@article{OberhaensliKoralayCandanetal.2013, author = {Oberh{\"a}nsli, Roland and Koralay, E. and Candan, Osman and Pourteau, Amaury and Bousquet, Romain}, title = {Late cretaceous eclogitic high-pressure relics in the Bitlis Massif}, series = {Geodinamica acta : revue de g{\´e}ologie dynamique et de g{\´e}ographie physique}, volume = {26}, journal = {Geodinamica acta : revue de g{\´e}ologie dynamique et de g{\´e}ographie physique}, number = {3-4}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0985-3111}, doi = {10.1080/09853111.2013.858951}, pages = {175 -- 190}, year = {2013}, abstract = {A new occurrence of eclogites was found in the Kesandere valley in the eastern most part of the Bitlis complex, SE Anatolia. These high-pressure (HP) relics were preserved in calc-arenitic metasediments within the high-grade metamorphic basement of the Bitlis complex. The eclogitic parageneses were strongly overprinted during decompression and heating. These new eclogites locality complements the evidence of blueschist-facies metamorphism documented recently in the meta-sedimentary cover sequence of this part of the Bitlis complex. Thermodynamic calculations suggest peak conditions of ca. 480-540 degrees C/1.9-2.4GPa. New U/Pb dates of 84.4 +/-.9 and 82.4 +/-.9Ma were obtained on zircons from two Kesandere eclogite samples. On the basis of geochemical criteria, these dates are interpreted to represent zircon crystallization during the eclogitic peak stage. Kesandere eclogites differ from those previously described in the western Bitlis complex (Mt. Gablor locality) in terms of lithologic association, protolithic origin, and peak P-T conditions (600-650 degrees C/1.0-2.0GPa, respectively). On the other hand, eclogitic metamorphism of Kesandere metasediments occurred shortly before blueschist-facies metamorphism of the sedimentary cover (79-74Ma Ar-40/Ar-39 white mica). Therefore, the exhumation of Kesandere eclogites started between ca. 82 and 79Ma, while the meta-sedimentary cover was being buried. During this short time span, Kesandere eclogite were likely uplifted from similar to 65 to 35km depth, indicating a syn-subduction exhumation rate of similar to 4.3mm/a. Subsequently, eclogite- and blueschist-facies rocks were likely retrogressed contemporarily during collision-type metamorphism (around 72-69Ma). The Bitlis HP rocks thus sample a subduction zone that separated the Bitlis-Puturge (Bistun?) block from the South-Armenian block, further north. To the south, Eocene metasediments of the Urse formation are imbricated below the Bitlis complex. They contain (post Eocene) blueschists, testifying separation from the Arabian plate and southward migration of the subduction zone. The HT overprint of Kesandere eclogites can be related to the asthenospheric flow provoked by subducting slab retreat or break off.}, language = {en} } @article{NegroBousquetVilsetal.2013, author = {Negro, Francois and Bousquet, Romain and Vils, Flurin and Pellet, Clara-Marine and H{\"a}nggi-Schaub, Jeanette}, title = {Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps}, series = {Swiss journal of geosciences}, volume = {106}, journal = {Swiss journal of geosciences}, number = {1}, publisher = {Springer}, address = {Basel}, issn = {1661-8726}, doi = {10.1007/s00015-013-0119-7}, pages = {63 -- 78}, year = {2013}, abstract = {In the Western Alps, the Piemont-Ligurian oceanic domain records blueschist to eclogite metamorphic conditions during the Alpine orogeny. This domain is classically divided into two "zones" (Combin and Zermatt-Saas), with contrasting metamorphic evolution, and separated tectonically by the Combin fault. This study presents new metamorphic and temperature (RSCM thermometry) data obtained in Piemont-Ligurian metasediments and proposes a reevaluation of the P-T evolution of this domain. In the upper unit (or "Combin zone") temperatures are in the range of 420-530 A degrees C, with an increase of temperature from upper to lower structural levels. Petrological evidences show that these temperatures are related to the retrograde path and to deformation at greenschist metamorphic conditions. This highlights heating during exhumation of HP metamorphic rocks. In the lower unit (or "Zermatt-Saas zone"), temperatures are very homogeneous in the range of 500-540 A degrees C. This shows almost continuous downward temperature increase in the Piemont-Ligurian domain. The observed thermal structure is interpreted as the result of the upper and lower unit juxtaposition along shear zones at a temperature of similar to 500 A degrees C during the Middle Eocene. This juxtaposition probably occurred at shallow crustal levels (similar to 15-20 km) within a subduction channel. We finally propose that the Piemont-Ligurian Domain should not be viewed as two distinct "zones", but rather as a stack of several tectonic slices.}, language = {en} } @misc{OmraniMoazzenOberhaenslietal.2013, author = {Omrani, H. and Moazzen, Mohssen and Oberh{\"a}nsli, Roland and Tsujimori, T. and Bousquet, Romain and Moayyed, M.}, title = {Metamorphic history of glaucophane-paragonite-zoisite eclogites from the Shanderman area, northern Iran}, series = {Journal of metamorphic geology}, volume = {31}, journal = {Journal of metamorphic geology}, number = {8}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0263-4929}, doi = {10.1111/jmg.12045}, pages = {791 -- 812}, year = {2013}, abstract = {The Shanderman eclogites and related metamorphosed oceanic rocks mark the site of closure of the Palaeotethys ocean in northern Iran. The protolith of the eclogites was an oceanic tholeiitic basalt with MORB composition. Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation. Minerals formed during the prograde stages are preserved as inclusions in peak metamorphic garnet and omphacite. The rocks experienced blueschist facies metamorphism on their prograde path and were metamorphosed in eclogite facies at the peak of metamorphism. The peak metamorphic mineral paragenesis of the rocks is omphacite, garnet (pyrope-rich), glaucophane, paragonite, zoisite and rutile. Based on textural relations, post-peak stages can be divided into amphibolite and greenschist facies. Pressure and temperature estimates for eclogite facies minerals (peak of metamorphism) indicate 15-20kbar at similar to 600 degrees C. The pre-peak blueschist facies assemblage yields <11kbar and 400-460 degrees C. The average pressure and temperature of the post-peak amphibolite stage was 5-6kbar, similar to 470 degrees C. The Shanderman eclogites were formed by subduction of Palaeotethys oceanic crust to a depth of no more than 75km. Subduction was followed by collision between the Central Iran and Turan blocks, and then exhumation of the high pressure rocks in northern Iran.}, language = {en} }