English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Minor amounts of markedly Cl-rich amphibole and biotite are found in the Archean (2.8–2.9 Ga) iron-formation lithologies from the eastern Beartooth Mountains, Montana, U.S.A. These rocks are typified by mineral assemblages of quartz + magnetite + orthopyroxene + garnet ± clinopyroxene ± plagioclase having equilibrated during granulite facies conditions of ~775–800 °C and 6–8 kbar. The metamorphic Cl-rich amphibole and biotite are prograde and occur as inclusions in orthopyroxene and garnet as well as in the matrix. The high-grade Fe-rich amphiboles (mostly Cl-rich potassic-hastingsite and magnesio-ferri-hornblende) and biotites contain concentrations of Cl reaching up to 2.9 and 3.4 wt%, respectively. Biotites contain up to 10.5 wt% BaO and 6.9 wt% TiO 2 . Substitution of Cl into amphibole and biotite is more likely where Cl-bearing anion sites are enlarged. In amphibole threshold values of the X Fe 2+  ,  A K, and  T Al appear to be a precondition before significant amounts of Cl are incorporated into the structure. In biotite, in addition to X Fe 2+  , substitution of  T Al also is positively correlated with Cl. The high Cl content in the minerals is suggestive of a coexisting high salinity aqueous fluid. Based on calculations using mineral chemistry, estimations of the aqueous fluid composition indicate a Cl-rich aqueous fluid (~25 wt% NaCl)with  f  H 2 O / f  HCl  ratios of ~0.68–0.82. There is evidence for brine-CO 2  immiscibility during peak metamorphism. In amphibole once the threshold values for significant Cl incorporation are attained, the Fe 2+ -Mg partitioning of the amphibole and the coexisting mafic silicates changes such that the amphibole more favorably partitions Fe 2+ . A feedback mechanism can be generated such that the more Cl available from a fluid the more Fe 2+ -rich the amphibole can become, and this produces a crystal structure that can accommodate more Cl, which makes this amphibole more favorable for Fe 2+ incorporation, and the cycle continues until Cl saturation in the crystal structures is reached or aqueous Cl – is fully equilibrated with the amphibole.

Chlorine incorporation into amphibole and biotite in high-grade iron-formations: Interplay between crystallography and metamorphic fluids