Tectonic framework of Bangladesh

Tectonic framework of Bangladesh

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  WELCOME TO OUR PRESENTATION
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  TOPIC: Tectonic Framework of Bangladesh
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  What is tectonicframework? • Tectonics are the processes that control the structure and properties of the Earth's crust and its evolution through time.These include the processes of mountain building, the growth and behavior of the strong, old cores of continents known as cratons and the ways in which the relatively rigid plates that constitute the Earth's outer shell interact with each other. Tectonics also provide a framework for understanding the earthquake and volcanic framework that directly affect much of the global population.
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  Tectonic framework ofBangladesh • Tectonic framework refers to the basic structural frame on which Bangladesh stands. It is essential to have a clear conception about the tectonic framework of Bangladesh in order to evaluate the prospect of mineral resources including oil and natural gas. Bangladesh occupies major part of Bengal Basin which is bordered by Precambrian Indian Shield in the west and north, Indo-burman range to the east and is open for considerable distance into the Bay of Bengal to the south
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  Bangladesh is dividedinto two major tectonics units: 1.Stable platform in the northwest 2.Deep(geosynclinal) basin to the southeast 3.A third unit, a narrow northeast-southwest trending zone called “Hinge Zone” separate the above two units diagonally almost through the middle of the country.The Hinge Zone is currently known as “Palaeo-Continental Slope”.
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  1.Stable platform inthe northwest • Stable Precambrian platform refers to the stable shelf of the bengal basin.This unit occupies Rajshahi-Bogra-Ranpur-Dinajpur areas and is charactarized by limited to moderate thickness of sedimentary rocks above a Precambrian igneous and metamorphic basement. On the basis of thickness of sediment cover,stable plateform is diveded into: i.Ranpur Saddle(130m-1000m) ii.Bogra shelf(1-6km)
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  i.Rangpur Saddle(referred toas Dinajpur shield): • Rangpur Saddle in the north with thin to limited(130m to 1000m) sedimentary cover above the precambrian basement. ii.Bogra shelf(referred to as foreland shelf): • B0gra shelf with mogerate(1 to 6km) sediment covers over the Precambrian basement.Sedimentary layers in the Bogra shelf dips very gently towards southeast until it reaches the hinge zone when the dips suddenly increase to 15 to 20 degrees and the sedimentary units plunge to great depths into the deep geosynclinal basin to the south and southeast
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  2.Deep(geosynclinal) basin tothe southest • This unit lies to the south and east of stable platform and is characterizing by huge thickness(maximum of about 22 km near the basin center) of sedimentary rocks mostly sandstone and shale of tertiary age.It occupies greater Dhaka-Faridpur-Noakhali-Sylhet-Comilla-Chittagong and Chittagong Hill tracts and the Bay of Bengal.The huge thickness of sediments in the basin is a result of tectonic mobility or instability of the areas causing rapid subsidence and sedimentation in relatively short span of geologic time.
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  i.Fordeep As the intensityof the folds decreases towards the west ,the fold belt unit merges with the foredeep unit which is characteized by only mild or no folding .So the sedimentary layers are generally horizontal to sub horizontal and are free from major tectonic deformation in the foredeep area.This unit covers the central part of the basin and is represented by river to delta plain topography at the surface.
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  i. Fold Belt: Thefold belt is characterized by folding of the sedimentary layers into a series of anticlines(upwards folds) and synclined(downward fold).The anticlines from the hills and the synclines from valleys as seen in the topography of the Chittagong-Comilla-Sylhet regions.The intensity of the folding is greater towards the east causing higher topographic elevation in the eastern Chittagong Hills tracks than the western part.
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  3.Hinge Zone The hingezone is a 25-km wide northeast-southwest zone that separates the Precambrian platform in the northwest from the geosynclinal basin to the southeast.There is no surface expression of this unit but it is marked by the sudden increase of dip in subsurface sedimentary layers as shown strongly by the seismic marker at the top of the Sylhet Limestone unit of Eocene age.This is why it is also known as the Eocene hinge zone.
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  The hinge zoneis not a tectonic hinge but represents Eocene shelf edge/slope break i.e. a paleo-continental slope.The western part of Bengal basin is marked by a series of migrating shelf breaks with the most prominent being the Eocene shelf edge.This is also known as Eocene hinge zone.