A trace of recycled continental crust in the Réunion hotspot
Introduction
Oceanic volcanic islands are of great interest to geologists because they provide indirect access to the structure and composition of mantle plumes, to their temporal variations, and hence to the dynamics of the Earth's mantle (Steinberger, 2000). Seismic tomography and isotope geochemistry have revealed that mantle plumes are highly variable in structure, composition and temporal evolution despite their common characteristics (thermal anomaly, buoyancy of deep mantle material, relatively fixed position through time, mixing of enriched lower mantle and depleted upper mantle) (Zhao, 2007).
Several suites of ocean island basalts (OIBs) from individual hotspots generally display large, correlated Sr-Nd-Pb variations (Hart et al., 1992). These arrays constrain the nature and distribution of components within mantle plumes (Abouchami et al., 2005; Bryce et al., 2005; Shorttle et al., 2013) and how they are sampled during the different stages of ocean island volcanism (Paul et al., 2005; Garcia et al., 2010).
One of these hotspots, the Réunion Island in the Indian Ocean, stands out because its basalts show limited isotopic range (Fisk et al., 1988, Graham et al., 1990, Albarède et al., 1997, Hanyu et al., 2001, Fretzdorff and Haase, 2002) and plot near the convergence point of many OIB isotopic arrays. This, together with the occurrence of incompatible trace element ratios similar to primitive mantle (Valer et al., 2017), unusually high Pd/Ir and Ru/Ir ratios (Peters et al., 2016), and 142Nd isotope anomalies (Peters et al., 2018), supports the idea, initially proposed by Vlastélic et al. (2006), that the Réunion mantle source has been isolated from the convecting mantle through much of Earth's history. Nevertheless, the increasing number and precision of isotope analyses has revealed small isotopic heterogeneities between the different volcanoes of Réunion Island (Bosch et al., 2008) and even among historical eruptions of the Piton de la Fournaise volcano (Vlastélic et al., 2009). However, these heterogeneities remain much smaller than those found in the three lava series of Mauritius, the second youngest island along the Réunion hotspot track (Nohda et al., 2005; Paul et al., 2005; Moore et al., 2011). The compositional variations of Réunion and Mauritius lavas have been interpreted as reflecting a heterogeneous plume structure (Paul et al., 2005; Bosch et al., 2008) with major contributions from the C-FOZO and EM-1 (Bosch et al., 2008) or EM-2 like plume components (Smietana, 2011), mixed with depleted mantle from the Central Indian Ridge (Nohda et al., 2005; Füri et al., 2011; Moore et al., 2011). Small variations in the historical volcanic activity of the Réunion hotspot have been interpreted as being due to interaction of Réunion magmas with the oceanic crust or the volcanic edifice (Pietruszka et al., 2009).
In contrast with this apparently simple geochemical model, recent seismic tomography and SKS splitting results depict the Réunion hotspot as a complex low-velocity structure interacting with the Central Indian Ridge (Mazzullo et al., 2017; Scholz et al., 2018). In addition, the recent discovery of Archean zircons in Mauritius has raised the possibility that plume magmas may also be contaminated by fragments of continental crust left behind when India separated from Madagascar (Torsvik et al., 2013; Ashwal et al., 2017).
Most of what we know about the isotopic signature of the Réunion plume over the past 10 Ma is derived from the study of Piton de la Fournaise (PF), which has received considerable attention due to its intense activity (>500 samples analyzed for at least one of Sr, Nd, Hf and/or Pb isotope systems since 2000). Mauritius Island is also relatively well studied (>140 samples, mostly after 2000). In comparison, Piton des Neiges (PN), the other now dormant volcano of Réunion Island, is less studied (<80 data, half of them prior to 1990). As PN is by far the largest and longest-lived emerged edifice on La Réunion Island, this relatively limited number of studied samples might bias our knowledge of the plume's isotopic signature.
Here, we present a new set of Sr-Nd-Pb isotope data from samples belonging to PN. Our first objective is to increase the number and precision of the isotope data for PN, and second to compare our data with those from PF and Mauritius Island. Based on this comparison, we propose a new plume model taking into account all the geochemical, geophysical and geodynamic studies available for the Indian Ocean. This model adds fuel to the controversy about the existence of hidden continental fragments left behind during the northward migration of Indian plate.
Section snippets
Geological setting
Plate displacement over the Réunion hotspot has resulted in an alignment of intraplate volcanism starting in the Indian plate at the Deccan Traps (66–61 Ma), continuing on to the Maldives (~58 Ma), the Chagos archipelagos (~50 Ma), and then on to the Somalian plate with the Saya de Malha bank (50–40 Ma), the Chargados-Carajos islands (~30 Ma), Mauritius (10–0 Ma) and finally Réunion Island (5–0 Ma) (Fig. 1a). Mauritius is built at the tip of the Mascarene plateau on a ~4000 m-deep ocean floor,
Materials and analytical methods
Great care was taken to constitute a suite of 43 samples spanning the entire lifetime of Piton des Neiges from its emergence, encompassing its shield building and differentiated stages, and including the whole range of intrusive and extrusive rock compositions (location Fig. 1b, Table 1). Two samples from Piton de la Fournaise were also collected to check the consistency of our analyses with previous isotopic studies. Samples were selected by cross-correlated dating and major element studies
Results
Sr-Nd-Pb isotope and major-trace element data are reported in Table 1. Sr and Nd isotope ratios for PN range from 0.70404 to 0.70429 and from 0.51282 to 0.51290, respectively. These data are within the range reported by previous authors (87Sr/86Sr: 0.70397–0.70437 and 143Nd/144Nd: 0.51280–0.51288, (Fisk et al., 1989, Smietana, 2011), Fig. 2). The variations are even more restricted compared to those from PF (87Sr/86Sr from 0.70398 to 0.70432 and 143Nd/144Nd from 0.512786 to 0.512786, (Vlastélic
Building a high-precision isotope database for the Réunion hotspot
The first step to be taken while interpreting the isotopic variations is to compile a reliable database of Réunion hotpot rocks younger than 10 Ma, i.e. including samples from Piton des Neiges, Piton de la Fournaise, Mauritius, and possibly Rodrigues. Regarding Piton des Neiges, seventy-eight Sr, Nd or Pb data are available in the literature (McDougall and Compston, 1965, Cooper and Richards, 1966, Oversby, 1972, Ludden, 1978, Dupré and Allègre, 1983, Fisk et al., 1988, Bosch et al., 2008,
Conclusion
We report a new set of Sr-Nd-Pb isotope compositions from samples collected at Piton des Neiges volcano. These data, together with filtered literature data from both Réunion and Mauritius Islands, are used to create a high-precision isotope database for the Réunion hotspot products younger than 10 Ma. This database is used to discuss the origin of the isotopic variations along the Mauritius-Réunion hotspot track. These variations best explained by a three-component, two-step mixing involving
Acknowledgement
Authors are pleased to thank the French Government Laboratory of Excellence initiative ANR-10-LABX-0006, and the INSU,CNRS for the financial and logistic supports. We would deeply thank B. Peters and B. Hanan for their thoughtful reviews that improved the manuscript and C. Chauvel for the Editorial handling. This is Laboratory of Excellence ClerVolc contribution number 354, and IPGP contribution 4047.
References (73)
- et al.
Le bassin des Mascareignes et le bassin de Laxmi (océan Indien occidental) se sont-ils formés à l'axe d'un même centre d'expansion ?
C. R. Acad. Sci. Ser. IIA Earth Planet. Sci.
(2000) - et al.
Pb, Hf and Nd isotope compositions of the two Réunion volcanoes (Indian Ocean): a tale of two small-scale mantle “blobs”?
Earth Planet. Sci. Lett.
(2008) - et al.
Lead isotopes and volcanic magmas
Earth Planet. Sci. Lett.
(1966) - et al.
Reunion hotspot activitity through tertiary time: initial results from the ocean drilling program, leg 115
J. Volcanol. Geotherm. Res.
(1989) - et al.
Orogen styles in the East African Orogen: a review of the Neoproterozoic to Cambrian tectonic evolution
J. Afr. Earth Sci.
(2013) - et al.
K-Ar chronology of the ultimate activity of Piton des Neiges volcano, Reunion island, Indian ocean
J. Volcanol. Geotherm. Res.
(1982) - et al.
Model for the structural evolution of the volcanoes of Réunion Island
Earth Planet. Sci. Lett.
(1994) - et al.
Pb-Sr-Nd isotopic data of Indian Ocean ridges: new evidence of large-scale mapping of mantle heterogeneities
Earth Planet. Sci. Lett.
(1986) - et al.
Pb and Hf isotope variations along the Southeast Indian Ridge and the dynamic distribution of MORB source domains in the upper mantle
Earth Planet. Sci. Lett.
(2013) - et al.
Noble gas study of the Reunion hotspot: evidence for distinct less-degassed mantle sources
Earth Planet. Sci. Lett.
(2001)
Sampling mantle heterogeneity through oceanic basalts: isotopes and trace elements
Nb and Pb in oceanic basalts: new constraints on mantle evolution
Earth Planet. Sci. Lett.
A general mixing equation with applications to icelandic basalts
Earth and Planetary Science Letters
Magmatic evolution of the basaltic shield volcanoes of Reunion Island
J. Volcanol. Geotherm. Res.
The geochronology and evolution of the young volcanic island of Réunion, Indian Ocean
Geochim. Cosmochim. Acta
Evolution of shield-building and rejuvenescent volcanism of Mauritius
J. Volcanol. Geotherm. Res.
Genetic relations among the volcanic rocks of Réunion: chemical and lead isotopic evidence
Geochim. Cosmochim. Acta
Early mantle heterogeneities in the Réunion hotspot source inferred from highly siderophile elements in cumulate xenoliths
Earth Planet. Sci. Lett.
Sequential separation of light rare-earth elements, thorium and uranium by miniaturized extraction chromatography: application to isotopic analyses of silicate rocks
Anal. Chim. Acta
Concomitant separation of strontium and samarium-neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography
Anal. Chim. Acta
Geomorphic evolution of the Piton des Neiges volcano (Réunion Island, Indian Ocean): competition between volcanic construction and erosion since 1.4Ma
Geomorphology
SKS splitting in the Western Indian Ocean from land and seafloor seismometers: plume, plate and ridge signatures
Earth Planet. Sci. Lett.
Geochemical provincialism in the Iceland plume
Geochim. Cosmochim. Acta
Origin and fate of sulfide liquids in hotspot volcanism (La Réunion): Pb isotope constraints from residual Fe–Cu oxides
Geochimica et Cosmochimica Acta
Short-term (1998–2006) fluctuations of Pb isotopes at Piton de la Fournaise volcano (Réunion Island): origins and constraints on the size and shape of the magma reservoir
Chem. Geol.
Pb isotope geochemistry of Piton de la Fournaise historical lavas
J. Volcanol. Geotherm. Res.
High-precision analysis of Pb isotope ratios by multi-collector ICP-MS
Chem. Geol.
Seismic images under 60 hotspots: search for mantle plumes
Gondwana Res.
Lead isotopes reveal bilateral asymmetry and vertical continuity in the Hawaiian mantle plume
Nature
The Geochemical Regimes of Piton de la Fournaise Volcano (Réunion) during the last 530 000 years
J. Petrol.
A mantle-derived origin for Mauritian Trachytes
J. Petrol.
Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius
Nat. Commun.
Magmatic Evolution of Mauritius, Western Indian Ocean
Petrology and geochemistry of Rodrigues Island, Indian Ocean
Contrib. Mineral. Petrol.
Structure, age et évolution du Bassin des Mascareignes, Océan Indien Occidental
Geochemical structure of the Hawaiian plume: Sr, Nd, and Os isotopes in the 2.8 km HSDP-2 section of Mauna Kea volcano
Geochem. Geophys. Geosyst.
Cited by (12)
An isotopically enriched mantle component in the source of Rodrigues, Réunion volcanic hotspot
2023, Geochimica et Cosmochimica ActaUpper mantle control on the W isotope record of shallow level plume and intraplate volcanic settings
2022, Earth and Planetary Science LettersOrigin and fate of hydrothermal fluids at Piton des Neiges volcano (Réunion Island): A geochemical and isotopic (O, H, C, Sr, Li, Cl) study of thermal springs
2020, Journal of Volcanology and Geothermal ResearchHeterogeneous Fossil Réunion Plume Component in the Source Region of Enriched MORB Along the Central Indian Ridge Between 12° and 17°S
2022, Journal of Geophysical Research: Solid Earth