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Igneous Rocks and Relative Time Homework 2: Due Wednesday

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Homework 2: EESC 2200 Due Wednesday The Solid Earth System Igneous Rocks And Relative Time 24 Sep 08 Continental Tectonics Relative Frequency of Rock Types A. Crust B. Surface Magma chemistry Two main classes mafic magmas + rocks ma - fic magnesium + iron (Ferrous) rich ES101--Lect 8 OR: felsic magmas + rocks fel - sic Feldspar and silica rich ES101--Lect 8 felsic ->intermediate-> mafic light dark large ions small ions (K, Na) (Mg, Fe) more Si (>60%) less Si (£ 50%) ES101--Lect 8 felsic ->intermediate-> mafic light dark large cations small cations (K, Na) (Mg, Fe) more Si (>60%) less Si (£ 50%) cooler magmas hotter magmas light minerals dense minerals which more explosive? minerals? ES101--Lect 8 Ultra- Felsic Intermediate Mafic mafic Quartz KSpar PlagSpar Micas Amph. Pyroxene Olivine ES101--Lect 8 Ultra- Felsic Intermediate Mafic mafic Diorite Perid- Granite Gabbro otite Quartz KSpar PlagSpar Micas Amph. Pyroxene Olivine ES101--Lect 8 Granite Diorite Gabbro felsic mafic ES101--Lect 8 Felsic Intermediate Mafic Granite Diorite Gabbro coarse Rhyolite Andesite Basalt fine rock slides ES101--Lect 8 Gabbro (coarse) Basalt (fine) Mafic Igneous Rocks Diorite (coarse) Andesite (fine) Intermediate Igneous Rocks Granite (coarse) Rhyolite (fine) Felsic Igneous Rocks Classifying igneous rocks by composition and texture Ridges: Mantle undergoes decompression melting --->>> Basalts (dry) 1300°C basalt = mantle melt ("blood of the Earth") ES101-Lect9 Mantle Melting Temperature 1100 °C 1300°C All Partial Liq Melting Depth All Solid Lower Pressure!! ES101-Lect9 water --> mantle wedge, --> basalt arc volcanism... ES101-Lect9 H2O -- Lowers Melting Point 800˚C 1100˚C T Depth Wet melting you are here ES101-Lect9 basaltic melts -> andesite melts basaltic andesitic magma magma Olivine Olivine+ Pyroxene cooling + Ca-f'spar ES101-Lect9 Mt. St. Helens Crust wet felsic magma H2O Mantle H O basalt 2 magma ES101-Lect9 Volcanic/Extrusive Rocks cool fast, fine-grained ES101--Lect 8 magma also cools under ground...... ES101--Lect 8 Plutonic/Intrusive Rocks cool slowly, coarse-grained ES101--Lect 8 ES101--Lect 8 ES101--Lect 8 Dike ES101--LectStephen Marshak 8 ES101--LectPaul Hoffmann 8 Geochronology Outline: 1) Relative ages 2. Absolute Radiometric Ages Geologic Time Principles of Geochronology How do we determine age in the geological record? Go out to the field. Observations yield relative age. RelativeRelative AgesAges Logical tools are useful for defining relative age. Principle of uniformitarianism. Principle of superposition. Principle of original horizontality. Principle of original continuity. Principle of cross-cutting relationships. Principle of inclusions. Principle of baked contacts. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? GeologicGeologic TimeTime Uniformitarianism – The present is key to the past. Physical processes that we observe today operated in the same way in the geological past. Modern processes help us understand ancient events in the rock record. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? Law of Superposition Each layer of rock is older than the layer above it and younger than the rock layer below it. Nicolaus Steno, a Danish anatomist, geologist, and priest (1636 - 1686) RelativeRelative AgeAge Horizontality and continuity. Strata often form laterally extensive horizontal sheets. Subsequent erosion dissects once-continuous layers. Flat-lying rock layers are unlikely to have been disturbed. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? Law of Cross-cutting Relationships A fault or dike that cuts through another body of rock must be younger than the rock it cuts Scotsman James Hutton (1726-1797) Law of Inclusions If a rock body (Rock B) contains fragments of another rock body (Rock A), it must be younger than the fragments of rock it contains. James Hutton RelativeRelative AgeAge Baked contacts. Thermal metamorphism occurs when country rock is invaded by a plutonic igneous intrusion. The baked rock must have been there first (it is older). Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? Law of Faunal Successions Fossils in rock layers appeared in a predictable sequence, within a discrete period of time. William Smith UnconformitiesUnconformities An unconformity is a time gap in the rock record. Nondeposition. Erosion. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? RelativeRelative AgeAge Determining relative ages empowers geologists to easily unravel complicated geologic histories. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? James Hutton (1726-1797) “... we find no vestige of a beginning,–no prospect of an end.” Images of Siccar point outcrop from http://www.wwnorton.com/college/geo/ earth2/content/index/animations.asp 1801 Winchester, S., 2001, The map that changed the world: William Smith and the birth of modern geology, HarperCollins. INTERNATIONAL STRATIGRAPHIC CHART ICS International Commission on Stratigraphy Ma Ma Ma Ma Era Era Era Era Eon Age Age Eon Age Age Eon Age Age Eon Age Stage Stage Stage GSSP GSSP GSSP GSSP GSSA Series Series Series Epoch Epoch Epoch Period Period Period Period System System System System Erathem Erathem Erathem Erathem Eonothem Eonothem 145.5 ±4.0 Eonothem 359.2 ±2.5 Eonothem 542 Holocene Tithonian Famennian Ediacaran 0.0118 150.8 ±4.0 Upper 374.5 ±2.6 Neo- ~630 Upper Upper Kimmeridgian Frasnian Cryogenian 0.126 155.7 ±4.0 385.3 ±2.6 proterozoic 850 Pleistocene Middle Oxfordian Givetian Tonian 0.781 161.2 ±4.0 Middle 391.8 ±2.7 1000 Lower Callovian Eifelian Stenian 164.7 ±4.0 Quaternary * 1.806 397.5 ±2.7 Meso- 1200 Gelasian Bathonian Emsian Ectasian proterozoic 2.588 Middle 167.7 ±3.5 Devonian 407.0 ±2.8 1400 Pliocene Piacenzian Bajocian Lower Pragian Calymmian 3.600 171.6 ±3.0 411.2 ±2.8 1600 Zanclean Aalenian Lochkovian Statherian Jurassic 5.332 175.6 ±2.0 416.0 ±2.8 Proterozoic 1800 Messinian Toarcian Pridoli Paleo- Orosirian 7.246 183.0 ±1.5 418.7 ±2.7 2050 Neogene Tortonian Pliensbachian Ludfordian proterozoic Rhyacian 11.608 Lower 189.6 ±1.5 Ludlow 421.3 ±2.6 2300 Serravallian Sinemurian Gorstian Siderian Miocene 13.65 196.5 ±1.0 422.9 ±2.5 2500 Langhian Hettangian Homerian 15.97 199.6 ±0.6 Wenlock 426.2 ±2.4 Neoarchean Burdigalian M e s o z i c Rhaetian Sheinwoodian 20.43 203.6 ±1.5 428.2 ±2.3 r e c a m b i n 2800 Silurian Aquitanian Upper Norian Telychian P 23.03 216.5 ±2.0 436.0 ±1.9 Mesoarchean C e n o z i c Chattian Carnian Llandovery Aeronian Oligocene 28.4 ±0.1 228.0 ±2.0 439.0 ±1.8 3200 Rupelian Ladinian Rhuddanian 33.9 ±0.1 Middle 237.0 ±2.0 443.7 ±1.5 Paleoarchean riassic Priabonian Anisian Archean T Hirnantian 37.2 ±0.1 245.0 ±1.5 445.6 ±1.5 3600 Bartonian Olenekian Upper Stage 6 Eocene 40.4 ±0.2 Lower 249.7 ±0.7 455.8 ±1.6 Eoarchean Lower limit is Lutetian Induan Stage 5 not defined 48.6 ±0.2 251.0 ±0.4 a l e o z i c 460.9 ±1.6 P h a n e r o z i c h a n e r o z i c Ypresian Changhsingian h a n e r o z i c Darriwilian 55.8 ±0.2 468.1 ±1.6 P P Lopingian 253.8 ±0.7 P Middle Paleogene Thanetian Wuchiapingian Stage 3 Subdivisions of the global geologic record are 58.7 ±0.2 260.4 ±0.7 471.8 ±1.6 formally defined by their lower boundary. Each unit Paleocene Selandian Capitanian Ordovician Stage 2 of the Phanerozoic (~542 Ma to Present) and the 61.7 ±0.2 265.8 ±0.7 Lower 478.6 ±1.7 base of Ediacaran are defined by a basal Global Danian Guadalupian Wordian Tremadocian Standard Section and Point (GSSP ), whereas 65.5 ±0.3 268.0 ±0.7 488.3 ±1.7 Maastrichtian Roadian Stage 10 Precambrian units are formally subdivided by 70.6 ±0.6 270.6 ±0.7 ~ 492.0 * absolute age (Global Standard Stratigraphic Age, Campanian Kungurian Furongian Stage 9 GSSA). Details of each GSSP are posted on the 83.5 ±0.7 Permian 275.6 ±0.7 ~ 496.0 * ICS website (www.stratigraphy.org). Santonian Artinskian Paibian International chronostratigraphic units, rank, Upper 85.8 ±0.7 Cisuralian 284.4 ±0.7 501.0 ± 2.0 Coniacian Sakmarian Stage 7 names and formal status are approved by the 89.3 ±1.0 294.6 ±0.8 ~ 503.0 * International Commission on Stratigraphy (ICS) Turonian Asselian Series 3 Stage 6 and ratified by the International Union of Geological 93.5 ±0.8 299.0 ±0.8 ~ 506.5 * Sciences (IUGS). Cenomanian Gzhelian Stage 5 Numerical ages of the unit boundaries in the 99.6 ±0.9 a l e o z i c Upper 303.9 ±0.9 ~ 510.0 * P Albian Kasimovian Cambrian Stage 4 Phanerozoic are subject to revision. Some stages 112.0 ±1.0 306.5 ±1.0 Series 2 ~ 517.0 * within the Ordovician and Cambrian will be formally Aptian Penn- Middle Moscovian Stage 3 named upon international agreement on their GSSP Cretaceous 125.0 ±1.0 sylvanian 311.7 ±1.1 ~ 521.0 * M e s o z i c limits. Most sub-Series boundaries (e.g., Middle Barremian Lower Bashkirian Stage 2 Lower 130.0 ±1.5 318.1 ±1.3 Series 1 ~ 534.6 * and Upper Aptian) are not formally defined.
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