Quiz Question Do you expect that the earthquake in Hawaii was: –Tensionsal (pull-apart movement) –Compressional (push-together movement) –Shear (moving-past movement) Given the geologic setting of Hawaii, why do you expect this?
Where does continental crust come from?
Continental Crust
What defines a specific mineral? Crystal structure and Chemical Composition Mineral Name Quartz Corundum Diamond Graphite Chemical Composition SiO 2 Al 2 O 3 C Crystal structure Framework Silicate 3-D framework Sheets
The Silicate Minerals Basic Building Block Silicate ion: SiO 4 -4 One Si surrounded by 4 O in a tetrahedron. Can be combined in different ways: Isolated tetrahedra Chains Sheets 3-D Framework
Isolated Tetrahedra ChainsSheets
Framework Silicates In framework silicates, every O is shared with two Si tetrahedra: Quartz: SiO 2
Rocks, some context What is a rock? –A coherent, natural, aggregate of minerals (or glass) Types of rocks –Igneous - formed from melt –Sedimentary - formed by surface processes –Metamorphic - formed by transforming other rocks
Let there be… magma Where is magma formed? In the lithosphere –At subduction zones (addition of water) –At midocean ridges (decompression) –At rifts (decompression) –At hot spots (decompression) –In next to other magma (contact) Plate Boundaries
Decompression melting Solid material rises Pressure decreases Surface
Hot Spot Vulcanism
Addition of volatiles (water and CO 2 )
Contact Melting
Where are Igneous Rocks Formed?
Intrusive (Plutonic) vs. Extrusive (Volcanic) Rocks
What is a Metamorphic Rock Metamorphic rocks are formed by metamorphism of other rocks –Changes in physical, chemical, and mineralogical characteristics –In Solid State
Metamorphism What causes rocks to metamorphose? –Heat (different mineral stability, faster reactions) –Hot water (addition/removal of elements) –Confining Pressure (different mineral stability) –Directional forces due to deformation
Kinds of Metamorphism Contact Metamorphism with hot rocks
Kinds of Metamorphism Burial Metamorphism of Sediments (think isostacy! And then think geotherm!)
Kinds of Metamorphism Regional Metamorphism from mountain building
Where do Metamorphic Rocks Form?
Weathering The conversion of solid rock to smaller pieces or other (non-rock-forming) minerals Physical v. Chemical weathering (they work together!)
Physical weathering … the process whereby large rocks are broken into smaller rocks. Many different processes
Chemical Weathering Dissolution = dissolving salt in water Hydrolysis 2 KAlSi 3 O H 2 CO 3 + H 2 O Al 2 Si 2 O 5 (OH) 4 + 4SiO 2 + 2K + + 2HCO 3 - Oxidation (where does the Fe +2 come from?) 4 Fe O 2 2 (Fe +3 ) 2 O 3 The role of organisms
Transport (erosion) What transports sediments? –Water, primarily –Wind Why? –Ultimately, for water: gravity
Sedimentary Rocks Sediments: layers of loose particles that originate from the weathering of the continents (solid debris or dissolved substances) Sedimentary Rocks: Rocks formed from sediments by the process of lithification. Two types –Clastic Sediments –Chemical and Biochemical Sediments Requirements –Weathering –Erosion –Deposition –Lithification
Sedimentary Environments
Principal of Original Horizontality and the The Law of Superposition Sediments (and sedimentary rocks) record conditions on the (local) earth’s surface at the time they were formed.
1000 mya 600 mya mya 420 mya 370 mya 270 mya 180 mya