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book review: Monika C. Müller (1991): Vergleichende morphologische Untersuchungen zum Sexualdimorphismus bei Webspinnen (Arachnida: Araneae)

Understanding the stability of magnesite in the presence of a hydrous fluid in the Earth's upper mantle is crucial for modeling the carbon budget and cycle in the deep Earth. This study elucidates the behavior of magnesite in the presence of hydrous fluids. We examined the brucite-magnesite [Mg(OH)2-MgCO3] system between 1 and 12 GPa by using synchrotron in situ energy-dispersive X-ray diffraction experiments combined with textural observations from quenched experiments employing the falling sphere method. By subjecting magnesite to varying pressure-temperature conditions with controlled fluid proportion, we determined the stability limits of magnesite in the presence of a fluid and periclase. The observed liquidus provides insights into the fate of magnesite-bearing rocks in subduction zones. Our findings show that magnesite remains stable under typical subduction zone gradients even when infiltrated by hydrous fluids released from dehydration reactions during subduction. We conclude that magnesite can be subducted down to and beyond sub-arc depths. Consequently, our results have important implications for the carbon budget of the Earth's mantle and its role in regulating atmospheric CO2 levels over geological timescales. [ABSTRACT FROM AUTHOR]

In this study, we investigated four different ferroan dolomite samples using in situ Raman spectroscopy and powder X-ray diffraction (XRD) at pressures up to 48 GPa and room temperature. Our results show that the transition from Dolomite-I (Dol-I) to Dolomite-II (Dol-II) occurs above 13–16 GPa, and the transition pressure depends on the composition of the solid solution. Compression above 32–35 GPa results in the appearance of Dolomite-IIIc (Dol-IIIc) or Dolomite-IIIb (Dol-IIIb). In the high-pressure XRD study, we found that the XRD patterns of Ca0.97(Mg0.77Fe0.23Mn0.03)(CO3)2 (xFe = 0.23, Ank23) can be indexed as Dol-IIIc at 44 GPa, while the rhombohedral Dol-IIIb structure matches better with the XRD patterns of the xFe = 0.40 (Ank40) and 0.64 (Ank64) solid solutions. Additionally, in the Raman spectra of the Fe-richest sample (Ank64), we observed an abrupt frequency downshift of the CO3-stretching vibrations between 40–42 GPa, which may reflect a pressure-induced Fe2+ spin transition. We further investigated two samples with xFe = 0.19 (Ank19) and 0.23 (Ank23) at high pressure and high temperatures, up to at least 2600 K. The experiments revealed that the unquenchable Dol-IIIc structure could be a stable high-pressure/high-temperature polymorph in ferroan dolomite up to at least 2600 K. [ABSTRACT FROM AUTHOR]