AN ASSESSMENT OF THE GEOTHERMAL ... - Orkustofnun

Report 5 5 Akbar
2. GEOLOGICAL SETTINGS OF BANGLADESH
2.1 Tectonic framework of Bangladesh
The Bengal Basin is the largest fluvio-deltaic sedimentary system on earth occupying most of
Bangladesh, West Bengal of India and part of the Bay of Bengal. Sediments accumulate in the GBM
basin and are dispersed into the Bay of Bengal forming the largest deep sea fan in the world.
Sedimentation in the Bengal Basin
started with the breakup of
Gondwanaland. The collision of
the Indian plate with the Tibetan
plate and with the Burmese plate
in the Miocene resulted in a rapid
switch in the sedimentation pattern
in the Bengal Basin. The basin
structure and sedimentation were
both strongly influenced by the
collision pattern of the plates and
by the uplift of the Himalayas
(Alam, 1989). Tectonic evolution
of the Bengal basin is directly
related to the orogenic phases of
the mighty Himalayas, although
the Cenozoic evolutionary history
of the eastern Bengal basin is
mainly related to the oblique
subduction phases of the Indian
plate beneath the Burma plate
(Alam et al., 2003). Major
tectonic elements of Bangladesh
(Figure 4) are briefly discussed in
the following.
The northwest stable shelf
The western and northwestern
parts of the Bengal Basin are occupied by a shelf, the margin of which has a northeast-southwest trend
along which the basement slopes downward to
form a hinge zone (Figure 5). The pre-collision
geology of Bangladesh can only be studied in
northwest Bangladesh, where the continental
Gondwana sequences are preserved in graben
structures of which the shallowest deposits can
be seen in the Barapukuria graben at depths of
only 117 m. The shelf region is marked by a
series of buried ridges and normal gravity faults.
To the northwest the basement slopes upward
and forms a prominent ridge, the Rangpur Saddle
(Bakhtine, 1966).
FIGURE 4: Generalized tectonic map of Bangladesh
(GSB, 1990)
FIGURE 5: Schematic west-east profile across
Bengal Basin (after Alam, 1989)
Rangpur saddle
The Rangpur saddle and the so called Garo-Rajmahal gap comprise the most uplifted part of the
basement in the country, concealed under a thin veneer of alluvium. In the Madhyapara area,
basement rock is encountered at a depth of 130 m. The Rangpur saddle represents a block of the