I. Chapter 9 - Chapter 9 The Seafloor Continents show...

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Chapter 9 The Seafloor Continents show considerable differences from the seafloor. Continental Crust Oceanic Crust Higher elevation Below sea level Thick (30-90 km) Thin (5-10 km) Less dense – can’t more dense – may be be subducted. subducted Composition: granitic, Composition: gabbro but many kinds of and basalt rocks. The Earth’s internal heat is responsible for this differentiation of the crust. Def’n: Outgassing – the release of volcanic gases into the atmosphere during a volcanic eruption. Oceanic Crust Composition Even before technology allowed exploration of the seafloor, geologists could infer the composition and structure by studying preserved slivers of oceanic crust and upper mantle that had been accreted to continents (ophiolites). An ideal ophiolite sequence consists of: Deep-sea sedimentary rocks Pillow lava and sheet lava flows (upper crust) Sheeted dike complexes (vertical basaltic dikes) Massive gabbro Layered gabbro Upper part of magma chamber Peridotite These inferences have been verified by sampling, drilling, and observation of the seafloor.
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Continental Margins The true geologic margin of a continent (where granitic continental crust changes to mafic oceanic crust) is below sea level. Def’n: Continental Margins – the area separating the part of a continent above sea level from the deep-seafloor. The Continental Margin is made up of: 1. Def’n: Continental Shelf – a gently sloping area between the shore and the more steeply dipping continental slope. 2. Def’n: Continental Slope – the relatively steep area between the shelf-slope break and either the more gently sloping continental rise or an oceanic trench. 3.
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I. Chapter 9 - Chapter 9 The Seafloor Continents show...

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