Thermal history of matrix forsterite grains from Murchison based on
  high-resolution tomography
  Protoplanetary disks are dust- and gas-rich structures surrounding
protostars. Depending on the distance from the protostar, this dust is
thermally processed to different degrees and accreted to form bodies of varying
chemical compositions. The primordial accretion processes occurring in the
early protoplanetary disk such as chondrule formation and metal segregation are
not well understood. One way to constrain them is to study the morphology and
composition of forsteritic grains from the matrix of carbonaceous chondrites.
Here, we present high-resolution ptychographic X-ray nanotomography and
multimodal chemical micro-tomography (X-ray diffraction and X-ray fluorescence)
to reveal the early history of forsteritic grains extracted from the matrix of
the Murchison CM2.5 chondrite. The 3D electron density maps revealed, at
unprecedented resolution (64~nm), spherical inclusions containing Fe-Ni, very
little silica-rich glass and void caps (i.e., volumes where the electron
density is consistent with conditions close to vacuum) trapped in forsterite.
The presence of the voids along with the overall composition, petrological
textures, and shrinkage calculations is consistent with the grains experiencing
one or more heating events with peak temperatures close to the melting point of
forsterite ($\sim$2100~K) and subsequently cooled and contracted, in agreement
with chondrule-forming conditions.
