The preserved plume of the Caribbean Large Igneous Plateau revealed by 3D data-integrative models

Remnants of the Caribbean Large Igneous Plateau (C-LIP) are found as thicker than normal oceanic crust in the Caribbean Sea that formed during rapid pulses of magmatic activity at similar to 91-88 and similar to 76 Ma. Strong geochemical evidence supports the hypothesis that the C-LIP formed due to melting of the plume head of the Galapagos hotspot, which interacted with the Farallon (Proto-Caribbean) plate in the eastern Pacific. Considering plate tectonics theory, it is expected that the lithospheric portion of the plume-related material migrated within the Proto-Caribbean plate in a north-north-eastward direction, developing the present-day Caribbean plate. In this research, we used 3D lithospheric-scale, data-integrative models of the current Caribbean plate setting to reveal, for the first time, the presence of positive density anomalies in the uppermost lithospheric mantle. These models are based on the integration of up-to-date geophysical datasets from the Earth's surface down to 200 km depth, which are validated using high-resolution free-air gravity measurements. Based on the gravity residuals (modelled minus observed gravity), we derive density heterogeneities both in the crystalline crust and the uppermost oceanic mantle (<50 km). Our results reveal the presence of two positive mantle density anomalies beneath the Colombian and the Venezuelan basins, interpreted as the preserved fossil plume conduits associated with the C-LIP formation. Such mantle bodies have never been identified before, but a positive density trend is also indicated by S-wave tomography, at least down to 75 km depth. The interpreted plume conduits spatially correlate with the thinner crustal regions present in both basins; therefore, we propose a modification to the commonly accepted tectonic model of the Caribbean, suggesting that the thinner domains correspond to the centres of uplift due to the inflow of the hot, buoyant plume head. Finally, using six different kinematic models, we test the hypothesis that the C-LIP originated above the Galapagos hotspot; however, misfits of up to similar to 3000 km are found between the present-day hotspot location and the mantle anomalies, reconstructed back to 90 Ma. Therefore, we shed light on possible sources of error responsible for this offset and discuss two possible interpretations: (1) the Galapagos hotspot migrated (similar to 1200-3000 km) westward while the Caribbean plate moved to the north, or (2) the C-LIP was formed by a different plume, which - if considered fixed - would be nowadays located below the South American continent

Processing and characterization of improved congruent lithium niobate

LiNbO3 exists in two forms: Most commercial devices are inexpensively fabricated from congruent melt that is ca. 1.5% off-stoichiometry. This produces devices of high optical quality for nonlinear optics but also high loss. Stoichiometric lithium niobate also exists, but in smaller more expensive specimens. Here we report the preparation and characterization of low-loss congruent samples. These are shown to be relatively free from extended defects.Publisher PDFPeer reviewe

The crustal stress field of Germany: a refined prediction

Information about the absolute stress state in the upper crust plays a crucial role in the planning and execution of, e.g., directional drilling, stimulation and exploitation of geothermal and hydrocarbon reservoirs. Since many of these applications are related to sediments, we present a refined geomechanical–numerical model for Germany with focus on sedimentary basins, able to predict the complete 3D stress tensor. The lateral resolution of the model is 2.5 km, the vertical resolution about 250 m. Our model contains 22 units with focus on the sedimentary layers parameterized with individual rock properties. The model results show an overall good fit with magnitude data of the minimum (S$_{hmin}$) and maximum horizontal stress (SS$_{Hmax}$) that are used for the model calibration. The mean of the absolute stress differences between these calibration data and the model results is 4.6 MPa for Shmin and 6.4 MPa for SS$_{Hmax}$. In addition, our predicted stress field shows good agreement to several supplementary in-situ data from the North German Basin, the Upper Rhine Graben and the Molasse Basin

Variations of atmospheric methane supply from the Sea of Okhotsk unduced by the seasonal in cover

Measurements of dissolved methane in the surface waters of the western Sea of Okhotsk are evaluated in terms of methane exchange rates and are used to assess the magnitude of seasonal variations of methane fluxes from the ocean to the atmosphere in this area. Methane concentrations northeast of Sakhalin were observed to range from 385 nmol L−1 under the ice cover in winter to 6 nmol L−1 in the icefree midsummer season. The magnitude of supersaturations indicates that this part of the Okhotsk Sea is a significant source for atmospheric methane. From the seasonal variation of the supersaturations in the surface waters it is evident that the air-sea exchange is interrupted during the winter and methane from sedimentary sources accumulates under the ice cover. According to our measurements an initial early summer methane pulse into the atmosphere of the order of 560 mol km−2 d−1 can be expected when the supersaturated surface waters are exposed by the retreating ice. The methane flux in July is approximately 150 mol km−2 d−1 which is of the order of the average annual flux in the survey area. The magnitude of the seasonal CH4 flux variation northeast of Sakhalin corresponds to an amount of 7.3 × 105 g km−2 whereby 74% or 5.4 × 105 g km−2 are supplied to the atmosphere between April and July. For the whole Sea of Okhotsk the annual methane flux is roughly 0.13 × 1012 g (terragrams), based on the assumption that 15% of the entire area emit methane. Variations of long-term data of atmospheric methane which are recorded at the same latitude adjacent to areas with seasonal ice cover show a regional methane pulse between April and July. The large-scale level of atmospheric methane in the northern hemisphere undergoes an amplitudinal variation of about 25 parts per billion by volume (ppbv) which translates into approximately 36 Tg. Thus the estimated 0.6 Tg of ice-induced methane dynamics in northern latitudes can hardly explain this seasonal signal. However, the effects of seasonal ice cover on pulsed release of methane appear strong enough to contribute, in concert with other seasonal sources, to characteristic short-term wobbles in the atmospheric methane budget which are observed between 50°N and 60°N

PLANE DOMAINS WITH SPECIAL CONE CONDITION

The paper considers the domains with cone condition in C. We say that domain G satisfies the (weak) cone condition, if p+V (e(p), H) ⊂ G for all p ∈ G, where V (e(p), H) denotes rightangled circular cone with vertex at the origin, a fixed solution ε and a height H, 0 < H ≤ ∞, and depending on the p vector e(p) axis direction. Domains satisfying cone condition play an important role in various branches of mathematic (e. g. [1], [2], [3] (p. 1076), [4]). In the paper of P. Liczberski and V. V. Starkov, α–accessible domains were considered, α ∈ [0, 1), — the domains, accessible at every boundary point by the cone with symmetry axis on {pt : t > 1}. Unlike the paper of P. Liczberski and V. V. Starkov, here we consider domains, accessible outside by the cone, which symmetry axis inclined on fixed angle ϕ to the {pt : t > 1}, 0 < ∥ϕ∥ < < π/2. In this paper we give criteria for this class of domains when the boundaries of domains are smooth, and also give a sufficient condition when boundary is arbitrary. This article is the full variant of [5], published without proofs