828 research outputs found
Arc Magmas from Slab to Eruption: The Case of Kliuchevskoy Volcano
Arc magmas are generated by a number of mantle and
crustal processes. Our multidisciplinary, long-term research is
aimed at deciphering these processes for a single arc volcano,
Kliuchevskoy volcano in Kamchatka. Some key results of the
study follow:
1) Modeling of trace element and H2O contents in melt
inclusions suggests that the primary magmas originate via
hydrous flux-melting of the mantle wedge at temperatures
close to the dry peridotite solidus. The role of decompression
melting is minor or absent at Kliuchevskoy and other arc
volcanoes built on relatively thick crust.
2) Geochemistry of high-Mg olivine suggests that primary
Kliuchevskoy magmas have substantial contribution from
olivine-free pyroxenite (up to 30 %), which could be formed
by reaction of slab melts (or supercritical fluids) with mantle
wedge peridotite.
3) Parental Kliuchevskoy melts start to crystallize as deep
as the Moho boundary, and the erupted magmas reflect multistage
and complex processes of crystallization, magma mixing
and crustal assimilation. None of the Kliuchevskoy rocks
analyzed thus far represent true primary melt compositions.
4) The Kliuchevskoy Holocene eruptive history is not
steady-state in terms of eruption rate and geochemistry. There
are two millenial cycles with major and trace element and OSr-
Nd-Pb and U-series isotope compositions of the magmas
changing gradually from more to less affected by crustal (?)
assimilation. The onset of the cycles correlates with periods of
enhanced volcanic activity in Kamchatka, suggesting that the
extent of magma-crust interaction is inversely related to
magma production rate and thus magma flux from the mantle
Enriched, HIMU-type peridotite and depleted recycled pyroxenite in the Canary plume : a mixed-up mantle
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 277 (2009): 514-524, doi:10.1016/j.epsl.2008.11.013.The Earth’s mantle is chemically and isotopically heterogeneous, and a component of recycled oceanic crust is generally suspected in the convecting mantle [Hofmann and White, 1982. Mantle plumes from ancient oceanic crust. Earth Planet. Sci. Lett. 57, 421-436]. Indeed, the HIMU component (high μ = 238U/204Pb), one of four isotopically distinct end-members in the Earth’s mantle, is generally attributed to relatively old (≥1-2 Ga) recycled oceanic crust in the form of eclogite/pyroxenite, e.g. [Zindler and Hart, 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493-571]. Although the presence of the recycled component is generally supported by element and isotopic data, little is known about its physical state at mantle depths. Here we show that the concentrations of Ni, Mn and Ca in olivine from the Canarian shield stage lavas, which can be used to asses the physical nature of the source material (peridotite versus olivine-free pyroxenite) [Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science 316, 412-417], correlate strongly with bulk rock Sr, Nd and Pb isotopic ratios. The most important result following from our data is that the enriched, HIMU-type (having higher 206Pb/204Pb than generally found in the other mantle endmembers) signature of the Canarian hotspot magmas was not caused by a pyroxenite/eclogite constituent of the plume but appears to have been primarily hosted by peridotite. This implies that the old (older than ~1 Ga) ocean crust, which has more evolved radiogenic isotope compositions, was stirred into/reacted with the mantle so that there is not significant eclogite left, whereas younger recycled oceanic crust with depleted MORB isotopic signature (<1 Ga) can be preserved as eclogite, which when melted can generate reaction pyroxenite.This work was supported by Wolfgang Paul Award, Alexander von Humboldt Foundation, to AVS, the Max Planck Society, DFG grants SCHM 250/64 and 82-1, HA3097/2 to HUS, KH and FH, NSF Grant EAR-9105113 to KH, Russian Basic Research Foundation and Russian Academy of Sciences
Geochemistry of the Late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems
We present new major and trace element, high-precision Sr-Nd-Pb (double spike), and Oisotope
data for the whole range of rocks from the Holocene Tolbachik volcanic field in
the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg
basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent
mostly Late Holocene eruptions (using tephrochronological dating), including historic
ones in 1941, 1975-1976 and 2012-2013. Major compositional features of the Tolbachik
volcanic rocks include the prolonged predominance of one erupted magma type, close
association of middle-K primitive and high-K evolved rocks, large variations in
incompatible element abundances and ratios but narrow range in isotopic composition.
We quantify the conditions of the Tolbachik magma origin and evolution and revise
previously proposed models. We conclude that all Tolbachik rocks are genetically related
by crystal fractionation of medium-K primary magmas with only a small range in trace
element and isotope composition. The primary Tolbachik magmas contain ~14 wt% MgO
and ~4% wt% H2O and originated by partial melting (~6%) of moderately depleted
mantle peridotite with Indian-MORB-type isotopic composition at temperature of
~1250oC and pressure of ~2 GPa. The melting of the mantle wedge was triggered by
slab-derived hydrous melts formed at ~2.8 GPa and ~725oC from a mixture of sediments
and MORB- and Meiji- type altered oceanic crust. The primary magmas experienced a
complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization
(REFC). First the original primary magmas underwent open-system crystal fractionation
combined with periodic recharge of the magma chamber with more primitive magma,
followed by mixing of both magma types, further fractionation and finally eruption.
Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic
trachyandesites erupted in 2012-2013 approach steady-state REFC liquid compositions at
different eruption or replenishment rates. Intermediate rocks, including high-K, high-Mg
basalts, are formed by mixing of the evolved and primitive magmas. Evolution of
Tolbachik magmas is associated with large fractionation between incompatible trace
elements (e.g., Rb/Ba, La/Nb, Ba/Th) and is strongly controlled by the relative difference
in partitioning between crystal and liquid phases. The Tolbachik volcanic field shows that
open-system scenarios provide more plausible and precise descriptions of long-lived arc
magmatic systems than simpler, but often geologically unrealistic, closed-system models
Limits on Dark Matter Effective Field Theory Parameters with CRESST-II
CRESST is a direct dark matter search experiment, aiming for an observation
of nuclear recoils induced by the interaction of dark matter particles with
cryogenic scintillating calcium tungstate crystals. Instead of confining
ourselves to standard spin-independent and spin-dependent searches, we
re-analyze data from CRESST-II using a more general effective field theory
(EFT) framework. On many of the EFT coupling constants, improved exclusion
limits in the low-mass region (< 3-4 GeV) are presented.Comment: 7 pages, 9 figure
The CRESST Dark Matter Search
We present first competitive results on WIMP dark matter using the
phonon-light-detection technique. A particularly strong limit for WIMPs with
coherent scattering results from selecting a region of the phonon-light plane
corresponding to tungsten recoils. The observed count rate in the neutron band
is compatible with the rate expected from neutron background. CRESST is
presently being upgraded with a 66 channel SQUID readout system, a neutron
shield and a muon veto system. This results in a significant improvement in
sensitivity.Comment: 6 pages, 3 figures, to be published in the proceedings of the 5th
International Workshop on the Identification and Detection of Dark Matter IDM
2004, Edinburgh, Sept. 2004, World Scientifi
Detection of the Natural Alpha Decay of Tungsten
The natural alpha decay of 180W has been unambiguously detected for the first
time. The alpha peak is found in a (gamma,beta and neutron)-free background
spectrum. This has been achieved by the simultaneous measurement of phonon and
light signals with the CRESST cryogenic detectors. A half-life of T1/2 = (1.8
+- 0.2) x 10^18 y and an energy release of Q = (2516.4 +- 1.1 (stat.) +- 1.2
(sys.)) keV have been measured. New limits are also set on the half-lives of
the other naturally occurring tungsten isotopes.Comment: Submitted to Physical Review C Revised versio
Exploring CEvNS with NUCLEUS at the Chooz Nuclear Power Plant
Coherent elastic neutrino-nucleus scattering (CENS) offers a unique way
to study neutrino properties and to search for new physics beyond the Standard
Model. Nuclear reactors are promising sources to explore this process at low
energies since they deliver large fluxes of (anti-)neutrinos with typical
energies of a few MeV. In this paper, a new-generation experiment to study
CENS is described. The NUCLEUS experiment will use cryogenic detectors
which feature an unprecedentedly low energy threshold and a time response fast
enough to be operated in above-ground conditions. Both sensitivity to
low-energy nuclear recoils and a high event rate tolerance are stringent
requirements to measure CENS of reactor antineutrinos. A new experimental
site, denoted the Very-Near-Site (VNS) at the Chooz nuclear power plant in
France is described. The VNS is located between the two 4.25 GW
reactor cores and matches the requirements of NUCLEUS. First results of on-site
measurements of neutron and muon backgrounds, the expected dominant background
contributions, are given. In this paper a preliminary experimental setup with
dedicated active and passive background reduction techniques is presented.
Furthermore, the feasibility to operate the NUCLEUS detectors in coincidence
with an active muon-veto at shallow overburden is studied. The paper concludes
with a sensitivity study pointing out the promising physics potential of
NUCLEUS at the Chooz nuclear power plant
The CRESST II Dark Matter Search
Direct Dark Matter detection with cryodetectors is briefly discussed, with
particular mention of the possibility of the identification of the recoil
nucleus. Preliminary results from the CREEST II Dark Matter search, with 730
kg-days of data, are presented. Major backgrounds and methods of identifying
and dealing with them are indicated.Comment: Talk at DSU workshop, ITP Beijing, Oct. 2011. 9 figures, 2 table
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