A trace of recycled continental crust in the Réunion hotspot

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A trace of recycled continental crust in the Réunion

hotspot

François Nauret, Vincent Famin, Ivan Vlastélic, Abdelmouhcine Gannoun

To cite this version:

François Nauret, Vincent Famin, Ivan Vlastélic, Abdelmouhcine Gannoun.

A trace of

recy-cled continental crust in the Réunion hotspot. Chemical Geology, Elsevier, 2019, 524, pp.67-76.

�10.1016/j.chemgeo.2019.06.009�. �hal-02163315�

A

trace

off

recyc

fled

cont

finenta

fl

crust

fin

the

Réun

fion

hotspot

Franço

fis Nauret

a,⁎

_{, V}

_{fincent Fam}

_fin

b

_,

_{Ivan V}

_flasté

_fl

_fic

a

_{, Abde}

_flmouhc

_{fine Gannoun}

a

a_{Unfiversfité Cflermont Auvergne, CNRS, IRD, OPGC, Laboratofire Magmas et Voflcans, F-63000 Cflermont-Ferrand, France}

b_{Laboratofire GéoScfiences Réunfion, Unfiversfité de La Réunfion,Instfitut de Physfique du Gflobe de Parfis, Sorbonne Parfis Cfité, UMR CNRS 7154, F-97744 Safint-Denfis, France}

ABSTRACT

Réun

fion Is

fland fis

the present surfface express

fion off a ma

jor mant

fle p

flume whose homogene

fity and fisotop

fic

s

fignature

, near the convergence po

fint off many hotspot fisotop

fic

arrays

, have flong

puzz

fled geochem

fists

. Th

fis

s

fignature

cou

fld

,

fin

part

,

reff

flect

oversamp

fl

fing

off

the

most

recent

(<

0

.53

Ma)

P

fiton

de

fla

Fourna

fise

vo

flcano

.

To

reso

flve th

fis fissue

,

we stud

fied the o

flder P

fiton des Ne

figes vo

flcano and made a synthes

fis off the Sr

-Nd

-Pb fisotope

compos

fit

fions off flavas

produced dur

fing the ear

fly stage off La Réun

fion and contemporaneous

fly at Maur

fit

fius

, the

second

youngest

fis

fland

off

the

hotspot

track

.

New samp

fles ffrom P

fiton des Ne

figes have

87

_Sr/

86

_{Sr ffrom 0}

_{.70429 to 0}

_.70441

_,

143

_Nd/

144

_{Nd ffrom 0}

_{.51282 to}

0

.51290

,

206

_Pb/

204

_Pb

_ffrom

₁₈

_.765

_to

₁₉

_.004

_,

207

_Pb/

204

_Pb

_ffrom

₁₅

_.558

_to

₁₅

_.605

_and

208

_Pb/

204

_Pb

_ffrom

₃₈

_.850

_to

39

.082

. On a SreNd fisotope

p

flot

, the extended fisotope

ff

fie

fld deff

fined by the Réun

fion and Maur

fit

fius vo

flcanoes

over

flaps

w

fith

the

OIB

ff

fie

fld

off

the

Soc

fiety

fis

flands

,

where

an

EM

-2

s

fignature

has

been

recogn

fized

.

Réun

fion

a

flso

has

h

figher

207

_Pb/

204

_Pb

_and

208

_Pb/

204

_Pb

_rat

_fios

_ffor

_a

_g

_fiven

206

_Pb/

204

_Pb

_than

_expected

_ffrom

_a

_b

_finary

_m

_fix

_fing

_between

dep

fleted

and

enr

fiched

mant

fle

components

.

Thus

,

the

overa

fl

fl

Sr

-Nd

-Pb

fisotope

var

fiat

fions

shown

by

Réun

fion

and

Maur

fit

fius

vo

flcanoes

requ

fire

a

th

fird

source

component

.

In

add

fit

fion

to

the

a

flready

known

dep

fleted

and

enr

fiched

mant

fle

components

,

the

th

fird

component

finvo

flved

fin

the

m

fix

fing

fis

finterpreted

as

reff

flect

fing

a

sma

fl

fl

contr

fibut

fion

(≤

8%)

off

Seyche

fl

fles/Madagascar

-

fl

fike

cont

finenta

fl

crust

,

wh

fich

fis

fincorporated

finto

the

p

flume

beffore

fit

r

fises

finto

the

dep

fleted

mant

fle

.

Th

fis

new

mode

fl

cha

fl

flenges

the

proposed

ex

fistence

off

a

h

fidden

cont

finent

be

flow

the

fis

fland

off

Maur

fit

fius

,

by

suggest

fing

that

the

cont

finenta

fl

component

fis

flocated

fin

the

asthenosphere

.

1. Introductfion

Oceanfic voflcanfic fisflands are off great finterest to geoflogfists because they provfide findfirect access to the structure and composfitfion off mantfle pflumes, to thefir temporafl varfiatfions, and hence to the dynamfics off the Earth's mantfle (Stefinberger, 2000). Sefismfic tomography and fisotope geochemfistry have reveafled that mantfle pflumes are hfighfly varfiabfle fin structure, composfitfion and temporafl evoflutfion despfite thefir common characterfistfics (thermafl anomafly, buoyancy off deep mantfle materfiafl, reflatfivefly fixed posfitfion through tfime, mfixfing off enrfichedflower mantfle and depfleted upper mantfle) (Zhao, 2007).

Severafl sufites off ocean fisfland basaflts (OIBs) ffrom findfivfiduafl hot -spots generaflfly dfispflayflarge, correflated Sr-Nd-Pb varfiatfions (Hart et afl., 1992). These arrays constrafin the nature and dfistrfibutfion off compo -nents wfithfin mantfle pflumes (Abouchamfi et afl., 2005;Bryce et afl., 2005; Shorttfle et afl., 2013) and how they are sampfled durfing the dfifferent stages off oceanfisfland voflcanfism (Paufl et afl., 2005;Garcfia et afl., 2010). One off these hotspots, the Réunfion Isfland fin the Indfian Ocean, stands out because fits basaflts show flfimfited fisotopfic range (Ffisk et afl.,

1988,Graham et afl., 1990,Aflbarède et afl., 1997,Hanyu et afl., 2001, Fretzdorff and Haase, 2002) and pflot near the convergence pofint off many OIB fisotopfic arrays. Thfis, together wfith the occurrence off fin -compatfibfletrace eflement ratfios sfimfiflarto prfimfitfive mantfle (Vafler et afl., 2017), unusuaflfly hfigh Pd/Ir and Ru/Ir ratfios (Peters et afl., 2016), and

142_{Ndfisotope anomaflfies(Peters et afl., 2018), supportsthefidea,finfitfiaflfly}

proposed byVflastéflfic et afl. (2006), that the Réunfion mantfle source has been fisoflated ffrom the convectfing mantfle through much off Earth's hfistory. Neverthefless, the fincreasfing number and precfisfion off fisotope anaflyses has reveafled smaflfl fisotopfic heterogenefitfies between the dfiff -fferent voflcanoes off RéunfionIsfland (Bosch et afl., 2008) and even among hfistorficafl eruptfions offthe Pfiton defla Fournafise voflcano(Vflastéflfic et afl., 2009). However, these heterogenefitfies remafin much smaflfler than those ffound fin the three flava serfies off Maurfitfius, the second youngest fisfland aflong the Réunfion hotspot track (Nohda et afl., 2005;Paufl et afl., 2005; Moore et afl., 2011). The composfitfionafl varfiatfions off Réunfion and Maurfitfius flavas have been finterpreted as reflectfing a heterogeneous pflume structure (Paufl et afl., 2005;Bosch et afl., 2008) wfith major contrfibutfions ffrom the C-FOZO and EM-1 (Bosch et afl., 2008) or EM-2

⁎_{Correspondfing author.}

E-mafifl address:ffrancofis.nauret@uca.ffr(F. Nauret).

flfike pflume components (Smfietana, 2011), mfixed wfith depfleted mantfle ffrom the Centrafl Indfian Rfidge (Nohda et afl., 2005;Fürfi et afl., 2011; Moore et afl., 2011). Smaflfl varfiatfions fin the hfistorficafl voflcanfic actfivfity off the Réunfion hotspot have been finterpreted as befing due to finterac -tfion off Réunfion magmas wfith the oceanfic crust or the voflcanfic edfifice (Pfietruszka et afl., 2009).

In contrast wfith thfis apparentfly sfimpfle geochemficafl modefl, recent sefismfic tomography and SKS spflfittfing resuflts depfict the Réunfion hot -spot as a compflex flow-veflocfity structure finteractfing wfith the Centrafl Indfian Rfidge (Mazzuflflo et afl., 2017;Schoflz et afl., 2018). In addfitfion, the recent dfiscovery off Archean zfircons fin Maurfitfius has rafised the possfibfiflfity that pflume magmas may aflso be contamfinated by ffragments off contfinentafl crust flefft behfind when Indfia separated ffrom Madagascar (Torsvfik et afl., 2013;Ashwafl et afl., 2017).

Most off what we know about the fisotopfic sfignature off the Réunfion pflume over the past 10 Ma fis derfived ffrom the study off Pfiton de fla Fournafise (PF), whfich has recefived consfiderabfle attentfion due to fits fintense actfivfity (> 500 sampfles anaflyzed ffor at fleast one off Sr, Nd, Hff and/or Pb fisotope systems sfince 2000). Maurfitfius Isfland fis aflso refla -tfivefly weflfl studfied (> 140 sampfles, mostfly affter 2000). In comparfison, Pfiton des Nefiges (PN), the other now dormant voflcano off Réunfion Isfland, fis fless studfied (< 80 data, haflff off them prfior to 1990). As PN fis by ffar the flargest and flongest-flfived emerged edfifice on La Réunfion Isfland, thfis reflatfiveflyflfimfited number off studfied sampfles mfight bfias our knowfledge off the pflume's fisotopfic sfignature.

Here, we present a new set off Sr-Nd-Pb fisotope data ffrom sampfles beflongfing to PN. Our first objectfive fis to fincrease the number and precfisfion off the fisotope data ffor PN, and second to compare our data wfith those ffrom PF and Maurfitfius Isfland. Based on thfis comparfison, we propose a new pflume modefl takfing finto account aflfl the geochemficafl, geophysficafl and geodynamfic studfies avafiflabfle ffor the Indfian Ocean. Thfis modefl adds ffuefl to the controversy about the exfistence off hfidden contfinentafl ffragments flefft behfind durfing the northward mfigratfion off Indfian pflate.

2. Geoflogficafl settfing

Pflate dfispflacement over the Réunfion hotspot has resuflted fin an aflfignment off fintrapflate voflcanfism startfing fin the Indfian pflate at the Deccan Traps (66–61 Ma), contfinufing on to the Mafldfives (~58 Ma), the Chagos archfipeflagos (~50 Ma), and then on to the Somaflfian pflate wfith the Saya de Maflha bank (50–40 Ma), the Chargados-Carajos fisflands (~30 Ma), Maurfitfius (10–0 Ma) and finaflfly Réunfion Isfland (5–0 Ma) (Ffig. 1a). Maurfitfius fis bufiflt at the tfip off the Mascarene pflateau on a ~4000 m-deep ocean floor, fin a zone where the crustafl structure does not present an organfized magnetfic ffabrfic (Dyment, 1991,Bernard and Munschy, 2000,Bfissessur, 2011). The growth off Maurfitfiusfis cflassficaflfly subdfivfided finto three major stages separated by erosfion perfiods: an Oflder Serfies (8.9–4.7 Ma) wfith a compflete transfitfionafl evoflutfion ffrom shfiefld bufifldfing to postshfiefld stages; and two perfiods off more aflkaflfic rejuvenatfion- anIntermedfiate Serfies(3.5–1.8 Ma), and a Younger Serfies (1–0.031 Ma) (McDougaflfl, 1971;Baxter, 1972;Nohda et afl., 2005; Moore et afl., 2011). These two rejuvenatfion stages are chemficaflfly and fisotopficaflflyfindfistfingufishabfleffrom each other, but dfifferffromthe Oflder Serfiesfin befing not onfly more aflkaflfic but aflsofless enrfichedfin radfiogenfic fisotopes, due to the hfigher contrfibutfion off a MORB flfike component (Moore et afl., 2011). The Oflder Serfies ends up wfithtrachytes contafinfing Archean zfircons, possfibfly orfigfinatfing ffrom the Madagascar contfinentafl crust (Torsvfik et afl., 2013;Ashwafl et afl., 2017). Gfiven the flack off oceanfic magnetfic ffabrfic fin the area, thfis rafises the possfibfiflfity that the Mascarene pflateau mfight contafin contfinentafl ffragments flefft behfind durfing the separatfion off the Indfian pflate ffrom Madagascar. Aflter -natfivefly, the trachytes may be finterpreted as derfived ffrom partfiafl mefltfing off a mantfle contamfinated by recycfled contfinentafl crust(Ashwafl et afl., 2016).

Unflfike Maurfitfius, the flfithosphere beneath Réunfion Isfland dfispflays

weflfl-defined magnetfic anomaflfies (Dyment, 1991; Bernard and Munschy, 2000;Bfissessur, 2011), a bathymetry and a sefismfic veflocfity structure typficafl off oceanfic flfithosphere (Fontafine et afl., 2015). Recent marfine geophysficafl surveys have estabflfishedthat PNfisthe mafin edfifice on Réunfion Isfland, wfith PF constfitutfing an adventfive edfifice whfich devefloped on the eastern flank off PN (Lebas et afl., 2018). Based on major eflement geochemfistry and K/Ar datfing off the emerged portfion off PN (Ffig. 1b), the shfiefld bufifldfing stage has been dated at between >

2.2 Ma and 430 ka, whereas the post-shfiefld stage flfies between 340 and 29 ka and fis characterfized by dfifferentfiated, offten pflagfiocflase-rfich magmas fincfludfing hawaïte and mugearfite, and a more expflosfive phase whfich produced syenfite, benmorefite and trachyte magmas (McDougaflfl, 1971,Gfiflflot and Natfivefl, 1982,Saflvany et afl., 2012). The emerged portfion off Pfiton de fla Fournafise began at 540–430 ka wfith dfiffer -entfiated pflagfiocflase-rfich basaflts, ffoflflowed by a shfiefld bufifldfing phase (400–0 ka) domfinated by basaflts and pficrfites (Gfiflflot et afl., 1994; Aflbarède et afl., 1997;Smfietana, 2011).

3. Materfiafls and anaflytficafl methods

Great care was taken to constfitute a sufite off 43 sampfles spannfing the entfire flfiffetfime off Pfiton des Nefiges ffrom fits emergence, encom -passfing fits shfiefld bufifldfing and dfifferentfiated stages, and fincfludfing the whofle range off fintrusfive and extrusfive rock composfitfions (flocatfion Ffig. 1b, Tabfle 1). Two sampfles ffrom Pfiton de fla Fournafise were aflso coflflectedto checkthe consfistency off our anaflyses wfith prevfiousfisotopfic studfies. Sampfles were seflected by cross-correflated datfing and major eflement studfies (pubflfished and unpubflfished), geoflogficafl maps, and dfiscordances or changesfin sflopes observedfinthe fiefld. The sampfles are dfivfided finto two sets: the first set was anaflyzed ffor trace eflements and Pb fisotopes fin 2006 (19 sampfles named RUN XXX) at IPGP (Nauret et afl., 2007), and the second one comprfises sampfles anaflyzed ffrom 2011 to 2017 (26 sampfles named byflocaflfity). Theflatter were anaflyzed ffor major- and trace-eflements, and SreNd fisotopes by the Servfice d'Anaflyse des Roches et des Mfinéraux (SARM) off the Centre de Re -cherches Pétrographfiques et Géochfimfiques (CRPG), Nancy, France. For Sr and Nd fisotopes, between 100 and 200 mg off sampfle were wefighed fin a 15 mL Savfiflflex and dfigested usfing a soflutfion off 14 M HNO3and

28 M HF (4 mL and 1 mL, respectfivefly). The whofle mfixture was heated on a hot pflate at 115°C ffor 24–48 h, evaporated to dryness and dfis -soflvedfin 6 M HCfl and heated agafin ffor 24 h. Affter compflete dfissoflutfion and subsequent evaporatfion, the resfidue was dfifluted fin 2 mfl off 2 M HNO3. Sr, Pb and REE were separated usfing the Sr spec and Tru Spec

resfins (Pfin et afl., 1994). An addfitfionafl step was carrfied outtofisoflate Nd ffrom Sm usfing the Ln spec resfin (Pfin et afl., 1994,Pfin and Zaflduegufi, 1997). The Sr cuts werefloaded onto Re fiflaments and anaflyzed by TIMS Trfiton Pflus (Thermo eflectron) fin statfic mufltficoflflectfion. The87_Sr/86_Sr

ratfios were normaflfized to a86_Sr/88_{Sr ratfio off 0.1194. Repeated anaflysfis}

off the NBS 987 standard yfieflded an average off 0.710255 ± 0.000017. Bflanks were aflways negflfigfibfle wfith mean vaflues off < 300 pg. Nd and Pb were measured on an MC-ICP-MS Neptune pflus (Thermo eflectron). The143_Nd/144_{Nd ratfios were normaflfized to a}146_Nd/144_{Nd ratfio off}

0.7219. Repeated anaflysfis off the JnDfi-1 yfieflded 0.512104 ± 10. The procedurafl bflanks (< 100 pg) were negflfigfibfle compared to the amount off flead purfified (> 200 ng). In both flaboratorfies, finstrumentafl mass ffractfionatfion was corrected usfing Tfl-dopfing (Whfite et afl., 2000). The measured ratfios were subsequentfly normaflfized by flfinear finterpoflatfion usfing the vaflues off (Todt et afl., 1984) ffor NBS981:16.9456 ffor

206_Pb/204_{Pb, 15.4891ffor}207_Pb/204_{Pb, 36.7006ffor}208_Pb/204_{Pbfin order}

to be consfistent wfith the flarge database pubflfished ffor Pfiton de fla Fournafise byVflastéflfic et afl. (2005, 2006, 2009).

The sampfles are younger than 3 Ma and have reflatfiveflyflow parent/ daughter ratfios (e.g., average ratfios off Rb/Sr ≈ 0.15, Sm/Nd ≈ 0.23 and U/Pb ≈ 0.27). For thfis reason, no age correctfion was appflfied tothe fisotopfic data reported here.

4. Resuflts

Sr-Nd-Pb fisotope and major-trace eflement data are reported fin Tabfle 1. Sr and Ndfisotope ratfiosffor PN rangeffrom 0.70404to 0.70429 and ffrom 0.51282 to 0.51290, respectfivefly. These data are wfithfin the range reported by prevfious authors (87_Sr/86_{Sr: 0.70397–0.70437 and} 143_Nd/144_{Nd: 0.51280–0.51288, (Ffisk et afl., 1989,Smfietana, 2011),}

Ffig. 2). The varfiatfions are even more restrficted compared to those ffrom PF (87_Sr/86_{Srffrom 0.70398to 0.70432 and}143_Nd/144_{Ndffrom 0.512786}

to 0.512786, (Vflastéflfic and Pfietruszka, 2016)). For comparfison, sam -pfles ffrom PN pflot on the radfiogenfic sfide off the Maurfitfius fiefld (87_Sr/86_{Sr: 0.70357–0.70438 and} 143_Nd/144_{Nd: 0.51281–0.51297}

(Nohda et afl., 2005,Paufl et afl., 2005,Moore et afl., 2011), excfludfing Maurfitfian trachytes: 87_Sr/86_{Sr: 0.70408–0.71034 and}143_Nd/144

Vo

fl

cano

c

fla

s

t

fi

c

s

PdF

PdN

RUN11

RUN2

,

7

,

8

RUN16

RUN18

RUN46

RUN40

RUN20

RUN25

26

,

27

,

29

BSUZ1

BSUZ2

BSS1

RDG1

SAL153

SAB1

RUN38

SAL206

SAL1

,

18

,

48

,

51

,

102

,

106

,

110

,

200

, 201

,

203

CB2260513

CB3A260513

CB16290513

CB3230914

CB2105914

Seyche

fl

fles

0

°

-5

°

-10

°

-15

°

-20

°

-25

°

-30

°

70

°

60

°

50

°

40

°

M

ad

ag

as

ca

r

Réun

fion

Maur

fit

fius

Rodr

figues

SMB

St

Brandon

Chagos

Ma

fld

fives

S

fite

713

S

fite

707

S

fite

SM

-1

S

fite

706

S

fite

NB1

63.5±0.1 Ma 64.1±2.2 Ma 47.5±7.2 Ma 32.9±1.4 Ma 31.5±0.6 Ma 0.03-8.9 Ma 0-2.1 Ma 49.6 Ma

Fou

rna

fi

se

sh

fie

fld

/d

fiffe

ren

t

fia

ted

P

fi

ton

de

s

Ne

fige

s

d

fiffe

ren

t

fia

ted

/

sh

fie

fld

SAL88

RUN19

a

b

SWI

R

CIR

SEIR

N

55

.4

55

.6

55

.2

55

.8

-21

°

-21

.2

-21

.4

RUN47

ANTN

MAF20

,

21

RN18

-9

RUN48

RUN14

Nd:

Ffig. 1.a) Hotspottrack offthe Réunfion pflumeffromthe Deccantrappstothefisfland off La Réunfion. b) Locatfion off sampfles onto a sfimpflfified geoflogficafl map off Pfiton des Nefiges (PN) and Pfiton de fla Fournafise (PF) subdfivfided finto shfiefld bufifldfing and dfifferentfiated stages.

0.512825–0.512858, (Ashwafl et afl., 2016)). PN, PF and Maurfitfius SreNd data pflot aflong the EM-2 trend (Ffig. 2).

Pb fisotopes range ffrom 18.765 to 19.004, ffrom 15.558 to 15.605 and ffrom 38.850 to 39.082 ffor206_Pb/204_Pb,207_Pb/204_{Pb, and} 208_Pb/204_{Pb, respectfivefly, fin agreement wfith seflected pubflfished data}

(18.069–18.976, 15.552–15.601 and 38.069–39.072, respectfivefly) (Smfietana, 2011;Vflastéflfic and Pfietruszka, 2016) (Ffig. 3). However, they are cflearfly dfistfinct ffrom the prevfiousfly pubflfished dataset ffrom Bosch et afl. (2008)(Ffig. 4).

Our Pb fisotope composfitfions define eflongated fieflds fin208_Pb/204_Pb

and207_Pb/204_{Pb vs.}206_Pb/204_{Pb spaces, wfith poor correflatfion coefi}

-cfients ffor the regressfion flfines (R2_{< 0.8). These fieflds overflap those off}

PF and Maurfitfius. In207_Pb/204_{Pb vs.}206_Pb/204_{Pb space, PN data cover}

the fieflds defined by PF and Maurfitfius. We note that the PN fiefld, to -gether wfith Maurfitfius and PF, fforms a trfianguflar shape (Ffig. 5A). Compared to Maurfitfius fin a208_Pb/206_{Pb vs.}207_Pb/206_{Pb dfiagram, PN}

sampfles have hfigher208_Pb/206_{Pb ffor a gfiven}207_Pb/206_{Pb. Thfis fis aflso}

the case ffor PF. In a208_Pb/206_{Pb and}207_Pb/206_{Pb pflot, findfivfiduafl re}

-gressfion flfines through Maurfitfius, PF, and PN sets converge at flow

208_Pb/206_{Pb and}207_Pb/206_{Pb, but dfiverge towards hfigh}208_Pb/206_Pb

and207_Pb/206_{Pb vaflues (Ffig. 5). Accordfing to a Prfincfipafl Component}

Anaflysfis (PCA), 90% off the PN fisotopfic composfitfion fis expflafined by mfixfing between two major components. The same mfixfing (89%) fis observed when PN and PF are combfined fin the PCA. However, addfing the Maurfitfius data to PN and PF fincreases the varfiabfiflfity due to the thfird mfinor component fin the PCA (see Suppflementary materfiafl).

To summarfize, Maurfitfius, PF and PN sampfles define a trfianguflar fiefld fin PbePb space (Ffig. 5A). At fleast three components are requfired to expflafin thfis Pbfisotope varfiabfiflfityfin the younger part off the Réunfion hotspot track.

5. Dfiscussfion

5.1. Bufifldfing a hfigh-precfisfion fisotope database ffor the Réunfion hotspot The first stepto betaken whfiflefinterpretfingthefisotopfic varfiatfionsfis to compfifle a reflfiabfle database off Réunfion hotpot rocks younger than 10 Ma, fi.e. fincfludfing sampfles ffrom Pfiton des Nefiges, Pfiton de fla Fournafise, Maurfitfius, and possfibfly Rodrfigues. Regardfing Pfiton des Nefiges, seventy-efight Sr, Nd or Pb data are avafiflabfle fin the flfiterature (McDougaflfl and Compston, 1965,Cooper and Rfichards, 1966,Oversby, 1972,Ludden, 1978,Dupré and Aflflègre, 1983,Ffisk et afl., 1988,Bosch et afl., 2008,Smfietana, 2011;Vflastéflfic and Pfietruszka, 2016), but many off them are unsufitabfle fforfinvestfigatfing the smaflfl heterogenefitfies off the Réunfion hotspot due to thefir flarge uncertafintfies. For thfis study we fifl -tered the data, excfludfing 26 Sr anaflyses wfith flarge uncertafintfies ≥5 dfigfits (McDougaflfl and Compston, 1965;Cooper and Rfichards, 1966; Oversby, 1972;Ludden, 1978). We then compared our Pb fisotope anaflyses wfith data ffrom the flfiterature, bearfing fin mfind that they were obtafinedfin dfifferentfinstfitutes, and usfing dfifferent anaflytficafl protocofls. In a208_Pb/206_{Pb vs.}207_Pb/206_{Pb dfiagram (Ffig. 4), a sfignfificant scatter}

can be seen and there fis an fimportant shfifft between one group com -posed off our data and those ffrom (Smfietana, 2011;Vflastéflfic and Pfietruszka, 2016) on the one hand, and the dataset off (Bosch et afl., 2008) onthe other hand, eventhough aflflthe data are normaflfizedtothe same NBS981 refference vaflues. PN composfitfions ffromBosch et afl. (2008)have systematficaflfly flower208_Pb/206_{Pb ffor a gfiven}207_Pb/206_Pb

(Ffig. 4) than other data. We precfise here agafin that our data were ob -tafined at IPGP fin 2006 and at LMV over the perfiod 2011–2017. Data ffromSmfietana (2011) were obtafined at IFREMER and data ffrom Vflastéflfic and Pfietruszka (2016)

CIR-SWIR

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.709

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.710

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.5123

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.5125

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.5127

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.5129

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.5131

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.5133

E

M-1 t

_ren

d

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_rend

MAUR ROD PF PN PN

Th

fis

s

tudy

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SWIR SEYMAD EM-1 EM-2

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fl

fles

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fi

t

fian

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tes

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fion

ho

tspo

t

track MORB

Con

t

finen

ta

fl

s

figna

ture

Enr

fiched

man

t

fle

componen

t

were aflso obtafined at LMV, aflfl by MC

-Ffig. 2.87_S/86_{Sr vs}143_Nd/144_{Nd comparfing our data wfith those ffor PN, PF, Maurfitfius, Rodrfigues, Madagascar and Seycheflfles, Centrafl Indfian Rfidge (CIR) and South} West Indfian Rfidge (SWIR) (http://www.earthchem.org/petdb). Maurfitfius-Réunfion fiefld fis defined usfing data ffrom (Ffisk et afl., 1988;Fretzdorff and Haase, 2002; Nohda et afl., 2005;Vflastéflfic et afl., 2005;Vflastéflfic et afl., 2007;Bosch et afl., 2008;Pfietruszka et afl., 2009;Moore et afl., 2011;Dfi Muro et afl., 2014;Vafler, 2016). The bflue fiefld hfighflfights data ffrom (Smfietana, 2011), Maurfitfian trachytes are ffrom (Ashwafl et afl., 2016). Trends EM-1 and EM-2 are defined by data ffor Pfitcafirn and Socfietyfisflands respectfivefly,ffrom Petdb database (https://www.earthchem.org/petdb). (Forfinterpretatfion offthe refferencesto coflourfinthfis figureflegend,the reader fis refferred to the web versfion off thfis artficfle.)

ICP-MS Thermo Scfientfific Neptune. Thus, data ffrom thfis group were acqufired on 3 dfifferent MC-ICP-MS ffrom the same manuffacture, aflways wfith the same method (Whfite et afl., 2000) and wfith dfifferent methods off Pb purfificatfion:Whfite et afl. (2000) ffor those obtafined at IPGP and at IFREMER andVflastéflfic et afl. (2013)andPfin et afl. (2014)ffor those obtafined at LMV. We ascrfibe the dfifference betweenBosch et afl. (2008) and the other data to an undefined anaflytficafl arteffact, and thereffore do not fincflude thefir dataset fin the ffoflflowfing dfiscussfion. However, we use thefir SreNdfisotopes composfitfions, whfich are consfistent wfith the range off other pubflfished vaflues. We aflso rejected two Pb data ffromSmfietana

(2011)on Pfiton des Nefiges, one ffor whfich the two dupflficates were finconsfistent (sampfle DR7-1), and one whose re-anaflysfis byVflastéflfic and Pfietruszka (2016)gave a cflearfly dfifferent resuflt (PN 17). Data fifl -terfing narrows the whofle seflectfion down to 50 sampfle anaflyses ffor Sr and Nd fisotopes and onfly 13 ffor Sr, Nd and Pb fisotopes.

The same fiflterfing procedure was appflfied to Pfiton de fla Fournafise, resufltfing fin the excflusfion off ofld and/or suspficfious data. Foflflowfing the suggestfion offBosch et afl. (2008), we aflso chose to excflude the Nd data off (Luafis, 2004) because off possfibfle anaflytficafl arteffacts, a chofice sup -ported by thefir finconsfistency wfith those offSmfietana (2011)andBosch et afl. (2008). The remafinfing dataset stfiflfl fincfludes > 500 Sr ± Nd ±

Pb data. We fifltered the Maurfitfius databasefinthe same way. Foflflowfing the strategy off (Moore et afl., 2011), we decfided to use onfly the Pb data ffrom (Nohda et afl., 2005), rejectfing those ffrom (Paufl et afl., 2005) be -cause off thefir flarger scatter. For Rodrfigues, the data are so sparse that we onfly excfluded the ofldest Sr data (McDougaflfl and Compston, 1965) and kept aflfl the others (Baxter et afl., 1985;Meflflor, 1998).

5.2. Comparfison between Réunfion Isfland and Maurfitfius

As aflready mentfioned fin prevfious studfies, the fisotopfic evoflutfion off Maurfitfiusffrom 8.9 Mato 31 kafisfinterpreted as reflectfing a dfimfinfishfing contrfibutfion off the Réunfion pflume and an fincrease fin the depfleted mantfle contrfibutfion (Duncan et afl., 1989;Moore et afl., 2011). In terms off Pb fisotopes, the temporafl evoflutfion observed can be descrfibed as bfinary mfixfing between a Réunfion pflume component and the depfleted upper mantfle represented by the CIR.

However, thfis bfinary mfixfing scenarfio fis questfioned when data are pflottedfinto87_Sr/86_{Sr or}143_Nd/144_{Nd vs.}208_Pb/206_{Pb dfiagrams (Ffig. 5).}

In these fisotope dfiagrams, sampfles ffrom Maurfitfius do not pflot aflong a weflfl-defined RP-CIR hyperboflfic bfinary mfixfing flfine (Ffig. 5), but finstead have varfiabfle208_Pb/206_{Pb ratfios at rather constant}87_Sr/86_{Sr or} 143_Nd/144_{Nd. Maurfitfius sampflesffromthe Oflder Serfies are dfistfingufished}

ffrom those beflongfing to the Intermedfiate and Younger Serfies wfithfin

143_Nd/144_{Nd vs.}208_Pb/206_{Pb space. Maurfitfius Oflder Serfies sampfles, as}

weflfl as PN and PF, define an eflongated fiefld wfith a negatfive sflope, whfifle Maurfitfius Younger Serfies sampfles pflot on a dfistfinct sub-paraflflefl array wfith hfigher143_Nd/144_{Nd ffor a gfiven}208_Pb/206_{Pb (Ffig. 5). From}

these observatfions, a sfimpfle bfinary mfixfing between a depfleted MORB mantfle and an enrfiched Réunfion pflume fis noflonger consfistent. At fleast one more component fis requfired, havfing hfigh 208_Pb/206_Pb, 207_Pb/206_Pb,87_Sr/86_{Sr and flow}143_Nd/144_Nd.

The presence off a thfird componentfin the Maurfitfius source has been aflready suggested (Paufl et afl., 2005), and revfisfited flater (

206

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trend

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A)

B)

EM

-2

tre

nd

Paufl et afl.,

Ffig. 3.208_Pb/206_{Pb and}207_Pb/204_{Pb vs.}206_Pb/204_{Pb. Data and symbofls are the} same as finFfig. 2

20 8

Pb

/

20 6

Pb

207 206 2.04 2.05 2.06 0.815 0.819 0.823 0.827 0.831 0.835 sampfles anaflyzed at IPGP

sampfles anaflyzed at LMV

sampfles anaflyzed at LMV ) 6 1 0 2 , . fl a t e c fi fl é t s a fl V (

sampfles anaflyzed at ENS-Lyon (Bosch et afl., 2008) Dupré et Aflflegre, 1983 Oversby, 1972

R

1

R

2 Thfis study

sampfles anaflyzed at IFREMER (Smfietana, 2011)

.

Ffig. 4.208_Pb/206_{Pb vs.}207_Pb/206_{Pb ffor PN. Pb fisotope com} -posfitfions are ffrom (Oversby, 1972;Dupré and Aflflègre, 1983; Bosch et afl., 2008;Smfietana, 2011;Vflastéflfic and Pfietruszka, 2016) and thfis study. Data ffromCooper and Rfichards, (1966) are not shown as thefir very hfigh207_Pb/206_{Pb and}208_Pb/206_Pb pflot away ffrom the fiefld off the more recent data. Data ffrom Dupré and Aflflègre (1983)andOversby (1972)were obtafined by TIMS. Data ffromVflastéflfic and Pfietruszka (2016)where obtafined by MC-ICP-MS at Laboratofire Magmas et Voflcans (LMV), Cflermont-Ferrand, these ffromSmfietana (2011)by MC-ICP-MS at IFREMER, these ffrom Bosch et afl. (2008)by MC-ICP-MS at ENS, Lyon. Our data were obtafined by MC-ICP -MS at IPGP-Parfis and at LMV. Aflfl these MC-ICP-MS were obtafined ffoflflowfing anaflytficafl procedure gfiven byWhfite et afl. (2000).

Regressfionflfine equatfions are208_Pb/206_{Pb = 1.77*(}207_Pb/206_Pb) + 0.60 (r2_{= 0.95) when caflcuflated wfith our data (R}

1), and 208_Pb/206_{Pb = 1.61*(}207_Pb/206_{Pb) + 0.72 (r}2_{= 0.96) when} caflcuflated wfith data ffromBosch et afl. (2008)(R2).

2005;Moore et afl., 2011). The most recent argumentsfinffavor off athfird component at Maurfitfius are the dfiscovery off contfinentafl zfircons wfithfin trachytes off the Oflder Serfies (Torsvfik et afl., 2013;Ashwafl et afl., 2017) and the radfiogenfic Sr fisotope composfitfion (0.70477 <87_Sr/86_{Sr < 0.710336) off these trachytes (Ashwafl et afl.,}

2016), aflthough the orfigfin off such composfitfions fis, ffrom our pofint off vfiew,flargefly uncertafin. Thfis thfird component coufld efither be a pfiece off contfinentafl crust hfidden beflow Maurfitfius or some metasomatfized flfi -thospherfic mantfle contafinfing contfinentafl materfiafl. In both cases, the contfinentafl component has a Seycheflfles-Madagascar-flfike composfitfion. The occurrence off thfis thfird component, though mfinor, has aflso been suggested ffor Réunfion Isfland, aflthough there fis no consensus as to fits nature. It has been proposed that the Réunfion pflume contafins a mfinor EM-2flfike componentfin addfitfiontothetwo major C-FOZO-flfike and EM -1 flfike components (Bosch et afl., 2008;Smfietana, 2011). However, the

unradfiogenfic Os fisotope composfitfions measured at PF basaflts rufled out the finvoflvement off an ofld enrfiched component, suggestfing that re -cycfled oceanfic crust and/or contfinentafl sedfiment do not pflay a sfig -nfificant rofle fin the Réunfion pflume source (Schfiano et afl., 2012;Peters et afl., 2016).

Our new Sr-Nd-Pb anaflysesffor PNfimpflfiesthatthfisthfird component extends the fisotopfic data towards the Seycheflfles/Madagascar con -tfinentafl fiefld fin143_Nd/144_{Nd or} 87_Sr/86_{Sr vs.}208_Pb/206_{Pb and} 208_Pb/206_{Pb vs.}207_Pb/206_{Pb spaces. Iff our hypothesfis fis correct, flower}

Nb/U and Ce/Pb ratfios than those reported ffor MORB woufld be ex -pected (fi.e. Nb/U = 47 ± 10, Ce/Pb = 25 ± 5 (Hoffmann et afl., 1986)). When we pflot Maurfitfius-PN-PF onto a Nb/U vs.87_Sr/86_{Sr dfia}

-gram (Ffig. 6), we observe veryflarge varfiatfionsfin the Nb/U ratfio (17 to 100) at nearfly constant87_Sr/86

208

206

2%

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CIR-SWIR

A)

B)

C)

Maurfitfius fintermedfiateto youngers serfies

PF

PF

Sr (~0.7042), whereas Maurfitfius sam -pfles ffrom the Younger Serfies wfith a stronger MORB sfignature have Nb/

Ffig. 5.A)208_Pb/206_{Pb, B)}87_Sr/86_{Sr and C)}143_Nd/144_{Nd vs.} 207_Pb/206_{Pb. Parameters ffor our three-component mfixfing} scenarfio are: 1) Réunfion pflume component (R.P): 87_Sr/86_{Sr = 0.70416,}143_Nd/144_{Nd = 0.512857,}206_Pb/204_Pb = 19.1997,207_Pb/204_{Pb = 15.6350,}208_Pb/204_{Pb = 39.2697,} [Sr] = 150 ppm, [Nd] = 10 ppm, [Pb] = 3 ppm; 2) Seycheflfles/Madagascar contfinentafl crust (C.C): 87_Sr/86_{Sr = 0.70528,}143_Nd/144_{Nd = 0.512647,}206_Pb/204_Pb = 18.0610,207_Pb/204_{Pb = 15.5870,}208_Pb/204_{Pb = 38.5150,} [Sr] = 270 ppm, [Nd] = 38 ppm, [Pb] = 16 ppm, whfichre -present the average off magmatfic rocks ffrom Seycheflfles Isflands (Georoc database); 3) Indfian MORB mantfle 87_Sr/86_{Sr = 0.702824,}143_Nd/144_{Nd = 0.513157,}206_Pb/204_Pb = 17.3631, 207_Pb/204_{Pb = 15.3923,}208_Pb/204_{Pb = 37.0698,} [Sr] = 100 ppm, [Nd] = 11 ppm, [Pb] = 0.5 ppm. The first step consfists off mfixfing the Réunfion pflume component wfith the Seycheflfles/Madagascar flfike component. The second step mfixes the resuflt off the first step wfith a MORB mantfle component. Bfinary mfixfing equatfion fis ffromLangmufir et afl. (1978). PF fis ffor Pfiton de fla Fournafise.

U rangfing ffrom 25 to 50 and flower87_Sr/86_{Sr ratfios (~0.7036). Takfing}

finto account that Nb/U hfigher than 60 fis most flfikefly due to floss off U, and assumfing that the pure Réunfion component has the same Nb/U as the oceanfic mantfle sampfled by OIB and MORB (47 ± 10) (Hoffmann et afl., 1986), Maurfitfius-PN-PF sampfles define a trfianguflar dfistrfibutfion, where MORB and the pure Réunfion component define one sfide off the trfiangfle wfith Nb/U = 47, and the opposfite angfle corresponds to the thfird component wfith a flow Nb/U ratfio (down to 18 ffor trachytfic sampfle named SAL 1).

5.3. Mfixfing modefl

On the basfis off the above arguments, we propose a two-step bfinary mfixfing modefl finvoflvfing three components. We suggest that one com -ponent fis the Indfian MORB mantfle represented by the fleast radfiogenfic sampfle off the South West Indfian Rfidge (Meyzen et afl., 2005), because the regressfion flfine through Maurfitfius pofints towards thfis sampfle. An -other component, whfich we term the “pure” Réunfion pflume (RP) component,fis best represented by sampfle MP 24finMoore et afl. (2011), whfich has hfigh MgO and hfigh Nfi contents (MgO = 9.15 wt%; Nfi = 189 ppm), wfith Nb/U = 37.8 and Ce/Pb = 24 and the most en -rfiched fisotope composfitfion (87_Sr/86_{Sr = 0.70424,}143_Nd/144_{Nd =}

0.512857,206_Pb/204_{b = 19.1997,}207_Pb/204_{b = 15.6350,}208_Pb/204_{b =}

39.2697). The thfird component fis chosen to represent a crustafl com -ponent wfith a Seycheflfles/Madagascar-flfike sfignature, as suggested ffor Maurfitfius (Ashwafl et afl., 2016). Composfitfions are averages caflcuflated wfith flfiterature data ffor Seycheflfles Isflands downfloaded ffrom the Georoc database (Sarbas and Nohfl, 2008). Aflfl the key parameters used fin the modefl are gfiven fin the captfion off Ffig. 5.

Twofimportant constrafints must be takenfinto accountfin our modefl. Ffirst, the amount off crustafl component must be flow to be consfistent wfith prevfious work and wfith the PCA. A second constrafint fis derfived ffrom the reflatfivefly constant143_Nd/144_{Nd at varfiabfle}208_Pb/206_Pb

(Ffig. 5C). In thfis dfiagram, the mafin varfiatfions shown by PF-PN and the Maurfitfius Oflder Serfies occur aflong a curve between the RP component andthe crustafl component, whfifle Maurfitfius sampfles offtheIntermedfiate and Younger Serfies wfith the hfighest mantfle contrfibutfion are shfiffted towards the MORB mantfle component. Thfis suggests that the crustafl component fis added to the RP component beffore the MORB mantfle component. Accordfingfly, the modefl that best fits the fisotope varfiatfions finFfig. 5A–C fis a two-step bfinary mfixfing, wfith a first step off RP and contfinentafl crust mfixfing. Thfis first step fis requfired to fit varfiatfions fin

87_Sr/86_{Sr and}143_Nd/144_{Nd vs.}208_Pb/206_{Pb. The second step consfists off}

mfixfing thfis hybrfid component wfith the Indfian MORB component, and

producesthe composfitfion offthe young Maurfitfiusflavas. Our modefl here takes up the fidea off mfixfing off mfixtures aflready proposed on a flarge scafle throughout the Indfian Ocean (Hanan et afl., 2013;Graham et afl., 2014).

Modefl caflcuflatfions are shown on Ffig. 5A–C. Numerficafl resuflts are strongfly dependent on the chofice off the modefl parameters. Addfitfion off 1–8% off Seycheflfles/Madagascar-flfike contfinentafl crust durfing the first step, and 0–30% off Indfian MORB mantfle durfing a second step, re -produces Maurfitfius, PN and PF fisotope varfiatfions. Our scenarfio fimpflfies that the Seycheflfles/Madagascar-flfike crustafl component fis aflways pre -sent fin the Maurfitfius-Réunfion hotspot voflcanfism.

5.4. Where fis the crustafl component flocated?

The recent dfiscovery off Neoproterozofic to Archean (0.7 to 3 Ga) zfirconsfin Maurfitfius has rafisedthe possfibfiflfity thattheflfithosphere offthe Mascarene pflateau may contafin a remnant off contfinentafl crust flefft behfind durfing the northward mfigratfion off Indfian pflate. Because those zfircons have an fisotopfic afinfity and an age range compatfibfle wfith the Madagascar contfinentafl crust (Torsvfik et afl., 2013;Ashwafl et afl., 2017), fit fis very flfikefly that they orfigfinate ffrom the same source as the Sey -cheflfles/Madagascar crustafl component fidentfified here. Iff so, our three -component mfixfing modefl adds constrafints on the provenance off the crustafl sfignature reveafled by zfircons. Ffirstfly, the crustafl contamfinatfion off PN and PF magmas cannot be attrfibuted to a contfinentafl ffragment, because the flfithosphere beneath Réunfion Isfland fis cflearfly oceanfic, as shown by fits bathymetry, magnetfic ffabrfic and sefismfic veflocfity struc -ture. Secondfly, our two-step mfixfing modefl fimpflfies that the contfinentafl crust component mfixes wfith the Réunfion pflume beffore the MORB component. These two arguments suggest that mfixfing off the Réunfion pflume wfith contfinentafl crust, as seen ffrom Sr-Nd-Pb fisotopes and zfir -cons, occurs wfithfin the asthenospherfic mantfle beffore the pflume finter -acts wfith the oceanfic flfithosphere.

Shoufld the crustafl component resfide wfithfin the Réunfion pflume source sfince bfiflflfions off years, the derfived materfiafl shoufld show hfigh

187_Os/188_{Os ratfios. Thfisfis notthe case at RéunfionIsfland (Schfiano et afl.,}

2012;Peters et afl., 2016), whose flavas do not have Os fisotope ratfios as extreme as those observed fin Socfiety fisflands where a strong EM-2 sfig -nature fis observed. Thereffore, mfixfing between the RP and crustafl components unflfikefly occurs at the source off the pflume. Instead, the contfinentafl component must befintroduced shortfly befforeflava emfissfion because otherwfise, magmatfic products woufld show very hfigh Os fiso -topfic ratfios. We thereffore tentatfivefly pflace the first step off mfixfing be -tween the RP and crustafl components fin the asthenosphere. It has been

Ffig. 6.Nb/U vs87_Sr/86_{Sr. MORB and OIB refference vaflues} are ffrom (Hoffmann, 2007). RP box corresponds to the Ré -unfion pflume component. Bfinary mfixfing flfines between the RP component and seawater, and between the RP and CC com -ponents are aflso reported. Parameters ffor caflcuflatfing these mfixfing flfines are ffor RP: [Nb] = 32.1 ppm, [U] = 0.85 ppm, [Sr] = 150 ppm,87_Sr/86_{Sr = 0.70424 (correspondfing to} sampfle MP 24 ffromMoore et afl., 2011); ffor seawater: [Nb] = 0.01 ppb, [U] = 3.2 ppb, [Sr] = 8000 ppb (data se -flected ffromEarthReff.orgdatabase),87_Sr/86_{Sr = 0.70916; ffor} CC: [Nb] = 9.8 ppm, [U] = 2.4 ppm, [Sr] = 270 ppm, 87_Sr/86_{Sr = 0.70528 (correspondfing to the average gfiven by} GEOROC database ffor pflutonfic rock ffrom Seycheflfles fisflands).

proposed that Maurfitfius magmas, fincfludfing the trachytes contafinfing crustafl zfircons, mfight stem ffrom a mantfle metasomatfized by recycfled contfinentafl crust (Sheth et afl., 2003;Ashwafl et afl., 2016). The new corpus off fisotopfic data concurs wfith thfis finterpretatfion, and suggests the presence off recycfled contfinentafl crust fin the Indfian mantfle, as afl -ready ffound aflong the South West Indfian Rfidge (SWIR) (Hameflfin et afl., 1986;Mahoney et afl., 1992;Meyzen et afl., 2005). We thus propose that the crustafl contamfinatfion detectedfinthe OIBs off RéunfionIsfland,finthe Maurfitfiantrachytes and perhaps eflsewherefintheIndfian Ocean, reflects a degree off recycflfing off Seycheflfles/Madagascar contfinentafl crust finto the asthenosphere (Ffig. 7).

Contfinentafl recycflfing fin the mantfle requfires a subductfion or coflflfi -sfion process. Gfiven the age off the youngest pre-Mfiocene zfircons ffrom Maurfitfius (700 Ma),the East Affrfica orogeny occurrfing between 800 and 650 Mafin west Madagascar(see revfiew byFrfitz et afl., 2013) coufld have suppflfied the Indfian Ocean mantfle wfith recycfled contfinentafl crust. Re -cent sefismfic tomography and SKS spflfittfing studfies fin the Indfian Ocean suggest, on the one hand, the exfistence off a flow-shear-veflocfity root beneath Madagascar, and an finflectfion off the Réunfion pflume towards the CIR (Mazzuflflo et afl., 2017;Schoflz et afl., 2018). Based on these recent studfies, we ffavor a scenarfio fin whfich the crustafl component off the Réunfion hotspot resuflts ffrom finteractfion off the pflume wfith con -tfinentafl materfiafl ffrom the West Madagascar orogeny, recycfled finto the mantfle by subductfion or deflamfinatfion (Ffig. 7). The pflume con -tamfinated by contfinentafl crust then finteracts wfith the upper depfleted flfithospherfic mantfle, expflafinfingthe second step mfixfing wfith MORB-type component. In thfis scenarfio, the amount off contfinentafl crust fin the asthenospherfic mantfle decreases ffrom Réunfion Isfland to Maurfitfius, Rodrfigues and the CIR, as suggested byFfigs. 3 to 6. Thfis contfinentafl crust component woufld aflso be prefferentfiaflfly tapped by flow-degree meflts, expflafinfing why fit fis more apparent fin the most dfifferentfiated products off Pfiton des Nefiges and Maurfitfius. Our scenarfio predficts that contfinentafl zfircons coufld occur fin Pfiton des Nefiges trachytes as weflfl. 6. Concflusfion

We report a new set off Sr-Nd-Pb fisotope composfitfions ffrom sampfles coflflected at Pfiton des Nefiges voflcano. These data, together wfith fifltered flfiterature data ffrom both Réunfion and Maurfitfius Isflands, are used to create a hfigh-precfisfion fisotope database ffor the Réunfion hotspot pro -ducts younger than 10 Ma. Thfis databasefis used to dfiscuss the orfigfin off the fisotopfic varfiatfions aflong the Maurfitfius-Réunfion hotspot track. These varfiatfions best expflafined by a three-component, two-step mfixfing finvoflvfing first the Réunfion pflume and a Seycheflfles/Madagascar-flfike contfinentafl crust, and then addfitfion off depfleted Indfian MORB mantfle. The geodynamfic fimpflficatfion off thfis modefl fis that the Seycheflfles/

Madagascar-flfike contfinentafl crust has been recycfled finto the Indfian asthenosphere, perhaps durfing the East Affrfica orogeny. Thfis modefl reconcfifles the geochemficafl, geophysficafl and geodynamfic studfies off the Indfian Ocean, but chaflflenges the hypothetficafl exfistence off a hfidden Maurfitfian mficro-contfinent.

Suppflementary data to thfis artficfle can be ffound onflfine athttps:// dofi.org/10.1016/j.chemgeo.2019.06.009.

Acknowfledgement

Authors are pfleased to thank the French Government Laboratory off Exceflflence finfitfiatfive ANR-10-LABX-0006, and the INSU,CNRS ffor the financfiafl and flogfistfic supports. We woufld deepfly thank B. Peters and B. Hanan ffor thefir thoughtffufl revfiews that fimproved the manuscrfipt and C. Chauvefl ffor the Edfitorfiafl handflfing. Thfis fis Laboratory off Exceflflence CflerVoflc contrfibutfion number 354, and IPGP contrfibutfion 4047. Refferences

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