primary_rock_structures - Deformation and Brittle Fracture...

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37 Deformation and Brittle Fracture I. Primary Rock Structure A. Tectonic Control of Rock Structure 1. Lithospheric Plates a. plate = crust + upper mantle above asthenosphere (1) Layered Crust (a) oceanic crust = i) volcanic/"basalt" ii) oceanic sediments (b) continental crust i) crystalline/"granite" ii) sedimentary cover a) marine sediments b) continental sediments (c) depth of crust: 5-10 km b. plate motion response to internal heat flux (1) internal heat source: radioactive decay (2) plate motion = rock motion = "geologic work" (a) work = (force)(displacement) (b) plate motion = force applied to rocks B. Primary Rock Structure/Architecture 1. Primary Structure/Architecture: a. geometries formed at the time of rock origin (1) deposition or crystallization b. Secondary Structure (1) geometries imparted by strain in response to stress applied after the rock forms 2. Rock Layering (1) Tendency for layered stratification in volcanic and sedimentary environments (2) Layered Plutonic Rocks (a) magmatic differentiation processes (b) diapiric intrusives (3) Deposition under force of gravity = (a) "blanket deposits" (b) ~parallel to horizontal 3. Examples of Primary Rock Structure a. Stratified bedding (volcanic or sedimentary) (1) beds = layers > 1 cm (2) laminae = layers < 1 cm b. bedding contacts = breaks or discontinuities in depositional
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38 process (1) Textural and compositional discontinuities (2) stratigraphy = study of time with respect to the rock record c. Unconformities = significant bedding contacts (1) = break or gap in rock-stratigraphic record (a) erosional truncation or removal (b) periods of non-deposition d. Internal stratification
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primary_rock_structures - Deformation and Brittle Fracture...

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