[MSA-talk] Notable Papers in Am Min, Nov. 2017

Keith Putirka kputirka at csufresno.edu
Tue Dec 5 15:34:42 EST 2017

Dear MSA Members,

Below are Editors' picks of notable articles, for this month’s issue (well,
actually, last month's issue) of the *American Mineralogist: Journal of
Earth and Planetary Materials*, and you can click here for the full Table
of Contents. <http://ammin.geoscienceworld.org/content/102/1>

You may view the American Mineralogist Noted Papers at
http://www.minsocam.org/MSA/Ammin/AM_Notable_Articles.html, or click on the
page numbers below. If you are not already logged into GeoScience World,
then from the *American Mineralogist *menu on http://www.minsocam.org/
<http://www.minsocam.org/MSA/Ammin/AM_Notable_Articles.html>, go to "Online
Access to MSA Publications <http://www.msapubs.org>" - look for and select
the "portal page" link, to access GeoScience World. Once at the portal
page, enter your user name (e-mail address), and your password (membership

Keith Putirka

Ian Swainso

*Editors Selections, November 2017*

*Highlights & Breakthroughs*

*Rutile is the Key*

On page 2153 <https://doi.org/10.2138/am-2017-6261> of this issue, Alicia
Cruz-Uribe provides an overview of Guo et al.
<https://doi.org/10.2138/am-2017-6120> (2017; p. 2268 of this issue), who
investigate rutile grains that form at the rims of Fe-Ti oxides in
greenschist facies metamorphic rocks. Associated mineral and inferred
reactions indicate that rutile forms by the action of highly oxidized
fluids, approaching nearly 4 log units above QFM, during retrograde
metamorphism. As Cruz-Uribe notes, this study illustrates a how rutile may
be a record of elevated *f*O2 fluids at subduction zones. The possibility
is that rutile is forming as the rocks intercept high *f*O2 fluids that are
driven off the slab, or are otherwise connected in some way to subduction
zone magmatism. These rutile grains, though, would not be responsible for
the high field strength element signatures of arc magmas.

*Volcanoes & Plutons: disconnected*

On page 2154 <https://doi.org/10.2138/am-2017-6260> of this issue, Calvin
Miller reviews the granite controversy of the prior century, and new
questions that have evolved since. The context involves new findings by Tang
et al. <https://doi.org/10.2138/am-2017-6071> (2017; p. 2190 of this issue)
who use zircon compositions from volcanic and intrusive felsic rocks from
Hong Kong, to test ideas of volcano-plutonic connections. Their work
indicates that at least at Hong Kong, plutons are not the residues of
felsic eruptions. Instead, felsic volcanic chambers are nearly completely
evacuated, and intrusive rocks are evolutionary analogs intruded when
conditions for eruption were unfavorable. Though closely related in space
and time, the felsic rocks of this region are not co-magmatic, but
generated independently and erupted, or not, as structural conditions allow.


*No Fe-Ti Oxide Magmas*

On page 2157 <https://doi.org/10.2138/am-2017-6091> of this issue, Lindsley
and Epler present new experimental data to re-examine the genesis of massive
Fe-Ti oxide bodies that occur mainly in association with anorthosites,
often as dikes. At issue is whether such oxide-rich bodies are crystalline
residues of a silicate melt, or were melts in and of themselves, possibly
formed along an oxide-silicate melt solvus (as an immiscible melt). These
authors conclude that such oxide bodies have bulk compositions that cannot
occur as melts at geologically reasonable temperatures. More likely
the oxide-rich
bodies were intruded as crystal-rich mushes, perhaps lubricated by small
amounts of a silicate melt. They also imply that some "jotunite"-like rocks
(having low Si and high Fe and Ti) are these very same lubricating silicate
melts, apparently acquiring their low Si and high Fe and Ti by dissolving
some of their otherwise mechanically associated Fe-Ti oxides.

*Review & Special Collection: Biomaterials—Mineralogy Meets Medicine*

*Orthophosphates: What can’t they do?*

On page 2170 <https://doi.org/10.2138/am-2017-6165> of this issue, Robert
Heimann reviews a class of orthophosphates with NASICON structure, which
nicely illustrate how fundamental concepts of mineralogy are pivotal in the
search for superior bioceramics used in a variety of medical applications.
Heimann proposes that Ca(Ti,Zr) hexaorthophosphates have bone
growth-mediating characteristics that are particularly well suited for use
as coatings on metallic implants (in knee or hip replacements) so as to aid
bio-integration of the foreign materials, and, based on the solid-state
ionic conductivity of these compounds, proposes a new device that is
expected to electrically stimulate bone growth. While the biological uses
are emphasized, the author suggests that these same structures should also
be useful for storage of radioactive waste or as electrodes in molten
Na-ion batteries, among other applications.


*Fables of the Reconstruction (of Liquids Using Amphibole)*

On page 2254 <https://doi.org/10.2138/am-2017-6110> of this issue, Shimizu
et al. develop parameterized lattice-strain models predictive of the
partitioning of REE into amphibole. They find that REE partition
coefficients are highly sensitive to the amphibole major element
compositions--with order of magnitude variations accompanying arc magma
genesis. Their new mineral-composition model allows one to reconstruct
equilibrium liquid REE concentrations from amphibole compositions alone,
provided that temperature is known, and a new thermometer is presented as
well. Application of these new models reveals a greater role for amphibole
fractionation of arc magmas, relative to clinopyroxene, and that REE-rich
amphiboles are likely records of particularly low-T amphibole

*Fast Moving Dunites (from 150 km)*

On page 2295 <https://dx.doi.org/10.2138/am-2017-5982> of this issue, Su et
al. describe magnesite + aragonite intergrowths within the Sulu UHP terrane
of eastern China, that form as breakdown products of dolomite, at >5 GPa.
The authors infer that the precursor dolomite formed from a metasomatic
melt, perhaps within the uppermost part of the mantle. In any case, because
the breakdown reaction of dolomite is not sensitive to T, it seems that the
carbonates were indeed formed at very high pressure, and the lack a
retrograde reaction of magnesite + aragonite back to dolomite further
indicates that the exhumation was rapid or dry or both. The authors infer
that other dunites may harbor the very same clues of a UHP history, if
similar textures and assemblages may be found.

Keith Putirka
Dept. Earth & Env. Sciences
California State University, Fresno
2576 E. San Ramon Ave. M/S ST24

kputirka at csufresno.edu
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