Untitled Document PDF - Geology

divergent = new plate Convergent = destroy plate Transform = slide by plate Earth surface is divided into13 lithospheric plates in motion Plates include lithospheric mantle (solid) crust (solid) Plates underlain by upper mantle (asthenosphere) (hot, plastic, convects) Three plate boundaries, diverge...

divergent = new plate Convergent = destroy plate Transform = slide by plate Earth surface is divided into13 lithospheric plates in motion Plates include lithospheric mantle (solid) crust (solid) Plates underlain by upper mantle (asthenosphere) (hot, plastic, convects) Three plate boundaries, divergent, convergent, transform. Mineral: a mineral is something forms naturally that is inorganic, chemical composition ( repetitive), crystal structure, homogenous solid Rock is something made up fo minerals There are 4000 minerals I need to know 25 of them Bone is not mineral (it is organic) Name igneous rocks Understand how mantle can melt Know Bowens reaction series Know the names of plutonic rock structures. Know the five types of volcanic structures Lava: flows, domes Pyroclastic: ash, cinder, bombs gasses:H2O, CO2, SO2 Each mineral has its own melting point How to melt mantle - Lower pressure (decompression melting) - Add volatile compounds (H2O,CO2)(dehydration melting) - Hot mantle plume (decompression) - The plate melting is very rare (oceanic plate) Intrusive igneous rocks have uniform large grain size because they cool slowly. Extrusive cools fast so small grain size You can name a rock knowing its minerals, texture, and chemical composition Minerals and crystalization temperatures High temperature: Olivene, Pyroxene, Ca-feldspar Intermediate temperature: Amphibole, Na-feldspar, biotite Low temperature: Biotite, Na-K feldspar, quartz. Vast majority of magma crystallize at depth 87% Plutonic igneous rocks are exposed due to erosion. Pluton: large massive intrusion Sills, and dyke: thin tabular intrusion Batholith: assemblage of plutons Dykes are about vertical (can be diagonal) Sills are horizontal Neck; solidified dyke within volcano Batholiths are granodiorite to granite in composition They represent eroded roots of subduction related volcanic complexes. Rift zone: Rift zones are areas where the volcano is rifting or splitting apart Subduction zone: Volcano types: - Shield volcano (fluid lavas, low slope) - Composite volcano (alternating layers of lava flow, and pyroclastic materials)(steep slopes, tall, snowcapped) they have explosive eruptions, pyroclastic flows, can surmount obstacles. Mudflows and avalanches are common as a result of these volcanoes. - Cinder cone: they are composed of basaltic pyroclasts (scoria) steep slopes, small size and a crater in the center. Has lava flow emitted from base. There are three basaltic lavas which are pahoehoe, A’a’ and pillow lavas Andesite lavas are more viscous, flow slower, and make thicker flows than basalt. Rhyolite lavas have a big obsidian flow Pyroclastic materials - Pumice or Scoria: lumps of frothy magma - Ash, dust: fine particles that leads to the change in climate - Bombs: ejected lava blobs. (they have aerodynamic shape) - Blocks: ejected solid pre-existing rock. Pumice is highly vesiculated magma, glassy, usually felsic. Scoria is vesicular basalt-not glassy forms cinder cones Pyroclastic flows are over 800 degrees celsius Mudflows can happen when eruptions melt snow, while it mixes with ash. If it is hot enough it is considered lahar Sediment Learning Outcomes Be able to understand how rocks are converted to sedimentary rocks by weathering, erosion, deposition, lithification. Know the difference between clastic and chemical sedimentary rocks. Know how clastic rocks named by clast size Understand sediment maturity: roundness, size, sorting, minerals present. Know sedimentary structures and relation to depositional setting Know environments where chemical sediments form: inorganic chert, limestone, evaporites, organic limestones. Erosion is in the form of wind and water. These transport the rock Deposition leads to sediment (river, lake, ocean) Lithification refers to the cementation and compaction There are two sedimentary rock types which are clastic and chemical. Clastic is the breakdown of rocks, transportation of particles, deposition, and lithification. Chemical refers to the precipitation of minerals from water. Then lithification. bedding(layering) Clastic sedimentary rocks - They are formed of particles - Most common minerals are quartz, feldspar, clay minerals - Named according to particle size Clastic rock names - Gravel: angular = breccia, rounded = conglomerate (these are a finer grained matrix) - SAND: sandstone (gritty in teeth), quartz sandstone, arkose (feldspar rich) - MUD; Shale or mudstone Clastic rock properties - Grain size - Roundness - Sorting - Mineral composition ( how tough it is a mineral) If they are close to their source they have a larger grain size, more angular clasts, and are poorly sorted. If they are far from source they have a smaller grain size, are more rounded clasts, and are better sorted Some minerals are more resistant to weathering than others The resistant minerals are quartz, and feldspar. The poorly resistant minerals are olivine, pyroxene, hornblende, micas. If a sediment is mature it is well sorted, fine-grained (sand or smaller), rounded, mostly quartz grains-far traveled If it is immature it is poorly sorted, coarse-grained, angular, very little quartz-deposited close to source. Immature Sediments that are deposited in layers are beds, and strata Chemical Sedimentary Rocks Material precipitated from water Inorganic: minerals crystallize from supersaturated water Organic: organisms extract compounds from seawater to form shell; when dies, sinks to bottom of ocean --> BIOCHEMICAL SEDIMENT Inorganic Types SiO2 --> chert, opal: MICROCRYSTALLINE - deposited in cavities in rocks --> geodes Colours: red-brown (jasper), grey (flint), banded (agate) CaCO3 and SiO2 Precipitates inorganically at hot springs: --> travertine (CaCO3) or sinter (SiO2) Cold water: stalactites and stalagmites (cave) Inorganic Types CaCO3 - limestone Also precipitates inorganically à layers around cores of sand grains - Requires warm, supersaturated, agitated marine environment - e.g., Bahamas - Called ooids Inorganic Types The Evaporites: precipitation due to evaporation of shallow lakes, inland seas Minerals precipitate in order of increasing solubility: 1) Ca, SO4 --> gypsum (least soluble) (CaSO4. H2O), anhydrite (CaSO4) 2) Na, Cl --> halite (NaCl) 3) K, Cl --> sylvite (KCl) (most soluble) Playa Lakes Desert environment: rain dissolves elements from rocks, washes down into valleys --> ephemeral lakes Water evaporates --> supersaturation of salts --> crystallization: salt flats Organic Types Ca, CO2 --> limestone (CaCO3) Most common chemical sediment Most are biochemical (fossils) coquina: predominantly fossils Coral reefs: preserved as limestone; oil reservoir rock SiO2 --> microfossils: chalk - plankton die, deposited on sea floor Metamorphism: Learning Outcomes Understand that metamorphism involves growth of new minerals and textural changes due to changes in temperature, pressure, and reaction with fluids Know the difference between contact vs. regional metamorphism, and metasomatism Understand the idea of grade of metamorphism Know what are foliated and non - foliated rocks and how they are named Know that high - P, low - T conditions are restricted to subducting plates Understand the concept of index minerals 3 Metamorphism: New Minerals, New Textures Recrystallization, growth of new minerals due to: Temperature Pressure Chemically active fluids (H2O, CO2) Metamorphism Types 1. Contact metamorphism: baking due to temperature increase (intruding pluton) 2. Regional metamorphism: increase in temperature and pressure due to burial 3. Metasomatism: fluids + rock --> new minerals Regional Metamorphic Grade Changes in minerals, texture termed degree or grade Low Grade: rock harder, more compact (interlocking crystals), minor increase in grain size Medium Grade: grain size increases, new mica crystals form Regional Metamorphic Grade High grade: grains recrystallize with preferred orientation - oriented perpendicular to stress - orientation = foliation Note: not all metamorphic rocks foliated: e.g., sandstone --> quartzite, grains only grow Metamorphic Rock Names Foliated, in order of increasing grade: Slate: planar cleavage, fine-grain Phyllite: cleavage, rock sheen Schist: large micas, platy look Gneiss: layered, often folded Migmatite: partially melted Metamorphic Rock Names Non-foliated: Quartzite: meta-sandstone Marble: meta-limestone Amphibolite: meta-basalt (medium-grade) Eclogite: meta-basalt (high-grade) Migmatite Partially melted: ribbons of quartz and K -feldspar (melt) in biotite and hornblende matrix - Looks a lot like gneiss, except melt ribbons crosscut the foliation - Quartz and K-feldspar euhedral, coarse -grain – IGNEOUS ROCK, not metamorphic Where Does Regional Metamorphism Occur? In continent-continent collisions, crust may be doubled in thickness Where Does Regional Metamorphism Occur? Cross -section through thickened crust shows higher grade of metamorphism at depth, lower grade closer to surface Metasomatic Rocks Interaction between hot fluids (H2O, CO2) and rocks a) Fluids released from cooling plutons b) Groundwater heated, circulated Fluids have dissolved ions (SiO2, metals) that react with rocks e.g., limestone --> skarn (brown zone above) basalt --> greenstone Porphyroblasts Large, generally euhedral crystals in metamorphic rocks that grew in the solid state