Abstract
Miller Range (MIL) 05029 is a slowly cooled melt rock with metal/sulfide depletion and an Ar-Ar age of 4517 ± 11 Ma. Oxygen isotopes and mineral composition indicate that it is an L chondrite impact melt, and a well-equilibrated igneous rock texture with a lack of clasts favors a melt pool over a melt dike as its probable depositional setting. A metallographic cooling rate of approximately 14 °C Ma-1 indicates that the impact occurred at least approximately 20 Ma before the Ar-Ar closure age of 4517 Ma, possibly even shortly after accretion of its parent body. A metal grain with a Widmanstätten-like pattern further substantiates slow cooling. The formation age of MIL 05029 is at least as old as the Ar-Ar age of unshocked L and H chondrites, indicating that endogenous metamorphism on the parent asteroid was still ongoing at the time of impact. Its metallographic cooling rate of approximately 14 °C Ma-1 is similar to that typical for L6 chondrites, suggesting a collisional event on the L chondrite asteroid that produced impact melt at a minimum depth of 5-12 km. The inferred minimum crater diameter of 25-60 km may have shattered the 100-200 km diameter L chondrite asteroid. Therefore, MIL 05029 could record the timing and petrogenetic setting for the observed lack of correlation of cooling rates with metamorphic grades in many L chondrites.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1868-1888 |
| Number of pages | 21 |
| Journal | Meteoritics and Planetary Science |
| Volume | 45 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 2010 |
Fingerprint
ASJC Scopus subject areas
- Geophysics
- Space and Planetary Science
Cite this
The Ar-Ar age and petrology of Miller Range 05029 : Evidence for a large impact in the very early solar system. / Weirich, J. R.; Wittmann, A.; Isachsen, C. E.; Rumble, D.; Swindle, Timothy; Kring, D. A.
In: Meteoritics and Planetary Science, Vol. 45, No. 12, 12.2010, p. 1868-1888.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The Ar-Ar age and petrology of Miller Range 05029
T2 - Evidence for a large impact in the very early solar system
AU - Weirich, J. R.
AU - Wittmann, A.
AU - Isachsen, C. E.
AU - Rumble, D.
AU - Swindle, Timothy
AU - Kring, D. A.
PY - 2010/12
Y1 - 2010/12
N2 - Miller Range (MIL) 05029 is a slowly cooled melt rock with metal/sulfide depletion and an Ar-Ar age of 4517 ± 11 Ma. Oxygen isotopes and mineral composition indicate that it is an L chondrite impact melt, and a well-equilibrated igneous rock texture with a lack of clasts favors a melt pool over a melt dike as its probable depositional setting. A metallographic cooling rate of approximately 14 °C Ma-1 indicates that the impact occurred at least approximately 20 Ma before the Ar-Ar closure age of 4517 Ma, possibly even shortly after accretion of its parent body. A metal grain with a Widmanstätten-like pattern further substantiates slow cooling. The formation age of MIL 05029 is at least as old as the Ar-Ar age of unshocked L and H chondrites, indicating that endogenous metamorphism on the parent asteroid was still ongoing at the time of impact. Its metallographic cooling rate of approximately 14 °C Ma-1 is similar to that typical for L6 chondrites, suggesting a collisional event on the L chondrite asteroid that produced impact melt at a minimum depth of 5-12 km. The inferred minimum crater diameter of 25-60 km may have shattered the 100-200 km diameter L chondrite asteroid. Therefore, MIL 05029 could record the timing and petrogenetic setting for the observed lack of correlation of cooling rates with metamorphic grades in many L chondrites.
AB - Miller Range (MIL) 05029 is a slowly cooled melt rock with metal/sulfide depletion and an Ar-Ar age of 4517 ± 11 Ma. Oxygen isotopes and mineral composition indicate that it is an L chondrite impact melt, and a well-equilibrated igneous rock texture with a lack of clasts favors a melt pool over a melt dike as its probable depositional setting. A metallographic cooling rate of approximately 14 °C Ma-1 indicates that the impact occurred at least approximately 20 Ma before the Ar-Ar closure age of 4517 Ma, possibly even shortly after accretion of its parent body. A metal grain with a Widmanstätten-like pattern further substantiates slow cooling. The formation age of MIL 05029 is at least as old as the Ar-Ar age of unshocked L and H chondrites, indicating that endogenous metamorphism on the parent asteroid was still ongoing at the time of impact. Its metallographic cooling rate of approximately 14 °C Ma-1 is similar to that typical for L6 chondrites, suggesting a collisional event on the L chondrite asteroid that produced impact melt at a minimum depth of 5-12 km. The inferred minimum crater diameter of 25-60 km may have shattered the 100-200 km diameter L chondrite asteroid. Therefore, MIL 05029 could record the timing and petrogenetic setting for the observed lack of correlation of cooling rates with metamorphic grades in many L chondrites.
UR - http://www.scopus.com/inward/record.url?scp=78651465662&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=78651465662&partnerID=8YFLogxK
U2 - 10.1111/j.1945-5100.2010.01124.x
DO - 10.1111/j.1945-5100.2010.01124.x
M3 - Article
AN - SCOPUS:78651465662
VL - 45
SP - 1868
EP - 1888
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 12
ER -