The Potential and Limitations of 2D Seismic Experiments for 3D Tomography

The Liguro-Provençal Basin is located in a complex tectonic area, at the junction of the Western Alps and Northern Apennines. Despite its central location within Europe, much about the basin, including the character of the crust, and the continuation of the Alpine orogen offshore, remain ambiguous. The basin began opening in the late Oligocene as a back-arc basin related to the retreat of the Apennine subduction zone. Opening continued into the early Miocene with the counter-clockwise rotation of the Corsica-Sardinia block to its current position. In the southern part of the basin where this rotation opened the widest, seismic tomography has shown evidence of oceanic crust, however, the extent of this spreading zone northward into the Ligurian Sea is poorly mapped. The nature of the crust in the basin, whether atypical oceanic crust or partially serpentinized mantle overlain by sediments or highly thinned continental crust is still a matter of debate. At a larger scale there are still open questions as to the continuation of the alpine orogen offshore, and the change in polarity between the Alp and Apennine subduction zones. As well, present day seismicity with thrust-faulting focal mechanisms have been observed in the basin, indicating that the stress field is now compressive. This could potentially reactivate rift-structures in the basin, which are difficult to map due to thick sediment cover including a layer of Messinian salt with variable thickness. These open questions, and the accessibility of the basin in the heart of Europe, have led to the collection of at least 18 active seismic profiles, and even more multi-channel seismic lines. Each of these studies have contributed to understanding the tectonics of the area through 2D tomography along the profile, but these are small snapshots of a complex setting. The amount of data that has been collected provides a unique opportunity to combine data sets and examine the possibility of gaining new information in the form of 3D tomography from existing 2D data sets. In this project we use active seismic data from the LOBSTER-AlpArray Experiment, the GROSMarin Experiment, and the SARDINIA Experiment, as well as passive seismic data from the AlpArray Experiment and the ISC Bulletin. We explore the potential and limitations of these data sets for use in 3D tomography using two new methods. We first use off-profile stations along a 2D seismic line combined with passive seismicity to provide back-shots for the stations, then in the Gulf of Lion we use two parallel seismic profiles where stations recorded shots from both profiles. This project is part of the DFG Priority Program “Mountain Building Processes in Four Dimensions (4DMB)”

Does gravity modelling justify a rifted "Ligurian Basin"?

The geo-historical development of the Ligurian Basin and the structure of the crust and upper mantle in this area are still being discussed. Yet it remains unclear if rifting caused continental break-up and seafloor spreading and one of the key questions is whether rifting can be identified in geophysical measurements. For our investigations we had the following updated data sets at our disposal: the new gravity maps of the AlpArray Gravity Working Group (complete Bouguer - CBA, Free air, and isostatic anomalies) the seismic results of the Lobster campaigns of our GEOMAR partners in the SPP MB4D as well as the dynamic modelling results from our own subproject. The constraining data are supplemented with seismic profile data from French and Italian offshore campaigns, as far as they are usable in publications for us. The GFZ modelling software IGMAS+ was used for an interactive 3D modelling. The resulting model contains density inhomogeneities in the crust as well as in the upper mantle down to a depth of 300 km following the results of dynamic models of our own subproject. Due to the special hybrid modelling of the crust (by polygonal structures) and the upper mantle (by voxels of recent velocity models), the individual contributions to the gravity field are clearly separable. As a further special feature, we point out that the density model used is based on the gravity modelling from the first phase of the SPP MB4D (our former subproject INTEGRATE). Thus, a largely consistent 3D density model for both the Alps and the Ligurian Sea is available for interpretation. The constrained 3D modelling of the gravity field, as well as numerical analyses of the fields (terracing, clustering, filtering, curvature), calculations of the vertical stress and Gravity Potential Energy (GPE) suggest that a rift structure in the area of the Ligurian Sea can be identified and mapped. The interactive modelling is supported by the use of geological maps in the Ligurian Sea area. By overlaying the model gravity maps and the geological maps, the good agreement becomes visible – refer to the attached figure

Investigations of the Oligocene-Miocene opening of the Ligurian Basin using amphibious refraction seismic data

The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast trench retreat of the Apennines-Calabrian-Maghrebides subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning and un-roofing of mantle material little is known about the style of back-arc rifting. To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. Two refraction seismic profiles were shot across and along the centre of the Ligurian Basin. P01 was shot in an E-W direction from the Gulf of Lion to Corsica. The profile extends onshore Corsica to image the necking zone of continental thinning. P02 is a transect along the basin in NE-SW direction extending a previous shot seismic profile reaching to the Italian cost near Genua. The majority of the ocean bottom seismometer data show sedimentary and crustal phases of good quality and weaker in amplitude mantle phases to offsets up to 70 km. The arrivals of seismic phases were picked and inverted in a travel time tomography. The results for p01 show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The crust-mantle boundary deepens from ~12 km to ~18 km within 25 - 30 km towards Corsica. The results do not map an axial valley as expected for oceanic spreading. However, an extremely thinned continental crust indicates a long-lasting rifting process that possibly did not initiate oceanic spreading before the opening of the Ligurian Basin stopped. This is in good agreement with recent kinematic modelling performed in the second phase of the SPP2017 4D-MB. The modelling results of p01 indicate that continental crust can be stretched over several million years when the opening rate is low, i.e. <2 mm/year, and syn-rift sedimentation rate is high. Subduction initiation could occur in ultra-thinned continental crust as basin inversion has been observed at the northern Ligurian margin as a result of the African-European convergence. Additionally, the observations from the Ligurian Basin might be transferred to the evolution of the Piemont-Liguro Ocean. So far oceanic crust was assumed as initial conditions for the subduction of the Piemont-Liguro Ocean. An ultra-thin continental crust as initial condition would explain the observed thin subducted Piemont-Liguro plate which seemed to be thinner than 6-7 km oceanic crust. Further, a dry continental crust could explain why no back-arc volcanism was observed. The along-basin profile p02 shows a deepening crust-mantle boundary from 11 to 13 km. Based on the retrieved velocity model, gravity modelling and further results from surrounding studies we conclude that the continental crust is thinning from the northeast to the southwest which is related to the increase of extension away from the rotation pole of the anticlockwise rotation of the Corsica-Sardinia block. It remains unclear if at the southern end of the profile the mantle is overlain directly by sediments or by extremely thinned continental crust of up to 2.5 km thickness. The results however document, that seafloor spreading and the formation of mantle-derived oceanic crust was not initiated during the extension of the Ligurian Basin

Ionian Abyssal Plain: a window into the Tethys oceanic lithosphere

The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. A NNE–SSW-oriented 131&thinsp;km long seismic refraction and wide-angle reflection profile, consisting of eight ocean bottom seismometers and hydrophones, was acquired in 2014. The profile was designed to univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys and to confute its interpretation as a strongly thinned part of the African continental crust. A P-wave velocity model developed from travel-time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6–7&thinsp;km thick crust with velocities ranging from 5.1 to 7.2&thinsp;km&thinsp;s−1, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina seamounts at the southern IAP boundary, the crust thickens to about 9&thinsp;km and seismic velocities decrease to 6.8&thinsp;km&thinsp;s−1 at the crust–mantle boundary. The seismic velocity distribution and depth of the crust–mantle boundary in the IAP document its oceanic nature and support the interpretation of the IAP as a remnant of the Tethys lithosphere with the Malta Escarpment as a transform margin and a Tethys opening in the NNW–SSE direction.</p

Fore-arc deformation and underplating at the northern Hikurangi margin, New Zealand

Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp > 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is >10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp > 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for

The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge

The breakup of Laurasia to form the Northeast Atlantic Realm was the culmination of a long period of tectonic unrest extending back to the Late Palaeozoic. Breakup was prolonged and complex and disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed, which are blanketed by lavas and underlain variously by magma-inflated, extended continental crust and mafic high-velocity lower crust of ambiguous and probably partly continental provenance. New rifts formed by diachronous propagation along old zones of weakness. North of the Greenland-Iceland-Faroe Ridge the newly forming rift propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge it propagated north through the North Atlantic Craton along an axis displaced ~ 150 km to the west of the northern rift. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed a transverse barrier. Thereafter, the ~ 400-km-wide latitudinal zone between the stalled rift tips extended in a distributed, unstable manner along multiple axes of extension that frequently migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day. It is the surface expression of underlying magma-assisted stretching of ductile mid- and lower continental crust which comprises the Icelandic-type lower crust that underlies the Greenland-Iceland-Faroe Ridge. This, and probably also one or more full-crustal-thickness microcontinents incorporated in the Ridge, are capped by surface lavas. The Greenland-Iceland-Faroe Ridge thus has a similar structure to some zones of seaward-dipping reflectors. The contemporaneous melt layer corresponds to the 3–10 km thick Icelandic-type upper crust plus magma emplaced in the ~ 10–30-km-thick Icelandic-type lower crust. This model can account for seismic and gravity data that are inconsistent with a gabbroic composition for Icelandic-type lower crust, and petrological data that show no reasonable temperature or source composition could generate the full ~ 40-km thickness of Icelandic-type crust observed. Numerical modeling confirms that extension of the continental crust can continue for many tens of Myr by lower-crustal flow from beneath the adjacent continents. Petrological estimates of the maximum potential temperature of the source of Icelandic lavas are up to 1450 °C, no more than ~ 100 °C hotter than MORB source. The geochemistry is compatible with a source comprising hydrous peridotite/pyroxenite with a component of continental mid- and lower crust. The fusible petrology, high source volatile contents, and frequent formation of new rifts can account for the true ~ 15–20 km melt thickness at the moderate temperatures observed. A continuous swathe of magma-inflated continental material beneath the 1200-km-wide Greenland-Iceland-Faroe Ridge implies that full continental breakup has not yet occurred at this latitude. Ongoing tectonic instability on the Ridge is manifest in long-term tectonic disequilibrium on the adjacent rifted margins and on the Reykjanes Ridge, where southerly migrating propagators that initiate at Iceland are associated with diachronous swathes of unusually thick oceanic crust. Magmatic volumes in the NE Atlantic Realm have likely been overestimated and the concept of a monogenetic North Atlantic Igneous Province needs to be reappraised. A model of complex, piecemeal breakup controlled by pre-existing structures that produces anomalous volcanism at barriers to rift propagation and distributes continental material in the growing oceans fits other oceanic regions including the Davis Strait and the South Atlantic and West Indian oceans

Lipid-mediated gene transfer of acidic fibroblast growth factor into human corneal endothelial cells

The aim of this study was to optimize non-viral gene transfer conditions and investigate the effect of fibroblast growth factor-1 (FGF-1) gene transfer on human corneal endothelial cell (HCEC) proliferation. Five non-viral vectors (Lipofectin™, DMRIE-C™, DAC-30, Effectene™, FuGene™6) were used to transfect HCEC with plasmids coding for enhanced green fluorescent protein (EGFP) and FGF-1. Transfection efficiency and toxicity (n=6) were quantified and optimized using the EGFP construct by FACS-analysis. Using optimal conditions HCEC were transfected with the FGF-1 plasmid and cell proliferation as well as expression of FGF-1 were determined at days 4 and 7 by counting and western blotting, respectively. Lipofectin (17±2·02%) transfected HCEC more successfully than DMRIE-C (11±1·46%), Effectene (9±0·62%), FuGene (9±0·93%) and DAC-30 (7±0·59%). Toxicity of the lipids ranged from 2 to 4%. Optimal HCEC proliferation was achieved with DAC-30/FGF-1 (P<0·05), whereas all other vectors did not result in significantly increased cell proliferation. However, all of the transfected cells produced FGF-1 in different amounts as indicated by western blotting. Efficient and almost non-toxic transfer of the FGF-1 gene into HCEC can be successfully achieved by lipid-based techniques. Using optimal conditions significantly increased cell proliferation was independent on gene transfer efficiency. This may indicate that even a low transfection rate is sufficient to produce a concentration of FGF-1 that will have a stimulatory effect on HCECs

Gentherapie in der Ophthalmologie. Uebersicht ueber Perspektiven und Moeglichkeiten fuer Erkrankungen der Kornea

Background: Gene therapy has gained increasing attention and a number of ongoing clinical trials have been iniciated. This article provides current perspectives and limitations on gene therapy in ophthalmology. Since a number of comprehensive studies on gene therapy for retinal diseases already exist, we focus attention to the treatment of anterior segment disorders of the eye. Material and methods: We undertook a reference search (DIMDI, PubMed) of articles published between (1989-2000) using the key words cornea, conjunctiva, eye, gene therapy, and keratoplasty. The search was restricted to publications in English, French and German. In addition, we incorporated some results of our recent experiments on cytokine gene transfer to the cornea. Results: Attention to gene therapy in ophthalmology is currently focused on retina and choroidea (40 articles) however, an increasing number of publications includes the cornea (12 articles). The majority of these contributions deals with improvements in the design of gene therapy vectors in particular for targeted application. Conclusions: Gene therapy to the cornea may offer interesting new venues. Currently, insufficient gene transfer technologies and safety concerns prevent the broad application in humans. However, a broad spectrum of applications can be supposed

Seismic structure of lithosphere emplaced at ultra-slow spreading rates

About 57% of the Earth’s surface is covered by oceanic crust and new ocean floor is continuously created along the 60.000 km long mid-ocean ridge (MOR) system. About 25% of the MOR spread at an ultra-slow spreading rate of 1.9, supporting serpentine. Domains of high Vp/Vs ratio also occur right at the seafloor, supporting large-scale exposure of mantle as proposed by geological evidence from ultra-slow spreading ridges. Ingo Grevemeyer (1), Michaela Merz (1), Anke Dannowski (1), Cord Papenberg (1), Nicholas Hayman (2), Harm van Avendonk (2), and Christine Peirce (3

Lithospheric structure of the eastern Mediterranean Sea: Inferences from surface wave tomography and stochastic inversions constrained by wide-angle refraction measurements

Highlights • Crust and mantle lithospheric structures beneath the eastern Mediterranean Sea are resolved from the joint inversion of surface wave measurements and wide-angle refraction seismics. • Vp/Vs and Poisson's ration estimates point to the presence of serpentinized oceanic crust beneath the Ionian Basin and thinned continental crust beneath the Levant Basin. • Oceanic lithosphere in the eastern Mediterranean Sea consists of three different domains: a) 180 km thick, Triassic Ionian lithosphere, b) 200 km thick, Permo-Carboniferous lithosphere beneath the Central Eastern Mediterranean and c) 180 km thick lithosphere beneath the eastern Herodotus Basin. • Thin continental lithosphere (75 km thick) beneath the Levant Basin underlain by the shallow Middle East Asthenosphere. • The spatial correlation between the shallow Middle East Asthenosphere and the Dead Sea Fault reveals focusing of lithospheric deformation in an area of thinned lithosphere. Abstract The tectonic plate under the eastern Mediterranean Sea shows a remarkable variability as it comprises Earth's oldest oceanic lithosphere as well as the transition towards continental lithosphere beneath the Levant Basin. Its thickness and other properties offer essential information on the lithospheric evolution but have been difficult to determine seismically due to the high heterogeneity of the region and its complex crustal structure. Here, we combine a large, new surface wave dataset with published wide-angle data in order to determine lithospheric properties in the eastern Mediterranean. Our stochastic inversions of broad-band, phase-velocity dispersion measurements resolve the crust-mantle structural trade-offs and yield robust, 1-D shear-wave velocity models down to 300 km depth beneath the Ionian and Levant Basins. The thickness of the crust beneath the two locations is 16.4 ± 3 km and 22.3 ± 2 km, respectively. The Poisson's ratio (σ) of 0.32 and Vp/Vs of 1.93 in the crystalline crust confirm the presence of serpentinized oceanic crust beneath the Ionian Basin. Beneath the Levant Basin, low crustal Vp/Vs (∼ 1.7) and Poisson's (∼ 0.24) ratios indicate continental crust. Beneath the Ionian Basin, the lithosphere is about 180 km thick. By contrast, thin, 75 km thick lithosphere is found beneath the Levant Basin. S-velocity tomography based on surface wave data also shows thick, spatially variable oceanic mantle lithosphere beneath the eastern Mediterranean. Thickness of the oceanic lithosphere increases eastwards from the Triassic Ionian towards the Permo-Carboniferous lithosphere in the Central Eastern Mediterranean. These results demonstrate that oceanic lithosphere can thicken by cooling substantially beyond the limits suggested by the plate cooling model. Beneath the eastern Herodotus oceanic Basin, lithospheric thickness is decreasing to about 180 km. Thin continental lithosphere and shallow asthenosphere are present beneath the Dead Sea Fault, demonstrating that the localization of the lithospheric deformation and crustal seismicity along the fault correlates spatially with the thinning of the underlying continental lithosphere