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Andrea Zanchi - One of the best experts on this subject based on the ideXlab platform.
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2009. The drift history of Iran from the Ordovician to the Triassic
2016Co-Authors: Giovanni Muttoni, Massimo Mattei, Marco Balini, Andrea Zanchi, Maurizio Gaetani, Fabrizio BerraAbstract:Abstract: New Late Ordovician and Triassic palaeomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician–Triassic. A robust agreement of palaeomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician–earliest Carboniferous, indicat-ing that Iran was part of Gondwana during that time. Data for the Late Permian–early Early Tri-assic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere. Since the late Early Triassic, Iran has been located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Palaeotethys in approximately 35 Ma, at an average plate speed of c. 7–8 cm year21, and was in part coeval to the transformation of Pangaea from an Irvin-gian B to a Wegenerian A-type configuration. According to Sengör (1979), a strip of Gondwanan terranes called the Cimmerian Continent, which includes Iran, broke off the eastern Gondwanan margin during the Permian–Triassic, drifted north
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Gulf PetroLink, Bahrain Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian
2016Co-Authors: Giovanni Muttoni, Massimo Mattei, Maurizio Gaetani, Fabrizio Berra, Eduardo Garzanti, D. Sciunnach, Dennis V. Kent, Andrea ZanchiAbstract:We studied the stratigraphy, composition, and paleomagnetic properties of lateritic weathering profiles of Permian age from northern Iran and western Karakoram, Pakistan. A limited set of samples deemed representative yielded stable low-inclination paleomagnetic components carried essentially by hematite of chemical origin isolated in massive, fine-grained, and homogeneous ferricrete facies. These laterites originated at equatorial paleolatitudes characterized by intense weathering processes under warm and humid climatic conditions. Paleomagnetic estimates of paleolatitude from Iran, Karakoram, and north Tibet from this study and the literature, albeit sparse, provide testable constraints on the motion of the Cimmerian terranes as the result of the opening of the Neo-Tethys Ocean along the eastern margin of Gondwana during the Permian. We confirm and help refine previous suggestions that the Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle Permian – Early Triassic. As a novel conclusion, we find that timing, rates, and geometry of Cimmerian tectonics are broadly compatible with the transformation of Pangea from an Irvingian B to a Wegenerian A-type configuration with Neo-Tethyan opening taking place contemporaneously essentially in the Permian
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Oblique convergence during the Cimmerian collision: Evidence from the Triassic Aghdarband Basin, NE Iran
Gondwana Research, 2016Co-Authors: Andrea Zanchi, Stefano Zanchetta, Marco Balini, Mohammad R. GhassemiAbstract:Abstract The Lower-Middle Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed arc-related marine succession deposited along the southern margin of Eurasia in a highly mobile tectonic context. This basin is a key-area for the study of the Cimmerian events, as the Triassic units show severe deformations, which occurred short time after the collision of Iran with Eurasia, and were sealed by the Middle Jurassic succession. In this work, we document the structural setting and evolution of this area, based on detailed mesoscopic structural analyses of faults and folds, paleostress reconstruction and revision of the Triassic stratigraphy. The Triassic sequences are deeply involved in a N-verging thrust stack interacting with an important left-lateral transpressional fault zone characterized by strike-slip faults, vertical folds and high angle reverse faults generating intricate positive flowers. Systematic folds asymmetry indicates that they developed in a left-lateral transpressional zone coeval to thrust imbrication to the south, due to a marked strain partitioning. The extent of the transpressional zone shows that important left-lateral movements developed parallel to the belt during the Cimmerian collision, in response to oblique convergence between Iran and Eurasia. Inversion of Triassic syn-sedimentary faults, possibly inherited from Palaeozoic structures of the Kopeh Dagh basement and favouring strain partitioning, is suggested by unconformities, significant differences in the sedimentary successions, repeated olistoliths, scarp-related coarse breccias and rapid tectonic drowning, occurring especially along the northern tectonic boundary of the basin. Paleostress analyses point to a complex stress pattern showing a 45° rotation of the stress field along the left-lateral fault system, related to a complete deformation partitioning in two domains respectively characterized by pure reverse dip-slip and strike-slip motions. The main direction of compression, possibly oriented NE–SW in present days coordinates, favoured the development of large shear zones disrupting the eastern portion of the Cimmerian orogen.
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The Cimmerian accretionary wedge of Anarak, Central Iran
Journal of Asian Earth Sciences, 2015Co-Authors: Andrea Zanchi, Stefano Zanchetta, Fabrizio Berra, Nadia Malaspina, L. Benciolini, Maria Bergomi, Alessandro Cavallo, Hamid Reza Javadi, Meyssam KouhpeymaAbstract:Abstract The occurrence in Iran of several ophiolite belts dating between Late Palaeozoic to Triassic poses several questions on the possible existence of various sutures marking the closure of the Palaeotethys ocean between Eurasia and this Gondwana-derived microplate. In this scenario, the Anarak region in Central Iran still represents a conundrum. Contrasting geochronological, paleontological, paleomagnetic data and reported field evidence suggest different origins for the Anarak Metamorphic Complex (AMC). The AMC is either interpreted, as: (1) relict of an accretionary wedge developed at the Eurasia margin during the Palaeotethys subduction as part of the Cimmerian suture zone of NE Iran, displaced to Central Iran by a large counter-clockwise rotation of the central Iranian blocks; (2) autochthonous unit forming a secondary branch of the main suture zone. Our structural, petrographic and geochemical data indicate that the AMC consists of several metamorphic units also including dismembered “ophiolites” which display different tectono-metamorphic evolutions. Three main ductile deformational events can be distinguished in the AMC. The Morghab and Chah Gorbeh complexes preserve a different M 1 metamorphism, characterized by blueschist relics in the S 1 foliation of the former unit, and greenschist assemblages in the latter. They share a subsequent similar D 2 deformational and M 2 metamorphic history, showing a prograde metamorphism with syn- to post-deformation growth of blueschist facies mineral assemblages on pre-existing greenschist facies associations. High pressure, low temperature (HP/LT) metamorphism responsible for the growth of sodic amphibole has been recognized also within marble lenses at the contact between the Chah Gorbeh Complex and serpentinites. Evidence of HP/LT metamorphism also occurs in glaucophane-bearing meta-pillow lavas and serpentinites, which contain antigorite and form most of the “ophiolites” within the AMC. Structural relationships show that the Chah Gorbeh and Morghab units and the “ophiolites” were tectonically coupled within an accretionary wedge before the D 2 folding stage. The other units of the AMC lack evidence of HP metamorphism in the area around Anarak, especially the Lakh Marble, a large thrust sheet that occupies the uppermost structural position in the AMC. Available radiometric ages of trondhjemite dikes and stocks that intruded the accretionary wedge, as well as our new data, constrain the subduction event at the end of the Carboniferous, before 290 Ma. These data suggest that the AMC is part of an allochthonous crustal fragment belonging to the Variscan belt developed along the southern Eurasian margin before the Cimmerian collision of Iran. Subsequent deformational events that occurred during the Mesozoic and the Cenozoic, up to the Miocene and possibly later, resulted in folding, thrusting and faulting that dismembered the original structure of the wedge accompanying its displacement to the present day position.
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The Cimmerian geopuzzle: new data from South Pamir
Terra Nova, 2013Co-Authors: Lucia Angiolini, Stefano Zanchetta, Andrea Zanchi, Alda Nicora, Giovanni VezzoliAbstract:Based on its Permian-Triassic stratigraphic and biotic evolution, we correlate the SE Pamir to the Karakoram terrane, and we consider them equivalent, along with the Central Pamir, to the Qiantang Terrane of Tibet, all of Palaeozoic Gondwanan ancestry. We prove the occurrence of a marked Cimmerian unconformity, documented by lowermost Jurassic deposits suturing intensively faulted and folded Permian and Triassic units, which suggests that the South Pamir collided around the T-J boundary with the Central Pamir along the Rushan-Pshart suture. Collision of the Karakoram to the South Pamir happened slightly later along the Wakhan-Tirich Boundary Zone. Progressive time shifting of deformation can be related to the complex setting of the Cimmerian belt, which was subdivided into minor blocks by incipient oceanic basins, providing strong crustal mobility. Terra Nova, 25, 352–360, 2013
Giovanni Muttoni - One of the best experts on this subject based on the ideXlab platform.
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2009. The drift history of Iran from the Ordovician to the Triassic
2016Co-Authors: Giovanni Muttoni, Massimo Mattei, Marco Balini, Andrea Zanchi, Maurizio Gaetani, Fabrizio BerraAbstract:Abstract: New Late Ordovician and Triassic palaeomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician–Triassic. A robust agreement of palaeomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician–earliest Carboniferous, indicat-ing that Iran was part of Gondwana during that time. Data for the Late Permian–early Early Tri-assic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere. Since the late Early Triassic, Iran has been located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Palaeotethys in approximately 35 Ma, at an average plate speed of c. 7–8 cm year21, and was in part coeval to the transformation of Pangaea from an Irvin-gian B to a Wegenerian A-type configuration. According to Sengör (1979), a strip of Gondwanan terranes called the Cimmerian Continent, which includes Iran, broke off the eastern Gondwanan margin during the Permian–Triassic, drifted north
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Gulf PetroLink, Bahrain Opening of the Neo-Tethys Ocean and the Pangea B to Pangea A transformation during the Permian
2016Co-Authors: Giovanni Muttoni, Massimo Mattei, Maurizio Gaetani, Fabrizio Berra, Eduardo Garzanti, D. Sciunnach, Dennis V. Kent, Andrea ZanchiAbstract:We studied the stratigraphy, composition, and paleomagnetic properties of lateritic weathering profiles of Permian age from northern Iran and western Karakoram, Pakistan. A limited set of samples deemed representative yielded stable low-inclination paleomagnetic components carried essentially by hematite of chemical origin isolated in massive, fine-grained, and homogeneous ferricrete facies. These laterites originated at equatorial paleolatitudes characterized by intense weathering processes under warm and humid climatic conditions. Paleomagnetic estimates of paleolatitude from Iran, Karakoram, and north Tibet from this study and the literature, albeit sparse, provide testable constraints on the motion of the Cimmerian terranes as the result of the opening of the Neo-Tethys Ocean along the eastern margin of Gondwana during the Permian. We confirm and help refine previous suggestions that the Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle Permian – Early Triassic. As a novel conclusion, we find that timing, rates, and geometry of Cimmerian tectonics are broadly compatible with the transformation of Pangea from an Irvingian B to a Wegenerian A-type configuration with Neo-Tethyan opening taking place contemporaneously essentially in the Permian
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Guadalupian (Middle Permian) paleobiogeography of the Neotethys Ocean
Gondwana Research, 2013Co-Authors: Lucia Angiolini, Giovanni Muttoni, Gaia Crippa, Johannes PignattiAbstract:Abstract A matrix of presence/absence data of Guadalupian (Middle Permian) brachiopod genera from Sicily, Tunisia, Oman, Turkey, north Iran, central Afghanistan, Karakoram, Salt Range, and south Thailand has been analyzed by multivariate methods (cluster analysis, principal coordinate analysis, minimum spanning trees) and Parsimony Analysis of Endemicity. The application of these different and independent paleobiogeographical methods has led to the individuation of three bioprovinces: the Cathaysian (Sicily and Tunisia), Cimmerian (Oman, Turkey, north Iran, Salt Range, south Thailand) and Transhimalayan (Karakoram and central Afghanistan) provinces. These provinces have been placed on a paleogeographical reconstruction based on paleomagnetic data, which we used to decipher the principal factors that governed brachiopod distribution in the Neotethys Ocean during the Guadalupian. As a conclusion, the pattern of biotic provinces at this time resulted from the complex interplay between latitudinal thermal gradient, oceanic paleocurrents, and the continental drift of the Cimmerian terranes across zonal climate belts.
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Paleobiogeography of the Permian Neo-Tethys Shores
GEO 2010, 2010Co-Authors: Lucia Angiolini, Giovanni Muttoni, Gaia Crippa, V. VernaAbstract:The Permian was a period of marked climate change and plate tectonic reconfiguration. Climate changed from glacial conditions at the dawn of the period to warm conditions in the Middle Permian. The Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle-Late Permian as the result of the opening of the Neo-Tethys Ocean. This opening was asymmetrical, with higher seafloor spreading rates for the central Cimmerian terranes (central Afghanistan, Pakistan Karakoram) than for the western terranes (Iran), and it took place contemporaneously with the transformation of Pangea from an Irvingian B to a Wegenerian Atype configuration. During this Early to Middle Permian tectono-climatic transition, bioprovincial patterns evolved rapidly across the southern and northern margins of the opening Neo-Tethys Ocean, as testified by the rich fossil record. Here we place climate-sensitive biotic associations on paleomagnetically based paleogeographic reconstructions of the Gondwanan margin and the Cimmerian blocks for the Early and Middle Permian and use them to reconstruct the evolution of oceanic circulation patterns, latitudinal thermal gradients, and biogeography in this time interval. We show that, in the Early Permian, the tropical Gondwanan margin and the western Cimmerian terranes benefited from a warm subtropical surface current gyre, which was confined to low latitudes. At the same time at higher southern latitudes, the central Cimmerian terranes were affected by cold surface currents promoted by the Gondwanan ice caps that distributed cold biota toward the tropics. These results suggest that low latitude sea surface temperature did not undergo significant cooling during the Gondwanan glaciation and that there was a steep thermal gradient between the compressed tropical belt and the expanded cold high latitude belt. This situation changed abruptly in the Middle Permian with the creation of current gyres in the newly opened Neo-Tethys Ocean that arranged biotic associations in distinct bioprovinces. Wordian brachiopods from the western Cimmerian terranes contain a significant proportion of Gondwanan taxa some of which are restricted to the Gondwanan margin (Tunisia, Turkey, Oman). Coeval brachiopods from central Cimmerian terranes are instead different and pertain to a separate, low-latitude bioprovince supporting the paleomagnetically derived differential drift of Cimmerian terranes.
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The Cimmerian evolution of the Nakhlak–Anarak area, Central Iran, and its bearing for the reconstruction of the history of the Eurasian margin
Geological Society London Special Publications, 2009Co-Authors: Andrea Zanchi, Stefano Zanchetta, Massimo Mattei, Marco Balini, Fabrizio Berra, Eduardo Garzanti, Giovanni MuttoniAbstract:New structural, sedimentological, petrological and palaeomagnetic data collected in the region of Nakhlak-Anarak provide important constraints on the Cimmerian evolution of Central Iran. The Olenekian- Upper Ladinian succession of Nakhlak was deposited in a forearc setting, and records the exhumation and erosion of an orogenic wedge, possibly located in the present-day Anarak region. The Triassic succession was deformed after Ladinian times and shows south-vergent folds and thrusts unconformably covered by Upper Cretaceous limestones following the Late Jurassic Neo-Cimmerian deformation. Palaeomagnetic data obtained in the Olenekian succession suggest a palaeoposition of the region close to Eurasia at a latitude around 208N. In addition, the palaeopoles do not support large anticlockwise rotations around ver- tical axes for central Iran with respect to Eurasia since the Middle Triassic, as previously suggested. The Anarak Metamorphic Complex (AMC) includes blueschist-facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and Carboniferous greenschist- facies 'Variscan' metamorphic rocks, including widespread metacarbonates. The AMC was formed, at least partially, in the Triassic. Its erosion is recorded by the Middle Triassic Baqoroq Formation at Nakhlak, which consists of conglomerates and sandstones rich in meta- morphic detritus. The AMC was repeatedly deformed during post-Triassic times, giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units. Based on these data, we suggest that the Nakhlak-Anarak units represent an arc-trench system developed during the Eo-Cimmerian orogenic cycle. Different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within Central Iran are critically discussed, as well as its relationships with a presumed 'Variscan' metamorphic event. The Cimmerian orogeny, affecting the southern Eurasian margin between Turkey and Thailand, is related to the collision of several microplates, most of which detached from northern Gondwana in the Early Permian during the opening of the
Stefano Zanchetta - One of the best experts on this subject based on the ideXlab platform.
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Oblique convergence during the Cimmerian collision: Evidence from the Triassic Aghdarband Basin, NE Iran
Gondwana Research, 2016Co-Authors: Andrea Zanchi, Stefano Zanchetta, Marco Balini, Mohammad R. GhassemiAbstract:Abstract The Lower-Middle Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed arc-related marine succession deposited along the southern margin of Eurasia in a highly mobile tectonic context. This basin is a key-area for the study of the Cimmerian events, as the Triassic units show severe deformations, which occurred short time after the collision of Iran with Eurasia, and were sealed by the Middle Jurassic succession. In this work, we document the structural setting and evolution of this area, based on detailed mesoscopic structural analyses of faults and folds, paleostress reconstruction and revision of the Triassic stratigraphy. The Triassic sequences are deeply involved in a N-verging thrust stack interacting with an important left-lateral transpressional fault zone characterized by strike-slip faults, vertical folds and high angle reverse faults generating intricate positive flowers. Systematic folds asymmetry indicates that they developed in a left-lateral transpressional zone coeval to thrust imbrication to the south, due to a marked strain partitioning. The extent of the transpressional zone shows that important left-lateral movements developed parallel to the belt during the Cimmerian collision, in response to oblique convergence between Iran and Eurasia. Inversion of Triassic syn-sedimentary faults, possibly inherited from Palaeozoic structures of the Kopeh Dagh basement and favouring strain partitioning, is suggested by unconformities, significant differences in the sedimentary successions, repeated olistoliths, scarp-related coarse breccias and rapid tectonic drowning, occurring especially along the northern tectonic boundary of the basin. Paleostress analyses point to a complex stress pattern showing a 45° rotation of the stress field along the left-lateral fault system, related to a complete deformation partitioning in two domains respectively characterized by pure reverse dip-slip and strike-slip motions. The main direction of compression, possibly oriented NE–SW in present days coordinates, favoured the development of large shear zones disrupting the eastern portion of the Cimmerian orogen.
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The Cimmerian accretionary wedge of Anarak, Central Iran
Journal of Asian Earth Sciences, 2015Co-Authors: Andrea Zanchi, Stefano Zanchetta, Fabrizio Berra, Nadia Malaspina, L. Benciolini, Maria Bergomi, Alessandro Cavallo, Hamid Reza Javadi, Meyssam KouhpeymaAbstract:Abstract The occurrence in Iran of several ophiolite belts dating between Late Palaeozoic to Triassic poses several questions on the possible existence of various sutures marking the closure of the Palaeotethys ocean between Eurasia and this Gondwana-derived microplate. In this scenario, the Anarak region in Central Iran still represents a conundrum. Contrasting geochronological, paleontological, paleomagnetic data and reported field evidence suggest different origins for the Anarak Metamorphic Complex (AMC). The AMC is either interpreted, as: (1) relict of an accretionary wedge developed at the Eurasia margin during the Palaeotethys subduction as part of the Cimmerian suture zone of NE Iran, displaced to Central Iran by a large counter-clockwise rotation of the central Iranian blocks; (2) autochthonous unit forming a secondary branch of the main suture zone. Our structural, petrographic and geochemical data indicate that the AMC consists of several metamorphic units also including dismembered “ophiolites” which display different tectono-metamorphic evolutions. Three main ductile deformational events can be distinguished in the AMC. The Morghab and Chah Gorbeh complexes preserve a different M 1 metamorphism, characterized by blueschist relics in the S 1 foliation of the former unit, and greenschist assemblages in the latter. They share a subsequent similar D 2 deformational and M 2 metamorphic history, showing a prograde metamorphism with syn- to post-deformation growth of blueschist facies mineral assemblages on pre-existing greenschist facies associations. High pressure, low temperature (HP/LT) metamorphism responsible for the growth of sodic amphibole has been recognized also within marble lenses at the contact between the Chah Gorbeh Complex and serpentinites. Evidence of HP/LT metamorphism also occurs in glaucophane-bearing meta-pillow lavas and serpentinites, which contain antigorite and form most of the “ophiolites” within the AMC. Structural relationships show that the Chah Gorbeh and Morghab units and the “ophiolites” were tectonically coupled within an accretionary wedge before the D 2 folding stage. The other units of the AMC lack evidence of HP metamorphism in the area around Anarak, especially the Lakh Marble, a large thrust sheet that occupies the uppermost structural position in the AMC. Available radiometric ages of trondhjemite dikes and stocks that intruded the accretionary wedge, as well as our new data, constrain the subduction event at the end of the Carboniferous, before 290 Ma. These data suggest that the AMC is part of an allochthonous crustal fragment belonging to the Variscan belt developed along the southern Eurasian margin before the Cimmerian collision of Iran. Subsequent deformational events that occurred during the Mesozoic and the Cenozoic, up to the Miocene and possibly later, resulted in folding, thrusting and faulting that dismembered the original structure of the wedge accompanying its displacement to the present day position.
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The Cimmerian geopuzzle: new data from South Pamir
Terra Nova, 2013Co-Authors: Lucia Angiolini, Stefano Zanchetta, Andrea Zanchi, Alda Nicora, Giovanni VezzoliAbstract:Based on its Permian-Triassic stratigraphic and biotic evolution, we correlate the SE Pamir to the Karakoram terrane, and we consider them equivalent, along with the Central Pamir, to the Qiantang Terrane of Tibet, all of Palaeozoic Gondwanan ancestry. We prove the occurrence of a marked Cimmerian unconformity, documented by lowermost Jurassic deposits suturing intensively faulted and folded Permian and Triassic units, which suggests that the South Pamir collided around the T-J boundary with the Central Pamir along the Rushan-Pshart suture. Collision of the Karakoram to the South Pamir happened slightly later along the Wakhan-Tirich Boundary Zone. Progressive time shifting of deformation can be related to the complex setting of the Cimmerian belt, which was subdivided into minor blocks by incipient oceanic basins, providing strong crustal mobility. Terra Nova, 25, 352–360, 2013
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is se pamir a Cimmerian block
Riunione Annuale GIGS 2012 Gruppo Italiano Geologia Strutturale Modena 25-26 Ottobre 2012, 2012Co-Authors: Andrea Zanchi, Stefano Zanchetta, Lucia Angiolini, Giovanni VezzoliAbstract:L'orogenesi Cimmerica in SE Pamir.La presenza di un'importante fase deformativa avvenuta tra la fine del Triassico e l'inizio del Giurassico e testimoniata in piu localita del SE-Pamir da spettacolari discordanze angolari a 90° tra le successioni Permo-Triassiche e i depositi del Giurassico basale. Pieghe da chiuse a isoclinali e sovrascorrimenti con direzione compresa tra N-S e NNW-SSE sono osservabili sia a scala mesoscopica, sia a quella regionale nella porzione orientale della catena dei Monti di Alichur, situati a E di Murgab. Queste strutture indicano un importante evento deformativo di tipo compressivo, connesso alla collisione di questo blocco con il margine meridionale di Eurasia. L'evoluzione paleogeografica, ricostruita attraverso l'analisi delle successione Permiane e Triassiche, indica infatti che il SE Pamir si e separato dal margine Gondwaniano nel Permiano Inferiore, per migrare verso N in seguito all'apertura della Neotetide e raggiungere il margine Eurasiatico alla fine del Triassico. La messa in posto di alcuni di corpi ofiolitici (Bashgumbaz Complex) presenti in quest'area del SE Pamir sembra essere legata allo stesso evento deformativo Cimmerico.
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The Cimmerian evolution of the Nakhlak–Anarak area, Central Iran, and its bearing for the reconstruction of the history of the Eurasian margin
Geological Society London Special Publications, 2009Co-Authors: Andrea Zanchi, Stefano Zanchetta, Massimo Mattei, Marco Balini, Fabrizio Berra, Eduardo Garzanti, Giovanni MuttoniAbstract:New structural, sedimentological, petrological and palaeomagnetic data collected in the region of Nakhlak-Anarak provide important constraints on the Cimmerian evolution of Central Iran. The Olenekian- Upper Ladinian succession of Nakhlak was deposited in a forearc setting, and records the exhumation and erosion of an orogenic wedge, possibly located in the present-day Anarak region. The Triassic succession was deformed after Ladinian times and shows south-vergent folds and thrusts unconformably covered by Upper Cretaceous limestones following the Late Jurassic Neo-Cimmerian deformation. Palaeomagnetic data obtained in the Olenekian succession suggest a palaeoposition of the region close to Eurasia at a latitude around 208N. In addition, the palaeopoles do not support large anticlockwise rotations around ver- tical axes for central Iran with respect to Eurasia since the Middle Triassic, as previously suggested. The Anarak Metamorphic Complex (AMC) includes blueschist-facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and Carboniferous greenschist- facies 'Variscan' metamorphic rocks, including widespread metacarbonates. The AMC was formed, at least partially, in the Triassic. Its erosion is recorded by the Middle Triassic Baqoroq Formation at Nakhlak, which consists of conglomerates and sandstones rich in meta- morphic detritus. The AMC was repeatedly deformed during post-Triassic times, giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units. Based on these data, we suggest that the Nakhlak-Anarak units represent an arc-trench system developed during the Eo-Cimmerian orogenic cycle. Different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within Central Iran are critically discussed, as well as its relationships with a presumed 'Variscan' metamorphic event. The Cimmerian orogeny, affecting the southern Eurasian margin between Turkey and Thailand, is related to the collision of several microplates, most of which detached from northern Gondwana in the Early Permian during the opening of the
Johann Genser - One of the best experts on this subject based on the ideXlab platform.
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The tectonic evolution of western Central Iran seen through detrital white mica
Tectonophysics, 2015Co-Authors: Fariba Kargaranbafghi, Franz Neubauer, Johann GenserAbstract:Abstract A first order survey of 40Ar/39Ar dating of detrital white mica from Jurassic to Pliocene sandstones has been carried out in order to reveal the tectonic evolution of blocks in Central Iran. The Central Iran block was believed to represent a stable Precambrian block. Our results indicate that: (1) Only a very small proportion of Precambrian but abundant Paleozoic and Mesozoic detrital white mica indicate the Phanerozoic, mostly Mesozoic age of metamorphic crust exposed in Central Iran. The oldest but scarce detrital white mica grains have ages ranging from 524 to 826 Ma heralding a Late Precambrian and Cambrian crystalline basement or cannibalism from older clastic successions. (2) Jurassic and Cretaceous sandstones from the west and east of the Chapedony fault yield different age spectra, with a dominance of Variscan ages (ca. 308–385 Ma) in the Biabanak unit west of the Chapedony fault compared to coeval sandstones from the block east of the Chapedony fault, where Variscan ages are subordinate and Cimmerian ages predominate. The micas from the Biabanak unit are most likely derived from the Variscan accretionary complex exposed in the Anarak–Jandaq areas further northwest. This result underlines the importance of a major block boundary identified as the Chapedony fault, which is in extension of a fault previously proposed. (3) Two stages of Cimmerian events are visible in our data set from Cretaceous and Paleogene sandstones, a cluster around 170 Ma and at ca. 205 Ma. These clusters suggest a two-stage Cimmerian evolution of the largely amphibolite-grade metamorphic Posht-e-Badam and Boneh Shurow complexes. (4) The youngest micas in Paleogene conglomerates have an age of ca. 100 Ma and are most likely derived from the base of the Posht-e-Badam complex. No record of the uplifted Eocene Chapedony metamorphic core complex has been found in Eocene and Pliocene clastic rocks.
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Cimmerian evolution of the Central Iranian basement: Evidence from metamorphic units of the Kashmar-Kerman Tectonic Zone
Tectonophysics, 2013Co-Authors: Mehdi Masoodi, Ali Yassaghi, Mir Ali Akbar Nogole Sadat, Franz Neubauer, Manfred Bernroider, Gertrude Friedl, Johann Genser, Abdolrahim HoushmandzadehAbstract:Abstract The Kashmar–Kerman Tectonic Zone (KKTZ) is an arcuate zone located between the Tabas and Yazd blocks in Central Iran. Detailed structural analysis and mapping of the metamorphic basement rocks of the KKTZ on the Boneh-Shurow, Tashk, Saghand and Sarkuh Metamorphic Complexes, as well as 40 Ar/ 39 Ar cooling ages on the Boneh-Shurow Metamorphic Complex indicate three deformation stages in the tectonometamorphic evolution of the KKTZ during the Cimmerian orogeny. The D 1–1 event corresponds to continental accretion through the progressive formation of dextral shear zones, which is equivalent to an Early Cimmerian event during Late Triassic–Early Jurassic times. The D 1–2 event is characterized by top-to-NE normal shear zones due to syn-collisional exhumation within the KKTZ and is considered to be a Mid-Cimmerian Middle Jurassic event at ca. 168 Ma. The progressive regional compressional deformation is continued by the D 2–1 and D 2–2 events through formation of reverse shear zones and faults, with their SW movement. The progressive D 2 event is considered to be Late Cimmerian and has taken place during Early Cretaceous. It is proposed that the mapped long-lived dextral shear zones within the KKTZ acted as block bounding faults between the Tabas and Yazd blocks in Central Iran.
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The Mesozoic-Cenozoic tectonic evolution of western Central Iran seen through detrital white mica
2009Co-Authors: F. Kargaranbafgi, Franz Neubauer, Johann GenserAbstract:A first order survey of Ar-Ar dating of detrital white mica from Jurassic to Pliocene sandstones has been carried out in order to reveal the tectonic evolution of blocks in Central Iran (Saghand area). The Central Iran block was believed to represent a stable Precambrian block. Our results indicate: (1) There is only a very small proportion of bearing detrital mica in the hinterland suggesting to full Phanerozoic nature of metamorphic crust exposed in Central Iran. The oldest but scarce detrital white mica grains have ages ranging from 517 to 817 Ma heralding a Late Precambrian and Cambrian crystalline basement or cannibalism from older clastic successions. (2) Jurassic and Cretaceous sandstones from west and east of the Chapedony fault yield different age spectra, with a dominance of Variscan ages (ca. 305 ‐ 360 Ma) compared to coeval sandstones from the block east of the Chapedony fault, where Variscan ages are subordinate and Cimmerian ages predominate. These micas are likely derived from the Variscan accretionary complex exposed in the Anarak-Jandaq areas further northwest. This result underlines a major block boundary identified as the Chapedony fault, which is in extension of a fault previously proposed. (3) Two stages of Cimmerian events are visible in our data set from Cretaceous and Paleogene sandstones, a cluster around 170 Ma and at ca. 205 Ma. These clusters suggest a two-stage Cimmerian evolution of the Posht-e-Badam and Bonev Shurov complexes not well understood up to now. (4) The youngest micas in Paleogene conglomerates have an age of ca. 100 Ma are likely derived from the base of the Post-e-Badam complex. No record of the uplifted Eocene Chapedony metamorphic core complex has been found in Eocene and Pliocene clastic rocks. These are likely due to the scarcity of white mica in that complex as fine-grained white mica only occurs in the Neybaz-Chatak shear zone along the hangingwall boundary of that complex.
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rugose corals at the tournaisian visean transition in the central taurides s turkey palaeobiogeography and palaeoceanography of the asian gondwana margin
Journal of Asian Earth Sciences, 2015Co-Authors: Julien DenayerAbstract:Abstract This paper gives the first taxonomic description of the Upper Tournaisian–Lower Visean rugose coral fauna of the Yaricak Formation (Aladag Unit, Central Taurides, South Turkey). Fifteen species belonging to twelve genera were identified, one species is newly described: Eokoninckocarinia gemmina . The corals are stratigraphically distributed in four assemblages. The two typical assemblages of the Upper Tournaisian are composed of widely distributed taxa ( Uralinia , Caninia , Proheterelasma , Zaphrentites ). The assemblage crossing the Tournaisian–Visean boundary is characterized by Eurasian and cosmopolitan and widely distributed taxa ( Calmiussiphyllum , Siphonophyllia , Bifossularia Amygdalophyllum , Caninophyllum , Keyserlingophyllum ) and Asian taxa ( Kueichouphyllum ). The youngest assemblage, dominated by Eokoninckocarinia gemmina sp. nov., has yielded foraminifers Moliniacian (Lower Visean) in age. These assemblages form a low diversity level-bottom community which is typical of the South Palaeotethys ‘ Kueichouphyllum Zone’ extending along the Asian margin of Gondwana (Cimmerian Terrane) during Lower Carboniferous times. As in the other Cimmerian blocks, all the corals are solitary and colonial taxa are virtually absent. This absence is tentatively explained by the high palaeolatitude (c. 50°S) position of the Cimmerian Terrane in the southern part of the Palaeotethys Ocean for this time slice. A cold-water palaeo-current running eastward along the Gondwana margin might also be considered as it possibly could explain the wide distribution of the Kueichouphyllum fauna, restricted east of Africa in the southern coast of the Palaeotethys. Palaeoceanography, palaeoclimate and facies issues are discussed as possible causes of the diversity gradient observed between the eastern (Australia, Malaya) and the western (North Africa) margin of the Gondwana.
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Rugose corals at the Tournaisian–Viséan transition in the Central Taurides (S Turkey) – Palaeobiogeography and palaeoceanography of the Asian Gondwana margin
Journal of Asian Earth Sciences, 2015Co-Authors: Julien DenayerAbstract:Abstract This paper gives the first taxonomic description of the Upper Tournaisian–Lower Visean rugose coral fauna of the Yaricak Formation (Aladag Unit, Central Taurides, South Turkey). Fifteen species belonging to twelve genera were identified, one species is newly described: Eokoninckocarinia gemmina . The corals are stratigraphically distributed in four assemblages. The two typical assemblages of the Upper Tournaisian are composed of widely distributed taxa ( Uralinia , Caninia , Proheterelasma , Zaphrentites ). The assemblage crossing the Tournaisian–Visean boundary is characterized by Eurasian and cosmopolitan and widely distributed taxa ( Calmiussiphyllum , Siphonophyllia , Bifossularia Amygdalophyllum , Caninophyllum , Keyserlingophyllum ) and Asian taxa ( Kueichouphyllum ). The youngest assemblage, dominated by Eokoninckocarinia gemmina sp. nov., has yielded foraminifers Moliniacian (Lower Visean) in age. These assemblages form a low diversity level-bottom community which is typical of the South Palaeotethys ‘ Kueichouphyllum Zone’ extending along the Asian margin of Gondwana (Cimmerian Terrane) during Lower Carboniferous times. As in the other Cimmerian blocks, all the corals are solitary and colonial taxa are virtually absent. This absence is tentatively explained by the high palaeolatitude (c. 50°S) position of the Cimmerian Terrane in the southern part of the Palaeotethys Ocean for this time slice. A cold-water palaeo-current running eastward along the Gondwana margin might also be considered as it possibly could explain the wide distribution of the Kueichouphyllum fauna, restricted east of Africa in the southern coast of the Palaeotethys. Palaeoceanography, palaeoclimate and facies issues are discussed as possible causes of the diversity gradient observed between the eastern (Australia, Malaya) and the western (North Africa) margin of the Gondwana.