Supercontinental breakup in the JurassicWhen continents break apart and new oceans form and grow bet

Supercontinental breakup in the JurassicWhen continents break apart and new oceans form and grow between them, they tend to follow a certain sequence. No one knows for sure what kick starts the process, but convection currents in the mantle building up heat under the blanketing effect of the continental crust and plumes of hot mantle rising from the depths are the main contenders. The crust starts to pull apart and thin, and molten rock starts to flow into and through the continental rocks. The same process is happening right now in the Great African Rift with its copious magmatism (such as the massed basalts of the Ethiopian highlands) accompanied by the widening of Earth’s youngest Sea, growing between Africa and Arabia and pushing the latter into Eurasia, resulting in the Zagros mountains of Iran. After the separation of the supercontinent Pangaea, two main land masses known as Laurussia and Gondwana drifted apart. As the era proceeded, forces stirring deep below started to prepare the scene for the rifting apart of Gondwana, which took up much of the Cretaceous. Vast outpourings of lava breached the crust, amongst others in what is now Antarctica some 180 million years ago. While subsequent erosion has removed much of the rock erupted above ground, the plumbing systems and large underground intrusions of lava into the country rocks that accompanied the event are some of the best exposed on the planet, and are unfortunately found in one of the globe’s remoter and harsher spots: the Dry Valleys. A sequence 4km thick is open for exploration to those geologists willing to endure the somewhat rough working conditions.These rocks are called the Ferrar dolerite complex (after the geologist on Scott’s 1901-4 expedition), and it comprises four massive horizontal sills extending for tens of kilometres and ranging from 100 to 350 metres thick, interconnected by a complex system of vertical dykes. The photo shows a split sill of black dolerite (a medium grained frozen magma of the same chemical composition as basalt) that intruded into the Beacon sandstone (an arkose, made of quartz and feldspar crystals deposited in shallow marine conditions between 400 and 250 million years ago) , where it stalled in the crust, intruding through and between the layers of sandstone.LozImage credit: Michael Hambreyhttp://bit.ly/1MPhWcxhttp://bit.ly/1r7D5Vxhttp://bit.ly/1NHD4fHhttp://bit.ly/1T5yk5h -- source link
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