. Collected reprints, Essa Institute for Oceanography. Oceanography GEOPHYSICAL SURVEY IN THE ANDAMAN SEA 501 island arc in the southern part of the area, but it moves up onto the insular shelf and disap- pears just north of 10°N. The westernmost belt of negative anomahes is coincident with the axis of the foredeep. Four profiles based on simultaneous measure- ment of gravity, magnetic field, and water depth cross the entire arc system and are shown in Figure 5. The magnetic field measurements generally indicate minor anomahes associated with the extension of the Java-Sumatra tre
. Collected reprints, Essa Institute for Oceanography. Oceanography GEOPHYSICAL SURVEY IN THE ANDAMAN SEA 501 island arc in the southern part of the area, but it moves up onto the insular shelf and disap- pears just north of 10°N. The westernmost belt of negative anomahes is coincident with the axis of the foredeep. Four profiles based on simultaneous measure- ment of gravity, magnetic field, and water depth cross the entire arc system and are shown in Figure 5. The magnetic field measurements generally indicate minor anomahes associated with the extension of the Java-Sumatra trench. The magnetic field is relatively smooth over the sedimentary island platform, and the relatively large and sharp anomalies are clear indications of the igneous belt to the east. Most of the mag- netic anomalies associated with the igneous belt are negative, indicating induced magnetization of the rocks in this equatorial region. Several sharp positive peaks suggest reverse remanent magnetization [Girdler and Peter, 1960]. The postulated continuity of the igneous belts of Burma and Sumatra is strengthened by this set of profiles. Although on profile A'-A" there is complete lack of bathymetric indication be- cause of burial due to the encroachment of the Irrawaddy delta from the north, the igneous trend is clearly indicated by both the positive free-air anomaly and the magnetic anomalies. In the south, the igneous trend is best indicated by the magnetic anomahes. Seismic reflection profile section 3 (Figure 6) indicates an almost direct correlation with the subaerial geological trends of northern Sumatra, and section 2 (Fig- ure 7), farther to the north, also shows signifi- cant similarity. The continuity is further strengthened by the very high sea-floor heat flux measured in the deepest part of the Anda- man basin (Figure 8), which is directly on the axis of the igneous trend (cf. the deep area near the eastern end of profile D-D'). Two other measurements of the heat
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