Evolution of a Small and a Large Rocky Planetary Body
- Stages shown in thin sections of NASA Lunar Samples and NIPR Antarctic Meteorites
Chondritic Parent Body Evolution

1994-1997.  Sz. Bérczi, B. Lukács, T. Földi, Á. Holba, S. Józsa, G. Marosi, L. Szabó-Soki, Gy. Szakmány
Eötvös University, Budapest, Hungary. 

Source: Antarctica

Chondrules and Matrix

H 3-6 Layers in a asteroid. Chonditic textures form metamorphic sequences: Van Schmus - Wood Petrologyc Classes No. 3. -6. 
H3-6: H means High Fe content (L: low). 
Sequence: E, H, L, LL, C types 

H3 Class: Sharp chondrule Boundaries, Chondrules and Matrix unequilibrated. 
Between 3 and 4. Classes, Thermal metamorphosis causes 3 main events: Equilibration, Reduction, Chondrule boundary fading. 

H4 matrix contains Carbon, Metal (Fe), SeS, and silicates with FeO. Between 3 and 4C (carbon) reduces some FeO: metal content increases. Equlibration results in more common FeO, MgO content in chondrules and matrix. 

H5: Between 4 and 5 further obscuring of chondrule boundaries happens and change in iron grain size distribution. 
H6: 6. classes  chondrules obscured, granular texture developed. 

H6: Iron grains began too percolate in a later stage iron would flow out: we meet them as Pallasites. 
H6 Mesosiderite

H6 Pallasite
After iron accumulation in the Core of the parent body, partial meltings produce basaltic liquids in the mantle. Eruptions of these liquids and their solidification produce basaltic achondrites.
 
  • Iron sank into the core
  • Basaltic partial melts erupted to the surface
  • Mantle rocks preserved most of primordial main silicates

Parend body mantle rocks preserve the main silicate mineral constituents of the primordial chondrites: olivine and pyroxene. 
Urelites retained high carbon content which accumulated at grain boundaries. By diffusion it migrated into silicates and reduced some amount of their FeO to Fe metal.