Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions
Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa
Gespeichert in:
| Veröffentlicht in: | Geochimica et cosmochimica acta 2005-04, Vol.69 (7), p.1873-1881 |
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| container_title | Geochimica et cosmochimica acta |
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| creator | Krot, Alexander N. Fagan, Timothy J. Nagashima, Kazuhide Petaev, Michael I. Yurimoto, Hisayoshi |
| description | Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa |
| doi_str_mv | 10.1016/j.gca.2004.06.046 |
| format | Article |
| fullrecord | <record><control><sourceid>proquest_cross</sourceid><recordid>TN_cdi_proquest_miscellaneous_29022715</recordid><sourceformat>XML</sourceformat><sourcesystem>PC</sourcesystem><els_id>S0016703704007793</els_id><sourcerecordid>29022715</sourcerecordid><originalsourceid>FETCH-LOGICAL-a448t-2b46d9a2272027120957de1269f3b0c1db600f3bc050dd00e1c5294908dfa8f43</originalsourceid><addsrcrecordid>eNqFkMFu2zAQRImiAeqm-YDceOpNypKSKCk9FUaSBjDgS3omaHIl0JC0Cim79t-HhntuTzsYzAywj7F7AbkAoR72eW9NLgHKHFQOpfrEVqKpZdZWRfGZrSCFshqK-gv7GuMeAOqqghVz2-B7P3Hq-EB_srXh8znQCSfkyTUj4Y684zT4o0-e6fuAvVkwPvKno3c4WeRdoJHT6dzjxH2khWZvuaVxpugXT1P8xm46M0S8-3tv2e_np7f1r2yzfXld_9xkpiybJZO7UrnWSFlLkLWQ0Fa1QyFV2xU7sMLtFECSFipwDgCFrWRbttC4zjRdWdyy79fdOdD7AeOiRx8tDoOZkA5RyxbSuKj-H2yUANVcFsU1aAPFGLDTc_CjCWctQF_A671O4PUFvAalE_jU-XHtYHr16DHoaP0FlPMB7aId-X-0PwAyDou6</addsrcrecordid><sourcetype>Aggregation Database</sourcetype><iscdi>true</iscdi><recordtype>article</recordtype><pqid>28610684</pqid></control><display><type>article</type><title>Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions</title><source>Elsevier ScienceDirect</source><creator>Krot, Alexander N. ; Fagan, Timothy J. ; Nagashima, Kazuhide ; Petaev, Michael I. ; Yurimoto, Hisayoshi</creator><creatorcontrib>Krot, Alexander N. ; Fagan, Timothy J. ; Nagashima, Kazuhide ; Petaev, Michael I. ; Yurimoto, Hisayoshi</creatorcontrib><description>Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa
<2), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (Åk
<15). ∼10% of AOAs contain low-Ca pyroxene (Fs
1–3Wo
1–5) that is in corrosion relationship with forsterite and is found in three major textural occurrences: (
i) thin (<15 μm) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (
ii) 5–10-μm-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and (
iii) shells of variable thickness (up to 70 μm), commonly with abundant tiny (3–5 μm) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%–20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally
16O-rich isotopic compositions (Δ
17O < −20‰). Low-Ca pyroxenes of the textural occurrences (
i) and (
ii) are
16O-enriched (Δ
17O < −20‰), whereas those of (
iii) are
16O-depleted (Δ
17O = −6‰ to −4‰). One of the extensively melted (>50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is
16O-rich (Δ
17O ∼ −22‰), whereas the neighboring plagioclase mesostasis is
16O-depleted (Δ
17O ∼ −11‰).
We conclude that AOAs are aggregates of solar nebular condensates (forsterite, Fe,Ni-metal, and CAIs composed of Al-diopside, anorthite, spinel, and ±melilite) formed in an
16O-rich gaseous reservoir, probably CAI-forming region(s). Solid or incipiently melted forsterite in some AOAs reacted with gaseous SiO in the same nebular region to form low-Ca pyroxene. Some other AOAs appear to have accreted
16O-poor pyroxene-normative dust and experienced varying degrees of melting, most likely in chondrule-forming region(s). The most extensively melted AOAs experienced oxygen isotope exchange with
16O-poor nebular gas and may have been transformed into chondrules. The original
16O-rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains.</description><identifier>ISSN: 0016-7037</identifier><identifier>EISSN: 1872-9533</identifier><identifier>DOI: 10.1016/j.gca.2004.06.046</identifier><language>eng</language><publisher>Elsevier Ltd</publisher><ispartof>Geochimica et cosmochimica acta, 2005-04, Vol.69 (7), p.1873-1881</ispartof><rights>2005 Elsevier Ltd</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-a448t-2b46d9a2272027120957de1269f3b0c1db600f3bc050dd00e1c5294908dfa8f43</citedby><cites>FETCH-LOGICAL-a448t-2b46d9a2272027120957de1269f3b0c1db600f3bc050dd00e1c5294908dfa8f43</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktohtml>$$Uhttps://dx.doi.org/10.1016/j.gca.2004.06.046$$EHTML$$P50$$Gelsevier$$H</linktohtml><link.rule.ids>315,781,785,3551,27929,27930,46000</link.rule.ids></links><search><creatorcontrib>Krot, Alexander N.</creatorcontrib><creatorcontrib>Fagan, Timothy J.</creatorcontrib><creatorcontrib>Nagashima, Kazuhide</creatorcontrib><creatorcontrib>Petaev, Michael I.</creatorcontrib><creatorcontrib>Yurimoto, Hisayoshi</creatorcontrib><title>Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions</title><title>Geochimica et cosmochimica acta</title><description>Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa
<2), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (Åk
<15). ∼10% of AOAs contain low-Ca pyroxene (Fs
1–3Wo
1–5) that is in corrosion relationship with forsterite and is found in three major textural occurrences: (
i) thin (<15 μm) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (
ii) 5–10-μm-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and (
iii) shells of variable thickness (up to 70 μm), commonly with abundant tiny (3–5 μm) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%–20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally
16O-rich isotopic compositions (Δ
17O < −20‰). Low-Ca pyroxenes of the textural occurrences (
i) and (
ii) are
16O-enriched (Δ
17O < −20‰), whereas those of (
iii) are
16O-depleted (Δ
17O = −6‰ to −4‰). One of the extensively melted (>50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is
16O-rich (Δ
17O ∼ −22‰), whereas the neighboring plagioclase mesostasis is
16O-depleted (Δ
17O ∼ −11‰).
We conclude that AOAs are aggregates of solar nebular condensates (forsterite, Fe,Ni-metal, and CAIs composed of Al-diopside, anorthite, spinel, and ±melilite) formed in an
16O-rich gaseous reservoir, probably CAI-forming region(s). Solid or incipiently melted forsterite in some AOAs reacted with gaseous SiO in the same nebular region to form low-Ca pyroxene. Some other AOAs appear to have accreted
16O-poor pyroxene-normative dust and experienced varying degrees of melting, most likely in chondrule-forming region(s). The most extensively melted AOAs experienced oxygen isotope exchange with
16O-poor nebular gas and may have been transformed into chondrules. The original
16O-rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains.</description><issn>0016-7037</issn><issn>1872-9533</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2005</creationdate><recordtype>article</recordtype><recordid>eNqFkMFu2zAQRImiAeqm-YDceOpNypKSKCk9FUaSBjDgS3omaHIl0JC0Cim79t-HhntuTzsYzAywj7F7AbkAoR72eW9NLgHKHFQOpfrEVqKpZdZWRfGZrSCFshqK-gv7GuMeAOqqghVz2-B7P3Hq-EB_srXh8znQCSfkyTUj4Y684zT4o0-e6fuAvVkwPvKno3c4WeRdoJHT6dzjxH2khWZvuaVxpugXT1P8xm46M0S8-3tv2e_np7f1r2yzfXld_9xkpiybJZO7UrnWSFlLkLWQ0Fa1QyFV2xU7sMLtFECSFipwDgCFrWRbttC4zjRdWdyy79fdOdD7AeOiRx8tDoOZkA5RyxbSuKj-H2yUANVcFsU1aAPFGLDTc_CjCWctQF_A671O4PUFvAalE_jU-XHtYHr16DHoaP0FlPMB7aId-X-0PwAyDou6</recordid><startdate>20050401</startdate><enddate>20050401</enddate><creator>Krot, Alexander N.</creator><creator>Fagan, Timothy J.</creator><creator>Nagashima, Kazuhide</creator><creator>Petaev, Michael I.</creator><creator>Yurimoto, Hisayoshi</creator><general>Elsevier Ltd</general><scope>AAYXX</scope><scope>CITATION</scope><scope>7QF</scope><scope>7SE</scope><scope>8BQ</scope><scope>8FD</scope><scope>JG9</scope><scope>H8D</scope><scope>L7M</scope></search><sort><creationdate>20050401</creationdate><title>Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions</title><author>Krot, Alexander N. ; Fagan, Timothy J. ; Nagashima, Kazuhide ; Petaev, Michael I. ; Yurimoto, Hisayoshi</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a448t-2b46d9a2272027120957de1269f3b0c1db600f3bc050dd00e1c5294908dfa8f43</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2005</creationdate><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Krot, Alexander N.</creatorcontrib><creatorcontrib>Fagan, Timothy J.</creatorcontrib><creatorcontrib>Nagashima, Kazuhide</creatorcontrib><creatorcontrib>Petaev, Michael I.</creatorcontrib><creatorcontrib>Yurimoto, Hisayoshi</creatorcontrib><collection>CrossRef</collection><collection>Aluminium Industry Abstracts</collection><collection>Corrosion Abstracts</collection><collection>METADEX</collection><collection>Technology Research Database</collection><collection>Materials Research Database</collection><collection>Aerospace Database</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Geochimica et cosmochimica acta</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Krot, Alexander N.</au><au>Fagan, Timothy J.</au><au>Nagashima, Kazuhide</au><au>Petaev, Michael I.</au><au>Yurimoto, Hisayoshi</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions</atitle><jtitle>Geochimica et cosmochimica acta</jtitle><date>2005-04-01</date><risdate>2005</risdate><volume>69</volume><issue>7</issue><spage>1873</spage><epage>1881</epage><pages>1873-1881</pages><issn>0016-7037</issn><eissn>1872-9533</eissn><abstract>Amoeboid olivine aggregates (AOAs) in primitive carbonaceous chondrites consist of forsterite (Fa
<2), Fe,Ni-metal, spinel, Al-diopside, anorthite, and rare gehlenitic melilite (Åk
<15). ∼10% of AOAs contain low-Ca pyroxene (Fs
1–3Wo
1–5) that is in corrosion relationship with forsterite and is found in three major textural occurrences: (
i) thin (<15 μm) discontinuous layers around forsterite grains or along forsterite grain boundaries in AOA peripheries; (
ii) 5–10-μm-thick haloes and subhedral grains around Fe,Ni-metal nodules in AOA peripheries, and (
iii) shells of variable thickness (up to 70 μm), commonly with abundant tiny (3–5 μm) inclusions of Fe,Ni-metal grains, around AOAs. AOAs with the low-Ca pyroxene shells are compact and contain euhedral grains of Al-diopside surrounded by anorthite, suggesting small (10%–20%) degree of melting. AOAs with other textural occurrences of low-Ca pyroxene are rather porous. Forsterite grains in AOAs with low-Ca pyroxene have generally
16O-rich isotopic compositions (Δ
17O < −20‰). Low-Ca pyroxenes of the textural occurrences (
i) and (
ii) are
16O-enriched (Δ
17O < −20‰), whereas those of (
iii) are
16O-depleted (Δ
17O = −6‰ to −4‰). One of the extensively melted (>50%) objects is texturally and mineralogically intermediate between AOAs and Al-rich chondrules. It consists of euhedral forsterite grains, pigeonite, augite, anorthitic mesostasis, abundant anhedral spinel grains, and minor Fe,Ni-metal; it is surrounded by a coarse-grained igneous rim largely composed of low-Ca pyroxene with abundant Fe,Ni-metal-sulfide nodules. The mineralogical observations suggest that only spinel grains in this igneous object were not melted. The spinel is
16O-rich (Δ
17O ∼ −22‰), whereas the neighboring plagioclase mesostasis is
16O-depleted (Δ
17O ∼ −11‰).
We conclude that AOAs are aggregates of solar nebular condensates (forsterite, Fe,Ni-metal, and CAIs composed of Al-diopside, anorthite, spinel, and ±melilite) formed in an
16O-rich gaseous reservoir, probably CAI-forming region(s). Solid or incipiently melted forsterite in some AOAs reacted with gaseous SiO in the same nebular region to form low-Ca pyroxene. Some other AOAs appear to have accreted
16O-poor pyroxene-normative dust and experienced varying degrees of melting, most likely in chondrule-forming region(s). The most extensively melted AOAs experienced oxygen isotope exchange with
16O-poor nebular gas and may have been transformed into chondrules. The original
16O-rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains.</abstract><pub>Elsevier Ltd</pub><doi>10.1016/j.gca.2004.06.046</doi><tpages>9</tpages></addata></record> |
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| title | Origin of low-Ca pyroxene in amoeboid olivine aggregates: Evidence from oxygen isotopic compositions |
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