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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

The >70 Ma Tristan-Gough hotspot track lavas have Gough-type isotopic compositions.On the (a) 206Pb/204Pb versus 207Pb/204Pb (uranogenic Pb) isotope diagram, older hotspot lavas (>70 Ma) fall solely within the Gough field of ref. 13. Even though they are completely separated on the uranogenic Pb isotope diagram, the Tristan and Gough fields completely overlap on the (b) 206Pb/204Pb versus 208Pb/204Pb (thorogenic Pb) isotope diagram, indicating that the Tristan compositions cannot simply be explained by mixing of Gough compositions with Atlantic MORB. Modelling shows that addition of 70 to >90% Atlantic N-MORB to Gough can explain the shift in Tristan to N-MORB in (a), but would require the Tristan field to be shifted towards Atlantic N-MORB in (b), for example, extending beyond the >90% mixing line towards N-MORB as in (a). Pb concentrations used for the mixing calculations are 0.57 p.p.m. for the MORB end members (based on average of global N-MORB62) and 3.2 p.p.m. for the Gough end members (average of Gough samples with MgO>1 wt.%) (Supplementary Dataset 1). Changing the assumed concentrations for Gough and MORB end members will simply shift the mixing percentages, but mixing of Gough and Atlantic N-MORB will still require Tristan to be shifted towards N-MORB compared with Gough on the thorogenic Pb isotope diagram. To compare isotope data of samples ranging in age between ∼0–115 Ma, we use the measured compositions, assuming that the parent-daughter ratios were not significantly fractionated during melting or subsequent differentiation. The ‘average ingrowth corr.' and associated 1σ variation is the average correction needed for radiogenic ingrowth for the plotted samples (Supplementary Dataset 1). Since the age correction moves the data sub parallel to the boundary between the Gough and Tristan fields in (a), radiogenic ingrowth does not cause overlap between Gough and Tristan samples and therefore does not affect the classification of the samples. Analytical errors of data (Supplementary Dataset 1) in these and all subsequent isotope diagrams are smaller than symbol size. Numbers in the legend refer to DSDP Sites (Fig. 1). Atlantic MORB from PetDB (http://www.earthchem.org/petdb) and additional Tristan-Gough data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
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f2: The >70 Ma Tristan-Gough hotspot track lavas have Gough-type isotopic compositions.On the (a) 206Pb/204Pb versus 207Pb/204Pb (uranogenic Pb) isotope diagram, older hotspot lavas (>70 Ma) fall solely within the Gough field of ref. 13. Even though they are completely separated on the uranogenic Pb isotope diagram, the Tristan and Gough fields completely overlap on the (b) 206Pb/204Pb versus 208Pb/204Pb (thorogenic Pb) isotope diagram, indicating that the Tristan compositions cannot simply be explained by mixing of Gough compositions with Atlantic MORB. Modelling shows that addition of 70 to >90% Atlantic N-MORB to Gough can explain the shift in Tristan to N-MORB in (a), but would require the Tristan field to be shifted towards Atlantic N-MORB in (b), for example, extending beyond the >90% mixing line towards N-MORB as in (a). Pb concentrations used for the mixing calculations are 0.57 p.p.m. for the MORB end members (based on average of global N-MORB62) and 3.2 p.p.m. for the Gough end members (average of Gough samples with MgO>1 wt.%) (Supplementary Dataset 1). Changing the assumed concentrations for Gough and MORB end members will simply shift the mixing percentages, but mixing of Gough and Atlantic N-MORB will still require Tristan to be shifted towards N-MORB compared with Gough on the thorogenic Pb isotope diagram. To compare isotope data of samples ranging in age between ∼0–115 Ma, we use the measured compositions, assuming that the parent-daughter ratios were not significantly fractionated during melting or subsequent differentiation. The ‘average ingrowth corr.' and associated 1σ variation is the average correction needed for radiogenic ingrowth for the plotted samples (Supplementary Dataset 1). Since the age correction moves the data sub parallel to the boundary between the Gough and Tristan fields in (a), radiogenic ingrowth does not cause overlap between Gough and Tristan samples and therefore does not affect the classification of the samples. Analytical errors of data (Supplementary Dataset 1) in these and all subsequent isotope diagrams are smaller than symbol size. Numbers in the legend refer to DSDP Sites (Fig. 1). Atlantic MORB from PetDB (http://www.earthchem.org/petdb) and additional Tristan-Gough data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).

Mentions: Recently published Sr–Nd–Hf–Pb isotope data of samples from the Tristan-Gough hotspot track reveal that bilateral chemical zonation can be traced from the Tristan da Cunha and Gough island groups along the Tristan and Gough subtracks for the last ∼70 Myr to the southwestern (SW) end of the Walvis Ridge13 (Fig. 1). The enriched Gough domain exhibits higher 207Pb/204Pb for a given 206Pb/204Pb and extends to lower 143Nd/144Nd and 176Hf/177Hf ratios and generally higher 87Sr/86Sr ratios compared with the more depleted (less enriched) Tristan domain. The domains form distinct fields on the uranogenic Pb isotope diagram (Fig. 2a). Published geochemical data are, however, insufficient to establish chemical zonation beyond 70 Ma.


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)

The >70 Ma Tristan-Gough hotspot track lavas have Gough-type isotopic compositions.On the (a) 206Pb/204Pb versus 207Pb/204Pb (uranogenic Pb) isotope diagram, older hotspot lavas (>70 Ma) fall solely within the Gough field of ref. 13. Even though they are completely separated on the uranogenic Pb isotope diagram, the Tristan and Gough fields completely overlap on the (b) 206Pb/204Pb versus 208Pb/204Pb (thorogenic Pb) isotope diagram, indicating that the Tristan compositions cannot simply be explained by mixing of Gough compositions with Atlantic MORB. Modelling shows that addition of 70 to >90% Atlantic N-MORB to Gough can explain the shift in Tristan to N-MORB in (a), but would require the Tristan field to be shifted towards Atlantic N-MORB in (b), for example, extending beyond the >90% mixing line towards N-MORB as in (a). Pb concentrations used for the mixing calculations are 0.57 p.p.m. for the MORB end members (based on average of global N-MORB62) and 3.2 p.p.m. for the Gough end members (average of Gough samples with MgO>1 wt.%) (Supplementary Dataset 1). Changing the assumed concentrations for Gough and MORB end members will simply shift the mixing percentages, but mixing of Gough and Atlantic N-MORB will still require Tristan to be shifted towards N-MORB compared with Gough on the thorogenic Pb isotope diagram. To compare isotope data of samples ranging in age between ∼0–115 Ma, we use the measured compositions, assuming that the parent-daughter ratios were not significantly fractionated during melting or subsequent differentiation. The ‘average ingrowth corr.' and associated 1σ variation is the average correction needed for radiogenic ingrowth for the plotted samples (Supplementary Dataset 1). Since the age correction moves the data sub parallel to the boundary between the Gough and Tristan fields in (a), radiogenic ingrowth does not cause overlap between Gough and Tristan samples and therefore does not affect the classification of the samples. Analytical errors of data (Supplementary Dataset 1) in these and all subsequent isotope diagrams are smaller than symbol size. Numbers in the legend refer to DSDP Sites (Fig. 1). Atlantic MORB from PetDB (http://www.earthchem.org/petdb) and additional Tristan-Gough data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
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Related In: Results  -  Collection

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Show All Figures
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f2: The >70 Ma Tristan-Gough hotspot track lavas have Gough-type isotopic compositions.On the (a) 206Pb/204Pb versus 207Pb/204Pb (uranogenic Pb) isotope diagram, older hotspot lavas (>70 Ma) fall solely within the Gough field of ref. 13. Even though they are completely separated on the uranogenic Pb isotope diagram, the Tristan and Gough fields completely overlap on the (b) 206Pb/204Pb versus 208Pb/204Pb (thorogenic Pb) isotope diagram, indicating that the Tristan compositions cannot simply be explained by mixing of Gough compositions with Atlantic MORB. Modelling shows that addition of 70 to >90% Atlantic N-MORB to Gough can explain the shift in Tristan to N-MORB in (a), but would require the Tristan field to be shifted towards Atlantic N-MORB in (b), for example, extending beyond the >90% mixing line towards N-MORB as in (a). Pb concentrations used for the mixing calculations are 0.57 p.p.m. for the MORB end members (based on average of global N-MORB62) and 3.2 p.p.m. for the Gough end members (average of Gough samples with MgO>1 wt.%) (Supplementary Dataset 1). Changing the assumed concentrations for Gough and MORB end members will simply shift the mixing percentages, but mixing of Gough and Atlantic N-MORB will still require Tristan to be shifted towards N-MORB compared with Gough on the thorogenic Pb isotope diagram. To compare isotope data of samples ranging in age between ∼0–115 Ma, we use the measured compositions, assuming that the parent-daughter ratios were not significantly fractionated during melting or subsequent differentiation. The ‘average ingrowth corr.' and associated 1σ variation is the average correction needed for radiogenic ingrowth for the plotted samples (Supplementary Dataset 1). Since the age correction moves the data sub parallel to the boundary between the Gough and Tristan fields in (a), radiogenic ingrowth does not cause overlap between Gough and Tristan samples and therefore does not affect the classification of the samples. Analytical errors of data (Supplementary Dataset 1) in these and all subsequent isotope diagrams are smaller than symbol size. Numbers in the legend refer to DSDP Sites (Fig. 1). Atlantic MORB from PetDB (http://www.earthchem.org/petdb) and additional Tristan-Gough data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
Mentions: Recently published Sr–Nd–Hf–Pb isotope data of samples from the Tristan-Gough hotspot track reveal that bilateral chemical zonation can be traced from the Tristan da Cunha and Gough island groups along the Tristan and Gough subtracks for the last ∼70 Myr to the southwestern (SW) end of the Walvis Ridge13 (Fig. 1). The enriched Gough domain exhibits higher 207Pb/204Pb for a given 206Pb/204Pb and extends to lower 143Nd/144Nd and 176Hf/177Hf ratios and generally higher 87Sr/86Sr ratios compared with the more depleted (less enriched) Tristan domain. The domains form distinct fields on the uranogenic Pb isotope diagram (Fig. 2a). Published geochemical data are, however, insufficient to establish chemical zonation beyond 70 Ma.

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