Micro-mineralogy and cosmochemistry of enstatite chondrites

Project: Research project

Description

Enstatite chondrites (ECs) are a major group of meteorites characterized by highly reduced mineral assemblages whose origins are unclear and remain a cause of speculation. Their reduced, anhydrous state implies formation in the inner solar system. They are the only meteorite group with O-isotope compositions matching Earth and the Moon and could therefore contain important information relevant to terrestrial planet formation (cf. the NASA MESSENGER spacecraft currently orbiting Mercury). A significant challenge is determining whether EC compositions and minerals developed in the nebula, by parent-body processing, through planetesimal collisions, or some combination of these and other processes. Chondrite matrix, because of its fine-grained character, is a sensitive indicator of alteration processes. It is also a possible repository of pristine nebular dust from the time of meteorite accretion. The EC matrix has been little studied, perhaps because of the relative rarity of unequilibrated meteorites. However, meteorite collection in the Antarctic and in desert regions has resulted in the recent availability of numerous EH3 and EL3 meteorites. Fractional condensation and high C/O ratios have been proposed as an explanation of the reduced EC mineralogy. However, sulfidation of silicates has also been suggested as a way to produce unusual sulfides of normally lithophile elements. Examples include niningerite, alabandite, and oldhamite (nominally MgS, MnS, and CaS, respectively). A combination of fractional condensation and secondary sulfidation of silicates and oxides may have produced the EC minerals. Major questions exist about the conditions under which such minerals could have formed. We propose (1) a comprehensive study and comparison of EC fine-grained matrix and chondrule rims to determine their composition, nature, and information they might provide about conditions of EC formation; (2) a nanoscale characterization of shocked material in order to establish guidelines for determining shock on extremely fine scales; (3) an examination of mineral assemblages to test the hypothesis that the EC minerals could have formed by a combination of fractional condensation and silicate sulfidation; and (4) to further constrain the origin and history of EC metal and sulfides by extending our measurement of siderophile elements in metal-sulfide nodules from Sahara 97072 to a larger group of E3 meteorites. We will use petrographic microscopy; electron microprobe analysis; scanning electron microscopy; laser-ablation, inductively-coupled, plasma mass spectrometry; and transmission electron microscopy for these studies. The overall goal is to improve understanding of the conditions giving rise to the unusual features of the ECs. The proposed studies will contribute to the NASA vision statement and goal to "Advance scientific knowledge of the origin and history of the solar system ..." (NASA Strategic Goals and Research Objectives, ROSES Table 1, p. 25). Fundamental new knowledge will be generated regarding important constituents of both highly reduced stony meteorites and the information they can provide regarding events in the early solar system. FORM NRESS-300 Version 2.0 Apr-06-05
StatusFinished
Effective start/end date4/1/103/31/14

Funding

  • NASA: Goddard Space Flight Center: $524,781.00

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cosmochemistry
enstatite chondrite
mineralogy
meteorite
mineral
solar system
condensation
silicate
sulfide
matrix
stony meteorite
siderophile element
chondrule
planetesimal
metal
parent body
rarity
history
chondrite
repository