products in leg 45 basement samples · this paper gathers the preliminary results of studies...

38. PRELIMINARY RESULTS: MINERALOGY AND GEOCHEMISTRY OF ALTERATIONPRODUCTS IN LEG 45 BASEMENT SAMPLES

Thierry Juteau, Feyzi Bingöl, Yves Noack, and Hubert Whitechurch, Université Louis Pasteur, Institut deGéologie, Laboratoire de Minéralogie-Pétrographie, 1 rue Blessig, 67084 Strasbourg-Cedex, France

Michel Hoffert and Denis Wirrmann, Université Louis Pasteur, Institut de Géologie, Centre de Sédimentologieet Géochimie de la Surface, 1 rue Blessig, 67084 Strasbourg-Cedex, France

andChantal Courtois, Université de Paris-Sud, Laboratoire de Géochimie des Roches Sédimentaires Bàtiment 504,

91405 Orsay, France

ABSTRACT

In the basaltic rocks from Hole 395A, secondary minerals havedeveloped in primary phenocrysts, in the groundmass, in the vesi-cles, and in the veinlets. Phenocrysts are weakly altered: Plagioclaseand clinopyroxene are quite fresh; olivine is partially pseudomor-phosed to iddingsite and Mg-carbonate in basalts, and to a celado-nite-clay association in dolerites. Glasses are generally devitrified inthe groundmass of the basalts; intermediate stages of the palagoni-tization process have been preserved in some samples. The glassyfragments in hyaloclastic breccias have concentric alteration rimssurrounding colorless isotropic fresh glass preserved in the centralpart of the fragments. The cement of the breccias is mainly zeolitic(90%) and calcitic (10%). Phillipsite, gismondine, and faujasiteconstitute the zeolitic association: the high water content of thesezeolites indicates a low temperature of formation, surely less than100°C, possibly around 10°C. Vesicles and veinlets are mainlyfilled with phillipsite, calcite, and tri-octahedral smectites (sapo-nite). Detailed study of the coating of an open fracture in a doleriteshows the successive development of (1) green smectite concre-tions, (2) white opaque stilbite concretions, and (3) scarce translu-cent phillipsite crystals.

In the ultramafic harzburgites recovered during Leg 45, the sec-ondary minerals are lizardite, chrysotile, talc, Mg-chlorite, dolo-mite, aragonite, magnetite, and goethite; the degree of serpentiniza-tion ranges from 50 to 100 per cent in the seven samples studied.

Preliminary rare-earth element (R.E.E.) distribution analyses infresh and altered basalts indicate a remarkable inertness of theseelements during halmyrolysis of basalts in oceanic environment.

INTRODUCTION

This paper gathers the preliminary results of studiescarried out in France on the detailed mineralogy andgeochemistry of alteration products in Leg 45 base-ment samples:

Mineralogy of basaltic phenocrysts and alterationproducts of vesicles, veinlets, and glasses from Hole395A were studied by T. Juteau, Y. Noack, and H.Whitechurch.

Detailed mineralogy of an open fracture in a doler-ite from Hole 395A was investigated by M. Hoffert andD. Wirrmann.

Serpentines and associated secondary minerals in ul-tramafic samples from Holes 395 and 395A were ex-amined by F. Bingöl.

REE distribution in fresh and altered basalts wasstudies by C. Courtois.

This paper is preliminary: the complete results anddiscussions concerning these studies will be publishedlater.

SECONDARY MINERALS IN LEG 45BASALTS

Thirty-one samples from Hole 3 95A have been ex-amined: Table 1 gives the sample numbers and depths,thin sections made, and X-ray (Debye-Scherrer) data.

Secondary minerals have developed (1) in primaryphenocrysts, (2) in the groundmass, mainly in theglassy zones, (3) in the vesicles, and (4) in the veinlets.

PhenocrystsPlagioclase. Plagioclase phenocrysts are remarkably

fresh. In the only transformations observed, plagio-clases of aphyric basalt samples in the immediate vicin-ity of veinlets filled with smectites and phillipsite have

613

o «

tho

lU

nia

ical

i6

Sample(Interval in cm)

TABLE 1Leg 45, Hole 395 A

Petrologic Types

TABLE 1 - Continued

Fractures

100 -

200 -

1 1

- 1

•

T4

-

•

s

~ 6

-7

- 8

9

• io

. TI12

—

- 13

T4" 15

-

B

D

Cl

C2_

C3

4-1,

5-1,

8-1,

15-2

15-2,

15-3,15-4,16-1

17-1

22-2

25-1

25-1

32-132-1

32-2

32-2

33-1

00-105 +

S0-63+

107-113+

100-109+

110-113+

62-74+°120-124+142-148+

136-142+

,25-33+

, 50-54+

, 56-60+

,85-91° „, 122-128+

,6-9+

, 64-67+°

,43-77+

S

A.B.

A.B.

D

P.B.

DP.B.P.B.

P.B.

P.B.

P.B.

P.B.

BBD

B

P.B.

SEA FLOOR

SEDIMENTS

Serpentinite

microlites PL-OL phenocryst-niicrolites AUdark glass-Fe alteration + opaque bodyfine-grained vesicles

microlites PL-skeletal OLdark glass - fibrous vesicles (Zeo ?)

phenocryst PL-small AU-rare OL fibrous vesicles

phenocryst PL-phenocryst OL-AU fibrous vesicles

PL An 60-rare OL AU-brown alteration opaque bodies CaPL An 55-phcnocryst OL-AU-opaquc bodies CaPL An 60-rare OL+iddingsite-microlitesAU-altered glass+phyllitesPL An 60-rare OL-small AU

PL An 60-rare OL+iddingsite-AU-fibrous zones, yellow in plane lightgray with crossed nichols

phenocryst PL An60, micro An35altered OL-AUPL An70-altered OL-AU

Doleritic elements-carbonated matrix

PL An60-AU-orange glassy elements

phyric elements-glass elements-carbonatedcementAn70, skeletal microlites-orange glassfibrous zones

100

500

600

7nn

- 16

. TL

18

19

~2021

22

-

- 23

-

E

E

—

—

C2'

—

G'

36-1,79-82+°

49-1, 106-112+

55-1,91-92+

56-1, 134-136+'

57-1, 100-105+°

58-2,75-81 +

59-1,44-48+

60-3, 70-80°62-1,40-42+63-2, 112-116+63-4, 80-88+63-4, 140+ „64-3, 54-58 +644,50° ,65-2, 70-90+66-1, 110+66-1,14366-3, 130-140+

67-1,54-58°67-1, 130-137+

A.B.

B

A.B.

A.B.

A.B.

11

11

Λ.B.A.B.

D

DI)

A.B.A.B.Λ.B.

11A.B.Λ.B.

A.B.11

skeletal PL-dark glass-grainy vesicles

aphyric elements-dark glassy elementscarbonated cement

PL An 50-AU-altered OL-dark glass-orange glassy elements-fibrous vesicles

skeletal PL An 58-AU-fibrous vesicles

skeletal PL An 40-AU-glass-fibrous vesicles

Glassy elements + OL-AU

glassy elementsl small brown spots in the fresh glass

PL radial structure-fibrous vesiclesPL An 40-AU-fibrous zones

PL An 60-altered OL-fractures

skeletal PL-AU-fibrous zones

Phi

Sm

Phi

Phi+Sm

Phi

Phi+Sm+Ca

microlites PL An 45-altered OL-fibrous vesicles + Ca fracturesglassy elements-zeolitic cement

skeletal PL-fibrous vesicles

glassy elements-zeolitic cement

Sm+CaPhi+Sm- Sm

Sm

Note:

Lithologic UnitsChemical types

See shipboard report

Legend

Samples: + Thin section, ° X-Ray film (Debye-Scherrer).

Petrologic types:

Fractures:

s:

CaSmMontPhi

A.P.

D:B:11:

B. : aphyric basaltB.: phyric basalt

doleritic basaltvolcanic brecciahyaloclastite

calcitesmectitemontmorillonitephillipsite

PL PlagioclaseAU augiteOL olivine

MINERALOGY AND GEOCHEMISTRY

been partially or completely replaced by zeolites andcalcite.

Olivine. Olivine phenocrysts are rarely fresh. Asusual, they are the most sensitive minerals to altera-tion: in phyric and aphyric basalts, olivine is partiallyor completely replaced by iddingsite (mixture of goe-thite and montmorillonite-type clay). An Mg-carbonate(magnesite) sometimes accompanies iddingsite aroundcores of altered olivines. In the doleritic basalts of thesection, the intersertal olivine is transformed to a cela-donite-clay association. In all cases, the initial shape ofthe mineral, skeletal, or idiomorphic, is preservedthrough pseudomorphosis.

In the hyaloclastic breccia of the section, olivine isalways fresh.

Pyroxene. The augitic clinopyroxene remains unal-tered. Only small quantities of tiny chlorite lamellae(< 20 µm) have crystallized around the pyroxenes of thephyric and doleritic basalts.

Conclusion. Primary phenocrysts are weakly alteredin Hole 3 95A. Olivine, the most sensitive mineral, ispseudomorphosed to iddingsite in the basalts, and to aceladonite-clay association in the dolerites. Plagioclaseis replaced by calcite and zeolites in the vicinity ofsmectite-phillipsite veinlets of phyric basalts. Clinopy-roxene is fresh. No evolution of alteration with depthhas been detected.

GlassesFresh or altered glasses have been found (1) in the

groundmass of phyric and aphyric basalts and (2) asfragments in the hyaloclastic breccias.

Groundmass of phyric and aphyric basalts. Primaryglasses are scarce. The groundmass is generally devitri-fied, with delicate submicroscopic pyroxene and Fe-ox-ides which exhibit "comb" and "feather" shapes. Aninterstitial palagonitized glass is well developed inSample 395A-16-1, 142-148 cm. In this orange iso-tropic glass, round domains about 500 µm in size aresurrounded by fibrous zeolitic rims; inside these do-mains, the glass is brown and slightly anisotropic. Ra-diating zeolite clusters occur between these domains.When the different brown zones join together, the glassis completely palagonitized. The evolution of this alter-ation is similar to that observed in the hyaloclastites.

Hyaloclastic breccias. This facies is the most inter-esting for observing all stages of alteration of basalticglasses. These breccias are made up mainly of glassyfragments with concentric zones of alteration, ce-mented by zeolites.

The center of the glassy fragments is often fresh col-orless or pale yellowish isotropic glass containing someskeletal or sub-automorphic unaltered olivine mi-crophenocrysts (maximum dimension: 1 mm). In somefragments, this glass shows evidence of the beginningof alteration: small brownish striated and lobated areasappear here and there in the glass (Plate 1, Figures 1and 2), often situated around the olivine micropheno-crysts. These areas are slightly anisotropic (Plate 1,Figures 3 and 4). In a next stage, these brownish areasare surrounded by a thin fibrous birefringent rim com-

posed of smectites and zeolites (Plate 2, Figures 1 and2). Two kinds of concentric alterations have been ob-served developing around the fresh isotropic centralglass:

The first type comprises three "aureoles" (Plate 2,Figures 3 and 4; Plate 3, Figures 1 to 3): (1) an or-ange isotropic rim, in contact with the fresh glass; (2)an orange-brown anisotropic zone, usually well devel-oped, composed mainly of clay minerals and hydratedaltered brownish glass; (3) a fibrous yellow zeoliticand/or chloritic outer rim.

This type of alteration is very similar to the "palag-onite neotype" defined and described by Stokes(1971), and to the palagonitized "granules" in thetuffs of Palagonia (Sicily), carefully described by Hon-norez(1972).

The second type comprises three tin "aureoles"(Plate 4, Figures 1 to 3): (1) a thin green isotropic rim,in contact with the fresh colorless glass; (2) a thinslightly brownish anisotropic rim; (3) a fibrous zeoliticand/or chloritic outer rim.

This type differs from the former one by the absenceof a brownish zone of altered glass between the freshcolorless glass and the fibrous rim; perhaps it is anearly stage of the first type.

The cement of the breccias is mainly zeolitic (90%)and calcitic (10%); phillipsite occurs as fan-shapedcrystals developing on the margin of the glassy frag-ments (Plate 3, Figure 3). Fine-grained gismondineand faujasite (determined by X-ray diffractometry) areposterior to phillipsite and cement it. The high watercontent of these zeolites indicates a low temperature offormation, surely less than 100°C (Coombs et al.,1959; Senderov, 1965), and perhaps very close to thenormal seawater temperatures proposed by Moore(1966) for contemporaneous palagonitization of Ha-waiian glasses.

The first chemical data obtained by electron micro-probe analysis are not yet satisfactory enough to bepublished here; they indicate, though, a tholeitic com-position for the fresh glass. By comparison, the palago-nitized zones show a strong depletion in CaO andhigher contents of H2O, and K2O; SiO2 is slightlydepleted; A12O3, total Fe, and TiO2 remain more orless unchanged.

VesiclesThe following filling associations have been found

in the vesicles (see Table 1): (1) phillipsite (Plate 5,Figures 1 and 2), (2) phillipsite + calcite, (3) phillip-site -I- clays, (4) clays.

No evolution with depth was found.

VeinletsThe following filling associations have been found

in the veinlets (see Table 1): (1) carbonates, (2) phil-lipsite, (3) phillipsite + iron-rich smectite (nontronite),(4) phillipsite + smectites + carbonates, (5) smectites.

As in the vesicles, phillipsite is the only zeolite founduntil now in the veinlets (Table 2). The carbonatephase is represented by calcite (Table 3). Smectites are

615

T. JUTEAU ET AL.

TABLE 2Zeolites of Veinlets in Hole 3 95A Basalts

(Debye-Scherrer exposures)

Phillipsite(ASTM 13-455)

hkl

101020012121022200101130200210012140131241201141150

36-1,

d(A)

8.227.196.43

4.96

4.13

3.97

3.202.97

2.73

79-82

I/Il

108510

30

70

10

10030

50

Sample (Interval in cm)

57-1,100-105

d(A)

7.22

4.09

3.172.98

2.71

I/Il

80

50

10020

20

60-3,

d(A)

8.227.08

5.37

4.98

4.08

3.18

2.85

70-80

I/Il

1060

10

20

50

100

10

66-3,

d(A)

8.267.166.415.385.02

4.314.11

3.973.483.283.202.96

2.762.70

143

I/Il

80203040

2070

101040

10040

4050

TABLE 3Carbonates of Veinlets in Hole 395A Basalts

(Debye-Scherrer exposures)

Calcite(ASTM 5-586)

hkl

102104006110113202108116212-21121420830020 10218-306220-11 122 14 1022620 1430 12-231

15-2110-113

d(A)

3.863.042.882.512.282.10

1.861.621.53

1.44

I/Il

5100

5555

555

5

Sample (Interval in cm)15-4,

120-124d(A)

3.02

2.502.572.09

1.88

I/Il

100

102010

20

32-1,122-128

d(A)

3.843.012.822.502.272.081.901.861.60

1.511.441.331.291.231.181.141.081.00

I/Il

20100

10205030501010

5

64-3,

d(A)

3.863.03

2.282.091.911.87

54-58

I/Il

30100

20102010

66-1,

d(A)

3.05

2.282.111.90

1.53

143

I/Il

100

101010

10

mainly of the trioctahedral type; they are represented bythe Mg-rich type saponite (Table 4). The dioctahe-dral type of montmorillonite has been found in oneveinlet, where it occurred alone (Table 5).

Coating of an Open Fracture

The coating of an open fracture in a doleritic basalt(Sample 395A-63-4, 80-88 cm) has been investigatedin detail. The fracture is coated by several types of sec-ondary minerals.

Plate 6 (Figures 1 and 2) shows the existence ofthree kinds of minerals with different colors:

1) a thin pale green coating less than 0.1 mm thick,with mamelon shapes, covering the whole surface ofthe fracture;

2) white opaque minerals forming radiatingspherules, rather abundant and irregulary disposedover the surface;

3) scarce white and translucent slab minerals.Each type of concretion has been observed under

the scanning electron microscope (CAMECA-07). Indi-cations on the chemistry of these minerals were ob-tained by energy-dispersive spectrometry (TRACORSystem). X-ray Debye-Scherrer exposures were alsomade.

Plate 7 shows the morphological aspect of the greenconcretions. They consist of the juxtaposed and anasto-mosing small spherules or glomerules, the diameters ofwhich are about 0.1 mm. Their surface is made of"folded sheets." In section, these spherules present amore massive radiating structure. That type of mor-phology is very similar to that described by Person(1976) as minerals of the smectite group. Chemicalcomponents of these glomerules are mainly Fe, Ca, Si,Al, and Mn. Debye-Scherrer exposures confirm thatthese minerals are smectites.

Plate 8 shows the morphological aspect of the whiteopaque concretions. These are "fusiform" balls, withan average diameter of 1 mm. They are composed ofslabs or scales with a "roofing tile" disposition. Carefulexamination of these slabs shows the existence of re-entrant angles in the middle part of the structures, indi-cating that each scale is probably made of two twinnedminerals. These structures are analogous to those de-scribed by Mumpton and Ormsby (1976). Chemicalcomponents of these scales are mainly Ca, Si, and Al.They grow over the green material, and their genesis istherefore posterior. Debye-Scherrer exposures indicatethat these concretions are stilbite.

Plate 9 shows the morphological aspect of the scarcetranslucent mineral. During observation with the SEM,this mineral became opaque and split into several frag-ments. Each fragment is made by the piling up of verythin parallel lamellae. Chemical components of thismineral are K, Si, Al, Na, and some Ca. Debye-Scher-rer exposures indicate phillipsite.

In conclusion, the open fracture of the sample stud-ied has been coated by three minerals that developedin the following order: (1) smectites, (2) stilbite, (3)phillipsite.

This order of appearance of the secondary mineralsis identical to that described by Honnorez (1972) forthe submarine alteration of basaltic glasses at Palago-nia (Sicily).

SECONDARY MINERALS IN LEG 45HARZBURGITES

Seven samples of more or less serpentinizedharzburgites gave been examined. The degree of ser-pentinization ranges from 50 to 100 per cent. Table 6gives the secondary paragenesis and degree of serpenti-nization for each sample.

616


TABLE 4Trioctaedral Smectites of Veinlets in Hole 3 95A Basalts

(Debye-Scherrer exposures, completed by diffractograms)

hkl

001110,020130,200310,150330,060260,400350,170190,530390,600

56-1,134-136

d(A)

12.804.572.56

1.53

I/Il

1005080

80

64-3, 54-58

d(Å) I/Ii

14 1004.55 50

1.53 50

Smectite(ASTM

Saponite11-56)


60-3, 70-80

d(A)

12.624.552.561.731.531.321.280.990.88

I/Il

1005040207030101010

66-1,

d(A)

12.994.572.54

1.531.32

143

I/Il

1005050

8030

66-3, 54-58

d(A)

13.594.552.561.731.531.32

0.990.88

I/Il

1005020205010

1010

66-3,130-140

d(A)

13.584.612.54

1.531.32

I/Il

1003050

5020

Smectite(ASTM

hkl

001110,120004130,200

008

330,060

Saponite13-86)

66-3130-140

d(A)

12.984.583.692.552.222.071.841.741.541.321.28

I/Il

10050601010303020801020

TABLE 5Dioctaedral Smectites ofVeinlets in Hole 395ABasalts (Debye-Scherrerexposures, completed

by diffractograms)

Montmorillonite(ASTM 13-259)

TABLE 6Secondary Paragenesis and Degree of Serpentinization for

Harzburgite Samples From Site 395


hkl

64-4,

d(A)

13.594.473.202.53

50

I/Il

100505040

All samples contain both lizardite and chrysotile(Figure 1) with the classical mesh structure around oli-vine relicts (Plate 10, Figures 1 and 2). Enstatite ispseudomorphosed by bastite, a fibrous variety of liz-ardite (Plate 10, Figure 3). Veinlets are filled bychrysotile, talc (Plate 10, Figure 4), Mg-rich chlorite(Plate 10, Figure 5), and carbonates (both dolomiteand aragonite (Plate 10, Figure 6) have been found).Serpentines are accompanied by a "dust" of tiny mag-netite and/or goethite grains.

Plates 11 and 12 show the morphological aspect,with associated microdiffractograms, of the secondaryminerals listed above.

REE DISTRIBUTION IN FRESH ANDALTERED BASALTS

It has been shown that during continental alteration,the rare-earth elements exhibit very homogeneous be-haviour (Ronov et al., 1967). Recent studies haveshown that the diverse layers in alteration profiles ex-hibit a rare-earth distribution generally identical to thatof the underlying mother-rock (Steinberg and Courtois,1976).

The aim of the present study is to determinewhether this remarkable inertness of the REE family

SampleLocation

395A-4-2,45-50 cm #2

395-18-2,139-141 cm#17f

395-18-2,62-70 cm #15

395-18-1,142-145 cm #2i

395-18-1,101-106 cm

395A-4-1,100-105 cm #9

395-18-2,7-10 cm #2

Rock Name

Seipentinizedharzburgite

Partly serpenti-nizedlherzolite

Serpentinizedharzburgite



SerpentiniteVery oxidized

Serpentinite

PrimaryMinerals

EnstatiteOlivine

OrthopyroxeneClinopyroxeneOlivineChromite

EnstatiteOlivinerelicts

EnstatiteOlivine

EnstatiteOlivine

BastiteEnstatite

Olivinerelicts,Enstatite

SecondaryMinerals

ChrysotileLizardite"Bastite"Talc (veinlets)

ChrysotileLizardite"Bastite"Magnetite

ChxysotileLizardite"Bastite"Magnetite andGoethiteCarbonates (vein-lets):(Dolomite)

ChrysotileLizardite"Bastite"Magnetite andGoethite

ChrysotileLizardite"Bastite"Magnetite andGoethite

ChrysotileLizardite"Bastite"

ChrysotileLizarditeCarbonates (vein-lets):Aragonite

Degree ofSerpentinization

80%

50%

80%

70%

70%

100%

95%

can also be found during submarine alteration of ba-salts, or whether a fractionation occurs during halmy-rolysis in oceanic environment.

As a first step, we tried to select some of the morerepresentative samples of fresh and altered basalts, andselected the following samples for REE analysis:

Hole 395:15-1, 112-119 cm #8C: fresh basalt15-1, 37-40 cm #5: altered basalt

617

T. JUTEAU ET AL.

C. Sample/ C. chondrites

Figure 1. Diffraction tracings of serpentines: (A)chrysotile + lizardite (Sample 395A-4-2, 45-50 cm 2);(B) chrysotile + lizardite (Sample 395-18-1, 101-106cm 2g); (C) chrysotile + enstatite (Sample 395-18-1,142-145 cm 2i).

Hole 395A:3-1, 140-142 cm #6 fresh basalt3-1, 100-102 cm # 4 altered basalt33-2, 112-118 cm #14 fresh basalt and its altera-

tion rim.

Hole 396:15-1, 80-88 cm #7A fresh basalt, alteration rim and

a third outer zone, honey-colored, probably palagonit-ized glass.

REE have been analyzed by neutron activation, us-ing the method of chemical separation described byTreuil et al. (1973). The results given in Table 7 showclassical ratios of REE (30 to 60 ppm) for oceanicbasalts. The absolute ratios for altered basalts areidentical to those for fresh material: it seems there is nodilution or concentration during halmyrolysis.

The REE distribution curves are built following theclassical normalization diagrams of Coryell et al.(1963). The REE ratios are normalized to chondritesfor fresh basalt samples (Figure 2) and for altered ba-salts that are not directly in contact with fresh material(Figure 3).

For the two samples where a separation has beenmade, the normalization has been made relative to thecorresponding fresh basalt (Figure 4).

La Ce Nd Sm Eu Tb

395A-3-1, 140-142 cm #6

yLa Ce Nd Sm Eu Tb

396-15-1, 80-88 cm #7 A

La Ce Nd Sm Eu Tb Yb LuAtomic Number

Figure 2. REE curves normalized to chondrites for freshbasalts.

The REE distribution in fresh basalts shows a frac-tionation with impoverishment in light REE especiallyfor La and Ce. That kind of profile is characteristic ofoceanic tholeiites (Frey and Haskin, 1964).

In altered basalts, the distribution curves normalizedto chondrites are identical to the curves for fresh ba-salts, except for Sample 395A-3-1 #4, which is not im-poverished in light REE. In the two samples whereboth fresh and altered zones of the same piece wereanalyzed, the curves normalized to the fresh basaltshave a completely flat profile. These curves, with ordi-nate 1, show that no fractionation occurred. It seems,therefore, that REE have a homogeneous geochemicalbehavior during submarine alteration.

The superficial altered glass of Sample 396-15-1,#7A is a peculiar case. Relative to the underlyingfresh basalt, its REE distribution curve presents a clearfractionation, with impoverishment in heavy REE. Thisfractionation probably reflects differences in mobility ofREE, and is related to the progressive decrease, withincreasing atomic weight, of the stability constantsof these elements in solution. This observation, how-ever, must still be considered in the context of mineral-ogical and geochemical analysis of this sample for amore precise interpretation.

618


TABLE 7REE Contents (ppm)


395-15-1, 119-122 cm #8C395-15-1, 37-40 cm #5395A-3-1, 140-142 cm #6395A-3-1, 100-102 cm #4395A-33-2, 112-118 cm #14

396-15-1, 80-88 cm #7A

Fresh basaltAltered basaltFresh basaltAltered basaltFresh basaltAltered basaltFresh basaltAltered basaltAltered glass (?)

La

4.13.86.29.17.57.63.753.734.03

Ce

11.29.2

20.719.422.221.79.49.1

12.0

Nd

11.13.3

16.814.419.518.48.77.65.7

Sm

3.63.35.35.25.96.32.762.951.22

Eu

1.31.21.981.852.22.41.051.080.42

Tb

0.880.821.31.21.41.50.70.650.22

Yb

3.63.35.74.36.46.22.62.80.97

Lu

0.650.571.00.721.11.10.50.460.14

Total

362559566665292825

C. Sample/ C. chondrites C. Sample/ C. corresponding fresh basalts

3 0 -

Atomic Number

Figure 3. REE curves normalized to chondrites foraltered basalts.

The present results must be considered with cautionfor the following reasons:

First, the small number of samples analyzed pre-vents any generalization of the conclusions of thisstudy.

Second, the separation of pure phases is probablyincomplete and a "contamination," even weak, of al-tered material by fresh material introduces an errorthat can be significant for trace elements.

Last, the alteration of the basalts is very superficial,so that the ratio between mobilized elements and resid-ual material is too weak for the geochemical evolutionof the REE distribution to be detected.

It is necessary to analyze samples where alteration ismore intense, and particulary to follow the REE evolu-tion during palagonitization of basaltic glasses.

ACKNOWLEDGMENTSWe want to thank Professor G. Dunoyer de Segonzac for

his critical review of this paper.

REFERENCES

Coombs, D. S., Ellis, A. J., Fyfe, W. S., and Taylor, A. M.,1959. The zeolite facies with comments on the interpreta-tion of hydrothermal syntheses, Geochim. Cosmochim.Acta, 17, p. 58-107.

Coryell, C. D., Chase, J. W., and Winchester, J. W., 1963. Aprocedure for geochemical interpretation of terrestrial rare

altered basalt: 396-15-1, 80-88 cm #7A

La Ce

La CeAtomic Number

Figure 4. REE curves of altered basalts normalized tocorresponding fresh basalts in contact with them.

earths abundance patterns, /. Geophys. Res., v. 68, p. 559-566.

Frey, F. A. and Haskin, L. A., 1964. Rare earths in oceanicbasalts, /. Geophys. Res., v. 69, p. 775-780.

Honnorez, J., 1972. La palagonitisation: 1'alteration sous-ma-rine du verre volcanique basique de Palagonia (Sicile),Kristallogr. Petrograph. Institut der Eidgenössischen Tech-nischen Hochschule Zurich No. 9.

Moore, J. G., 1966. Rate of palagonitization of submarinebasalt adjacent to Hawaii., U. S. Geol. Survey Prof. Paper550-D,p.D 163-D 171.

Mumpton, F. A. and Ormsby, W. C , 1976. Morphology ofzeolites in sedimentary rocks by scanning electron micros-copy, Clays and Clays Minerals, v. 24, p. 1-23.

Person, A., 1976. Recherches sur les néoformations argil-euses dans 1'environment volcanique, These 3ème cycle,Paris VI, p. 166.

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Ronov, A. B., Balashov, Yu, A., and Migdisov, A. A., 1967.Geochemistry of the rare earths in the sedimentary cycle,Geochem. Intern, v. 4., p. 1-17.

Senderov, E. E., 1965. Features of the conditions of zeoliteformation, Geochem. Intern., 2, p. 1143-1155 (translatedby Dr. Zen).

Steinberg, M. and Courtois, C, 1976. Le comportement desterres rares au cours de 1'alteration et ses consequences,Bull. Soc. Géol. France, v. XVIII, p. 13-20.

Stokes, K. R., 1971. Further investigations into the nature ofthe materials chlorophaeite and palagonite, MineralogicalMagazine, v. 38, p. 205-214.

Treuil, M., Jaffrezic, H., Deschamps, N., Derre, C, Guichard,F., Joron, J. L., Pelletier, B., Courtois, C , and Novotny,S., 1973. Analyse des lanthanides, du hafnium, du scandi-um, du chrome, du manganese, du cobalt, du cuivre et duzinc dans les mine'raux et les roches par activation neutroni-que, J. Radioanal. Chem., v. 18, p. 55-68.

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PLATE 1Early Stages of Alteration in Colorless Isotropic Glass of

Hyaloclastic Fragments

Figure 1 Photomicrograph of small brownish striatedand lobated areas in the colorless isotropicglass, central zone of a hyaloclastic fragment.These areas often develop around fresh olivinemicro-phenocrysts (OL).Sample 395A-59-1, 44-48 cm #6; magnification×35; plane polarized light.

Figure 2 Photomicrograph of small brownish striatedand lobated areas in the colorless isotropicglass, central zone of a hyaloclastic fragment.Sample 395A-58-2, 75-81 cm #6c; magnifica-tion ×35, plane polarized light.

Figure 3 Detail of Figure 1, by crossed polars: thebrownish striated areas are anisotropic and po-larize to first order white; they are probablycomposed of crystallized zeolitic materialaround fresh olivine crystals (OL). Magnifica-tion X137.

Figure 4 Figure 2 by crossed polars, showing same phe-nomena (olivine microphenocrysts are not visi-ble here).

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PLATE 2Intermediate Stages of Palagonitization in Hyaloclastic

Fragments

Figure 1 Photomicrograph of brownish striated aniso-tropic areas in colorless isotropic glass, now sur-rounded by a thin fibrous rim of zeolites-smectites.Sample 395A- 58-2, 75-81 cm #6c; magnifica-tion ×35; polarized light.

Figure 2 Detail of Figure 1; magnification ×137.

Figure 3 Photomicrograph showing the altered marginsof two isotropic glassy fragments set in a zeo-litic cement. The upper right one shows the threealteration rims of the second type of alteration:Zone B: orange isotropic glass, with someanisotropic areas; note the anisotropic zone welldeveloped around the olivine microphenocryst.Zone C: slightly brownish anisotropic rim. ZoneD: fibrous anisotropic rim.Sample 395A- 67-1, 130-137 cm; magnification×137; plane polarized light.

Figure 4 Figure 3, by crossed polars.

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PLATE 3Altered Margins of Glassy Fragments in Hyaloclastic Breccias

Figure 1 Photomicrograph of palagonitized glassy frag-ments cemented by zeolites. Two main zonesare visible in the fragment (alteration type 1,see text): Zone A: colorless isotropic glass. ZoneB: orange-brown isotropic altered glass, inplaces slightly anisotropic. The two thin outerrims (Zones C and D, see text) are not clearlyvisible here.Sample 395A-67-1, 130-137 cm; magnification×35; plane polarized light.

Figure 2 Photomicrograph of palagonitized glassy frag-ments (type 1), with the different concentricrims A, B, C + D (together, because they arevery thin) clearly visible. Notice that the smallshards of glass in the middle are completely al-tered: their central zone is made of brownish al-tered glass B.Sample 395A-59-1, 44-48 cm #6; magnification×35; plane polarized light.

Figure 3 Detail of Figure 2: the zones C (slightly brown-ish anisotropic rim) and D (fibrous outer rim)are clearly visible now. Fan-shaped radiatingphillipsite of the cement has nucleated on theboundary of the fragment. Magnification× 137; plane polarized light.

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PLATE 4Altered Margins of Glassy Fragments in Hyaloclastic Breccias

Figure 1 The two types of alterations described in thetext are visible here: (1) The big fragment mar-gin in the lower part shows the four Zones A,B, C, D of the first type, with a well-developedintermediate brownish Zone B. (2) In the cen-ter of the photograph, a small fragment exhibitsthe sharp transition from fresh glass A to thethin outer rims, without intermediate brownishglass. This part is enlarged in the followingfigures.Sample 395A-58-2, 75-81 cm #6c; magnification×35; plane polarized light.

Figure 2 Detail of Figure 1, showing the typical zones ofthe second type of alteration: Zone A: colorlessisotropic glass; Zone B: green, slightly aniso-tropic rim; Zone C: very thin, slightly brownishanisotropic rim; Zone D: fibrous outer rim (zeo-lites + chlorites). Magnification ×137; planepolarized light.

Figure 3 Idem, crossed polars.

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PLATE 5Secondary Minerals in Vesicles

Figure 1 Photomicrograph of a small vesicle filled withzeolites and smectites, cut by a calcitic veinlet,in an aphyric basalt.Sample 395A-65-2, 70-90 cm; magnification×35; plane polarized light.

Figure 2 Detail of Figure 1; magnification ×137; crossedpolars.

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PLATE 6Coating of an Open Fracture

Figure 1 Three kinds of minerals are visible: (1) a thinpale green coating covering the whole surfaceof the fracture (smectites); (2) white opaqueminerals forming radiating spherules, ratherabundant and irregulary disposed over the sur-face (stilbite); (3) scarce translucent minerals(phillipsite).Sample 395A-63-4, 80-88 cm.

Figure 2 Detail of Figure 1.

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PLATE 7Coating of an Open Fracture: Morphology of the Green

Concretions, by Scanning Electron Microscopy

Figure 1 Spherules of green smectites, ×350. (NegativeSEM 761232.)

Figure 2 Internal radiating structure of one spherule,X900. (Negative SEM 761229.)

Figure 3 Detail of the surface of a spherule, showing thecharacteristic morphology of neoformed smec-tites, X4000. (Negative SEM 761285.)

Figure 4 Detail of Figure 3, × 10,000. (Negative SEM761286.)

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PLATE 8Coating of an Open Fracture: Morphology of the WhiteOpaque Concretions, by Scanning Electron Microscopy

Figure 1 General morphology of the stilbite concretions:"fusiform" balls, ×30. (Negative SEM761231.)

Figure 2 Idem, general morphology of the "fusiform"balls, ×35. (Negative SEM 761233.)

Figure 3 Detail of the "roofing tile" disposition of thestilbite crystals in the balls. Notice the presenceof a re-entrant angle in each "tile," which isformed by two twinned stilbite crystals. ×400.(Negative SEM 761288.)

Figure 4 Detail of a "tile." X4000. (Negative SEM761287.)

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PLATE 9Coating of an Open Fracture: .Morphology of the ScarceTranslucent Crystals, by Scanning Electron Microscopy

Figure 1 Morphological aspect of a fragment of phillip-site, made of lamellae piled up on one another.X700. (Negative SEM 761291.)

Figure 2 Morphological aspect of the phillipsite crystal,intensely fractured by the electron beam undervacuum. X30. (Negative SEM 761290.)

Figure 3 Detail of the lamellae, X3000. (Negative SEM761292.)

Figure 4 Another aspect of the piling up of the lamellae.×900. (Negative SEM 761235.)

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PLATE 10Serpentines and Associated Minerals in Leg 45 Harzburgites

Figure 1 Mesh serpentine (chrysotile), around olivinerelicts. Serpentinized harzburgite. Crossed po-lars; magnification ×7.5;Sample 395-18-2, 62-70 cm #15.

Figure 2 Mesh serpentine with fibrous serpentineCHR = chrysotile) and olivine relicts in themeshes. Serpentinized harzburgite, crossed po-lars. Magnification ×48;

Sample 395-18-2, 62-70 cm #15.

Figure 3 Serpentinization of orthopyroxene (enstatite).The serpentine is a bastite ( = flaky lizardite)with its main cleavage (001) oriented parallelto the cleavage (100) of pyroxene. Serpenti-nized harzburgite, crossed polars. Magnification×48;Sample 395-18-2, 62-70 cm #15.

Figure 4 Talc (TA) cutting orthopyroxene (enstatite).Serpentinized harzburgite, crossed polars. Mag-nification ×7.5;

Sample 395A-18-2, 45-50 cm #2.

Figure 5 Chlorite vein in a serpentinite. Crossed polars.Magnification ×48;Sample 395-18-2, 7-10 cm #2.

Figure 6 Carbonate veins (AR = aragonite) in a serpen-tinite. Crossed polars. Magnification ×7.5;Sample 395-18-2, 7-10 cm #2.

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Figure 1 Chrysotile, (left) electron micrograph of a dis-persion and (right) an electron-diffraction pat-tern from a single crystal. × 45,000.Sample 395A-4-2, 45-50 cm #2.

Figure 2 Lizardite, (left) electron micrograph of a dis-persion and (right) an electron-diffraction pat-tern from a crystal. × 60,000.Sample 395-18-2, 7-10 cm #2.

Figure 3 Talc (left) electron micrograph of a dispersionof talc (platy aggregate) and chrysotile and(right) an electron-diffraction pattern from acrystal of talc. × 60,000.Sample 395A-4-2, 45-50 cm #2.

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Chlorite, (left) electron micrograph of a disper-Figure 1 s j o n an (j (right) an electron-diffraction pattern

from a single crystal. × 37,500.

Sample 395-18-2, 7-10 cm #2.

Figure 2 Carbonate (Dolomite), (left) electron micro-graph of dispersion and (right) an electron-dif-fraction pattern from a crystal. × 48,000.Sample 395-18-2, 138-141 cm #17f.

Figure 3 Goethite (left) electron micrograph of a disper-sion and (right) an electron-diffraction patternfrom a crystal. × 37,500.Sample 395-18-1, 101-106 cm #2g.

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products in leg 45 basement samples · this paper gathers the preliminary results of studies...

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