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Hawaiian-derived volcanic ash layers in equatorial northeastern Pacific sediments
Marine Geology, 50 (1982) 25--40
25
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
HAWAIIAN-DERIVED VOLCANIC ASH LAYERS IN EQUATORIAL NORTHEASTERN PACIFIC SEDIMENTS
E. REHM and P. HALBACH
Institut fiir Meeresforschung, Am Handelshafen 12, D-2850 Bremerhaven (F.R.G.) Research Group for Sediment Ore Formation, Technical University of Clausthal, D-3392 Clausthal-Zellerfeld (F.R. G.) (Received December 8, 1981; revised and accepted May 5, 1982)
ABSTRACT Rehm, E. and Halbach, P., 1982. Hawaiian-derived volcanic ash layers in equatorial northeastern Pacific sediments. Mar. Geol., 50: 25--40. Volcanic ash layers with thicknesses of up to 30 cm and ages between 1 and 2 m.y. were found in equatorial northeastern Pacific sediments. Grain-size distributions, mineralogical composition and alteration of the ashes are described. Chemical analyses of major, trace and rare-earth elements and trace-element correlations indicate a basaltic composition of the ocean-island tholeiitic type. Comparison with Hawaiian tholeiitic rocks indicates the Island of Maul as the source of material for the ash sequence in the investigated area. The composition of an ash layer north of the area indicates it was associated with volcanism of Mauna Loa or Kilauea. INTRODUCTION
Volcanic ashes are widely distributed in deep-sea sediments from marginal Pacific regions. They are observed in subantarctic latitudes (Huang et al., 1973, 1975), in the Gulf of Alaska and the Aleutian area (Nayuda, 1964; Horn et al., 1969; Hays and Ninkovitch, 1970; Pratt et al., 1973; Scheidegger and Kulm, 1975) b u t also near the Pacific coast of Central America (Bowles et al., 1973; Hahn et al., 1979). In the area of the Hawaiian Ridge, Edsall (1975) described volcanic glass in more than 70% of the investigated cores but found ash layers only in 9 cores. According to paleomagnetic and biostratigraphic investigations, volcanic glass is frequently distributed in Pleistocene sediments southeast of the Hawaiian Islands. This paper describes ash layers that originated from Hawaiian eruptions and were carried up to 928 km from the islands. SITE VA 18
The area VA 18 is situated within the Clarion fracture zone south-southeast of the Island of Hawaii centered at 14°N and 153°W (Fig.l). The bathymetric chart of this region shows a horst structure with two parallel grabens 0025-3227/82/0000--0000/$02.75
© 1982 Elsevier Scientific Publishing Company
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separated by a distance of a b o u t 25 km (Herbst et al., 1980). In the survey area waterdepth for the southern graben amounts to 6400 m. However, the major part of area VA 18 has normal abyssal-hill topography with waterdepths from 5600 to 5900 m (Fig.l). A single 400-m submarine basaltic seamount in the western area is the only volcanic structure observed. METHODS Eleven piston cores with a total length of 83.3 m were available for investigation. Concerning the " n o r m a l " sediment, the cores were continuously divided into 10--15-cm sections. Within the ash layers, the sections were reduced to 2--5 cm. " N o r m a l " sediment was classified according to grain-size distribution, composition of the sand fraction and X-ray results. The mineralogical composition of the ash layers was mostly determined by X-ray phase analyses. In order to get pure-glass concentrates for chemical analyses, the > 63-pm fraction was treated with heavy liquids and separated by Frantz-Isodynamic Separator. Chemical analyses of major- and trace-elements were done at the BGR (Hannover, F.R.G.) using Philips Sequenzspektrometer PW 1450 and metaborate fusion. REE were determined by NAA at the Hahn-Meitner Institute (West Berlin).
27 CHARACTERIZATION OF N E A R - S U R F A C E SEDIMENTS
From radiographic and microscopic investigations, Von Stackelberg (1981) classified the sediments of the area into three facies. Facies I is mostly dark brown in colour (10 YR 3/2) (Munsell, 1975) and normally with no distinct sedimentary structure. This facies is mainly found in cores from the northern part of the area. Facies II shows dark reddish-brown colours (5 YR 3/2-2.5/2) (Munsell, 1975) and different burrows (Von Stackelberg, 1981). Facies III is similarly colored to facies II but with fine lenticular lamination. Facies II and III are mainly found in cores from the southern part of the area. The boundary between facies II and III is relatively sharp with attributes of a hiatus. The results of the X-ray investigations of the > 63 pm- and < 63 #mfraction show increasing parts of smectite and phillipsite with increasing sediment depth in facies I samples of the northern cores (Fig.2). Whereas in samples from facies II smectite and phillipsite contents are already high, at the boundary to facies III phillipsite decreases and clinoptilolite appears (Fig.2) (Rehm, 1981). In addition, sediments of facies III contain reworked Relative (110,020)
oc
~
intensity smectite
~
Relative
intensity
(020,002)
12o z
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0
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80 120 , , NorthernePgrt
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60 ,
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100 I
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intensity
(020,002)
phi[lipsite
60 '
100 i
Southern
140 ,
part
180 i
220
/i
.E
~4
E vi
t/1
39
151
10
99
.e_ 4
~ B 10
Fig.2. Distribution of smectite, phillipsite and clinoptilolite with depth in sediments of site VA 18. eHiatus according to Von Stackelberg (pers. c o m m u n . , 1982); eehiatus according to own investigations.
28
late Cretaceous radiolaria (Von Stackelberg, 1981) which are completely transformed to opal-CT and quartz. Whereas the facies I sediment is of plio-Quatenary age, the age of facies II is unclear because of the absence of radiolaria. For facies III a late Eocene to early Oligocene age is assumed (Von Stackelberg, 1981; Wolfart, 1981). Sediment grain-size investigations in most cases show lognormal distributions. Portions of the coarse fraction ( > 63 pm) range between 0.01 and 0.70% for facies I sediment and between 0.4 and 6.5% for facies II; the portions for the grain-size < 4 pm range between 57 and 74%, resp. 45 and 60%. In spite of a different mineralogical composition, facies III sediments are comparable with facies I. Mean values for median, mean and standard deviation are listed in Table I. VOLCANIC ASH LAYERS
Characterization and distribution
Volcanic ash layers have been observed in nearly all facies I sediments of site VA 18 and also in a spade-core sample (224 GK: 15°23'N, 153°W) north of the VA 18 area. Compared with the sediment, the ash layers show marked differences in porosity, water content, shear-strength (Wiistenhagen, 1976) and grain size. Colours vary between 10 YR 3/2 and 2.5 Y 4/2 (Munsell, 1975). A fine lamination (Fig.3) and a sharp lower boundary are typical for all ash-layers. The u p p e r m o s t part is generally disturbed by bioturbation and mixed with facies I sediment. The thickness and the position of the individual layers within the cores are different for the northern and the southern part of the area. In the northern part (core 136--115, see Fig.4) three ash-layers, each with a thickness up to 30 cm, are found. Depth positions of the youngest layer and interlayer distances vary somewhat because of changing accumulation rates for the facies I sediment. TABLE I M e a n values for m e d i a n , m e a n a n d s t a n d a r d d e v i a t i o n f o r n o r m a l s e d i m e n t s f r o m t h e area V A 18 (C-units) Core-no.
Median
Mean
S t a n d a r d dev.
Number of samples
4 7 19 39 121 136 151
7.99 7.92 9.38 8.73 9.12 9.16 8.55
8.54 8.43 9.64 8.99 9.32 9.36 8.72
2.12 2.25 2.67* 2.01 2.10 2.11 1.95
8 6 6 9 9 10 7
* O n l y 1 e v a l u a t i o n possible.
29
Fig.3. Thin-stratified structure and alternating bedding in the 224 GK sample, depth between 15 and 25 cm, Radiograph (positive) from 5 ram-thick sediment slice. Photo by H. Karmann, with permission of Von Stackelberg. Scale bar = 2 cm. In t h e c o r e s f r o m t h e s o u t h e r n p a r t (core 9 9 - - 4 , see Fig.4) t h e t h r e e ash layers are r e d u c e d t o o n e l a y e r at t h e s e d i m e n t surface, i.e., t h e t o t a l thickness decreases. This o b s e r v a t i o n c a n be e x p l a i n e d b y higher a c c u m u l a t i o n rates in the n o r t h e r n p a r t a n d r e d u c e d d e p o s i t i o n or e r o s i o n in the s o u t h e r n p a r t o f site V A 18. A c c o r d i n g t o p a l e o m a g n e t i c investigations (Meyer, 1977} t h e age o f t h e ashes was c a l c u l a t e d t o be 1--2 m . y .
30
+15"
136
147 151 151 115
14 °
! i
99
65
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2
105
o
7
;:::::
-5"
883
~1
E c
5
~lq
~ m
E tA 10
726
Fig.4. D e p t h p o s i t i o n and t h i c k n e s s o f ash layers in cores f r o m the V A 18 area.
Grain-size investigations Grain-size distributions of the ash layers are quite different from those of the facies I sediment. The portion of the coarse fraction ranges between 0.6 and 6.1%, that of the fraction < 4 pm between 8 and 45% (Rehm, 1981). Mean values for median, mean and standard deviation in Table II reveal distinct differences between unaltered (core 151, 224 GK) and altered (core 136, 29) ash layers. For completely altered ashes in core 39 maximum values of 8.79 ~ for median and 9.80 ~ for mean were found. Standard deviation varies between 2.29 and 2.95 (Rehm, 1981).
Mineralogical aspects The mineralogical composition of the ashes (Table III) was determined from X-ray investigations of the predominant grain-size fraction (coarse silt fraction). Core 151 and 224 GK contain ash layers with only small amounts of alteration products. In this case, volcanic glass occurs as dark-brown, flattened and brittle particles (Figs.5 and 6) with a refractive index of n = 1.585, indicating a basaltic composition. In the other cores volcanic glass is completely transformed into smectite. T A B L E II Mean values for m e d i a n , m e a n and standard deviation for volcanic ashes in the area V A 18 (~-units) Core-no.
Median
Mean
Standard dev.
N u m b e r o f samples
151 136 39 224 GK
5.84 7.03 7.67 6.37
6.32 7.04 8.55 6.50
1.46 1.36 2.59 1.53
15 32 17 10
31 TABLE III Semi-quantitative mineralogical c o m p o s i t i o n of t h e coarse-silt fraction of volcanic ashes from t h e area VA 18 Core-no.
Smectite
Plagioclase
Augite
Olivine
Phillipsite
Glass
151 136 121 39 224 GK
2 5 6 6 3
5 4 4 4 6
3 3 3 3 4
1 1 1 1 2
1 1 2 2 1
5 2 1 1 4
i = absent, 2 = rare, 3 = present, 4 = c o m m o n ,
5 = abundant, 6 = m o s t abundant.
Fig.5. Volcanic glass f r o m core 1 5 1 P. S E M , scale bar = 5 0 ~ m .
82
Fig.6. Volcanic glass from the 224 GK sample. SEM, scale bar = 50 ~m. Plagioclase (an40-ss) and augite are c o m m o n in all ash samples whereas olivine (fo6s-70 ; Stoll, 1980) was only found in 224 GK. Several cores at the top of the ash layer are enriched in well-rounded micronodules with diameters up to 400/~m and with distinct silicate inclusions. The chemistry of these micronodules (Rehm, 1981) indicates hydrogenetic growth (Halbach and Ozkara, 1979) over a longer period on a stable sediment surface. As seen by SEM, the alteration of the ashes and the formation of smectite proceeds by means of dissolution of glass particles and recrystallization from pore solution. This process leads to agglomeratic particles often with a plagioclase nucleus (Figs.7 and 8).
33
Fig.7. Agglomeratic particles, mainly of new-formed smectite. SEM, scale bar = 50 ~m.
Geochemistry of the ash layers For the chemical investigations, 12 pure glass concentrates were separated (9 samples from core 151 and 3 samples from 224 GK) for analysis. Results are listed in Table IV. As clearly indicated from these data, all samples correspond to tholeiitic basalts with small but significant differences in TiO2, MgO, Cr, Co and Ni. The oldest ash layer in core 151 is characterized by TiO2 values greater than 2.45%, somewhat lower MgO contents, Cr between 441 and 461 ppm and Ni about 145 ppm. The younger ash layers in the core are lower in TiO2 ( ~ 2.4%) but distinctly higher in MgO, Cr and Ni. The differentiation index varies between 58.8 and 60.2 in the oldest ash layer and between 61.5 and 65.9 in the younger ones. The calculated norm shows normative quartz of 3.8 to 5.9%.
34
Fig.8. Single particle showing overgrowth of smectite on plagioclase. SEM, scale bar =
5#m. The inverse sequence of higher differentiated tephra in the oldest ash layer agrees with observations of Murata and Richter (1966) on eruption products of Kilauea Volcano. Compared with these analyses, the chemistry of 224 GK-glass is characterized by higher concentrations of MgO (8.81--10.07%), Ni (273--307 ppm) and Co (71--135 ppm), indicating more olivine in solution. TiO2 contents are low and range a b o u t 2%. The differentiation index varies between 61.9 and 65.2. Normative quartz was calculated to 1.3--3.3%. The rare-earth element analyses of all samples are quite uniform. The chondrite-normalized curves are described by La~f. between 30 and 40, (La/Sm)e.f. of 1.24--1.54, and La/Yb between 4.19 and 5.29 (~= 4.96).
35 Using the trace-element correlations Sr--Zr and TiO2--P2Os (Fig.9) (Bass et al., 1973; Ridley et al., 1974} or 100Ti--Zr--3Y (Pearce and Cann, 1973), most glass samples plot in the field for ocean-island tholeiites. The REE distributions are quite similar to those described by Schilling and Winchester (1966) for Hawaiian tholeiitic basalts.
Origin and transport of the ash layers F o r the interpretation of the chemical data we must consider two facts: (1) There was no submarine volcanic activity of the ocean-island type at site VA 18 at the time of deposition of the basaltic tephra (otherwise this would imply the existence of a new mantle plume southeast of the Hawaiian plume). (2) Basaltic rocks dredged at site VA 18 are ocean-ridge basaltic rocks of the oceanic basement (Rehm, in prep.). Thus, in view of the trace-element compositions, REE data and age of the ash-layers, the southern Hawaiian islands are the only conceivable source. If we compare the age and the chemistry of the ash sequence with the volcanic history of the Hawaiian Islands (McDonald and Katsura, 1964; McDonald and A b b o t t , 1970; Beeson, 1976), a more precise localization of the potential source area is possible. As shown in Fig.10, most of the analyses for core 151 glass fall within the field of "West Maui and Haleakala" and "Kilauea and Mauna L o a " tholeiitic basaltic rocks. Since the latter are younger than a b o u t 500,000 yrs (McDonald and A b b o t t , 1970), they are only relevant in the discussion of the ash layers in the spade-core sample 224 GK. Thus we believe that volcanic eruptions on Maui most probably have provided the material for the ash sequences in the VA 18 area. Concerning the ash layer in 224 GK the formation might be associated with the tholeiitic volcanism of Mauna Loa or Kilauea. In discussing the problem of transport we must consider a graben 20 km north of site VA 18 which developed long before the deposition of the ash layers (Herbst et al., 1980; U. Von Stackelberg, pers. commun., 1982). This trough, a b o u t 400 m in depth, would certainly have acted as a sediment trap for any submarine density currents (Menard, 1956) which might have carried debris down the slope of the Hawaiian Ridge. Therefore we assume eolian transport from Hawaii to be the most probable mechanism for site-VA 18 tephra. Concerning the spade-core station 224 GK, submarine density currents might be possible. If we consider the fact that in the May, 1980 eruption of Mt. St. Helens the average ashfall-thickness at a distance of 435 km was only 0.6 cm (Hammond, 1980), it is quite clear that the thickness of up to 30 cm for each single ash layer at site VA 18 precludes a "one-step" deposition.
IV
Sc V Cr Co Ni Cu Zn Sr Ba Y Zr Rb
(Mg + F e 2+)
F%O 3/FeO 1 0 0 Mg
SiO 2 TiO 2 AI~O 3 F%O 3 FeO MnO MgO CaO Na20 KsO P205 LOI
33 269 588 57 268 144 115 294 99 39 145 19
29 266 517 56 212 172 117 304 111 27 150 8
0.17
61.47
0.22
99.84
99.55
63.06
51.33 2.37 13.69 1.48 8.68 0.18 7.77 10.77 2.09 0.50 0.22 0.76
1512 455--458
28 275 512 59 199 168 107 311 105 27 142 2
65.88
0.27
99.46
50.20 2.27 13.02 2.20 8.27 0.18 8.96 10.20 1.86 0.49 0.21 1.61
34 280 485 59 202 227 136 282 103 34 113 8
62.20
0.25
99.56
50.19 2.31 13.03 2.10 8.34 0.17 7.70 10.10 1.94 0.46 0.22 3.00
1514 537--541
32 282 518 61 209 200 138 280 105 25 110 6
63.31
0.27
99.39
51.15 2.38 13.52 2.20 8.20 0.21 7.94 10.57 1.94 0.46 0.22 0.60
1515 549--554
in ppm)
36 290 441 55 149 163 114 318 108 23 157 4
58.79
0.13
99.60
51.64 2.47 13.59 1.20 9.27 0.18 7.42 10.78 1.96 0.47 0.22 0.40
1516 644--648
core 151 P and 224 GK (trace elements
1513 458-461
in volcanic glass from
50.81 2.35 13.66 1.84 8.29 0.18 7.94 10.57 1.99 0.50 0.21 1.21
1511 450--455
Major and trace elements
TABLE
32 290 457 54 143 160 110 338 83 25 145 --
58.80
0.16
99.36
51.57 2.48 13.65 1.40 9.03 0.17 7.23 10.76 1.98 0.47 0.22 0.40
1517 648--651
35 282 461 54 149 235 133 288 112 29 122 2
60.18
0.21
99.40
51.58 2.45 13.74 1.81 8.55 0.17 7.25 10.77 1.98 0.48 0.22 0.40
1518 651--655
36 289 455 51 145 213 112 283 107 33 123 2
59.12
0.17
99.71
51.71 2.46 13.69 1.50 9.02 0.17 7.32 10.79 1.96 0.48 0.21 0.40
1519 655--658*
o~
*Sediment
Y Zr Rb
Ba
Sc V Cr Co Ni Cu Zn Sr
(Mg + F e 2+)
1 0 0 Mg
~O 2 TiO 2 AI203 Fe203 MnO MgO CaO Na20 K20 P205 LOI
depth
35 263 505 80 327 149 114 230 78 43 91 25
in centimeters.
35 278 478 71 307 172 118 261 103 20 102 6
65.22
99.70
99.90
63.14
49.77 1.92 12.33 11.82 0.21 10.07 9.93 1.69 0.50 0.20 1.87
224/2 10---15
50.78 2.03 12.90 11.87 0.24 9.23 9.74 1.90 0.45 0.21 0.56
224/1 5--10
32 277 433 135 273 177 120 234 109 25 94 3
61.91
99.90
50.78 2~6 13.10 11.93 0.26 8.81 9.67 1.89 0.47 0.21 0.71
224/3 15--20"
38
4ooj
I I /
I
I \ . , ~ l k a t i c ~ basalt ~-.~."
I thoteiit
I I I
•
S /" I
i
I
! !
0.5
300
*~\
11
iALkatJc basait
0,7
I
•
l
i
! I / I Ocean-isLand
I I I
11
i i
'~
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AVA 13 1,151 PIO0 j
.,~/r idge basalt
0.1
' , VA 18, 224 GK l
100
1
I
I
I
100
200 Zr [ p p m ]
300
I
2 3 Ti % [°/o]
l
4
Fig.9. Trace-element correlations Sr--Zr and TiO2--P205 for volcanic glass from 151 P and 224 GK. Field boundaries according to Bass et al. ( 1 9 7 3 ) and Ridley et al. (1974). 16
I
ci
15
1',. i IX
¥/',
l( "~ 14
w.onoe,oo.u Kohala,
Hawaii
I ~
le/
x
--,--
/ X" X/
West maui and Hateaka[~ 13 --x--
Lanai :~x Kitauea and Mauna Loa \ C o r e 151 224 GK
12
0
x -.._. x
I 1
I 2 °/o
/
3
NQ20
Fig.10. Na20--AI203 diagram for volcanic rocks from Hawaiian Islands (CaO > MgO).
39 ACKNOWLEDGEMENTS The authors express appreciation for the financial support from the Deutsche Forschungsgemeinschaft. We are grateful to the Bundesanstalt fiir Geowissenschaften und Rohstoffe and the Hahn-Meitner Institute for running chemical analyses. REFERENCES Bass, M.N., Moberly, R., Rhodes, J.M., Chi-Yu-Shih and Curch, S.E., 1973. Volcanic rocks cored in the Central Pacific, Leg 17, DSDP. In: P.M. Roth, J.R. Hatting et al., Initial Reports of the Deep Sea Drilling Project, Vol.XVII. U.S. Govt. Printing Office, Washington, D.C., pp.429--446. Beeson, M.H., 1976. Petrology, mineralogy and geochemistry of East Molokai volcanic series, Hawaii. Geol. Surv. Prof. Pap., 961: 1--24. Bowles, F.A., Jack, R.N. and Carmichael, I.S.E., 1973. Investigations of deep-sea volcanic ash layers from Equatorial Pacific cores. Geol. Soc. Am. Bull., 84: 2371--2388. Edsall, D.W., 1975. Submarine Geology of Volcanic Ash Deposits: Stratigraphy, Age and Magmatic Composition of Hawaiian and Aleutian Tephra, Eocene to Recent. Ph.D. Diss., Columbia University, New York, N.Y., 206 pp. Hahn, G.A., Rose, W.I. and Meyers, T., 1979. Geochemical correlation of genetically related rhyolitic ash-flows and air-fall ashes, central and western Guatemala and the Equatorial Pacific. In: C.E. Chapin and W.E. Elston (Editors), Ash-Flow Tufts. Geol. Soc. Am. Spec. Pap., 180: 101--112. Halbach, P. and Ozkara, M., 1979. Morphological and geochemical classification of deepsea ferromanganese nodules and its genetical interpretation. In: La Gen~se des Nodules de Manganese. Colloq. Int. C.N.R.S., 289: 77--88. Hammond, P.E., 1980. Mt. St. Helens blasts 400 m off its peak. Geotimes, 25: 14--16. Hays, J.C. and Ninkovitch, D., 1970. North Pacific deep-sea ash chronology and the age of.present Aleutian underthrusting. Geol. Soc. Am. Mere., 126: 263--290. Herbst, K., Beiersdorf, H. and Von Stackelberg, U., 1980. Correlation of acoustic and lithologic facies within the Clarion fracture zone SSE of Hawaii. "Meteor" Forschungsergeb., Reihe C, 33: 1--13. Horn, D.R., Delach, M.N. and Horn, B.M., 1969. Distribution of volcanic ash layers and turbidites in the North Pacific. Geol. Soc. Am. Bull., 80: 1715--1724. Huang, T.C., Watkins, N.D., Shaw, D.M. and Kennett, J.P., 1973. Atmosphaerically transported volcanic dust in South Pacific deep-sea sedimentary cores at distances over 3000 km from the eruptive source. Earth Planet. Sci. Lett., 20: 119--124. Huang, T.C., Watkins, N.D. and Shaw, D.M., 1975. Atmosphaerically transported volcanic glass in deep-sea sediments: volcanism in suhantarctic latitudes of the South Pacific during Late Pliocene and Pleistocene time. Geol. Soc. Am. Bull., 86: 1305--1315. McDonald, G.A. and Abbot, A.T., 1970. Volcanoes in the Sea. The Geology of Hawaii. University Press of Hawaii, Hawaii, 441 pp. McDonald, G.A. and Katsura, T., 1964. Chemical composition of hawaiian lavas. J. Petrol., 5: 82--133. Menard, H.W., 1956. Archipelagic aprons. Bull. Am. Assoc. Pet. Geol., 40: 2195--2210. Meyer, H., 1977. Untersuchungen an Sedimentkernen aus dem zentralen Pazifik yon der "Valdivia"-Fahrt VA 13/1. Forschungsbericht BMfT/FB M 77/08, 44 pp. Munsell, 1975. Soil Colour Charts. Kollmorgen, Baltimore, Md. Murata, K.J. and Richter, D.H., 1966. Chemistry of the lavas of the 1959--60 eruption of Kilauea Volcano, Hawaii. U.S. Geol. Surv., Prof. Pap., 537-A: 1--26. Nayuda, Y.R., 1964. Volcanic ash deposits in the Gulf of Alaska and problems of correlation of deep-sea ash deposits. Mar. Geol., 1: 194--212.
40 Pearce, J.A. and Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth Planet. Sci. Lett., 19: 290--300. Pratt, R.M., Scheidegger, K.F. and Kulm, L.D., 1973. Volcanic ash from DSDP Site 178, Gulf of Alaska. In: L.D. Kulm, R. yon Huene et al., Initial Reports of the Deep Sea Drilling Project, Vol.XVIII. U.S. Govt. Printing Office, Washington, D.C., pp. 833-834. Rehm, E., 1981. Sedimentologische und geochemische Untersuchungen an vulkanogenen Sedimentanteilen, vulkanischen Aschen und Vulkaniten aus dem Nordost-Pazifik. Ph.D. Diss., Tech. Univ. of Clausthal, Clausthal, 210 pp. Rehm, E., in prep. Basaltic rocks from the Clarion fracture zone SSE of Hawaii. Ridley, W.I., Rhodes, J.M., Reid, A.M., Jakes, P., Shih, C. and Bass, M.N., 1974. Basalts from Leg 6 of the Deep Sea Drilling Project. J. Petrol., 15: 140--159. Scheidegger, K.F. and Kulm, L.D., 1975. Late Cenozoic volcanism in the Aleutian Arc: Informations from ash layers in the northeastern Gulf of Alaska. Geol. Soc. Am. Bull., 86: 1407--1412. Schilling, J.G. and Winchester, J.W., 1969. Rare Earth contribution to the origin of Hawaiian lavas. Contrib. Mineral. Petrol., 17: 275--314. Stoll, M.-L., 1980. Einfluf$ der Fr/ihdiagenese und Halmyrolyse auf den Mineralbestand pelagischer Sedimente aus dem Zentralpazifik. UnverSffentliche Diplomarbeit, Technische Universit~it Clausthal, Clausthal, 189 pp. Von Stackelberg, U., 1981. Model site VA-18. In: P. Halbach (Editor), The Manganese Nodule Belt of the Pacific Ocean -- Scientific, Technic and Economic Aspects. Ferd. Enke, Stuttgart (in prep.). Wolfart, R., 1981. Radiolarian biostratigraphy of the Cenozoic. In: P. Halbach (Editor), The Manganese Nodule Belt of the Pacific Ocean -- Scientific, Technic and Economic Aspects. Ferd. Enke, Stuttgart (in prep.). Wiistenhagen, K., 1976. Bodenmechanische Untersuchungen im Rahmen der Forschungsfahrt VA 13/1-1976. In: H. Beiersdorf (Editor), Ergebnisse der Manganknollen Wissenschaftsfahrt VA 13/1, zentraler Pazifischer Ozean, 1976. Fachlicher Bericht, Bundesanstalt ffir Geowiss. und Rohstoffe, Hannover, pp. 23--57.
25
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
HAWAIIAN-DERIVED VOLCANIC ASH LAYERS IN EQUATORIAL NORTHEASTERN PACIFIC SEDIMENTS
E. REHM and P. HALBACH
Institut fiir Meeresforschung, Am Handelshafen 12, D-2850 Bremerhaven (F.R.G.) Research Group for Sediment Ore Formation, Technical University of Clausthal, D-3392 Clausthal-Zellerfeld (F.R. G.) (Received December 8, 1981; revised and accepted May 5, 1982)
ABSTRACT Rehm, E. and Halbach, P., 1982. Hawaiian-derived volcanic ash layers in equatorial northeastern Pacific sediments. Mar. Geol., 50: 25--40. Volcanic ash layers with thicknesses of up to 30 cm and ages between 1 and 2 m.y. were found in equatorial northeastern Pacific sediments. Grain-size distributions, mineralogical composition and alteration of the ashes are described. Chemical analyses of major, trace and rare-earth elements and trace-element correlations indicate a basaltic composition of the ocean-island tholeiitic type. Comparison with Hawaiian tholeiitic rocks indicates the Island of Maul as the source of material for the ash sequence in the investigated area. The composition of an ash layer north of the area indicates it was associated with volcanism of Mauna Loa or Kilauea. INTRODUCTION
Volcanic ashes are widely distributed in deep-sea sediments from marginal Pacific regions. They are observed in subantarctic latitudes (Huang et al., 1973, 1975), in the Gulf of Alaska and the Aleutian area (Nayuda, 1964; Horn et al., 1969; Hays and Ninkovitch, 1970; Pratt et al., 1973; Scheidegger and Kulm, 1975) b u t also near the Pacific coast of Central America (Bowles et al., 1973; Hahn et al., 1979). In the area of the Hawaiian Ridge, Edsall (1975) described volcanic glass in more than 70% of the investigated cores but found ash layers only in 9 cores. According to paleomagnetic and biostratigraphic investigations, volcanic glass is frequently distributed in Pleistocene sediments southeast of the Hawaiian Islands. This paper describes ash layers that originated from Hawaiian eruptions and were carried up to 928 km from the islands. SITE VA 18
The area VA 18 is situated within the Clarion fracture zone south-southeast of the Island of Hawaii centered at 14°N and 153°W (Fig.l). The bathymetric chart of this region shows a horst structure with two parallel grabens 0025-3227/82/0000--0000/$02.75
© 1982 Elsevier Scientific Publishing Company
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separated by a distance of a b o u t 25 km (Herbst et al., 1980). In the survey area waterdepth for the southern graben amounts to 6400 m. However, the major part of area VA 18 has normal abyssal-hill topography with waterdepths from 5600 to 5900 m (Fig.l). A single 400-m submarine basaltic seamount in the western area is the only volcanic structure observed. METHODS Eleven piston cores with a total length of 83.3 m were available for investigation. Concerning the " n o r m a l " sediment, the cores were continuously divided into 10--15-cm sections. Within the ash layers, the sections were reduced to 2--5 cm. " N o r m a l " sediment was classified according to grain-size distribution, composition of the sand fraction and X-ray results. The mineralogical composition of the ash layers was mostly determined by X-ray phase analyses. In order to get pure-glass concentrates for chemical analyses, the > 63-pm fraction was treated with heavy liquids and separated by Frantz-Isodynamic Separator. Chemical analyses of major- and trace-elements were done at the BGR (Hannover, F.R.G.) using Philips Sequenzspektrometer PW 1450 and metaborate fusion. REE were determined by NAA at the Hahn-Meitner Institute (West Berlin).
27 CHARACTERIZATION OF N E A R - S U R F A C E SEDIMENTS
From radiographic and microscopic investigations, Von Stackelberg (1981) classified the sediments of the area into three facies. Facies I is mostly dark brown in colour (10 YR 3/2) (Munsell, 1975) and normally with no distinct sedimentary structure. This facies is mainly found in cores from the northern part of the area. Facies II shows dark reddish-brown colours (5 YR 3/2-2.5/2) (Munsell, 1975) and different burrows (Von Stackelberg, 1981). Facies III is similarly colored to facies II but with fine lenticular lamination. Facies II and III are mainly found in cores from the southern part of the area. The boundary between facies II and III is relatively sharp with attributes of a hiatus. The results of the X-ray investigations of the > 63 pm- and < 63 #mfraction show increasing parts of smectite and phillipsite with increasing sediment depth in facies I samples of the northern cores (Fig.2). Whereas in samples from facies II smectite and phillipsite contents are already high, at the boundary to facies III phillipsite decreases and clinoptilolite appears (Fig.2) (Rehm, 1981). In addition, sediments of facies III contain reworked Relative (110,020)
oc
~
intensity smectite
~
Relative
intensity
(020,002)
12o z
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Southern
140 ,
part
180 i
220
/i
.E
~4
E vi
t/1
39
151
10
99
.e_ 4
~ B 10
Fig.2. Distribution of smectite, phillipsite and clinoptilolite with depth in sediments of site VA 18. eHiatus according to Von Stackelberg (pers. c o m m u n . , 1982); eehiatus according to own investigations.
28
late Cretaceous radiolaria (Von Stackelberg, 1981) which are completely transformed to opal-CT and quartz. Whereas the facies I sediment is of plio-Quatenary age, the age of facies II is unclear because of the absence of radiolaria. For facies III a late Eocene to early Oligocene age is assumed (Von Stackelberg, 1981; Wolfart, 1981). Sediment grain-size investigations in most cases show lognormal distributions. Portions of the coarse fraction ( > 63 pm) range between 0.01 and 0.70% for facies I sediment and between 0.4 and 6.5% for facies II; the portions for the grain-size < 4 pm range between 57 and 74%, resp. 45 and 60%. In spite of a different mineralogical composition, facies III sediments are comparable with facies I. Mean values for median, mean and standard deviation are listed in Table I. VOLCANIC ASH LAYERS
Characterization and distribution
Volcanic ash layers have been observed in nearly all facies I sediments of site VA 18 and also in a spade-core sample (224 GK: 15°23'N, 153°W) north of the VA 18 area. Compared with the sediment, the ash layers show marked differences in porosity, water content, shear-strength (Wiistenhagen, 1976) and grain size. Colours vary between 10 YR 3/2 and 2.5 Y 4/2 (Munsell, 1975). A fine lamination (Fig.3) and a sharp lower boundary are typical for all ash-layers. The u p p e r m o s t part is generally disturbed by bioturbation and mixed with facies I sediment. The thickness and the position of the individual layers within the cores are different for the northern and the southern part of the area. In the northern part (core 136--115, see Fig.4) three ash-layers, each with a thickness up to 30 cm, are found. Depth positions of the youngest layer and interlayer distances vary somewhat because of changing accumulation rates for the facies I sediment. TABLE I M e a n values for m e d i a n , m e a n a n d s t a n d a r d d e v i a t i o n f o r n o r m a l s e d i m e n t s f r o m t h e area V A 18 (C-units) Core-no.
Median
Mean
S t a n d a r d dev.
Number of samples
4 7 19 39 121 136 151
7.99 7.92 9.38 8.73 9.12 9.16 8.55
8.54 8.43 9.64 8.99 9.32 9.36 8.72
2.12 2.25 2.67* 2.01 2.10 2.11 1.95
8 6 6 9 9 10 7
* O n l y 1 e v a l u a t i o n possible.
29
Fig.3. Thin-stratified structure and alternating bedding in the 224 GK sample, depth between 15 and 25 cm, Radiograph (positive) from 5 ram-thick sediment slice. Photo by H. Karmann, with permission of Von Stackelberg. Scale bar = 2 cm. In t h e c o r e s f r o m t h e s o u t h e r n p a r t (core 9 9 - - 4 , see Fig.4) t h e t h r e e ash layers are r e d u c e d t o o n e l a y e r at t h e s e d i m e n t surface, i.e., t h e t o t a l thickness decreases. This o b s e r v a t i o n c a n be e x p l a i n e d b y higher a c c u m u l a t i o n rates in the n o r t h e r n p a r t a n d r e d u c e d d e p o s i t i o n or e r o s i o n in the s o u t h e r n p a r t o f site V A 18. A c c o r d i n g t o p a l e o m a g n e t i c investigations (Meyer, 1977} t h e age o f t h e ashes was c a l c u l a t e d t o be 1--2 m . y .
30
+15"
136
147 151 151 115
14 °
! i
99
65
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2
105
o
7
;:::::
-5"
883
~1
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5
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726
Fig.4. D e p t h p o s i t i o n and t h i c k n e s s o f ash layers in cores f r o m the V A 18 area.
Grain-size investigations Grain-size distributions of the ash layers are quite different from those of the facies I sediment. The portion of the coarse fraction ranges between 0.6 and 6.1%, that of the fraction < 4 pm between 8 and 45% (Rehm, 1981). Mean values for median, mean and standard deviation in Table II reveal distinct differences between unaltered (core 151, 224 GK) and altered (core 136, 29) ash layers. For completely altered ashes in core 39 maximum values of 8.79 ~ for median and 9.80 ~ for mean were found. Standard deviation varies between 2.29 and 2.95 (Rehm, 1981).
Mineralogical aspects The mineralogical composition of the ashes (Table III) was determined from X-ray investigations of the predominant grain-size fraction (coarse silt fraction). Core 151 and 224 GK contain ash layers with only small amounts of alteration products. In this case, volcanic glass occurs as dark-brown, flattened and brittle particles (Figs.5 and 6) with a refractive index of n = 1.585, indicating a basaltic composition. In the other cores volcanic glass is completely transformed into smectite. T A B L E II Mean values for m e d i a n , m e a n and standard deviation for volcanic ashes in the area V A 18 (~-units) Core-no.
Median
Mean
Standard dev.
N u m b e r o f samples
151 136 39 224 GK
5.84 7.03 7.67 6.37
6.32 7.04 8.55 6.50
1.46 1.36 2.59 1.53
15 32 17 10
31 TABLE III Semi-quantitative mineralogical c o m p o s i t i o n of t h e coarse-silt fraction of volcanic ashes from t h e area VA 18 Core-no.
Smectite
Plagioclase
Augite
Olivine
Phillipsite
Glass
151 136 121 39 224 GK
2 5 6 6 3
5 4 4 4 6
3 3 3 3 4
1 1 1 1 2
1 1 2 2 1
5 2 1 1 4
i = absent, 2 = rare, 3 = present, 4 = c o m m o n ,
5 = abundant, 6 = m o s t abundant.
Fig.5. Volcanic glass f r o m core 1 5 1 P. S E M , scale bar = 5 0 ~ m .
82
Fig.6. Volcanic glass from the 224 GK sample. SEM, scale bar = 50 ~m. Plagioclase (an40-ss) and augite are c o m m o n in all ash samples whereas olivine (fo6s-70 ; Stoll, 1980) was only found in 224 GK. Several cores at the top of the ash layer are enriched in well-rounded micronodules with diameters up to 400/~m and with distinct silicate inclusions. The chemistry of these micronodules (Rehm, 1981) indicates hydrogenetic growth (Halbach and Ozkara, 1979) over a longer period on a stable sediment surface. As seen by SEM, the alteration of the ashes and the formation of smectite proceeds by means of dissolution of glass particles and recrystallization from pore solution. This process leads to agglomeratic particles often with a plagioclase nucleus (Figs.7 and 8).
33
Fig.7. Agglomeratic particles, mainly of new-formed smectite. SEM, scale bar = 50 ~m.
Geochemistry of the ash layers For the chemical investigations, 12 pure glass concentrates were separated (9 samples from core 151 and 3 samples from 224 GK) for analysis. Results are listed in Table IV. As clearly indicated from these data, all samples correspond to tholeiitic basalts with small but significant differences in TiO2, MgO, Cr, Co and Ni. The oldest ash layer in core 151 is characterized by TiO2 values greater than 2.45%, somewhat lower MgO contents, Cr between 441 and 461 ppm and Ni about 145 ppm. The younger ash layers in the core are lower in TiO2 ( ~ 2.4%) but distinctly higher in MgO, Cr and Ni. The differentiation index varies between 58.8 and 60.2 in the oldest ash layer and between 61.5 and 65.9 in the younger ones. The calculated norm shows normative quartz of 3.8 to 5.9%.
34
Fig.8. Single particle showing overgrowth of smectite on plagioclase. SEM, scale bar =
5#m. The inverse sequence of higher differentiated tephra in the oldest ash layer agrees with observations of Murata and Richter (1966) on eruption products of Kilauea Volcano. Compared with these analyses, the chemistry of 224 GK-glass is characterized by higher concentrations of MgO (8.81--10.07%), Ni (273--307 ppm) and Co (71--135 ppm), indicating more olivine in solution. TiO2 contents are low and range a b o u t 2%. The differentiation index varies between 61.9 and 65.2. Normative quartz was calculated to 1.3--3.3%. The rare-earth element analyses of all samples are quite uniform. The chondrite-normalized curves are described by La~f. between 30 and 40, (La/Sm)e.f. of 1.24--1.54, and La/Yb between 4.19 and 5.29 (~= 4.96).
35 Using the trace-element correlations Sr--Zr and TiO2--P2Os (Fig.9) (Bass et al., 1973; Ridley et al., 1974} or 100Ti--Zr--3Y (Pearce and Cann, 1973), most glass samples plot in the field for ocean-island tholeiites. The REE distributions are quite similar to those described by Schilling and Winchester (1966) for Hawaiian tholeiitic basalts.
Origin and transport of the ash layers F o r the interpretation of the chemical data we must consider two facts: (1) There was no submarine volcanic activity of the ocean-island type at site VA 18 at the time of deposition of the basaltic tephra (otherwise this would imply the existence of a new mantle plume southeast of the Hawaiian plume). (2) Basaltic rocks dredged at site VA 18 are ocean-ridge basaltic rocks of the oceanic basement (Rehm, in prep.). Thus, in view of the trace-element compositions, REE data and age of the ash-layers, the southern Hawaiian islands are the only conceivable source. If we compare the age and the chemistry of the ash sequence with the volcanic history of the Hawaiian Islands (McDonald and Katsura, 1964; McDonald and A b b o t t , 1970; Beeson, 1976), a more precise localization of the potential source area is possible. As shown in Fig.10, most of the analyses for core 151 glass fall within the field of "West Maui and Haleakala" and "Kilauea and Mauna L o a " tholeiitic basaltic rocks. Since the latter are younger than a b o u t 500,000 yrs (McDonald and A b b o t t , 1970), they are only relevant in the discussion of the ash layers in the spade-core sample 224 GK. Thus we believe that volcanic eruptions on Maui most probably have provided the material for the ash sequences in the VA 18 area. Concerning the ash layer in 224 GK the formation might be associated with the tholeiitic volcanism of Mauna Loa or Kilauea. In discussing the problem of transport we must consider a graben 20 km north of site VA 18 which developed long before the deposition of the ash layers (Herbst et al., 1980; U. Von Stackelberg, pers. commun., 1982). This trough, a b o u t 400 m in depth, would certainly have acted as a sediment trap for any submarine density currents (Menard, 1956) which might have carried debris down the slope of the Hawaiian Ridge. Therefore we assume eolian transport from Hawaii to be the most probable mechanism for site-VA 18 tephra. Concerning the spade-core station 224 GK, submarine density currents might be possible. If we consider the fact that in the May, 1980 eruption of Mt. St. Helens the average ashfall-thickness at a distance of 435 km was only 0.6 cm (Hammond, 1980), it is quite clear that the thickness of up to 30 cm for each single ash layer at site VA 18 precludes a "one-step" deposition.
IV
Sc V Cr Co Ni Cu Zn Sr Ba Y Zr Rb
(Mg + F e 2+)
F%O 3/FeO 1 0 0 Mg
SiO 2 TiO 2 AI~O 3 F%O 3 FeO MnO MgO CaO Na20 KsO P205 LOI
33 269 588 57 268 144 115 294 99 39 145 19
29 266 517 56 212 172 117 304 111 27 150 8
0.17
61.47
0.22
99.84
99.55
63.06
51.33 2.37 13.69 1.48 8.68 0.18 7.77 10.77 2.09 0.50 0.22 0.76
1512 455--458
28 275 512 59 199 168 107 311 105 27 142 2
65.88
0.27
99.46
50.20 2.27 13.02 2.20 8.27 0.18 8.96 10.20 1.86 0.49 0.21 1.61
34 280 485 59 202 227 136 282 103 34 113 8
62.20
0.25
99.56
50.19 2.31 13.03 2.10 8.34 0.17 7.70 10.10 1.94 0.46 0.22 3.00
1514 537--541
32 282 518 61 209 200 138 280 105 25 110 6
63.31
0.27
99.39
51.15 2.38 13.52 2.20 8.20 0.21 7.94 10.57 1.94 0.46 0.22 0.60
1515 549--554
in ppm)
36 290 441 55 149 163 114 318 108 23 157 4
58.79
0.13
99.60
51.64 2.47 13.59 1.20 9.27 0.18 7.42 10.78 1.96 0.47 0.22 0.40
1516 644--648
core 151 P and 224 GK (trace elements
1513 458-461
in volcanic glass from
50.81 2.35 13.66 1.84 8.29 0.18 7.94 10.57 1.99 0.50 0.21 1.21
1511 450--455
Major and trace elements
TABLE
32 290 457 54 143 160 110 338 83 25 145 --
58.80
0.16
99.36
51.57 2.48 13.65 1.40 9.03 0.17 7.23 10.76 1.98 0.47 0.22 0.40
1517 648--651
35 282 461 54 149 235 133 288 112 29 122 2
60.18
0.21
99.40
51.58 2.45 13.74 1.81 8.55 0.17 7.25 10.77 1.98 0.48 0.22 0.40
1518 651--655
36 289 455 51 145 213 112 283 107 33 123 2
59.12
0.17
99.71
51.71 2.46 13.69 1.50 9.02 0.17 7.32 10.79 1.96 0.48 0.21 0.40
1519 655--658*
o~
*Sediment
Y Zr Rb
Ba
Sc V Cr Co Ni Cu Zn Sr
(Mg + F e 2+)
1 0 0 Mg
~O 2 TiO 2 AI203 Fe203 MnO MgO CaO Na20 K20 P205 LOI
depth
35 263 505 80 327 149 114 230 78 43 91 25
in centimeters.
35 278 478 71 307 172 118 261 103 20 102 6
65.22
99.70
99.90
63.14
49.77 1.92 12.33 11.82 0.21 10.07 9.93 1.69 0.50 0.20 1.87
224/2 10---15
50.78 2.03 12.90 11.87 0.24 9.23 9.74 1.90 0.45 0.21 0.56
224/1 5--10
32 277 433 135 273 177 120 234 109 25 94 3
61.91
99.90
50.78 2~6 13.10 11.93 0.26 8.81 9.67 1.89 0.47 0.21 0.71
224/3 15--20"
38
4ooj
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200 Zr [ p p m ]
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Fig.9. Trace-element correlations Sr--Zr and TiO2--P205 for volcanic glass from 151 P and 224 GK. Field boundaries according to Bass et al. ( 1 9 7 3 ) and Ridley et al. (1974). 16
I
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/ X" X/
West maui and Hateaka[~ 13 --x--
Lanai :~x Kitauea and Mauna Loa \ C o r e 151 224 GK
12
0
x -.._. x
I 1
I 2 °/o
/
3
NQ20
Fig.10. Na20--AI203 diagram for volcanic rocks from Hawaiian Islands (CaO > MgO).
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