19. oceanic basalts from the tyrrhenian basin, dsdp …

OCEANIC BASALTS, HOLE 373

19. OCEANIC BASALTS FROM THE TYRRHENIAN BASIN, DSDP LEG 42A, HOLE 373A

Volker Dietrich, Institut für Kristallographie und Petrographie, ETH Zurich, Switzerland,Rolf Emmermann and Harald Puchelt, Institut für Petrographie und Geochemie der Universitat, Karlsruhe,

Germany,and

Jörg Keller, Mineralogisches Institut der Universitat, Freiburg/Br., Germany

ABSTRACT

During Leg 42A, drilling in Hole 373A in the Central Tyrrhe-nian Sea penetrated Miocene basaltic basement for 190 meters andrecovered basalt from up to 450 meters below the sea floor. Despitemineralogical and chemical alteration due to hydrothermalprocesses in the Tyrrhenian marginal basin, petrological analogiesto high-Al abyssal basalts can be traced.

Two types of interlayered basalt were recognized: (a) a lower Tigroup (Core 5, Sections 1-2; Cores 7 and 10), and (b) a higher Tigroup (Core 5, Section 3; Cores 11 and 12; and outer barrel). Wedistinguish two magma series: a more primitive magma leading tothe plagioclase-bearing low-titanium basalts with affinities to high-Al abyssal tholeiites, and a more differentiated magma leading tothe basalts with higher titanium content.

INTRODUCTION

During DSDP Leg 42A, basalt was recovered fromHole 3 73A in the abyssal plain of the Central Tyrrhe-nian Sea (Figure 1). Basaltic breccia was first encoun-tered under a Quaternary and Pliocene sediment coverabout 270 meters below the sea floor. Then it wasdrilled 190 meters through a basaltic sequence ofbreccia and lava flows and took 11 cores at depths asindicated on Figure 2.

Site 373A is on the lower flanks of one of the largeTyrrhenian seamounts (Figure 1) and the basaltsbelong to the acoustic basement (Site 373A report, thisvolume). Assuming that the age of the overlyingsediments is its upper limit, the basaltic, basement isprobably lower Pliocene/upper Miocene (Barberi etal., 1977, Kreuzer et al., 1977).

GEODYNAMICS OF THE TYRRHENIAN SEA

The formation of small ocean basins in the westernMediterranean has caused considerable discussion (seeRitsema, 1970) since the discovery of their youthfulage and the nature (oceanic to transitional) of the crustand mantle beneath became evident (Menard, 1967).Early geological work in the borderlands of the Tyrre-nian Sea had revealed the existence of a formerlandmass in the area presently occupied by the basin.Evidence of currents and clastic sedimentary compo-nents in the sedimentary sequence point to the exis-tence of such a landmass until Miocene time. Follow-ing the earlier concept of the tectonic break-up of aTyrrhenian continent, several other concepts involvingcomplicated oceanization models were presented.These are reviewed by Ritsema (1970).

The plate tectonics concept invokes spreadingprocesses with formation of new basaltic crust in

widening basins. In this context Boccaletti and Guaz-zone (1972), Dewey et al. (1973), and Barberi et al.(1973) have compared the Tyrrhenian Basin withformerly spreading but now inactive marginal basinswhich nevertheless still have high heat flow values(Karig, 1971).

The deep-focus earthquakes which occur in thesoutheastern Tyrrhenian Sea and the calcalkaline mag-matism which occurs in the Aeolian Islands are charac-teristic of an active island arc (Barberi et al., 1973;Keller, 1974). The age of the exposed island arcvolcanic rocks, however, is less than 1 m.y.B.P. (Bar-beri et al., 1974), whereas the Tyrrhenian Basinformed about 10 m.y. ago. The high heat flow valuesand a rather indistinct pattern of magnetic anomaliesin the Tyrrhenian Basin suggest that it was a spreadingmarginal basin (Ryan et al., 1970). But the pattern ofthe Tyrrhenian spreading centers that can be inferredfrom the magnetic anomalies does not exhibit anysimple regularity. The picture is certainly complicatedby the rotation of individual crustal blocks such asSardinia-Corsica, the Italian penisula, and smallermicroplates (Alvarez et al., 1974; Lowrie and Alvarez,1974). Spreading centers may have developed betweensuch rotating blocks and the existence of areas withcontinental crust within such a domain is possible.(Honnorez and Keller, 1968; Heezen et al., 1971).

The main purpose of drilling in the Tyrrhenianbasement was to test whether the chemical characteris-tics of abyssal basalts, formed at oceanic spreadingcenters or their marginal basin analogs, are present. Ifso, we could conclude that upper mantle processessimilar to those occurring under mid-ocean ridges haveacted as well, in the Tyrrhenian Basin.

Dredge samples of basalt from the Tyrrhenianseamounts (mainly from Mount Marsili) were availa-

515

V. DIETRICH, R. EMMERMANN, H. PUCHELT, J. KELLER

50 100 150 200

— - - - +gravimetricmGal anomaly (Bouger, d = 2,67)

..-•• \. Cenozoic and Quarternary•...: volcanics

• DSDP Leg 42 A, Drill site 373 A

Figure 1. The Tyrrhenian Basin.

ble for study (Maccarone, 1970; Del Monte, 1972;Keller and Leiber, 1974) (Figure 1). These basaltsamples are mostly alkaline. No data were published tosupport a more detailed characterization (for example,designation as "abyssal tholeiite") for there were fewsamples with tholeiitic affinity (e.g., No. 29M of DelMonte, 1972). Nevertheless, such designation was wide-ly quoted to support the existence of spreading precesseswithin the Tyrrhenian Sea. Moreover, seamountvolcanism apparently occurred much later than basinformation and lasted until the upper Quaternary (Kellerand Leiber, 1974).

PETROGRAPHIC DESCRIPTION OF ANALYZEDSAMPLES

Most basalt samples are well crystallized and haveintergranular textures of fresh plagioclase, clinopyrox-ene, and titanomagnetite in a matrix of smectite,

chloritic minerals, or both. This matrix constitutes up to30% of the rock volumes. X-ray analyses, with use ofethylene glycol treatment, on three samples showed thetypical shift of the 100 montmorillonite peak from 14 to18Å. A chlorite + montmorillonite mixture is abundantin two of the samples (7-2, 136-140 cm, and 7-3, 111-112.5 cm). Some smectite patches, clearly pseudo-morphs after olivine and very rarely occurring olivinerelics are preserved (e.g., 7-4, 135-140 cm, and 7-5, 10-14 cm). However, the extent of original modal olivineremains uncertain.

Two petrographic types of basalt are recognized; (1)plagioclase phyric and (2) aphyric to sparsely micro-phyric. This distinction corresponds to a chemicalgrouping explained below (Table 4).

Plagioclase phenocrysts are calcic with compositionsranging up to An84. Groundmass plagioclase rangesmainly from An50.60 (Figure 3, Table 1). Along with

516

LITHOLOGICUNITS

^744.5 m Pliocene marls

basaltic brecciaIII ?pillow breccia with

calcareous matrix

300

basaltic breccia andpillow breccia withinterlayeredamygdalar andporphyritic basalts

basaltic flows,porphyritic

T. D. = 3964.5 m450

Core

2

3

4

5

6

7

8

9

10

11

12

Rec<>very

A A A A

A A A A

A À J • •

Tyrrhenian Sea 27-29 April 1975

39°43.68'N, 12°59.56'E

SAMPLES

5-1,68-775-1,90-935-2, 35-385-2, 53.5-575-3, 74-75.5

1 5-3, 129-131

6-1,72-756-1,96-100

. 6, CC

'7 -1 , 139-1447-2, 136-1407-3, 111-112.57-4, 19-237-4, 135-140

'7-5,10-14

— 10-1, 123-125

r-11-1, 114-117—11-1, 130-135

— 1 2 , CC

ROCK TYPE

low Ti basaltlow Ti basaltlow Ti basaltlow Ti basalthigh Ti basalthigh Ti basalt

brecciahigh Ti basalthigh Ti basalt

low Ti basaltlow Ti basaltlow Ti basaltlow Ti basaltlow Ti basaltlow Ti basalt

high Ti basalthigh Ti basalthigh Ti basalt

•OB 1 . high Ti basalt. O c B J outer barrel h i ^ n T i b a s a l t

Figure 2. Graphic lithology of Site 373A. The drillingstarted at a depth of 96.5 meters sub-bottom withinQuaternary Nannofossil marls (lithologic Unit I; Site373A Report, this volume). At 270 meters, GlomarChallenger drilled into basaltic breccias (containing pil-low fragments) associated with lava flows. The drillingwas terminated at 457.5 meters in basaltic lava flows.Twenty basaltic samples from six cores out of Units IVand V were analyzed.

these groundmass labradorites, almost pure albite(with an increased orthoclase component) has beenfound by microprobe analysis. This suggests the begin-ning of a process of mineralogical readjustment andchemical exchange which is more pronounced in trueocean-floor metamorphic spilites (Cann, 1969).

Chlorite and an unidentified green amphibole-likemineral (riebeckite?) developed as small rims sur-rounding the groundmass clinopyroxene and as tiny,but discrete, crystals within the chlorite/smectitepatches. X-ray powder data from Sample 7-4, 10-4 cm,confirmed the existence of chlorite. Thus, the firstindication of a change toward a greenschist facies


mineralogy as described for oceanic basalts by Mi-yashiro et al. (1971) is apparent.

In general, however, groundmass clinopyroxenes arefresh. Their composition (Table 2, Figure 4) is saliticand similar to the clinopyroxenes reported by Ridley etal. (1974). Iron enrichment is present but not pro-nounced. No Ca-poor pyroxene has been detected.

Calcite occurs as veinlets, vesicle fillings, andpatches within the groundmass and plagioclase pheno-crysts. All samples analyzed contain only minoramounts of calcite. Zeolites replace plagioclase and fillvesicles in the most altered samples, but these are notsuitable for chemical analysis (5-1, 68-71 cm; 5-2, 35-38 cm; and 6-1, 133-136 cm).

GEOCHEMICAL METHODS AND DISCUSSIONOF RESULTS

Twenty samples were analyzed by X-ray fluores-cence, atomic absorption, ionic neutron activation, andwet chemical methods to determine their major and traceelement contents. All major element determinationswere made at least three times by each of the differentlaboratories involved (Freiburg i.Br., Karlsruhe, Zu-rich, and Canberra). The results given in Table 3 are ingood agreement. Determinations were carried out by:

a) XRF for SiO2, TiO2, A12O3, Fe2O3 (total),MnO, MgO, CaO, and K2O;

b) AAS for Na2O, K2O, CaO, MgO, Fe2O3 (total),and A12O3;

c) INAA for Na2O, K2O, CaO, MnO, and Fe2O3(total);

d) Wet chemical methods for SiO2, TiO2, FeO,P2O5, H2O+, and CO2;

e) Electron microprobe analysis (by J. Keller) onplagioclase and pyroxene phenocrysts.

All samples were analyzed for the following ele-ments by INAA, but these elements were below thedetection limits indicated:

Sb(<l ppm), Ta(<l ppm), U(<1.5 ppm), Th(<lppm), and Cs(<2 ppm). The trace element data areincluded in Table 3. the methods applied were: (a)XRF for Rb, Sr, Zr, Y, Pb, and U; (b) AAS for Li, Sr,and Cu; (c) INAA for Sc, Cr, Co, Hf, La, Ce, Sm, Eu,Tb, Dy, Yb, and Lu

Or

• •10

groundmass

50 90

phenocrysts

Figure 3. Plagioclase plot for Hole 3 73A basalts.

517


TABLE 1

Chemical Composition and Structural Formula of Phenocrystic and Groundmass Plagioclases from 37 3A Basalts (microprobe analyses)

Siθ2AI2O3FeO totalCaONa2OK2O

32 O

SiAlFeCaNaK

Na:

K: Mol%Ca:

Grdm.

56.6627.02

0.869.056.41

10.2035.7330.1291.7462.238

20.049

56.20

43.8

5-1

Pheno.

45.7534.720.24

17.461.700.13

8.4377.5460.0373.4510.6090.031

20.111

14.90.8

84.4

,90-93 cm

Grdm.

50.7730.97

0.613.71

3.850.09

9.2696.6630.0922.6821.3640.022

20.092

33.50.5

65.9

Grdm.

54.8828.56

0.999.445.820.31

9.9206.0850.1501.8272.0410.071

20.094

51.81.8

46.4

Grdm.

58.6125.06

1.067.157.620.32

10.5415.3120.1591.3782.6570.074

20.121

64.41.8

33.5

5-2, 53.5-57 cm

Grdm.

54.5628.28

0.9010.575.530.16

9.8836.0380.1372.0511.9420.037

20.088

48.20.9

50.9

Grdm.

65.1620.55

1.271.71

10.191.00

11.5684.3000.1890.3253.5090.226

20.117

86.45.68.0

6,CC

Grdm.

52.8429.460.68

12.154.770.09

9.5606.3150.1042.3681.6820.020

20.049

41.30.5

58.2

7-1, 139-144 cm

Pheno.

45.9734.290.33

17.381.750.15

8.4837.4580.0503.4360.6280.035

20.090

15.30.8

83.8

Grdm.

53.1129.320.63

11.824.890.23

9.6496.2790.0962.3011.7210.053

20.099

42.21.3

56.5

11-1,130-135 cm

Grdm.

53.4229.13

1.6711.084.440.26

9.7196.2390.2532.1581.5660.060

19.995

41.41.6

57.0

Grdm.

53.6529.02

0.6611.355.170.16

9.7316.2030.0992.2061.8170.037

20.093

44.80.9

54.3

Grdm.

53.1029.83

1.4310.195.280.17

9.6396.3830.2171.9831.8570.040

20.119

47.91.0

51.1

Grdm.

53.3229.19

0.6411.545.130.19

9.6826.2470.0972.2441.8070.043

20.120

44.11.0

54.8

12, CC

Grdm.

66.2220.61

0.421.32

10.550.88

11.6794.2840.0620.2503.6080.198

20.081

89.04.9

6.2 ,

Grdm.

66.7520.08

0.570.65

10.681.26

11.7784.1770.0850.1243.6550.284

20.103

9073

Grdm.

67.7618.900.750.31

10.531.76

11.9653.9330.1110.0593.6040.396

20.068

88.89.81.4

TABLE 2Chemical Composition and Structural Formula of Groundmass CUnopyroxenes from 373A Basalts (microprobe analyses)

SiO 2

TJO2A1 2O 3

FeO totalMnOMgOCaONa2θ&2O3

S i = 2 0AlAlFeMnMgCa •~ 2 . 0 'Na

CrTi

Mg:Ca: Mol%Fe:

5-90-93 cm

49.721.035.756.47

14.9820.92

0.410.65

1.8360.1640.0860.200

0.8250.8270.030*

0.0190.029

48.611.674.43

10.800.15

13.5820.650.590.23

1.8310.1690.0310.3180.0050.7620.8330.043

0.0070.047

*+0.003 K

44.544.710.8

39.843.516.6

5-2,5 3.5-57 cm

48.211.624.32

13.350.26

11.4820.09

0.550.13

1.8400.1600.0340.4260.0080.6530.8220.041

0.0040.047

34.343.222.4

50.300.915.005.71

15.0622.110.480.43

1.8550.1450.0720.176

0.8280.8740.034

0.0130.025

44.146.5

9.4

6,

50.451.043.877.61

14.7521.58

0.460.24

1.8770.1230.0460.237

0.8170.8590.033

0.0070.029

42.744.912.4

CC

50.051.194.297.440.13

14.8121.370.360.36

1.8590.1410.0470.2310.0040.8200.8500.026

0.0110.033

43.144.712.1

50.200.904.506.52

15.1421.73

0.270.75

1.8560.1440.0520.202

0.8350.8610.019

0.0220.025

44.045.410.6

7-1, 139-144 cm

51.990.593.295.31

15.8722.22

0.73

1.9080.0920.0500.163

0.8680.874

0.0210.016

45.645.9

8.6

50.330.844.685.80

15.1321.96

0.320.94

1.8580.1420.0620.179

0.8330.8680.023

0.0270.023

44.346.2

9.5

51.060.953.627.12

15.0221.720.310.20

1.8900.1100.0480.221

0.8240.8610.023

0.0050.026

43.445.111.5

11-1,130-135 cm

48.891.814.329.930.12

13.2320.83

0.620.24

1.8400.1600.0320.3120.0040.7420.8400.045

0.0070.051

39.244.316.5

52.620.581.917.69

16.4220.320.280.18

1.9410.0590.0240.237

0.9030.8030.020

0.0050.016

46.541.312.2

12

52.350.732.477.21

16.2020.600.220.22

1.928

0.0720.0350.222

0.8890.8130.015

0.0070.020

46.242.211.5

CC

49.041.594.837.900.12

14.4420.90

0.550.64

1.829

0.1710.04P0.2460.0040.8030.8350.040

0.0190.045.

= 20

' ~ T π~ Z.U

42.644.313.1

To check accuracy, standard reference samples werealso analyzed. The values obtained for USGS-BCR-1in the Karlsruhe laboratory are given by Puchelt et al.(1976) in the Initial Reports of the Deep Sea DrillingProject, Volume 37.

In addition, the abundance of a large number oftrace elements was determined by XRF, AAS, andINAA. A few samples were tested by Spark SourceMass Spectroscopy for Rb, Sr, Ba, Pb, La, Ce, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y, Nb, Zr, Th,andU.

A close scrutiny of Table 3 reveals that the basaltsdiffer markedly in their TiO2 contents and may bedivided into two groups, the averages of which aresignificantly different. Accordingly, we have discernedlower Ti and higher Ti basalts. Once the grouping ismade, further distinctions become obvious for other

elements. To obtain a suitable basis for comparison,the actual analytical data have been recalculated on aH2O and CO2-free basis. The averages for the twogroups are listed together with the standard deviationin Table 4. Along with the quite pronounced differ-ences in TiO2, a similar clustering of values occurs forA12O3, Na2O, and P2O5. Their respective concentra-tions versus TiO2 are shown in Figure 5. The higher Tigroup is enriched in SiO2, Fe2O3, Na2O, P2O5, and rareearth element (REE) concentrations, whereas the lowerTi group is enriched in A12O3, MgO, and CaO.

All basalts from Site 373A show secondary hydra-tion and oxidation (Figure 6). Samples 5-1, 68-75cmand 5-2, 35-38 cm, are high in CaCO3.

On an alkali-silica diagram, the Hole 373A basaltsfall close to the alkaline field boundary or even in thehigh-alumina basalt field (Figure 7). Most samples are

518


r /

FsFigure 4. Clinopyroxene plot for Hole 373A basalts.

nepheline-normative (Table 5 and Figure 8) using acorrected iron oxidation of Fe2O3/FeO 0.15. Thismay not reflect the original chemistry. Na2O couldhave been introduced (spilitization). In some of thesesamples the content of CaO is 7-8%. This is well belowoceanic tholeiite concentrations whose range is exem-plified, for example, in the CaO/Al2O3 plot of Kay etal. (1970). Miyashiro et al. (1971) reported considera-ble loss of CaO with increase of Na2O in metabasaltsof the Mid-Atlantic Ridge.

On the other hand, the higher Ti basalts show aconsistent enrichment of SiO2, Na2O, Fe2O3, P2O5, andREE.

The data suggest that the two groups represent twoinitially different basalt types (Figures 7, 9, 10, 11,12,13, and 14). The higher Ti basalts have higher norma-tive contents of the Fe-Ti-oxides and apatite, and lowercontents of olivine (Table 5 and Figure 8). Each typehas a different degree of fractionation (Figure 10). TheMgO/FeO ratio expressed as Mg-numbers (molecular100 Mg/Mg + Fe+2 (Green and Ringwood, 1967).The Fe~1"2, standardized as Fe2O3/FeO = 0.15, shows abroad range of fractionation with Mg-numbers from 74to 46 (Table 5). The higher Ti basalts (Mg-numbers:46-66 and differentiation index: 33-41) could representa more fractionated part of the magma than the lowerTi basalts. The highest Mg-numbers (65-74 for thelower Ti basalts) are consistent with a direct partialmelting from upper mantle peridotite (Green, 1970).Magma segregation following about 15% partial melt-ing at about 9 kb at a depth range of 15-35 km wouldyield a high-alumina olivine tholeiite of appropriatecomposition. The low TiO2, very high A12O3 and highnormative olivine content (up to 20%) may require arefinement of the model with a greater degree ofpartial melting in a Al-rich source. The lower Ti basaltscould be plagioclase-tholeiites of Shido et al. (1971).However, this terminology is not adopted, because the

alteration of olivine obscures the crystallizationsequence.

TRACE ELEMENTSTrace element concentrations are given in Table 3.

Chondrite normalized REE patterns are shown inFigure 14.

Concentrations of large-ion-lithophile (LIL) ele-ments (such as Rb, Sr, Ba, Y, Zr, Hf, U) are low,indicating that these basalts are similar to abyssaltholeiites. Correlation plots of alteration-resistant ele-ment pairs, such as Zr-Sr, Zr-Nb, or P2O5-TiO2 (notillustrated), clearly fall in the field of oceanic ridgebasalts (Bass et al., 1973; Ridley et al., 1974). Zr-Tiand Y-Ti correlations also fall on the positive correla-tion line outlined for ocean floor basaltic rocks byCann (1970). This emphasizes that Zr and Y haveslightly lower than average concentrations in the Tyr-rhenian lower Ti basalts, and that they are markedlyhigher in the higher Ti basalts. La and Hf also aredifferent in the two basalt types previously distin-guished (Figure 13).

Rb, Sr, Ba, Pb, U, and Th have concentrationsslightly but consistently above those found in oceanfloor basalts (Engel et al., 1965; Kay et al., 1970; Hart,1971; Church and Tatsumoto, 1975).

Relative to chondrites, the shape of the rare earthpatterns and the Eu anomalies (Figure 14) are interest-ing. All samples have a similar general REE pattern.They are light REE enriched with (La/Sm)ef of about1.5. The enrichment of the heavy REE shows differ-ences which coincide with the grouping into the lowerTi and higher Ti groups of basalts (Table 4 andFigures 7-13). This high (Ls/Sm)ef is a distinctivefeature of our REE patterns and is at variance withabyssal tholeiites which typically have (La/Sm)ef <l(Schilling, 1971).

519

•

DSDPLeg42A-373A

SiO2

Tiθ2A12O3

F e 2 O 3

FeOMnOMgOCaONa 2OK 2 0

P2O5H 2 0C 0 2

Total

LiRbSrBaPbCuCoCrScYLaCeSmLuTbDyYbLuZrHfNbTaThU

(1)

5-168-71

40.91.12

17.85.122.780.23

•7.0314.1

3.020.320.203.714.42

100.75

10<l

200n.d.n d6829

20134n.d.5.8

14.02.60.861.13.22.20.27

n.d.2.2

n.d.< l

<.3<.2

(2)

5-190-93

49.21.08

18.74.482.800.117.03

10.52.930.300.172.49

<O.l

99.8

29<l

250n.d.n.d.7632

1993228

5.610.9

1.91.04

< l3.010.26

81<ln.d.< l

<.3<.2

(3)

5-235-38

41.51.07

17.95.402.180.177.9

12.92.430.280.164.804.12

100.8

33<l

225n.d.n d8633

2063128

5.211.5

2.00.82

< l3.41.60.28

822.0

nd< l

<.3<.2

(4)

5-253.5-57

47.11.03

18.95.292.300.117.60

11.42.970.320.122.400.1

99.54

32<l

215n d .n d .7629

20729n.d.6.2

11.92.31.10

< l3.22.40.27

n.d.0.9

n.d.< l

<.3<.2

TABLE 3Chemical Composition of the Leg 42A Hole 373A Basalts, (n.d.

(5)

5-374-75.5

48.11.55

17.46.892.950.194.83

10.43.840.290.261.880.1

98.63

18<l

230n.d.n.d.9837

19039n.d.

7.316.0

3.21.441.55.24.40.40

n.d.2.7

n.d.0.85<.3<.2

(6)

5-3129-131

48.41.71

16.16.613.380.195.72

10.24.220.430.232.38

<O.l

99.57

27<l

220n.d.n d7231

1993537

9.320.1

3.51.431.54.53.50.43

1422.7

n.d.<l

<.3<.2

(7)

6-196-100

51.11.75

17.17.162.980.174.029.54.650.380.250.92

<O.l

99.98

9<l

160n.d.n d .2632

16936n.d.9.1

22.93.61.371.25.12.80.37

n.d.3.0

n.d.< l

<.3<.2

(8)

6cc

49.21.41

16.15.633.840.167.54

10.03.610.320.191.97

<O.l

100.02

29<l

205n dn d8435

2074328

6.115.1

3.21.251.04.72.90.38

1072.2

n.d.0.77<.3<.l

(9)

7-1139-144

48.00.92

18.35.192.650.107.66

10.33.160.330.123.39

<O.l

100.12

29<2.5

23258.5

2.26130

2272923

6.315.0

1.90.900.63

< l2.20.29

771.63.1<.l0.420.24

(10)

7-2136-140

47.80.84

20.24.824.950.137.56

11.172.610.270.102.510.1

99.8

27<l

215n.d.n.d.6639

28532n.d.

3.78.91.80.84

< l2.61.50.26

n.d.1.9

n.d.<.l<.3<.2

(11)

7-3111-112.5

47.71.02

18.25.282.810.168.35

11.82.730.210.132.41

<O.l

100.89

29< l

225n.d.n.d.6933

2553322

4.711.8

2.10.89

< l3.21.80.31

692.0

n d.< l

<.3<.2

(12)

7-419-23

44.50.84

20.35.062.500.158.65

10.82.830.240.123.22

<O.l

99.21

343

237n.d.

1.56734

25 33018

6.113.0

2.30.92

< l2.8

< l0.28

611.5

n.d.< l

<.30.11

= not determined)

(13)

7-4135-140

43.20.91

18.05.542.510.17

10.311.1

2.530.230.114.441.5

100.54

502

215n.d.

1.58431

2103321

5.312.0

3.40.71

< l3.21.10.25

541.2

n d .< l

<.30.21

(14)

7-510-14

44.21.09

18.25.93.300.279.58

10.32.270.250.144.580.8

100.89

46<l

235n.d.n.d.

15039

2103426

4.511.1

2.30.851.13.22.20.30

792.0

n.d.0.95<.3<.2

(15)

10-1123-125

49.21.11

18.14.242.470.128.769.243.240.270.143.00

<O.l

99.89

34<l

210n.d.n.d.

10535

2213528

5.212.2

2.20.98

< l3.52.30.30

901.5

n d< l

<.3<.2

(16)

11-1114-117

51.01.68

16.55.654.290.177.057.574.130.270.242.27

<O.l

100.22

11<l

180n.d.n.d.8432

1383240

9.320.0

2.91.431.64.83.00.46

1563.3

n d<l

<.3<2

(17)

11-1130-135

50.51.57

16.94.714.500.167.957.34.280.280.222.14

<O.l

100.51

17<l

20558

2.47032

1333439

9.120.2

3.41.24

< l5.63.40.49

1403.26.51.080.630.8

(18)

12cc

50.01.56

16.44.814.030.168.137.04.400.320.222.31

<O.l

99.34

11<l

155n.d.n.d.6830

14233n.d.9.2

20.33.71.34

< l5.23.50.42

n.d.3.3

n.d.< l

<.3<.2

(19)

OB 2Outer

50.11.72

16.84.984.230.187.217.704.180.320.262.12

<O.l

99.80

8<l

197n.d.n.d.7631

1153243

8.718.9

3.81.301.25.92.80.46

1652.4

n.d.< l

<.3<.2

(20)

Ocbbarrel

50.61.86

16.35.204.330.167.017.234.440.370.262.56

<O.l

100.32

15<l

230n.d.n.d.7231

100293610.020.5

4.21.57

< l5.32.50.50

1533.1

n.d.< l

<.3<.2

ET

RIC

H, R

. EM

M!

>

Z

X•ac0PCm

-t—1

; *

a


TABLE 4Chemical and Petrographical Characteristics of

the Two Basalt Types of Hole 37 3A on a(dry) Volatile Free Basis

SiO2 (Wt %)TiO2

AI2O3Fβ2θ3 TotalMnOMgOCaONa2OK 2 O

P2O5Σ REE (ppm)Cr (ppm)

Mg numberDifferentiationIndex

Lower TiGroup

(11 samples)X± I S

47.8 ± 2.21.05 ± 0.12

19.4 ± 0.88.65 ± 0.970.16 ± 0.058.60 ± 1.13

11.8 ±1.62.92 ± 0.300.29 ± 0.030.14 ± 0.03

40.1 ±4.2255 ± 36

65 - 7 420 - 2 9

plagioclasephyric

Higher TiGroup

(9 samples)X± 1 S

51.0 ± 1.11.68 ±0.14

17.0 ± 0.410.2 ± 0.42

0.17 ± 0.016.75 ± 1.478.74 ± 1.444.29 ± 0.310.34 ±0.040.24 ± 0.03

64.4 ± 5.4155 ± 27

46 - 6 633 - 4 1

mainlya phyric

The positive Eu anomaly is obviously linked tosamples with high A12O3 contents, indicating thatplagioclase is the Eu-bearing phase.

PETROGENETIC DISCUSSION

Drilling on Leg 42A encountered, for the first time,abyssal basalts in the young Mediterranean deep-seabasins. Two significantly different and interlayeredtypes of basalts were recovered from Hole 373A; lowerTi basalts with affinities to high-alumina abyssal tholei-ites, and higher Ti basalts.

Alteration of these basalts is widespread and in-volves chemical migrations. It is most evident in theCaCO3 bearing samples and in apparently Na-enrichedand Ca-depleted samples (spilitization). The oceanfloor metamorphic processes responsible are probablyrelated to circulation of hydrothermal solutions in areasof higher heat flow; they merit further study. Atpresent, we concentrate primarily upon the recognitionof original magma types.

According to Green and Ringwood (1967, 1969),01-normative, high-alumina tholeiite (the Site 373Alow-Ti basalts) is generated at a relatively shallowmantle depth (about 9 kb or a model depth of 15-35km) and by high degree of partial melting (25%-30%).The origin of basalt within these limitations is thoughtto be related to upwelling or intrusion of partly moltenmantle material from the low-velocity zone into shal-lower levels of a narrow axial zone at spreadingcenters. High heat flow is related to the rising, hotmantle material. Basalts of the lower Ti group withhighest Mg numbers can be directly related to thismodel and do not require large-scale fractionationprocesses to account for their composition. Plagioclaseaccumulation can explain the extremely high A1O3

enrichment and a possibly existing Eu anomaly relatedto high Sr contents.

Variations in LIL and other incompatible elementsbetween abyssal basalts from different regions may

1 "CO

19

18

17

16 -

0.75 1.00 1.25 1.50(α)

— 5.0

oσ ù.5Z

u.o

3.5

3.0

2,5

1.75 2.00

TiO 2 (%)

0.75 1.00(b)

_ 0.30

6£0.25

0.20

0.15

1.25 1.50 1.75 2.00

> T i O 2 (%)

0.10

0.75 1.00 1.25«0

1.50 1.75 2.00

- TiO2(0/°)

Figure 5. Variation diagrams for Hole 3 73A basalts,(a) AI2O3/T1O2, (b) Na2θ/Tiθ2; (c) P2O5/TiO2.Solid circles - low-Ti basalts; solid squares high-Tibasalts. For location see Figure 2.

521


5 r -

H2O

%

1 ~

*vo * .

/ *

//«

.e>/ <?/

/core5/3, \

3 4 5 6 7Fe 2 O 3 %

Figure 6. Increase of Fe?O3 and H2O within the 373Abasalts indicating the degree of weathering and meta-morphism. Solid circles = Ti basalts, solid squares = highTi-basalts.

reflect different concentrations in the source rocks. Thesource of the most unfractionated Tyrrhenian basaltsyields lower Ti, Y, Zr and is enriched in light REE, Ba,Rb, Sr, Th, U, Pb, compared with oceanic basalts. Kayet al. (1970) showed that extremely low LIL elementconcentrations along the Mid-Atlantic Ridge resultedfrom depletion during previous partial melting epi-sodes. The depletion under the Tyrrhenian Basin is lesspronounced.

A postulated vertical zoning of the upper mantle,reflected in the enrichment of LIL elements in theupper levels of the low velocity zone (Green, 1970),can also lead to increased LIL element concentrations

Na2O•K2O

2 -

ALKALI BASALTS

× HIGH-ALUMINA/ BASALTS

THOLEIITES

50 SiO260

Figure 7. Alkali ISiO 2 plot on water-free basis (solid circles =low-Ti basalts, solid squares = high-Ti basalts).

in partial melts. If the upper mantle below the Tyrrhe-nian Sea has a structure similar to that beneath theBalearic Basin (Berry and Knopoff, 1967), then anultra-low velocity channel upwarp to only 50 km belowthe central basin could well provide higher LIL ele-ments even in tholeiites representing high degrees ofpartial melting.

The Hole 373A higher Ti basalts could have origi-nated as Qz-normative basalts (containing lower Na20contents, averaging approximately 2.8 wt.%). Suchoriginal rocks apparently were more fractionated thanthe lower Ti basalts. No simple fractionation linerelates the two groups. To account for the higher Tibasalts, we envision a complex origin involving a lesserdegree of partial melting (to explain higher Ti, Hf, Zr,

oi Hy

Figure 8. Normative compositions of the Hole 373Abasalts plotted in the system Ne-01-Di-Hy-Q. Theencircled area represents the range of abyssal tholeiitesfrom oceanic ridges. Solid circles low-Ti basalts, solidsquares = high-Ti basalts.

522

TABLE 5CIFW Norm and Mineralogical Criteria


5-1,68-71 5-1,90-93 5-2, 35-38 5-2,53.5-57 5-3,74-75.5 5-3, 129-131 6-1,96-100

orabanne

di

hy

ol

mtilapcc

fwo•I enUsren

UsrI fa

1.8920.8534.07

2.55

5.38

-

17.7

1.552.130.47

10.05

f2.77-f 1.69

I .92

rll.08JI 6.62

1.7724.7936.99

-

11.32

12.03

6.17

1.422.050.40_

f5.84^ 3.6911.79f8.09

13.94f4.02

12.15

1.6520.5636.90

—

—

8.76

14.37

1.482.030.389.36

f6.02

12.74f9.57

U.80

1.8923.9237.30

0.66

13.33

_

15.51

1.461.960.28_

f6.89J 4.3812.07

[10.20

1 5.31

1.7130.6529.39

1.00

16.88

_

11.03

1.912.940.620.02

f 8.54] 4.30U.05

f5.42

15.62

2.5428.9423.72

3.67

20.84

_

11.22

1.943.250.54

rlθ.60

IU.53

f5.98

15.24

2.2538.5124.67

0.46

17.31

_

9.41

1.973.320.59

r8.70\ 4.0414.57

T4.19

15.23

H2OTotal100 Mg

Mg+Fe2

Different. Ind.

3.71100.34

65.32

25.29

2.4999.44

67.43

26.57

4.80100.36

69.12

22.22

2.4098.71

68.42

26.47

1.8898.05

51.36

33.36

2.3899.04

55.12

35.15

0.9299.40

46.15

41.21

Phenocrysts[size inmm]Ground mass[plag sizein mm]Calcite

[vesiclesize in mm]

plag1-3

cpx+plag0.1-0.3

in veins+ vesicles

0.1-1

plag

cpx+plag

in vesicles+ groundmass

0.1-1

plag1-2

cpx+plag0.1

plag

cpx+plag(albite)

cpx+plag cpx+plag cpx+plag

M

Figure 9. AFM diagram (Na2θ + K2θ)/FeθTotalMgOshowing the distribution of 20 analyses of the Hole3 73A basalts. Solid circles = low-Ti basalts; solidsquares = high-Ti basalts.

Y, REE), extensive olivine-pyroxene fractionation, andprobably a lack of plagk>clase accumulation. But thiscannot be further quantified because of the extensivealteration of this group. In conclusion, the trace ele-ments of the Tyrrhenian basalts collected during Leg42A show low LIL element concentrations similar toabyssal tholeiites. Within this level some elements (K,Rb, Sr, Ba, Pb, U, light REE) have concentrations atthe upper limit of the abyssal range, and higherconcentrations of these elements in the source rocks.Major element abundances are also similar to those atof abyssal tholeiites (Kay et al, 1970; Cann, 1971;Hart, 1971) and to marginal basin basalts (Hart et al.,1972; Ridley et al., 1974; Hawkins, 1976).

ACKNOWLEDGMENTS

The authors are indebted to P. Beasly for carrying out theXRF analysis of some trace elements; N. Ware for instruc-tion in the use of the microprobe; S. R. Taylor and P. Muirfor running two cross check samples at the spark source massspectrometer; and to K. J. Hsü, F. Fabricius and D. Bernoullifor providing the core samples. The samples were irradiatedin the Karlsruhe reactor FR2, and were analyzed by U.Kramer with equipment supplied by the Ministry of Researchand Technology (FRG). W. G. Ernst read the draft and of-fered helpful criticism.

523


TABLE 5 - Continued

6, CC 7-1,139-144 7-2,136-140 7-3,111-112.5 7-4, 19-23 7-4, 135-140

orabanne

di

hy

ol

mtilapcc

rwo•1 enUsren

Ifs

I fa

1.8930.5526.78

—

17.57

.94

14.86

1.862.68

.45

f9.01J5.3713.18r

1.35f 8.99

15.88

1.9926.7434.78

_

12.5 8

1.56

15.16

1.541.750.28_

f6.49-(4.0712.02(1.04

1 .52f9.79

U.37

1.6022.0942.61

—

11.89

3.58

12.11

1.191.600.24_

r6.17(4.12U.59f2.58

l l . O Or8.49

I3.6I

1.2422.8836.790.12

16.90

-

16.23

1.581.940.31_

r8.735.55

12.62

rlθ.68

1 5.55

1.4217.2141.98

3.65

8.72

-

19.26

1.481.600.28

f4.52J2.94U.27

f 13.04

I 6.22

1.3619.5237.08

1.02

6.26

-

23.45

1.571.730.263.41

f3.252.17

I .84

r 16.46

I 6.99

H2OTotal100 Mg

Mg+Fe2

Different. Ind.

1.9799.54

62.94

32.44

3.3999.72

67.84

28.69

2.5199.40

72.62

23.68

2.41100.39

68.82

24.24

3.2298.82

71.02

22.28

4.44100.09

73.29

21.90

Phenocrysts[size inmm]Groundmass[plag sizein mm]Calcite[vesiclesize in mml

cpx+plag cpx+plag

plag2-3

cpx+plag0.3-0.5

plag1-3

cpx+plag0.2-0.4

cpx+plag cpx+plag

in vesicles

REFERENCES

Alvarez, W., Cocozza, T. and Wezel, F. C, 1974. Fragmenta-tion of the Alpine orogenic belt by microplate dispersial:Nature, 248, 309-314.

Barberi, F., Bizouard, H., Capaldi, G., Ferrara, G., Gaspa-rini, P., Innocenti F., Lambert, B., and Treuil, M., 1977.Age and nature of basalts from the Tyrrhenian AbyssalPlain; this volume.

Barberi, F., Gasparini, P., Innocenti, F., and Villari, L., 1973.Volcanism if the Southern Tyrrhenian Sea and its Geody-namic implications: J. Geophys. Res., 78, 5221-5232.

Barberi, F ., Innocenti, F., Ferrara, G., Keller, J., Villari, L.,1974. Evolution of Eolian arc volcanism: Earth Planet. Sci.Lett, 21, p. 269-276.

Bass, M. N., Moberly, R., Rhodes, J. M., Shih, C, andChurch, S. E., 1973. Volcanic rocks cored in the CentralPacific, Leg 17 DSDP: Am. Geophys. Union Trans., 54, p.991-995.

Berry, M. J. and Knopoff L., 1967. Structure of the uppermantle under the Western Mediterranean basin: J. Geo-phys. Res., 72, p. 3613-3626.

Boccaletti, M. and Guazzone, G., 1972. Gli archi appeninici,il Mar Ligure ed il Terreno nel guadro della tettonica deibacini marginali retroareo: Mem. Soc. Geol. It. 11, p. 201-216.

Cann, J. R., 1969. Spilites from the Carlsberg Ridge, IndianOcean: J. Petrol, v. 10, p. 1-19.

, 1970. Rb, Sr, Y, Zr, and Nb in some ocean floorbasaltic rocks: Earth Planet. Sci. Lett., v. 10, p. 7-11.

, 1971. Major element variations in ocean-floorbasalts: Phil. Trans. Roy. Soc. London, Sec. A, v. 268, p.495-505.

Church, S. E. and Tatsumoto M., 1975. Lead isotopicrelations in oceanic ridge basalts from the Juan de Fuca -Gorda Ridge area, NE Pacific Ocean: Contrib. Mineral.Petrol.,v. 53, p. 253-279.

Del Monte, M., 1972. II vulcanesimo del Mar Tirreno: Notapreliminare sui vulcani Marsili e Palinuro: Giorn. Geol., v.38, p. 231-252.

Dewey, J. F., Pitman, W. C, Ryan, W. B. F., and Bonin, J.,1973. Plate tectonics and the evolution of the Alpine sys-tem: Geol. Soc. Am. Bull., v. 84, p. 3137-3180.

Engel, A. E. J., Engel, C. G., and Havens, R. G., 1965.Chemical characteristics of oceanic basalts and the uppermantle: Geol. Soc. Am. Bull.,v. 76, p. 719-754.

Green, D. H., 1970. The origin of basaltic and nepholiniticmagmas: Leichester Lit. Phils. Soc. Trans., v. 64, p. 28-54.

Green, D. H. and Ringwood,, A. E., 1967. The genesis ofbasaltic magmas: Contrib. Mineral. Petrol., v. 15, p. 103-190.

, 1969. The origin of basaltic magmas. In Am.Geophys. Union Monogr. 13: Hart, P. J., (Ed.) p. 489-495.

Hart, S. R., 1971. K, Rb, Cs, Sr, and Ba contents and Srisotope ratios of ocean floor basalts: Phil. Trans. Roy. Soc.London Sec. A, v. 268, p. 573-587.

Hart, S. R., Glassley, W. E., and Karig, D. E., 1972. Basaltsand sea-floor spreading behind the Mariana island arc:Earth Planet. Sci. Lett. v. 15, p. 12-18.

524


TABLE 5 - Continued

7-5,10-14 10-1,123-125 11-1,114-117 11-1,130-135 12, CC

OB 2 OcbOuter Barrel

1.4819.2138.73

5.17

5.35

19.90

1.802.070.331.82

f2.67jl.69I .81T3.62

U.73M3.03

I 6.87

1.6027.4234.05

8.73

10.01

11.01

1.322.11

.33

f4.54J3.10U.09|"7.40

U.61f7.93

I3.O8

1.6034.9525.69

8.39

14.11

7.24

1.863.190.57

r4.30k.55U.54f8.80

15.31J-4.35

12.89

1.6536.2226.08

7.06

7.67

14.02

1.832.980.52

r3.63J2.23U.20r4.99

12.68f8.81

15.21

1.8937.2324.05

7.48

5.21

15.60

1.752.960.52_

f3.86J2.42U.21r3.48

U.74flθ.06

I 5.54

1.8935.3726.13

8.43

8.00

11.77

1.833.270.62—

r4.33J2.60U.50r5.08

U.92r7.20

U.57

2.1937.5723.45

8.72

7.81

11.61

1.883.530.62—

f4.47J2.6511.60f4.87

12.94r6.97

14.64

4.58100.44

68.79

20.69

3.0099.57

73.63

29.01

2.2799.85

61.54

36.54

2.14100.17

64.61

37.87

2.3199.01

66.04

39.12.

2.1299.43

62.40

37.26

2.5699.94

60.96

39.76

cpx+plag

in vesicles

0.1-0.2

plag1-2

cpx+plag0.1-0.2

few vesicles

0.2-1

plag0.5

cpx+plag0.2-0.3

zeolites

0.3-0.4

cpx+plag cpx+plag(albite)

cpx+plag0.3-0.5

plag1-2

cpx+plag0.3-0.6

Hawkins, J. W., 1976. Petrology and geochemistry of basalticrocks of the Lau basin: Earth Planet. Sci. Lett. v. 28, p.283-297.

Heezen, B. C, Gray, C, Segre, A. G., and Zarndzki, E. F. K.,1971. Evidence of foundered continental crust beneath theCentral Tyrrhenian Sea: Nature v. 229, p. 327-329.

Honnorez, J., and Keller, J., 1968. Xenolithe in vulkanischenGesteinen der Aeolischen Inseln: Geol. Rdschau v. 57, p.719-736.

Karig, D. E., 1971. Origin and development of marginalbasins in the Western Pacific: J. Geophys. Res. v. 76, p.2542-2561.

Kay, R., Hubbard, N. J., and Gast, P. W., 1970. Chemicalcharacteristics and origin of oceanic ridge volcanic rocks:J. Geophys. Res., v. 75, p. 1985-1613.

Keller, J., 1974. Petrology of some volcanic rock series of theAeolian arc, Southern Tyrrhenian Sea: Calcalkaline andshoshonitic associations: Contrib. Mineral. Petrol., v. 46, p.29-47.

Keller, J., and Leiber, J., 1974. Sedimente, Tephralagen undBasalte der südtyrrhenischen Tiefsee-Ebene im Bereichdes Marsili-Seeberges: Meteor. Forschung. v. 19, p. 62-76.

Kreuzer, H., Mohr, M., and Wendt, I., 1977. Potassium-argon age determination of Leg 42A, drillhole 373A, Core7, basalt samples: this volume.

Lowrie, W. and Alvarez, W., 1974. Rotation of the ItalianPeninsula: Nature v. 251, p. 285-288.

Maccarone, E., 1970. Notizie petrografiche e petrochimichesulle lave sottomarine del Seamount 4 (Tirreno Sud): Boll.Soc. Geol. Ital., v. 89, p. 159-180.

Menard, H. W., 1967. Transitional types of crust nuclei smallocean basins: J. Geophys. Res. v. 72, p. 3061-3073.

Miyashiro, A., Shido., F., and Ewing, M., 1971. Metamor-phism in the Mid-Atlantic Ridge near 24° and 30° N:Phil. Trans. R oy. Soc. London Sec. A, v. 268, p. 589-603.

Miyashiro, A., 1975. Volcanic rock series and tectonic setting:An. Rev. Earth Planet. Sci., v. 3, p. 251-269.

Ogniben, L., Martinis, B., Rossi, P. M., Fuganti, A.,Pasquare, G., Sturani, C, Nardi, R., Cocozza, T., Pratur-lon, A ., Parotto, M., d'Argenio, B., Pescatore, T., Scan-done, P., Vezzani, L., AGIP-Attivita Minerarie, Finetti, I.,Morelli, C, Caputo, M., Postpichel, D. and Giese, P.,1973. Modello strutturale d'Italia, 1:1000 000: Consiglionazionale delle richerche, Roma.

Puchelt, H., Emmermann, R ., and Srivastava, K., 1976. Rareearth and other trace elements in basalts from the Mid-Atlantic Ridge 36°N., DSDP Leg 37: In Aumento, F.Melson, W. G., et al., Initial Reports of the Deep SeaDrilling Project, Volume 37: Washington (U.S. Govern-ment Printing Office), p. 581-590.

Ridley, W. I., Rhodes, J. M., Reid, A. M., Jakes, P., Shih, C,and Bass, N. M., 1974. Basalts from leg 6 of DSDP: J.Petrol., v. 15, p. 140-159.

Ritsema, A. R., 1970. On the origin of western Mediterra-nean sea basins: Tectonophysics, v. 10, p. 609-623.

Robinson, P. T. and Whitford D. J., 1974. Basalts from theEastern Indian Ocean, DSDP Leg 27. In Heirtzler, J.,Veevers, J., et al., Initial Reports of the Deep Sea DrillingProject Volume 27: Washington (U.S. Government Print-ing Office), p. 551-559.

Ryan, W. B. F., Stanley, D. J., Hersey, J. B., Fahlquist, D. A.,and Allan, T. D., 1970. The tectonics and geology of theMediterranean Sea. In Maxwell, A. F. (Ed.), The sea, v.4,p. 387-492.

525


5 -

1 "

FeO tota,/MgO

Figure 10. FeOTotal and TiO2 versus Fe0Totai/Mg0 of the Hole 373Abasalts. The Fe0jotaiJMg0 ratio indicates the degree of fractionalcrystallization (after Miyashiro, 1975). Stippled area = low-Ti basalts;hachured area = high-Ti basalts.

Shido, F., Miyashiro, A., and Ewing, M, 1971. Crystalliza-tion of abyssal tholeiites: Contrib. Mineral. Petrol., v. 31,p. 251-266.

Schilling, J. G., 1971. Sea floor evolution: rare earth evi-dence: Phil. Trans. Roy. Soc. London, Ser. A, v. 268, p.663-706.

526


25 -

20 -

15 -

10 -

5 -

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OLIVINE %

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1.0 FeOtotal/MgO1.5 2.0

Figure 11. MgO, AI2O3, and normative olivine contents versus FeOjotallMgO. Trend of compositional variationis indicated by straight lines.

527

V. DIETRICH, R, EMMERMANN, H. PUCHELT, J. KELLER

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Figure 12. Oxide percents plotted against the solidification index (SIJ=MgO/MgO + FeO + 0.9Fe203 + Na2θ + K2O) 100.

La ppm TiO2 %

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Figure 13. La/Hf and Tiθ2Hf plots for Hole 373A.

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LαCe Nd SmEu TbDy Yb Lu Lα Ce Nd Sm Eu Tb Dy Yb Lu

LαCe Nd SmEu TbDy Yb Lu Lα Ce Nd Sm Eu Tb Dy Yb Lu

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LαCe Nd SmEu TbDy Yb Lu LαCe Nd SmEu TbDy Yb Lu

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Lα Ce Nd Sm Eu Tb Dy Yb Lu Lα Ce Nd Sm Eu Tb Dy

Figure 14. REE pattern of the 20 basaltic samples, Hole 373A.

Yb Lu

529


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LαCe Nd Sm Eu Tb Dy Yb Lu LαCe Nd Sm Eu TbDy Yb Lu

LαCe Nd Sm Eu TbDy Yb Lu LαCe Nd Sm Eu TbDy Yb Lu

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LαCe Nd SmEu TbDy Yb Lu LαCe Nd SmEu TbDy Yb Lu

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LαCe Nd SmEu TbDy

Figure 14. (Continued).

YbLu LαCe Nd SmEu TbDy Yb Lu

530

19. oceanic basalts from the tyrrhenian basin, dsdp …

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