Bulletin of the Geological Survey of Japan,voL43(4),p・207-235,1992
Heat皿ow in the Iz聰一〇gasawara(Bonin)一Mariana A肥
*
Toshitsugu YAMAzAKI
YAMAzAKI Toshitsugu (1992) Heat flow in
GθoJS%γ妙.∫α伽,vo1.43(4),P.207-235,
the Izu-Ogasawara(Bonin)一Mαriana Arc.B棚。
11fig.,1tab.
Abstract:This report presents218new heat flow(iata obtained from1984to1989in theIzu-Ogasawara(Bonin〉一Mariana Arc.The purpose of the measurements is to evaluate the
potential of hydrothermal activity an〔l to understand better the tectonics of this region.Main
target areas are (1)the Sumisu Rift,one of active backarc rifts in the northem Ogasawara
Arc,(2)the Nishinoshima Trough,a paleorift of Ohgocene(?)age in the mi(1dle Ogasawara
Arc,which lies oblique to the strike of the present arc,an(i(3)the northem Mariana Trough
from20。N to24。N.
The Sumisu Rift has high and variable heat now values,which suggests the existence of
hy(irothermal circulation.Anomalously low temperature gradients(close to zero)are common-
Iy observed in the upper several tens of centimeters of the surface sediments.Bioturbation by
high activity of benthic organisms may be responsible for the low gradient.The Nishinoshima
Trough is boun(led on the west by a steep(max.1500m)fault scarp.Heat flow is generally
higher in the trough than to the west of the scarp.This contrast would reflect difference in
crustal thickness cause(i by o1(1rifting.Local high heat flow associated with a intrusive bo(iy is
observed in the trough.The Mariana Trough north of22。N,which is now in a rifting stage,
shows thermal asymmetry。High heat flow occurs only along the eastem margin of the trough.
In the Mariana Trough south of22。N,which has developed to a spreading stage,anomalous
temperature profiles suggesting hydrothermal circulation are observed near the spreading cen-
ters.
1. 亙恥troduction
Extensive heat flow measurements were carried
out in the Izu-Ogasawara(Bonin)一Mariana Arc
as a part of the research program “Submarine
Hydrothermal Activity in the Izu-Ogasawara Arc”
from1984to1989using R/V Hakurei-maru.The
purpose of the measurements is to know the ther-
mal structure of these area an(l to obtain basic
〔lata to evaluate the potential of hy(1rothermal
activity.This report presents218new heat flow
(1ata obtaine(l through this research program,and
briefly (iiscuss their geological significance.Only
a minor part of these data has been reporte(1be・
fore(Yamazaki,1988;Nishimura8‘α’.,1988).
The main target areas are(1)the Sumisu Rift,
one of backarc rifts in the northern Izu-Ogasa・
*Marine Geology Department
wara Arc,(2)aroun(1the Nishinoshima Trough
an〔l the Sofugan Tectonic Line,which is a geolo-
gical structure obli〔luely crossing the mi(ldle
Izu-Ogasawara Arc, an(i (3) the northern
Mariana Trough(Figure1).Geological settings
an〔l previous works of these areas are briefly in-
troduce(l in the following.
In the northem Izu-Ogasawara Arc, top-
ographic (iepressions, first note(i by Mogi
(1968),existjustbehindthev・lcanicfr・nt(the
Shichito Ridge) from Hachilolima Is.to Nishi-
noshima Is.These segmented depressions havebeen considered to be young(Karig and Moore,
1975)or Quaternary (Honza an(i Tamaki,1985〉
extensional basins.These grabens are calle〔i the
Hachijo, Aogashima, Sumisu, Torishima an(i
Nishinoshima Rifts after nearby volcanic islands。
Keywords:heat flow,Izu-Ogasawara(Bonin)Arc,Mariana
Trough,Sumisu Rift,backarc,rifting,hy(1rothermal circulation
一207一
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Shik・kul圃『・吻〆 ~
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Fig.1 Structural framework of the Izu-Ogasawara
-Mariana arc.Dotted lines represent1000m
and3000m iso-depths.S.T.L.:Sofugan Tecto-
nic Line(mo(1ifie(1from Yuasa(1985)).
Brown and Taylor(1988)and Murakami(1988)
reveale〔i(ietaile(l geological structure of the Sumi-
su Rift.Dives of submersible Alvin in1987(iiscov-
ered silica barite chimneys near the summits of
dacite.volcanoes in the Sumisu Rift (Taylor切
α」.,1990;Urabe and Kusakabe,1990).Recent
ODP (Ocean Drilling Program)Drilling reveale(l
that the floor o{the Sumisu Rift is filled with vol-
caniclastic sediments not older than l.1Ma(Leg
126Scientific Drilling Party,1989).
In the backarc of the Izu-Ogasawara Arc,θ%
66配伽arrangement of topographic highs an〔l lows
oblique to the tren(l of the arc is remarkable
(Karig and Moore,1975;Honza and Tamaki,
1985).The most prominent among them is a steep
cliff linearly trending SSW from south of Sofugan
Islan(i,which woukl probably be a normal fault.
Yuasa(1985)considered that the Izu-Ogasawara
Arc can be structurally divi(ie(i into the southern
and northern part by this fault,and calle(i it the
Sofugan Tectonic Line.The Nishinoshima Trough
lies on the east of the Sofugan Tectonic Line.The
Nishinoshima Trough is bor(iere〔l on the east by
the Shichito Ri(1ge.(The“Mshinoshima Trough少’
of Honza an(i Tamaki(1985)and Yuasa (1985)
includes other topographic lows lying between the
Shichito Ri(lge and the Izu Ri(lge, but in this re-
port does not).Yuasa(1991,1992〉propose(1that
the Nishinoshima Trough was formed as a north-
ern tip of the incipient opening of the Parece Vela
Basin in Oligocene time(Mrozowski and Hayes,
1979).The sediment thickness on the acoustic
basement of the Nishinoshima Trough excee(is2
km in the southwestem part,and it decreases to-
war(is northeast.
Afewworkersreporte(lheatflowdataintheIzu-Ogasawara Arc (Vacquier θ歩α」., 1966 1
Watanabeθ孟α1.,1970;Matsubara,1981).But,
the amount of the data was still too small to(1is-
cuss thermal structure an(l hydrothermal activity
of the arc.
The Mariana Trough is known as one of active
backarc basins on the globe (Karig,1971).The
rifting of the Mariana Trough is considered to
have begun in the latest Miocene(Hussong an(1
Uyed&8‘α∫.,1982).Recentresearches・fthe
Mariana Trough including the DSDP dr皿ing havebeen focuse(l at the area of18QN latitu(ie(Ander-
son,1975;Bibee8‘αZ.,1980;Sager,1980;Hus.song an(l Uye(la6‘α」.,1982;Lon8dale an(i Haw-
kins,1985〉.Extremely high heat flow values
were observe(i there(Hobart6‘α」.,1983),an(l
active hydrothermal vents were discovered bysubmersible Alvin(Craig6‘αZ.,1987;Moore and
Stakes,1990).Ontheotherhand,studiesinother areas of the Mariana Trough have yet been
scarce,and heat flow(1ata were reported sparsely
(Watanabe,1970;Sclater8渉α1.,1972;Ander-
son,1980;Yamano,1985).Most of my measure-
ments in the Mariana Trough are concentrated in
the northem part from20。to24。N,an(167new
(lata in the area are presente(1in this report.
一208一
∫をα‘刀oω伽飾619%一〇8αsαωα観一Mα短α%α/1鴬‘T.rα㎜α之α彦9
H179
2.D飢&島c偲is亘tiona麟re磁uct亘磯
2.l T恥e灘抗且gr麟e髄t
I used four sets (three types)of temperature
recor(1ers.They are two GH80-1type,a NTS10
type,and a NTSll type recor(iers manufacture(i
by Nichiyu-Giken Co。The GH80-1type recor〔1er
has three channels for thermistors an(12mK re-
solution(Matsubayashi,1982).The NTS10type
has three channels,and the NTSll has six.The
resolution of both NTS10an(l NTSll type is l
mK.The NTSll type has a tilt sensor.Tempera-
ture data were〔ligitize(l every150r30secon(1s
except for sites from H111to H138at which they
wereevery60seconds.
Several types of thermistor probe systems
penetrating sediments were provided,and they
were properly use〔l depen(ling on the stiffness of
bottom se〔liments an(l on the purpose ofmeasurements.They are (1)a2m long gravity
corer or a piston corer of40r8m long with three
to six thermistor probes mounted in outrigger
fashion (Ewing type),(2)a1.50r2.5m long
lance without coring which was equippe(1with
three to six thermistor probes in outrigger fashion
(Ewing type),(3)a thin (20mm in(iiameter)
probe of O.70r O.9m in length to which three to
five thermistors were attache(1(Bullard type).A
weight of about500kg were used for the systems
・ftypes(1)and(2),andちhat・fab・ut50kgf・r
the type(3).The systems of types(2)and(3)
allow multiple penetration(iuring a single lower-
ing.The type (3)system was use〔l only in the
Sumisu Rift.
Each thermistor was sealed in a tef夏on tube,
and capped by a brass tube of5mm in(iiameter.
The thermistor in each probe of the type(1)and
(2)systems was at2to3cm from the outrigger
fins.This distance might not be long enough to
completely avoid effects of axial heat conduction,
but I believe it di(i not cause serious error.Ther-
mistor probes were angularly offset from each
other so that no probes passes through the same
sediments.
Decay of frictional heating of the thermistors
during Penetration into sediments was monitore(i
for10to15minutes.Equilibrium temperature of
each thermistor was obtaine(l by the extrapolation
0.7
0.6
0,5
^ 0.400》ト
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O,2
0.1
0
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説
諺避
轡6&e
謬ら’。竃’
Upperセherml8量or
0 0.01 0.02
F(A昼pha,’『au》
0.03
Fig.2
co 600 400 Timeくsec.》
200
Plot of thermistor temperatures versusF(α,τ)ofBullard(1954)forfrictionalheat-
ing(iecay at site H179.Best-fit lines are calcu-
late(1 for each thermistor using the leastsquares metho(1.The intercept at F(α,τ)ニO
gives the equilibrium temperature。
usingcylin(irical(iecayfunctionF(α,τ)of
Bullard(1954).AtypicalexampleisshowninFigure2.I used a simple linear fit to the F(α,
τ)vs.temperature plot.The(iecy origin time
was adluste(i by trial and error to get linear F(α,
τ)decay(Villinger and Davis,1987).Thermal
(listurbances(iue to the movement of the probe
(iuring the frictiona蔓decay monitoring cause non-
linear,anomalous F (α,τ)〔1ecay plots,an(i
these measurements were(iiscarded.
2。2騒e懸我亘co翻鵬tiv直苞y
Thermal con(iuctivity was measure(l on se(ii-
ment cores by a QTM(Quick Thermal Conductiv-
ity Meter,Showa Denko Co.).This instrument
adopts a transient line-heat-source method(lto8‘
αZ.,1975)。The QTM was calibrated using stan-
dar(1s of fused quartz and acrylic resin(manufac-
ture’s recommende(i values are1.39an(i O.241
W/mK,respectively).The accuracy,is within±
一209一
B%πθ孟伽(ゾ地εG60’09歪oα1S%ηノθツ(ゾ∫αρα%,γo’。43.ノ〉o。4
5%(Sassε‘αZ.,1984;Galson6云α」.,1987).
The se(1圭ment cores were split in halves and co-
vered with thin plastic film(commercial transpa-
rent foo(1-wrapping film)to prevent evaporation
of pore water before measurement。The effect of
this film’on the con(iuctivity is negligible(Sass認
αZ.,1984).Measurements were done on board as
soon as the thermal steady state was attaine(i at
room temperature(20to25℃)a few hours after
the core was retrieved.The values measure(l in
the laboratory were correcte(i to伽3琵%con(1itions
of temperature and pressure following Ratcliffe
(1960).For the sites where no sediments were
obtaine(1 due to multiple-penetration measure-
ments or failure of coring,the conductivity at the
nearest site was adopte(L
2.3 Positioning and shipboar“operation
Real-time navigation of the ship was done by
Loran-C,which was calibrate(i by satelhte fixes
(NNSS).Absolute accuracy of the ship’s position
is about100m after post processing.A position of
a heat flow probe relative to the ship could not be
known accurately because we (ii〔l not use an
acoustic positioning system. But it would be
almost just un(ier the ship because(luring the
measurements the ship was not let(irifting but
was controlle(i strictly to keep wire angle as ver-
tical as possible.The amount of slack wire while
the instrument was in the bottom was only3to
5m in usual.
Our procedure of the multi-penetration
measurement was as follows. After one
meaSurement,we raiSed the inStrument up tO
100m(sometimes1000m)above the seafloor.We
moved slowly(about2knots)to the next station
which was several hun(ire(i meters apart,and
then letting the wire angle as vertical as possible
befo聡the next penetration.We could make more
than one measurement per hour.
The positions of the measurement sites listed in
Table A-1are based on the Tokyo geo(1etic datum
except for the sites at the Mariana Trough l8。N
(H334,H335,H336and H338)which are base(i
on the WGS-72.Note that the difference between
the two system is as much as several hun(ired
meters.
3. Results
The results of 218 successful heat flow
measurements are summarized in Table A-1.
Temperature profiles in se(iiments are pre-
sente〔1in Figure A-1.The accurate depths to
which probes penetrate(l coul(l not be known
while rough estimation of them are inclu(ie(1in
Table A-1.Thus,the lengths of the probes are
adopted as vertical axes in the figures.When bot-
tom sediments were soft enough to be penetrate(1,
lower part of core head in which the pressure ves-
sel of the temperature recor(ier was placed was
burie(1in the se(liments.In this case the tip of the
probe would have reached to the(iepth of l to2m
more than the length of the probe。
An error of a temperature of each thermistor is
assigned as
△T=±(0.005十〇.001・G〉 (oK〉
where G is a gradient of the line being fitted on
the F(α,τ)vs.temperature plot of frictional
heat decay [4T/4F(α,τ)].The latter term is
intro(luced because a larger error in the (leter-
mination of equilibrium temperature may be ex-
pected for larger frictional heating on penetration
into hard se〔liments.The estimated uncertainty of
the extrapolate(i temperature at or(linary sites
with moderate frictional heating is about±10
mK.At some sites of har(1bottom sediments such
as in the Sumisu Rift an(l a part of the Mariana
Trough,it excee(1s±20mK.Temperature(lata
of some sites are consi(iered to be less re正iable,
an(l such sites are note(i in Table A-1.The
reasons are that small thermal(listurbance was
recognized on the frictional(lecay plots or the cor-
er fell down before the completion of the frictional
(leCay mOnitOring.
Thermal gra(iient was obtaine(i in principle by
fitting a straight line using the least-squares
metho(i when temperatures at three or more(liffe-
rent depths were available.The gra(lients of some
sites were calculate(i from only two temperature
points.These(iata should be treated as low-grade
ones,an(l are notice(i in Table A-1.
Temperature profiles are significantly non-
linear at some sites.Several naturally occurring
一210一
地αげZ伽伽地ε伽一〇8αsα脚名α一愉γ伽伽肋ピTrα働α2α岡
phenomena can be responsible for a non-linear
temperature profile(Noel,1984).That is,verti-
cal pore water a(lvection,changes in bottom wa-
te「 temPe「atu「e’ se(1imentation effects such as
slumping an(i erosion,local topographic effect,
θホo.It is difficult,however,to specify the cause
of these non-linearities unless closely space(i de-
nse heat flow measurements an〔1(1etaile(i〔lata of
local topography,sedimentation an(l bottom water
temperature variation are available. For this
reason,a straight line was fitted even in the case
of the non-linear temperature profile,an(i these
sites are noted in Table A-1.The sites.in the
Sumisu Rift are exceptions。Thermal gradients
obtained from the two lowermost thermistors in
the sediments were adopted,which will be(1iscus-
sed la.ter.
No correction for sedimentation,surface and
basement topography鉦ave been applied because
this report puts emphasis on presenting data。
However,effects of these factors are of course not
negligible.They wil豆amount up to30%because
many of the measurement stations woul(l have
fairlyF high sedimentation rate and rough topog-
raphy。
Unfortunately,most of the penetrations in the
Sumisu Rift reache(l to the(iepth of only lm or
less,and many heat flow values were calculate〔l
from the temperatures of only two thermistors.A
we翌1-sorte(l volcanic ash layer is encountere(i
within lm below the seafloor in the whole Soutぬ
Basin of the Sumisu Rift(Nishimura and Muraka、
mi,1988).This ash layer causes large friction
against the penetration of the probes。The Ewing
probe using a gravity corer of2m long often fell
down on the hit to the bottom.Even in the case of
successful penetration,extremely large frictional
heat cause(i a large error in extrapolating equilib-
rium temperature。If we aban〔lon to penetrate the
ash layer,measurements in soft hemipelagic mu(l
of less than lm thick on the ash layer can be(ione
easily using the thin Bullar〔1 probe of }ight
weight.
4.Discussion
4.1 The Sumisu Rift
Heat flow values of40 measurements in the
Sumisu Rift range from O to700mW/㎡.These
values have large uncertainty because the quality
of the(1ata there is low as mentioned above.
However,we can safely say that both high an(1
10w values exist in a narrow area (the detaile(i
survey area) (Figure3).The existence of high
values an(l local variability can be explaine(i by
hydrothermal circulation。 Conductive effects
(e.9.theeffectsofsurfacetopographyandbase-
ment topography) cannot explain such local
variability.
At the ODP drilling sites in the Sumisu Rift,
chemical composition of pore water in the se(ii-
ments is not〔lifferent from that of sea water(Leg
30。50」
48『
O 2km
o
Oo○
o
○
○
○
o
o
2呼○
Heat fbw O
50 0100
獣 00
00 mW1め
○o
139。50’ 52『 54」 56’
Fig.3 Distribution of heat f互ow values in the(ietailed study area ill the
South Basin of the Sumisu Rift.
一211一
β沼6伽のん6G60Zo8づ6αZS%榴ッの砂伽,γoJ.43,ノ〉o。4
126Scientific Drilling Party,1989).This is prob-
ably because the ODP sites would be located in a
recharge zone of hy(lrothermal circulation.Low
heat flow values(less than60mW/m2,H370-1,
2)are observed in the immediate vicinity of one
of the two ODP sites (Site 791) (no data at
anothersite).
Anomalously low temperature gra(iients
(sometimes close to zero)are commonly observed
in the surface se(liments of several tens of centi-
meters in the(ietaile(l survey area of the Sumisu
Rift (H322,H327,H331,H370,H371,H374,H379) (Figure A-1).The thin Bullar(i probe of
light weight was use(i at ail these sites.The gra-
dient determine(i using the lowermost two (but
less than lm in depth)thermistors is consi(ierably
higher than that of the near-surface thermistor
pair。 Submersible Alvin made temperaturemeasurements within the〔iepth of50cm in the de-
taile(i survey area an(i found similar low gradient
(K.Becker,personal communication,1989).
It is difficult to specify the cause of the low gra-
dient,but a possible explanation is well-mixing
of col〔l bottom water with the surface se(iiments
by intensive bioturbation.Observation by Alvin
revealed that the activity of benthic organisms are
very high on the floor of the Sumisu Rift (A。
Nishimura, personal communication, 1989).
Generally,non-linear,downwar(i convex temper-
ature profiles can be cause(i by variations of bot-
tom water temperature or sudden(ieposition of
sufface se(iiments by turbi(iite。The latter seems
unlikely in the Sum圭su Rift ju(iging from the hthol-
ogy o{the surface se(1iments,hemipelagic mu(i.
The former mechanism cannot be exclu(ie(1,but
the possibility of the temperature variation of
short perio(is such as the annual variation can be
rejected because the clata taken・in (iifferent sea-
sons an〔l years have similar ten(iency. The
temperature gra(lients of the(ieepest pair of ther-
mistors are use(l here for the calculation of heat
flow values because they are considered to be
least disturbe(1no matter what is the cause of the
low gra(iient.
It is rather confusing that the measurements us-
ing the heavy gravity corer show a ten(iency of
having a higher thermal gradient than those by
the small Bullard probe,an(i the former dose not
show the surface low gradient.The example is
H206an(1H379-2(Figure A-1).They are located
at almost the same point,and the penetrated
depths seem to be nearly equal to each other.The
gravity corer was use(l for the former site and the
Bullard probe for the latter.At H379-2,all five
thermistors of20 cm intervals penetrated the
sediments,an(l only the deepest pair showe〔l
large gradient.At H206,0n the other han(i,two
thermistors of45cm interval in the sediments
showed
H379-2.
nO Slgnpossible
larger gradient than the deepest part of
The uppermost thermistor of H206has
of having penetrated the se(liments.A
explanation for this discrepancy is (1is一
turbance of the se(1iments by the gravity corer as
illustrated in Figure4.The surface hemipelagic
mu(1may be scattered by the hit of the thick,
heavy gravity corer of high penetrating spee(1,
which will cause the apparent loss of the surface
low gradient.Furthermore,the depth of the gra一
(lient measurement may be larger in actual at
H206using the gravity corer than at H379-2using
the Bullar(i probe.Downwarping of the har(l ash
layer by the large friction (iuring the penetration
of the gravity corer woul(i cause the increase in
temperature gra(iient.On the other hand,the
sediments would be less deformed by slowly low-
ere(1thin Bullar(l probe of light weight.In the
Sumisu Rift thus the measurements by the gravity
corer may have overestimated the temperature
gra(iient.
4.2 z魎!o腿醜d t恥le N量s恥亘醜os恥面誼亘我Tro1颯9恥
The(iistribution of heat flow values in the mid・
dle Ogasawara Arc from Sofugan Is。to Nishi・
noshima Is.is shown in Figure5.The area east
of the Sofugan Tectonic Line has generally higher
heat flow than the area west of it.The Nishi-
noshima Trough has relatively uniform heat flow
of about100mW/m2except for some sites which
will be mentione〔i later.Co-existence of high and
low heat flow values is observe〔1in small grabens
along the Shichito Ri〔1ge,which suggests the ex-
istence of hy(1rothermal circulation. These
grabens are considere(1 to be incipient rifts like
the Sumisu Rift although their size is much smal-
ler.The area west of the Sofugan Tectonic Line,
on the other han(i,has generally low heat now。
The Sofugan Tectonic Line is consi(iere(i to be a
large normal fault system which bounds the west一
一212一
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Fig.4
』りαΦ
o
△丁
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一 一 一 日 胃 一 一 一 ロ 厨F 一 田 一
__一一一一層 一曹一一一一一冒
一 一 一薗 一 一 一 一 一 一 層 F 一 胃
一 一 一 一 一 一 一 一 一 F 胃 雪 一 一 一
幽oヱoの
…
σ)
xooり
l
i講鑛議,、、、
ll…illiiiiil灘1霧灘
灘難iii灘1灘難灘難灘ll.
Small Bullard-type
probe
∈
7dQ
HemipelagiG mud(biotu rbated)
撒難撚灘ll騰.,隅V。lcaniCaSh
難灘灘鑛i難叢
Ewing type probeUSing a gravity COrer
Aschematic(liagramofthemeasurementintheSumisuRift。Temperaturegradientofthesur-face sediments of several tens of centimeters(highly bioturbate(1hemipelagic mud)is very low.
Wel1-sorted volcanic ash layer underlying the hemipelagic mud is hard to be penetrated.The
penetration using a gravity corer may seriously disturb the sediments,which can cause overes-
timation of the gra(lient.
ern en(i of the rift graben of possib互y Oligocene
age.The contrast in heat flow would reflect the
difference in crustal thickness caused by the past
rifting.
Extremely high heat flow values over 400
mW/m2(H168and H200-3)are observed in the
southwestem part of the Nishinoshima Trough(26052.0’N,139。46.0’E) (Figure5).An intru-
sive bo(ly exists in the thick sediments just blow
the high heat flow sites,which is clearly shown
on a seismic reflection profile (Figure6).Dis・
turbance of the very surface se(liments probably
caused by the intrusion can be recognize(1 0n a
3.5kHz echogram(Figure6).The high heat flow
and the recent deformation of the sediments in(1i-
cate that the intrusive activity is quite youn9・
Multi-penetration measurements revealed the ex-
istence of a low heat flow site(45mW/m2,
H200-4)close to the high heat flow sites(Figure
7),suggestingtheoccurrenceoflocalhydrother-
mal circulation.Several similar intrusive bo(iies
are found on seismic reflection records in the
trough.
Two sites on or close to the Sofugan Tectonic
Line(H171and H173)show high an(i low values,
217and65mW/m2,respectively.Pore water cir-
culation through this fault system woul(i be re-
sponsible for the variation of heat flow values。
To the northwest of the Nishinoshima↑rough,
another SSW trending depression lies parallel
with it(from29。N,139059’E to280N,139。20’E)
(Figure5).The strike of the depression suggests
that its origin is relate(i to the past rifting which
formed the Nishinoshima Trough although the re-
lief of the basement of this depression (max.
several hun(ire〔1meters) is much smaller than
一213一
B%’Z6渉f物qプ渉んoG召oZo8づ6αJS%㌍u61y(~ズノ41)απ,レ「o‘.43,ノ〉o.4
030
029
28。
27
o V )
o 〃 . 麟b
Hea量f
0(■75●
魅 o 鱒15(
菱鎗詳・
黛砂
30(麟
o
国観
強.
●
も●も ♂
塁匡
ユ ●
o Q輪。饒●
o
じ●
心
ぴ 1一◎・毛 三● 魅 o
o q◎
o〃∂ o
(]
9略D
o
●o㌔孕
◎●
網◎D
、Ω o直』〉 、
o
⑨⑨.
ミ
◎oεo
男
β鰍 o
shlnoshima
のoε 鯨◎
黛孫q巡肯。
O● 4
~ど O
o 諭
o 麟
0 50km1 慶 o
一一 0140 141。
0(mW/m2》
Fig.5 Distribution of heat flow values in the Nishinoshima Trough and its environs.Solid circles are
the data of this study,and open circles are from Vacquierαα」.(1966),Anderson(1980)and
Yasui(unpublishe(i).Topographic contours are at500m intervals.Bold contours are.2500m
iso一(iepths.LineAisthelocationoftheseismicprofilesshowninFigure6.
一214一
π6α‘刀oωf%地θ12%一〇9αsα”α名α一Mα再α冗αみ%ピT.γα獅α~α彦の
o恩麗
◎
o⑪
ω
監
①
痘
5
W闘IS㎞1聡◎S臨1鵬凝丁『oug㎞
E.._』:i
←の∫
’僻㊧翻慮留◎駆‘摺騨/鵬2ノ・
呼讐①◎、⑩1蒙篭、潔專簿醤
◎軸》
ハ9》躍一盤⑪
o
38ゆ◎
Fig.6 Asingle-channelairgunseismicprofile(top)an(la3.5kHzechogram(bottom)runningthrough a high heat flow point in the Nishinoshima Trough.The location of this line is shown
in Figure5.High heat flow values occur lust above a intrusive bo(ly。The heat flow value in
the parentheses was measured not on this line but at about2miles south・S・T・L・l the Sofugan
Tectonic Line of Yuasa(1985).
一215一
」
B彿π6あ%ρプ孟んεGεo‘08・づoαZ S彿γ砂θッのF∫α1)α究,γo’.43,ハ汚o.4
53’
52’
2げ5ず
馳噛68
404購
45
7傑》 一5
蜘a酬o駆侮騨/伽り
プ04 開200儘1
胃3 92
-3
43⑨
一4
0
踊一75
醸脅0
1km
一一13go45」 46♂ 4プ
Fig.7 Detailed heat flow measurements around the high heat flow point
in the Nishinoshima Trough.
that of the Nishinoshima Trough.Eleven measure-
ments in this(iepression showed uniformly very
low heat flow,less than30mW/m2(from m39to
H145,H291),which is in contrast with the mod.一
erate or high heat flow in the Nishinoshima
Trough.This value is too low for the con(iuctive
component of the heat flow from the oceanic
islan(i-arc of not older than Eocene age.It is thus
considered that some Leat should be transported
by convection。Although the(iepression is well
sedimente(i(about300minthickness)an〔ino
outcrops of basement occur within5km of the
measuring sites,long wave-1ength (10 km or
more?)pore-water advection may have occurred
here.
4.3丁恥e聡戚恥emM麟&盤Tro腿9恥 The Mariana Trough north of220N is consid-
ere(l to be now in a rifting stage based on geolo-
gical structure and magnetic anomalies(Yamazaki
ε孟α♂.,1988,1991;Murakami8‘α」.,1989).The
rifting north of220N is characterized by thermal
and stmctural asymmetry.High and variable heat
flow are observed only in or close to a row of
small grabens along the eastern margin of the
trough (Figure8).The floor of the rift is com-
prised of tilte(l blocks boun(ie(i by normal faults,
and steps(lown to the east(Figure9).Except for
the eastern margin,the trough has uniformly low
heat flow.In the trough north of22。N,therefore,
the existence of hydrothermal activity can be ex-
pected only along the eastern margin.
Pattems of heat flow across rifts can give signi.
ficant constraint on the mode of lithospheric ex-
tension during rifting(Buck6診α∫.,1988;Mar、
tinez an(i Cochran,1989).The discovery of the
thermal asymmetry of the northem MarianaTrough is hence important to understand better
the rifting processes here。This subject is beyond
the scope of this report,an(l will be discusse(i
elsewhere(Yamazaki,1992).
The Mariana Trough south of22QN,on the
other hand, has (ieveloped to a sprea(ling stage
(Yamazaki6診α‘.,1988,1991;Murakami8‘α∫.,
1989).Spreadingcenterstherecanbeidentified
from geological structure an(l magnetic lineations.
Anomalous temperature profiles in sediments sug-
gesting intense hy(irothermal circulation are
observe(l at several sites close to a sprea(iing
center.
Extraordinary large temperature(iifference be-
tween the uppermost thermistor in the se(liments
and bottom water is observe(1at H341although
the thermal gradient among three thermistors is
low (Figure A-1).The(1epth of the penetration
of the probe coul(i not be known accurately,but
一216一
Hoα’刀oωづπ孟んθ王~%一〇8αsαωα侶α一ハ4α再α%α/1猶6‘T・γα解α9α観ノ
249
23。
D魎・・
◎
1
鵠縞騰唇国恩溺◎葦琶鵬翻 量s塾
禽 ◎
の◎
◎ q▽
◎
9
慣4調Q
22。
o恥δ
/G・.
D髪
◎ §◎駄朧
一一
Q愈
閣曹題電 育国◎騨
0(繭Wノ齢2》
㊥7暴
⑱ 5◎
00
麗重1《駄◎ s朧量。
翰0 0
⑳
●②倉
、 ●
o
o
り
。膜
も
あ
斜 ◎
㊧
も⑲
璽
郷 一黙
oo
略
。’織
s 解腿k脳。量晶 Sm匙凹
唱42。
輪q q
ハ幅
唱43。
◎ 叉
144Q
Fig. 8 Distribution of heat flow values in the northem Mariana Trough.High heat flow occurs only in
or close to a row of small grabens along the eastern margin of the trough。Topographic con.
tours are at500m intervals.Bold contours are2500m iso-depths.Line A is the location of the
seismic profile shown in Figure9.
the temperature profile of subsurface l or2m at
this site must be extremely non-linear.Further・
more,temperature gra(iients among sites around
H341 are highly・ variable. H377-1 through
H377-51ie on a line starting from H341at about
300m intervals(westwar(1),and H342-1,一2and
-4at300to800m intervals(southward) (Figure
10).H377-1,which is locate(1nearest to H341,
and H377-5show slightly upwar(1convex subsur・
face temperature profiles。The rest are,on the
other hand,linear an(i relatively low temperature
gradients.The gradient of H342-4 is close to
zero.These anoma正ous temperature profiles and
local variations in the gradient can be explaine(i
by hy〔irothermal circulation.Pore water woul(l be
moving upwar(i at H341,and nearby low-gradient
sites woul(1be in a recharge zone(Figure10).
Another type of a shallow hy(irocirculation
effect can be seen at H344an〔l H367,showing
temperature profiles with ben(is in the mi(i(ile.
The measurements were (ione independently(separate cruises〉,but the two sites are only ab一
一217一
團a調a醜a T『◎蟹9恥
雇
1曽OQ
20㊤
℃霊
oo①
め
霊 3①
置
=
3》 4霊一
》03占3 5ト
6一
闇ea量鯛OW《朧W/m2》’
る
謄鞭
盗
描
ヤ
oじ
蒙
蒙i,欝,
一籏
議繍
雛 購
.諜二., 綴_
婁選燕
叢 心慮譲
10km 一、ド
を
馨・・
臼←一
鐘
《39》.4◎2.
- 拙 鶴..
甦、
蓋
76
諺
59
?難灘・
監
唱36 260
騒難覆仁
凝
鵠 鷺 .弛 瞭
懸
∫
《34◎》
(230》
一憩
巽=.
灘署’レ蓋》潔
傑
冨爵.
’議・臼
詠難
灘菱灘
篇
霧鞭莚騒謙讐
覗灘 黎
獄
叢難
灘難黎翻蚕
難霧
難難鞭
ドロ も・§ ..多
・= . ;o
照
驚
甲 , ロ じロペ ル
じ 黛 ロ 岬,4 。 ■、
■
翠
,塞
bロ
ミ融融.
§
黛さ駄
oも匙馨.
匙
防駅
§遷
黛
ξ§
5轟
ξ叙
Fig.9 A single-channel airgun seismic profile crossing the northem Mariana Trough at23。N and heat
flow values on this line.The location of the line is shown in Figure8.The rifting at the north-
em Mariana Trough shows thermal and structural asymmetry.Heat flow values in the parenth-
eses are locate(i not on this line but in the northern continuity of the basin.
飽αげ’伽伽飾ε伽一〇8αsαωα箔α一Mαγ伽α肋ピT.y㈱α~剃
06ρ
ロ ず
2105
春 †
毯 ε咀 9
O
牽口 寺 心
㌣ ロ 7講 ぬ ト
9おH34轟轡 =
H342-1叫
1km
一2叫
一範↓
Fig.10
’143。’17 18ρ
Pore water circulation deduced from tempera-
ture profiles in sediments。This area is located
close to the spreading center of the Mariana
Trough at21。N.The direction of the arrows
(up or down)shows the direction of the pore
water movement.The width of the arrows rep.
resent the relative intensity of the pore water
movement.Soli(i squares are the sites at which
non-1illear temperature profiles (upwar(i con-
vex)areobserved.Opensquaresarethesitesof linear profiles。
out300m apart.The two anomalous profiles are
goo(l evidence for lateral flow of pore water near
the crest of an active sprea(ling center.
Ac㎞owledgements:The heat flow measure-
ments were performe(l with cooperation of all
on-boar(i scientists,officers and crew of the
Izu-Ogasawara-Mariana cruises of R/V
Hakureimaru.I wish to thank A.Nishimura,F.
Murakami,E.Saito,M.YuasaandA.Usuiforhelp and(1iscussion through this work.I also
thank K.Becker an(l B.Taylor for giving me un・
published data,M。Yamano for allowing me to
use his compilation of heat flow (lata aroun(1
Japan,and O.Matsubayashi for useful comments
on the manuscript。This work was supported by
the special research program,“Submarine Hy(lro-
thermal Activity in the Izu-Ogasawara Arc”,
fun(le(i by the Agency of Industrial Science an(i
Technology from1984to1989.
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nic front, Izu-Ogasawara Arc. B%μ.
G60」.S%γッ.ノ1αρα物,vol.43,in press。
一221一
B%JZ8勘げ地召G60Zo8づ6αZS%7丁召ッげ紳伽,yo’.43,ノ〉o,4
Ap耳》endix
Temperature difference(oC)
0
E て
‘
αΦ
0 20》
虫Φ 3匡
4
0,0 O.2 0.4 0,6
=
O.00
0
1
2
o,噂o
コ= :1: 工 工
σ1 『◎ 轟 ω
0
て
2
O,0 0.2 0.4 0.6 0,8
0
1
0,0 0,1 0.2 0,3 0,4
工
σ》
2工
悼
… …
お 曽
0
1
臼0,0 0.毛 O,2 0.3 0,4
2
0
1
o.o
期
… ≡
陪 製
…蕊
2
O,1 0,2
0
1
2
o.o
≡≡鵬霧
0,{ O,2
0
蓬
0.0
o
≡鵠
ヱ
ωo
2
0,1 O.2
…≡ 器器
=
¢
0
1
2
O,0 0,1
00.0
≡ ≡
撃 3
o.1 O.2 O,3
1
2
3
4工
ωo
o
1
2
0・9 o,1
oo,o
=
ω}
=
ωCD
o,1
1
2
3
4
矧
=
あ
= 工
ω 斜o o
oO,0 O,1
1
2
3
4
o
1
o、o
剛
剛
= 工 = =:
ホ爵畠 云
2
o。1 O.2
工
“N
oo,o
=
轟
o
0.2 o.4 0.6
1
2
3
4
o
1
0.O
9
…i≡
畠
工
轟o
2
0.1 O.2 O,3
工
q≡
8
Fig.A-1 Se(liment temperature profiles for all successful penetrations.Vertical axis represents the
lengths of a probe.Horizontal axis represents(iifference from the temperature of bottom wa-
ter just above the seafloor of each site.The uncertainty range is given for each temperature
point according to the amount of frictional heating(see text).Thermal gradient is calculate(l
by fitting a straight line using the least squares metho(i if three or more temperature points
are available.The points connected with dashe(i lines were not used for the calculation of the
gradient(explainedinthetext).
一222一
飽αげZ伽伽地61~%一〇9αsα㈱名α一M副伽一瞬丁.γα蹴α~襯ノ
Temperature difference(oC)
E
o
よ
審層D1……
甲慧
可匡
2
0。0, 0.1 O,2 0,0
工
㎝ω
0
1
= 20沁
O,1 0.2
0
1
2
O.0
工
oo
…≡
匁
O.1 0,0 0.2 0.4 0.6
0
1
2
3
エ= 赫 4- oσ》
o
≡…
里 工=: _』
一 〇① u1ω
0
、
2
3
4
0.0 0。2 0.4 0.6 0.0
エエσ》σ》
刈①
0
て
2
3
4
1,0 2.0
o
1
2
3
4
0,0 0.2 0.4 0,6 0,0 0.2 0,4 0。6 0.8
i≡
雷
==工
σ》 刈
o o
o
1
2工
刈ω
工
刈
o
1
2
3
4
O,O O,2 0,4 0.6
コ:エエ:1:
お蓉瞬刺
o
1
2
O。O O.て O.2 0,3 0.O
、工一 工刈 一〇D 刈
o
o
1
2
0,1 0.2 0.O O。1 0.2 0.3
工
oo
o
0
1
2工
ooω
=
CP
o
{
2
O。0 0,1 0。2 0,3 0,00
工
QOり
コ: コ=
鶏 8
0O.05 O,10 0,0
1
2
3
工 4エ のお器①
酬
工
o
o0.1 0,2 0,0 0,1 0,2 0,3
墨
2
0
1
=
oω
工
o悼
2ii…
零
=:【 り一 σ》
o㎝
Fig.A-1 Continued
一223一
Bπμα伽(ゾ孟h召G60‘08歪oα’S%γ”の7(ゾ∫αραπ,γoム43,No.4
TemperatUredifference(。C)
o
E)1£
α①
℃
Φ2.≧
誌旬
α=3
4
0.O O,1 0.2 0,3 0.4
0
1
2
= 300
0.O O,1 0.2 0、3
工
o刈
o
1
2
工 おエエエ ≡甲おおお o㎝ 3鯛器窒
0,0 0,5 1,0 1.5
o
2
4
6工沁
o“ω 8
O,0 0.2 0.4 0,6 0.8
コ:工工=:
NINNgNレooooo《P~》?ムq一沁
=悼
o
O。O O.2 04 0,6 O。0 O、2 0.4 O,0 0.1 0.2 0,3 0.0 0.1 0,2 0、3
0
1
2
3 =工工コ:
8888h⊃鴨》甲甲
ムσ1障一
0
1
工
8 2ドω
=卜⊃
o刈 焉
8
o
1
2
ヱ障
oco
=卜⊃
oo
0
1
2
回
焉 蔚一 〇
0.0 0。1 O,2 0.O o,1 0。2 0.O o,1 O,2 0.O O。1 0,2 0.3
O
1
2曲
工沁
ω
曲
=悼
隠
o
1
2
工悼
“
剛
工h⊃
①
0
1
2
剛
剛
工悼
o
0
1
2工卜⊃
OD
剛
工
陪o
訴
0
1
2
0,0 O.1
00,0 O,5 1,0 0.0
2
4
6
8工
B轟
輔o刈
◆
o
0
1
2
3
工
B 4①
0.1
o
1
工 2BOD
0.O 0,1 0.2
弱
工
馨
工
蹄o
Fig.A-1 Continued
一224一
飽αげ」伽伽地61~%一〇8αsα磁名α一Mαγ伽α。肋ピT.y㈱α宕α切
Temperature difference(oC)
∈
O0.O O,1 0.2 0.3
‘
αΦで 1①>
o可匡
2
0
1
0.O O.2 0.4 0,6
エ
80 工h⊃
ω
o
工
8刈
2 ヱ陣轟悼
0
1
2
.0。2 0,0 0.2 0,4
工陪“ω
0り0,1
麗
憲 雨
倉 a 工
撃①
0.O o。1 O,2
1
2 工卜⊃
轟co
O,0 0,1 0.2 0,3
0
1
2
oO,O O,1 0,2 0.3 0.4
1
2
oO.0
国
工 工へ》 『9σ1 σ》
OD 一
H
工ω
oo
1
2
O,2 0.4
0
1
0.0
志零
エ
8障
隔
工障
oω
エ
霧 2
0.1 O。2 O.3
彊憂エ
鵬刈
0.0 0、2 0.4 0,0 0,1 0.2 0.3 0.0 0.1 0.2 O、3 o、o o.1 O、2
0
1
2
工悼刈障
工 工N) 悼㍉』 刈轟 ω
o
1
工 2ゆ刈
q
工旧刈刈
o
1
焉お 2
器お
工障OD
o
工沁刈OD
O
1
2 工 邸工 o◎Nレ N〕OD
0
1
2
O,0 0.2 O,4 0,0
雨語器
田
O
1
工
NGQ 20
0,2 O,4 0,00
o0.05 0.10
1
2
3co
瀦焉焉㊤o o orbあ本ム
o
1
O,OO
2
0,05 o,10
エ
器“
工悼
oN
Fig.Aヨ Continue〔1
一225一
B%〃6あ%のr地召G:60Jo8f6α∫S彿吻θツ(ゾ∫αρα%身yoJ.43,No.4
Temperature di歪ference (。C)
E
O,000,0’
0,05 0.0
‘
ユ
8Φ0・5
.≧
筍可匡
{.o
工工望望一令
0
1
0,2 0,4 0,00O,0
0。02 O.04 0。OO
O.5
1,0
畔
工 =の ゆ
繋 B
0.O
0.05
O.5
1.O
議、
器霧
0.00O。0
O.5
1.0
0,05
o0,0 0,1 0,2 0.3 0,00
トP輔 H酬
工ω悼N
工ω障刈
悼
1
2工ω障Co
O.0
0.02 0.04 -O.02 0.00 0,02 0.04
0.5
1,0
エ
8”
0。0
O,5
1.o
脚
=ωω
基基望望山南
O.OOo,o
0.05
O.5
1.o
oo.o
轟
H甲串
エ
8甲悼
1
2
O.2 0。40
0.0
阿
国
回
エ
聾
1
2
0,2 0。4o
1
0.O
工ωω①
…ii
綜
0,1 0.2
工ωの甲
エ
8堕
N
0。00 0.05 0,10
o
1
2
o
1
2
0,0
工ωωo
O,5 1。0 -0,1
工ω轟
0
1
2
O.0 0,10.0
1,0
0。O
工ω“悼ム
エコニ撃象甲甲障 一
O,1 0.2
コ:コ=
撃袈甲甲悼 一占
Fig.A-1 Continue(1
一226一
飽αげ’α〃伽地61z%一〇8αs伽億一Mα吻%翻瞬丁γ伽α~α切
Temperature difference(oC)
E
o
£αoη
Φ)
邸一 1Φ
匡
0.0 O,1 0.2 0。OO O,05 0,噛0
=:工
撃撃の くゆ
ム山
0
1
2
0。OO
閥
脚
嘲
曲エ
撃
0
1
O,05 O.OO
蚕鼓甲甲甲N》 ω」』
0
1
0.05
聾饗
工
匁
9q
o
1
2
O,O O,{ 0.2 0.3 0。0
工ω①①
0
1
2
O,1
o0,0
晒喝・、、
袖
甲
幽工ω①圃
1
2
0.1 0.2 一〇,02 0.00 0,02 0.04
工ω①
o
0,0
0,5
1。0
嚇
き 塁刈 刈o 早障
O、OOo.o
Q,02 0,Q4 Q,OQ
O.5
1,0
一 器
Σ 山
o,o
O,02 O、04 0.OO 一
O.5
1
1,0
一『t畔←一仁トー{
工ω刈ω
o,o
0.5
工ω刈ω
沁 て,o
O。05
o
コ: エエ エの のの のリ リリ リ
&詠童宝 2
O、O O.2 0.4 0,6
=ω図α
工ω刈o
0.0 O,1 0.2 0.OO 0.05 0,10
0
1
2
『
、
器基吉マママ山ム南
工ω刈刈
工ω刈刈
o
o,o
O.5
1.o
紳、、
焦、工ω刈
o
=ω刈
oω
工ω刈
oトの
Fig.A-1 Continued
一227一
」
NNOQ
site No,
H111P442H112RO350H113RC351H114RC352H115Rca53
H斜6RC354H119RC357H120RC358H121RC359H122RC360H123RC361H124RC362H125RC363H126RC364H128RC366H130RC368H131RC369H132RC370H133RC371H134RC372H135RC373H136P443H137RC374H138RC375H139P444H140P445H141P446H142P447H143P448H144P449H145P450H146RC376
Lat,IN)
30◆51,75’
30◆03,92’
30.09,91’
29。56,06コ
29059,86’
29◆55,983
30.17,941
30◎13,92’
30.11,945
29.39,95量
29.33,06’
29.26,88じ
29◆20.93’
29.17,98’
28.56,81置
28●39,07’
28.49,20『
28●50,73’
28◆29.67’
28014,93’
28.24.20’
27・29,95’
29●14,84置
28.59,971
28.59,59’
28.51,99’
28.44,97’
28.37,91’
28026.08”
28.17,99’
28.07,919
27◆59.635
Lon、IE)
139.09,375
139056,60’
139.40,261
139.38、58’
140◆01,91’
140000,418
139φ57,700
139058,79璽
140◆01、40-
139.52,93聖
140.12,79’
140●27,88’
140●35,311
140●14,46’
140039,29’
14α03,36’
140。03.23’
140011,938
140●35.26’
140006,131
140●04,951
141018、23’
139。30.54匿
139◎25,22’
139●50.02’
139’47.84’
139。47,04’
139◎36,95’
139●35.78’
139●33,90,
139◎30.948
140じ39。74監
Table A-1 Summary of heat flow meaSUrementS.
epth P.robe A P dT/dz N Cond. s,d, Nc Q Rem, Area
003 P4 2 F 0,131 3 0,981 0,035 15 129
970 G2 1 F 0,023 3 0,862 0,032 9 20 To面shima Ri配
207 G2 1 F 0,043 3 0,895 0,051 9 38 1550 G2 1 F 0,035 3 0、9肇3 0,036 10 32
975 G2 1 1.3 0,038 2 0,860 0,033 7 33 3 Torlshima Ri性恥§驚
960 G2 2 F 0,237 3 0,864 0,031 10 205 Torishima Rifし’ 恥弊
ρ,
480 G2 1 1.3 0,394 2 0,843 0,024 8 332 3 Torishima R醗 容
540 G2 2 F 0,167 3 0,866 0,036 10 145 2 To酉shima Rift 魚飾
538 G2 1 F 0,062 3 0,861 0,041 10 53 To而shima Rift 討鳴
648 G2 1 1.3 0,167 2 0,854 0,028 8 142 3 Sofugan Is,一Nishinoshlma Is, o鳴
649 G2 1 1.6 0,322 3 0,843 0,043 7 272 2 Sofugan ls,・Nishinoshima is、 oho784 G2 1 1.6 0,156 3 0,867 0,016 7 135 Sofuganls,・NishinOShimals.
閃一。ら
808 G2 2 F 0,061 3 0,907 0,048 7 56 Sofugan Is、一N除hinoshima Is、臼N
618 G2 1 1.6 0,106 3 0,868 0,026 8 92 Sofugan Is。9Mshinoshima Is.のミ
651 G2 1 1.6 0,100 3 0,973 0,066 5 97 Sofugan is.・Mshinoshima ls。 §趣
320 G2 1 F 0,072 3 0,933 0,010 8 67 Sofugan ls.一Nishinoshlma ls。只
719 G2 2 F 0,074 3 0,922 0,018 8 68 Sofugan is.一Mshinoshima ls. 旨718 G2 1 F 0,040 3 0,958 0,028 8 38 So佃gan ls.・Nlshinoshima ls. 暦
9ミ
653 G2 1 1.3 0,076 2 0,857 0,027 6 65 3 Sofugan Is.・Nishinoshima Is, }
998 G2 1 F 0,055 3 0,876 0,029 9 48 Sofugan ls,一Nishinoshima Is・ ぎN
644 G2 2 F 0,025 3 0,893 0,015 9 23 Sofugan ls.一Nishhoshima Is,へ
123 P4 1 2 0,184 2 0,868 0,053 9 159 3 OgasawaraTrough 免}
010 G2 1 F 0,033 3 0,935 0,021 8 31 ξ175 G2 1 F 0,069 3 0,905 0,037 9 62 2 へ
038 P4 1+2 F 0,029 5 0,906 0,015 13 26 Sofugan ls.一Nishinoεhima ls,
303 P4 1←2 F 0,029 5 0,897 0,016 12 26 Sofugan ls。一Nishinoshima ls、
531 P4 1+2 F 0,017 5 0,900 0,014 10 16 Sofugan is.・Nishinoshima Is、
638 P4 1+2 F 0,021 5 0,903 0,023 12 19 Sofugan Is,一Nishinoshima ls.
485 P4 1+2 F 0,014 5 01935 0,013 11 13 Sofuga国s.りNishinoshima Is.
550 P4 1+2 F 0,018 5 0,922 0,023 11 17 Sofugan ls.一Nishinoshima Is、
597 P4 1+2 F 0,026 5 0,917 0,021 11 24 Sofugan ls。・Nishinoshima Is.
367 G2 1 1.3 0.斜0 2 O,913 0,065 9 100 3 Sofugan ls,・Nlshinosわima ls,
塑
1ゆ認
H147RC377H148P451H149P452H150RC378H151RC379H152RC380H153RC381H154RC382H155RC383H159RC387H160RC388H163P453H164P454H165P455H166P456H167P457H168P458H169P459H170P460H171RC391H173RC394H174P461H175P462H176P463H177P464H178RC395H179RC396H180RC397H18{RC398H183RC398H186RC402H187RC403H188RC404H189RC405H190RC406
H19てP483
27.53,621
27.53,82-
27◎45,093
27044,96’
27◆35,75’
31.16,951
31◆07。671
26◆59,97’
26◆58,32’
24●00.08’
24●02,68’
27。20,029
27●12,03唇
27000.06。
27000,16酵
27000,105
26.52,03’
26.52.00’
26052,11’
26。59.90’
26052.10’
26.50,62’
26◆52,06-
26.52,15’
27.33,21’
3C卜55,73’
31012,92[
31◆≦6,87’
30◆4ア,86’
30●47。94’
23.02,64’
22◎56,12’
22.49,62臼
22●36,849
22。38,525
22・30,82響
140.40,275
140ゆ09,06’
140◆09,141
140.36,18-
140032,15’
139◎54,659
139。52,76’
140◎17,12,
141.00,088
14肇◎33,02”
141。32,46,
140000,05,
140●OO,09陰
13go45.47’
139◆47,55’
139●49。81’
139●45.85’
139043.13’
139・44,85’
139●43,75『
139039,46’
139●23,60量
139●46,66’
139●48,381
139●59,87’
139ρ41,23’
139・54,63’
139。53,99’
139◎53,56『
139◎42,72’
142●04,42’
142,08,00-
142●34,66量
142●09,74’
142◆18,’161
142018,95’
3574
3ア153755
3490
35851985
2135
3488
2655
2253
22463895
3778
3835
38453851
3845
38553851
38023845
48483835
3835379522202123
2045
22932235
2560
3103
2928
33793471
3483
G2P4P4
G2G2G2G2G2G2G2G2P4P4P4P4P4P4P4P4G2G2P4P4P4P4
G2G2G2G2G2G2G2G2G2G2P4
Table A-1 Continued
2
1+2
1+2
2
1
1
1
1
1
1
1
1+2
2
1
2
1+2
1+2
1+2
1+10 1
1
1+101+2
2+101+2
2
10
1
1
2
1
2
1
1
2
1÷10
1,6
F
F
F
F
1
1
F
F
1
1,3
FFF
F
FFFFFFFFFF
1.6
1,6
1.6
11,5
FFlFFF
0.145
0,101
0,118
0,斜0
0,046
0,284
0,086
0,059
0.031
0.129
0,039
0,093
0,023
0,124
0,122
0,115
0,471
0,107
0,134
0,246
0,075
0.111
0,129
0,118
0,143
0,186
0,187
0.139
0,482
0.043
0,104
0,017
0,438
0,009
0.053
0.0~1
0,891
0。852
0.828
0.902
0,893
10.850】
0,840
0.885
0.880
0,858
0,823
0,849
0,838
0.829
0,830
0,823
0.859
0,825
0.848
0.885
0。864
0,789
0,859
0,839
0,838
0,826
0,838
0.850
0,831
0,871
0,858
0,805
0,919
0,766
0,792
0,727
0,036
0,018
0,030
0.057
0,037
0,024
0,025
0,031
0,010
0,033
0,025
0,017
0,028
0,012
0。023
0.026
0,040
0.015
0,022
0.023
0,018
0.0.17
0.032
0,026
0.021
0.010
0.009
0,007
0,007
0,025
0,051
0,142
0.034
0.040
0,025
7
10
11
9
9
0
6
9
8
5
5
9
9
11
10 9
10
10
10
8
8
10
10
10
10
78563986879
130
86
98100
41
241
72
52
28
110
32
79
19
103
101
95
404
88
114
217
65
88110
99
120
153
156
118
401
38
8914
402
7
42
8
Sofugan Is。卿Nishinoshima ls、
2 NishinoshimaTrough NishinoshimaTrough Sofugan Is.一NishirIoshima Is,
Sofuganls,・Nishino3himals,
Sumi3u Ri就
Sumisu Ri代
Nishinoshima Trough
North of Kaika槍Smt,
Ma㎡anaTrough
MarianaTrough
NishinoshimaTrough
NlshlnoshimaTrough
Nishinoshima Trough
醐shinoshima Trough
Ni師noshimaTrough Nishinoshi㎞aTrough
NishinoshimaTrough
Nishinoshima Tr℃ugh
Nishinoshima Trough
NishinoshimaTrough
Nishinoshima Trough
Nishinoshima Trough
肘ishinoshimaTrough
Nishinoshima Trough
2 Sumisu Ri乱
Sumisu Rift
Sumisu Ri仕
1,3 Sumisu Ri忙
Sumisu Rift
Marlana Trough
MarianaTrough
3 MarianaTrough MarianaTrough
l MarianaTrough Mariana Trough
331
1β
1,3
評ミ
喬§§’
誉も
紺零
o晦9的9ミヨ
李さミ・
蓉>§
9ざ
……
翁ε
器○
H192RC40アH193RC408H194RC409H195RC410H196RC411H197P484H198働1
H198-2
H198-3
H198-4
H198-5
H199P485H200-1
H200・2
H200-3
H200-4
H200-5
H201P486H202・1
H202-2
H202・3
H202・4
H202-5
H206H207H208H209H210H211
H212RC431H213RO432
H215RC434H216RC435H218RC437H219RC438H220RC439
22。33,99’
22◆23,01’
21。51,148
22◎02,191
22’12,33’
27。06,18’
27●07,83’
27.07,63’
27.07,45墨
27●07,25暫
27.07.14’
26.49,96撃
26◎52,268
26052,181
26.52,00唇
26。51.82’
26.51,7α
27005,33’
27◎07,33’
27.07,25’
27。07,17曇
27◎07.08’
27◆06,93’
3Cド47、94’
30947。951
29.59,97量
29ゆ59,80‘
29059,741
29ひ59,88’
27●35,801
27◎53,90,
28◎50,96,
28.49.29酵
29033.019
29・32,99,
29・33.041
142◎37,19’
142017,40’
142032,01,
142●39.06’
142’53.86’
140◎00.02’
140●00,13巳
140.00.13’
140。00,04’
139●59,92’
139’59。83’
139054.43’
139ひ46.26’
139◎46,14’
139045,96旧
139の45,821
139,45,731
139046.591
140,00,15’
140。00,10,
139’59.98’
139レ59,811
139’59,65’
139●54.03’
139.54,329
140.0璽,56’
140・02,158
140●02,389
140●02.66’
140032,92’
140◎36,759
140●35,15’
140●34。941
140◎05,319
140◎08.149
140。10,699
33663385
4263
38844557
3762
3761
37603759
37603760
38363834
383638403841
3841
378837553757
3749
37603761
2290
22882980
29842970
2960
35673522
3765
3780
29132914
2812
Table A-1 Continued
G2 1
G2 10
G2 1 G2 2
G2 10 P4 1+2
E2,5M 10
P4 1+2
E2,5M 10
P8 1申2
E2,5M 10
E1,5
E1,5
E1,5
E1,5
E1,5
E1,5
G2G2G2G2G2G2G2
10
110
1≦0
110
10憶0
110
11
F
F
F
F
l
F
F
F
F
F
F
F
F
FFFFFFFFFF
O.7
1,3
FFFFFFFF
重,6
1,5
1.5
0,068
0,007
0,009
0,060
0,396
0,039
0,008
0,024
0,044
0,071
0,1,2
0,124
0,121
0,138
0,511
0,052
0.117
0.124
0,078
0,043
0,174
0,039
0,030
0,842
0.149
0.061
0.204
0,145
0.008
0,062
0,009
0,094
0.斜7
0,083
0,113
0,970
0,752
0.739
0,768
0,841
0,856
10,856》
10,8561
10.856》
10.856》
10.856)
0,840
(0。859》
10。859》
10,859)
〔0,8591
10,859》
0,849
10.8561
{0,856》
10,856》
lO.856》
{0,856》
10.831》
10.831)
10、874)
{0,8741
{0.8741
(0,8741
0.876
0,910
0,883
0,919
0.971
0,941
0,892
0,113
0,053
0,012
0,018
0,003
0,033
0.027
0,017
0,046
0,055
0.034
0,050
0,014
0,093
0,052
8
8
8
8
3
9
0
0
0
0
0
9
0
0
0
0
0
15 0
0
0
0
0
0
000008743776
66
5
6
46
333
33
7
2~
3861
96
104
104
119
439
45
100
105
67
37
149
34
26
700124
54179
127
7
54
8
871i4
78
101
1
3
31,3
2
4312
2
Mariana Trough
Ma㎡anaTroughMarianaTrough
M副anaTroughMarianaTrough
NishinoshlmaTrough
NishinoshimaTrough
NishinoshimaTrough
Nishinoshima Trough
NishinoshimaT飾Dugh
NishinoshimaTrough
NishinoshimaTrough
Nis翫inoshimaτrough
NishinoshimaTrOugh
Nishinoshima Trough
NishinoshimaTr◎ugh
Nishinoshima Trough
NishinoshimaTrough
Nishinoshima’『rough
Nishihoshima Trough
麗ishinoshima T『ough
Nishlnoshima†rough
Nishinoshima Trough
Sumisu Ri仕
Sumisu Ri舵
To『壷shima Ri穐
To丙shima Ri穐
’『o㎡shima Rlft
To㎡shima Ri鷺
Sofugan ls。・Nishinoshima ls.
Sofugan Is、・Ni3hinoshima!s・
So旬ganlS、・Nisめlnoshlmals・
Sofugan Is,一Nishinoshima Is,
Sofugan Is.一Nishinoshima ls,
Sofugan Is.一Nishinoshima Is.
Sofugan Is。一Nishinoshima ls、
切ミざ融ミ
黛§鳴
o鳴も
ご鷺.
ミ
いま
§塁
魚
ξ§
ご
叙釦
さ心
1ロ田
H221RC440H222RC441H224RC443H225P488H226P489H227P490H228P491H229RC444H230RC445H231 RC446
H235RO450H236H237
H242RC452H243RC453H244RC454H245RC455H246RC456H247RC45アH248RC458H253H258RC497H260RC499H261RC500H262RC501H263RC502H265RC504H266RC505H267:RC506
H268RC507H270RC509H271RC510H272RC511H273RC512H274RC513H275RC514
29φ32,97’
29◆26,96’
27.30,10酢
24●48,77’
24026,99書
24044,70’
24043,53’
24。41,12’
24・28,05’
24.29,278
29059.965
30◆00,08’
29●59,83-
30◆47,97『
30.47,97’
32◆17、95’
32’15,83’
32◎15.98’
32’15,88”
32.09,891
30.47,79奮
21◎44,345
21。36,621
21●34,9筆1
21●27,響2’
21●21,72’
22053,76’
22●51,98’
22049,57’
22●35,84’
22◆28,25『
22◎20,65’
22.34,82’
22・43.55’
22044.39酢
22◆46,015
140.13,605
140。32,06’
141。23,86’
138008,51’
138・47,328
138018,709
140.23。42’
140◎22,61’
140●17.30『
140●17,79,
140006,94’
140●05,55陰
140◎05,079
139●53,13’
139052.44’
139ら42.51’
139ρ47,78匿
139045,24,
139●39.821
139。39,959
139D55,63’
143,52.21,
143ひ56,44-
143ゆ57,18’
143ゆ02。95騒
143D15,36’
142D22,73’
142024,235
142●25,74’
142●36,311
142。37.95’
142ひ34.Oア
142001,19’
142.03.711
14200ア.96’
142016,02’
2654
28404125
5391
5666
52183241
3210
3925
3919
2935
2931
2950
2270
22601579
15951609
1589
1610
228035443525351242953917374537453720
3375
3450
33752950
3140
3130
3450
G2G2G2P8P8P8P4G2G2G2G2E1,5
E1.5
G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2G2
Table A-1 Continued
10
10
10
1+10
2+101+10
1+10 1
10
10
1
2
1
2
1
1
2
1
2
1
1
喋0
210
10
10
10
210
10
210
10
10
22
1
1。6
F
F
F
F
1,5
1,5
1
1,5
1,5
0,8
0,8
F l
FFF
1,6
10,8
FFlF
1,5
F1,5
1,5
1,5
FFFFFF
0,340
0,226
0,057
0,008
0,117
0,019
0.085
0,044
0.271
0,020
0.05i
O,194
0,539
0,33ア
0,315
0,086
0,045
0,204
0,188
0,076
0。586
0,079
0,220
0,229
0.012
0,233
0.040
0,366
0.232
0,139
0,036
0.049
0,096
0,102
0,074
0.165
0,854
0,867
0,870
0.785
0.764
0,795
10.8751
(O。8751
0。875
(0.8751
(0,874)
10.874)
10,874》
0,934
0.839
10,930》
0,890
0.890
0,941
1,006
(0,830》
0,883
0。877
0,892
0、786
0,870
0,981
0,929
0,989
1,030
0,970
0,801
0,795
0,744
0,793
0,826
0,008
0,022
0,026
0,02ア
0,024
0,035
0,019
0,083
0,015
0,016
0,047
0.071
0,041
0.039
0.027
0.034
0,037
0。055
0,118
0,093
0.085
0,112
0,099
0,058
0,021
0。044
0,027
0,053
475
14
12
15
003000084058350674846777878888
290
195
50
6
90
15
74
38
237
17
44
169
471
315
26480
40
181
176
77
48770
193
20410
202
39
340
230
143
35
40
76
76
59
136
32
1,3
31,3
333
1,3
31,5
55
Sofugan I$.一Nishinoshima ls。
SofUgan IS.一Nishinoshima IS,
Ogasawara T70ughParece Vela Basin
Parece Vela Basin
Pa陀ce Vela Basin
West of lwolima ls,
West of Iwolima is,
West of lwojima ls,
WeSt Of IWojima Is.
Torishima Ri耽
TorlSれima Ri鮭
Torishima Ri丘
Sumisu Rift
SumisuRift
Aggashima Ri丘
Aogashima Rift
Aogashima Rift
1,3,5Aogashima Rifヒ
1,3,5AogashimaR流
3323
32
3
Sumisu Ri僅
Ma㎡anaTrcughMa㎡anaTroughMarianaTrough
Ma繍aTroughMarianaTrough
Ma㎡anaTroughMarlanaTrough
MarbnaTroug斜Mar悟na Trough
Ma虚鵬a Trough
Mar匿naTroughMarぬnaTroughMariana Trougれ
Ma丙ana Trough
Ma㎡ana Trough
寒ミ
る§§0
さぷ
寂零
o晦9ω
9ミま
李さ蓉・
蓉』§
鳶
ぎ§器鳶望
1認⑳
H276RC515H277RC516H278RC517H279RC518H280RC519H281RC520H282RC521H283RC522H286RC525H287RC526H288RC527H289RC528H291・1
H291・2
H291。3
H291-4
H292RC530H294RC531H311H314-1
H316H322H324H325H326H327-1
H327・2
H328RC535H330-1
H331-1
H331-2
H331-3
H332H333-1
H333-2
H334RC561
22.46.959
23◎13.03’
23●15.02’
23●16,86’
23・13、561
23.05,451
23φ11,579
230て6,46‘
23ρ15,48量
23●16,43露
26◎41,31’
26・42,11’
28●37,781
28●37,799
28●37.91’
28.38,07’
27●30,08’
30・47,97,
30.47,971
30◎47,958
26●41,60’
30048,418
30050,11’
30.49,76-
30◆48、25’
30.49,530
30。49,341
31。08,75’
31◆08,77’
30048,10’
30・48,159
30。48、229
30048,06’
30049,13’
30048,953
18◆00,99露
142◎21,63’
142。08,568
142007.13’
142004.10’
142.07,94’
142002,48’
141.59。231
142●03.16’
142・03,781
142002,19’
140・30、73’
141019,849
139037,25’
139◎37.379
139ゆ37,669
139.38,03’
141。40,03匿
139●55.11’
139●54,9α
13go55,95肚
140053,51’
139’53,53’
139◎53,09’
139953.17’
139,53,46’
139D53,22’
139。53.50’
139956.221
139ゆ56;3α
139051,20f
139●51,715
139’52,291
139◎50,82’
139953,191
139D56。59’
144053,31『
Table A-1 Continued
3450
2ア302705
2710
2ア202530
2460
2710
2730
2685
3400
3280
3635
36403640
3640
4120
22852285
2280
1315
2290
2285
2285
2290
2290
2285
2045
2050
2260
2260
22602240
2290
2290
4405
G2
G2
G2
G2
G2
G2
G2
G2
G2 G2
G2
G2
E2,5M
G2
G2
BO,7
BO,7M
E1,0
BO,7
BO,7
BO,7
BO,7
BO,7M
G2BO,7M
BO,7M
BO.7
BO,7M
10
10
210
2210
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
G2 10+11
1,4
F
1,5
1
F
F
1,3
0,9
1,5
0,9
FO,9
FFFFF
1,2
FF
O,5
FFFFFF
1,3
FFFFFFFF
0,299
0,026
0,252
0,516
0,145
0,074
0,238
0、473
0,334
0,441
0,121
0,496
0.022
0,022
0,024
0.029
0.039
0,021
0,036
0,060
1.063
0.080
0,012
0,040
0,040
0,048
0,斜6
0.331
0,016
0,000
0,072
0,060
0.028
0.148
0,084
0,188
333233323232333333222332333323333334
0,871
0,824
0.817
0.837
0.805
0,854
0,809
(0,8301
0,825
0,814
0,864
0,850
10,9201
(0。9201
10,920》
10,920》
0.851
0,827
(0、8301
(0,8301
10,850)
〔0,830}
〔0,8301
〔0.8301
10、8301
10,8301
{0,8301
{0,8501
(0,8501
(0,8301
10,830》
10,8301
{0,8301
(O.8301
10,830}
0,866
0,056
0,008
0,006
0,012
0.012
0,031
0、013
0,011
0,021
0,034
0,011
0,028
0,017
0,043
26021
205
432
117
63
193
392
276
359105
421
20
20
22
26
3318
30
50
904
6610
33
33
40
96281
14
0
60
50
23123
70
≦63
33
3,5
11、2
11,2
2
Mariana Trough
Mariana Trough
Mariana Trough
3 Mariana Trough
MarianaTrough
Mariana’『rough
MarianaTrough
3 Mariana T酢ough
MarianaTrough
3 Mariana Trough
West of Kaikata Smt,
3 Eastof Kaikata Smt,
Sofugan ls、一Nishinoshima ls,
Sofugan ls.一Nishinoshima ls,
Sofugan ls。一Nishinoshima ls.
Sofugan ls,一Nishinoshima ls.
OgaSawara Trough
Sumisu Ri費
Sumisu R流
Sumisu Ri穐
Kaikata Smt,
SumisuRift
Sumisu Rift
1,3 Sumisu Rift
Sumisu Rift
SumisuRi靴
Sumisu Rift
Sumisu Rift
3 Sumisu Ri代
SumisuRift
l Sumisu Rift
Sumisu Ri鴛
Sumisu Ri段
Sumisu R流
Sumisu Ri俺
Mariana Tl℃ugh
ヒロ
黛
鳴討.
§
9導恥
○鴨ロざ閃8’
§
のま
§遷
魚
ξ§
ぎ
へ和
さ職
一
1器ω
1
H335RC562H336RC563H338-1
H338。2
H339RC564H341RC566H342-1
H342-2
H342-4
H343-1
H343-2
H343-3
H343-4
H344RC567H345-1
H345-2
H345-3
H345。4
H345-5
H366RC569H367RC570H369RC571H370-1
H370-2
H371-1
H371・3
H373-1
H373・2
H374-1
H374-2
H374・3
H374-4
H375RC601H376RC602H377・1
H377-2
18●00,841
18・00,958
18。00,941
18●00,925
20.54.16’
21φ05,94’
21005,81’
21.05,605
21.05,153
21010,70’
21.10,49-
21●10,31’
21◆10,11’
21030,52’
21.27,10’
2喋.27,09’
21.27,139
21●27.13’
21。27,13’
21●23,69’
21◎30.531
30◎54,93’
30●54,87’
30●54,80’
30●47,83’
30.47.82’
30054.83’
30054.75’
30●47,86『
30●47,65量
30◆47.55重
30.47,46屡
20049,57’
20●49,02’
21006,10’
21。06,10『
144◆55,76匹
145・01,225
144◆56,57’
144.56,34’
143012,38’
143018、121
143◆18,191
143◆18,195
143018,13’
143.11,13’
143011,14’
143●11,13量
143011.09’
143●13,55’
143●02,72B
143●02。50-
143902,269
143ρ02,01’
143●01,73’
143●14,54’
143◆13.711
139.51,28’
139●51,75’
139ひ52、235
139●53.60’
139,53.52’
139053,41’
139◆53,79’
139053,93-
139ゆ53,78’
139053,511
139053,22’
144,38,40’
144036,09’
143。17,905.
143ひ17,691
Table A-l Continued
3608 G2
3770 G23710 E1,5M3708
4220 G2
4392 G24390 E1,5M4400
4439
3730 E1.5M3730
3720
3728
3670 G24298 E1,5M4296
42924291
4287
3915
36682245
22752280
2290
229022802285
2280
2285
G2
G2
G2BO,7M
BO,7M
BO、7M
BO,7M
2285
2270
2555 G2
2515 G2
4405 E1。5M
4352
10
11
11
11
11
11
11
11
11
11
11
11
10
10
10
10
11
11
11
F
1,2
1.2
1,2
F
F
F
F
F
F
F
FFFFFFFF
1、4
1,4
0,9
FFFFFFFFFFFFFF
0,106
0,038
0,105
0,152
0,014
0,018
0,054
0,038
0,001
0,071
0,059
0,070
0,061
0,012
0,022
0,012
0,005
0,023
0,261
0,474
0,068
0,028
0,072
0.052
0,012
0,012
0,120
0,132
0,044
0,120
0,040
0,224
0,043
0,037
334443554555545555544233333333335566
0,857
10,857》
(0,857》
(0.8571
0.744
0,743
(0,7431
〔0,743》
10、743)
10,743)
10,7431
10,743》
{0,743》
0,828
(0,786》
(0.786》
{0,786)
〔0,786》
{0,7861
0,798
0,840
0,838
{0,838}
(0,8381
(0。8301
(0,8301
(0,838)
10,8381
(0.830)
10,8301
〔0,8301
(0,8301
0,832
0,852
《0.743}
(O,7431
0,067
0,013
0,012
0,026
0,011
0.019
0,028
0,059
0,065
500065000000060000026500000000006700
91
32
90
131
10
13
40
28 1
53
44
52
45
9
18
10
4
18
208
397
56
23
60
4310
10
100
110
37
100
33191
40
27
6
4
43
22
6
Mariana Trough
Mariana Trough
Ma再ana Trou9h
Ma締ana’『rough
Ma丙anaTroughMariana Trough
MadanaTroughMariana Tr℃ugh
Mariana Trough
Mariana TrDugh
Mariana Trough
Mariana Trough
Maria自a Trough
Mariana Trough
Marian4Trough
Mariana Trough
Mariana Trough
MarianaTrough
Mariana Trough
Mariana Trough
Mariana Trough
Sumisu Rift
Sumisu R流
Sum盲su Ri覚
Sumisu Ri粍
Sumisu Ri允
Sumisu Rift
Sumisu Ri仕
Sumisu Ri丘
Sumisu Ri仕
Sumisu Rift
Sumisu Ri代
MarianaTrough
Mariana Trough
Mariana Trough
Mariana Trough
評ミ
る§§◎
§鳴
凝書
o偽自Gつ
9ミ9寧§蓉・
蓉』§
へsぎ
…ii
馨ぎ℃
Table A-1 Continued
H377-3
H377-4
H377-5
H379・1
H379-2
H379-3
21.06,16”
21.06,21-
21。06,21’
30.47,81’
30047,901
30◎47,845
143。17.543
143.17,289
143φ17,04’
139.53.82’
139●53,98-
139.54,19量
43524345
4300
2295 BO,9M
2290
2290
F
F
F
l l F
F
F
0,022
0,029
0,075
0,060
0。325
0.105
666555
lO,7431
10.743》
(0,743)
(0、8261
(0,826》
(0.8261
000000
16
22
56
50
270
87
6
22
Mariana Tめugh
MarianaT酬ghMarianaT酬φSumisu届段
SumisuRi俺
SumisuRi俺
器晶
Foot note of Table
Probe l the type of thermistor probe used.G:a gravity corer with three to six thermistors in outrigger fashion(a number attached to the let-
ter is the length of the probe),P:a piston corer with three to five thermistors in outrigger fashion,E:a lance without coring with three to
sixthermistorsinoutriggerfashion,B:athin(20mmφ)Bullar(itypeprobewiththreetofivethemistors,M:multi-penetration
meaSUrement.
A=theapparatusused;1:GH80-1-No.1,2:GH80-1-No.2,10:NTS10,11:NTSllP:estimated penetration(1epth(m);F:fu11(or over)penetration.
dT/(iz:thermal gradient(。K/m).
Ng:number of active thermistors in se(iiments.
Cond.:themal conductivity(W/mK).
s.(1.:standard deviation of the thermal con(1uctivity(1ata.
Nc:number of thermal conductivity measurements.Q:heat flow(mW/m2).
Remarks: 1.Accuracy of temperature data is low.
2.Non-linear temperature profile.
3.Gradient was calculated from only two temperature data.
4.Anomalous temperature profile.
5.Gra(iient may be affected by bottom water temperature variation because of shallow water depth.
6.Large temperature increase at very surface sediments。
bロ
ミ
鴨
蔑ミ
黛導“
o鳴ロ
ご閃80
&
の§
§塁
黛
ξ…i
ぎ
心和
ξ心
飽α壇伽伽伽19%一〇8αsα襯搬一M副α冗αz4影6‘T.y齢α~α初
伊豆・小笠原弧及びマリアナ弧の地殻熱流量
山 崎俊嗣
要 旨
伊豆・小笠原弧及びマリアナ弧において,1984年から1989年にかけて218点で新たに測定された熱流
量値とその解釈を報告する.測定の目的は,熱水活動の可能性を評価することと,表記の海域のテクト
ニクスの理解を深めることであった.主に研究対象とした海域は,(1)伊豆・小笠原弧北部に発達す
る活動的背弧リフト群のひとつであるスミスリフト,(2)伊豆・小笠原弧中部に現在の島弧に斜交し
て存在する,漸新世の古リフトと考えられる西之島トラフの周辺,(3)北部マリアナトラフ(200N-24。N)
である.
スミスリフトでは高い熱流量を示す地点の存在及び分散の大きな熱流量分布より,熱水循環系の存在
が推定される.ここでは,表層数十cmの温度勾配が異常に小さいことが多いが,底生生物の活動が盛ん
なことによる堆積物の擾乱が原因かもしれない.西之島トラフは,西側を正断層の急崖(嬬婦岩構造線)
により限られているが,熱流量はここを境にトラフ内では比較的高く,構造線の西側では低くなってい
る.このコントラストは,過去のリフティングに起因する地殻の厚さの差を反映しているものと推定さ
れる.西之島トラフ内には,貫入岩体に伴って局地的な高熱流量域が存在する。マリアナトラフの
22。N以北では現在リフティングが起こっているが,ここは熱的に非対称である.高熱流量はトラフの
東縁のみで観測される.マリアナトラフの220N以南では,海洋底拡大が起こっており,拡大軸付近で
は熱水循環に起因すると考えられる異常な温度プロファイルが観測される.
(受付:1991年6月18日;受理:1991年7月24日)
一235一