Hotspots and the opening of the Atlantic
This figure shows the location of 4 “hotspots” that are thought to be key to the opening of the Atlantic Ocean.
The Central Atlantic Magmatic Province (CAMP) is a series of volcanic rocks erupted across the Eastern US starting in the early Jurassic. The St. Helena hotspot started erupting about 145 million years ago later in the Jurassic, and today it is represented by a series of small, submarine volcanoes called seamounts running from the coast of Africa to the Mid-Atlantic Ridge. The Parana-Etendeka province is 2 flood basalts, today found on opposite sides of the Atlantic that erupted about 140 million years ago when the continents were joined together. Finally, the North Atlantic Igneous province (NAIP) started erupting about 60 million years ago and today is represented by Iceland. Several of these igneous provinces are geographically famous. The amazing Iguazu Falls on the border between Brazil and Argentina is formed by water flowing over the Parana flood basalts (https://tmblr.co/Zyv2Js1tbuMfh). The Jurassic-aged igneous rocks of the CAMP are spread out over a wide area and likely include the Palisades Sill and the diabase dikes that hosted the battle of Gettysburg (https://tmblr.co/Zyv2Js1vOvtpU and https://tmblr.co/Zyv2Js2NQvaAo). The rocks of the Giant’s Causeway and Fingal’s Cave in Ireland and Scotland were produced as part of the NAIP (https://tmblr.co/Zyv2Js1DzHVVL and https://tmblr.co/Zyv2Js1j-ZS5n).
We don’t fully understand everything that happens inside the Earth’s mantle, but these large provinces of igneous rocks are thought to relate to the opening of the Atlantic Ocean. Start with a blob of hot rocks in the mantle; those extra-hot rocks would move upwards until the blob hit Earth’s crust. Once it hit the crust, it would spread out and begin melting and removing the bottom of the crust while still trying to force its way upwards. Eventually, the relentless force of this buoyant, hot blob pushing upwards would start rupturing the crust itself, breaking it into pieces. For the Atlantic Ocean and the breakup of Pangaea, 4 different plumes are involved, and the shape of the ocean today almost plays connect-the-dots between them. The Atlantic as we know it today was likely formed by this series of hot upwellings, which pushed apart the former supercontinents.
There are some thoughts that these hot upwellings are actually caused by the presence of supercontinents, creating a supercontinent cycle. The large supercontinent would work like a huge blanket, keeping the mantle from removing heat. Eventually, the mantle heats up, triggering the formation of the plumes that broke apart the supercontinent. However, there are other ideas about this effect – Africa today sits above an unusual portion of mantle and recent studies suggest that this unusual mantle has existed for at least 4 billion years. It could be instead that the supercontinent was ruptured by something much more ancient, buried deep in the mantle.
-JBB
Image source: Ernst, 2014 https://doi.org/10.1017/CBO9781139025300.011
Read more: http://bit.ly/2HKXTu2 http://bit.ly/2FT6YAB http://adsabs.harvard.edu/abs/2015AGUFM.T32D..06R http://bit.ly/2GGrc1M
