierra Rodriguez, G. I. A1 - Scheffler, F. A1 - Oberhänsli, Roland T1 - The Garzn Massif, Colombia-a new ultrahigh-temperature metamorphic complex in the early Neoproterozoic of northern South America JF - Mineralogy and petrology N2 - The Garzn Complex of the Garzn Massif in SW Colombia is composed of the Vergel Granulite Unit (VG) and the Las Margaritas Migmatite Unit (LMM). Previous studies reveal peak temperature conditions for the VG of about 740 A degrees C. The present study considers the remarkable exsolution phenomena in feldspars and pyroxenes and titanium-in-quartz thermometry. Recalculated ternary feldspar compositions indicate temperatures around 900-1,000 A degrees C just at or above the ultra-high temperature-metamorphism (UHTM) boundary of granulites. The calculated temperatures range of exsolved ortho- and clinopyroxenes also supports the existence of an UHTM event. In addition, titanium-in-quartz thermometry points towards ultra-high temperatures. It is the first known UHTM crustal segment in the northern part of South America. Although a mean geothermal gradient of ca 38 A degrees C km(-1) could imply additional heat supply in the lower crust controlling this extreme of peak metamorphism, an alternative model is suggested. The formation of the Vergel Granulite Unit is supposed to be formed in a continental back-arc environment with a thinned and weakened crust behind a magmatic arc (Guapotn-Mancagua Gneiss) followed by collision. In contrast, rocks of the adjacent Las Margaritas Migmatite Unit display "normal" granulite facies temperatures and are formed in a colder lower crust outside the arc, preserved by the Guapotn-Mancagu Gneiss. Back-arc formation was followed by inversion and thickening of the basin. The three units that form the modern-day Garzn Massif, were juxtaposed upon each other during collision (at ca. 1,000 Ma) and exhumation. The collision leading to the deformation of the studied area is part of the Grenville orogeny leading to the amalgamation of Rodinia. Y1 - 2012 U6 - https://doi.org/10.1007/s00710-012-0202-1 SN - 0930-0708 VL - 105 IS - 3-4 SP - 171 EP - 185 PB - Springer CY - Wien ER - TY - JOUR A1 - Düsterhöft, Erik A1 - Bousquet, Romain A1 - Wichura, Henry A1 - Oberhänsli, Roland T1 - Anorogenic plateau formation The importance of density changes in the lithosphere JF - Journal of geophysical research : Solid earth N2 - Away from active plate boundaries the relationships between spatiotemporal variations in density and geothermal gradient are important for understanding the evolution of topography in continental interiors. In this context the classic concept of the continental lithosphere as comprising three static layers of different densities (upper crust, lower crust, and upper mantle) is not adequate to assess long-term changes in topography and relief in regions associated with pronounced thermal anomalies in the mantle. We have therefore developed a one-dimensional model, which is based on thermodynamic equilibrium assemblage computations and deliberately excludes the effects of melting processes like intrusion or extrusions. Our model calculates the "metamorphic density" of rocks as a function of pressure, temperature, and chemical composition. It not only provides a useful tool for quantifying the influence of petrologic characteristics on density, but also allows the modeled "metamorphic" density to be adjusted to variable geothermal gradients and applied to different geodynamic environments. We have used this model to simulate a scenario in which the lithosphere-asthenosphere boundary is subjected to continuous heating over a long period of time (130 Ma), and demonstrate how an anorogenic plateau with an elevation of 1400 m can be formed solely as a result of heat transfer within the continental lithosphere. Our results show that, beside dynamic topography (of asthenospheric origin), density changes within the lithosphere have an important impact on the evolution of anorogenic plateaus. Y1 - 2012 U6 - https://doi.org/10.1029/2011JB009007 SN - 2169-9313 SN - 2169-9356 VL - 117 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Koralay, O. E. A1 - Candan, Osman A1 - Chen, F. A1 - Akal, Cemal B. A1 - Oberhänsli, Roland A1 - Satir, M. A1 - Dora, O. O. T1 - Pan-African magmatism in the Menderes Massif - geochronological data from leucocratic tourmaline orthogneisses in western Turkey JF - International journal of earth sciences N2 - The Menderes Massif, exposed in western Anatolia, is a metamorphic complex cropping out in the Alpine orogenic belt. The metamorphic rock succession of the Massif is made up of a Precambrian basement and overlying Paleozoic-early Tertiary cover series. The Pan-African basement is composed of late Proterozoic metasedimentary rocks consisting of partially migmatized paragneisses and conformably overlying medium- to high-grade mica schists, intruded by orthogneisses and metagabbros. Along the southern flank of the southern submassif, we recognized well-preserved primary contact relationship between biotite and leucocratic tourmaline orthogneisses and country rocks as the orthogneisses represent numerous large plutons, stocks and vein rocks intruded into a basement of garnet mica schists. Based on the radiometric data, the primary deposition age of the precursors of the country rocks, garnet mica schist, can be constrained between 600 and 550 Ma (latest Neoproterozoic). The North Africa-Arabian-Nubian Shield in the Mozambique Belt can be suggested as the possible provenance of these metaclastics. The intrusion ages of the leucocratic tourmaline orthogneisses and biotite orthogneisses were dated at 550-540 Ma (latest Neoproterozoic-earliest Cambrian) by zircon U/Pb and Pb/Pb geochronology. These granitoids represent the products of the widespread Pan-African acidic magmatic activity, which can be attributed to the closure of the Mozambique Ocean during the final collision of East and West Gondwana. Detrital zircon ages at about 550 Ma in the Paleozoic muscovite-quartz schists show that these Pan-African granitoids in the basement form the source rocks of the cover series of the Menderes Massif. KW - Menderes Massif KW - Leucocratic tourmaline orthogneisses KW - Pan-African magmatism KW - Zircon U/Pb and Pb-Pb ages KW - Mozambique Ocean KW - Gondwanaoberh Y1 - 2012 U6 - https://doi.org/10.1007/s00531-012-0775-2 SN - 1437-3254 VL - 101 IS - 8 SP - 2055 EP - 2081 PB - Springer CY - New York ER - TY - JOUR A1 - Oberhänsli, Roland A1 - Bousquet, Romain A1 - Candan, Osman A1 - Okay, Aral I. T1 - Dating subduction events in East Anatolia, Turkey JF - Turkish journal of earth sciences = Türk yerbilimleri dergisi N2 - Metamorphic studies in the cover sequences of the Bitlis complex allow the thermal evolution of the massif to be constrained using metamorphic index minerals. Regionally distributed metamorphic index minerals such as glaucophane, carpholite, relics of carpholite in chloritoid-bearing schists and pseudomorphs after aragonite in marbles record a LT-HP evolution:This demonstrates that the Bitlis complex was subducted and stacked to form a nappe complex during the closure of the Neo-Tethys. During late Cretaceous to Cenozoic evolution the Bitlis complex experienced peak metamorphism of 1.0-1.1 GPa at 350-400 degrees C. During the retrograde evolution temperatures remained below 460 degrees C. Ar-39/Ar-40 dating of white mica in different parageneses from the Bitlis complex reveals a 74-79 Ma (Campanian) date of peak metamorphism and rapid exhumation to an almost isothermal greenschist stage at 67-70 Ma (Maastrichtian). The HP Eocene flysch escaped the greenschist facies stage and were exhumed under very cold conditions. These single stage evolutions contrast with the multistage evolution reported further north from the Amassia-Stepanavan Suture in Armenia. Petrological investigations and isotopic dating show that the collision of Arabia with Eurasia resulted in an assemblage of different blocks derived from the northern as well as from the southern plate and a set of subduction zones producing HP rocks with diverse exhumation histories. KW - Bitlis complex KW - HP metamorphism KW - Ar dating KW - geodynamic evolution of SE Anatolia KW - subduction history Y1 - 2012 U6 - https://doi.org/10.3906/yer-1006-26 SN - 1300-0985 VL - 21 IS - 1 SP - 1 EP - 17 PB - Tübitak CY - Ankara ER - TY - JOUR A1 - Saki, Adel A1 - Moazzen, Mohssen A1 - Oberhänsli, Roland T1 - Mineral chemistry and thermobarometry of the staurolite-chloritoid schists from Poshtuk, NW Iran JF - Geological magazine N2 - The Poshtuk metapelitic rocks in northwestern Iran underwent two main phases of regional and contact metamorphism. Microstructures, textural features and field relations indicate that these rocks underwent a polymetamorphic history. The dominant metamorphic assemblage of the metapelites is garnet, staurolite, chloritoid, chlorite, muscovite and quartz, which grew mainly syntectonically during the later contact metamorphic event. Peak metamorphic conditions of this event took place at 580 degrees C and similar to 3-4 kbar, indicating that this event occurred under high-temperature and low-pressure conditions (HT/LP metamorphism), which reflects the high heat flow in this part of the crust. This event is mainly controlled by advective heat input through magmatic intrusions into all levels of the crust. These extensive Eocene metamorphic and magmatic activities can be associated with the early Alpine Orogeny, which resulted in this area from the convergence between the Arabian and Eurasian plates, and the Cenozoic closure of the Tethys oceanic tract(s). KW - thermobarometry KW - HT/LP metamorphism KW - Poshtuk metapelites KW - northwestern Iran Y1 - 2012 U6 - https://doi.org/10.1017/S0016756812000209 SN - 0016-7568 VL - 149 IS - 6 SP - 1077 EP - 1088 PB - Cambridge Univ. Press CY - New York ER -