112lect22 - 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 More Proterozoic Tectonics Lecture Goals : A) The Trans Hudson Orogenic Belt B) The Grenville Orogeny C) Diamonds Textbook reference: Levin 7 th edition (2003) Chapter 7; Levin 8 th edition (2006), Chapter 9 A) The Trans Hudson Orogeny Last time we discussed Proterozoic paleogeography and the Coronation Geosyncline (Wopmay Orogeny). The main thing to remember from that lecture is that full blown plate tectonics appears to have begun around 2 billion years ago. Plate collisions, the opening of new oceans and the destruction of old ones has been occurring ever since. One most impressive orogeny took place between 1.8 and 1.9 billion years ago (about the same time as the Wopmay event) and involved two or three large provinces of the Canadian Shield. The event is called the Trans Hudson Orogeny because it involved a belt of rocks now exposed from Hudson Bay well down into the United States. The Hearne Province and the Wyoming Provinces (possibly previously docked) appear to have collided with the Superior Province through a collisional tectonic event. Like the Wopmay Orogeny, this event was preceded by initial rifting and the formation of oceanic crust (i.e., divergent plate tectonics) before the collision occurred. It would seem as if the Canadian Shield experienced yet another Wilson Cycle ( see color diagram from http://csmres.jmu.edu/geollab/ on the next page). The Trans Hudson Orogenic Belt is linear in disposition and comprises mostly mafic and other oceanic crustal rocks. It is best exposed in northern Saskatchewan and Manitoba, in Canada and in the Black Hills of South Dakota.
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GY 112 Lecture Notes D. Haywick (2006) 2 So what happened? Rifting began to occur around 2.0 billion years ago and resulted in a ocean of unknown width. It was a real ocean – i.e., flood basalts formed indicating the eruption of large quantities of mafic lava and new oceanic crust. Plate motion reversed itself and ultimately developed an island arc complex. To the best of my knowledge, the Wopmay Orogeny did not produce an island arc, so there may be some fundamental differences between the two orogenies. In fact, some people regard the Wopmay Orogeny to have been more of an accretionary event than the Trans Hudson Orogeny (which was more of a pure collisional event). In case you don’t already know this, island arcs are linear volcanic islands chains formed through the eruption of intermediate igneous rocks like andesite. They are found along most subduction zones in oceans (e.g., the Aleutian Islands, Japan, etc.) and rocks interpreted to have formed in island arc tectonic settings are common in most Phanerozoic mountain belts like the Appalachians and Rockies. Their presence in the Trans Hudson Orogenic Belt may indicate a relatively wide ocean and a significant amount of subduction prior to the collision. Any way you want to look at it, the collision
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GY 112 Lecture Notes D. Haywick (2006) 3 between the Superior and Hearne/Wyoming Provinces squeezed the heck out of the
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This note was uploaded on 02/04/2012 for the course GLY 112 taught by Professor Haywick during the Spring '12 term at S. Alabama.

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112lect22 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

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