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112lect21 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Proterozoic Tectonics Part One Lecture Goals : A) The Proterozoic time frame B) Paleogeography C) Tectonics 1 (Wopmay Orogeny) Textbook reference: Levin 7 th edition (2003) Chapter 7; Levin 8 th edition (2006), Chapter 9 A) Time frame Last time we discussed the Archean and Hadean Eons. The Hadean Eon represents the period of time without a rock record on this planet. The Archean is recorded through rocks of granulite and greenstone associations. The next eon, and the subject of this weeks material is the Proterozoic (2.5 GA to 550 MA). Unlike the Hadean and Archean, a lot of major developments in Earth history started in this eon (which incidentally, covers more than 40% of all geological time), including the first eukaryotic life and the first “modern-type” plate tectonics. Like the Archean, the Proterozoic is divided up into early, middle and late division, except this time, we use the terms Paleo (old), Meso (middle) and Neo (new): Division Age Neoproterozoic 900 MA to 550 MA Mesoproterozoic 1.6 GA to 900 MA Paleoproterozoic 2.5 GA to 1.6 GA B) Paleogeography As we discussed during the lectures on the Archean, continents of the early Earth were small and numerous. With time they combined together to form larger masses shields, provinces, platforms and cratons. A large “ super continent” consisting of what is today North American and Europe may have formed early in the Proterozoic (although this is not entirely certain), and an even larger mass of continental rocks amassed in the late Neoproterozoic (see adjacent image). The formation of super continents has occurred several times in the Earth’s history and it is traditional to name them. The last major grouping of continental landmasses which occurred during the late Paleozoic resulted in Pangaea . Laurentia (North
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GY 112 Lecture Notes D. Haywick (2006) 2 America and Europe) and Gondwana (Africa, Antarctica, India, Australia and South America) also formed during the Paleozoic. The large super continent that formed in the later part of the late Meso-NeoProterozoic (C. 1.0 GA) was called Rodinia . A quick check of the diagram below will show that the configuration of continental masses was very different then compared to today. Most of the continents were in the southern hemisphere and continents that are today very far apart were then close neighbors. For example, Australia and Antarctica both lay just to the southwest of North America (you could walk from one continent to the next) and most of South America lay to the east.
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