Mantle Sources and the Highly Variable Role of Continental Lithosphere in Basalt Petrogenesis of ...

29 Pages·2002·0.47 MB·English

JOURNALOFPETROLOGY VOLUME43 NUMBER7 PAGES1177–1205 2002
Mantle Sources and the Highly Variable
Role of Continental Lithosphere in Basalt
Petrogenesis of the Kerguelen Plateau
and Broken Ridge LIP: Results from
ODP Leg 183
C. R. NEAL1∗, J. J. MAHONEY2 AND W. J. CHAZEY III1
1DEPARTMENTOFCIVILENGINEERINGANDGEOLOGICALSCIENCES,UNIVERSITYOFNOTREDAME,NOTREDAME,
IN46556,USA
2SCHOOLOFOCEANANDEARTHSCIENCEANDTECHNOLOGY,UNIVERSITYOFHAWAII,HONOLULU,HI96822,USA
RECEIVED JULY 13, 2001; REVISED TYPESCRIPT ACCEPTED JANUARY 31, 2002
OceanDrillingProgram(ODP)Leg183wasdesignedtoinvestigate melts that overlies a thick tholeiitic lava pile. The tholeiite and
the origin and evolution of the large igneous province composed of pebbles from the top of a probable talus deposit (Unit 2) at
the Kerguelen Plateau and Broken Ridge. Of the eight sites drilled, Site 1142 have geochemical signatures consistent with a minor
basalt was recovered from seven, five on the plateau and two on contribution from continental material. This signature is absent in
Broken Ridge. We present results from four of these sites, 1136, the other units from these two sites, which have ocean-island-like
1138, 1141 and 1142. Although this large igneous province is incompatibleelementratiosandage-correctedisotopiccharacteristics
interpreted as being derived from the Kerguelen mantle plume, the similar (but not identical) to those proposed for the post-30Ma
geochemicalcharacteristicsofbasaltfromsomepartsoftheprovince Kerguelen plume. These alkalic basalts may be the purest rep-
indicatearoleforcontinentallithosphere.The118–119Mabasalt resentatives of the Cretaceous plume tail composition yet found.
flowsrecoveredintheSouthernKerguelenPlateau(Site1136)have
a more subtle continental signature than shown by basalt at Leg
119Site738.Acontinentalsignatureisabsentinthe100–101Ma
tholeiitic basalts at Site 1138 in the Central Kerguelen Plateau KEYWORDS:assimilation;basalt;largeigneousprovince;mantleplume;
(CKP); their age-corrected Nd–Sr–Pb isotopic values and in- OceanDrillingProgram
compatibleelementratiosaresimilartothoseestimatedforprimitive
mantle. These flows may represent a major mantle source in the
Kerguelen starting-plume head. The 20 basalt units identified are
a product of magma chamber replenishment, fractional crys- INTRODUCTION
tallization,andresorptionofcrystallizingphases.Thetopmostunit, The Kerguelen Plateau and Broken Ridge constitute a
Unit 1, is a dacite that evolved from a basalt magma similar to large igneous province (LIP) in the southern Indian
those represented by Units 3–22; unlike the basalts the dacite Ocean that originated after the >132Ma break-up of
magma was probably influenced by continental material. Middle IndiaandAustralia(e.g.Kentetal.,2002).Theconsensus
Cretaceous (>95Ma) lavas of Sites 1141 and 1142 on Broken view is that this LIP represents the volcanic outpouring
Ridge (originally part of the CKP) are alkalic, with one exception from a starting-plume head that also produced mag-
(a tholeiite at the base of Site 1142). The alkalic lavas may matism in NE India (Rajmahal Traps; e.g. Mahoney et
representalate-stagecaporcarapaceofrelativelylow-degreepartial al.,1983;Kentetal.,1997,2002),theBunburyBasaltof
∗Correspondingauthor.Telephone:[phone].Fax:[phone]-
9236.E-mail:[email protected] OxfordUniversityPress2002
JOURNALOFPETROLOGY VOLUME43 NUMBER7 JULY2002
southwestern Australia, and the Naturaliste Plateau off Leg 121 (Sites 756, 757, and 758) (see Frey et al., 1977,
the southwestern coast of Australia (e.g. Storey et al., 1991; Mahoney et al., 1983; Baksi et al., 1987; Davies et
1992; Mahoney et al., 1995; Frey et al., 1996). Recent al.,1989;Storeyetal.,1989,1992;Saundersetal.,1991;
data from Leg 183 suggest several distinct stages of Frey & Weis, 1995, 1996). Dredged basalts from the
plateau building (Pringle & Duncan, 2000; Coffin et KerguelenPlateau,NaturalistePlateauandBrokenRidge
al., 2002; Duncan, 2002). The Kerguelen Plateau is were studied by Davies et al. (1989), Weis et al. (1989),
200–600km wide, extends for >2300km from 46°S to Storey et al. (1992), and Mahoney et al. (1995). The
64°S and contains the volcanic islands of Heard and majorityofbasaltsassociatedwiththeKerguelenhotspot
McDonald, as well as the Kerguelen Archipelago (Fig. aretholeiiticortransitionalbetweentholeiiticandalkalic
1). If a plume model is accepted, these islands represent (Coffin et al., 2000) as defined by Macdonald & Katsura
the most recent volcanic products of a long-lived Ker- (1964).
guelen plume tail that also produced the Ninetyeast Leg 183 of the Ocean Drilling Program drilled eight
Ridge (e.g. Frey et al., 1991; Saunders et al., 1991; Frey sites on the Kerguelen Plateau–Broken Ridge LIP
& Weis,1995). Broken Ridge, located>1800km to the (Coffin et al., 2000). Seven of these sites reached
north, was separated from the main plateau by the igneousbasement.Site1135(whichcoredonlysediment)
opening of the Southeast Indian Ridge (SEIR) during and Site 1136 were drilled in the SKP, Site 1137 in
the Early Tertiary (e.g. Tikku & Cande, 2000). Located Elan Bank, Site 1138 in the CKP, Sites 1139 and
approximately midway between the Kerguelen Ar- 1140 in the NKP, and Sites 1141 and 1142 in Broken
chipelago and Broken Ridge on the SEIR are the rel- Ridge (CKP; see Fig. 1). The focus of this paper is
ativelyrecentoceanicislandsofAmsterdamandSt.Paul the basement rocks recovered from Kerguelen Plateau
(Fig.1),thelargestvolcanoesoftheAmsterdam–St.Paul Sites 1136 and 1138, and from Sites 1141 and 1142
hotspot. on Broken Ridge.
The Kerguelen Plateau is broadly divided into south-
ern, central, and northern domains (Fig. 1), each with a
distinct crustal structure and thickness (e.g. Coffin et al.,
1990;Schaming&Rotstein,1990;Freyetal.,2000).The
General background
Southern Kerguelen Plateau (SKP) is composed of an
igneous crust of >22km thickness that, on the basis of The influences of continental crust and/or lithospheric
seismic velocities, may contain fragments of continental mantlehavebeendocumentedinthecontinentalportions
material, especially in the northern SKP (Operto & of the Kerguelen LIP, the Rajmahal Traps (see Kent et
Charvis, 1995, 1996; Charvis et al., 1997). The igneous al., 1997, 2002) and Bunbury Basalt (Frey et al., 1996).
crustoftheCentralKerguelenPlateau(CKP)isbetween In the oceanic parts of the LIP, it has also has been
19 and21km thickand does notcontain theseismically recognized that a continental lithospheric mantle and/
reflective transition zone suggestive of continental ma- or crust signature is present in lavas of the SKP and
terialasseenintheSKP.TheCKPincludesthevolcanic CKP, Broken Ridge and the Naturaliste Plateau (e.g.
islandsofHeardandMcDonald,and,originally,Broken Storey et al., 1992; Mahoney et al., 1995; Frey et al.,
Ridge;ElanBankextendswestwardfromtheCKP(Fig. 2002), and that at least a small amount of continental
1). Seismically, the igneous basement of the Northern lithospheric mantle is present in the NKP (Hassler &
Kerguelen Plateau (NKP) is divided into an upper crust Shimizu,1998).OneofthemajordiscoveriesofLeg183
(8–9·5kmthick)andalowercrust(6–9·5kmthick)(Recq was the presence of garnet–biotite gneiss cobbles in an
et al., 1990, 1994; Charvis et al., 1995). inter-flowconglomeratefromSite1137(Freyetal.,2000;
Basement rocks of the Kerguelen Plateau have been Nicolaysen et al., 2001; Weis et al., 2001; Ingle et al.,
sampledviadredginganddrilling.Basaltwasencountered 2002a), which demonstrated thepresence of Proterozoic
at one drill site during Ocean Drilling Program (ODP) continental crust in Elan Bank.
Leg 119 (Site 738) and four drill sites during ODP Leg The longevity of the Kerguelen hotspot (which has
120 (Sites747–750). Sites 738, 748,749, and 750are in been active for at least 120Myr; Duncan, 2002) affords
the SKP, and Site 747 is in the CKP (Fig. 1). Basalt at the opportunity to examine temporal compositional
Site 748 was an inter-sediment unit, whereas the cored changesinhotspot-derivedmagmas.However,thehighly
basalt sequences at Sites 738, 747, 749, and 750 were variableinfluenceandgeochemicalheterogeneityofcon-
more substantial and were considered to represent ig- tinental lithospheric material complicate interpretation
neous basement (e.g. Barron et al., 1989; Schlich et al., of geochemical data. Variations documented from pre-
1989;Saltersetal.,1992;Storeyetal.,1992).TheNinety- Leg183samplingweregenerallyinterpretedintermsof
east Ridge was cored at four sites during Deep Sea a plume-type model. Most workers have interpreted the
DrillingProject(DSDP)Legs22(Sites214and216)and lavas associated with the Kerguelen hotspot to reflect
26 (Sites 253 and 254), and at three sites during ODP variable mixtures of a dominant Kerguelen plume
1178
NEALetal. PETROGENESISOFKERGUELENPLATEAUANDBROKENRIDGE
Fig.1. MapoftheIndianOceanhighlightingthefeaturesattributedtotheKerguelenhotspotandindicatingtheSoutheastIndianRidge.Both
drill and dredge sample sites are numbered. On the Kerguelen Plateau, drill sites that did not reach basement are in italics. Adapted from
Mahoneyetal.(1995).NKP,NorthernKerguelenPlateau;CKP,CentralKerguelenPlateau;SKP,SouthernKerguelenPlateau.
component,asecond,minorplume-typecomponent(sim- SAMPLE PREPARATION AND
ilarisotopicallytorecentproductsoftheAmsterdam–St.
ANALYSIS
Paul hotspot), plus small amounts of Indian mid-ocean
ridge basalt (MORB)-type mantle (Storey et al., 1988; The analytical strategy was to analyze, where possible,
Frey&Weis,1995,1996)andisotopicallyheterogeneous onesampleformajorandtraceelementsfromeachunit
continental crustal and/or lithospheric mantle material defined during shipboard description of the core (Coffin
(e.g. Weis et al., 1989, 1991, 2001; Storey et al., 1992; et al., 2000). For the thicker units, at least two samples
Mahoney et al., 1995; Frey et al., 2002). were analyzed. Unless otherwise stated, the samples
1179
JOURNALOFPETROLOGY VOLUME43 NUMBER7 JULY2002
2 8 5 4 9 9 2 5 1 7 3
138 5R B 5 48·6 2·6 13·0 15·7 0·2 5·9 8·8 3·7 0·6 0·3 4·6 14·3 0·7 48·5 96 25·6 54·8 38·1 43 90 20·0 7·9 24 39·8 03 17·5 0·7 0·8 26
1 8 2 7 1 6 2 1 3 2 2
6 6 7 9 3 9 3 3 4 5 1
42 138 5R 6 4 48·0 2·5 13·8 15·2 0·3 5·9 9·9 2·9 0·3 0·3 2·5 16·8 0·7 40·2 65 46·0 46·5 35·1 02 62 22·8 4·9 10 48·2 03 17·2 0·9 0·1 07
1 1 8 1 1 1 4 2 1 2 2 1
1
d 8 5 0 8 1 7 8 8 6 1
an 38 R 8·6 2·1 4·4 4·5 0·2 5·6 0·7 2·8 0·2 0·2 1·3 6·8 1·0 4·1 8 3·5 0·1 2·5 7 9 0·1 1·0 9 7·2 1 4·9 0·6 0·0 3
1 4 3 4 1 1 1 4 8 8 5 4 6 2 2 0 3 8 1 2
1, 1 8 5 9 1 3 1 1 2 1 1
4
1 2 4 8 4 0 0 9 9 9 8 1
8,1 1138 84R 1 1E 12 48·8 2·3 14·6 13·9 0·3 5·9 9·9 3·0 0·5 0·2 3·6 7·6 0·6 48·3 409 55·8 48·7 43·8 180 148 21·7 5·4 245 36·2 166 15·6 0·5 0·0 98·5
3
1
1 9 9 2
36, 1138 83R 6 5B 11 10·6 0·4 48·8 461 85·0 52·9 49·7 179 170 22·9 2·9 212 37·5 193 16·3 0·7 0·0 91·2
1
1
6 3 5 8 3 6 6 3 8 2
Sites 1138 83R 6 3 10 47·8 2·2 14·5 14·2 0·3 6·0 10·9 2·7 0·3 0·2 1·9 6·2 0·7 46·7 486 58·6 46·2 46·4 150 131 19·8 3·0 199 33·8 168 13·9 0·8 0·0 90·0
3
8 2 5 3 2 0 6 6 9 1 2
Leg1 1138 82R 5 2 9 48·2 2·1 14·2 14·9 0·2 5·8 10·8 2·9 0·2 0·2 2·5 5·3 0·7 49·1 547 49·1 56·9 50·9 204 162 20·3 6·5 205 33·7 151 12·9 1·4 0·1 86·0
P 9 1 5 2 3 8 3 9 3 3
OD 138 2R B 47·3 2·1 14·6 14·7 0·4 6·2 10·5 2·7 0·4 0·2 1·3 12·0 0·7 46·8 10 87·9 42·3 50·1 39 20 19·7 5·4 10 34·9 62 14·5 0·5 0·0 04
1 8 1 7 8 4 1 1 2 1 1
m
o
r 4 7 7 2 6 2 3 9 8 3
sf 38 R 8·0 2·0 5·5 3·1 0·3 6·3 0·3 2·7 0·8 0·2 1·3 8·9 0·4 7·5 9 9·6 7·2 7·6 9 3 0·3 1·2 5 9·3 0 1·5 0·5 0·1 7
ple 11 81 4 10 7 4 1 1 1 4 36 6 4 5 18 13 2 1 20 2 12 1 11
m
a 5 8 2 4 6 2 5 4 5 4
salts 1138 81R 2 12 6 48·7 2·0 15·5 12·5 0·2 6·1 11·2 2·6 0·7 0·2 2·0 7·0 0·3 50·9 435 84·7 49·2 56·4 133 135 20·8 9·2 205 29·7 128 11·8 0·2 0·0 86·4
a
b
6 7 6 5 1 3 5 3 9 3
s)of 1138 80R 5 1D 5 48·9 2·1 15·9 11·6 0·2 5·7 11·5 2·9 0·2 0·2 2·4 7·0 0·7 55·8 509 101 50·7 67·0 157 147 21·8 1·3 254 30·8 138 12·7 0·4 0·0 104
nt
me 7 3 2 7 2 5 3 7 7 1
ele 138 0R 48·7 2·1 16·0 12·4 0·3 5·8 11·1 2·9 0·2 0·2 2·4 6·2 0·8 48·9 13 69·7 40·1 49·9 73·9 07 19·5 2·1 45 31·3 59 13·6 0·4 0·0 88·9
e 1 8 2 1 4 4 1 2 1
c
a
dtr 38 R 9·2 1·92 6·5 2·0 0·29 5·17 1·6 2·71 0·19 0·21 2·05 6·2 0·89 8·5 3 6·3 0·9 7·3 9 0 0·2 2·0 4 2·8 4 1·2 0·46 0·01 1·3
n 1 0 3 4 1 1 1 4 7 8 5 5 3 3 2 3 3 2 1 8
a 1 8 1 1 3 3 1 1 2 1
r
majo 38 R 3·9 1·53 4·8 9·33 0·04 0·25 3·58 3·53 2·70 0·58 1·69 5·9 7·5 6·4 7·8 9·64 2·4 1·7 4 1·83 0·1 7 8·0 3 7·3 3·24 0·43 4
( 11 74 1 4 1 6 1 5 1 1 4 11 6 18 5 48 3 52
n
o
mpositi 1136 19R 2 9 3 0·19 9·1 0·85 39·8 325 288 22·0 34·7 150 82·0 22·0 20·9 257 50·3 103 7·2 0·98 0·41 133
o
c 5 3 5 0 7 8 5 8 2 3
ck 36 R 0·8 1·6 4·5 2·8 0·2 6·6 0·0 2·8 0·2 0·1 1·1 5·9 0·6 6·2 3 1 8·9 9·8 8 1 9·4 4·0 2 7·1 1 6·2 0·5 0·1 1·3
o 1 8 5 1 1 1 3 9 7 4 5 1 1 1 3 2 0 8
-r 1 1 6 6 2 1 1 1 1 2 1
e
Whol 36 R 1·5 1·68 5·2 1·7 0·20 6·25 9·25 3·18 0·32 0·19 2·17 8·7 0·70 3·7 9 6 1·6 9·3 8 2 1·8 2·7 0 7·7 6 6·6 0·72 0·03 0
1 8 5 1 1 2 2 7 4 5 2 2 2 4 2 0 1
1: 1 1 3 2 2 2 1 1 1 2 1 1
e 5 2 6 4 4 2 8 7 4 6 6
Tabl 136 6R A 50·5 1·7 15·9 12·0 0·1 6·5 9·2 3·2 0·3 0·1 3·7 3·7 0·4 36·2 78 70 46·0 65·3 48·7 12 19·6 4·1 29 25·8 93·0 6·1 0·4 0·0 72·3
1 1 2 2 1 2 1 1 2
n:
Site: Core: Sectio Piece: Unit: wt% SiO2 TiO2 AlO23 FeO23 MnO MgO CaO NaO2 KO2 PO25 LOI ppm Li Be Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Mo Cs Ba
1180
NEALetal. PETROGENESISOFKERGUELENPLATEAUANDBROKENRIDGE
138 5R 6 5 7·2 6·6 5·73 5·0 6·17 2·13 7·38 1·22 7·54 1·59 4·47 0·61 4·15 0·60 4·76 0·91 2·19 1·83 0·38
1 8 2 1 1 1 3 2
138 5R 4 6·9 2·4 6·22 6·4 6·65 2·07 7·99 1·31 8·46 1·78 5·09 0·72 4·97 0·69 5·41 1·04 3·75 1·95 0·48
1 8 1 9 1 1 4 2
138 4R E 3 5·1 6·6 4·98 1·7 5·77 1·76 6·66 1·10 6·99 1·48 4·27 0·59 4·03 0·61 4·97 0·96 2·85 1·59 0·40
1 8 5 1 1 1 3 2
138 4R B 2 4·3 6·2 5·28 3·0 5·80 1·99 6·78 1·15 7·30 1·56 4·29 0·59 3·94 0·59 4·51 0·80 1·95 1·69 0·31
1 8 1 5 1 1 3 2
4
138 3R 1 4·1 2·9 4·77 2·0 5·67 2·04 6·88 1·12 6·67 1·42 4·09 0·58 4·00 0·58 4·57 1·07 2·51 1·81 0·39
1 8 6 3 1 1 3 2
138 3R 0 4·4 1·6 5·00 2·4 5·63 1·95 6·43 1·10 6·98 1·49 4·09 0·56 3·75 0·55 4·74 0·92 2·27 1·80 0·35
1 8 6 2 1 1 3 2
138 2R B 3·9 9·9 4·49 9·9 5·08 1·76 5·92 1·00 6·25 1·34 3·82 0·52 3·53 0·53 3·85 0·70 1·61 1·32 0·25
1 8 5 7 9 1 2 1
138 2R 0 2·9 2·2 4·70 1·5 5·51 1·88 6·29 1·08 6·80 1·44 3·93 0·53 3·63 0·50 4·25 0·80 1·63 1·50 0·27
1 8 1 1 8 1 3 2
138 1R 2 1·2 7·5 3·85 7·5 4·70 1·71 5·46 0·96 5·90 1·25 3·46 0·53 3·41 0·48 3·38 0·72 1·34 1·24 0·24
1 8 4 1 7 1 2 1
138 1R D 1·3 7·1 3·91 7·4 4·58 1·66 5·35 0·93 5·97 1·22 3·42 0·50 3·04 0·46 3·61 0·63 1·01 0·98 0·15
1 8 2 1 6 1 2 1
138 0R 1·2 6·8 3·91 7·7 4·61 1·66 5·41 0·89 5·62 1·15 3·32 0·50 3·19 0·44 3·75 0·70 1·21 1·20 0·14
1 8 5 1 5 1 2 1
138 0R 3 2·2 8·7 4·23 8·9 4·87 1·74 5·53 0·93 5·68 1·16 3·18 0·45 3·00 0·45 3·75 0·72 1·52 1·35 0·15
1 8 2 1 4 1 2 1
138 0R 1·0 5·9 3·83 7·1 4·49 1·58 5·33 0·92 5·73 1·26 3·64 0·54 3·35 0·49 3·36 0·66 0·48 1·02 0·18
1 8 1 7 3 1 2 1
138 4R 8·1 7·6 3·1 3·7 2·8 3·37 1·8 1·90 1·1 2·17 5·94 0·83 5·16 0·69 2·3 2·59 1·26 6·48 1·24
1 7 1 4 1 4 9 1 5 1 1 1 1
136 9R 1·1 0·3 4·74 4·0 7·91 2·35 8·38 1·41 8·63 1·77 4·66 0·64 3·91 0·56 2·69 0·57 0·78 1·10 0·33
1 1 2 9 3 1 3 2
136 8R 8·52 0·2 2·96 3·8 4·03 1·44 5·07 0·88 5·21 1·02 3·00 0·43 2·67 0·40 2·65 0·51 2·39 1·02 0·22
1 1 6 6 2 2 1
136 8R 8·79 1·5 3·08 4·2 4·12 1·58 5·44 0·86 5·56 1·07 3·15 0·46 2·95 0·39 2·54 0·52 3·19 0·91 0·19
1 1 3 2 2 2 1
136 6R A 7·51 7·2 2·61 2·6 3·64 1·45 4·55 0·80 4·91 0·98 2·75 0·41 2·55 0·31 2·57 0·35 1·42 0·93 0·08
1 1 2 2 1 1 1
n:
Site: Core: Sectio Piece: Unit: La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U
1181
JOURNALOFPETROLOGY VOLUME43 NUMBER7 JULY2002
4 6 5 1 6 7 0 0 2
141 4R B 47·7 2·7 16·3 11·8 0·1 6·4 10·9 2·7 0·7 0·4 2·7 1·3 28·6 16 22 51·6 95 02 19 18·4 8·7 43 27·6 61 25·6 0·9 0·2 13
1 2 3 3 6 2 3 1 2 1 4 1 3
5 6 3 4 9 8 1 3 2
141 4R C 47·5 2·7 16·7 11·7 0·1 6·4 10·9 2·7 0·7 0·4 2·6 1·5 30·3 11 62 53·9 00 38 30 18·0 8·6 61 28·5 15 26·7 0·8 0·1 18
1 2 3 2 6 3 3 2 2 1 4 2 3
6 9 6 3 0 8 7 5 7 8
41 R 6·9 2·7 6·7 1·9 0·1 6·3 0·7 2·6 0·8 0·4 5·0 1·9 1·0 7·3 4 4 7·8 9 3 0 0·5 7·4 2 7·0 8 5·6 0·7 0·0 2
1 3 4 1 1 1 2 7 7 4 7 1 0 2 2 2 1 2 9
1 2 4 2 6 2 2 1 2 1 4 2 2
4 8 9 3 1 1 5 5 0 1 9
141 1R D 49·7 3·1 17·8 11·8 0·1 3·1 9·4 3·1 0·9 0·5 4·7 4·0 1·2 29·3 18 00 58·9 08 94 26 18·5 6·7 23 27·2 32 25·9 0·6 0·0 64
1 2 2 1 5 2 3 2 1 1 5 1 2
7 1 2 3 4 6 7 2 7
41 R 7·2 2·7 5·9 2·3 0·1 6·1 1·4 2·9 0·7 0·4 2·4 1·4 0·1 4 0 5·4 5 6 7 0·5 8·7 7 9·9 5 8·4 0·8 0·0 3
1 9 4 1 1 1 3 6 5 3 4 5 1 2 7 2 8 2 2
1 1 2 7 4 2 3 1 2 1 4 1 3
1 4 3 1 4 7 4 0 8
41 R 7·1 2·8 5·8 2·4 0·1 6·0 1·2 2·8 0·7 0·4 4·0 1·3 9·5 5 8 7·0 8 4 2 9·3 6·2 3 8·5 6 6·3 0·5 0·0 1
1 9 4 1 1 1 2 8 5 5 9 1 3 1 9 2 7 2 6
1 1 1 2 4 2 3 1 2 1 4 1 2
3 0 2 6 2 7 0 1 2 4
41 R 7·8 3·1 6·9 2·6 0·2 4·7 0·4 2·9 0·6 0·6 6·4 2·4 1·4 7·4 9 8 0·9 8 6 8 2·5 0·8 7 2·1 6 1·8 1·1 0·2 6
1 8 4 1 1 1 2 4 0 5 3 3 7 2 1 3 3 4 3 6
1 1 2 1 4 3 1 1 3 1 5 2 2
2 9 3 6 4 3 4 3 3 2 5
1141 17R CC 4 47·2 3·5 18·3 14·7 0·2 2·3 8·4 3·2 0·6 0·7 7·3 0·4 1·4 27·8 285 191 60·3 166 216 148 22·3 3·3 591 40·2 266 35·1 0·7 0·0 287
5 5 2 6 9 3 6 2 2 4
41 R 8·2 2·8 9·7 9·3 0·1 4·9 0·7 2·9 0·9 0·4 5·5 0·8 9·1 3 0 5·7 5·2 5 5 7·4 3·0 8 4·3 4 0·5 1·1 0·0 3
1 3 4 1 1 2 6 3 3 9 9 5 1 1 5 2 4 3 3
1 1 1 1 3 2 1 1 4 2 2
5 2 4 8 4 5 0 6 7 4 3
138 9R A 2 47·6 3·0 13·5 17·2 0·3 4·7 9·6 2·8 0·2 0·4 1·5 12·4 1·2 43·6 93 44·6 51·8 28·2 38 75 23·0 3·1 31 52·2 31 22·7 1·0 0·0 25
1 8 3 1 2 3 2 1 2 2 1
5 7 6 8 5 8 9 6 8 6 1
38 R 7·4 2·9 3·5 7·5 0·3 4·9 9·5 2·8 0·2 0·3 1·1 5·4 0·7 9·6 0 1·3 2·6 5·6 4 3 1·0 2·6 4 5·5 5 0·6 0·9 0·1 5
1 8 0 1 4 1 1 1 3 6 1 5 2 8 5 2 1 4 2 2 1
1 8 2 1 2 3 1 1 2 2 1
5 5 7 6 3 3 9 2 4 3 6
138 8R B 0 46·6 2·9 14·3 17·4 0·3 4·9 9·5 2·8 0·3 0·3 4·1 13·8 0·8 43·6 09 11·1 52·4 26·7 04 68 21·5 2·9 21 49·8 42 21·3 0·9 0·0 16
1 8 1 6 2 5 2 1 2 2 1
0 6 0 9 8 6 0 0 1 9 9
38 R 8·4 2·9 4·2 5·4 0·3 4·8 8·8 3·8 0·3 0·4 1·5 4·8 0·8 1·7 8 2·0 4·2 5·5 4 8 6·8 3·9 7 4·8 0 0·4 0·7 0·6 7
1 7 9 4 1 1 1 4 6 1 4 2 1 6 1 5 4 2 2 4
1 8 2 1 1 4 2 1 3 2 1
3 5 5 7 0 0 3 4 7 4 3
38 R 6·6 2·8 4·6 6·5 0·2 5·3 9·7 2·7 0·6 0·3 2·3 4·0 0·6 6·3 6 3·1 0·4 1·6 7 9 1·4 9·2 6 8·1 4 1·0 0·5 0·1 7
d 1 6 8 4 1 1 2 4 2 2 5 3 9 8 2 0 4 2 2 1
e 1 8 4 3 1 4 1 1 2 2 1
u
n
onti 38 R 7·6 2·72 3·8 6·9 0·36 5·20 8·73 3·72 0·23 0·36 2·42 4·5 0·94 6·7 8 6·2 1·2 2·6 9 8 0·9 2·8 1 8·5 5 1·8 0·99 0·47 0
c 1 6 7 4 1 1 2 4 7 1 5 3 0 8 2 1 4 6 2 1
1: 1 8 3 6 1 5 2 1 2 2 1
e 1 8 9 0 0 7 0 8 9 0 3
Tabl 138 6R C 6 47·4 2·9 13·9 16·6 0·3 5·5 9·2 3·0 0·4 0·4 3·1 21·9 0·7 43·2 96 14·4 46·7 28·9 90 78 23·0 17·7 16 46·8 07 19·6 0·8 0·3 35
1 8 1 2 1 3 1 1 2 2 1
n:
Site: Core: Sectio Piece: Unit: wt% SiO2 TiO2 AlO23 FeO23 MnO MgO CaO NaO2 KO2 PO25 LOI ppm Li Be Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Mo Cs Ba
1182
NEALetal. PETROGENESISOFKERGUELENPLATEAUANDBROKENRIDGE
141 4R B 1·1 2·9 7·43 1·3 7·09 2·26 7·31 0·99 5·87 1·11 3·05 0·33 2·56 0·33 4·36 1·64 2·42 1·20 0·22
1 2 3 3 6 2 5 3
141 4R C 1·8 5·0 7·87 3·2 7·36 2·38 7·28 0·99 6·26 1·16 3·23 0·40 2·81 0·40 5·83 1·62 2·51 1·22 0·32
1 2 3 2 6 2 5 3
141 3R 0·2 6·2 7·50 1·5 7·22 2·27 7·08 1·03 5·74 1·11 2·83 0·35 2·48 0·35 5·92 1·45 2·23 1·27 0·25
1 2 4 2 6 2 4 3
141 1R D 0·5 2·7 7·48 1·9 7·01 2·19 7·12 1·00 5·71 1·06 2·77 0·35 2·52 0·35 3·56 1·53 2·27 1·06 0·15
1 2 2 1 5 2 5 3
141 9R 2·8 7·2 8·18 3·4 7·85 2·41 7·80 1·06 6·37 1·15 3·28 0·39 2·86 0·39 4·97 1·65 2·66 1·24 0·18
1 1 2 7 4 2 5 3
141 9R 0·3 1·9 7·32 0·6 7·04 2·37 7·40 0·96 5·75 1·09 2·96 0·31 2·38 0·31 4·68 1·50 7·2 1·02 0·24
1 1 1 2 4 2 5 3 1
141 8R 6·4 1·6 9·55 9·8 8·84 2·72 8·90 1·28 7·06 1·27 3·48 0·38 2·76 0·38 6·75 1·59 2·63 1·21 0·22
1 1 2 1 4 2 6 3
1141 17R CC 4 30·0 71·9 10·5 43·0 9·75 3·11 9·78 1·40 7·75 1·40 3·85 0·46 3·33 0·46 6·98 1·83 4·18 1·10 0·18
141 3R 3·5 6·4 7·34 1·0 6·73 2·07 4·79 0·78 4·97 0·92 2·43 0·27 1·94 0·27 4·99 1·76 2·49 1·60 0·44
1 1 1 1 2 5 3
138 9R A 2 3·2 5·2 7·67 2·1 8·37 2·60 9·53 1·53 9·80 2·11 5·96 0·83 5·69 0·83 6·00 1·21 3·20 2·39 0·54
1 8 3 1 2 2 5 3
138 8R 0 1 0·7 1·5 7·40 0·5 7·85 2·32 8·89 1·51 9·35 1·98 5·72 0·78 5·29 0·78 6·41 1·32 3·94 2·37 0·50
1 8 2 1 2 2 5 3
138 8R B 0 2·2 7·5 7·41 1·8 8·25 2·56 9·37 1·56 9·53 2·05 5·80 0·76 5·41 0·76 6·44 1·26 2·90 2·59 0·52
1 8 1 6 2 2 4 3
138 7R 9 0·7 5·4 6·90 9·4 7·61 2·40 8·73 1·47 9·11 1·95 5·65 0·76 5·37 0·76 6·13 1·18 2·87 2·63 0·52
1 8 2 1 1 2 4 2
138 6R 8 3·1 2·3 7·02 9·8 7·55 2·53 8·79 1·45 8·92 1·90 5·43 0·74 5·02 0·74 6·25 1·11 2·56 2·22 0·41
1 8 4 3 1 2 5 2
138 6R 7 9·3 2·4 6·47 8·8 7·30 2·35 8·40 1·40 8·55 1·83 5·07 0·76 4·69 0·70 5·89 1·10 2·82 2·44 0·50
1 8 3 6 1 1 4 2
138 6R C 6 2·2 3·2 7·27 0·7 7·75 2·51 8·92 1·51 9·60 2·03 5·80 0·79 5·43 0·71 5·74 1·14 2·93 2·43 0·44
1 8 1 2 1 2 5 3
n:
Site: Core: Sectio Piece: Unit: La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U
1183
JOURNALOFPETROLOGY VOLUME43 NUMBER7 JULY2002
1
m) 00 45 13 20 7 6 75 51 5 21 62 55 4 66 3 72 10 03 47
SD (pp 0· 0· 0· 1· 38· 41· 1· 8· 18· 8· 0· 0· 14· 0· 7· 0· 0· 0· 5·
BHVO-1 Average=(n8) ∗0·272 4·8 0·98 32·5 317 302 47·2 124 156 123 21·9 9·8 402 24·5 169 19·1 1·03 0·08 132
1 3
BHVO- (Cert.) 0·27 4·6 1·10 31·8 317 289 45·0 121 136 105 21·0 11·0 403 27·6 179 19·0 1·02 0·13 139
1 4 3 1 4 7 2 7 7 8
42 R 7·1 2·8 5·8 2·4 0·1 6·0 1·2 2·8 0·7 0·4 5·9 1·8 0·7 3·5 4 0·7 4·8 0·5 1 2 5·7 3·2 4 6·9 3 5·6 0·5 0·0 3
1 0 4 1 1 1 3 0 2 6 4 7 4 2 0 3 9 1 1
1 1 3 1 6 4 1 1 2 1 3
9 4 1 1 7 1 0 8 7 9 4
142 R 52·6 2·1 15·8 12·8 0·3 3·9 8·1 3·0 0·8 0·4 1·2 4·1 1·0 30·4 46 50·3 39·4 34·2 58 31 19·0 12·0 78 36·1 82 14·3 0·5 0·1 44
1 9 3 8 6 3 1 1 1 1 3
1 0 6 0 4 0 5 0 9 7 5
d 142 R 48·5 2·8 18·9 11·5 0·1 2·9 8·8 3·8 2·1 0·4 2·3 3·5 1·4 30·0 69 96 52·1 97 13 24 18·3 13·7 44 29·1 12 26·8 0·9 0·1 85
e 1 3 1 9 2 2 3 1 2 1 4 2 2
u
n
conti 142 R 46·7 2·77 16·2 11·9 0·16 6·56 11·3 2·69 0·69 0·48 5·5 1·77 25·1 60 51 31·4 92·2 22 98·6 23·5 14·8 45 33·2 24 30·9 0·41 0·17 15
1: 1 3 1 6 2 2 1 1 4 3 5
e 8 8 1 4 6 9 8 9 5 6
Tabl 142 R A 47·2 2·7 15·8 12·2 0·1 7·4 10·6 2·6 0·6 0·4 3·1 3·9 1·5 30·2 86 05 55·8 20 56 21 16·9 14·0 60 28·5 23 26·8 0·9 0·1 60
1 2 1 2 1 3 4 2 2 1 4 2 2
n:
Site: Core: Sectio Piece: Unit: wt% SiO2 TiO2 AlO23 FeO23 MnO MgO CaO NaO2 KO2 PO25 LOI ppm Li Be Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Mo Cs Ba
1184
NEALetal. PETROGENESISOFKERGUELENPLATEAUANDBROKENRIDGE
1
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BHVO-1BHVO-1SD (Cert.)Average(ppm) =(n8) 15·815·50·55 39·039·51·71 5·705·610·19 25·224·71·11 6·206·360·34 2·062·070·08 6·406·510·31 0·960·980·08 5·205·400·17 0·990·990·04 2·402·590·09 0·330·340·04 2·022·120·11 0·290·260·04 4·384·480·19 1·231·220·12 2·0512·080·27 1·2331·250·08 0·420·410·05 andareshipboardXRFdatafrysisoftheSite1136Unit3safordetailsandexplanation.)
1:continued 1142114211421142 3R3R9R10R 1133 6981 47·222·020·121·5 91·355·445·044·5 12·47·865·686·12 48·635·323·924·1 9·567·566·055·53 2·842·371·892·05 9·527·686·866·61 1·351·111·051·04 6·986·037·146·31 1·361·151·481·27 3·723·214·093·85 0·530·450·620·59 3·222·724·123·95 0·440·350·590·57 8·765·645·235·44 2·091·621·010·98 4·582·394·574·50 6·111·233·203·64 0·280·240·580·56 aretakenfromCoffinetal.(2000)1analyzedtwiceduringtheanalseehttp://www.nd.edu/~icpmslab
Table 1142 2R 1 2A 21·3 55·4 7·78 33·3 7·59 2·35 7·47 1·02 5·86 1·10 3·02 0·43 2·58 0·36 5·87 1·60 3·52 1·15 0·32 italicsBHVO-italics,
nrn
n: sifosi
Site: Core: Sectio Piece: La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U Value∗OP25value
1185
JOURNALOFPETROLOGY VOLUME43 NUMBER7 JULY2002
analyzedweretheleastalteredavailableandwerechosen age-correct the isotopic ratios. Because these meas-
on the basis of the following criteria: (1) macroscopic urements were made on small (>2mm) chips hand-
observation; (2) thin section examination; (3) relative pickedfromthebulkrockandsubsequentlysubjectedto
density and hardness. Trace element analyses (Table 1) acid-cleaning and, in many cases, to a multi-step acid-
were carried out at the University of Notre Dame (see leaching procedure before dissolution, the elemental
http://www.nd.edu/>icpmslab). All surfaces that had abundances derived by isotope dilution generally do not
been in contact with the drill bit were removed from represent whole-rock values.
samples with a water-cooled rock saw and the interior
portionswerecutintoslabsof>1cmthickness.Allsawn
surfaceswerethenremovedusingadiamondwheel.The
RESULTS
slabs were placed inside a plastic bag, sealed with duct
Site 1136
tape, and struck with a duct-tape-covered hammer to
reducethesampletosmallenoughchips(>1cm)topass Basement recovered at Site 1136 was divided into three
through alumina jaw crushers. A portion of these chips basaltic units by the shipboard scientific party (Coffin et
was separated for isotope analysis at the University of al., 2000). Only 53cm of the highly altered rubbly top
Hawaii. The remaining chips were lightly leached in of Unit 3 was recovered and the sample had to be
dilute (Ζ0·25 N) HCl in an ultrasonic bath and then carefullyhand-pickedtoobtainenoughmaterialsuitable
rinsedseveraltimesinhigh-puritydeionized(18M(cid:1)cm) for trace element and isotopic work. All three Site 1136
water. After drying on a hot plate at >50–75°C, the units are plagioclase, clinopyroxene, ±olivine phyric.
chips were examined under a binocular microscope and Units 1 and 2 exhibit little variation in major element
pieces containing veins or vesicles were removed. Re- composition (e.g. mg-number = 0·55–0·56; TiO2 =
maining pieces were passed through the jaw crushers 1·65–1·75wt%;Table1),consistentwiththeshipboard
XRF data (Coffin et al., 2000). Except for their higher
andthenreducedtoapowderinanaluminamill.Wetook
(207Pb/204Pb), Units 1 and 2 are isotopically similar to
greatcaretoremoveandavoidmetalliccontaminationas t
theSite1138basaltunits(Table2,Figs3and4);relative
certain trace elements (Pb, for instance) are significantly
affected by such contamination. Splits of the powders to their (cid:2)Nd(t) values, which are near zero, their (206Pb/
204Pb) and (87Sr/86Sr) are slightly lower than found for
were dissolved for trace element analysis by inductively t t
the Kerguelen Archipelago, and (206Pb/204Pb) is much
coupled plasma mass spectrometry (ICP-MS) using the t
lower than for Heard Island at similar (cid:2) .
methoddescribedbyNeal(2001).TheICP-MSanalyses Nd
TraceelementandisotopedatademonstratethatUnit
were conducted in six separate batches, resulting in 10
3isdistinct(Tables1and2;Figs3–5),withhigherREE
analysesofreferencematerialBHVO-1.Reproducibility
(rare earth element) and Y abundances, a depletion in
is generally better than 3–5% on the basis of duplicate
theLREE(lightREE)relativetotheheavyREE(HREE),
analyses (Fig. 2). All the samples for which data are
markedlyhigher(cid:2) (t),andmoreradiogenic(208Pb/204Pb)
reported here were analyzed by ICP-MS at least twice. Nd t
and (87Sr/86Sr) than Units 1 and 2. The sample is the
If the data suggested dissolution might have been in- t
most altered of any that we analyzed in this study, as
complete(i.e.depletionsinZrandHfonprimitivemantle
indicated by the marked elevation of normalized U, Ba
normalized plots), a LiBO fusion method of sample
2 and,particularly,RbabundancesrelativetoThandNb
preparation was employed. The latter preparation was
(Fig. 5a). In contrast to Units 1 and 2, Unit 3 is not
conducted to ensure that Zr and Hf were not being
anomalouslyenrichedinPb.Highfieldstrengthelement
retained in phases resistant to conventional inorganic
abundances are broadly similar for all three units, al-
acid attack (e.g. zircon). Major element compositions of
though Units2 and3 haveprimitive mantlenormalized
thepowderswereanalyzedbyX-rayfluorescence(XRF)
(Sun & McDonough, 1989) Nb/Ta ratios [(Nb/Ta) ]
PM
at the University of Massachusetts [see Rhodes (1996)
<1; these signatures, and the marked depletion in Zr
andhttp://www.geo.umass.edu/xrffordetails].Themg- and Hf relative to the REE in the Unit 3 pattern, have
number [molar Mg/(Mg + Fe2+)] of the samples was been replicated through two different dissolutions of the
calculatedassumingthat15%ofthetotalironwasFe3+. rock powder and one LiBO fusion. The age-corrected
2
XRFdataqualitywasmonitoredbyanalyzingreference (cid:2) (t)value(+5·1)oftheUnit3lavaisbyfarthehighest
Nd
material K-1919 and undertaking replicate analyses. of any among our Leg 183 samples and similar to the
Isotopic ratios of Sr, Nd, and Pb (Table 2) were highest values measured for basalts from Leg 120 Sites
measured following preparation and measurement pro- 749 and 750 (Storey et al., 1992; Frey et al., 2002). Its
cedures outlined by Mahoney et al. (1998). As in our (87Sr/86Sr) (0·70502) is similar to values for Site 750,
t
previous studies, isotope-dilution measurements of Rb, which are higher for their (cid:2) (t) than seen for any other
Nd
Sr, U, Th, Pb, Sm, and Nd abundances were made on Kerguelen Plateau, Broken Ridge, Kerguelen Archi-
thesamesplitsof sampleasusedforisotopicanalysis,to pelago, or Heard or McDonald Island lavas. However,
1186