Description: The gravimetric data was acquired with a sea gravimeter KSS32-M system, which was installed on RV Sonne near its centre of gravity during the SO267 cruise. The instrumental drift of the data was approximated by repeated gravity observations in the harbour of Suva both at the beginning and at the end of the expedition. In order to tie the measurements to the International Gravity Standardization Net IGSN71, gravimetric measurements with a LaCoste&Romberg gravity metre, model G, no. 480 (LCR G480) were executed both at the pier next to RV Sonne and at the next absolute gravity reference station at the Mineral Resources Department in Suva, Fiji. Additional processing of the data comprised the correction of the Eötvös effect using navigation data and the subtraction of the normal gravity. Data was acquired along a E-W trending profile in the northern Lau Basin at ~ 16°S between the 13.01.2019 and the 14.01.2019.

Description: The dataset comprises measurements of the total intensity of the magnetic field measured with a towed Overhauser sensor and calculated magnetic anomalies. The data were measured along a E-W trending profile at ~16°S in the northern Lau Basin and were acquired in January 2019 as part of the SO267 cruise.

Description: The northern Lau Basin, at the Australian-Pacific plate boundary, is one of the fastest opening back-arc basins on earth. An amalgamation of active rifts and spreading centers accommodates the extension. The current configuration of micro-plates, motions and plate-boundaries within the northern Lau Basin has been studied, but remains complex. Especially in the southern part of the Lau Basin questions remain about the crustal structure. In this area, the Central Lau Spreading Center (CLSC) and the southern tip of the Fonualei Rift and Spreading Center (FRSC) define the diffuse southern boundary of the Niuafo’ou microplate. It remains unclear where the southern plate boundary is located and what kind of boundary it is. We present seismic refraction and reflection data of a 200-km long transect in the transition zone from the eastern side of the CLSC to the southern tip of the FRSC. The seismic data recording was accompanied by parametric sediment echosounder data, gravimetric and magnetic measurements and dredged samples of the seafloor in the vicinity of the profile. A travel time tomography reveals a pronounced lateral variation in seismic P-wave velocities from west to east, within the 7-8 km thick back-arc-crust. Towards the east the crust gradually thickens to 13 km of arc-crust. The reflection seismic data reveals sediment pockets that vary between 300m to 1000m depth and are located on both the thinner back-arc crust and thicker arc-crust. Rock sampling along the transect retrieved predominantly massive aphyric basalts from the back-arc-crust in the west. Ol-Px-Pl-phyric basalts, andesites, and a broad spectrum of volcaniclastic rocks are the most common rock-type collected from the arc-crust in the east. These rocks are currently analyzed to determine the age and geochemical (major, trace element and Sr-Nd-Pb-Hf isotopic) composition of the sampled structures. The lack of a thinner crust near the southern tip of the FRSC is located and a wide distribution of normal faults in the sedimentary basins that reach the surface suggest that the southern plate boundary of the Niuafo’ou microplate actively accommodates extension in a wide rift setting.

Description: Cruise SO299 DYNAMET from Townsville (Australia) to Singapore aimed at studying the links between geodynamics (regional-scale plate tectonics, local structural geology and volcanism) and metallogeny with a special emphasis on the Au-rich mineralisation on and in the vicinity of Lihir Island, Papua New Guinea. The research programme started on 13th June and ended on 15 th July 2023, totalling to 32.5 working days within the Exclusive Economic Zone of Papua New Guinea and international waters. Underway hydroacoustic and gravity data were additionally recorded in international waters during the transit towards Singapore. The three main working areas targeted the New Ireland Basin at the newly discovered Karambusel vent field (Conical Seamount) and Mussel Cliff, the Weitin Fault area south of New Ireland, and the Mussau Ridge. We performed 〉4,800 kilometers of hydroacoustic (multibeam echosounder and sub-bottom profiler) and gravimetric surveys, twelve dives with the remotely operated vehicle (ROV) KIEL 6000 from GEOMAR, 16 stations with the TV-guided grab, 20 chain bag dredge and 20 heat flow stations. We recovered a total of 447 rock and 346 sediment samples and took 570 individual gas and fluid samples. We deployed and recovered 18 ocean bottom seismometers (OBS) and 16 ocean bottom magneto-telluric (OBMT) instruments in the vicinity of Lihir island. The wealth of samples and data collected during the cruise and complemented by a variety of geophysical, petrological and geochemical analyses post-cruise will aid the development of a new spatial and temporal model of the magmatic and hydrothermal evolution in response to recent plate tectonic changes.

Description: The crustal structure and continental margin between southern Nares Strait and northern Baffin Bay were studied based on seismic refraction and gravity data acquired in 2010. We present the resulting P wave velocity, density and geological models of the crustal structure of a profile, which extends from the Greenlandic margin of the Nares Strait into the deep basin of central northern Baffin Bay. For the first time, the crustal structure of the continent-ocean transition of the very northern part of Baffin Bay could be imaged. We divide the profile into three parts: continental, thin oceanic, and transitional crust. On top of the three-layered continental crust, a low-velocity zone characterizes the lowermost layer of the three-layered Thule Supergroup underneath Steensby Basin. The 4.3–6.3 km thick oceanic crust in the southern part of the profile can be divided into a northern and southern section, more or less separated by a fracture zone. The oceanic crust adjacent to the continent-ocean transition is composed of 3 layers and characterized by oceanic layer 3 velocities of 6.7–7.3 km/s. Toward the south only two oceanic crustal layers are necessary to model the travel time curves. Here, the lower oceanic crust has lower seismic velocities (6.4–6.8 km/s) than in the north. Rather low velocities of 7.7 km/s characterize the upper mantle underneath the oceanic crust, which we interpret as an indication for the presence of upper mantle serpentinization. In the continent-ocean transition zone, the velocities are lower than in the adjacent continental and oceanic crustal units. There are no signs for massive magmatism or the existence of a transform margin in our study area.

Description: Up to Jurassic times the Antarctic and African continents were part of the supercontinent Gondwana. Since some 185 Ma the rifting in our research area caused the dispersal of Gondwana and Eastern Africa. The timing and geometry of the break-up as well as the amount of volcanism connected to the Jurassic rifting are still controversial. In the southern part of the Mozambique channel a prominent basement high, the Beira High, forms a specific crustal anomaly along the margin. It is still controversial if this high is a continental fragment or was formed during a period of enhanced magmatism. Therefore a deep seismic profile with 37 OBS/H was acquired from the deep Mozambique Channel, across the Beira High and terminating on the shelf. The main objectives are to provide constraints on the crustal composition and origin of the Beira High as well as the amount of volcanism and the continent-ocean transition below the Zambezi Delta. To obtain a P-wave velocity model of this area the data was forward modelled by means of 2D-Raytracing. Furthermore, potential field data acquired in parallel to the seismic data were used to calculate a 2D gravity model. Preliminary results indicate a 20-24 km thick crust for the Beira High. In good agreement to the adjacent oceanic crust in the Mozambique Channel the upper crust has velocities between 5.5-5.9 km/s. The middle crust is characterised by velocities between 6.2-6.7 km/s and the lower crust higher than 6.7 km/s and a density of 3.0 g/cm3. However, these velocities are only constrained by Moho reflections, since no diving waves are observed for the lower crust. In the area of the Zambezi Delta Depression the top of the acoustic basement is at 11.5 km depth and the crust thickness thins to 7 km. The basement here is overlain by a 2 km thick layer of 4.9-5.1 km/s, which we interpret as pre-rift sediments (Karoo-Belo-Group, including Lava Flows on top). Furthermore, evidence for the presence of a high velocity body (HVB) at below the western part of Beira High with a velocity of 7.2-7.4 km/s and 3 km thickness is found. Below the shelf our results indicate evidences for an increased volcanism during the initial break-up. The location of the continent-ocean boundary as well as the geometry of the break-up depend strongly on the tectonic classification of Beira High. Future work will provide further constraints by amplitude modelling, a 3D gravity model of Beira High and by means of interpretation of the magnetic anomalies.

Description: Up to Jurassic times the Antarctic and African continents were part of the supercontinent Gondwana. Some 185 Ma the onset of rifting caused the dispersal of this vast continent into several minor plates. The timing and geometry of the initial break-up between Africa and Antarctica as well as the amount of volcanism connected to this Jurassic rifting are still controversial. In the southern part of the Mozambique Channel a prominent basement high, the Beira High, forms a distinct crustal anomaly along the Mozambican margin. It is still controversial if this area of shallow basement is a continental fragment or was formed during a period of enhanced magmatism and is of oceanic origin. Therefore, a wide-angle seismic profile with 37 OBS/H was acquired starting from the deep Mozambique Channel, across the Beira High and terminating on the shelf off the Zambezi River. The main objectives are to provide constraints on the crustal composition and origin of the Beira High as well as the amount of volcanism and the position of the continent-ocean transition below the Zambezi Delta. To obtain a P-wave velocity model of this area the data were forward modeled by means of the 2D-Raytracing method. Preliminary results indicate a clear thickening of the crust below the Beira High up to 20-24 km. Evidences for a high velocity body are found in the area below the Zambezi shelf with velocities of 7.2-7.4 km/s and up to 5 km thickness. Oceanic basement velocities at the very eastern part of the line start with values of 5.5 km/s, and increase to 6.9 km/s at lower crustal levels, that are typical for Jurassic oceanic crust. Across the Beira High the starting velocity and its gradient slightly change, presenting typical values for continental fragments. However, due to a sparse ray coverage of diving waves for the Beira High lower crust, these velocities still have to be proved. Thus, we will introduce the final results of a Finite Difference amplitude modeling, which will constrain the lowermost velocity gradients to allow a sound interpretation of the Beira High origin. The acquired shipborne, magnetic data show a complex magnetic pattern and strong influences by the presence of lava flows and intrusions and require further investigations. We will introduce the latest results of the joint interpretation of seismic and potential field data sets.