Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 54-814, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Published: October 2008
AI Article Synopsis
Article Abstract
Angrites are among the oldest known pristine basaltic meteorites and record the earliest stages of planet formation and differentiation. Our paleomagnetic analysis of three angrites found that they record a past magnetic field of approximately 10 microteslas on the angrite parent body extending from 4564 to at least 4558 million years ago. Because the angrite paleomagnetic record extends beyond the expected lifetime of the early circumstellar disk, these paleofields were probably generated internally on the angrite parent body, possibly by an early dynamo in a rapidly formed metallic core.
The planetesimals in the solar system exhibit varying degrees of moderately volatile elements (MVEs) depletion compared to the protosolar composition. Revealing the relevant mechanisms is crucial for exploring early solar system evolution. Most volatile-depleted materials in the solar system exhibit enrichments in the heavier isotopes of MVEs, which have traditionally been attributed to the loss of volatiles through partial evaporation.
Volatiles are vital ingredients for a habitable planet. Angrite meteorites sample the most volatile-depleted planetesimal in the Solar System, particularly for the alkali elements. They are prime targets for investigating the formation of volatile-poor rocky planets, yet their exceptionally low volatile content presents a major analytical challenge.
The angrites are a class of achondrites that encompass a wide range of igneous textures from quenched, volcanic, and subvolcanic stones to slowly cooled, plutonic rocks. The compositions of the various geochemical reservoirs generating this variety of rocks have not been investigated fully because historically the numbers and masses of angrites available for study have been quite small. However, the rapid increase in meteorites from Northwest Africa (NWA) has enabled a renewed opportunity for such an investigation.
Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth-Moon system. Using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-Solar-System objects predominantly reflects spatial heterogeneity.
Inner Solar System bodies are depleted in volatile elements relative to chondrite meteorites, yet the source(s) and mechanism(s) of volatile-element depletion and/or enrichment are poorly constrained. The timing, mechanisms and quantities of volatile elements present in the early inner Solar System have vast implications for diverse processes, from planetary differentiation to the emergence of life. We report major, trace and volatile-element contents of a glass bead derived from the D'Orbigny angrite, the hydrogen isotopic composition of this glass bead and that of coexisting olivine and silicophosphates, and the Pb-Pb age of the silicophosphates, 4568 ± 20 Ma.
