On the origin of porphyritic chondrules Page: 5 of 32
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
could have condensed at pressures ranging from about 10-2 to 1 atmospheres with
compositions resembling the low FeO type IA Semarkona chondrules forming a
temperatures with are 1190 to 1570 higher than compositions resembling the high FeO
type I Semarkona chondrules. It is postulated that crystallization of the metastable liquids
after spontaneous nucleation or nucleation induced by nebular perturbations, freezes in
these compositions. Droplets which do not nucleate to crystallize to type IA or II
chondrules, survive to lower temperatures and will pick up more silica to be pyroxene
normative and be high in iron oxide. Because pyroxene is difficult to nucleate, these
droplets will tend to form type Ill chondrules (excentroradial pyroxene chondrules
nucleated by an external seed, or glassy or cryptocrystalline chondrules).
This mode of formation of chondrules gets around an unsurmountable difficulty with
current mechanisms for forming porphyritic chondrules which appear to require external
heating of materials of different compositions and different locations to just below their
very different liquidus temperatures, a very unlikely process. Crystallization of metastable
subcooled liquids (recalescence) does just that in the first step. Recalescence and the
temperature cycling expected in a convective nebula are likely to lead to the properties
and textures observed in porphyritic and type Ill chondrules. However, experiments will
be needed to test our hypotheses and to further define nebular conditions which can
produce these chondrule types.
The most important aspects of our results are that (1) the different types of
chondrules (types I, 11, III) could have been produced from the same (solar) gas and do
not need a different gas for each apparent oxidation state and (2) the overwhelming
Here’s what’s next.
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Blander, M.; Unger, L.; Pelton, A. & Ericksson, G. On the origin of porphyritic chondrules, report, May 1, 1994; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1320106/m1/5/: accessed June 4, 2020), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.