M_W_Chapter_19-4_Precambrian_Tectonics_short_version

M_W_Chapter_19-4_Precambrian_Tectonics_short_version -...

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Precambrian Tectonics Archean Greenstone belts  (back-arc extensional basins?) Volcanics at base of the typical sequence, including mafic  and ultramafic lavas (basalts, komatiites) Sandstones, shales and cherts Low grade metamorphism (green chlorite) High grade metamorphics (roots of convergence zone  mountain belts) and ophiolites indicate sutures of  small continents to form larger ones Granite “seas” – crust being differentiated from  mantle Thin crust, small continents, small plates, hot earth  interior
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Precambrian Tectonics Proterozoic Continuation of Archean story of small  continents colliding and merging into fewer,  larger ones. Crust becoming thicker, Earth’s interior  cooler, not all the Proterozoic rocks have  experienced metamorphism Carbonates (limestones, dolomites) become  abundant) – extensive shallow seas on  continents Supercontinent (Rodinia) by about 1,000 Mya 
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Unformatted text preview: Rodinia Grenville metamorphic belt is one of the sutures formed during merging of smaller continents to make one big one. Rodinia included almost all the continents of the time, and was located near the equator Tropical weathering on Rodinia absorbed much of the atmospheres CO 2 , removing greenhouse gas, precipitating late Proterozoic glaciation Rodinia Break-up started about 750 Mya Ancestral Atlantic Ocean formed (called Iapetus) NW Scotland on American side of Iapetus, E Newfoundland on European side of the ocean Paleozoic Life recap latest Precambrian events : 1. Late Proterozoic glaciation (?snowball) was followed by . . . 2. Ediacaran Fauna soft-bodied animals, probably ancestors to jellyfish and sea anemones (Hydrozoa) Earliest shells ( Cloudina ) followed by major extinction before the Cambrian....
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M_W_Chapter_19-4_Precambrian_Tectonics_short_version -...

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