Pangaea Theory

Topics: Plate tectonics, Pangaea, Permian Pages: 7 (2027 words) Published: May 14, 2013
The Pangaea Theory

The Pangea theory describes that all continents were joined together in one enormous land mass millions of years ago. Later on the continents broke apart and start drifting in opposite directions and still continued to make another arrangement. In 1912, Alfred Wegner, a German meteorologist and geologist gave the hypothesis the all the continents were joined together in a single continental land mass surrounded by a single ocean (Panthalassa) Late Paleozoic times. The Wegner used the term Kontinentalverschiebung for the breakup and displacement of crustal blocks. Pangea situated around where Antarctica is now presently. During Jurassic Period the Pangaea started to break up into smaller units called Laurasia and Gondwanaland. In late Cretaceous period, the continents were further separated and transformed as present day continents (William Lowrie, 2007). Figure-1 shows the reconstruction of Wegener’s continental mass using paleo-climatic data from Carboniferous, Permian, Eocene and to Quarternary.

Figure-1 (a) Pangaea reconstruction by Wegener in Late Carboniferous time (b) continents in Eocene times (c) continents in Early Quaternary, where K, S, W, E refers coal, salt, desert areas, ice sheets respectively (after William Lowrie, 2007).

Evolution of Himalayas

The Himalaya holds very important geological and tectonic history. The arc of Himalayan belt is about 2500 km from northwest to southeast. It comprises of well-known famous peaks like Nanga Parbat, Evereast and Namche Barwa etc. The Himalayan ranges hold a huge concentration of lithospheric mass comprising Precambrian to Recent sediments.

The contnent to continent collision of Indian and Asian plates is considered as the grave reason for the origion and development of Himalaya. This collision occurred in last 100 Ma yielding the uplifting of Himalayan chain of mountains. This lead the closing of Tethyian sea during 60-50 Ma. The over trust sheets and formation of nappe and klipps was generated as a result of crustal shortening.

The uplift resulted huge erosion and deposition phases in the Arabian sea and Bay of Bengal. The subduction process is still under continuation causing earthquakes and tsunamis in the entire region (Anshu Kumar Sinha, August 2008),(An Yin et. al, May 2000) During cretaceous age the indian plate started it journey of collision with Eurasian plate. The subduction of the Indian plate occurred under Eurasia making Tibetan crust with huge thickness (Figure-2). The Tsangpo Indus suture zone was formed in western while MKT/ MMT zones were created. Several regional faults like main continental and boundary thrusts as well as salt range thrusts were generated (Klootwijk et al., 1992). Figure-3 show the distribution of major thrust faults associated with the indianeurasian plate collision Hamalyian orogeny.

Figure-2, The subduction of Indian plate under Eurasian plate (after Klootwijk et al., 1992).

Figure-3, Regional thrust faults distribution due to the collision of Indian plate (after Harald Drewes, 1995)

Tectonics of Sulaiman & Kirthar Range

Sulaiman Range The Sulaiman & Kirthar ranges comprises of about 1250 km long and 75 to 180 km wide zone. The zone is highly complex structurally (Figure-4). There are regional thrust belts in northern and southern side of these ranges. On the eastern and southern side of these belts the successions are highly folded. The intensity of folding diminishes as we move more eastward and southward. A huge foredeep zone containing 10 km thick Jurassic to Recent sediment is present in front of these ranges in the eastern and southern direction (A. H. Kazmi et al., 1997).

Sulaiman & Kirthar ranges comprises of various tectonos tratigraphic zones. The fold belt contains arc shaped zone is east-west direction. There is exposure of Jurassic to recent strata having a regional unconformity at the base of Dungan Limestone of Palaeocene age having Biabi volcanics a protolith....

References: William Lowrie, [2007], Fundamentals of Geophysics, 2nd edition Anshu Kumar Sinha, [August 6-14, 2008], The evolution of Himalayas and tectonic framework, International Geological Congress, Norway An Yin & T. Mark Harrison, [May 2000], Geologic Evolution of the Himalayan-Tibetan Orogen, Vol. 28 Klootwijk, C.T., Gee, J.S., Peirce, J.W., Smith, G.M. and McFaddan, [P.L. 1992]: An early India–Asia contact: Palaeomagnetic constraint from Ninetyeast Ridge, ODG Leg 121. Geology 20, 395–98 Harald Drewes, [1995], Tectonics of the Potwar Plateau Region and the Development of Syntaxes, Punjab, Pakistan, U.S. geological survey bulletin 2126 A. H. Kazmi & M. Qasim Jan, [1997], Geology & Tectonics of Pakistan
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