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 - Scheffler, Franziska A1 - Immenhauser, Adrian A1 - Pourteau, Amaury A1 - Natalicchio, Marcello A1 - Candan, Osman A1 - Oberhänsli, Roland T1 - A lost Tethyan evaporitic basin BT - Evidence from a Cretaceous hemipelagic meta-selenite - red chert association in the Eastern Mediterranean realm JF - Sedimentology : the journal of the International Association of Sedimentologists N2 - Ancient evaporite deposits are geological archives of depositional environments characterized by a long‐term negative precipitation balance and bear evidence for global ocean element mass balance calculations. Here, Cretaceous selenite pseudomorphs from western Anatolia (‘Rosetta Marble’) — characterized by their exceptional morphological preservation — and their ‘marine’ geochemical signatures are described and interpreted in a process‐oriented context. These rocks recorded Late Cretaceous high‐pressure/low‐temperature, subduction‐related metamorphism with peak conditions of 1·0 to 1·2 GPa and 300 to 400°C. Metre‐scale, rock‐forming radiating rods, now present as fibrous calcite marble, clearly point to selenitic gypsum as the precursor mineral. Stratigraphic successions are recorded along a reconstructed proximal to distal transect. The cyclical alternation of selenite beds and radiolarian ribbon‐bedded cherts in the distal portions are interpreted as a two type of seawater system. During arid intervals, shallow marine brines cascaded downward into basinal settings and induced precipitation. During more humid times, upwelling‐induced radiolarian blooms caused the deposition of radiolarite facies. Interestingly, there is no comparable depositional setting known from the Cenozoic world. Meta‐selenite geochemical data (δ13C, δ18O and 87Sr/86Sr) plot within the range of reconstructed middle Cretaceous seawater signatures. Possible sources for the 13C‐enriched (mean 2·2‰) values include methanogenesis, gas hydrates and cold seep fluid exhalation. Spatially resolved component‐specific analysis of a rock slab displays isotopic variances between meta‐selenite crystals (mean δ13C 2·2‰) and host matrix (mean δ13C 1·3‰). The Cretaceous evaporite‐pseudomorphs of Anatolia represent a basin wide event coeval with the Aptian evaporites of the Proto‐Atlantic and the pseudomorphs share many attributes, including lateral distribution of 600 km and stratigraphic thickness of 1·5 to 2·0 km, with the evaporites formed during the younger Messinian salinity crisis. The Rosetta Marble of Anatolia may represent the best‐preserved selenite pseudomorphs worldwide and have a clear potential to act as a template for the study of meta‐selenite in deep time. KW - Blueschist metamorphism KW - depositional environment KW - evaporites KW - Neotethys KW - pseudomorphism KW - sedimentology Y1 - 2019 U6 - https://doi.org/10.1111/sed.12606 SN - 0037-0746 SN - 1365-3091 VL - 66 IS - 7 SP - 2627 EP - 2660 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Pourteau, Amaury A1 - Oberhänsli, Roland A1 - Candan, Osman A1 - Barrier, Eric A1 - Vrielynck, Bruno T1 - Neotethyan closure history of western Anatolia: a geodynamic discussion JF - International journal of earth sciences N2 - This paper addresses the lithosphere-scale subduction-collision history of the eastern termination of the Aegean retreating subduction system, i.e. western Anatolia. Although there is some general consensus on the protracted subduction evolution of the Aegean since the early Cenozoic at least, correlation with western Anatolia has been widely debated for more than several decades. In western Anatolia, three main tectonic configurations have been envisaged in the past years to reconstruct slab dynamics during the closure of the Neotethyan oceanic realm since the Late Cretaceous. Some authors have suggested an Aegean-type scenario, with the continuous subduction of a single lithospheric slab, punctuated by episodic slab roll-back and trench retreat, whereas others assumed a discontinuous subduction history marked by intermittent slab break-off during either the Campanian (ca. 75 Ma) or the Early Eocene (ca. 55-50 Ma). The third view implies three partly contemporaneous subduction zones. Our review of these models points to key debated aspects that can be re-evaluated in the light of multidisciplinary constraints from the literature. Our discussion leads us to address the timing of subduction initiation, the existence of hypothetical ocean basins, the number of intervening subduction zones between the Taurides and the Pontides, the palaeogeographic origin of tectonic units and the possibility for slab break-off during either the Campanian or the Early Eocene. Thence, we put forward a favoured tectonic scenario featuring two successive phases of subduction of a single lithospheric slab and episodic accretion of two continental domains separated by a continental trough, representing the eastern end of the Cycladic Ocean of the Aegean. The lack of univocal evidence for slab break-off in western Anatolia and southward-younging HP/LT metamorphism in continental tectonic units (from similar to 85, 70 to 50 Ma) in the Late Cretaceous-Palaeogene period suggests continuous subduction since similar to 110 Ma, marked by roll-back episodes in the Palaeocene and the Oligo-Miocene, and slab tearing below western Anatolia during the Miocene. KW - Subduction KW - Anatolia KW - Aegean KW - Neotethys KW - Slab break-off KW - Slab roll-back Y1 - 2016 U6 - https://doi.org/10.1007/s00531-015-1226-7 SN - 1437-3254 SN - 1437-3262 VL - 105 SP - 203 EP - 224 PB - Springer CY - New York 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 -