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 URGE TO CHECK SOCIAL NETWORKING SITES: ANTECEDENTS AND CONSEQUENCES

Social networking sites (SNSs), combined with the rapid growth trajectory of mobile devices, and widespread deployment of mobile data services, have evolved as a primary platform for daily social interaction. While the majority of users enjoy frequent interactions with their friends and family members, some users suffer from incessant urges to check up on the lives of others on their social networks. In the last decade, the use of SNSs has received much attention in the IS literature. Not until recently, researchers have begun to examine the dark side of using SNSs. In this study, we attempt to advance existing literature by exploring the role of urges in the context of SNSs. Particularly, we propose a research model that examines the antecedents and consequences of the urge to check SNSs. We will test the model with SNS users using structural equation modeling. We believe that current work will enrich the existing literature on the dark side of SNS use, and raise the awareness in the community regarding this emerging phenomenon

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

Tectono‐Stratigraphic Evolution of the Kerguelen Large Igneous Province: The Conjugate William’s Ridge‐Broken Ridge Rifted Margins

AbstractExtensive investigation of continental rift systems has been fundamental for advancing the understanding of extensional tectonics and modes of formation of new ocean basins. However, current rift classification schemes do not account for conjugate end members formed by Large Igneous Province crust, referring to thick mafic crust, sometimes including continental fragments. Here, we investigate the rifting of William's Ridge (Kerguelen Plateau) and Broken Ridge, components of the Kerguelen Large Igneous Province now situated in the Southeast Indian Ocean, and incorporate these end members into the deformation migration concept for rifted margins. We use multichannel seismic reflection profiles and data from scientific drill cores acquired on both conjugate margins to propose, for the first time, a combined tectono‐stratigraphic framework. We interpret seismic patterns, tectonic features, and magnetic anomaly picks to determine an across‐strike structural domain classification. This interpretation considers the rift system overall to be “magma‐poor” despite being located proximal to the Kerguelen plume but suggests that syn‐rift interaction between the Kerguelen mantle plume and the lithospheric structure of William's Ridge and Broken Ridge has controlled the along‐strike segmentation of both conjugates. We integrate seismic reflection and bathymetric data to test the hypothesis of predominantly transform motion, between the Australian and Antarctic plates, in Late Cretaceous and Paleogene time.</jats:p

Hydrogen Epoch of Reionization Array (HERA)

The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and to explore earlier epochs of our Cosmic Dawn ($z\sim30$). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA's scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table

WSClean : an implementation of a fast, generic wide-field imager for radio astronomy

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Astronomical widefield imaging of interferometric radio data is computationally expensive, especially for the large data volumes created by modern non-coplanar many-element arrays. We present a new widefield interferometric imager that uses the w-stacking algorithm and can make use of the w-snapshot algorithm. The performance dependencies of CASA's w-projection and our new imager are analysed and analytical functions are derived that describe the required computing cost for both imagers. On data from the Murchison Widefield Array, we find our new method to be an order of magnitude faster than w-projection, as well as being capable of full-sky imaging at full resolution and with correct polarisation correction. We predict the computing costs for several other arrays and estimate that our imager is a factor of 2-12 faster, depending on the array configuration. We estimate the computing cost for imaging the low-frequency Square-Kilometre Array observations to be 60 PetaFLOPS with current techniques. We find that combining w-stacking with the w-snapshot algorithm does not significantly improve computing requirements over pure w-stacking. The source code of our new imager is publicly released.Peer reviewedFinal Published versio

Brute-Force Mapmaking with Compact Interferometers: A MITEoR Northern Sky Map from 128 MHz to 175 MHz

We present a new method for interferometric imaging that is ideal for the large fields of view and compact arrays common in 21 cm cosmology. We first demonstrate the method with the simulations for two very different low-frequency interferometers, the Murchison Widefield Array and the MIT Epoch of Reionization (MITEoR) experiment. We then apply the method to the MITEoR data set collected in 2013 July to obtain the first northern sky map from 128 to 175 MHz at ∼2° resolution and find an overall spectral index of −2.73 ± 0.11. The success of this imaging method bodes well for upcoming compact redundant low-frequency arrays such as Hydrogen Epoch of Reionization Array. Both the MITEoR interferometric data and the 150 MHz sky map are available at http://space.mit.edu/home/tegmark/omniscope.html.National Science Foundation (U.S.) (AST-0908848)National Science Foundation (U.S.) (AST-1105835)National Science Foundation (U.S.) (AST-1440343