Central Indian Ocean, and previously published deformation in the Central Indian Ocean Basin data show that heat flow is significantly higher seems to be ...
JOURNALOF GEOPHYSICALRESEARCH•VOL. 88, NO. B2, PAGES1018-1032,
HEAT
TRANSFER IN
AND
THE
INTRAPLATE
CENTRAL
FEBRUARY10, 1983
DEFORMATION
INDIAN
OCEAN
Carol A. Geller, 1 Jeffrey K. Weissel, and Roger N. Anderson1 Lamont-Doherty
Abstract.
Geological
Observatory
of Columbia University,
Nineteen new heat flow measurements
made across deformed oceanic lithosphere in the Central
Indian
Ocean,
and previously
published
data show that heat flow is significantly than predicted by models for cooling
higher oceanic
ciated
with
Palisades,
the initial
New York
10964
stages of the collision
of India and Asia.
The beginning of intraplate
deformation
Central
in
the
Indian
Ocean Basin
seems to be connected with the Miocene Himalayan orogenic phase of this collision [Weissel et al.,
lithosphere over much of the region. Many of the temperature-depth profiles are nonlinear. Upward convection of water is the most likely explanation for the curvature of the temperature profiles, since other possible causes, including variations in bottom water temperatures, conductivity changes with depth in the sediments, and experimental error, can be eliminated. This
from the Himalayas (which rising since the middle Miocene; Powell and Conaghan [1973]) are a major source for the world's largest deep-sea fan that is n• topographically divided by the Ninetyeast Ridge into the Bengal (west) and the Nicobar (east) fans. The Bengal Fan is an enormous sedi-
interpretationrequires watervelocitiesof the m/s, which is unusual because
near its proximal (northern) end at least 16 km
the
thick
order of 7 x 10lithosphere
is
relatively
old
(72-82 m.y.)
and a thick sedimentary cover (1-2.5 km) is present. These observations suggest that the
processes causing deformation
of the plate
than 35 km) in the plate,
mentarywedge3000kmlong, 1000kmwide, and [Curray
have
0.3
the
theory
although the specific
of
plate
1974].
km east of 95øE [Bowles et al.,
The
1978].
The
terrigenous sediments were supplied from the west
is
until Pliocene [Bowles et al., 1978], or middle Pleistocene time [Curray and Moore, 1974; Curray et al.,
to
1971,
thicknesses of at least portion, decreasing to
Ntcobar Fan has been isolated from the sediment sources to the northwest by the collision of the Ninetyeast Ridge and the Sunda-AndamanArc. Some
Introduction According
and Moore,
Nicobar Fan has sediment 1.6 km in the northern
increased the heat flux through the sedimentwater interface. We infer that extra heat is being generated at shallow depths (perhaps less
mechanism by which deformational energy converted into heat is difficult to determine.
1980]. Sediments eroded have been rapidly
1982].
The thick fan sediments record the history of internal deformation of this part of the IndoAustralian plate. Seismic reflection records
tectonics,
rigid lithospheric 'caps' move over a weaker asthenosphere, deforming at their edges (by interaction with other plates) but not internally.
from the southern portion of the Bengal Fan show the widespread deformation of originally flat lying sediments (Figure 2). There are two 'wave-
There are three major categories
lengths'
aries:
extensional,
The Indo-Australian
convergent,
plate
of plate
bound-
and strike
slip.
(Figure
First,
1) is bounded
of deformation acoustic
[Weissel
et al.,
1980].
basement has been deformed into
undulations (Figures 2 and 3)with
wavelengths of
by all three types. However, deformation of the sediments and acoustic basement, the large amount of intraplate seismicity, and the abnormally high heat flow (greater than predicted from models for
100-300 km and up to 3 km of relief (associated with 30-80 mGal free air gravity anomalies). A conspicuous effect of the long 'wavelength' deformation is to elevate portions of the crust and
cooling oceanic lithosphere) indicate that the Indo-Australian plate is not perfectly rigid. The collision of the continents of Asia and India
sediments of the Bengal Fan, creating barriers to a continuous sediment distribution. At Deep-Sea Drilling Project (DSDP) site 218 (Figure 1) the
has been proposed as the cause of this intraplate
age for
deformation [Weissel et al., 1980; Eittreim and Ewing, 1972; Curray and Moore, 1971]. North of the Indo-Australian plate, the unusually widespread deformation of Asia is also the result of this collision [Molnar and Tapponnier, 1975]. Approximately 44 m.y. B.P. (anomaly 19 time) India's speed and direction changed, from a rapid (c. 150 mm/yr) northward course to a slower (c.
rates deformed strata from overlying deposits is uppermost Miocene [Moore et al., 1974]. Second, high-angle faults, spaced 3 to 10 km apart (Figure 2) with strikes approximately parallel to the magnetic lineations, affect the oceanic crust, suggesting that the forces producing the deformation have reactivated old fault scarps and initial zones of weakness in the crust [Weissel
50 mm/yr) northeast direction [Sclater et al., 1981; Peirce, 1978]. This event is probably asso-
and Geller, 1981]. Morphologicsurveys of the Mid-Atlantic Ridge [Laughton and Searle, 1979]
the widespread unconformity
that
sepa-
and the Galapagos Spreading Center [Klitgord and Mudie, 1974] found faulted ocean crust with
•Also at Department of Geological Sciences, Columbia University, Copyright
Palisades,
scarps parallel
New York 10964.
1983 by the American Geophysical
to the ridge axis at a spacing of
1-5 km. The strike of the horst and graben pattern mapped on the part of the Cocos plate
Union.
undergoing is closely
flexure at the Middle Americas Trench parallel to the magnetic lineations
Paper number2B1346.
yet at a 20ø-30• angle to the strike
0148-0227/83/002B-1346505.00
trench, 1018
suggesting
the
reactivation
of the
of fractures
Geller
et al.:
7'5
Heat Flow and Deformation
80
85
in the Indian
90
Ocean
1019
95
IOO 15
15 x41
IO
5
o
5
IO
15
7 5 80 8 5 9 0 95 I00 Fig. 1. Heat flow values (from Andersonet al. [1977], Kutas et al. [1979], and V3616). Crossesrepresent the locations of heat flow measurements.The small square at the southern end of the Bengal Fan is the average heat flow from site 4.
Note that
1 HFU-- 10-v cal/cm2/s--41.87 mW/m 2. Asterisks indicate DSDP locations. A.N. is
Afanazy Nikitin seamountgroup. Solid dots are intraplate earthquakes. Triangles denote thrust focal mechanisms, circles strike slip mechanisms, and squares normal mechanisms. The dotted lines roughly show the southern limit of fan deposits. The dashed line
in
the upper right
deformation. Strikes Indo-Australian plate Sykesand Sbar, 1974; in preparation, 1982] Conrad and Vema heat
hand corner
is
the southern
limit
of
the observed
of principal stress axes for intraplate earthquakes within the [Sykes, 1970; Banghar, 1972; Fitch, 1972; Fitch et al., 1973; Stein and Okal, 1978; C. A. Geller and J. K. Weissel, manuscript are shown by arrows. Depths are contoured in meters. (All flow
stations
have
been
reevaluated
since
Anderson et
al.
[1977].)
generated at the East Pacific Rise [Aubouin et al., 1982]. The unusual amount of intraplate seismicity [Gutenburg and Richter, 1954; Stover, 1966; Sykes, 1970; Fitch, 1972; Stein and Okal, 1978] indicates that deformation is currently occurring
(Figure 1). Sykes [1970] suggested that the seismicity maybe an indication of a nascent subduction zone that will accommodate plate motions resisted by the collision of the Indian subcontinent with Asia. However, no definitive evidence for the formation of a subduction zone has yet
1020
Geller et al.'
Heat Flow and Deformation in the Indian Ocean
.i
i
I
Z
.,' -:•:J:;:".!? ......:"•':•:: ,.•,• ,•..ß..•m•.-.½•.:•t;m:::, •.::;•½ ..•
"'z::.-."'"': • ;:.S:•.. .•.:-,•:--.BQ• ,:•.'::'•"•.•:• ":2': •':t•:•; -'
....-..• ....:'
!
-:..=..-,.• .:..
..... :•,..>"---•'•"••:•••.' .•
.I
! .!
i..•.'•: ",:'•?•:.• •: ::'•.g.. >•:•. '••
..
"-:t':::>>:• '•" ::..:a..::::
• • •
''?'========================= • o.• o
:... _•::,.•.. =======================
ß' •.•--_:.•t ::,:{:;,•.: ...... -':' .t-
Geller et al.:
7 6
6
7 8
Heat Flow and Deformation in the Indian Ocean
80
82
8
8 6
1021
88
9 0
e53 .,
..:
56e ..
ß
49 'e•54
41© ,,
:.... "
'•o':'
0
'"
.•-.:
"
•
•
4
ß 54
•
•,
•"
o
•
o
"e52
•
• ••
,•' 5
2 .'
.,
_
Fig. 3. Acousticbasement highsandlows. Plussignsdenoterelative basement highs
andminus signsrelativel_•s. Numbered dotsareheatflowvaluesin mW/m • (1 HFU--
10-6 cal/cm2/s -- 41.87mW/m ). Thesquare symbol withintheboxed arearepresents the
average heat flow of site 4. the same as Figure 1.
Principal stress directions for intraplate earthquakes
A major fracture
zone at about 85øE with 850 km of left-lateral
offset [Sclater and Fisher, 1974] is denotedby the single hatching. Ship tracks are
shown by light
dotted lines.
Depths are contoured in kilometers.
been found. Stein and Okal [1978] found that a numberof large earthquakes are associated with
the northern part of the Ninetyeast Ridge with moments of the three largest events indicating left-lateral
slip,
of the order of 2.2 cm/yr,
along the ridge. Minster and Jordan [1978] showed that if the Indo-Australian plate were divided into two separate plates along 90øE,
accommodating about 1 cm/yr of NW-SE convergence, their global model of present-day plate motions
1022
Geller
et al.:
Heat Flow and Deformation in the Indian
C 0 N D U C T I
would more closely fit observed spreading rates and directions along the Southeast and Central Indian
Ocean
0
Ocean ridges.
V I
T Y
.5
I0
i
i
( W /
M-øC) 1.5 I
Many heat flow measurementsin the deformed
region of the Central Indian Ocean(Figure 1) recorded before
1980 [Kutas et al.,
1979; Anderson
et al., 1977; Langseth and Taylor, 1967; Vacquier and Taylor, 1966] were significantly higher than theoretical
models
values
calculated
from simple
[Parsons and Sclater,
1977;
ß
A o
cooling
Parker
[]
and
,6AO
ß
Oldenberg, 1973; $clater and Francheteau, 1970]. Worldwide averages of heat flow [Sclater et al., 1980] for the age range of the affected lithosphere (65-90 m.y.) are close to theoretically
predicted, 50-60 mW/m 2.
heat
flow
The average of the 26
measurements located
ß
between 78ø and
ß
90øE and 10øS to 5øN is 71 mW/m 2. Eight values are between 50 and 60 mW/m 2. Twelve are greater
,, V36-59
than 60 mW/m 2, with an average of 96 mW/m 2.
ß
Weissel et al. [1980] suggested that additional heat has been generated by the deformational processes. In this paper we will present data from Verna 3616, September-October 1980 in order to examine the relationship between heat flow and
o V$6-61
tntraplate Ocean. heat
deformation
We will
transfer
tent
with
the
Central
discuss possible
to
the
in
the
seafloor
mechanisms for
which
are
consis-
The Field
V$6-6
,
V$
2
6-6,3
[]
VI9-69
-
CI7-75
Fig. 4b. Conductivity with depth measured from piston cores taken during V3616, using the needle-probe
Program and Data Analysis
•
I0-
Indian
observations.
V$6-60
method.
Nineteennewhigh-qualityheat flow measure- standardecho sounding recorderin an analog
mentswere madeduring the recent cruise of the R/V Vema(Figures4 and 5, Table 1). Heat flow measurements taken during V3616 were madewith a
mode. Thedata are also simultaneously stored in digital formonmagnetictape inside the modified 'Von Herzen' instrument package. The resistance
digital instrument usingfive thermistors mounted fromeachthermistoris recorded onceevery30 s. on a spear (a steel pipe 5.5 m long with 6.4 cm outer diameter and with 1.3-cm-thick walls) or a
piston core pipe, with a sixth thermistorplaced on the core head to measure bottom water tern-
perature.
Temperatures,water pressure, and
instrument tilt
are transmitted
temperature
brations and the behavior of the thermistors
while in the sediments. The thermistors used in
this survey were calibrated by SandiaLabs at
by
Albuquerque, New Mexico, to an absolute accuracy
a 12-kHzptnger, to the surface and recordedon a
better than •0.01øC. Duringpenetrationinto the
DELTA
acoustically,
Possible sources of error in
measurementarise fro• error in thermistor call-
TEMPERATURE
(øC )
DELTA
T
E M P E R A T
O I
U R E
(øC)
ß
0
.2 øC
2
u.J
8L*J
ß
V36-
60
o
V36--
61
•
V36-
62
ß
V36-
63
o
V36-
Co5A
.
V36-
65E
m
Vl9-69
ß
CI7-75
-r-
3
a_
4
n
5
--
co
I0-
A I
i
i
o
I
I
BCD
EF
ß V 5
6-5
6
•' V 5
6-5
9
-V
6-5
8
-
6-6
4
04
_
Fig. 4a.
Nonlinear temperature-depth profiles,
determined using equations (1)-(3).
Fig. 4c.
3
V 3
Linear temperatureprofiles measured
during V3616.
Geller et al.'
75 ,•
Heat Flow and Deformation in the Indian Ocean
80,•
85 ø
90 •,
95 ø
1025
I00 ø 15.
10%
I0 o
I0 o
V3616
TRACK &HEAT FLOW
STATIONS
7'5ø •S.
5.
Sh•p •a•
,
,,
•oo
oE E/V Ve•
•5o
{V36•6).
•e
ø l;
•joo
•oca•ons oE •he d•s•a•
•5o
'
L5 o
,ooo
hea• E•ow (DE•)
s•a•ons and associated se•s•c •eE•ec•on surveys •n a• s• sh•p speed a•e show•. •nc•pa• s•ess d•ec•oas and •oca• mechanisms a•e as • •su•e •. •shed •nes a•e •he •oca•ons oE •he p•oE•es •n ••e 2.
sedimentsthe thermistors are frictionally heated with the temperature disturbance decaying with
rected for in situ conditions [Ratcliffe, 1960]. At three locations during V3616 and two on
time [Bullard, 1954]. Standard deviationsof the
previouscruises (Table 2), the sedimenttempera-
calculated temperaturesat equilibrium are seldom greater than 0.004øC. Bottomwater temperatures measuredafter each penetration are subtracted from the in situ temperaturesbefore temperature gradients are determined. Measurements madeon this cruise are generally moreaccurate and of better quality than previous measurements in the Indian Oceanon the R/V Vemaand the R/V Robert Conrad, which were madewith an instrument of older design [Langseth, 1965]. Thermalconduet!vity
values
were determined
from piston
cores
tures did not increase linearly with depth, and attemptingto fit the data using a linear least squares fit gave errors m•ch greater than the possible errors in measurement.However,good fits
for the nonlinear temperature profiles can
be calculated using an analysis suggestedby Bredehoeftand Papadopulos[1965]. Assumingthat a fluid convects through a uniformly permeable and porousmediumwith a constant velocity, the temperatureT, as a function of depth, is
taken during V3616 using theneedle probe technique [VonHerzenand Maxwell, 1959] and cot-
T(z) ={TL-TUI (e•Z/L-1)+ TU (e•-l)
(1)
O0
•0
0
0
I
0
0
0
O•
0
0
O0
O0
O0
O0
O0
O0
O0
O0
O0
r•
O0
O0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Geller
TABLE 2.
Central
et al.:
Indian
Heat Flow and Deformation
Ocean Heat Flow Measurements With Nonlinear
dT/ dz, Q,W/m 0.001øC/m 0.001 2
Station
in the Indian
B/_L m1,
Ocean
1025
Temperature-Depth
Profiles
K,oC W/m
10_v •am/s
C17-75 V19-69 V36-60 V36-61 V36-62 V36-63
218.9 101.4 98.9 130.2 149.5 159.7
207 75 93 109 122 144
-0.339 -0.096 -0.167 -0.323 -0. 286 -0.331
0.946b 0.736b 0.945b 0.837b 0.814b 0.903b
-7 -2 -4 -6 -5 -7
V36-65A
138.2
147
-0.369
1.063 c
-9
V36-65E
146.0
155
-0.517
1.063 c
- 13
aEqualto BK/LpC, wherep -- 1.03 g/cm3 andC -- 4.187 Ws/gøC. bMeasured. CEstima ted.
where
In addition, conductivity
TL = temperature of the bottomthermistor; TU --temperatureof the top thermistor in the
five sites (Figure 5), near someof the heat flow locations, seismic reflection surveys at slow
sediment; -- depth from
z
the
top
thermistor
in
ship
the cores were used to and age of the sediments.
determine Also, at
speed were undertaken.
the
sediment;
• -v p C K L
vpCL/K;
: velocity of fluid; = density of the fluid; -- specific heat of the fluid; : conductivity of the sediment; -- distance between bottom and top in
the
5
5
thermistors
sediment.
Nonlinear curves are fit to the temperature data by determining the value of • that minimizes the difference between the temperatures calculated from (1) and the measured temperatures for the thermistors. The temperature gradient at the sediment-water surface is calculated by first finding the depth at which the change in the temperature is zero from
,
L
-TL-TU e•
z =• In [TL_Tu ] Then
the
gradient
at
the
(2)
surface
is
-5
-5
calculated
from
dT
•Sz*/L
• I* =(TL-TU)• eB_l z
,
The calculated determined
z is from
usually core
very pipe
(3)
soo{ nr
close to that penetration
0.•.
indications.
-1¸ V3616
We encountered unexpected difficulties (due to the coarse grain size of the sediments) obtaining sufficient penetration for temperature measurements using the spear. Because of this problem we took measurements at DHF stations 59-63 with a piston core instead of a spear (used during DHF stations
56-58
and 64)
-1¸ 95
Data
to
improve
penetration.
Fig. 6a. Magnetic anomalies along ship tracks in the northwestern Wharton Basin. Magnetic lineations corresponding to the geomagnetic time scale of LaBrecque et al. [1977] are shown. DHF 56 locates the heat flow measurement (Figure 6b) east of the Ninetyeast Ridge (outlined by 3-km
isobath) trench
obtained during V3616.
axis
is shown by saw-teeth.
Position
of the
1026
Geller et al.:
Heat Flow and Deformration in the Indian Ocean
time,
V3616 DHF 56
ment
and the horizontal cannot
be
ment of the faults
/??W/m
component of displace-
determined.
The
nature
of
move-
appears to be reverse with the
northside down andthe southside2uP. Theone heat flow value of 83 mW/m (Figure 4c)
reliable
was obtained
near
one of
these
faults
(Figure
6b). This is high forflow crust •0 m.•i in heat i sO%about 7 mW/m•). nce
age (theoretical no other
reliable
measurements
were
obtained,
it
is difficult to place properly this measurement in any large-scale geological perspective. Site 2 (DHF 57 and 58) was chosen in the
vicinity of the 1970 strike slip earthquake(Ms -6.1; Figure 1). C. A. Geller and J. K. Weissel (manuscript in preparation, 1982) examined first
motions, shallow to that
surface
waves, and body waves of
event and found a solution of Fitch [1972], who first
earthquake. Because of penetration problems at DHF 57 and 58, the net result was one broken, one
ME. -• /3.2'/
bent spear, and one reliable
Fig.
6b.
this
very similar examined this
Site 1 seismic reflection profile
7).
record. The location of DHF 56 is indicated by the arrow.
measurement(Figure
The seismic survey at slow ship speedshows
sediment thickness approximately 1 s of two-way travel time with steeply dipping reverse faults. The dips of the two focal planes determined for the 1970 event are greater than 80ø. The crustal
TheNtcobar Fansediments are deformed [Bowles ageof this area2is65 m.y.witha predicted heat
et al., 1978] but not nearly as substantially as the Bengal Fan deposits. Site 1 (DHF 56) is
flow of 59 mW/m, asain substantially less than the measured 82 mW/m • (Table 1).
located (Figure 5) east of the NinetyeastRidge slightly south of a segment of an extinct spread-
Two heat flow measurements (DHF59 and 60), taken using the piston core device, weremadebe-
ing axis. From an analysis of magnetic anomalytween seismic sur•eysites2 and3 (Figure5). A data (Figures 6a and 6c) we determined that
value of 78 mW/m was measuredfor DHF59.
spreadingceasedapproximately44 m.y. ago (anomaly 19). Liu et al. [1982] have independently
sedimentthicknessis about 1 s of two-waytravel time. The measurement wasmadeslightly south of
heat
region that has been uplifted and quite severely
come to the same conclusion.
flow
The few scattered
measurements previously
the
obtained
crest
of an undulation
The
in a very deformed
(Figure 1) did not include any abnormallyhigh
faulted (Figures 3 and 8).
values. The seismic survey at slow ship speed showedthat this region has an average of 0.6 s
tic basement between DHF 59 station location and 15 km to the south is almost 1 s of two-way
The relief of acous-
of two-way travel time of sedimentarycover with
travel time.
faults spaced every3-5 kin. Thevertical dis-
with a P2redicted theoreticalheatflowvalueof
placementsare less than 0.1 s of two-waytravel
25
o
•I
V3616 AS: I10ø
o
/vo
24 25 I I
o•
,NT•Z
•e=•o .
DHF•
5OO l
W1811 Ae:90
54 mW/m .
I
II
MODE•• 25
Fig. 6c.
% % •
J II
24• •25•
,.
22
•
21 20•20 21
The age of the crust is 77 m.y.
The temperature-depth profile
22
2:5
24
25
II
I
II
I
'I
I
II
I II
iI
I LUS7
i •e=•o • II II 22
•25• • 24 •
Comparisonbetween observed magnetic anomaly profiles from the northwestern
anomaly19 (formed 44 m.y. ago), was computedusing the spreading rates (in mm/yr) The four observed profiles were projected onto a by the Ae values to achieve symmetric anomaly
shapes [see Schoutenand McCamy,1972].
I
'
I
Wharton Basin (Figure 6a) and a model profile calculated from the geomagnetic reversal time scale of LaBrecque et al. [1977]. The model profile, which is symmetric about shown at the bottom of the figure. N-S azimuth and were phase shifted
is
25
Geller
V3616 •
et
al.:
Heat Flow and Deformation
8•m•//m •
in the
Indian
Ocean
1027
difficult to understand, but perhaps the large
DHF 5• ...]. changes inbasement elevation and sedimen ._•--:_..•--.'•,••.-.•i•;•.•.'•-,•,-"........'_•.'•i•-Mi•-•-•[••__•_• Theheatfl• stations (DHF 61-63) at site3 •..,.•
•
••"•'•'•=•??•'•••:•"•?j•?•:'•:•,•:••••• •.•:•:.:•:•,•./•..•.•
thickness
influence
the pattern
this location.
of heat
flow
at
are locatedon a series of large high-angle faults (Fibre 10) Offsetsof acoustic basement
•,?•½•?•::=•2.•.•.:..•. ....•=•,•..•.=.:...•= ..... .==•:=.•. ............... •
are up to 0 75 s of two-waytravel time
•••f•:?%':/:•½•??•.:•:•%V
side d•n.
Fault
Z•••'•; •:?•..;•.:•.:•?•?•.,.•.f:•:•F•?•:•;•:,•?i•¾•:• spacing is3-5 • with the sense ofand motion on •.••.•??•?•)•?•:.•?•.•r•p•.•?*•??•?•.•:=••?•=•F.•:•: most faults having the north sideup south •
?•:::?•?::•::k•
••'•f•'•:•:.::(.?¾•..:t::•,.:..'•....:.:: 'i•'•:L•;:•.:••:•
resolve
•e
from
t•e our
fault
dips are impossible to
seis•c
reflection
data.
•e
••..,'.:::Y..:.•.•E?:?•:;½?:'•'"':?::? *t ..... :.' allel tothe maEnetic linearions. •esedime •..,
•.,,,
.,•..,
• .,..
..........
;•.':r• ......... "..': ......... .-'..•q;:[•.',;¾..'..;' : '..
.
.
, .....
•.
•
.,....,
......
.-,' ..... •,: .... :•:L..•'•:.:•'.'.;.:...'; .;•.2•:,[
. • , .,.:..'-..•:.5,•. •,'
...:....,.,.•.;...,:r,:•..•; .... ',•,',::,.'•.' :,,:'.: .......•:-,,'?.-:?-' :',,'"::': ':..... [•,:.' ....:?:.,.::•:: ',.t:-."..,.:v',.•.: ....,...•
trend of the faultinE
cover time.
is
par-
between 1 and 1.3 s of two-way travel All three temperature profiles (spaced
4 • apart)sh• s•ilar curvature (Fibre 4a•. •e heat flow values are 109, 1•2, and 144 mW/m,
•,•'•/'.j.3.2 - .
6
'
'
•
•ch
Z•.O,/
Ereater
for c•st
Fig. 7. Site 2 sei•ic reflectionrecord.•e locationof DHF 58is indicated bythearr•.
three
A piston core obtained7 •
southwest was dated as upper •ocene
depth from radiolaria com•nication, 1982).
(J.
temperature
Morley,
profile
at 200-ca
personal
was •asured
predicted
cores were e•mined
for
age dating
pur-
423ca, hadanageof uppe•ostMiocene-l•e•ost ervation
linear (Fibre 4c).
than the 56 mW/m • value
of 72 m.y. age. •e bottompart of all
poses. •e bottom of the corefor D• 61, at
Pliocene,
A nonlinear
is 093 ø, appro•mately
from abundant radiolaria. is
insufficient
age for the botto• alth•gh
to
an age of uppe•ost fourth
site
a
reliable
of the other two cores,
Pltocene is suggested (J. commnication, 1982). •e
Faunal pres-
dete•ne
•ocene
Morley,
to •d-
personal
(DHF 64) is at the distal
end
(DHF60, Figures 4a and 9) west of the Ninetyeast Ridge and just south of the equator at an outcrop of one of the undulations of the c•st and
of the Bengal Fan (Figure 5). •e sediment is only 0.5 s (two-way travel time) thi•. Only slightly farther to the south of this survey the
gradientwascalculated using(3). •e heatflow valueof 93mW/m is 2tachhigherthanthe pre-
gionwassurveyed by EittreimandEwing[1972]. •e heat fl• profile was obtainedover the
m.y. •o near• measurementstaken previously on Conrad 1708 and Ve• 2901 had linear te•eraturedepth profiles with heat fl• values of 72 and
to the magnetic lineations. Most faults have the north side up and the south side d•n. Just
sediment (Figure 9).
The surface temperature
dicted value, 52 mW/mfor c•st
whoseage is 82
deposits of the fan sediments thin out.
•is
re-
faulted crest of one of the undulations (Fibre 11), where fault trends (090ø-100ø) are parallel
48 mW/m 2, respectively (Figure 9). Although nort•of • 64a heatfl• measurement of 92 there was insufficient faunal preservation to mW/m was taken on Conrad 1402. Just to the date the core from •
60, the core from V2901
was dated at 1090 cm as uppermost •ocene
(G.
Blechschmidt, personal Communication, 1980).
•e
variation
between
these
heat
flow
measurements
south a value of 58 mW/m 2 was obtainedon Verna 1909.
•ere
is a general increase in temperature
is
C1708
Fig. 8. Seismic reflection profile and location of DHF59. A piston core taken just to the south of DHF 59 was dated as upper Miocene at 200-ca depth.
Fig. 9. Conrad 1708 seismic reflection profile taken close to DHF60 (part of profile c, Figure 5). V3616 (DHF 60) and V2901 heat flow station are projected onto the track.
1028
Geller
et al.'
Heat Flow and Deformation
in the Indian
v 3616 DH F' 65
V3616
•
DH F 63, 62,61
144
laa
1o•
Ocean
•
155 147mW/m
6 V.E.
gradientstowardthe north. All of thesevalues
are linear (Figure4c). The average 2 of our 10 measurements at DHF 64 is 68 mW/m with a standarddeviation of 6 mW/m 2 (Table 1).
Fig. 12. seismic
'
2b km
'2•.2'I
DHF65 locationsprojectedonto a
profile
record near site
5.
All
measurements are towhich or greater tha•the cruise heat flow 14 predicted value at equal 67 m.y. is 58 mW/m. An and 155(Figur• mW/m •, 4a). muchThe greater than valu,e•re the mW/m •z examination of the heat flux relative to the position of the faults (Figure 11) suggests some
correlation; navigation
however, more data and better bottom are needed.
had a
At site 5 (DHF 65), measurementswere made on crust of 75 m.y. age. The sediment thickness is greater than 2 s of two-way travel time. The seafloor surface is flat. As in DHF 60-63, nonlinear temperature profiles were recorded. The seismic survey at slow ship speed reveals reverse faults with basement displacements showing the south cases.
side up and the north side down in None of the fault surfaces disrupt
sediment-water
interface.
The
two
DHF
64
SURVEY --80
ß
ß
_T_H_E_O_ R_ E_ T_ LC_A_ L__ ' ......
HEAT
._,_
. ß
ß
of
120 mW/m •.
The heat
flow
pre-
Discussion
reliable
ß
.
value
dicted from using just the topmost probe and the estimated penetration depth from the nonlinear profile fits from DHF 65 A and E are close to this previously measured value, suggesting that the high heat flow measured on the Verna 2901 might actually have a nonlinear temperature gradient as well.
most the
temperature gradients measured have curvatures greater than any previously measured during this V$616
predicted for crust of this age (Figure 12). A nearby measurement (14 km northwest) made on Verna 2901 with only one penet•ating temperature probe
.
--
•
60
At many sites in the deformed region of the Central Indian Ocean, high heat flow has been measured. The most striking measurements are the eight with nonlinear temperature profiles because these are on crust older than 65 m.y., with a thick sedimentary cover. There are four possible
mW
explanations for this phenomenon:(1) changesin
--zm
conductivity with depth, (2) bottom water temperature changes, (3) one-way upward advection of water, and (4) convection of water between the
FLOW
ocean, crust, and sediments. Of the four possible explanations, changes in conductivity with depth are the easiest to rule out. If conductivity increases significantly with depth, then the temperature profiles are nonlinear, decreasing with depth. Conductivity measured and
for
in
four
cores
the
two
stations
from Vema 3616 on Verna
(DHF 60-63)
2901
and
Conrad
1708 are uniform with depth (Figure 4b). the
Fig. 11. DHF 64 locations projected onto slow speed seismic reflection profile from site 4.
A change in sediments
bottom water temperature affects near the surface, and until
sediment temperatures reequilibrate, temperaturedepth profiles will be nonlinear [Lachenbruchand
Geller
Marshall,
Indian
Ocean
Bottom water temperatures of
1977; Williams et al.,
1974].
Ocean Basin are considered
Spreading
1968].
the Central
Indian
et
al.:
Heat
Flow
and Deformration
to
in
the
Center,
1029
Near the Galapagos
convection
of
seawater
occurs
be very stable [Kolla et al., 1976a]. Seafloor features that normrally indicate current activity
in cells aligned along strike of the ridge axis and topography with upwelling limbs associated
appear largely absent in the Central Indian Ocean Basin. This region has the highest bottom water temperatures of any basins in the Indian Ocean at this latitude, suggesting at most a small influx
with fault scarps and mounds [Green and Von Herzen, 1979]. Because of water circulation, the average measured heat flow is much less than values predicted from simple thermal models [Parsons and Sclater, 1977; Parker and Oldenberg, 1973; Sclater and Francheteau, 1970], and there is a
of Antarctic bottom water [Kolla et al., 1976a]. The Ninetyeast Ridge is an effective barrier to bottom water
movement between the colder
Wharton
large
standard
deviation
about
the
mean.
Often
Basin and the Central Indian Ocean Basin. However, some exchange may occur through topographic
the heat flow oscillates with a wavelength of 5 to 15 km [Anderson et al., 1979; Williams et al.,
gaps at 10øS and 5øS [Warren, 1982]. To the north, in the Bay of Bengal, bottom photographs and fairly high turbidity values suggest some southward flow of non-Antarctic bottom water.
1974]. As the sediment cover approaches a uniform thickness of 100 to 200 m and the age of the oceanic lithosphere increases, the measured heat flow becomes more uniform and approaches the
This activity
theoretical
tor
mmrkedly decreases toward the equa-
[Kolla et al.,
1976b].
A short fluctuation
in bottom water temperature, of the order of 15 days and a decrease of 0.1øC will affect the top 2 m of the sediment; however, this cannot explain the continued nonlinearity of the measured profiles below 2 m. If there was a decrease in
values
for
a
cooling
lithosphere,
suggesting that convection of water is less vigorous and conduction is a more significant heat transfer mechanism in the crust and sediments. Anderson et al. [1977] found that this change occurs at different ages for different parts of the oceans (the Atlantic at 80 m.y., the East Pacific
bottom water temperaturea relatively long time
Rise at 20 m.y., the Galapagosat 5 m.y., and in
before Vemm3616, it
is difficult
most parts of the Indian Ocean at 50 m.y.).
two
(DHF 59 and 64)
of
the
stations
to explain do not
why have
Convection
can
occur
in
crust
remote
from
nonlinear temperature profiles too. Thus we can safely rule out bottom water temperature fluctuations as a possible mechanism generating nonlinear profiles in our data set. Convex upward temperature profiles indicate upward flow of water (Figure 4a). If there is only one-way advection of water (no circulation and recharge mechanism), the two possible sources of water are the crust and the sediments. Four of the five areas where nonlinear temperature gradients were measured (Table 2, DHF 60-63, and
presently active spreading centers. For example, in the south and southwest Indian Ocean, closely spaced measurements on 45-m.y. crust in the Crozet Basin and on 55-m.y. crust in the Madagascar Basin (with 100 and 200 m of sediment, respectively) delineated an oscillatory heat flow pattern (wavelength of 5 to 10 kin) with average values slightly greater than theoretical [Anderson et al., 1979]. Half of the temperature profiles are nonlinear in these two survey areas with uniform sedimentary cover, suggesting that
C1775) are located on areas uplifted since'late
hydrothermmlconvection is still
Miocene time with sedimentation rates of a few
upper crust and sediments in these regions.
meters per million
reactivation
of
the
years (based on the age dating
Lamont-Doherty Geological
Observatory
Calculations from the results of the
or
nonlinear
temperature
existing
analysis
give an
faults
in
the
averagevolumeof 2000m3 of water per 1000years
dramatically
If
The
deformed Central
Indian Ocean Basin may have restarted
cores).
profile
of
occurring in the convection
increased circulation
within
systems.
a two-way circulation system of water
through a square meter of seafloor. This flux is too great to be accounted for without any recharge mechanism if water flow has been occurring for any significant period of time. Thus if there is only one-way flow of water, we must assume that the movement is generated in short and infrequent pulses and is limited in regional
exists in the Central Indian Ocean Basin, lack of observations indicating oscillatory heat flow patterns, including low values and nonlinear profiles indicating downward flow, needs to be explained. Most of the heat flow measurements for the similarly aged crust in other oceans, including other basins in the Indian Ocean, were
extent (perhaps associated with earthquake activity). If some unusual deformational mechanism
randomly taken, and those measurementsaverage close to the theoretical values (Figure 13). In
causes release
the
of water,
the probability
of de-
region
of
intraplate
deformation
in
the
tecting the resulting flow is small. It is also unlikely that we would encounter this type of phenomenon in three locations (DHF60, DHF61-63, and DHF 65) in a short time span. Extra heat is carried upward with water, implying that after
Central Indian Ocean most values are equal to or greater than theoretical (Figure 1). Heat flow higher than the expected average can be explained if the processes causing intraplate deformation have added heat to the lithosphere. Thus regard-
the flow has endedthere must follow a period of low conductive flux until heat from below reestablishes the normal thermal state of the crust
less how manyadditional measurements are made, the average would still be greater than calculated from cooling models. The apparent lack of
and sediment.
Because we found five
locations
of
low heat flow values associated with a convection
high heat flow and advection of water and no sites of low heat flow, one-way upward advection of water cannot explain the observed nonlinearity
system may be due to the additional heat flux. Perhaps heat flow values that are considered normml for the crustal age, such as for the 48 mW/m 2
of temperature
value
with depth.
Convectionof water removesa large amount
from Vema 2901
to
the
north
of
DHF 60
(Figure 9), are the low values in an oscillatory
of heat from young oceanic crust and sediment
system. Downwardflow of water produces a convex
[Andersonand Hobart, 1976; Davis and Lister,
downwardtemperature profile
with the greatest
1050
Geller
.2
et
al.:
Heat
Flow
and Deformation
-I
co,
I NDIAN OCEAN •
200
4
o
II ',
