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Download Igneous, Metamorphic, and Sedimentary Rocks
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CEE 437 Lecture 11 Rock Classification Thomas Doe Translation of Mineral Properties to Rock Properties Comparison of mineral properties to rock properties Rocks have lower strength, especially tensile strength Anisotropy of minerals and heterogeneity of minerals Elasticity Thermal expansion Diversity of mineral orientation Creation of microcracks on mineral boundaries Minerals – Summing Up Most earth materials are minerals, that is, they are crystalline Mineral structures can lead to anisotropic properties Silicates are the dominant rock-forming minerals Sheet silicates are important for engineering – micas and clays Mineral heterogeneity and anisotropy leads to microcrack formation which greatly influences rock properties Sedimentary Rocks Clastics, Siliciclastics, and Evaporites Clastic rocks, depositional medium, and energy Diagenesis — chemical changes after deposition Sedimentary Rocks and Rock Properties Properties for a given geologic description vary wildly based on cementation, porosity and other diagenetic factors. Properties can be strongly anisotropic and heterogeneous based on bedding Clastic Sedimentary Rocks Clastic — broken like iconoclast) Often referred to as Siliciclastics as having Si based rock forming minerals Based on grain size and to a lesser extent composition Grain size related to energy of depositional environment Relationship of medium velocity to maximum grain size) Clastic Sedimentary Rocks Clay, muds → shales, mudstones, claystones (difference based on fissility) Silts → siltstones Sands → sandstones Gravels → Conglomerates (Breccia if angular, breccia may also be a term for tectonically fragmented rock) Weathering Cycle Clastic Sediments Lithification Cementation Crystallization deposition of a material different from clasts crystal growth on clasts to fill pore space Compaction Diagenesis Early post-depositional chemical transformation of sediments, e.g. calcite to dolomite Carbonates Generally like siliciclastics — carbonate muds, sands, etc. Often deposited in reefs Major portion of world oil deposits Properties depend strongly on post-depositional pore chemistry Cementation Dissolution Karst topography, cave formation Carbonate Environments Evaporites Rock salt (NaCl), Gypsum-Anhydrite (CaSO4), Sylvite (KCl) Deposition in regions where evaporation exceeds recharge desert lakes restricted seas (Mediterranean) lagoons, back-reef areas Subject to flow and diapirism Other Sedimentary Rocks Chert: finely crystalline silica as replacement/diagenetic nodules as bedded material from silica-shelled biota Coal Derived from vegetation Banded Iron Formation Likely bacteria derived, mainly Pre-Cambrian Igneous Origins Intrusive Batholithic or plutonic: phaneritic Dikes or sills that chill rapidly: aphanitic Extrusive deposition as melt (lava) pyroclastic tuff tephra pyroclastic flows Geologic Settings for Igneous Rocks Oceanic Hi Fe, Mg, Ca, low Si basalt, gabbro Continental Hi Si, Na, K granite, rhyolite, andesite Differentiation of Crustal Composition Weathering differentiating towards higher Silica Concentration of C, Ca, Na, K in sea and air Carbonate concentrated by organic processes Preferential melting of high-silica materials Original basaltic composition of crust Identifying Igneous Rocks Chemistry Acidic: Basic (more Si, less Si) Texture Aphanitic: crystals not visible Phaneritic: made of visible crystal components Porphyritic: Larger crustals in aphanitic or phaneritic ground mass Bowen’s Reaction Series Igneous Rock Classification Acidic, Felsic Basic, Mafic Ultramafic SERPENTINITE Extrusives Viscosity varies with Si and water content Basalt — low viscosity Rhyolite — high viscosity Rhyolite flows relatively unusual as rhyolite does not flow well Explosive Tuffs, pyroclastics Volcano Types Basaltic: low viscosity — Hawaii, Columbia Plateau Andesitic/Rhyolitic Structures of Basalt Flows Lava Tubes Flow Stratigraphy collonade entablature flow top breccia/scoria Hawaii Basalt Flows Basalt Flow Structures Eruptions of Acid-Rock Volcanoes Rhyolite Dome Mt. St. Helen’s Blast Zone Mt. Mazama Ash Distribution Basic Metamorphic Types Quartz Sandstone → Quartzite Limestone, Dolomite → Marble Shale → Slate — cleavage, no visible xl’s Phyllite — foliation, mica sheen but xl’s not visible Schist — clear foliation, visible mica Gneiss — like granite but with foliation/gneissosity Basalt → greenschist, amphibolite Non-foliated Metamorphic Rocks Sandstone —> Quartzite Limestone —> Marble Dolomite —> Dolomitic Marble Foliated Metamorphic Rocks Shale/Mudstone Slate Phyllite (Greek for leaves e.g. phyllo dough) Schist Gneiss Origin of Foliation (gneissosity, schistosity) Engineering Properties Anisotropy of strength and elastic properties Preferred failure on foliation Slate Phyllite Schist Gneiss Banded Gneiss Metamorphic Grade Subduction-Zone Metamorphism Metamorphism at Continental Collisions Contact Metamorphism
