TY - JOUR
T1 - Chondrules as products of dust collisions with totally molten droplets within a dust-rich nebular environment
T2 - An experimental investigation
AU - Connolly, Harold C.
AU - Hewins, Roger H.
N1 - Funding Information:
Acknowledgments-We would like to thank Dr. Jeremy S. Delaney and Dr. Gary E. Lofgren for numerous discussions and help with various parts of this project and Drs. R. Jones, A. Krot, M. Prinz, and C. Koeberl for helpful reviews. We would also like to thank Dr. William Skinner for numerous discussions, encouragement, and enthusiasm for this project. This research was funded by NASA grant NGW 9-35 and NAGW 3391.
PY - 1995/8
Y1 - 1995/8
N2 - Chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting. If barred olivine (BO) chondrules formed by nearly total melting at their respective liquidi, i.e., over a wide temperature range, it is surprising that there are so few totally glassy chondrules. The occurrence of fine-grained, accretionary rims on chondrules suggests mineral dust in the chondrule-forming environment which might have collided with totally molten droplets to produce chondrule textures. We have, therefore, conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500°C/h and cause nucleation. Our experiments reproduce the majority of common chondrule textures. The production of textures in our experiments is a function of the temperature at which dust is encountered, the number of dust grains encountered and, to a lesser extent, the mineralogy of the encountered mineral grains. Crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters. We have produced some less commonly discussed types of chondrule textures, e.g., barred-olivine-porphyritic-olivine pyroxene (BO/POP) by dust seeding that have not been reproduced by the incomplete melting of starting materials. The reproduction of BO/POP and excentroradial textures by dust collisions, and the scarcity of natural totally glassy chondrules, suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures, e.g., FeO-rich chondrules. From these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs. However, we have reproduced the very fine-grained microporphyritic textures characteristic of Type IA chondrules only by incomplete melting. Such chondrules could not have reached average internal temperatures above their liquidus temperatures. The conclusion, that at least some chondrules formed from total melts that collided with mineral dust during cooling, indicates that chondrule formation occurred within a region of the nebula rich in mineral dust.
AB - Chondrules are usually interpreted as the products of incomplete melting of mineral aggregates in the solar nebula and have textures controlled by the number of residual nuclei present after melting. If barred olivine (BO) chondrules formed by nearly total melting at their respective liquidi, i.e., over a wide temperature range, it is surprising that there are so few totally glassy chondrules. The occurrence of fine-grained, accretionary rims on chondrules suggests mineral dust in the chondrule-forming environment which might have collided with totally molten droplets to produce chondrule textures. We have, therefore, conducted experiments in which mineral dusts encounter molten droplets during their cooling at 500°C/h and cause nucleation. Our experiments reproduce the majority of common chondrule textures. The production of textures in our experiments is a function of the temperature at which dust is encountered, the number of dust grains encountered and, to a lesser extent, the mineralogy of the encountered mineral grains. Crystal growth rates increase with lower dust encounter temperatures giving a textural range with increasingly skeletal or elongated crystals for lower temperature encounters. We have produced some less commonly discussed types of chondrule textures, e.g., barred-olivine-porphyritic-olivine pyroxene (BO/POP) by dust seeding that have not been reproduced by the incomplete melting of starting materials. The reproduction of BO/POP and excentroradial textures by dust collisions, and the scarcity of natural totally glassy chondrules, suggest that formation by seeding of total melts was common for chondrules with the lowest liquidus temperatures, e.g., FeO-rich chondrules. From these seeding experiments we suggest that the maximum melting temperature chondrules experienced is limited only to the temperature at which evaporation of chondrule liquid occurs. However, we have reproduced the very fine-grained microporphyritic textures characteristic of Type IA chondrules only by incomplete melting. Such chondrules could not have reached average internal temperatures above their liquidus temperatures. The conclusion, that at least some chondrules formed from total melts that collided with mineral dust during cooling, indicates that chondrule formation occurred within a region of the nebula rich in mineral dust.
UR - http://www.scopus.com/inward/record.url?scp=0029539024&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0029539024&partnerID=8YFLogxK
U2 - 10.1016/0016-7037(95)00207-G
DO - 10.1016/0016-7037(95)00207-G
M3 - Article
AN - SCOPUS:0029539024
VL - 59
SP - 3231
EP - 3246
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
IS - 15
ER -