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Kiglapait mineralogy IV: The augite series

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Published/Copyright: March 28, 2015
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American Mineralogist
From the journal American Mineralogist Volume 89 Issue 10

Abstract

Based on twenty-five new chemical analyses, augites from the Upper Zone of the Kiglapait layered intrusion, Labrador, span the range from En73 to En0, disposed about a straight line sloping slightly upward from Wo40 to Wo42 in the pyroxene quadrilateral. They contain little tetrahedral Al, which decreases with Fe enrichment as tetrahedral ferric Fe3+ increases. Little or no jadeite or Ca-Tschermaks component is present. Titanium rises only slightly with Fe, and the acmite component is scattered near mole fraction 0.03. Excess cations relative to 6 oxygen atoms occur chieß y by solid solution toward olivine, the only co-crystallizing mafic silicate phase. Values of nβ increase linearly over the range 1.670 at fictive En100 to 1.7448 at En0. The position of the 150 powder X-ray diffraction peak shifts regularly from 5.0372 to 4.1727 degrees away from the 220 peak of silicon metal over the same composition range. Exsolution of orthopyroxene near (100) is succeeded up-stratigraphy by that of pigeonite near (001), and the switch occurs at about the same augite composition as the switch from external orthopyroxene to pigeonite in the Skaergaard intrusion. Exsolution of ilmenite in or near (100) and magnetite-ulvöspinel near the a and c directions in (010) produces the black color of these augites in hand specimen. Subsolidus augite-olivine tie lines and exchange relations in Fe-Mg allow the distinction between equilibrium pairs and those affected by exchange with external Fe-Ti oxide minerals or with intercumulus liquid in Upper Border Zone lithologies. Liquids producing augite and olivine with plagioclase follow a Ca-depletion trend until crystallization of abundant olivine and titanomagnetite drives them on a Ca-enrichment trend, to a point near Mg-free augite. Activities of silica consistent with augite-olivine pairs range from <0.6 to 0.98. The Kiglapait augite series exemplifies the crystallization of a magma occupying the narrow regime between silica saturation and undersaturation, in extreme fractionation from troctolite to Mg-free syenite.

Received: 2003-12-12
Accepted: 2004-5-6
Published Online: 2015-3-28
Published in Print: 2004-10-1

© 2015 by Walter de Gruyter Berlin/Boston

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  2. “Invisible„ gold revealed: Direct imaging of gold nanoparticles in a Carlin-type deposit
  3. Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites
  4. Displacement and strain fields around a [100] dislocation in olivine measured to sub-angstrom accuracy
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  6. Metasomatic formation of kosmochlor-bearing diopside in peridotite xenoliths from North Island, New Zealand
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  18. New developments in two-feldspar thermometry
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  26. Piston-cylinder calibration at 400 to 500 MPa: A comparison of using water solubility in albite melt and NaCl melting
  27. Letter. Comparative planetary mineralogy: V/(Cr + Al) systematics in chromite as an indicator of relative oxygen fugacity
  28. Letter. Porous titanosilicate nanorods in the structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(⃞,Mn,Fe) {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, resolved using synchrotron radiation
https://doi.org/10.2138/am-2004-1005

Articles in the same Issue

  1. The origin of the color of pearls in iridescence from nano-composite structures of the nacre
  2. “Invisible„ gold revealed: Direct imaging of gold nanoparticles in a Carlin-type deposit
  3. Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites
  4. Displacement and strain fields around a [100] dislocation in olivine measured to sub-angstrom accuracy
  5. Kiglapait mineralogy IV: The augite series
  6. Metasomatic formation of kosmochlor-bearing diopside in peridotite xenoliths from North Island, New Zealand
  7. Determination of standard thermodynamic properties of sulfides in the Ag-Au-S system by means of a solid-state galvanic cell
  8. Hydroxyl ordering in igneous apatite
  9. Accommodation of the carbonate ion in apatite: An FTIR and X-ray structure study of crystals synthesized at 2–4 GPa
  10. Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO2-H2O system
  11. The activity of silica, water, and the equilibration of intermediate and silicic magmas
  12. The CO2–H2O system: IV. Empirical, isothermal equations for representing vapor-liquid equilibria at 110–350 °C, P ≤ 150 MPa
  13. Repercussions of size heterogeneity on the measurement of specific surface areas of colloidal minerals: Combination of macroscopic and microscopic analyses
  14. The crystal-structure of synthetic NaNa2Mg5Si8O21(OH)3, a triclinic C1̄ amphibole with a triple-cell and excess hydrogen
  15. High-pressure phase transitions in Ca0.2Sr0.8Al2Si2O8feldspar
  16. Phase transition of Ca-perovskite and stability of Al-bearing Mg-perovskite in the lower mantle
  17. Mineralogy and petrology of a mullite-bearing pseudotachylyte: Constraints on the temperature of coseismic frictional fusion
  18. New developments in two-feldspar thermometry
  19. Ordered distribution of Au and Ag in the crystal structure of muthmannite, AuAgTe2, a rare telluride from Sacarîmb, western Romania
  20. Polytypism of cookeite in low-grade metapelites of the Cameros Basin, Spain: Lack of correlation of well-ordered polytypes with pressure
  21. Evolution of mineral compositions during eclogitization of subducting basaltic crust
  22. Mass balance during retrogression of eclogite-facies minerals in the Rongcheng eclogite, eastern Sulu ultrahigh-pressure terrane, China
  23. Synthesis of REE and Y phosphates by Pb-free flux methods and their utilization as standards for electron microprobe analysis and in design of monazite chemical U-Th-Pb dating protocol
  24. The chemistry and crystal structure of okanoganite-(Y) and comparison with vicanite-(Ce)
  25. An automated system for phase identification and quantitative composition determination using the electron microprobe: Theory and applications
  26. Piston-cylinder calibration at 400 to 500 MPa: A comparison of using water solubility in albite melt and NaCl melting
  27. Letter. Comparative planetary mineralogy: V/(Cr + Al) systematics in chromite as an indicator of relative oxygen fugacity
  28. Letter. Porous titanosilicate nanorods in the structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(⃞,Mn,Fe) {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, resolved using synchrotron radiation
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