Presentation on theme: "Part 1 Sedimentary Rocks Kyanite, Sillimanite, and Andalucite Lecture 6-7 Sedimentary and Metamorphic Rocks."— Presentation transcript:
Part 1 Sedimentary Rocks Kyanite, Sillimanite, and Andalucite Lecture 6-7 Sedimentary and Metamorphic Rocks
What is a sedimentary rock? What is a sedimentary rock? Sedimentary rocks result from mechanical and chemical weathering Comprise ~ 5% of Earth’s upper crust About 75% of rocks at surface Contain evidence of past environments Record how sediment is transported Often contain fossils
What is the economic importance of sedimentary rocks? They are important for economic reasons because they contain Coal Petroleum and natural gas Iron, aluminum, uranium and manganese Geologists use them to read Earth’s history
Cementation Precipitation of chemicals dissolved in water binds grains of a sediment together. After the cements solidify, compaction drives out the excess water. Important part of Lithification Remember where cements come from?
Types of sedimentary rocks Chemical rocks – sediment from ions that were once in solution Detrital rocks –sediment transported as solid particles
Detrital sedimentary rocks Detrital sedimentary rocks Constituents of detrital rocks can include Clay minerals Quartz Feldspars Micas Particle size is used to distinguish among the various types of detrital rocks
Detrital sedimentary rocks Detrital sedimentary rocks Mudrocks: less than.063 mm –1. Mud : small particles easily kept in suspension –Settles in quiet water –Includes Shale: mud-sized particles <.004 mm deposited in thin bedding layers called laminae Most common sedimentary rock 2. Larger mudrock grains called silts silt-sized particles.004-.063 mm Gritty grains can be felt
Detrital sedimentary rocks SandstoneSandstone –Made of sand-sized particles larger than.063 mm and less than 2mm –Forms in a variety of environments –Sorting, angularity and composition of grains can be used to interpret the rock’s history –Quartz is the predominant mineral (due to its durable nature)
Detrital sedimentary rocks Conglomerate and breccia –Both composed of particles > 2mm in diameter –Conglomerate consists largely of rounded clasts. Rounded pebbles in high velocity areas –Breccia is composed of large angular particles Breccia is made of shattered rock that accumulates at the base of a cliff
Energy Coarse sediments are deposited in high energy (fast water) environments such as under breaking waves at the beach, or in the beds of fast streams. Fine sediments are deposited in low energy environments, e.g. the slow water of deep lagoons, the abyssal plain, etc.
Chemical sedimentary rocks Precipitated material once in solution Precipitation of material occurs two ways: Inorganic processes: the minerals precipitate out of water Organic processes: animals and plants precipitate the minerals to use as shells or skeletons http://www.ucmp.berkeley.edu/collections/micro.html
Common chemical sedimentary rocks Limestone –Most abundant chemical rock –Made of the mineral calcite CaCO 3 –Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms) –Inorganic limestones include travertine (caves) and oolitic limestone (Bahamas)
Common chemical sedimentary rocks Evaporites –Evaporation triggers deposition of chemical precipitates –Examples include rock salt and rock gypsum http://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpg
Chemical Sediments: Coal Chemical Sediments: Coal
6_5 Particles are large and irregular, and consist of a variety of lithologies, including the least resistant. Particles are mid-sized and of intermediate sphericity, and include resistant and nonresistant lithologies. Particles are small and nearly spherical, and consist mainly of the most resistant lithologies, such as quartz. Character of detrital sediments depends on time, distance, and energy. For example, in streams: HIGHLANDS LOWLANDS NEAR-COASTAL Sedimentary environment determines roundness sorting, mineral diversity
6_6 Fine-grained sediment On floodplain Flood water Erosion of uppermost fine-grained sediment Older sediment 1Pre-flood Flood stage 2 Post-flood 3 Coarse-grained below Bedding plane Floods change the local conditions Waning flow Bounders on bottom, sands and muds suspended Graded bedding Fine-grained above
Sedimentary Facies Different sediments accumulate next to each other at same time Each unit (called a facies) possesses a distinctive characteristics reflecting the conditions in a particular environment The merging of adjacent facies tends to be a gradual transition
Nearshore sandsStillwater mudsAbyssal Ooze Some Facies in an oversimplified drawing
Cross Beds are ripples in cross section Irregularities lead to ripples, dunes, sand bars. In cross section these look like lines at an angle to the horizontal – “cross beds” Ripples can indicate direction of air or water flow if asymmetrical, a tidal environment if symmetrical. Size and shape indicate fluid velocity.
Cross bedding in Sand Dune deposits Sandstone deposited in ancient sand dunes Frosted Grains, well sorted Navaho Sandstone
Mud Cracks: clay layer shrinks during drying, curls upward; cracks fill next flood. Useful for right-side up
6_27 Continental shelf Continental slope Shallow marine Deep marine Submarine volcanoes Terms for Marine (i.e. Ocean) Environments and some characteristic sediment facies Abyssal Plain Define Graded Beds
Fossils are traces of prehistoric life generally preserved in sedimentary rock Fossils are traces of prehistoric life generally preserved in sedimentary rock
Dinosaur footprint in mudstone Dinosaur footprint in mudstone
Metamorphism Metamorphism … is the transformation of rock by high temperatures (heat) and pressure Metamorphic rocks are produced by transformation of: Sedimentary and Igneous rocks, and by the further alteration of other metamorphic rocks These are the source of many important minerals – Talc (lubricant, insulators, refractories), Corundum, Garnet (abrasives), Kyanite (ceramics), Micas (insulators), Chrysotile (“asbestos” for fireproofing), etc., etc.
0 km Sedimentary rock Metamorphic rock Igneous rock 50 km 10 km ~200ºC ~800ºC Increasing depth and temperature Melting Metamorphism Sedimentary rock Sediment Metamorphism occurs between about 10 and 50 km of depth Minerals do not melt during metamorphism
What causes metamorphism? 1. Heat Most important agent Heat drives recrystallization - creates new, stable minerals Increasing Heat with Depth
What causes metamorphism? 2. Pressure (stress) Increases with depth Pressure can be applied equally in all directions or differentially All Directions = “Confining Pressure” Differential = “Directed Pressure”
Origin of pressure in metamorphism Origin of pressure in metamorphism (Burial) (Convergent Margin)
Directed Pressure causes rocks to become folded, and minerals to reorient perpendicular to the stress: “foliation” Source: Kenneth Murray/Photo Researchers Inc.
Main factors affecting metamorphism Main factors affecting metamorphism 3. Parent rock Metamorphic rocks usually have the same chemical composition as the rock they were formed from. Different minerals, but made of the same atoms. Exception: water carries in new atoms and removes others. Important at MOR and in subduction zones.
Metamorphic Settings Metamorphic Settings Three types of metamorphic settings: Contact metamorphism – due heat from adjacent rocks Hydrothermal metamorphism – chemical alterations from hot, ion-rich water Regional metamorphism -- Occurs in the cores of mountain belts and subduction zones (Converging Margins). Makes great volumes of metamorphic rock. Includes: –Burial Metamorphism – e.g. Burial of sediments deeper than 10 km – non-foliated –Dynamothermal Metamorphism – Directed pressure in Plate Tectonic Processes - foliated
Contact metamorphism Produced mostly by local heat source
2. Hydrothermal Metamorphism Due circulation of water near Magma Important at mid-ocean ridge
Metamorphism in a Subduction Zone Near trench Deep Lithosphere Shallow Lithosphere
Metamorphic Grade and Index Minerals Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form
Note Quartz and Feldspar are not index minerals: Why? Some index minerals give us temperature info Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form Notice Quartz and Feldspars are useless
Some Useful as Thermometers and Pressure Gauges Polymorphs of Al 2 SiO 5 Kyanite Sillimanite Andalusite
7_21 CANADA NEW YORK CANADA U.S.A. Albany Boston Scranton Long Island Binghamton ATLANTIC OCEAN Unmetamorphosed Chlorite/muscovite zone Biotite zone Garnet zone Staurolite zone Sillimanite zone High grade Medium grade Low grade Augusta PENNSYLVANIA NEW HAMPSHIRE MAINE MASSACHUSETTS Concord Montpelier VERMONT CONNECTICUT NEW JERSEY R.I. Providence Hartford Newark Increasing pressure and temperature DIAGENESIS LOW GRADE Chlorite and muscovite Biotite Garnet Staurolite Sillimanite INTERMEDIATE GRADE HIGH GRADEMELTING New England Dynamothermal Metamorphism Mapped by index minerals r i f t v a l l e y
Common metamorphic rocks 1. Nonfoliated rocks Quartzite –Formed from a parent rock of quartz-rich sandstone –Quartz grains are fused together –Forms in intermediate T, P conditions
Common metamorphic rocks Nonfoliated rocks (cont.) Marble –Coarse, crystalline –Parent rock usually limestone –Composed of calcite crystals –Fabric can be random or oriented
Change in metamorphic grade with depth Increasing Directed Pressure and increasing Temps Metamorphism of a mudstone
A mica garnet schist A mica garnet schist Garnets are abrasives, long lasting bearings, and jewels Definition: Schist
Gneiss displays bands of light and dark minerals
Development of foliation due to directed pressure Development of foliation due to directed pressure GranodioriteGneiss
Migmatites- When Partial Melting Starts Heat the rock, when the minerals with the lowest melting points (Quartz, Feldspar) at that pressure melt, then recrystallize. We get separate regions of Metamorphic (dark, mafic) and Igneous (light, felsic) rock Part igneous, part metamorphic