Day%2012-Early%20Proterozoic

Day%2012-Early%20Proterozoic - Early Proterozoic Time The...

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Early Proterozoic Time
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The Proterozoic is the 3rd of 4 eons in Earth history, from 2500 Ma to about 542 Ma. In this unit we will discuss only the first half of the Proterozoic 542 Ma 2500 Ma
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Outline of our discussion • Continental growth • Climate and atmosphere • Life
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Proterozoic Continental Growth
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By the Early Proterozoic the earth had cooled sufficiently to possess plate tectonics of a type nearly indistinguishable from that occurring today Canada’s Wopmay Orogen, at about 1900 Ma, is one of the oldest examples of a volcanic arc that collided with a continent.
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Soon a much larger chunk of land would be added to North America, a chunk that included Colorado. Archean North America in gray
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Throughout Colorado and Arizona, gneiss metamorphosed at 1700 Ma is abundant
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Clicker Question #1 What situation might have existed 1700 Ma to create so much gneiss in Colorado? A. Gneiss is a clastic rock that indicates rapid sediment deposition B. Gneiss is a foliated metamorphic rock that indicates differential pressure, likely at a convergent boundary C. Gneiss is an extrusive rock that indicates volcanic activity in the area D. Gneiss is a non-foliated rock that indicates uniform pressure during metamorphism E. Gneiss is an intrusive rock that indicates heating deep in the earth.
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Numerous granite dikes cut through the gneiss and through dark schist that was also metamorphosed at 1700 Ma
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The protolith (parent rock) of the schist was volcanic ash
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And the dikes are connected with 1700 Ma batholiths of granite
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Clicker Question #2 Given the gneiss and volcanic ash of the same age, what is the likely cause of the granite batholiths at 1700 Ma in Colorado? A. The granite was erupted at
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This note was uploaded on 05/01/2010 for the course GEOL 1020 taught by Professor Pranter during the Spring '07 term at Colorado.

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Day%2012-Early%20Proterozoic - Early Proterozoic Time The...

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