  Compound chondrules, i.e. chondrules fused together, make a powerful probe of
the density and compositional diversity in chondrule-forming environments, but
their abundance among the dominating porphyritic textures may have been
drastically underestimated. I report herein microscopic observations and
LA-ICP-MS analyses of lobate chondrules in the CO3 chondrites Miller Range
07193 and 07342. Lobes in a given chondrule show correlated volatile and
moderately volatile element abundances but refractory element concentrations
are essentially independent. This indicates that they formed by the collision
of preexisting droplets whose refractory elements behaved in closed system,
while their more volatile elements were buffered by the same gaseous medium.
The presence of lobes would otherwise be difficult to explain, as surface
tension should have rapidly imposed a spherical shape at the temperature peak.
In fact, since most chondrules across chondrite groups are nonspherical, a
majority are probably compounds variously relaxed toward sphericity. The lack
of correlation of refractory elements between conjoined compound chondrule
components is inconsistent with derivation of chondrules from the disruption of
homogenized melt bodies as in impact scenarios and evokes rather the melting of
independent mm-size nebular aggregates. Yet a "nebular" setting for chondrule
formation would need to involve not only increased solid concentration, e.g. by
settling to the midplane, but also a boost in relative velocities between
droplets during chondrule-forming events to account for observed compound
chondrule frequencies .
