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 - Oberhänsli, Roland A1 - Bousquet, Romain A1 - Goffe, B. T1 - Comment to "Chloritoid composition and formation in the eastern Central Alps : a comparison between Penninic and Helvetic occurrences" by M. Rahn, M. Steinmann and M. Frey Y1 - 2003 SN - 0036-7699 ER - TY - JOUR A1 - Omrani, Hadi A1 - Moazzen, Mohssen A1 - Oberhänsli, Roland T1 - Geodynamic evolution of the Sabzevar zone, northern central Iranian micro-continent JF - Mineralogy and petrology N2 - The Northern Central Iranian Micro-continent (CIM) represents Neotethys-related oceanic crust remnants, emplaced due to convergence between CIM and Eurasia plates during Eocene. Mafic and ultramafic units are exposed along the northern part of the CIM in the Sabzevar area. The geology and field relation of Sabzevar ophiolite indicate northward subduction of the Sabzevar basin. The average whole rock chemistry of mafic (gabbros) and ultramafic samples (lherzolite, harzburgite and dunite) is characterized by a range of MgO of 11.16-31.88, CaO 5.22-11.53 and Al2O3 2.77-14.57, respectively. Low LREE/HREE ratio of ultramafic samples is accompanied by enrichment of large ion lithophile elements (LILE) such as Sr, Pb and K. Mafic samples show two distinct groups with low and high LREE/HREE ratios. The spider diagram of mafic samples indicates enrichment in Sr, Pb and K and depletion in REE. Petrological and geochemical evidence and field relations show that the mafic rocks formed in a supra-subduction zone setting. Petrological studies reveal the role of fractional crystallization and assimilation effect by released fluids during subduction related generation of the Sabzevar mafic rocks. We suggest that the studied mafic rocks likely represent the basement of an initial island arc, which was generated in a supra-subduction zone setting within the Neotethys branch of the Sabzevar Ocean at the north of CIM. Copper, gold and chromite mineralizations are studied in relation to island arc setting and supra-subduction environment. Similarities in lithology, ophiolite age and mineralization between Sabzevar ophiolite and Bardaskan-Torbat Heydariyeh ophiolites testify for their separation due to rotation (or faulting) of the Central Iranian Micro-continent. KW - Supra-subduction zone KW - Ophiolite KW - Island arc KW - Mineralization KW - Neotethys KW - Iran Y1 - 2017 U6 - https://doi.org/10.1007/s00710-017-0505-3 SN - 0930-0708 SN - 1438-1168 VL - 112 IS - 1 SP - 65 EP - 83 PB - Springer CY - Wien ER - TY - JOUR A1 - Dorani, Maryam A1 - Arvin, Mohsen A1 - Oberhänsli, Roland A1 - Dargahi, Sara T1 - P-T evolution of metapelites from the Bajgan complex in the Makran accretionary prism, south eastern Iran JF - Chemie der Erde : interdisciplinary journal for chemical problems of the geo-sciences and geo-ecology = Geochemistry N2 - The Bajgan Complex, one of the basement constituents of the arc massif in Iranian Makran forms a rugged, deeply incised terrain. The complex consists of pelitic schists with minor psammitic and basic schists, calc silicate rocks, amphibolites, marbles, metavolcanosediments, mafic and felsic intrusives as well as ultramafic rocks. Metapelitic rocks show an amphibolite facies regional metamorphism and contain garnet, biotite, white mica, quartz, albite ± rutile ± apatite. Thermobarometry of garnet schist yields pressure of more than 9 kbar and temperatures between 560 and 675 °C. The geothermal gradient obtained for the peak of regional metamorphism is 19 °C/km, corresponding to a depth of ca. 31 km. Replacement of garnet by chlorite and epidote suggest greenschist facies metamorphism due to a decrease in temperature and pressure through exhumation and retrograde metamorphism (370–450 °C and 3–6 kbar). The metapelitic rocks followed a ‘clockwise’ P–T path during metamorphism, consistent with thermal decline following tectonic thickening. The formation of medium-pressure metamorphic rocks is related to presence of active subduction of the Neotethys Oceanic lithosphere beneath Eurasia in the Makran. KW - Bajgan Complex KW - Makran KW - Metapelitic rock KW - Garnet schist KW - Thermobarometry KW - Clockwise P-T path Y1 - 2017 U6 - https://doi.org/10.1016/j.chemer.2017.07.004 SN - 0009-2819 SN - 1611-5864 VL - 77 IS - 3 SP - 459 EP - 475 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Oberhänsli, Roland T1 - Deep-time Digital Earth (DDE) the first IUGS big science program JF - Journal of the Geological Society of India Y1 - 2020 U6 - https://doi.org/10.1007/s12594-020-1420-5 SN - 0016-7622 SN - 0974-6889 VL - 95 IS - 3 SP - 223 EP - 226 PB - Springer India CY - New Delhi ER - TY - JOUR A1 - Wawrzenitz, Nicole A1 - Romer, Rolf L. A1 - Oberhänsli, Roland A1 - Dong, Shuwen T1 - Dating of subduction and differential exhumation of UHP rocks from the Central Dabie Complex (E-China) : constraints from microfabrics, Rb-Sr and U-Pb isotope systems N2 - The correlation of deformation fabrics and metamorphic reactions with geochronologic data of UHP metamorphic rocks demonstrate that the multistage subduction and exhumation history of the Central Dabie Complex requires rapid subduction and rapid initial exhumation. Moreover, these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems. Thus, our age data do not simply reflect a thermal/cooling history. In the investigated section, the maximum age for UHP is given by the 244 +/- 3 Ma (2 sigma) U-Pb age of a pre-UHP titanite phenocryst that survived UHP metamorphism and subsequent tectonometamorphic events. A minimum age for UHP is set by the 238 +/- 1 Ma (2 sigma) U-238-Pb-206 mineral isochron age of titanite and cogenetic epidote. These minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust. In the period of ca. 238-218 Ma, the UHP terrain records HT metamorphism, local partial melting, and extensive pervasive strain below the eclogite (jd+grt) stability field. Exhumation was polyphase with a first phase of fast exhumation, succeeded by episodes of HT metamorphism and concomitant deformation at deep/mid crustal level between 238 and 218 Ma. Slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca. 209-204 Ma. The resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep, which was the dominant deformation mechanism in quartz-feldspar rocks, in combination with fluid influx. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2006 UR - http://www.sciencedirect.com/science/article/pii/S0024493705002306 U6 - https://doi.org/10.1016/j.lithos.2005.12.001 ER - TY - JOUR A1 - Candan, O. A1 - Cetinkaplan, Mete A1 - Oberhänsli, Roland A1 - Rimmele, Gaetan A1 - Akal, Cemal B. T1 - Alpine high-P/low-T metamorphism of the Afyon Zone and implications for the metamorphic evolution of Western Anatolia, Turkey N2 - Carpholite+chloritoid+pyrophyllite association occurs widely in the Triassic metaclastic rocks of the Afyon Zone in west-central Turkey. Fe-Mg-carpholite is associated with rare aragonite pseudomorphs and glaucophane in marbles and metabasites, respectively. The Afyon Zone consists stratigraphically of a Pan-African basement and an overlying Mesozoic cover sequence. The Pan-African basement, which shows Barrovian-type amphibolite-facies metamorphism, comprises garnet-mica schists, intruded by sodic amphibole-bearing metagabbros and leucocratic metagranites. It is unconformably overlain by a continuous metasedimentary sequence extending from Triassic to early Palaeocene. This cover sequence begins with metaconglomerates, which pass upwards into phyllites. Fe-Mg-carpholite occurs within this metaclastic sequence as rosette-like crystals in metapelites and fibres in quartz segregations. The metaclastic rocks are succeeded by metamorphosed platform carbonates, grading into Latest Mesozoic metamorphosed pelagic limestones, which in turn progress up to a Late Mesozoic-Early Tertiary olistostrome. This sequence is tectonically overlain by the blueschists of the Tavsanh Zone. Fe-Mg-carpholite-bearing assemblages imply temperatures of about 350 degrees C and minimum pressures of 6-9 kbar, corresponding to burial depths of about 30 km for the Mesozoic passive continental margin sediments and the underlying Pan-African supracrustal metasediments and metaintrusives. The metamorphic rocks of the Afyon Zone are unconformably overlain by Upper Palaeocene-Lower Eocene sedimentary rocks, indicating a Paleocene age for the regional HP/LT metamorphism. This implies continuous younging of HP/LT metamorphism in the Anatolides related to northward subduction of the Anatolide-Tauride platform beneath the Sakarya Zone. From north to south this involved the Tavsanh Zone (Campanian, 80 +/- 5 Ma), the Afyon Zone (Palaeocene?), the Menderes Massif (Middle Eocene) and the Lycian Nappes (Late Cretaceous-Eocene?), all of which were probably derived from the frontal part of the Anatolide-Tauride platform. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0024-4937 ER - TY - JOUR A1 - Rimmele, Gaetan A1 - Parra, T. A1 - Goffe, B. A1 - Oberhänsli, Roland A1 - Jolivet, L. A1 - Candan, O. T1 - Exhumation paths of high-pressure-low-temperature metamorphic rocks from the Lycian Nappes and the Menderes Massif (SW Turkey) : a multi-equilibrium approach N2 - The Menderes Massif and the overlying Lycian Nappes occupy an extensive area of SW Turkey where high-pressure- low-temperature metamorphic rocks occur. Precise retrograde P-T paths reflecting the tectonic mechanisms responsible for the exhumation of these high-pressure-low-temperature rocks can be constrained with multi-equilibrium P-T estimates relying on local equilibria. Whereas a simple isothermal decompression is documented for the exhumation of high-pressure parageneses from the southern Menderes Massif, various P-T paths are observed in the overlying Karaova Formation of the Lycian Nappes. In the uppermost levels of this unit, far from the contact with the Menderes Massif, all P-T estimates depict cooling decompression paths. These high-pressure cooling paths are associated with top-to-the-NNE movements related to the Akcakaya shear zone, located at the top of the Karaova Formation. This zone of strain localization is a local intra-nappe contact that was active in the early stages of exhumation of the high-pressure rocks. In contrast, at the base of the Karaova Formation, along the contact with the Menderes Massif, P-T calculations show decompressional heating exhumation paths. These paths are associated with severe deformation characterized by top-to-the-east shearing related to a major shear zone (the Gerit shear zone) that reflects late exhumation of high-pressure parageneses under warmer conditions Y1 - 2005 SN - 0022-3530 ER - TY - JOUR A1 - Jolivet, L. A1 - Rimmele, Gaetan A1 - Oberhänsli, Roland A1 - Goffe, B. A1 - Candan, O. T1 - Correlation of syn-orogenic tectonic and metamorphic events in the Cyclades, the Lycian nappes and the Menderes massif : Geodynamic implications N2 - The recent discovery of HP-LT parageneses in the basal unit of the Lycian nappes and in the Mesozoic cover of the Menderes massif leads us to reconsider and discuss the correlation of this region with the nearby collapsed Hellenides in the Aegean domain. Although similarities have long been pointed Out by various authors, a clear correlation has not yet been proposed and most authors insist more on differences than similarities. The Menderes massif is the eastern extension of the Aegean region but it has been less severely affected by the Aegean extension during the Oligo-Miocene. It would thus be useful to use the structure of the Menderes massif as an image of the Aegean region before a significant extension has considerably reduced its crustal thickness. But the lack of correlation between the two regions has so far hampered Such comparisons. We describe the main tectonic units and metamorphic events in the two regions and propose a correlation. We then show possible sections of the two regions before the Aegean extension and discuss the involvement of continental basement in the Hellenic accretionary complex. In our interpretation the Hellenic- Tauric accretionary complex was composed of stacked basement and cover units which underwent variable P-T histories. Those which were not exhumed early enough later followed a high-T evolution which led to partial melting in the Cyclades during post-orogenic extension. Although the Menderes massif contains a larger volume of basement units it does not show significant evidence for the Oligo-Miocene migmatites observed in the center of the Cyclades suggesting that crustal partial melting is strictly related to post-orogenic extension in this case Y1 - 2004 SN - 0037-9409 ER - TY - JOUR A1 - Liu, Xiaochun A1 - Jahn, Bor-Ming A1 - Dong, Shuwen A1 - Li, Huimin A1 - Oberhänsli, Roland T1 - Neoproterozoic granitoid did not record ultrahigh-pressure metamorphism from the Southern Dabieshan of China N2 - It has been often debated whether all granitic gneisses associated with coesite-bearing eclogites in southern Dabieshan, China, have also been subjected to ultrahigh-pressure (UHP) metamorphism. We show here that a metagranitoid adjacent to the Bixiling eclogite-ultramafic complex has preserved primary granitic textures and an igneous mineral assemblage of biotite + plagioclase + microcline + quartz + allanite +/- amphibole. The absence of UPH recrystallization for the metagranitoid is particularly manifested by the conservation of euhedral-zoned plagioclase phenocrysts, the lack of corona garnets around igneous biotite, and the presence of an igneous mineral assemblage in zircons. The only metamorphic overprint was the epidote-amphibolite facies metamorphism characterized by the assemblage of biotite + phengiticmica + epidote + albite + K-feldspar + quartz +/- amphibole Metamorphic conditions are estimated at ca. 550degrees-680degreesC and 6-13 kbar for the metagranitoid and its amphibolitic enclave. Geochemically, the metagranitoid is similar to its country gneiss and shows an affinity to volcanic arc granitoid. Zircon U-Pb dating suggests that the Bixiling metagranitoid was emplaced during the Neoproterozoic (729+/-4 Ma), when most other granitic rocks and the protoliths of eclogite were also formed in Dabieshan. Taking into account the discovery of non-UHP granitic gneisses in other places, we argue that part of Neoproterozoic granitic rocks in the Dabieshan and Sulu terranes have escaped UHP metamorphism during the Triassic deep subduction of the continental crust as a consequence of a lack of penetrative deformation and fluid-rock interaction Y1 - 2003 SN - 0022-1376 ER -