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How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot.

Hoernle K, Rohde J, Hauff F, Garbe-Schönberg D, Homrighausen S, Werner R, Morgan JP - Nat Commun (2015)

Bottom Line: The origin of this zonation is currently unclear.Recently zonation was found along the last ∼70 Myr of the Tristan-Gough hotspot track.Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.

View Article: PubMed Central - PubMed

Affiliation: 1] GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany [2] CAU Kiel University, Institute of Geosciences, Ludewig-Meyn-Strasse 10, D-24118 Kiel, Germany.

ABSTRACT
Increasingly, spatial geochemical zonation, present as geographically distinct, subparallel trends, is observed along hotspot tracks, such as Hawaii and the Galapagos. The origin of this zonation is currently unclear. Recently zonation was found along the last ∼70 Myr of the Tristan-Gough hotspot track. Here we present new Sr-Nd-Pb-Hf isotope data from the older parts of this hotspot track (Walvis Ridge and Rio Grande Rise) and re-evaluate published data from the Etendeka and Parana flood basalts erupted at the initiation of the hotspot track. We show that only the enriched Gough, but not the less-enriched Tristan, component is present in the earlier (70-132 Ma) history of the hotspot. Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.

No MeSH data available.


Related in: MedlinePlus

Larger range in isotopic composition of the continental flood volcanism most likely reflects continental lithospheric contamination.The range in isotopic composition of continental flood volcanism and Tristan-Gough oceanic hotspot track volcanism are shown on (a) 87Sr/86Sr versus 143Nd/144Nd and (b) 206Pb/204Pb versus 207Pb/204Pb isotope correlation diagrams. In (a) samples with MgO>11 wt.% (enclosed within dashed line) show a much more restricted range in isotopic composition, yet 87Sr/86Sr ratio in some mafic samples is still higher than in the oceanic part of the hotspot track, either reflecting contamination by crustal material or lithospheric mantle, both of which can have extremely radiogenic Sr2728. In (b), if only Etendeka and Parana flood basalts with 87Sr/86Sr<0.7067 (highest value in the oceanic hotspot track) are considered on the uranogenic Pb isotope diagram (marked with a cross and enclosed within the field defined by the dashed line), they only show a slightly greater range than the Gough field, suggesting that 87Sr/86Sr ratio can be used to effectively filter for continental lithospheric contamination. Arrows denote directions for upper and lower crustal and/or lithospheric mantle contamination. In (a) the arrow labelled ‘Upper continental crust contamination' extends into the field for Damara S-type granites and points to the field for Damara metasediments27. The arrow labelled ‘Lower continental crust contamination' points toward the Kaokoland gneisses (Pre-Damara basement)27. In (b) the ‘Lower crustal contam. (contamination)' arrow overlaps with and points to lower crustal granulites from the Namaqua-Natal Belt in South Africa28. The ‘Upper crustal/lithospheric mantle contamination' arrows point to the following rock groups in Namibia: (1) upper arrow–Khan granodiorites (samples G12 and G13 (ref. 30) and 02/99 and 03/99 (ref. 31)) and (2) lower arrow–Kuiseb schists (sample Kh27 (ref. 30)) and lithospheric mantle, estimated to have a present-day composition of 206Pb/204Pb∼19.8 and 207Pb/204Pb ∼15.7 (based on sample VB32) beneath the Spitzkoppe region in Namibia27. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/). Average radiogenic ingrowth correction and 1σ variation for Parana and Etendeka as defined in the Fig. 3 caption.
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f4: Larger range in isotopic composition of the continental flood volcanism most likely reflects continental lithospheric contamination.The range in isotopic composition of continental flood volcanism and Tristan-Gough oceanic hotspot track volcanism are shown on (a) 87Sr/86Sr versus 143Nd/144Nd and (b) 206Pb/204Pb versus 207Pb/204Pb isotope correlation diagrams. In (a) samples with MgO>11 wt.% (enclosed within dashed line) show a much more restricted range in isotopic composition, yet 87Sr/86Sr ratio in some mafic samples is still higher than in the oceanic part of the hotspot track, either reflecting contamination by crustal material or lithospheric mantle, both of which can have extremely radiogenic Sr2728. In (b), if only Etendeka and Parana flood basalts with 87Sr/86Sr<0.7067 (highest value in the oceanic hotspot track) are considered on the uranogenic Pb isotope diagram (marked with a cross and enclosed within the field defined by the dashed line), they only show a slightly greater range than the Gough field, suggesting that 87Sr/86Sr ratio can be used to effectively filter for continental lithospheric contamination. Arrows denote directions for upper and lower crustal and/or lithospheric mantle contamination. In (a) the arrow labelled ‘Upper continental crust contamination' extends into the field for Damara S-type granites and points to the field for Damara metasediments27. The arrow labelled ‘Lower continental crust contamination' points toward the Kaokoland gneisses (Pre-Damara basement)27. In (b) the ‘Lower crustal contam. (contamination)' arrow overlaps with and points to lower crustal granulites from the Namaqua-Natal Belt in South Africa28. The ‘Upper crustal/lithospheric mantle contamination' arrows point to the following rock groups in Namibia: (1) upper arrow–Khan granodiorites (samples G12 and G13 (ref. 30) and 02/99 and 03/99 (ref. 31)) and (2) lower arrow–Kuiseb schists (sample Kh27 (ref. 30)) and lithospheric mantle, estimated to have a present-day composition of 206Pb/204Pb∼19.8 and 207Pb/204Pb ∼15.7 (based on sample VB32) beneath the Spitzkoppe region in Namibia27. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/). Average radiogenic ingrowth correction and 1σ variation for Parana and Etendeka as defined in the Fig. 3 caption.

Mentions: Evaluating the composition of the mantle plume head linked to the 132 Ma Parana-Etendeka flood basalt event is difficult because of potential interaction of melts with the continental lithosphere (both crust and mantle), which overall has a geochemically enriched composition in comparison with oceanic lithosphere. Lavas and dykes associated with the 132 Ma volcanic event range from pricritic and tholeiitic basalts through highly silica-undersaturated nephelinites to highly evolved rhyolites through phonolites. Intrusive equivalents range from gabbros to granites to syenites. These magmatic rocks show an extremely large range in measured 87Sr/86Sr of ∼0.703–0.743 (with one sample having 0.924) and 143Nd/144Nd of ∼0.5117–0.5129 (Figs 3 and 4a). On plots of MgO versus 87Sr/86Sr and 143Nd/144Nd isotope ratios (Fig. 3), the most magnesium-rich samples have the lowest 87Sr/86Sr and highest 143Nd/144Nd isotope ratios and show the least variation. With decreasing MgO, the range in 87Sr/86Sr and 143Nd/144Nd increases systematically with 87Sr/86Sr extending to higher and 143Nd/144Nd to lower ratios. If only samples with MgO ⩾11 wt.% (Sr>600 p.p.m.; Supplementary Fig. 1) are considered, for example, the range in 87Sr/86Sr (0.7044–0.7091) and 143Nd/144Nd (0.51240–0.51288) is considerably reduced. The much larger range present in the more evolved compositions most likely reflects derivation through continental lithospheric melting or through assimilation of such melts by differentiated mantle melts. Extensive feldspar fractionation in many highly evolved melts reduces the Sr concentration to very low values, whereas Rb continues to be incompatible in the melts and thus its concentration increases, resulting in very high Rb/Sr ratios. Radiogenic ingrowth in the evolved rocks with very high Rb/Sr ratios contributes to the elevated 87Sr/86Sr ratios. Although the 143Nd/144Nd of the mafic (MgO ⩾11 wt.%) flood basalts is similar to the oceanic Tristan-Gough track rocks (Fig. 4a), the 87Sr/86Sr in some mafic samples extends to higher ratios, which can be explained by small amounts of assimilation of crust with very radiogenic 87Sr/86Sr (for example, some crustal rocks have extreme 87Sr/86Sr up to 1.18) and/or through melting of enriched portions of the lithospheric mantle with radiogenic Sr and Pb isotope ratios27.


How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot.

Hoernle K, Rohde J, Hauff F, Garbe-Schönberg D, Homrighausen S, Werner R, Morgan JP - Nat Commun (2015)

Larger range in isotopic composition of the continental flood volcanism most likely reflects continental lithospheric contamination.The range in isotopic composition of continental flood volcanism and Tristan-Gough oceanic hotspot track volcanism are shown on (a) 87Sr/86Sr versus 143Nd/144Nd and (b) 206Pb/204Pb versus 207Pb/204Pb isotope correlation diagrams. In (a) samples with MgO>11 wt.% (enclosed within dashed line) show a much more restricted range in isotopic composition, yet 87Sr/86Sr ratio in some mafic samples is still higher than in the oceanic part of the hotspot track, either reflecting contamination by crustal material or lithospheric mantle, both of which can have extremely radiogenic Sr2728. In (b), if only Etendeka and Parana flood basalts with 87Sr/86Sr<0.7067 (highest value in the oceanic hotspot track) are considered on the uranogenic Pb isotope diagram (marked with a cross and enclosed within the field defined by the dashed line), they only show a slightly greater range than the Gough field, suggesting that 87Sr/86Sr ratio can be used to effectively filter for continental lithospheric contamination. Arrows denote directions for upper and lower crustal and/or lithospheric mantle contamination. In (a) the arrow labelled ‘Upper continental crust contamination' extends into the field for Damara S-type granites and points to the field for Damara metasediments27. The arrow labelled ‘Lower continental crust contamination' points toward the Kaokoland gneisses (Pre-Damara basement)27. In (b) the ‘Lower crustal contam. (contamination)' arrow overlaps with and points to lower crustal granulites from the Namaqua-Natal Belt in South Africa28. The ‘Upper crustal/lithospheric mantle contamination' arrows point to the following rock groups in Namibia: (1) upper arrow–Khan granodiorites (samples G12 and G13 (ref. 30) and 02/99 and 03/99 (ref. 31)) and (2) lower arrow–Kuiseb schists (sample Kh27 (ref. 30)) and lithospheric mantle, estimated to have a present-day composition of 206Pb/204Pb∼19.8 and 207Pb/204Pb ∼15.7 (based on sample VB32) beneath the Spitzkoppe region in Namibia27. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/). Average radiogenic ingrowth correction and 1σ variation for Parana and Etendeka as defined in the Fig. 3 caption.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525177&req=5

f4: Larger range in isotopic composition of the continental flood volcanism most likely reflects continental lithospheric contamination.The range in isotopic composition of continental flood volcanism and Tristan-Gough oceanic hotspot track volcanism are shown on (a) 87Sr/86Sr versus 143Nd/144Nd and (b) 206Pb/204Pb versus 207Pb/204Pb isotope correlation diagrams. In (a) samples with MgO>11 wt.% (enclosed within dashed line) show a much more restricted range in isotopic composition, yet 87Sr/86Sr ratio in some mafic samples is still higher than in the oceanic part of the hotspot track, either reflecting contamination by crustal material or lithospheric mantle, both of which can have extremely radiogenic Sr2728. In (b), if only Etendeka and Parana flood basalts with 87Sr/86Sr<0.7067 (highest value in the oceanic hotspot track) are considered on the uranogenic Pb isotope diagram (marked with a cross and enclosed within the field defined by the dashed line), they only show a slightly greater range than the Gough field, suggesting that 87Sr/86Sr ratio can be used to effectively filter for continental lithospheric contamination. Arrows denote directions for upper and lower crustal and/or lithospheric mantle contamination. In (a) the arrow labelled ‘Upper continental crust contamination' extends into the field for Damara S-type granites and points to the field for Damara metasediments27. The arrow labelled ‘Lower continental crust contamination' points toward the Kaokoland gneisses (Pre-Damara basement)27. In (b) the ‘Lower crustal contam. (contamination)' arrow overlaps with and points to lower crustal granulites from the Namaqua-Natal Belt in South Africa28. The ‘Upper crustal/lithospheric mantle contamination' arrows point to the following rock groups in Namibia: (1) upper arrow–Khan granodiorites (samples G12 and G13 (ref. 30) and 02/99 and 03/99 (ref. 31)) and (2) lower arrow–Kuiseb schists (sample Kh27 (ref. 30)) and lithospheric mantle, estimated to have a present-day composition of 206Pb/204Pb∼19.8 and 207Pb/204Pb ∼15.7 (based on sample VB32) beneath the Spitzkoppe region in Namibia27. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/). Average radiogenic ingrowth correction and 1σ variation for Parana and Etendeka as defined in the Fig. 3 caption.
Mentions: Evaluating the composition of the mantle plume head linked to the 132 Ma Parana-Etendeka flood basalt event is difficult because of potential interaction of melts with the continental lithosphere (both crust and mantle), which overall has a geochemically enriched composition in comparison with oceanic lithosphere. Lavas and dykes associated with the 132 Ma volcanic event range from pricritic and tholeiitic basalts through highly silica-undersaturated nephelinites to highly evolved rhyolites through phonolites. Intrusive equivalents range from gabbros to granites to syenites. These magmatic rocks show an extremely large range in measured 87Sr/86Sr of ∼0.703–0.743 (with one sample having 0.924) and 143Nd/144Nd of ∼0.5117–0.5129 (Figs 3 and 4a). On plots of MgO versus 87Sr/86Sr and 143Nd/144Nd isotope ratios (Fig. 3), the most magnesium-rich samples have the lowest 87Sr/86Sr and highest 143Nd/144Nd isotope ratios and show the least variation. With decreasing MgO, the range in 87Sr/86Sr and 143Nd/144Nd increases systematically with 87Sr/86Sr extending to higher and 143Nd/144Nd to lower ratios. If only samples with MgO ⩾11 wt.% (Sr>600 p.p.m.; Supplementary Fig. 1) are considered, for example, the range in 87Sr/86Sr (0.7044–0.7091) and 143Nd/144Nd (0.51240–0.51288) is considerably reduced. The much larger range present in the more evolved compositions most likely reflects derivation through continental lithospheric melting or through assimilation of such melts by differentiated mantle melts. Extensive feldspar fractionation in many highly evolved melts reduces the Sr concentration to very low values, whereas Rb continues to be incompatible in the melts and thus its concentration increases, resulting in very high Rb/Sr ratios. Radiogenic ingrowth in the evolved rocks with very high Rb/Sr ratios contributes to the elevated 87Sr/86Sr ratios. Although the 143Nd/144Nd of the mafic (MgO ⩾11 wt.%) flood basalts is similar to the oceanic Tristan-Gough track rocks (Fig. 4a), the 87Sr/86Sr in some mafic samples extends to higher ratios, which can be explained by small amounts of assimilation of crust with very radiogenic 87Sr/86Sr (for example, some crustal rocks have extreme 87Sr/86Sr up to 1.18) and/or through melting of enriched portions of the lithospheric mantle with radiogenic Sr and Pb isotope ratios27.

Bottom Line: The origin of this zonation is currently unclear.Recently zonation was found along the last ∼70 Myr of the Tristan-Gough hotspot track.Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.

View Article: PubMed Central - PubMed

Affiliation: 1] GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany [2] CAU Kiel University, Institute of Geosciences, Ludewig-Meyn-Strasse 10, D-24118 Kiel, Germany.

ABSTRACT
Increasingly, spatial geochemical zonation, present as geographically distinct, subparallel trends, is observed along hotspot tracks, such as Hawaii and the Galapagos. The origin of this zonation is currently unclear. Recently zonation was found along the last ∼70 Myr of the Tristan-Gough hotspot track. Here we present new Sr-Nd-Pb-Hf isotope data from the older parts of this hotspot track (Walvis Ridge and Rio Grande Rise) and re-evaluate published data from the Etendeka and Parana flood basalts erupted at the initiation of the hotspot track. We show that only the enriched Gough, but not the less-enriched Tristan, component is present in the earlier (70-132 Ma) history of the hotspot. Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.

No MeSH data available.


Related in: MedlinePlus