The Aegean Sea area is thought to be an actively extending back-arc region,north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean.The area shows extensive normal ...The Aegean Sea area is thought to be an actively extending back-arc region,north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean.The area shows extensive normal faulting,ductile‘extensional’shear zones and extensional S-C fabrics throughout the islands that have previously been related to regional Aegean extension associated with slab rollback on the Hellenic Subduction Zone.In this paper,we question this interpretation,and suggest the Cenozoic geodynamic evolution of the Aegean region is associated with a Late Cretaceous-Eocene NE-dipping subduction zone that was responsible for continentcontinent collision between Eurasia and Adria-Apulia/Cyclades.Exhumation of eclogite and blueschist facies rocks in the Cyclades and kyanite-sillimanite grade gneisses in the Naxos core complex have pressures that are far greater than could be accounted for purely by lithospheric extension and isostatic uplift.We identify four stages of crustal shortening that affected the region prior to regional lithospheric extension,herein called the Aegean Orogeny.This orogeny followed a classic Wilson cycle from early ophiolite obduction(ca.74 Ma)onto a previously passive continental margin,to attempted crustal subduction with HP eclogite and blueschist facies metamorphism(ca.54-45 Ma),through crustal thickening and regional kyanite-sillimanite grade Barroviantype metamorphism(ca.22-14 Ma),to orogenic collapse(<14 Ma).At least three periods of‘extensional’fabrics relate to:(1)Exhumation of blueschists and eclogite facies rocks showing tight-isoclinal folds and top-NE,base-SW fabrics,recording return flow along a subduction channel in a compressional tectonic setting(ca.50-35 Ma).(2)Extensional fabrics within the core complexes formed by exhumation of kyanite-and sillimanite gneisses showing thrust-related fabrics at the base and‘extensional’fabrics along the top(ca.18.5-14 Ma).(3)Regional ductile-brittle‘extensional’fabrics and low-angle normal faulting related to the North Cycladic Detachment(NCD)and the South(West)Cycladic Detachment(WCD)during regional extension along the flanks of a major NW-SE anticlinal fold along the middle of the Cyclades.Major low-angle normal faults and ductile shear zones show symmetry about the area,with the NE chain of islands(Andros,Tinos,Mykonos,Ikaria)exposing the NE-dipping NCD with consistent top-NE ductil e fabrics along 200 km of strike.In contrast,from the Greek mainland(Attica)along the SE chain of islands(Kea,Kythnos,Serifos)a SW-dipping low-angle normal fault and ductile shear zone,the WCD is inferred for at least 100 km along strike.Islands in the middle of the Cyclades show deeper structural levels including kyanite-and sillimanite-grade metamorphic core complexes(Naxos,Paros)as well as Variscan basement rocks(Naxos,Ios).The overall structure is an~100 km wavelength NW-SE trending dome with low-angle extensional faults along each flank,dipping away from the anticline axis to the NE and SW.Many individual islands show post-extensional large-scale folding of the low-angle normal faults around the domes(Naxos,Paros,Ios,Sifnos)indicating a post-Miocene late phase of E-W shortening.展开更多
The dynamic biogeography of glacial refugia may cause complex patterns of genetic admixture between parapatric taxa,which in turn can mislead their systematics,diversity,and distributions.We investigated this issue fo...The dynamic biogeography of glacial refugia may cause complex patterns of genetic admixture between parapatric taxa,which in turn can mislead their systematics,diversity,and distributions.We investigated this issue for green toads(Bufotes)inhabiting the circum-Aegean region,a biodiversity hotspot of the Eastern Mediterranean.A previous phylogeographic study based on mitochondrial and microsatellite loci identified the hybrid zone between the European(viridis)and Anatolian(sitibundus)lineages of B.viridis all over the Balkan Peninsula,but subsequent range-wide genomic analyses(>1000 SNPs)located this transition in Turkey,a thousand kilometers eastwards.In order to clarify the diversity and taxonomy of the circum-Aegean populations,we reconciled these conflicting findings by integrating previous data with pure sitibundus individuals.Our results confirmed that the viridis/sitibundus hybrid zone extends in Western Anatolia,but that southeastern European populations feature cytonuclear discordances and a high and structured microsatellite diversity.This remarkable situation may stem from a massive geographic displacement of the hybrid zone during the last glacial fluctuations,an underappreciated yet seemingly common feature among the herpetofauna of the region.Our study thus contributes to the rising view that mitochondrial DNA can be a poor predictor of current phylogeographic structure,hence the need for genomic data,especially for narrowly distributed taxa.Finally,the analyses unambiguously support the distinction of a micro-endemic clade of green toads unique to some Cyclades islands,for which we provide a formal taxonomic description.展开更多
基金Natural Environment Research Council grant NE/L0021612/1NERC Isotope Geoscience Laboratory grant IP-1597-1115 for funding。
文摘The Aegean Sea area is thought to be an actively extending back-arc region,north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean.The area shows extensive normal faulting,ductile‘extensional’shear zones and extensional S-C fabrics throughout the islands that have previously been related to regional Aegean extension associated with slab rollback on the Hellenic Subduction Zone.In this paper,we question this interpretation,and suggest the Cenozoic geodynamic evolution of the Aegean region is associated with a Late Cretaceous-Eocene NE-dipping subduction zone that was responsible for continentcontinent collision between Eurasia and Adria-Apulia/Cyclades.Exhumation of eclogite and blueschist facies rocks in the Cyclades and kyanite-sillimanite grade gneisses in the Naxos core complex have pressures that are far greater than could be accounted for purely by lithospheric extension and isostatic uplift.We identify four stages of crustal shortening that affected the region prior to regional lithospheric extension,herein called the Aegean Orogeny.This orogeny followed a classic Wilson cycle from early ophiolite obduction(ca.74 Ma)onto a previously passive continental margin,to attempted crustal subduction with HP eclogite and blueschist facies metamorphism(ca.54-45 Ma),through crustal thickening and regional kyanite-sillimanite grade Barroviantype metamorphism(ca.22-14 Ma),to orogenic collapse(<14 Ma).At least three periods of‘extensional’fabrics relate to:(1)Exhumation of blueschists and eclogite facies rocks showing tight-isoclinal folds and top-NE,base-SW fabrics,recording return flow along a subduction channel in a compressional tectonic setting(ca.50-35 Ma).(2)Extensional fabrics within the core complexes formed by exhumation of kyanite-and sillimanite gneisses showing thrust-related fabrics at the base and‘extensional’fabrics along the top(ca.18.5-14 Ma).(3)Regional ductile-brittle‘extensional’fabrics and low-angle normal faulting related to the North Cycladic Detachment(NCD)and the South(West)Cycladic Detachment(WCD)during regional extension along the flanks of a major NW-SE anticlinal fold along the middle of the Cyclades.Major low-angle normal faults and ductile shear zones show symmetry about the area,with the NE chain of islands(Andros,Tinos,Mykonos,Ikaria)exposing the NE-dipping NCD with consistent top-NE ductil e fabrics along 200 km of strike.In contrast,from the Greek mainland(Attica)along the SE chain of islands(Kea,Kythnos,Serifos)a SW-dipping low-angle normal fault and ductile shear zone,the WCD is inferred for at least 100 km along strike.Islands in the middle of the Cyclades show deeper structural levels including kyanite-and sillimanite-grade metamorphic core complexes(Naxos,Paros)as well as Variscan basement rocks(Naxos,Ios).The overall structure is an~100 km wavelength NW-SE trending dome with low-angle extensional faults along each flank,dipping away from the anticline axis to the NE and SW.Many individual islands show post-extensional large-scale folding of the low-angle normal faults around the domes(Naxos,Paros,Ios,Sifnos)indicating a post-Miocene late phase of E-W shortening.
基金Most of the data combined in this paper was originally published by Dufresnes et al.(2018,2019b)who made it available on dryad(doi:10.5061/dryad.6qv8666)NCBI SRA(BioProject PRJNA542138),respectively。
文摘The dynamic biogeography of glacial refugia may cause complex patterns of genetic admixture between parapatric taxa,which in turn can mislead their systematics,diversity,and distributions.We investigated this issue for green toads(Bufotes)inhabiting the circum-Aegean region,a biodiversity hotspot of the Eastern Mediterranean.A previous phylogeographic study based on mitochondrial and microsatellite loci identified the hybrid zone between the European(viridis)and Anatolian(sitibundus)lineages of B.viridis all over the Balkan Peninsula,but subsequent range-wide genomic analyses(>1000 SNPs)located this transition in Turkey,a thousand kilometers eastwards.In order to clarify the diversity and taxonomy of the circum-Aegean populations,we reconciled these conflicting findings by integrating previous data with pure sitibundus individuals.Our results confirmed that the viridis/sitibundus hybrid zone extends in Western Anatolia,but that southeastern European populations feature cytonuclear discordances and a high and structured microsatellite diversity.This remarkable situation may stem from a massive geographic displacement of the hybrid zone during the last glacial fluctuations,an underappreciated yet seemingly common feature among the herpetofauna of the region.Our study thus contributes to the rising view that mitochondrial DNA can be a poor predictor of current phylogeographic structure,hence the need for genomic data,especially for narrowly distributed taxa.Finally,the analyses unambiguously support the distinction of a micro-endemic clade of green toads unique to some Cyclades islands,for which we provide a formal taxonomic description.
