IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Interplay between faults and lava flows in construction of the upper oceanic crust : the East Pacific Rise crest 9°25′–9°58′N

Abstract: The distribution of faults and fault characteristics along the East Pacific Rise (EPR) crest between 9°25′N and 9°58′N were studied using high-resolution side-scan sonar data and near-bottom bathymetric profiles. The resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older, sediment-covered seafloor of the same spreading age. We estimate that the expression of tectonic deformation and associated strain on “old” seafloor is ∼5 times greater than that on “young” seafloor, owing to the frequent fault burial by recent lava flows. Thus the unseen, volcanically overprinted tectonic deformation may contribute from 30% to 100% of the ∼300 m of subsidence required to fully build up the extrusive pile (Layer 2A). Many longer lava flows (greater than ∼1 km) dam against inward facing fault scarps. This limits their length at distances of 1–2 km, which are coincident with where the extrusive layer acquires its full thickness. More than 2% of plate separation at the EPR is accommodated by brittle deformation, which consists mainly of inward facing faults (∼70%). Faulting at the EPR crest occurs within the narrow, ∼4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber. Deformation at greater distances off axis (up to 40 km) is accommodated by flexure of the lithosphere due to thermal subsidence, resulting in ∼50% inward facing faults accommodating ∼50% of the strain. On the basis of observed burial of faults by lava flows and damming of flows by fault scarps, we find that the development of Layer 2A is strongly controlled by low-relief growth faults that form at the ridge crest and its upper flanks. In turn, those faults have a profound impact on how lava flows are distributed along and across the ridge crest.

The structure of crystals, glasses, and melts along the CaO-Al2O3 join: Results from Raman, Al L- and K-edge X-ray absorption, and 27Al NMR spectroscopy

Abstract: Calcium aluminate glasses are important materials where AlO 4/2 − is the only network former. Aluminum in crystals or glasses between CaO and Al 2 O 3 can have different environments as a function of the CaO/Al 2 O 3 ratio. Using X-ray absorption at the Al K - and L -edges, Raman and 27 Al NMR spectroscopies, we have determined the structural surroundings of Al in glasses, crystals, and melts in this binary system. Aluminum is in octahedral coordination at high-Al 2 O 3 content (>80 mol%) and essentially in fourfold coordination with 4 bridging O atoms (BOs) at Al 2 O 3 contents between 30 and 75 mol%. At around 25 mol% Al 2 O 3 , Al is in tetrahedral coordination with two BOs. The presence of higher-coordinated species at high-Al 2 O 3 contents and their absence at low Al 2 O 3 imply different viscous flow mechanisms for high- and low-concentration Al 2 O 3 networks.

A compositional tipping point governing the mobilization and eruption style of rhyolitic magma

Abstract: Measurements of the composition-dependent viscosity of rhyolitic magma reveal a tipping point that changes the physical properties of the melt and controls the transition between effusive and explosive eruptions. Calcalkaline rhyolites produce the largest explosive volcanic eruptions, but these eruptions can switch repeatedly between being effusive and explosive. This is difficult to attribute to the rheological effects of magma water content or crystallinity. Danilo Di Genova and co-authors report the viscosity of a series of melts spanning the compositional range of the Yellowstone rhyolitic volcanic system. They find that, within a narrow compositional zone, melt viscosity increases by up to two orders of magnitude, which they propose to be the consequence of melt structure reorganization. The authors confirm that such a compositional tipping point exists in the global geochemical record of rhyolites, which separates effusive from explosive deposits. They conclude that the anhydrous (water-free) composition of calcalkaline rhyolites is decisive in determining mobilization and eruption dynamics of the Earth's largest volcanic systems. The most viscous volcanic melts and the largest explosive eruptions1 on our planet consist of calcalkaline rhyolites2,3. These eruptions have the potential to influence global climate4. The eruptive products are commonly very crystal-poor and highly degassed, yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content5. It is unclear how magma mushes are mobilized to create large batches of eruptible crystal-free magma. Further, rhyolitic eruptions6,7,8 can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity9,10. Here we measure the viscosity of a series of melts spanning the compositional range of the Yellowstone volcanic system and find that in a narrow compositional zone, melt viscosity increases by up to two orders of magnitude. These viscosity variations are not predicted by current viscosity models11,12 and result from melt structure reorganization, as confirmed by Raman spectroscopy. We identify a critical compositional tipping point, independently documented in the global geochemical record of rhyolites, at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide. This correlation between melt structure, viscosity and eruptive behaviour holds despite the variable water content and other parameters, such as temperature, that are inherent in natural eruptions. Thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity. However, the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style. We conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of Earth’s largest volcanic systems, resulting in a better understanding of how the melt structure controls volcanic processes.

Description of new shock‐induced phases in the Shergotty, Zagami, Nakhla and Chassigny meteorites

Abstract: — The Shergottite, Nakhlite and Chassignite (SNC) meteorites, Shergotty, Zagami, Nakhla and Chassigny, have been studied by analytical transmission electron microscopy. New phases, characteristic of strong shock conditions, have been discovered: calcium-rich majorites in Shergottty, wadsleyite with anomalously elevated iron content in Chassigny, and impact melts in Shergotty, Zagami and Nakhla. Cristobalites (α and β polymorphs) observed in Shergotty and Zagami may also be related to shock and are interpreted as back transformation products of post-stishovite silica polymorphs. Shocks corresponding to pressure and temperature conditions characteristic of the Earth's transition zone and lower mantle have occurred in those meteorites. Moreover, impact melts indicate high-temperature conditions in localized areas. On the other hand, no massive impact melting is observed in those meteorites, consistent with previous descriptions. These observations provide evidence of highly heterogeneous shock conditions at the scale of few micrometers in these meteorites. Strongly heterogeneous conditions such as those suggested by the present study may help to explain the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock-metamorphized minerals.