ALBERT

Description: Passerines are the largest avian order, and the 6,000 species comprise more than half of all extant bird species. This successful radiation probably had its origin in the Australasian region, but dating this origin has been difficult due to a scarce fossil record and poor biogeographic assumptions. Many of New Zealand’s endemic passerines fall within the deeper branches of the passerine radiation, and a well resolved phylogeny for the modern New Zealand element in the deeper branches of the oscine lineage will help us understand both oscine and passerine biogeography. To this end we present complete mitochondrial genomes representing all families of New Zealand passerines in a phylogenetic framework of over 100 passerine species. Dating analyses of this robust phylogeny suggest Passeriformes originated in the early Paleocene, with the major lineages of oscines "escaping" from Australasia about 30 Ma, and radiating throughout the world during the Oligocene. This independently derived conclusion is consistent with the passerine fossil record.

Description: SUMMARY This study images upper-mantle structure beneath different tectonic and geomorphological provinces in southern Scandinavia by P -wave traveltime tomography based on teleseismic events. We present results using integrated data from several individual projects (CALAS, MAGNUS, SCANLIPS, CENMOVE and Tor) with a total of 202 temporary seismological stations deployed in southern Norway, southern Sweden, Denmark and the northernmost part of Germany. These stations, together with 18 permanent stations, yield a high density data coverage and enable presentation of the first high resolution 3D seismic velocity model for the upper mantle for this region, which includes the entire northern part of the prominent Tornquist Zone and the Southern Scandes Mountains. P -wave arrival time residuals of up to ±1 s are observed indicating large seismic velocity contrasts at depths. Relative regional as well as absolute global tomographic inversion is carried out and consistently show upper-mantle velocity variations relative to the ak135 global reference model of up to ±2–3 per cent corresponding to P -wave velocity differences of 0.4–0.5 km s –1 from depths of about 100 km to more than 300 km. High upper-mantle velocities are observed to great depth to the east in Baltic Shield areas of southwestern Sweden suggesting the existence of a deep lithosphere keel. Lower velocities are found to the west and southwest beneath the Danish and North German sedimentary basins and in most of southern Norway. A well defined, generally narrow and deep boundary is observed between areas of contrasting upper-mantle seismic velocity. In the southern part of the study area, this boundary is localized along and east of the Sorgenfrei–Tornquist Zone. It seems to follow the eastern boundary of a zone of significant Late Carboniferous–Permian volcanic activity from southwestern Sweden to the Oslo Graben area. To the north, it crosses shield units, Caledonides as well as areas of high topography. Supported by independent results of surface wave studies, we interpret this velocity boundary as a first order lithosphere boundary representing the southwestern edge of thick shield lithosphere. In basin areas to the southwest, low upper-mantle velocities are associated with asthenosphere beneath thinned lithosphere and velocity contrasts are likely to arise mainly from temperature differences. To the north structural and geodynamic relations are more complex and both temperature and compositional differences may play a part. Reduced upper-mantle velocity beneath southern Norway also seems, despite relatively low heat flow, to be associated with areas of thinned lithosphere, pointing towards increased temperatures and reduced density in the upper mantle. This feature extends over large areas and seems not directly correlated to the shorter wavelength high topography of the Scandes Mountains, but may contribute with some isostatic buoyancy on a regional scale. For this northern area, there is no obvious geodynamic explanation to reduced upper-mantle velocity. A number of candidates are available including deep transient thermal influence from basin areas to the southwest.

Description: The relative traveltime residuals of more than 20 000 arrival times of teleseismic P and S waves measured over a period of more than 10 yr in five separate temporary and two permanent seismic networks covering the Scandinavian (Scandes) Mountains and adjacent areas of the Baltic Shield are inverted to 3-D tomograms of P and S velocities and the V P / V S ratio. Resolution analysis documents that good 3-D resolution is available under the dense network south of 64° latitude (Southern Scandes Mountains), and patchier, but highly useful resolution is available further north, where station coverage is more uneven. A pronounced upper-mantle velocity boundary (UMVB) that transects the study region is defined. It runs from SE Norway (east of the Oslo Graben) across the mountains to the Norwegian coast near Trondheim (around the Møre–Trøndelag Fault Complex), after which it follows closely along the coast further north. Seismic velocities in the depth interval 100–300 km change significantly across the UMVB from low relative V P and even lower relative V S on the western side, to high relative V P and even higher relative V S to the east. This main velocity boundary therefore also separates relatively high V P / V S ratio to the west and relatively low V P / V S to the east. Under the Southern Scandes Mountains (most of southern Norway), we find low relative V P , even lower relative V S and hence high V P / V S ratios. These velocities are indicative of thinner lithosphere, higher temperature and less depletion and/or fluid content in a relatively shallow asthenosphere. At first sight, this might support the idea of a mantle buoyancy source for the high topography. Under the Northern Scandes Mountains, we find the opposite situation: high relative V P , even higher relative V S and hence low V P / V S ratios, consistent with thick, dry, depleted lithosphere, similar to that in most of the Baltic Shield area. This demonstrates significant differences in upper-mantle conditions between the Southern and Northern Scandes Mountains, and it shows that upper-mantle velocity anomalies are very poor predictors of topography in this region. An important deviation from this principal pattern is found near the topographic saddle between the Southern and Northern Scandes Mountains. Centred around 64°N, 14°E, a zone of lower S velocity and hence higher V P / V S ratio is detected in the depth interval between 100 and 300 km. This ‘Trøndelag–Jämtland mantle anomaly’ (TJMA) is still interpreted as part of relatively undisturbed lithosphere of shield affinity because of high relative P velocity, but the relatively low V P / V S ratios indicate lower depletion, possibly higher fluid content, and most likely lower viscosity relative to the adjacent shield units. We suggest that this mantle anomaly may have influenced the collapse of the Caledonian Mountains, and in particular guided the location and development of the Møre–Trøndelag Fault Complex. The TJMA is therefore likely to have played an important role in the development of the ‘two-dome architecture’ of the Scandes Mountains.

Description: We present a new Moho depth model of the British Isles and surrounding areas from the most up-to-date compilation of Moho depth estimates obtained from refraction, reflection and receiver function data. We use a probabilistic, trans-dimensional and hierarchical approach for the surface reconstruction of Moho topography. This fully data-driven approach allows for adaptive parametrization, assessment of relative importance between different data-types and uncertainties quantification on the reconstructed surface. Our results confirm the first order features of the Moho topography obtained in previous work such as deeper Moho (29–36 km) in continental areas (e.g. Ireland and Great Britain) and shallower Moho (12–22 km) offshore (e.g. in the Atlantic Ocean, west of Ireland). Resolution is improved by including recent available data, especially around the Porcupine Basin, onshore Ireland and Great Britain. NE trending features in Moho topography are highlighted above the Rockall High (about 28 km) and the Rockall Trough (with a NE directed deepening from 12 to about 20 km). A perpendicular SE oriented feature (Moho depth 26–28 km) is located between the Orkney and the Shetland, extending further SW in the North Sea. Onshore, our results highlight the crustal thinning towards the N in Ireland and an E–W oriented transition between deep (34 km) and shallow (about 28 km) Moho in Scotland. Our probabilistic results are compared with previous models showing overall differences around ±2 km, within the posterior uncertainties calculated with our approach. Bigger differences are located where different data are used between models or in less constrained areas where posterior uncertainties are high.