In search of late-stage planetary building blocks
In search of late-stage planetary building blocks
Loading...
Files
Publication or External Link
Date
2015
Authors
Walker, Richard
Bermingham, Katherine
Liu, Jingao
Puchtel, Igor
Touboul, Mathieu
Advisor
Citation
http://dx.doi.org/10.1016/j.chemgeo.2015.06.028
DRUM DOI
Abstract
Genetic contributions to the final stages of planetary growth, including materials associated with the giant Moon forming
impact, late accretion, and late heavy bombardment are examined using siderophile elements. Isotopic similarities
between the Earth and Moon for both lithophile and siderophile elements collectively lead to the suggestion
that the genetics of the building blocks for Earth, and the impactor involved in the Moon-forming event were broadly
similar, and shared some strong genetic affinities with enstatite chondrites. The bulk genetic fingerprint of materials
subsequently added to Earth by late accretion, defined as the addition of ~0.5 wt.% of Earth's mass to the mantle,
following cessation of core formation, was characterized by 187Os/188Os and Pd/Ir ratios that were also similar to
those in some enstatite chondrites. However, the integrated fingerprint of late accreted matter differs from enstatite
chondrites in terms of the relative abundances of certain other HSE, most notably Ru/Ir. The final ≤0.05 wt.% addition
of material to the Earth and Moon, believed by some to be part of a late heavy bombardment, included a component
with much more fractionated relative HSE abundances than evidenced in the average late accretionary component.
Heterogeneous 182W/184Wisotopic compositions of some ancient terrestrial rocks suggest that some very early formed
mantle domains remained chemically distinct for long periods of time following primary planetary accretion.
This evidence for sluggish mixing of the early mantle suggests that if late accretionary contributions to the
mantle were genetically diverse, it may be possible to isotopically identify the disparate primordial components
in the terrestrial rock record using the siderophile element tracers Ru and Mo.