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INTRODUCTION TO PETROLOGY WHAT IS PETROLOGY??? WHAT IS PETROLOGY??? Study of rocks (“petros”) igneous & metamorphic chiefly in the lithosphere WHAT IS PETROLOGY??? Study of rocks (“petros”) igneous & metamorphic chiefly in the lithosphere We will be dealing with hot rocks tell us about composition & history of lithosphere origin of rocks involves: transfer of heat (energy) movement of material WHAT IS PETROLOGY??? Study of rocks (“petros”) igneous & metamorphic chiefly in the lithosphere We will be dealing with hot rocks tell us about composition & history of lithosphere origin of rocks involves: transfer of heat (energy) movement of material LITHOSPHERE THINK LIKE A PETROLOGIST what criteria do we use to distinguish rocks? what do we want to know? how do we answer these questions? WHAT DO WE WANT TO KNOW? how do we make melts? what is melted, and where? what is the role of water? how do melts behave during solidification? what causes metamorphism? how are metamorphism & deformation related? how to rocks flow in the interior of mountain belts? how do tectonic rates compare to heat conduction rates? in what tectonic settings do these rocks form? BASIS FOR UNDERSTANDING field methods & sample study (observation) theory, experiment & modeling (analytical) THINGS TO CONSIDER THINGS TO CONSIDER materials of earth THINGS TO CONSIDER materials of earth physical conditions energy pressure temperature & heat THINGS TO CONSIDER materials of earth physical conditions energy pressure temperature & heat relationship to tectonics THINGS TO CONSIDER materials of earth physical conditions energy pressure temperature & heat relationship to tectonics EgyPT Fe-rich Si-rich EARTH INTERIOR Fe-rich Structure of Earth: Si-rich EARTH INTERIOR Structure of Earth: Si-rich EARTH INTERIOR core, mantle & crust Fe-rich chemical divisions Structure of Earth: Si-rich EARTH INTERIOR core, mantle & crust mechanical divisions mesosphere, asthenosphere & lithosphere Fe-rich chemical divisions Fe-rich Si-rich EARTH INTERIOR Fe-rich Core: Si-rich EARTH INTERIOR Si-rich EARTH INTERIOR Core: Fe-Ni metallic alloy inner core is solid Fe-rich outer core is liquid (no S-waves) Si-rich EARTH INTERIOR Core: Fe-Ni metallic alloy inner core is solid differentiation at work! compositional separation within the planet (fractionation) Fe-rich outer core is liquid (no S-waves) Fe-rich Si-rich EARTH INTERIOR Fe-rich Mantle: Si-rich EARTH INTERIOR peridotite (ultramafic) greatest V, m & E (moves & carries heat) Fe-rich Mantle: Si-rich EARTH INTERIOR Mantle: peridotite (ultramafic) greatest V, m & E (moves & carries heat) Si-rich EARTH INTERIOR contains low velocity layer 60-220 km Fe-rich upper layer to 410 km (olivine to spinel) Mantle: peridotite (ultramafic) greatest V, m & E (moves & carries heat) Si-rich EARTH INTERIOR contains low velocity layer 60-220 km transition zone between 410-660 km (spinel to perovskite) SiIV to SiVI Fe-rich upper layer to 410 km (olivine to spinel) Mantle: peridotite (ultramafic) greatest V, m & E (moves & carries heat) Si-rich EARTH INTERIOR contains low velocity layer 60-220 km transition zone between 410-660 km (spinel to perovskite) SiIV to SiVI lower mantle has more gradual velocity increase Fe-rich upper layer to 410 km (olivine to spinel) Fe-rich Si-rich EARTH INTERIOR Fe-rich Crust: Si-rich EARTH INTERIOR mafic (magnesium + ferric) to felsic (feldspar + silica) rich in Si, Al, K, Na, Ca Fe-rich Crust: Si-rich EARTH INTERIOR mafic (magnesium + ferric) to felsic (feldspar + silica) rich in Si, Al, K, Na, Ca two main types: oceanic continental + “transitional” Fe-rich Crust: Si-rich EARTH INTERIOR EARTH INTERIOR EARTH INTERIOR Oceanic crust: EARTH INTERIOR Oceanic crust: thin: ~10 km on average EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments pillow basalt EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments pillow basalt sheeted dikes EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments pillow basalt sheeted dikes massive gabbro EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments pillow basalt sheeted dikes massive gabbro ultramafic rocks (mantle) EARTH INTERIOR Oceanic crust: thin: ~10 km on average dense: ρavg = 3.0 g/cm3 relatively uniform stratigraphy (= ophiolite suite) sediments pillow basalt sheeted dikes massive gabbro ultramafic rocks (mantle) mafic rocks CONTINENTAL OCEANIC EARTH INTERIOR EARTH INTERIOR Continental crust: thicker: 20-90 km (avg = 35 km) less dense: ρavg = 2.7 g/cm3 highly variable composition average = granodiorite CHEMICAL DIVISIONS CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process how do we know these things??? CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process how do we know these things??? seismic velocity structure CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process how do we know these things??? seismic velocity structure meteorites CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process how do we know these things??? seismic velocity structure meteorites xenoliths in volcanics CHEMICAL DIVISIONS divisions separate Earth into Si-rich and Fe-rich spheres, largely a result of early chemical differentiation based on a redistribution of matter, prior to major solidification, by density later, continued differentiation was (and is) mostly a result of melting and igneous process how do we know these things??? seismic velocity structure meteorites xenoliths in volcanics experimental petrology MECHANICAL DIVISIONS Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS Velocity structure (v) Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS Velocity structure (v) v increases with density (ρ) v = f (ρ) Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS Velocity structure (v) v increases with density (ρ) v = f (ρ) ρ dependent on physical properties & compositions ρ = f (X, T) Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS Velocity structure (v) v increases with density (ρ) v = f (ρ) ρ dependent on physical properties & compositions ρ = f (X, T) v increases with depth (z) — mostly! Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS Velocity structure (v) v increases with density (ρ) v = f (ρ) ρ dependent on physical properties & compositions ρ = f (X, T) v increases with depth (z) — mostly! v discontinuities indicate a change in material composition ± properties Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. MECHANICAL DIVISIONS composition property LVZ CMB OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ CMB OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? CMB OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? warmer? liquid? CMB OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? warmer? liquid? source of CMB? CMB OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? warmer? liquid? source of CMB? CMB change in composition OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? warmer? liquid? source of CMB? CMB change in composition source of OC-IC? OC-IC MECHANICAL DIVISIONS composition property Velocity boundaries LVZ source of LVZ? warmer? liquid? source of CMB? CMB change in composition source of OC-IC? phase change (S to L) OC-IC MECHANICAL DIVISIONS composition Velocity boundaries source of LVZ? warmer? liquid? source of CMB? property LVZ LET’S LOOK IN MORE DETAIL CMB change in composition source of OC-IC? phase change (S to L) OC-IC PETROLOGY & TECTONICS major mineral transformations occur at ~410 and ~660 km result from isochemical phase changes due to increased P marked by seismic velocity discontinuities Mineral Structure olivine tetrahedral spinel perovskite dense tetrahedral octahedral Depth Density low ~410 km ~660 km high VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE LO HI VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE LO HI LO HI VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE LO HI LO HI MG-SILICATES VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE LO LO . H SP O N HE T S A T.Z. HI H P S HI E R E O S E M MG-SILICATES VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE PETROLOGY & TECTONICS Resulting divisions lithosphere asthenosphere mesosphere PETROLOGY & TECTONICS Resulting divisions lithosphere asthenosphere mesosphere properties? PETROLOGY & TECTONICS Resulting divisions lithosphere asthenosphere mesosphere properties? connections? PETROLOGY & TECTONICS Resulting divisions lithosphere asthenosphere mesosphere properties? connections? is the mantle solid everywhere? MANTLE GEOTHERM MANTLE GEOTHERM compare continental, oceanic & ridge MANTLE GEOTHERM compare continental, oceanic & ridge typical continental geotherm = 25 °C/km MANTLE GEOTHERM compare continental, oceanic & ridge typical continental geotherm = 25 °C/km T @ 100 km = 1000 °C (enough to melt rocks!) MANTLE GEOTHERM compare continental, oceanic & ridge typical continental geotherm = 25 °C/km T @ 100 km = 1000 °C (enough to melt rocks!) are they molten? P too high? where? CAN MELTING OCCUR? compare geotherm to petrologic solidus for mantle rocks (peridotite) if “dry” conditions, no melting possible (geotherm below solidus) solid lherzolite is stable at T above geotherm CAN MELTING OCCUR? under “wet” conditions (with H2O or CO2), solidus shifts to lower T melting can occur where T > solidus low seismic velocities indicate partial melting between 100-250 km (the LVZ) the LVZ marks the base of “plates” formed by rigid lithosphere CAN MELTING OCCUR? under “wet” conditions (with H2O or CO2), solidus shifts to lower T melting can occur where T > solidus low seismic velocities indicate partial melting between 100-250 km (the LVZ) the LVZ marks the base of “plates” formed by rigid lithosphere LITHOSPHERE LITHOSPHERE LITHOSPHERE lithosphere includes crust + upper mantle LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) lowest densities (2.7-3.0 g/cm3) LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) lowest densities (2.7-3.0 g/cm3) slowest seismic velocities (6-8 km/sec) LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) lowest densities (2.7-3.0 g/cm3) slowest seismic velocities (6-8 km/sec) internal boundary is the Moho (density boundary) LITHOSPHERE lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) lowest densities (2.7-3.0 g/cm3) slowest seismic velocities (6-8 km/sec) internal boundary is the Moho (density boundary) base of lithosphere is the low-velocity zone (LVZ) LITHOSPHERE lithosphere = plate lithosphere includes crust + upper mantle can be oceanic, continental, or both typical lithosphere is 100 km (70-125 km) largely solid material (silicates) lowest densities (2.7-3.0 g/cm3) slowest seismic velocities (6-8 km/sec) internal boundary is the Moho (density boundary) base of lithosphere is the low-velocity zone (LVZ) EgyPT Physical conditions of Earth necessary to understand petrologic process: 1. pressure 2. temperature 3. energy & heat PRESSURE GRADIENT Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT P = ρgh Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT P = ρgh P increases with depth Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT P = ρgh P increases with depth Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT P = ρgh P increases with depth Mantle: nearly linear through mantle ~ 30 MPa/km ≈ 1 GPa at base of avg crust Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT P = ρgh P increases with depth Mantle: nearly linear through mantle ~ 30 MPa/km ≈ 1 GPa at base of avg crust slope (ΔP/Δz) depends on density (composition & compressibility) of material Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE GRADIENT H IG H Y IT S Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. N slope (ΔP/Δz) depends on density (composition & compressibility) of material DE ~ 30 MPa/km ≈ 1 GPa at base of avg crust Y SIT Mantle: nearly linear through mantle DEN P increases with depth LOW P = ρgh PRESSURE GRADIENT P = ρgh P increases with depth Core: ρ increases more rapidly since alloy is more dense smaller increase in P with depth suggests inner core is more uniform, solid, and has decreasing compressibility Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science. PRESSURE IN THE CRUST h ρgh PRESSURE IN THE CRUST in the crust, rocks “feel” a lithostatic pressure like a submarine feels hydrostatic pressure on its hull implies equal pressure in all directions when materials can flow h ρgh PRESSURE IN THE CRUST in the crust, rocks “feel” a lithostatic pressure like a submarine feels hydrostatic pressure on its hull implies equal pressure in all directions when materials can flow h for shallow rocks, can have differential pressure (where horizontal stress ≠ vertical stress), causing rocks to deform ρgh PRESSURE IN THE CRUST in the crust, rocks “feel” a lithostatic pressure like a submarine feels hydrostatic pressure on its hull implies equal pressure in all directions when materials can flow h for shallow rocks, can have differential pressure (where horizontal stress ≠ vertical stress), causing rocks to deform ρgh PRESSURE IN THE CRUST in the crust, rocks “feel” a lithostatic pressure like a submarine feels hydrostatic pressure on its hull implies equal pressure in all directions when materials can flow h for shallow rocks, can have differential pressure (where horizontal stress ≠ vertical stress), causing rocks to deform based on normal crustal densities, 1 kbar = 3.3 km ρgh ENERGY ENERGY Energy is the capacity to do work (subatomic, to mountain, to mantle scale) ENERGY Energy is the capacity to do work (subatomic, to mountain, to mantle scale) 1. kinetic energy: EK = 1/2mv2 • motion of a body ENERGY Energy is the capacity to do work (subatomic, to mountain, to mantle scale) 1. kinetic energy: EK = 1/2mv2 • motion of a body 2. potential energy: EP = mgz • energy of position; can be converted to Ek ENERGY Energy is the capacity to do work (subatomic, to mountain, to mantle scale) 1. kinetic energy: EK = 1/2mv2 • motion of a body 2. potential energy: EP = mgz • energy of position; can be converted to Ek 3. thermal energy: ET = EK + EP • motions & attractions in a body (subatomic and larger) • ET ≠ heat (transferred energy) HEAT SOURCES IN THE EARTH HEAT SOURCES IN THE EARTH 1. Heat from the early accretion and differentiation of the Earth • “original heat” of early core separation (PV work of compression) • still slowly reaching surface as geotherm decays HEAT SOURCES IN THE EARTH 1. Heat from the early accretion and differentiation of the Earth • “original heat” of early core separation (PV work of compression) • still slowly reaching surface as geotherm decays 2. Heat released by the radioactive breakdown of unstable nuclides • heat production (A) from decay of U, Th & K • mostly in crustal rocks HEAT SOURCES IN THE EARTH 1. Heat from the early accretion and differentiation of the Earth • “original heat” of early core separation (PV work of compression) • still slowly reaching surface as geotherm decays 2. Heat released by the radioactive breakdown of unstable nuclides • heat production (A) from decay of U, Th & K • mostly in crustal rocks 3. Latent heat associated with outer core crystallization • continues today! HEAT PRODUCTION Rock Abundance of radioactive element Heat produced (joules/kg/yr) U Th K A Granite 4 13 4 0.03 Basalt 0.5 2 1.5 0.005 Peridotite 0.02 0.06 0.02 0.0001 from Decker & Decker (1981) HEAT PRODUCTION Rock Abundance of radioactive element Heat produced (joules/kg/yr) U Th K A Granite 4 13 4 0.03 Basalt 0.5 2 1.5 0.005 0.02 0.06 0.02 0.0001 If more heat-producing elements in continental crust, why are T’s lower?? Peridotite from Decker & Decker (1981) HEAT PRODUCTION Crustal T’s are lower because of: 1. less of it compared to mantle 2. continental crust is a good insulator 3. it’s thicker 4. it suffers from surface cooling HEAT TRANSFER 1. radiation • conversion of IR energy from hot body; travels as a wave • efficient in a vacuum or transparent material; not efficient in rocks! HEAT TRANSFER 2. conduction • transfer of EK by vibration & contact, one molecule to another • does not occur in a vacuum • greatest transfer with greatest ΔT (thermal gradient) • conduction increases with increasing surface area • depends on thermal conductivity (k) of material, given by: q = kΔT/Δz HEAT TRANSFER 3. convection • movement of material with contrasting T, which changes density • gravity acts on Δρ, in which less dense material (ie, hotter) rises • movement of solid can occur in viscous mantle rocks, including rise of plumes HEAT TRANSFER 4. advection • heat “carried” by flowing liquids or viscous bodies (e.g., water, magma) to cooler surroundings LAVA FLOW MAGMA WHAT FORMS OF HEAT TRANSFER? GEOTHERMAL GRADIENT Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. GEOTHERMAL GRADIENT ΔT/Δz is the slope of T variation with depth Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. GEOTHERMAL GRADIENT ΔT/Δz is the slope of T variation with depth gradient drives conductive cooling toward the surface Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. GEOTHERMAL GRADIENT ΔT/Δz is the slope of T variation with depth gradient drives conductive cooling toward the surface why steeper curve at depth? Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. GEOTHERMAL GRADIENT ΔT/Δz is the slope of T variation with depth gradient drives conductive cooling toward the surface why steeper curve at depth? more heat production in crust Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. GEOTHERMAL GRADIENT ΔT/Δz is the slope of T variation with depth gradient drives conductive cooling toward the surface why steeper curve at depth? more heat production in crust more efficient convective mixing of heat in the mantle Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. IGNEOUS TECTONIC SETTINGS 1. mid-ocean ridge 5. back-arc basin 2. continental rift 6. oceanic hotspot 3. oceanic island arc 7. continental hotspot 4. continental-margin arc IGNEOUS TECTONIC SETTINGS 1. mid-ocean ridge 5. back-arc basin 2. continental rift 6. oceanic hotspot 3. oceanic island arc 7. continental hotspot 4. continental-margin arc WHAT’S MELTING? HOW? WHERE DOES IT GO? IGNEOUS ROCKS next week we’ll begin igneous rocks!