Substitution of Fe3+into anorthite in oxidized, Al-deficient ferrobasaltic systems with implications for the petrogenesis of angrite meteoritesOPEN ACCESS 

· by · in

Seann J. McKibbin, Dominique Tanner, Hugh St. C. O’Neill

MAPS, Version of Record online: 04 February 2026

LINK (OPEN ACCESS)
PDF (OPEN ACCESS)

“Angrite meteorites are critically silica-undersaturated igneous rocks with high Ca/Al and Fe/Mg, along with depletion in volatile lithophile elements Na and K such that they crystallize anorthite along with olivine and calcic pyroxene. The anorthite in angrites contains substantial Fe, and in NWA 1670 and NWA 1296, it is present at major element levels correlated with deficiency in Al, suggesting abundant Fe2O3-Al2O3 exchange. One possible explanation is that these angrites had higher Fe3+ contents and their final interstitial melts crystallized under higher oxygen fugacities (fO2) than those of other angrites. Here, we present melting experiments on angritic compositions over a range of fO2 conditions. These experiments crystallized anorthite and Ca-rich pyroxene among other phases, showing that large substitutions of Fe3+ into Al-deficient anorthite (a “ferri-anorthite” component) are natural consequences of angritic melt crystallization at high fO2. At face value, these experiments suggest substantial anorthite Fe2O3-Al2O3 exchange in NWA 1670 and NWA 1296 due to fractionated magmas crystallizing near the surface of the angrite parent body under oxidizing conditions. However, the inferred fO2 is several log units higher than the iron-wüstite redox buffer and even higher than the fayalite–magnetite–quartz redox buffer. While extensive fractional crystallization might raise fO2 by ~1 log unit by removal of ferrosilicates, it seems unlikely to explain the occurrence of this phase. The presence of Fe3+-rich anorthite might be attributed to rapid crystallization driving kinetic incorporation of excess Fe and disequilibrium degassing of SO2 from a small dissolved sulfate component, leading to metastable preservation of this phase.”

Related posts (automatically generated):

  1. Petrogenesis of D’Orbigny-like angrite meteorites and the role of spinel in the angrite source
  2. Trace element geochemistry of coarse‐grained angrites from Northwest Africa: Implications for their petrogenesis on the angrite parent body
  3. Cosmic ray exposure and gas retention ages of the shocked angrite Northwest Africa 7203: Implications for a collisional history of angrites’ parent bodyOPEN ACCESS 
  4. Unique igneous textures and shock metamorphism of the Northwest Africa 7203 angrite: Implications for crystallization processes and the evolutionary history of the angrite parent body
  5. Appraising the Late-Stage Magmatic fO2 of Diabasic Angrites with a Novel Phase Equilibrium Approach. Implications for New and Existing Models of Angrite Petrogenesis
  6. Timing and Origin of the Angrite Parent Body Inferred from Cr IsotopesOPEN ACCESS 
  7. The case for the angrite parent body as the archetypal first-generation planetesimal: Large, reduced and Mg-enriched
  8. 147,146Sm-143,142Nd, 176Lu-176Hf, and 87Rb-87Sr Systematics in the Angrites: Implications for Chronology and Processes on the Angrite Parent Body
  9. Evolution of the angrite parent body: Implications of metamorphic coronas in NWA 3164
  10. Remnants of a lost Planetesimal: Searching for the Angrite parent bodyOPEN ACCESS 
Tags: , , , ,