Geology 101 Outline of Last Lecture Divergent Plate Boundaries Convergent Plate Boundaries Transform Plate Boundaries Plate Boundaries along West Coast Testing the Plate Tectonics Model Outline of Current Lecture Measuring Plate Motion What Drives Plate Motions Importance of Plate Tectonics Animation of Hotspot and Volcanic Tracks Minerals Building Blocks Atoms Building Blocks of Minerals Chemical Bonds Isotopes and Radioactive Decay Formation of Minerals Measuring Plate Motion o Measuring Plate Velocities from space Various methods used GPS Global Positioning System What Drives Plate Motions o Plate Mantle Convection Convective flow in the mantle is considered as the basic driving force of plate tectonics o Forces that drive plate motion Slab pull Major Resulting from sinking of a cold dense slab of lithosphere Main cause of motion Ridge Push Gravity driven force that results from elevated position of the ridge Works with slab pull Mantle drag Enhances plate motion when the velocity of the asthenosphere exceeds that of the plate Resists subduction If slower delays plate motion Friction resistance Between the overriding plate and subducing slab Geology 101 Prevents sliding between two plates Earthquakes resistance is overcome by the stress o Models of Mantle convection Layering at 660 km Chemically distinct magma sources as hot sports vs MOR Whole mantel convection Seismic waves suggest subducting slabs penetrate the 660 km boundary at least some More popular model Importance of Plate Tectonics o The theory provides explanations Earth s major surface processes Distribution of earthquakes and volcanoes and mountains Distribution of ancient organisms and mineral deposits Animation of Hotspots and Volcanic tracks o Areas of intense of heat that cannot be explained by plate boundaries o Made by magma o Volcanoes form impinge between plate o New volcanoes appear as it moves away once the hot spot has moved away it becomes inactive What is the age of the oldest sediments recovered by Deep Ocean drilling o 180 Million Assuming hot spots remained fixed in what direction was the Pacific plate moving while the Hawaiian Islands were forming o Northwest Which is the most important force in driving plate motion o Slab pull Minerals Building Blocks o Geologically a mineral is defined as Naturally occurring An inorganic solid Orderly crystalline structure Definite chemical composition o Rock Solid aggregate of minerals Can be more than one type of mineral Implies that the minerals are found together as mixture in which the properties of the individual minerals are retained Animation Matter and Minerals o Crust source of variety of minerals o Talc makeup Gold is a mineral o Yes Synthetic diamonds are minerals Geology 101 o No Minerals most be solid o True Quartz is considered a mineral o Yes Petroleum is a mineral o False Animal bone is a mineral o False Ice is a mineral o True Granite is a mineral o False Steel is a mineral o False Atoms building blocks of minerals o Elements A group of same kind of atoms atomic number of protons 90 naturally occurring o Atoms Central region is called the nucleus Protons and Neutrons no charge o mass Electrons Surround the nucleus o Volume Chemical Bonds o Bound because of octet rule Atoms tend to lose gain share electrons until they are surrounded by 8 valence electrons o Chemical bonding Formation of a compound by combining two or more atoms o Ionic bonding Atoms gain or lose outermost electrons to form ions Halite example o Na is positively charged and Cl is negatively charged Ionic compounds consist of an orderly arrangement of oppositely charged ions Attraction of oppositely charged ions o Covalent bond Atoms share electrons H2 Generally stronger than ionic bonds o Metallic bond Valence electrons are free to migrate among the atoms o Hybrid bond Geology 101 Combination of above Two or three Isotopes and Radioactive Decay o Mass number protons neutrons o Isotopes are atoms of the same elements but different mass numbers Different number of neutrons o Unstable isotopes emit particles and energy in a process known as radioactive decay Carbon 12 13 14 Chemically identical Formation of Minerals o Crystallization Atoms ions chemically bond to dorm an orderly internal structure Precipitation from saturated solutions o Grow from aqueous solution containing dissolved material matter Drop in temperature Water lost through evaporation o Halite Cooling of liquids o Magma Igneous rocks Biological processes o Deposition o Limestone Growth of a mineral Growth starts from a central seed crystal Growth expands outward as atoms accumulate filling available space Resulting crystal shape governed by surrounding o Grow without interference open space Euhedral o Grow with interference grown in confined space Anhedral Without well formed crystal faces Atoms in mineral are specifically order A solid with disordered atoms is called a glass Geology 101