Abstract
We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse-grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg-rich pyroxene. The coarse-grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse-grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two-stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ∼1000 °C than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite-taenite boundaries indicates that the cooling rate was very slow at lower temperatures (∼1-10 °C/Myr at <600-700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two-stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.
| Original language | English |
|---|---|
| Pages (from-to) | 863-874 |
| Number of pages | 12 |
| Journal | Meteoritics and Planetary Science |
| Volume | 41 |
| Issue number | 6 |
| DOIs | |
| Publication status | Published - 2006 Jan 1 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Geophysics
- Space and Planetary Science
Cite this
An anomalous eucrite, Dhofar 007, and a possible genetic relationship with mesosiderites. / Yamaguchi, Akira; Setoyanagi, Takehiko; Ebihara, Mitsuru.
In: Meteoritics and Planetary Science, Vol. 41, No. 6, 01.01.2006, p. 863-874.Research output: Contribution to journal › Article
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TY - JOUR
T1 - An anomalous eucrite, Dhofar 007, and a possible genetic relationship with mesosiderites
AU - Yamaguchi, Akira
AU - Setoyanagi, Takehiko
AU - Ebihara, Mitsuru
PY - 2006/1/1
Y1 - 2006/1/1
N2 - We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse-grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg-rich pyroxene. The coarse-grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse-grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two-stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ∼1000 °C than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite-taenite boundaries indicates that the cooling rate was very slow at lower temperatures (∼1-10 °C/Myr at <600-700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two-stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.
AB - We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse-grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg-rich pyroxene. The coarse-grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse-grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two-stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ∼1000 °C than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite-taenite boundaries indicates that the cooling rate was very slow at lower temperatures (∼1-10 °C/Myr at <600-700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two-stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.
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U2 - 10.1111/j.1945-5100.2006.tb00491.x
DO - 10.1111/j.1945-5100.2006.tb00491.x
M3 - Article
VL - 41
SP - 863
EP - 874
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 6
ER -