Volcanism and Subduction: The Kamchatka Region (Geophysical Monograph Series)

Geophysical Monograph Series
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Fo core and Ni core are the initial values in the crystal at time 0, Fo dm and Ni dm are compositions for olivine in equilibrium with more evolved surrounding melt on the dissolved margin of the crystal. By analogy with heat conduction, it is possible e. The dependence of Fo is quantitatively represented in Fig. On the other hand, these limitations do not affect the curvature of the modeled diffusion trend. The problem regarding component concentration in a diffusion sphere with a finite radius at any time is accurately solved by equation 6.

The details of these analyses, however, are beyond the scope of this paper. Thus, concave trends in Ni-Fo space in olivine that run contrary to typical trends during fractional crystallization can be taken as solid evidence for diffusion. Examples of such model fits can be found in Fig. Based on the entire data set, we conclude that the time scale of diffusion that modified the outer cores of the crystals range from to days Fig.

Since outer core diffusion is only a particular case of advanced core diffusion for the largest grains, both diffusion time estimates should be similar, which is indeed the case to days for outer core diffusion vs. Instead, our olivine crystals from Shiveluch must have had unusually fast ascent times, as discussed in more detail below. Such concave compositional trends have previously been documented in olivine crystals from komatiites and kimberlites 45 — 51 and probably indicate similar diffusion process.

Diffusion between crystal core and overgrowth followed after mixing with, and growth from, a more mafic higher-temperature recharge magma into the reservoir where the olivine crystals resided in a more evolved melt.

The Fo and NiO profiles from group 4 olivines Fig. As an alternative interpretation to the origin of the four groups of olivine cores, low-Mg olivine could also form after fractional crystallization in a more evolved melt, rather than exchange by diffusion with an evolved melt after magma mixing. Irrespective of the origin of group 4 olivine cores, a magma mixing event is clearly indicated by the resorption interface and so we can use the width of the transition zone to determine the time elapsed since the mixing event.

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As emphasized above, there are continuous transitions from core group 1 to group 4, which would not be expected if there had been two distinct processes and two distinct magmas that formed these cores. Therefore, we prefer the interpretation of diffusive exchange to explain the different core types. In previous studies, such diffusion modeling was performed separately either for forsterite 38 or for nickel 5 and modeling of olivine profiles with simultaneous exchange Fo and NiO has only been described previously for the rims of crystals 1 , However, as we show in this study, such rims may be affected by both diffusion and crystal growth and comparing results for Ni and Fo may not be reasonable in this case.

However, the measured data and our modeling across the resorption interface allows us, for the first time, to directly assess the contribution of each diffusion component. An example of a model fit to the data can be found in Fig. The diffusion times range from 1 to 10 days Fig. Thus, the time of diffusion between core and overgrowth is orders of magnitude shorter than the time of diffusion that had affected the cores prior to their resorption.

Zoning and diffusion in the overgrowth must have postdated the resorption event and at least partly the subsequent overgrowth. All profiles outside the transition zone towards the margin show the same compositional Fo-Ni trends blue lines in Fig. The widths of the Fo and Ni gradients in this growth zone are significantly wider than widths across the resorption interface. This indicates that smoother gradients within the overgrowth cannot result from diffusion, because the time of diffusion within cannot be longer than for diffusion further inside the crystal.

Thus, the formation of the overgrowth reflects olivine growth in a progressively evolving melt.

1. Introduction

Volcanism and Subduction: The Kamchatka Region, Volume Editor(s). John Eichelberger Book Series:Geophysical Monograph Series. Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume The Kamchatka Peninsula and contiguous North .

Repeated excursions to more mafic compositions high Cr are inferred to reflect minor recharge events during the fractional crystallization process. However, these high Cr growth zones are also enriched in Ca, Al, and P. Slow-diffusing P can be strongly affected by slow kinetics during fast crystal growth 13 , 53 — Therefore we ascribe the narrow oscillatory growth bands to kinetic effects rather than growth from changing melt compositions.

Successive stages of olivine growth and diffusion history are schematically shown in Fig. When the diffusion process did not reach the inner cores group 1 this indicates times scales ranging from to days Fig. The inner cores of olivine of groups 2 and 3 were affected by diffusion to variable degrees with diffusion times ranging from to days Fig. Some olivine crystals completely equilibrated with this evolved melt group 4. The next event in the history of these olivine crystals was magma mixing with a new high-Mg and high-Ni melt.

Due to the high temperature of this melt, the rims of olivine cores were partly dissolved creating a prominent resorption interface between cores and their overgrowths Fig. Subsequent cooling resulted in new high-Fo and high-Ni olivine growths over the resorption interface that formed the overgrowth of the crystals Fig.

Newly grown olivine in this zone is enriched in Cr 2 O 3 up to 0. Further crystallization produced olivine down to Fo 80 towards the rims of crystals and concentric, oscillatory and correlated growth bands of slow-diffusing elements Cr, Al, P; Fig.

I include some inset figures in the poster.

The relatively high pressures and temperatures suggest that the cores and overgrowth of the olivine crystals were formed under mantle conditions. Making andesites in a lower crustal hot zone: Preconditioning the lithosphere of Taupo Volcanic Zone. Access personal reporting. M, Price, R. At its heart is the uniquely acute subduction cusp where the Kamchatka and Aleutian Arcs and Emperor Seamount Chain meet. New techniques were developed for event detection, satellite tasking, data distribution, and data analysis. Part 4: Subduction-truncated sectors of Pacific margin, Mexico to Tierra del Fuego From north to south, evidence for subduction erosion truncation of eastern Pacific margins is described for Mexico by Schaaf et al.

While Cr, Al, and P show sharp growth bands in the overgrowth, Fo and NiO variations were partly smoothed out by diffusion at the same time during which diffusion modified the resorption interface Fig. The duration of this last growth and diffusion stage is only 1—10 days Fig. This suggests a very short time between the last recharge event core resorption and surface eruption. The schematic evolution of the complex growth, dissolution and diffusion history of olivine crystals from high-Mg middle-K Shiveluch basalt is depicted in simplified centre-to-margin Fo-profiles.

Earthquake Report: Bering fracture zone: UPDATE #1

As a result, olivine crystals were affected by diffusion to differing extents and decreasing Fo is observed. Compare these final Fo-profiles to the measured profiles in Fig. Blue dotted line indicates the position of the resorption interface. Thus, high-Mg high-Ni overgrowths on the cores were formed only a few days after the last mixing event and this mixing event likely triggered the eruption.

By contrast, the formation of the cores, their storage and magma mixing and diffusion must have all occurred at mantle levels around to days before eruption. Fast ascent may be more frequent than previously thought because slow cooling during the late stages of ascent and cooling in lava flows or recharge into larger shallow magma reservoirs within volcanic edifices, generally erases zoning records like those described here. One possibility for preserving records of fast ascent of mafic magmas from great depth is the nature of the maar eruption which has formed the BP Shiveluch tephra deposit.

Such phreatomagmatic eruptions in general tend to 1 be derived from basalts that ascend relatively fast, possibly driven by deep CO 2 -degassing and 2 therefore often carry abundant xenoliths. Relatively short timescales of hundred days to a few years were documented for ascent of mafic magmas from mantle depths 5.

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The time scales for ascent of magmas and olivine crystals in lavas of the Shiveluch BP eruption apparently rose to the surface by orders of magnitude faster. Our research shows that crystal growth, mixing and diffusion processes on the way from mantle source to surface may be quite complex and the time of ascent can be fast — just a few days before the eruption. We used specifically designed high-precision methods based on increased current and increased voltage The methods allowed us to analyse olivine profiles for major and trace elements, to conduct precision microelement measuring for thermobarometry, and to build elemental maps.

Every sample was covered with a very thin carbon layer to minimize electrostatic charge due to the high vesicularity of the samples. Several points were measured along the compositional profile of every grain to ensure that crystal orientation does not change within the crystal due to cracks or deformation. Oxygen fugacity was estimated by using the improved Ballhaus-Berry-Green ol-opx-sp oxybarometer Pressure was determined from cpx-melt compositions and cpx-only barometry In our calculations for every profile we selected the values of the slowest and fastest diffusion coefficients.

For modelling of diffusion inside the cores we used external P-T- f O 2 conditions determined for the transition zones. For modeling of diffusion in the transition zone we used P-T- f O 2 conditions determined for the overgrowth. For the approximation of the measured profiles by the least square method in the case of outer core diffusion we used the analytical solution of the one-dimensional problem for diffusion in a semi-infinite medium Eq.

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For the initial conditions and the boundary condition at infinity we used the values of Fo and Ni in the centres of a olivine cores. For the boundary conditions of the dissolved margin of the cores we used the estimate Fig. Simultaneous adjustment for Fo and Ni solutions allowed to find the diffusion times and the position of the dissolved margin for every profile.

An example of the approximation between data and the model is given in Fig. For the approximation of the measured profiles by the least squares method in the case of advanced core diffusion we used the analytical solution of the spherically symmetric problem for diffusion in a sphere Eq. Simultaneous adjustment for Fo and Ni solutions allowed us to find the diffusion time and the position of the dissolved margin for every profile. For the approximation of the measured profiles by the least squares method in the case of transition zones we used the analytical solution of the one-dimensional problem for diffusion in an infinite medium Eq.

The initial and boundary conditions on both sides of the diffusion zones were automatically determined by parameter fitting of the analytical solution. The solutions for Fo and Ni were approximated independently. We thank Simon Turner, Alexander Iveson, and Ekaterina Rossovskaya for careful proof reading and language editing and two reviewers and editor for their constructive comments. All authors prepared the Supplementary Materials and participated in discussions related to topics of this manuscript.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Supplementary information accompanies this paper at National Center for Biotechnology Information , U. Sci Rep. Published online Aug 6.

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Author information Article notes Copyright and License information Disclaimer. Boris Gordeychik, Email: ur. Corresponding author. Received Mar 12; Accepted Jul Associated Data Supplementary Materials Supplementary materials.

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Abstract Complex core-rim zoning of Mg-Fe-Ni-Ca-Cr-Al-P in high-Mg olivine crystals from a tuff ring of Shiveluch volcano, Kamchatka, enables reconstruction of the entire olivine crystallization history from mantle conditions to eruption. Introduction We have a good understanding of the principal processes of compositional differentiation and mixing of magmas prior to their eruption.

Shiveluch Volcano, Kamchatka: Geology and Sampling Kamchatka is one of the most active magmatic arcs in the world with abundant mafic lavas that contain high-Mg olivine phenocrysts. Open in a separate window. Figure 1. Figure 3. Figure 2. Figure 4.

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Discussion: Growth and Diffusion History The olivine crystals record two distinct stages of crystallization for core and overgrowth, which are separated by a dissolution interface. Figure 5. Figure 6. Figure 7.