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How and When Plume Zonation Appeared During the 132&Thinsp

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ARTICLE Received 10 Oct 2014 | Accepted 10 Jun 2015 | Published 27 Jul 2015 DOI: 10.1038/ncomms8799 OPEN How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot Kaj Hoernle1,2, Joana Rohde1, Folkmar Hauff1, Dieter Garbe-Scho¨nberg2, Stephan Homrighausen1, Reinhard Werner1 & Jason P. Morgan3 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 B70 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. 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. 3 Royal Holloway, University of London, Department of Earth Sciences, Egham Hill, Egham TW20 0EX, UK. Correspondence and requests for materials should be addressed to K.H. (email: [email protected]). NATURE COMMUNICATIONS | 6:7799 | DOI: 10.1038/ncomms8799 | www.nature.com/naturecommunications 1 & 2015 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms8799 lthough it has been proposed that some plumes have formation of the South Atlantic Ocean basin23. As the Atlantic had constant compositions through time, such as the opened, ALouisville1 and Kerguelen2,3, spatial geochemical zonation the ridge-centred plume tail formed the Walvis Ridge on the has been found in a variety of hotspot tracks in the Pacific Ocean. African Plate and the Rio Grande Rise (possibly underlain by a These include the Galapagos4–7, Hawaiian8,9, Samoan10, thinned continental block) on the South American Plate. As the Marquesan10,11 and Society12 hotspot tracks, which are believed South Atlantic mid-ocean ridge drifted westwards away from the to be located at the border of the large, lower mantle, low plume tail B50–60 Ma, the hotspot became intraplate forming shear-wave velocity province (LLSVP) beneath the southern the Guyot Province, consisting of separate volcanic tracks leading Pacific9,10,12,13. The longevity of plume zonation is variable for to the active volcanic islands of Tristan da Cunha and Gough24. the different Pacific hotspots. It can be traced for 15–20 Myr Recently published Sr–Nd–Hf–Pb isotope data of samples from along the Galapagos hotspot track6,7, for B4 Myr along the the Tristan-Gough hotspot track reveal that bilateral chemical Society hotspot track12,14, for B5.5 Myr along the Marquesas11,15 zonation can be traced from the Tristan da Cunha and Gough and for up to 2 Myr along the Samoan Islands10,14,16. island groups along the Tristan and Gough subtracks for the last The coexistence of the geochemically distinct Loa and Kea B70 Myr to the southwestern (SW) end of the Walvis Ridge13 trends of the Hawaiian mantle plume has been traced for the last (Fig. 1). The enriched Gough domain exhibits higher 207Pb/204Pb 5 Myr along the island chain9. Little evidence exists for the for a given 206Pb/204Pb and extends to lower 143Nd/144Nd and presence of the Loa component in the Hawaiian seamounts, 176Hf/177Hf ratios and generally higher 87Sr/86Sr ratios compared located west of the Hawaiian Islands and only the Kea component with the more depleted (less enriched) Tristan domain. The has been recognized so far in the Emperor Seamounts and domains form distinct fields on the uranogenic Pb isotope diagram older accreted Hawaiian complexes in Kamchatka17. To address (Fig. 2a). Published geochemical data are, however, insufficient to questions concerning the longevity of plume zonation and how it establish chemical zonation beyond 70 Ma. originates, we investigate the entire history of the Tristan-Gough Here we present new Sr–Nd–Hf–Pb double spike (DS) isotope hotspot here and compare it with what is known about the data from additional samples from the Guyot Province (obtained history of the Hawaiian hotspot. during R/V Akademik Kurchatov, AII-93 Atlantis II, ANT-XXIII/ The Tristan-Gough hotspot track (Fig. 1) represents the classic 5 Polarstern, VM29 Vema, 51 S.A. Agulhas and SO233 Sonne evolution of a hotspot18 with active volcanic islands at its young cruises) and Deep Sea Drilling Programme (DSDP) Sites 525A, end and flood basalt provinces at its older end. It has been termed 527 and 528 at the SW end of the Walvis Ridge to test whether one of the seven hotspots most likely to be derived from the this part of the hotspot track is indeed zoned. More importantly lowermost mantle from a ‘primary’ plume19 with its base we present new data from dredge (VM29 Vema, CIRCE Argo, currently located at the margin of the African LLSVP20,21. The AII–93 Atlantis II, CH19 Jean Charcot, WALDAA–002 Jean emplacement of a Tristan-Gough plume head at the base of the Charcot, RC11 Robert D. Conrad and SO233 Sonne cruises) and Gondwana lithosphere caused massive volcanism forming the DSDP Leg 72 drill samples from the older part of the hotspot Parana (eastern South America) and Etendeka (western Africa) track (central and northeast Walvis Ridge and Rio Grande Rise) flood basalts at B132 Ma22 and may have contributed to determine whether the zonation can be traced further back in to the breakup of Africa from South America and the time, that is, going northeast along the hotspot track. Finally, we ge d 15°S e i R g is d i lv a Etendeka R W c CFBs i Paraná CFBs t n 132 Ma 108–114 Ma a k l c 132 Ma t a A r - t Rio Grande Rise k d n 20°S i ta c s a M ri r T t h g u o G Guyot Province 107 Ma – 87 25°S Site 527 Site 528 Site 525A Site 516F 58–67 Ma 71–72 Ma 30°S 80–87 Ma 47 Ma 49 Ma 36 Ma 33 Ma 35°S Walvis Ridge 46 Ma 27 Ma Rio Grande Rise Tristan da Cunha Islands Guyot Province (Gough track) 37 Ma 27 Ma Gough Island DSDP site 525A Guyot Province (Tristan track) Gough Island 40°S Tristan da Cunha Islands DSDP sites 527 and 528 40°W 35°W 30°W 25°W 15°W 10°W 5°W0° 5°E 10°E Figure 1 | Bathymetric map of the South Atlantic Ocean and its margins showing the Tristan-Gough hotspot track. The map shows the Tristan-Gough hotspot track including the B132 Myr (ref. 22) old Etendeka and Parana continental flood basalt provinces, the Rio Grand Rise and Walvis Ridge (both within the age range B60–115 Ma), the Guyot Province at the southwestern end of the Walvis Ridge containing the Tristan da Cunha and Gough Island groups (B0–60 Ma)24. Ages for late-stage volcanism are not shown. Age range in italics (87–107 Ma) is estimated using a spatial age progression equation24. Sample locations are denoted by symbols: large symbols this study and small symbols as reported in ref. 13. Source of base map is http:// www.geomapapp.org. All sites are from the Deep Sea Drilling Project. The scale bar in the lower right hand corner indicates a distance of B500 km. 2 NATURE COMMUNICATIONS | 6:7799 | DOI: 10.1038/ncomms8799 | www.nature.com/naturecommunications & 2015 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms8799 ARTICLE 15.68 and Hawaiian plumes and evaluate the origin of geochemical Gough track Tristan track Gough Island Tristan Islands zonation in both plumes. 15.64 DSDP 525A 527 and 528 Walvis Ridge Results 15.60 Rio Grande Rise 80% 90% Isotopic composition of Tristan-Gough hotspot track lavas. Pb 204 15.56 The new Sr–Nd–Hf–Pb isotope data are presented in (Table 1). Average Pb/ ingrowth corr. We report details about the samples, the major and trace element 207 15.52 data and isotope data with errors in Methods and Supplementary Dataset 1. The Sr–Nd–Hf–Pb isotope data of the new samples 15.48 80% from the Guyot Province and DSDP Sites 525A, 527 and 528 at Atlantic N-MORB 15.44 90% the SW end of the Walvis Ridge confirm the spatial geochemical zonation of the r70 Ma hotspot track proposed by (ref.13; Fig. 2a). The data from the older (470 Ma) hotspot track, central 39.6 and northeast portion of the Walvis Ridge and the Rio Grande 24 39.2 Rise , plot exclusively within the Gough field. They also 80% completely cover the range of the r70 Ma Gough track, Pb 38.8 90% 204 showing that there is no systematic temporal change in the Gough source through time. The Rio Grande Rise samples and Pb/ 38.4 208 some samples from the Walvis Ridge are isotopically as enriched 38.0 as DSDP Site 525A: the enriched mantle one (EMI) end member 80% Atlantic N-MORB 25,26 90% in the South Atlantic .
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    Implications of Subduction Rehydration for Earth’s Deep Water Cycle Lars Rüpke Physics of Geological Processes, University of Oslo, Oslo, Norway, and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jason Phipps Morgan Cornell University, Ithaca, New York, USA and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jacqueline Eaby Dixon RSMAS/MGG, University of Miami, Miami, Florida, USA The “standard model” for the genesis of the oceans is that they are exhalations from Earth’s deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et al. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et al. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consis- tent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components.