Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints
Abstract Continental flood basalts are more prone to compositional modification from passage through thicker and (or) more felsic crust in comparison to their oceanic counterparts. The Steens Basalt in southeast Oregon (~17 Ma) is among the oldest and most mafic members of the Columbia River Basalt...
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| Format: | Article |
| Language: | English |
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Wiley
2020-08-01
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| Series: | Geochemistry, Geophysics, Geosystems |
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| Online Access: | https://doi.org/10.1029/2020GC008910 |
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| author | N. E. Moore A. L. Grunder W. A. Bohrson R. W. Carlson I. N. Bindeman |
| author_facet | N. E. Moore A. L. Grunder W. A. Bohrson R. W. Carlson I. N. Bindeman |
| author_sort | N. E. Moore |
| collection | DOAJ |
| description | Abstract Continental flood basalts are more prone to compositional modification from passage through thicker and (or) more felsic crust in comparison to their oceanic counterparts. The Steens Basalt in southeast Oregon (~17 Ma) is among the oldest and most mafic members of the Columbia River Basalt Group and provides a record of the early stages of flood basalt volcanism. We evaluate the balance of mantle sources in time during the onset of Columbia River Basalt Group magmatism and assess the effect of crustal passage using stratigraphically controlled Sr, Nd, Pb, Hf, Os, and O isotopic compositions, as well as whole rock major and trace element data. Mixing models indicate that depleted and enriched mantle sources identified by previous workers contribute in varying proportions during the life of the magmatic system, with the greatest contribution by depleted mantle when eruption rate and presumed intrusion rate increase. During waxing, enrichment of δ18O in some flows signals cryptic deep fractionation of abundant clinopyroxene followed by shallow fractionation of olivine ± clinopyroxene ± plagioclase. Os concentrations are among the highest worldwide at a given MgO (0.29–0.86 ppb at 6.0 to 10.9 wt.%). We argue that high Os results from scavenging of sulfides by recharging magmas passing through earlier crystallized magmas. Elevated 87Sr/86Sr in the latest stage supports modest assimilation of partial melts from mafic accreted terranes, facilitated by thermal priming of crust by persistent magmatism. This work provides a more detailed schematic view of the Steens Basalt magmatic system, from mantle origin through crustal staging. |
| first_indexed | 2024-03-11T12:59:02Z |
| format | Article |
| id | doaj.art-f3beb98500c343a8a9921ff5504d501b |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:59:02Z |
| publishDate | 2020-08-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-f3beb98500c343a8a9921ff5504d501b2023-11-03T16:55:28ZengWileyGeochemistry, Geophysics, Geosystems1525-20272020-08-01218n/an/a10.1029/2020GC008910Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic ConstraintsN. E. Moore0A. L. Grunder1W. A. Bohrson2R. W. Carlson3I. N. Bindeman4College of Earth, Ocean and Atmospheric Sciences Oregon State University Corvallis OR USACollege of Earth, Ocean and Atmospheric Sciences Oregon State University Corvallis OR USADepartment of Geological Sciences Central Washington University Ellensburg WA USAEarth and Planets Laboratory Carnegie Institution for Science Washington DC USADepartment of Earth Sciences University of Oregon Eugene OR USAAbstract Continental flood basalts are more prone to compositional modification from passage through thicker and (or) more felsic crust in comparison to their oceanic counterparts. The Steens Basalt in southeast Oregon (~17 Ma) is among the oldest and most mafic members of the Columbia River Basalt Group and provides a record of the early stages of flood basalt volcanism. We evaluate the balance of mantle sources in time during the onset of Columbia River Basalt Group magmatism and assess the effect of crustal passage using stratigraphically controlled Sr, Nd, Pb, Hf, Os, and O isotopic compositions, as well as whole rock major and trace element data. Mixing models indicate that depleted and enriched mantle sources identified by previous workers contribute in varying proportions during the life of the magmatic system, with the greatest contribution by depleted mantle when eruption rate and presumed intrusion rate increase. During waxing, enrichment of δ18O in some flows signals cryptic deep fractionation of abundant clinopyroxene followed by shallow fractionation of olivine ± clinopyroxene ± plagioclase. Os concentrations are among the highest worldwide at a given MgO (0.29–0.86 ppb at 6.0 to 10.9 wt.%). We argue that high Os results from scavenging of sulfides by recharging magmas passing through earlier crystallized magmas. Elevated 87Sr/86Sr in the latest stage supports modest assimilation of partial melts from mafic accreted terranes, facilitated by thermal priming of crust by persistent magmatism. This work provides a more detailed schematic view of the Steens Basalt magmatic system, from mantle origin through crustal staging.https://doi.org/10.1029/2020GC008910Steens BasaltColumbia River Basalt Groupcontinental flood basaltSr, Nd, Pb, Hf, Os, and O isotopic compositionsmantle sourcescrustal contamination |
| spellingShingle | N. E. Moore A. L. Grunder W. A. Bohrson R. W. Carlson I. N. Bindeman Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints Geochemistry, Geophysics, Geosystems Steens Basalt Columbia River Basalt Group continental flood basalt Sr, Nd, Pb, Hf, Os, and O isotopic compositions mantle sources crustal contamination |
| title | Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints |
| title_full | Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints |
| title_fullStr | Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints |
| title_full_unstemmed | Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints |
| title_short | Changing Mantle Sources and the Effects of Crustal Passage on the Steens Basalt, SE Oregon: Chemical and Isotopic Constraints |
| title_sort | changing mantle sources and the effects of crustal passage on the steens basalt se oregon chemical and isotopic constraints |
| topic | Steens Basalt Columbia River Basalt Group continental flood basalt Sr, Nd, Pb, Hf, Os, and O isotopic compositions mantle sources crustal contamination |
| url | https://doi.org/10.1029/2020GC008910 |
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