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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

Evolved Parana and Etendeka continental flood volcanism shows much greater isotopic variation than the oceanic Tristan-Gough hotspot track lavas.On plots of MgO vs. (a) 87Sr/86Sr and (b) 143Nd/144Nd, the oceanic lavas have relatively constant composition and unradiogenic 87Sr/86Sr but radiogenic 143Nd/144Nd regardless of MgO content (degree of differentiation). The continental volcanism, however, shows a greater range in 87Sr/86Sr and 143Nd/144Nd extending to systematically more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd with increasing degree of differentiation (decreasing MgO). The increasing and substantially greater range in 87Sr/86Sr and 143Nd/144Nd for the continental, compared with oceanic, volcanic rocks primarily reflects increasing amounts of assimilation during fractional crystallization of continental lithosphere by some magmas. Radiogenic ingrowth in some of the most evolved silica-saturated samples with very high Rb/Sr ratios also contributes to the extremely radiogenic 87Sr/86Sr. Average correction for radiogenic ingrowth for Parana and Etendeka is based on 498 (87Sr/86Sr) and 280 (143Nd/144Nd) analyses for which parent/daughter ratios are available. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
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f3: Evolved Parana and Etendeka continental flood volcanism shows much greater isotopic variation than the oceanic Tristan-Gough hotspot track lavas.On plots of MgO vs. (a) 87Sr/86Sr and (b) 143Nd/144Nd, the oceanic lavas have relatively constant composition and unradiogenic 87Sr/86Sr but radiogenic 143Nd/144Nd regardless of MgO content (degree of differentiation). The continental volcanism, however, shows a greater range in 87Sr/86Sr and 143Nd/144Nd extending to systematically more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd with increasing degree of differentiation (decreasing MgO). The increasing and substantially greater range in 87Sr/86Sr and 143Nd/144Nd for the continental, compared with oceanic, volcanic rocks primarily reflects increasing amounts of assimilation during fractional crystallization of continental lithosphere by some magmas. Radiogenic ingrowth in some of the most evolved silica-saturated samples with very high Rb/Sr ratios also contributes to the extremely radiogenic 87Sr/86Sr. Average correction for radiogenic ingrowth for Parana and Etendeka is based on 498 (87Sr/86Sr) and 280 (143Nd/144Nd) analyses for which parent/daughter ratios are available. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).

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)

Evolved Parana and Etendeka continental flood volcanism shows much greater isotopic variation than the oceanic Tristan-Gough hotspot track lavas.On plots of MgO vs. (a) 87Sr/86Sr and (b) 143Nd/144Nd, the oceanic lavas have relatively constant composition and unradiogenic 87Sr/86Sr but radiogenic 143Nd/144Nd regardless of MgO content (degree of differentiation). The continental volcanism, however, shows a greater range in 87Sr/86Sr and 143Nd/144Nd extending to systematically more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd with increasing degree of differentiation (decreasing MgO). The increasing and substantially greater range in 87Sr/86Sr and 143Nd/144Nd for the continental, compared with oceanic, volcanic rocks primarily reflects increasing amounts of assimilation during fractional crystallization of continental lithosphere by some magmas. Radiogenic ingrowth in some of the most evolved silica-saturated samples with very high Rb/Sr ratios also contributes to the extremely radiogenic 87Sr/86Sr. Average correction for radiogenic ingrowth for Parana and Etendeka is based on 498 (87Sr/86Sr) and 280 (143Nd/144Nd) analyses for which parent/daughter ratios are available. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Evolved Parana and Etendeka continental flood volcanism shows much greater isotopic variation than the oceanic Tristan-Gough hotspot track lavas.On plots of MgO vs. (a) 87Sr/86Sr and (b) 143Nd/144Nd, the oceanic lavas have relatively constant composition and unradiogenic 87Sr/86Sr but radiogenic 143Nd/144Nd regardless of MgO content (degree of differentiation). The continental volcanism, however, shows a greater range in 87Sr/86Sr and 143Nd/144Nd extending to systematically more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd with increasing degree of differentiation (decreasing MgO). The increasing and substantially greater range in 87Sr/86Sr and 143Nd/144Nd for the continental, compared with oceanic, volcanic rocks primarily reflects increasing amounts of assimilation during fractional crystallization of continental lithosphere by some magmas. Radiogenic ingrowth in some of the most evolved silica-saturated samples with very high Rb/Sr ratios also contributes to the extremely radiogenic 87Sr/86Sr. Average correction for radiogenic ingrowth for Parana and Etendeka is based on 498 (87Sr/86Sr) and 280 (143Nd/144Nd) analyses for which parent/daughter ratios are available. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
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