Dear Colleagues,

The deadline for submissions is approaching (Wednesday, 4 August 2021).
We invite contributions to the session “Multidisciplinary perspectives on
the formation and early evolution of terrestrial worlds
https://agu.confex.com/agu/fm21/prelim.cgi/Session/123642” at the AGU
Fall Meeting https://www.agu.org/Fall-Meeting from 13–17 December 2021,
New Orleans, USA & Online. Contributions from different perspectives are
encouraged to address the early history of rocky planets, including, but
not limited to, geochemistry, cosmochemistry, astronomy, mineral physics,
petrology, and planetary sciences. We look forward to seeing you in New
Orleans and online!

Session Description: Accretionary processes are fundamental to our
understanding of the thermal and compositional evolution of rocky planets
in the solar system and beyond. Advances in experiments under extreme P-T
conditions, theoretical modelling across atomic and planetary scales, and
observations at a system-level are key to unravelling the early history of
rocky, potentially habitable worlds. In particular, processes related to
planetary accretion and evolution, such as condensation, impacts,
(de-)volatilization, atmosphere formation, core-mantle differentiation, and
climate diversity have been increasingly constrained by planetary sample
analysis, laboratory experiments, theoretical simulations, and astronomical
observations of extrasolar planetary system. In this session, we invite
interdisciplinary contributions that address the various physical and
chemical aspects of planetary accretion and differentiation, including
geochemistry, cosmochemistry, astronomy, mineral physics, petrology, and
planetary sciences. Session mentee: Gabriel Nathan

Invited Speakers: Asmaa Boujibar (Carnegie), Jie Li (U Michigan)

Kind regards from the conveners:
Dongyang Huang, Rebecca Fischer, Tim Lichtenberg, Laura Schaefer

Dongyang Huang
Post-doctoral researcher
Institute of Geochemistry and Petrology
ETH Zürich
Sonneggstrasse 5 CH-8092 Zürich

Dear American Mineralogist Readers,

Below are the Paper Highlights for this month’s issue of the American Mineralogist: International Journal of Earth and Planetary Materials. You may also view the American Mineralogist Paper Highlights list at here (http://www.minsocam.org/MSA/Ammin/AM_NotableArticles.html).
The DOI links below will take you to the abstract on GeoScienceWorld.
If you have “IP” access via your institution’s library, it should reveal the whole paper. Consult your institution’s IT department or friendly librarian.
If you have MSA membership, then authenticate in from the American Mineralogist menu (herehttp://www.msapubs.org/ directly). Once at the portal page, click the right-side American Mineralogist link, enter your user name (e-mail address), and your password (membership number). Then search via your browser’s search tools for the paper you want to read. (On Rachel’s computer, it is control-f but we think that is little different for everyone.)
Note that on GSW you can sign up for a table of contents to be sent you when the issue is live -- this is a feature open to anyone who registers on the site.
Thank you for reading American Mineralogist.
Sincerely,
Hongwu Xu
Don Baker

August 2021 Paper Highlights

Highlights and Breakthroughs: Crustal melting: deep, hot, and salty
Lamadrid and Steele-MacInnis provide perspective on the study by Ferrero et al.: High pressure, halogen-bearing melt preserved in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (U.S.A.) (see below).
https://doi.org/10.2138/am-2022-8108

Petrogenetic and tectonic interpretation of strongly peraluminous granitic rocks and their significance in the Archean rock record
https://doi.org/10.2138/am-2022-8001
Strongly peraluminous granitic rocks first become abundant in the rock record in the Neoarchean. In this study by Frost and Da Prat (MSA Presidential Address by Carol Frost), six suites of Neoarchean strongly peraluminous granitic rocks are described from the Wyoming province. These are shown to form in both subduction and collisional environments from a variety of sources, including hornblende-plagioclase rocks, biotite-bearing gneisses, and two-mica metapelitic rocks. The appearance of strongly peraluminous granitic rocks in the rock record signals the development of strong, thick felsic continental crust and the formation of the first supercontinents.

Partial melting and P-T evolution of eclogite-facies metapelitic migmatites from the Egere Terrane (Central Hoggar, South Algeria)
https://doi.org/10.2138/am-2021-7342
This contribution by Arab et al. improves our understanding of high-pressure metapelites from Central Hoggar, provides very advanced P-T modeling, and shows the first description of evidence of partial melting phenomena from Hoggar. This study resolves numerous problems regarding the metamorphic evolution of the Egere area and their geodynamic implication within the Tuareg belt.

High pressure, halogen-bearing melt preserved in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (US)
https://doi.org/10.2138/am-2021-7690
Ferrero et al. performed micro-petrology experiments on preserved droplets of melt in garnet from the ultrahigh temperature felsic granulites of the Central Maine Terrain (Connecticut, U.S.A.). The results reveal a history of metamorphism and melting at a depth consistent with the orogenic roots, ~70 km, twice the previous estimates for these rocks. The high-pressure melt here preserved is peculiar: it has an uncommonly high mafic component, coupled with significant amounts of carbon dioxides and halogens (chlorine and fluorine). Whereas the first phenomenon results from the extreme melting temperatures, the halogens abundance likely relates to the presence of brines (highly saline liquids) at depth during melting. The latter is a direct evidence that brines may play a role in promoting melt production when the crust attains temperature in excess of 1000 °C, where melt production is actually expected to be hindered by the extremely dehydrated character of the rocks.

Targeting Jarosite -- Clay-mineral mixtures for Mars exploration
https://doi.org/10.2138/am-2021-7415
Hinman et al. compared, with multiple techniques, the detectability and abundance of organic matter associated with clay minerals and the sulfate salts, alunite, and jarosite, from a hydrothermal area in Yellowstone National Park, Wyoming, U.S.A. Spectroscopy and diffractometry produced comparable mineral identifications in sample matrices. The matrix material (clay minerals or sulfate salts) had no effect on the detection of organic matter by Raman spectroscopy. However, mineral matrix composition had a significant effect on the detectability of organic matter by laser-desorption, Fourier transform mass spectrometry (LD FTMS). Indeed, LD FTMS detected diverse organic compounds in samples containing jarosite, more so than in samples dominated by aluminosilicate minerals, despite higher organic content in the later matrix. Further, organic compounds were detected more frequently in jarosite samples than in aluminosilicate samples. Consequently, jarosite-bearing sites on Mars could be potential targets for life detection, especially if associated with clay minerals.

Zirconolite from Larvik Plutonic Complex, Norway, its relationship to stefanweissite and nöggerathite, and contribution to the improvement of zirconolite end-member systematics
https://doi.org/10.2138/am-2021-7510
Haifler et al. performed crystal-chemical characterization of a complex zirconolite from Larvik Plutonic Complex, Norway. A concept called "edgemembers" was introduced to quantitatively express compositional variation of a complex solid solution. Moreover, a modified scheme of zirconolite end-member set and redefinition of a composition space was suggested.

Nanomineralogy of hydrothermal magnetite from Acropolis, South Australia: Genetic implications for iron-oxide copper gold mineralization
https://doi.org/10.2138/am-2021-7557
The Acropolis prospect is a magnetite dominant iron-oxide copper gold (IOCG) prospect in the Olympic Dam district (South Australia). Verdugo-Ihl et al. used complementary microbeam techniques (HAADF  STEM, XMg-in-magnetite thermometry, and nanothermobarometry using ilmenite-magnetite pairs) to characterize titanomagnetite from veins hosted in volcanic rocks and Ti-poor magnetite from a granite body stratigraphically higher in the sequence. Hydrothermal titanomagnetite from Acropolis is comparable with magmatic magnetite in granites across the district and should typify early alkali-calcic alteration. Open-fracture circulation, inhibiting additional supply of Si, Ca, K, etc., during magnetite precipitation, prohibits formation of silician magnetite hosting calc-silicate NPs, as known from IOCG systems characterized by rock-buffered alteration of host lithologies. Obliteration of trellis textures during subsequent overprinting could explain the scarcity of this type of hydrothermal magnetite in other IOCG systems.

Effect of magnesium on monohydrocalcite formation and unit cell parameters
https://doi.org/10.2138/am-2021-7673
Vereshchagin et al. report the phase diagrams for monohydrocalcite (MHC), calcite, aragonite, and dypingite precipitation, as a function of pH and Mg/Ca ratio in solution. They demonstrate that elevated magnesium content and low temperature are favorable for MHC formation. On the basis of changes in the unit cell parameters, the possibility of the significant incorporation of magnesium into the crystal structure of MHC has been unequivocally proven. The increase in Mg in MHC is accompanied by an increase in water content, which leads to multidirectional changes in a and c cell parameters.

Formation pathway of norsethite dominated by solution chemistry under ambient conditions
https://doi.org/10.2138/am-2021-7348
"Dolomite problem" is a long-standing puzzle in geology. Zhang et al. investigated low-temperature formation of norsethite [BaMg(CO3)2] as a dolomite-analog under different solution chemistry conditions. The results reveal that the initial Mg/Ba ratio in solution is a crucial factor controlling the formation pathway of norsethite. At low Mg/Ba ratios, a multistep pathway occurs, i.e., a precursor witherite first forms, followed by norsethite precipitation and transformation from witherite to norsethite. In contrast, at Mg/Ba ratio > 20, norsethite can be directly precipitated from aqueous solution. This is the first report on direct precipitation of dolomite analogs under ambient conditions, and the findings provide new insights into the formation pathways of dolomite analogs and thus low-temperature dolomite.

A model for the kinetics of high-temperature reactions between polydisperse volcanic ash and SO2 gas
https://doi.org/10.2138/am-2021-7691
Scientists have collected volcanic ash from eruptions and noticed that tiny salt crystals exist on their surfaces. Wadsworth et al. use experiments and mathematics to work out how quickly those salt crystals grow. Because the salts contain sulfur, they propose that some of the sulfur that would have ended up in the atmosphere actually ends up on ash surfaces. They further propose that these equations could tell us just how much sulfur is removed from the atmosphere in this process.

Redox control and measurement in low-temperature hydrothermal experiments
https://doi.org/10.2138/am-2021-7687
Fang and Chou propose a new oxygen buffer technique for hydrothermal experiments carried out at temperatures below 450 °C and demonstrate its success in redox control and monitoring. Their work extends the low-temperature limit of previously well-developed redox control techniques to, at least, 200 °C, and it has promising prospects of application in low-temperature hydrothermal experiments.

Heat capacity and thermodynamic functions of partially dehydrated sodium and zinc zeolite A (LTA)
https://doi.org/10.2138/am-2021-7726
Dickson et al. offer a thermodynamic perspective into cation exchange, water sorption, and sorbate-induced structural transformations in zeolites. Heat capacities and thermodynamic functions are reported for industrially important zeolite A and for the ion-exchanged version zinc zeolite A. In addition, zeolitic water in sodium zeolite A is compared with that in other zeolites. Inflections common to all the zeolitic water heat capacities suggest that the hydration-influenced framework flexibility that has been found in zeolite A may be present in other zeolites as well.

P-V-T measurements of Fe3C to 117 GPa and 2100 K
https://doi.org/10.2138/am-2021-7581
McGuire et al. measured the unit-cell volume of an iron carbide, Fe3C, by X-ray diffraction at simultaneous extreme pressure and temperature conditions relevant to the deep interior of the Earth. These measurements are used to construct a thermodynamic model of Fe3C for the Earth's core. They find that existing measurements support two possible scenarios for the Earth's core in the Fe-C system: (1) Fe3C is the stable end-member at inner core conditions but cannot explain the inner core density; and (2) Fe7C3 is stable and may explain the inner core density at relatively low temperatures.

New Mineral Names
https://doi.org/10.2138/am-2021-NMN106818

Erratum
https://doi.org/10.2138/am-2021-E106817

Book Review
https://doi.org/10.2138/am-2021-B106819