Untersuchung der Krustenstruktur des Manihiki Plateaus im Rahmen der Expedition SO-224

Das Manihiki Plateau ist ein untermeerisches Lavaplateau, eine sogenannte „Large Igneous Province“ (LIP), im zentralen Westpazifik (Abb. 1). Es ent-stand in der frühen Kreide (ca. 125 Ma) wahrscheinlich als ein Teilstück der „Super-LIP“ Ontong Java Nui (Chandler et al., 2013; 2012; Taylor, 2006). Dieses vulkanische Plateau bestand neben dem Manihiki Plateau aus dem Ontong Java Plateau und dem Hikurangi Plateau (Abb.1), sowie weiteren Teilstücken, die mittlerweile subduziert wurden (Larson et al., 2002; Viso et al., 2005). Man geht davon aus, dass Ontong Java Nui ungefähr 1% der Erd-oberfläche bedeckte. Eine vulkanische Provinz entsteht meist durch eine massive erste vulkanische Phase, gefolgt von mehreren kürzeren vulkani-schen Phasen (Coffin and Eldholm, 1994). Ontong Java Nui brach zwischen diesen zwei plateaubildenden Phasen auseinander (Hoernle et al., 2010; Timm et al., 2011), und die Teilplateaus durchliefen jeweils eine individuelle tektonische und petrologische Entwicklung. Während der Expedition SO-224 im Jahr 2012 wurden zwei refraktions- und weitwinkelreflexionsseismische Profile aufgenommen (Fig. 1). Hierzu wurden jeweils 33 Ozeanbodenseismometer ausgebracht. Diese Daten erlauben uns einen Einblick in die Struktur der Kruste und oberen Mantels des Manihiki Pla-teaus. Somit können die Hypothesen über die gemeinsame Entstehung des Manihiki Plateaus mit dem Ontong Java Plateau und dem Hikurangi Plateau überprüft werden. Ebenso ist es möglich, die Struktur der zwei größten Un-terprovinzen des Manihiki Plateaus, das High Plateau und die Western Plateaus, zu vergleichen. Bei der Modellierung der Krustenstruktur der beiden Unterprovinzen traten einige Gemeinsamkeiten, aber auch erstaunliche Unterschiede zu Tage (Abb. 2). Generell besteht eine LIP aus einer unteren Kruste, die sehr hohe P-Wellengeschwindigkeiten (7.1 bis 7.7 km/s) aufweist. Diese Schicht ist in bei-den Teilprovinzen vorhanden. Die Krustenmächtigkeit variiert zwischen 9 und 17 km an den Western Plateaus (Abb. 2a) und beträgt konstant 20 km am High Plateau (Abb. 2b). Die Struktur der oberen Kruste weist große Unter-schiede zwischen den verschiedenen Teilprovinzen auf. Das High Plateau ist durch basaltische Flussstrukturen geprägt. Zahlreiche intrusive und extrusive vulkanische Strukturen, wie beispielsweise Tiefseeberge sind hier belegt (Abb. 1 und 2b). Dies deutet auf eine massive vulkanische Aktivität während späte-rer vulkanischer Phasen hin. Im Gegensatz dazu zeigen die Western Pla-teaus nur einen sehr lokalen und geringen Vulkanismus. Mehrere Horst- und Grabensysteme sowie Sedimentbecken können dort identifiziert werden (Abb. 2a). Dieses deutet auf eine starke tektonische Deformation der Western Pla-teaus hin. Auch der graduelle Anstieg der Kruste-Mantelgrenze weist auf eine gedehnte Kruste hin (Abb. 2a). Somit zeigen die beiden Unterprovinzen des Manihiki Plateaus eine unterschiedliche Entwicklung nach ihrer gemeinsamen Entstehung als eines Teils von Ontong Java Nui. Das High Plateau wurde nur an seinen Rändern tektonisch beansprucht und durchlief weitere Phasen exzessiver vulkanischer Aktivität. Die Western Pla-teaus wurden wahrscheinlich starken Dehnungskräften im Zusammenhang mit dem Abbruch des Ontong Java Plateaus ausgesetzt. Somit liegt hier eine Dehnung der vorher entstandenen LIP-Kruste und geringer Vulkanismus vor. Diese Erkenntnisse können uns genaueren Aufschluss darüber geben, welche Prozesse den Aufbruch der „Super-LIP“ Ontong Java Nui begünstigt haben und stellen wichtige Rahmenbedingungen für eine plattentektonische Rekon-struktion des zentralen Westpazifiks in der Kreide dar. Durch eine Kartierung der Ränder und Beschaffenheit der Kruste der verschiedenen Teilplateaus Ontong Java Nuis können die ursprüngliche Positionierung der verschiedenen Plateaus zueinander rekonstruiert werden. Dies bildet die Grundlage einer er-folgreichen plattenkinematischen Rekonstruktion

The Psychology of Beethoven and The Eroica Symphony

As a concert pianist and chapel organist, Beethoven rose to a fame in Vienna which allowed him patrons and friends who would support his compositions. One such patron was Count Waldstein, who claimed that Beethoven would inherit the spirit of Mozart in his famous prediction of Beethoven’s success. To study composition Beethoven turned to two prominent Viennese composers: Haydn and Salieri. As his fame grew, his health decreased until he was diagnosed with deafness and moved to Heiligenstadt. Here Beethoven wrote a letter to his brothers called the Heiligenstadt Testament, which was never sent but expressed his troubled mental state. Beethoven composed his Eroica Symphony in a time in his life when, accepting the onset of his deafness, he also experienced the onset of depression. The Eroica Symphony has threads of Heroism running throughout it, and tells the story of life over death. But a question remains surrounding the work: Who is the Hero

High geothermal heat flow beneath Thwaites Glacier in West Antarctica inferred from aeromagnetic data

Geothermal heat flow in the polar regions plays a crucial role in understanding ice-sheet dynamics and predictions of sea level rise. Continental-scale indirect estimates often have a low spatial resolution and yield largest discrepancies in West Antarctica. Here we analyse geophysical data to estimate geothermal heat flow in the Amundsen Sea Sector of West Antarctica. With Curie depth analysis based on a new magnetic anomaly grid compilation, we reveal variations in lithospheric thermal gradients. We show that the rapidly retreating Thwaites and Pope glaciers in particular are underlain by areas of largely elevated geothermal heat flow, which relates to the tectonic and magmatic history of the West Antarctic Rift System in this region. Our results imply that the behavior of this vulnerable sector of the West Antarctic Ice Sheet is strongly coupled to the dynamics of the underlying lithosphere

Playing jigsaw with large igneous provinces - a plate-tectonic reconstruction of Omtong Java Nui

Ontong Java Nui is a Cretaceous large igneous province (LIP), which was rifted apart into various smaller plateaus shortly after its emplacement around 125 Ma in the central Pacific. It incorporated the Ontong Java Plateau, the Hikurangi Plateau and the Manihiki Plateau as well as multiple smaller fragments, which have been subducted. Its size has been estimated to be approximately 0.8% of the Earth’s surface. A volcanic edifice of this size has potentially had a great impact on the environment such as its CO2 release. The break-up of the “Super”-LIP is poorly constrained, because the break-up and subsequent seafloor spreading occurred within the Cretaceous Quiet Period. The Manihiki Plateau is presumably the centerpiece of this “Super”-LIP and shows by its margins and internal fragmentation that its tectonic and volcanic activity is related to the break-up of Ontong Java Nui. By incorporating two new seismic refraction/wide-angle reflection lines across two of the main sub-plateaus of the Manihiki Plateau, we can classify the break-up modes of the individual margins of the Manihiki Plateau. The Western Plateaus experienced crustal stretching due to the westward motion of the Ontong Java Plateau. The High Plateau shows sharp strike-slip movements at its eastern boundary towards an earlier part of Ontong Java Nui, which is has been subducted, and a rifted margin with a strong volcanic overprint at its southern edges towards the Hikurangi Plateau. These observations allow us a re-examination of the conjugate margins of the Hikurangi Plateau and the Ontong Java Plateau. The repositioning of the different plateaus leads to the conclusion that Ontong Java Nui was larger (~1.2% of the Earth’s surface at emplacement) than previously anticipated. We use these finding to improve the plate tectonic reconstruction of the Cretaceous Pacific and to illuminate the role of the LIPs within the plate tectonic circuit in the western and central Pacific

4D Antarctica: a new effort aims to help bridge the gap between Antarctic crust and lithosphere structure and geothermal heat flux

Seismology, satellite-magnetic and aeromagnetic data, and sparse MT provide the only available geophysical proxies for large parts of Antarctica\u2019s Geothermal Heat Flux (GHF) due to the sparseness of direct measurements. However, these geophysical methods have yielded significantly different GHF estimates. This restricts our knowledge of Antarctica\u2019s contrasting tectono-thermal provinces and their influence on subglacial hydrology and ice sheet dynamics. For example, some models derived from aeromagnetic data predict remarkably high GHF in the interior of the West Antarctic Rift System (WARS), while other satellite magnetic and seismological models favour instead a significantly colder rift interior but higher GHF stretching from the Marie Byrd Land dome towards the Antarctic Peninsula, and beneath parts of the Transantarctic Mountains. Reconciling these differences in West Antarctica is imperative to better comprehend the degree to which the WARS influences the West Antarctic Ice Sheet, including thermal influences on GIA. Equally important, is quantifying geothermal heat flux variability in the generally colder but composite East Antarctic craton, especially beneath its giant marine-based basins. Here we present a new ESA project- 4D Antarctica that aims to better connect international Antarctic crust and lithosphere studies with GHF, and assess its influence on subglacial hydrology by analysing and modelling recent satellite and airborne geophysical datasets. The state of the art, hypotheses to test, and methodological approaches for five key study areas, including the Amundsen Sea Embayment, the Wilkes Subglacial Basin and the Totten catchment, the Recovery and Pensacola-Pole Basins and the Gamburtsev Sublgacial Mountains/East Antarctic Rift System are highlighted

Recent magnetic views of the Antarctic lithosphere

Magnetic anomaly investigations are a key tool to help unveil subglacial geology, crustal architecture and the tectonic and geodynamic evolution of the Antarctic continent. Here, we present the second generation Antarctic magnetic anomaly compilation ADMAP 2.0 (Golynsky et al., 2018), that now includes a staggering 3.5 million line-km of aeromagnetic and marine magnetic data, more than double the amount of data available in the first generation effort. All the magnetic data were corrected for the International Geomagnetic Reference Field, diurnal effects, high-frequency errors and leveled, gridded,and stitched together. The new magnetic anomaly dataset provides tantalising new views into the structure and evolution of the Antarctic Peninsula and the West Antarctic Rift System within West Antarctica, and Dronning Maud Land, the Gamburtsev Subglacial Mountains, the Prince Charles Mountains, Princess Elizabeth Land, and Wilkes Land in East Antarctica, as well as key insights into oceanic gateways. Our magnetic anomaly compilation is helping unify disparate regional geologic and geophysical studies by providing larger-scale perspectives into the major tectonic and magmatic processes that affected Antarctica from Precambrian to Cenozoic times, including e.g. the processes of subduction and magmatic arc development, orogenesis, accretion, cratonisation and continental rifting, as well as continental margin and oceanic basin evolution. The international Antarctic geomagnetic community remains very active in the wake of ADMAP 2.0, and we will showcase some of their key ongoing study areas, such as the South Pole and Recovery frontiers, the Ross Ice Shelf, Dronning Maud Land and Princess Elizabeth Land

Seamounts off the West Antarctic margin: A case for non-hotspot driven intraplate volcanism

Highlights: • Marie Byrd Seamounts (MBS) formed off Antarctica at 65-56 Ma in an extensional regime • MBS originate from HIMU-type mantle attached at the base of the Antarctic lithosphere • Continental insulation flow transferred HIMU mantle into the oceanic mantle New radiometric age and geochemical data of volcanic rocks from the guyot-type Marie Byrd Seamounts (MBS) and the De Gerlache Seamounts and Peter I Island (Amundsen Sea) are presented. 40Ar/39Ar ages of the shield phase of three MBS are Early Cenozoic (65 to 56 Ma) and indicate formation well after creation of the Pacific-Antarctic Ridge. A Pliocene age (3.0 Ma) documents a younger phase of volcanism at one MBS and a Pleistocene age (1.8 Ma) for the submarine base of Peter I Island. Together with published data, the new age data imply that Cenozoic intraplate magmatism occurred at distinct time intervals in spatially confined areas of the Amundsen Sea, excluding an origin through a fixed mantle plume. Peter I Island appears strongly influenced by an EMII type mantle component that may reflect shallow mantle recycling of a continental raft during the final breakup of Gondwana. By contrast the Sr-Nd-Pb-Hf isotopic compositions of the MBS display a strong affinity to a HIMU type mantle source. On a regional scale the isotopic signatures overlap with those from volcanics related to the West Antarctic Rift System, and Cretaceous intraplate volcanics in and off New Zealand. We propose reactivation of the HIMU material, initially accreted to the base of continental lithosphere during the pre-rifting stage of Marie Byrd Land/Zealandia to explain intraplate volcanism in the Amundsen Sea in the absence of a long-lived hotspot. We propose continental insulation flow as the most plausible mechanism to transfer the sub-continental accreted plume material into the shallow oceanic mantle. Crustal extension at the southern boundary of the Bellingshausen Plate from about 74 to 62 Ma may have triggered adiabatic rise of the HIMU material from the base of Marie Byrd Land to form the MBS. The De Gerlache Seamounts are most likely related to a preserved zone of lithospheric weakness underneath the De Gerlache Gravity Anomaly

Bathymetric controls on calving processes at Pine Island Glacier

Pine Island Glacier is the largest current Antarctic contributor to sea level rise. Its ice loss has substantially increased over the last 25 years through thinning, acceleration and grounding line retreat. However, the calving line positions of the stabilizing ice shelf did not show any trend within the observational record (last 70 years) until calving in 2015 led to unprecedented retreat and changed alignment of the calving front. Bathymetric surveying revealed a ridge below the former ice shelf and two shallower highs to the north. Satellite imagery shows that ice contact on the ridge likely was lost in 2006 but was followed by intermittent contact resulting in back stress fluctuations on the ice shelf. Continuing ice shelf flow also led to occasional ice shelf contact with the northern bathymetric highs, which initiated rift formation that led to calving. The observations show that bathymetry is an important factor in initiating calving events

Geothermal heat flux in the Amundsen Sea sector of West Antarctica: New insights from temperature measurements, depth to the bottom of the magnetic source estimation, and thermal modeling

Focused research on the Pine Island and Thwaites glaciers, which drain the West Antarctic Ice Shelf (WAIS) into the Amundsen Sea Embayment (ASE), revealed strong signs of instability in recent decades that result from variety of reasons, such as inflow of warmer ocean currents and reverse bedrock topogra- phy, and has been established as the Marine Ice Sheet Instability hypothesis. Geothermal heat flux (GHF) is a poorly constrained parameter in Antarctica and suspected to affect basal conditions of ice sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations. We present an approach to investigate ranges of realistic heat fluxes in the ASE by different methods, discuss direct observations, and 3-D numerical models that incorporate boundary conditions derived from various geophysical studies, including our new Depth to the Bottom of the Magnetic Source (DBMS) estimates. Our in situ temperature measurements at 26 sites in the ASE more than triples the number of direct GHF observations in West Antarctica. We demonstrate by our numerical 3-D models that GHF spatially varies from 68 up to 110 mW m-2