The super-continent, Pangea, it is long 100 million years. But, together we have actually seen, the Earth"s late is not static. The direction that plate motion shifted end time and also the continents began to pull apart quite than converge. Rifts arisen in the curst, ultimately breaking totally through the crust and also leading come the breakup the the supercontinent. Contemporary day rifting can be observed in the eastern African Rift Valley. Anxiety (two pressures pulling in the opposite directions) slowly began to pull North America far from the other an unified continents. As the crust to be pulled apart, it stretched, thinned and also uplifted come the point of breaking.

You are watching: What caused it to break up after it formed


The same processes that are today tearing apart east Africa, to be tearing personally Pangea 180 million years ago. In east Africa, the african plate is pulling away from the Arabian plate, stressing the crust to the suggest of breaking apart.

*
*

Figure 1.19 and also 1.20: together rifting occurred, block of tardy slid down faults to type a basin. The basin was filled with sediments and also lava flows. Eventually, the entire container was tilted and faulted. Figure by J. Houghton.

The rifts arisen along a series of cracks in the Earth"s crust around parallel to the present coastline. Along a collection of faults, block of late slid down the faults to type down-dropped containers bounded by tall cliffs that happened known together Triassic rift containers (Figures 1.19 and 1.20). The eroding cliffs to fill the surrounding basins v poorly sorted, red-colored sandstones and shales. These container deposits are part of a sequence of rocks understand as the Newark Supergroup, v thicknesses getting to up to 6 kilometres in some places. Shop are uncovered in the Connecticut sink of Massachusetts and also Connecticut, and also in the Newark Basin, which stretches from southeastern brand-new York across brand-new Jersey, Pennsylvania and also Maryland. Over there are an ext Triassic rift basins located off the east shore that are hidden by continent shelf sediments (Figure 1.21 ). During the Jurassic, the last break in between the bowl of north America, Africa and also Baltica arisen many kilometers to the eastern of today"s coastline at what is now the Mid-Atlantic Ridge. Other fragments of Pangea gradually broke into the contemporary continents, progressively moving into their existing positions over the following several hundred millions of years.


*

Figure 1.21: The Triassic rift containers of the Northeast formed as phibìc America damaged away from Pangea during the Triassic and Jurassic. Figure by J. Houghton.


*

Figure 1.22: The softer sediments the the Newark rift container were conveniently worn away, creating valleys between the more resistant ridges of hardened lava flows. Figure by J. Houghton. 


The anxiety released by the pulling personal of plates, resulted in plenty of faults and also volcanoes. Alternating with the sandstone and shale gift deposited in the containers were store of ash and lava flows originating from volcanoes follow me the rift area. The flay-lying bed of the Newark and also Connecticut Valley containers were at some point faulted again and tilted, exposing the edges of the class of sediment and cooled lava. The hardened lava was more resistant come the erosion the the sediments in the basin, for this reason ridges the cooled lava to be left standing as the sediments roughly them wore away (Figure 1.22).


Rocks that form ridges

Some rocks stay down fairly quickly, if others deserve to withstand the power of erosion for much longer. Softer, weaker rocks such together shale and poorly cemented sandstone and limestone space much much more easily worn away 보다 hard, crystalline igneous and metamorphic rocks, or fine cemented sand- rock and limestone. More tough rocks are often left was standing alone as ridges since surrounding softer, much less resistant rocks were quickly worn away.


*
 

Figure 1.23: Triassic: 273 million years ago.

See more: In The Book The Westing Game Who Is The Murderer, Who Is The Murderer In The Westing Game

*

Figure 1.24: Cretaceous: 94 million years ago.


As the supercontinent gradually broke apart, the continent moved right into the geographical positions us see now (Figures 1.23 and 1.24). The Atlantic Ocean started to widen. The east coastline of north America no longer experienced the strong tectonic activity associated with the compression and also rifting the a key margin. Instead, the tectonic task gradually moved with the Mid-Atlantic Ridge thousands of kilometers turn off the coast in the Atlantic Ocean. The Northeast, staying a “passive margin” through to the present, began a long duration of erosion the would continue through the Cretaceous and also into the Tertiary. 


*

Figure 1.25: Pangea division Up:

Pangea begins to split.Rifts are created in the crust.Triassic/Jurassic rift containers form.Rift basins filled with sediments and lava flows.Rift containers later tilted, faulted and eroded.Long duration of erosion.