A SYSTEMATIC CLASSIFICATION OF METEORITES
PART IV

PART I: CHONDRITES, METACHONDRITES
PART II: PRIMITIVE ACHONDRITES, ACHONDRITES, STONY-IRONS, IRONS
PART III: MARTIAN METEORITES—GEOCHEMICAL CLASSIFICATION
PART V: ENSTATITE CHONDRITES—SUBGROUP CLASSIFICATION
PART VI: STONY METEORITES—METAMORPHIC FACIES SERIES

DIOGENITES

HED (Vesta) material of ultramafic composition (olivine+orthopyroxene ≥90 vol%)
Classification Based on IUGS Taxonomy

DIOGENITES (6 subclasses known based on modal mineralogy)
1. ORTHOPYROXENITIC:  ≥90 vol% orthopyroxene
    (e.g. Bilanga, Johnstown, NWA 1821, NWA 3329, QUE 99050, Tatahouine)
2. OLIVINE–ORTHOPYROXENITIC:  orthopyroxene + 10–40 vol% olivine
    (e.g. ALHA77256, GRA 98108, LEW 88679, NWA 5312, NWA 5405)
3. HARZBURGITIC:  >40 vol% olivine
    (e.g. EETA79002, MIL 07001, NWA 1459, 1877 and pairings, NWA 4223, NWA 5480, NWA 6157)
4. DUNITIC:  ≥90 vol% olivine
    (e.g. MIL 03443, NWA 2968)
5. NORITIC:  orthopyroxene + <5 vol% olivine + >10 vol% plagioclase
    (e.g. NWA 5315, NWA 6928, NWA 8000, NWA 8367, NWA 8744, NWA 10268, NWA 10388)
6. POLYMICT:  dunite ± harzburgite ± orthopyroxenite ± eucrite (<10 vol%)
    (e.g. ALH 85015, LEW 88008, NWA 1239, NWA 1648, NWA 4473, NWA 6945 [w/ noritic clasts])

standby for diogenite triangle plot
Diagram credit: Irving et al., 47th LPSC, #2264 (2016)

According to Beck and McSween (2010), diogenites represent two separate ultramafic lithologies formed by fractional crystallization in multiple plutons. Of these two lithologies, one consists of olivine + magnesian orthopyroxene, and the other consists of ferroan orthopyroxene. It is thought that these two lithologies occur in varying amounts among the different diogenites as a result of brecciation and mixing, sometimes forming polymict diogenites containing olivine with two pyroxenes.

An alternative scenario was proposed by Mitchell and Tomkins (2019) based on data from a study of 200 diogenites. They determined that the compositional diversity among diogenites is caused primarily by variability in the oxygen fugacity (ΔIW –1.6 to –1.4) induced by sulfidation reactions (reduction of olivine by sulfer to produce troilite and orthopyroxene) within individual magma chambers. The formation of these diogenite crustal intrusions and the metasomatism process that affected their orthopyroxene composition occurred after the removal of a Ca-rich melt to produce the eucritic crust.

The diogenite classification scheme and data used on this page are adapted from Beck and McSween Jr., MAPS, vol. 45, #5, pp. 850-872 (2010). An extension of their scheme was suggested by Wittke et al. (2011). The diogenite classification ternary diagram shown below is from Wittke et al. 74th MetSoc, #5223 (2011).



PART I: CHONDRITES, METACHONDRITES
PART II: PRIMITIVE ACHONDRITES, ACHONDRITES, STONY-IRONS, IRONS
PART III: MARTIAN METEORITES—GEOCHEMICAL CLASSIFICATION
PART V: ENSTATITE CHONDRITES—SUBGROUP CLASSIFICATION
PART VI: STONY METEORITES—METAMORPHIC FACIES SERIES


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