Tectonophysicx, 103 (1984) 235-237

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

235

GRAVITY MAP AND HEAT FLOW MEASUREMENTS IN INDONESIA

RONALD GREEN

Lkpartmeni of Geophysics, ~nil~ersit~ of New England. Armidak, N.S. W. 23.51 ~(A~strai~a~

(Received September 7, 1982: accepted October 12. 1982)

ABSTRACT

A detailed gravity map (1 : 5,000,000, in colour) of Indonesia has been prepared

by Green et al. (1979). A regional base-station network was established throughout

Indonesia and gravity measurements from each of the local island surveys have been

incorporated. In total, some l~,~ gravity values have been used in the production

of the map.

The heat-flow data have been provided by the Geological Survey of Indonesia,

and it is based on the work of various diverse sources. Subduction zones stand out as

lows in both gravity and heat flow. The high heat-flow values occur along the

volcanic arc. The volcanic arc is on the concave side of the gravity high.

Heat-flow highs are related to areas of supposedly new crust. This is true in most

cases but not in all cases.

The gravity coverage in the Banda Sea area is detailed, and additional intensive

work is going on in Irian Jaya. There is inadequate heat-flow data from the

tectonically complex Banda Sea area.

I began in 1981 to assemble all the heat flow data, both oceanic and on-shore, for

the Indonesian region.

In a definitive paper, Watanabe et al. (1977) had examined in broad outline, the

relationship between the heat-flow data and zones in which the movement of

tectonic plates was assumed to be occurring. Watanabe et al. (1977) came to the

opinion that: (a) the volcanic belts have high heat-flow values but there is a large

variation in the magnitudes of the values; (b) the regions between the volcanic zones

and the axes of the trenches (as seen from the bathymetry) have low values. This

leads to the consequence of a close physical juxtaposition of high and low heat-flow

regions; (6) the heat-flow is variable in value in the back-arc basins but the heat-flow

values depend upon the age of the basins.

For the younger crusts Anderson et al. (1977) advocate the quantitative relation-

ship of qzlI/t . ‘I* Data from the neighbouring Philippine Sea is to be found in

Sclater et al. (1976b).

~40-1951/84/$03.~ 0 1984 Eisevier Science Publishers B.V.

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On the other hand, Correy et al. (1968) had carried out heat-flow measurements

in the Banda Sea and the values they obtained would be anomalously low if the sea

were an active inter-arc basin but the values are consistent with an early Tertiary or

older age. Some higher values have been reported by Anderson et al. (1978) for

North Buru. Sclater et al. (1980) has published heat-flow values for the Banda, Sulu

and Celebes Sea.

Carvalho et al. (1978) had access to much of the commercial heat-flow data from

Sumatra which is a young back-arc basin and they found high heat-flow values

which is in accordance with Watanabe’s postulate (c) above. The heat-flow values for

the region of the southwestern coast of Kalimantan, are normal.

In view of the general correlation as noted by Watanabe et al. (1977) it was

thought that there may well be a close correlation between the heat-flow data and

the Bouguer gravity anomalies which also reflect a significant correlation with the

tectonics of Indonesia as noted by Green et al. (19’79, 1980).

Consequently, I prepared on the basis of the data given in the reference to

published work, a contour map which was presented subsequently divided into just

three regions designated low, average and high.

One immediate and obvious difficulty was the lack of heat-flow data in the

shallow seas of Indonesia. A substantial area of western Indonesia is shallow sea

covering the ancient craton of Sundaland built around Kalimantan.

Another difficulty was the paucity of data in the Banda Sea area. The most recent

available being Correy et al. (1968). A most excellent article on the tectonics of the

Banda Sea region has been prepared by Bowin et al. (1980). However, it was

reported at the Liblice Workshop by Uyeda (1982) that operations had commenced,

enabling reliable measurements of heat-flow in shallow sea to be obtained.

A final difficulty stemming from the rapid special change in heat-flow values-a

phenomenon already explicitly stated by Hobart et al. (1979)-is that there appears

to be no very satisfactory method of contouring heat-flow data. The rapid special

change in heat-flow data results in numerous poles and sinks in the contours brought

about by isolated high values and isolated low values (Sclater et al., 1976a).

My approach for the map presented at the Liblice Workshop was to filter the

map data with a symmetrical low pass filter. This procedure has been criticised at

the conference and consequently it has led me to revert to the expedient of providing

reference to the published gravity and heat-flow data. It is therefore not possible to

put a quantitative value on the correlation between gravity and heat-flow data but

visual inspection leads one to affirm the validity of the assertion in the abstract of

this paper.

It is my expectation that the demonstration of availability of gravity data and

some heat-flow data which is now being continually SuppIemen~ed, will lead to

increased activity in the measurement of heat flow, especially in the shallow sea of

Western Indonesia and in the Banda Sea region of Eastern Indonesia and this will

encourage the quantitative testing of hypotheses (such as Watanabe et al., 1977) in

this most classical and interesting area on the Earth’s surface.

231

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