Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

Comparison of plate convergence with the timing and magnitude of upper crustal shortening in collisional orogens indicates both shortening deficits (200–1700 km) and significant (10–40%) plate deceleration during collision, the cause(s) for which remains debated. The Greater Caucasus Mountains, which result from postcollisional Cenozoic closure of a relict Mesozoic back‐arc basin on the northern margin of the Arabia‐Eurasia collision zone, help reconcile these debates. Here we use U‐Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now‐consumed Mesozoic back‐arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350–400 km. We propose that closure of the back‐arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia‐Eurasia collision along the Bitlis‐Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Postcollisional subduction of such small (102–103 km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back‐arc basins and fringing arcs, such as those in the modern South Pacific.Key PointsU‐Pb provenance indicates Greater Caucasus formed by postcollisional Cenozoic closure of a Mesozoic back arc basin likely ~350–400 km widePostcollisional subduction/underthrusting of such relict basins helps account for shortening deficits and delayed plate decelerationPlate convergence should not be expected to balance upper crustal shortening or the length of subducted slab following collisionPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135981/1/tect20504.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135981/2/tect20504_am.pd

Influenza A virus evolution and spatio-temporal dynamics in Eurasian wild birds: a phylogenetic and phylogeographical study of whole-genome sequence data.

Low pathogenic avian influenza A viruses (IAVs) have a natural host reservoir in wild waterbirds and the potential to spread to other host species. Here, we investigated the evolutionary, spatial and temporal dynamics of avian IAVs in Eurasian wild birds. We used whole-genome sequences collected as part of an intensive long-term Eurasian wild bird surveillance study, and combined this genetic data with temporal and spatial information to explore the virus evolutionary dynamics. Frequent reassortment and co-circulating lineages were observed for all eight genomic RNA segments over time. There was no apparent species-specific effect on the diversity of the avian IAVs. There was a spatial and temporal relationship between the Eurasian sequences and significant viral migration of avian IAVs from West Eurasia towards Central Eurasia. The observed viral migration patterns differed between segments. Furthermore, we discuss the challenges faced when analysing these surveillance and sequence data, and the caveats to be borne in mind when drawing conclusions from the apparent results of such analyses.We thank all ornithologists and other collaborators for their continuous support. We thank V. Munster, E. Skepner, O. Vuong, C. Baas, J. Guldemeester, M. Schutten, G. van der Water, D. Smith and E. Bortz for technical support and stimulating discussions. This manuscript was prepared while D.E. Wentworth was employed at the JCVI. The opinions expressed in this article are the author’s own and do not reflect the view of the Centers for Disease Control, the Department of Health and Human Services, or the United States government. This work was supported by NIAID/NIH contract HHSN266200700010C, HHSN272201400008C, HHSN272201400006C and HHSN272200900007C, a Wellcome Trust Fellowship Strategic Travel Award under contract WT089235MF, a DTRA FRCWMD Broad Agency Announcement under contract HDTRA1-09-14-FRCWMD GRANT11177182, by the EU Framework six program NewFluBird (044490) by contracts with the Dutch Ministry of Economic Affairs and a NIAID/NIH CEIRS travel grant under contract HHSN266200700010C. The Swedish sampling and analysis was supported by the Swedish Research Councils VR and FORMAS.This is the final version of the article. It first appeared from the Society for General Microbiology via http://dx.doi.org/10.1099/vir.0.00015

Avian Influenza Virus Surveillance in Wild Birds in Georgia: 2009-2011

The Caucasus, at the border of Europe and Asia, is important for migration and over-wintering of wild waterbirds. Three flyways, the Central Asian, East Africa-West Asia, and Mediterranean/Black Sea flyways, converge in the Caucasus region. Thus, the Caucasus region might act as a migratory bridge for influenza virus transmission when birds aggregate in high concentrations in the post-breeding, migrating and overwintering periods. Since August 2009, we have established a surveillance network for influenza viruses in wild birds, using five sample areas geographically spread throughout suitable habitats in both eastern and western Georgia. We took paired tracheal and cloacal swabs and fresh feces samples. We collected 8343 swabs from 76 species belonging to 17 families in 11 orders of birds, of which 84 were real-time RT-PCR positive for avian influenza virus (AIV). No highly pathogenic AIV (HPAIV) H5 or H7 viruses were detected. The overall AIV prevalence was 1.6%. We observed peak prevalence in large gulls during the autumn migration (5.3-9.8%), but peak prevalence in Black-headed Gulls in spring (4.2-13%). In ducks, we observed increased AIV prevalence during the autumn post-moult aggregations and migration stop-over period (6.3%) but at lower levels to those observed in other more northerly post-moult areas in Eurasia. We observed another prevalence peak in the overwintering period (0.14-5.9%). Serological and virological monitoring of a breeding colony of Armenian Gulls showed that adult birds were seropositive on arrival at the breeding colony, but juveniles remained serologically and virologically negative for AIV throughout their time on the breeding grounds, in contrast to gull AIV data from other geographic regions. We show that close phylogenetic relatives of viruses isolated in Georgia are sourced from a wide geographic area throughout Western and Central Eurasia, and from areas that are represented by multiple different flyways, likely linking different host sub-populations

Active deformation and Plio-Pleistocene fluvial reorganization of the western Kura fold-thrust belt, Georgia: Implications for the evolution of the Greater Caucasus Mountains

© The Author(s), 2020. Published by Cambridge University Press. Since Plio-Pleistocene time, southward migration of shortening in the eastern part of the Greater Caucasus into the Kura foreland basin has progressively formed the Kura fold-thrust belt and Alazani piggyback basin, which separates the Kura fold-thrust belt from the Greater Caucasus. Previous work argued for an eastward propagation of the Kura fold-thrust belt, but this hypothesis was based on coarse geological maps and speculative ages for units within the Kura fold-thrust belt. Here we investigate the initiation of deformation within the Gombori range in the western Kura fold-thrust belt and evaluate this eastward propagation hypothesis. Sediments exposed in the Gombori range have a Greater Caucasus source, despite the modern drainage network in the NE Gombori range, which is dominated by NE-flowing rivers. Palaeocurrent analyses of the oldest and youngest syntectonic units indicate a switch happened between ∼2.7 Ma and 1 Ma from dominantly SW-directed flow to palaeocurrents more similar to the modern drainage network. A single successful 26Al-10Be burial date indicates the youngest syntectonic sediments are 1.0 ± 1.0 Ma, which, while not a precise age, is consistent with original mapping suggesting these sediments are of Akchagylian-Apsheronian (2.7-0.88 Ma) age. These results, along with recent updated dating of thrust initiation in the eastern Kura fold-thrust belt, suggest that deformation within the Kura fold-thrust belt initiated synchronously or nearly synchronously along-strike. We additionally use topographic analyses to show that the Gombori range continues to be a zone of active deformation

Flyway map of Eurasia showing the location and subtype of the closest phylogenetic relative to each Georgian isolate.

<p>Georgia is shown as an orange circle and the subtype icons are colored according to the flyway in which the place of isolation lies. The flyway colors are: East Atlantic (green), Black Sea-Mediterranean (blue), East Africa-West Asia (red), Central Asia (black), East Asia Australian (purple).</p

A–B. Longitudinal surveillance effort and AIV prevalence and subtype data in the two main species groups.

<p>Number of individual ducks (A) and gulls (B) sampled, the percentage of AIV positive birds and the subtype isolated during the study period January 2010–November 2011.</p

Maximum likelihood phylogenetic trees based on HA (left) and NA (right) nucleotide sequences of low pathogenic avian influenza A viruses isolated from wild birds between 1956–2011.

<p>The isolate names in the tree are colored according to migratory flyway: East Atlantic (green), Black Sea-Mediterranean (blue), East Africa-West Asia (red), Central Asia (black), East Asia Australian (purple). The isolates from Georgia are marked with a black asterisk and the subtype indicated on the panel.</p