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@ARTICLE{Lathe:476406,
author = {Lathe, Christian and Koch-Mueller, Monika and Wunder, Bernd
and Appelt, Oona and Bhat, Shrikant and Farla, Robert},
title = {{I}n situ reinvestigation of reaction phase {A} plus
high-pressure clinoenstatite to forsterite plus water in the
system {M}g{O}-{S}i{O}$_2$-{H}$_2${O} ({MSH})},
journal = {European journal of mineralogy},
volume = {34},
number = {2},
issn = {0935-1221},
address = {Göttingen},
publisher = {Copernicus Publications},
reportid = {PUBDB-2022-01721},
pages = {201 - 213},
year = {2022},
abstract = {The dehydration reaction of phase A + high P clinoenstatite
to forsterite + water was experimentally investigated at
water-saturated conditions in the pressure range between 7.0
and 10.0 GPa by in situ reversal runs in a multi-anvil
press at the synchrotron source of PETRA III in Hamburg. By
using closed watertight X-ray transparent Ti capsules, its
position is determined by reversal brackets at 8.3 GPa
(700–760 ∘C), 8.6 GPa (700–740 ∘C), and
9.8 GPa (750–800 ∘C); thus, the equilibrium of the
reaction corresponds ideally to the data reported by Wunder
(1998). Optical investigations of the quenched product
phases show strong grain coarsening of phase A and
clinoenstatite, whereas nucleated forsterite from the
breakdown of the aforementioned phases is very fine grained.
This corresponds to recent experimental observations that
the grain size of phases formed in hydration reactions are
significantly larger than those from dehydration
reactions.In addition, we performed three time-dependent in
situ experiments at 9–10 GPa and 800–870 ∘C and
monitored the reaction progress every 10 min to determine
the kinetics of the forsterite formation from phase
A + high P clinoenstatite. The growth of forsterite at
these P–T conditions, already visible after 10 min,
confirms the results of the bracketing experiments. However,
the reaction is extremely slow, and even after more than
3 h, significant amounts of phase A and high P
clinoenstatite are still present. This is in contradiction
to other dehydration reactions of former experimental
studies, e.g. the fast dehydration of serpentine, which
completely dehydrates within 3 h, even at much lower
temperatures, closely overstepping serpentine
stability.Despite its reaction sluggishness, which would
contradict the concept of earthquake initiation, the
observed formation of nano-sized forsterite as a dehydration
product may still indicate the potential of this reaction to
cause mechanical instabilities and, thus, seismicity within
cold subduction zones at depths of the Earth's mantle.
Additionally, at depths exceeding serpentine dehydration,
the phase A + high P/low P clinoenstatite breakdown to
forsterite + water might induce geochemical and
geophysical processes, including the formation of
low-velocity zones within the overlying mantle wedge from
the large amounts of fluid liberated by this water line
reaction. After the breakdown of antigorite, the assemblage
phase A + clinoenstatite might act as a bridge to
transport water to larger depths during cold subduction,
followed by the formation of other hydrous high P phases.},
cin = {DOOR ; HAS-User / FS-PETRA-D / GFZ},
ddc = {550},
cid = {I:(DE-H253)HAS-User-20120731 /
I:(DE-H253)FS-PETRA-D-20210408 / I:(DE-H253)GFZ-20120731},
pnm = {631 - Matter – Dynamics, Mechanisms and Control
(POF4-631) / 6G3 - PETRA III (DESY) (POF4-6G3) /
FS-Proposal: I-20210162 (I-20210162)},
pid = {G:(DE-HGF)POF4-631 / G:(DE-HGF)POF4-6G3 /
G:(DE-H253)I-20210162},
experiment = {EXP:(DE-H253)P-P61.2-20150101},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000776254100001},
doi = {10.5194/ejm-34-201-2022},
url = {https://bib-pubdb1.desy.de/record/476406},
}