Rodinia, Rifting, Iapetus and the Great American Bank

General Structure of Continents Shields – old, tectonically stable foundation of continent Cratons – parts of shield with thin cover of sedimentary rocks Passive Margins – continental shelves, mid-plate Convergent Margins – zones of subduction and collision at edge of plate

Precambrian Shield Predominantly crystalline (granite & gneiss) Divided into “Provinces” by age and structureal “grain” Provinces represent the roots of long gone mountains Each Province produced during a specific Orogeny Narrow greenstone belts Commonly between provinces Metamorphosed mafic volcanics Ophiolites Immature sedimentary rocks Remnants of subducted oceanic lithosphere

The Grenville Province Last Precambrian Orogeny in North America 1.2-0.9 Ga Regional metamorphism from Maritime Canada to Georgia Last event in the assembly of the supercontinent Rodinia

Grenville Gneiss

Assembling Rodinia: the Grenville Orogeny

Rodinia – a supercontinent 700 Ma before Pangea

Potsdam (C) – Grenville (Pre-C) Nonconformity in New York

Precambrian – Cambrian Nonconformity - Colorado

Precambrian – Cambrian Nonconformity – Grand Canyon, AZ

Precambrian – Cambrian Nonconformity Widespread across North America Extensive erosion of shield and Grenville Orogen (Mountains) Worldwide Transgression in Latest Precambrian into Cambrian Similar pattern on other continents Post-unconformity rocks are Quartz Arenites and Limestones Typical cratonic association

Rifting Rodinia – Opening the Iapetus Ocean, Birth of the Great American Bank

Great American Bank Opening of Iapetus Ocean Creates passive margin Thermal subsidence produces accommodation space Thousands of meters of quartz arenites and limestones/dolomites deposited in shallow water Stromatolites, Mudcracks, Intraclasts Exposed in Cumberland/Great Valley and Shenandoah Valley Sequence is thinner in New York more inboard position – less subsidence

Wading in Iapetus - Stromatolites

Wading in Iapetus – Quartz Arenites, Limestones, Burrows & Ripples

Great American Bank Carbonates – Mohawk Valley, New York