Models of tectonic activities

 (i)                 A model of sea-floor spreading

American oceanographer Harry Hess proposed his sea-floor spreading model in 1960’s. It contains that oceanic ridges are originated by deep – seated material and risen currents. Volcanic eruptions also help to form new oceanic floor. New crusts occur at ridges and move slowly outwards. Other regions of ocean basin, in trench boundaries old crust descends into interior crust. It called as subduction. 

This model proved by two evident. They are, (i) paleomagnetism, (ii) core sampling. When a rock formed with iron it contains magnetism. Therefore iron grains move towards magnetic polar. The rocks become solid in a time, magnetic pole change as earth consistency magnetic pole. Sea-floor spread sideward since new materials accumulated at oceanic ridges. Both side of the ridges contents similar sediments. These reflected the past magnetic orientation. 

According to final research, sediments near the ridges are prolonging for long time. Sediments contiguity the ridges are known as thin, younger or recently accumulated. These materials are combined with small sediments and emissions from volcanic eruptions. 

Tectonic activities concept approved by base on these information’s and other evident.

(ii)               A model of continental drifting

Alfred Wegener developed his theory of continental drift in 1912’s. Plate tectonic theory approved by base this model. This model accepted since the sea floor spreading. 

Present continental were formed from a single mass which called as a pangea. These land mass drifted apart from each other and formed today’s continentals. These are proved through present continental positions.

• ·         Reconstructions of ancient super continental land mass shows that this continental once connected.

• ·         Many plants and animals fossils were occur in similar aged rocks and dispersed across today’s continents. 

Reference:

(i) Tom L. McKnight (1990): Physical Geography - A Landscape Appreciation: Prentice Hall: USA.
(ii)  http://www.ucmp.berkeley.edu/fosrec/Metzger3.html#

(iii)  http://en.wikipedia.org/wiki/Plate_tectonics