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Igneous Environments lecture 2a Intrusive vs. Extrusive • Melt that exists below the surface is called _______ and rocks formed by this process are ______ (pushed) into preexisting rocks and referred to as _________ _______ • Melt that is erupted on the surface is called _____ and rocks formed by this process are ________ (pushed) onto the surface and referred to as __________ ______ ERSC 3P21 Brock University Greg Finn 2005 Intrusive Environments • Rising magma moves through preexisting rock and crystallizes at depth - Intrusive igneous rocks • Rocks formed in this type of setting are termed __________ – from Greek Plouton - god of the underworld • Results are observed at the surface due to ___________ ERSC 3P21 Brock University Greg Finn 2005 Intrusive Environments • Preexisting rocks are referred to as _______ rock or _______ rock • The contact between the two is an ________ contact • Chunks of country rock can be incorporated into the magma forming _____________ ERSC 3P21 Brock University Greg Finn 2005 1 Igneous Environments lecture 2a Intrusive Environments • The hot magma comes in contact with colder country rock • country rock is _______ and may be ______ along the contact • magma cools quickly along contact and ________ remainder of intrusion to allow for ________ cooling COLD HOT From: Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 ERSC 3P21 Brock University Greg Finn 2005 ERSC 3P21 Brock University Greg Finn 2005 2 Igneous Environments lecture 2a Intrusive Environments From: Marshak 2001 Rising magma ( _________ - upward excavation) into country rock creates the magma chamber Country rock is ______ and ________ by the magma, with unmelted blocks forming xenoliths within the magma ERSC 3P21 Brock University Greg Finn 2005 Types of Intrusives • Distinguished by shapes • Tabular intrusions – generally ________ features with _______ sides, extending over ______ to ____’s of km, of uniform thickness ranging from mm to 100’s of metres • _________ intrusions are termed dykes • _________ intrusions are termed sills ERSC 3P21 Brock University Greg Finn 2005 DYKE From: Marshak 2001 SILL ERSC 3P21 Brock University Greg Finn 2005 3 Igneous Environments lecture 2a From: Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 ERSC 3P21 Brock University GregHoffmann Finn 2005 Paul Types of Intrusives • Where a sill is domed upwards a blisterlike intrusion results - a ___________ • _______ are ______ shaped intrusions ranging in size from from 10’s of m to 10’s of km across • Intrusion of numerous plutons in one area creates a composite body - a ____________ – 100’s of km long X 10’s to 100’s of km wide ERSC 3P21 Brock University Greg Finn 2005 4 Igneous Environments lecture 2a Sierra Nevada Batholith ERSC 3P21 Brock University Greg Finn 2005 Mount Whitney Crest, SN Batholith ERSC 3P21 Brock University Greg Finn 2005 Types of Intrusives • Intrusive igneous rocks form _________ the Earth’s surface • We can observe them at present as they are brought to the surface over long periods of geologic time through: • • • ERSC 3P21 Brock University Greg Finn 2005 5 Igneous Environments lecture 2a Intrusive Environments Ash Lava Flow Sill Dyke Magma Chamber Laccolith From: Marshak 2001 At an active volcano a magma chamber is present in the subsurface and serves as the source of magma that forms dykes, sills, laccoliths below ground, and lava and ash above ground. ERSC 3P21 Brock University Greg Finn 2005 Intrusive Environments From: Marshak 2001 As a result of crystallization, the magma chamber becomes a pluton. The softer portions of the volcano erode, leaving wall-like dykes and resistant lava plateaus. ERSC 3P21 Brock University Greg Finn 2005 Intrusive Environments From: Marshak 2001 As weathering and erosion continue the volcanic rocks and shallow intrusions are removed and plutonic rocks are exposed. ERSC 3P21 Brock University Greg Finn 2005 6 Igneous Environments lecture 2a From: Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 Intrusive vs. Extrusive • Melt that exists below the surface is called magma and rocks formed by this process are intruded (pushed) into preexisting rocks and referred to as Intrusive Rocks • Melt that is erupted on the surface is called lava and rocks formed by this process are extruded (pushed) onto the surface and referred to as Extrusive Rocks ERSC 3P21 Brock University Greg Finn 2005 Extrusive Environments • Not all volcanic eruptions are the same so not all extrusive rocks are the same • Volcanoes may erupt: – __________________________________ __________________________________ __________________________________; – __________________________________ _______________________________; – _______________________________. ERSC 3P21 Brock University Greg Finn 2005 7 Igneous Environments lecture 2a Volcanic Eruptions • Volcanic eruptions transfer material form the Earth’s interior to its surface • Material erupted falls into three categories: – ______________ • sheets or mounds that flow onto the surface or sea floor and then solidify – _______________ • fragmented material thrown out of a volcanic vent and lands on the ground surface or sea floor as a solid – _______________ • elements or compounds that bubble out of the lava ERSC 3P21 Brock University Greg Finn 2005 Extrusive Environments ERSC 3P21 Brock University Greg Finn 2005 Lava and Lava Flows • Lava displays a variety of compositions, and are described using the range of SiO2 content – ________ lavas • high SiO2, rhyolite – ____________ lavas • andesite – __________ lavas • low SiO2, basalt • All are __________, SiO2-rich are glassier than SiO2-poor, ERSC 3P21 Brock University Greg Finn 2005 8 Igneous Environments lecture 2a Lava and Lava Flows • Viscosity (__________________) is dependent on _____________ and _____________: • _______ the SiO2, the _____ the viscosity so the ________ the ease with which it will flow • ______ a lava, the _______ the viscosity • More gas-rich a magma the _____ the viscosity • Volcanic rock formed by extrusion is a Lava Flow, and the ________ of the resulting flow reflects the ______ of the lava ERSC 3P21 Brock University Greg Finn 2005 Increasing Viscosity Lava and Lava Flows Basaltic Flow Andesitic Flow Rhyolitic Dome From: Marshak 2001 Rhyolitic Spire ERSC 3P21 Brock University Greg Finn 2005 Basaltic Lava Flows • Due to ___ viscosity, capable of flowing great distances 10s to 100s of km From: Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 9 Igneous Environments lecture 2a Basaltic Lava Flows • Surface textures of flow reflects the timing of __________ relative to ____________ From: Marshak 2001 From: Marshak 2001 Pahoehoe (ropey) Aa (blocky) ERSC 3P21 Brock University Greg Finn 2005 Basaltic Lava Flows • After the surface of the flow cools, the interior remains molten and continues to move downslope, draining out and leaving a ______ _______ From: Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 Basaltic Lava Flows From: Marshak 2001 During the final stages of cooling the interior of the lava flow contracts and fractures into roughly hexagonal columns resulting in __________ __________ ERSC 3P21 Brock University Greg Finn 2005 10 Igneous Environments lecture 2a Basaltic Lava Flows From: Marshak 2001 Copyright Peter Kresan Basaltic lava extruded under water cools much quicker than on land and has a distinctive _______ shape Copyright Greg Finn ERSC 3P21 Brock University Greg Finn 2005 Andesitic Lava Flows • Due to ______ SiO2 content and _____ viscosity andesitic lava does not ___ as easily as basaltic lava • Andesitic lava moves 1-5 m/day and rarely reaches lengths of 10 km • Due to slow movement the outer surface _________ while the interior continues to _____ causing the surface to break into angular blocks ERSC 3P21 Brock University Greg Finn 2005 Andesitic Lava Flows • Andesitic volcanic cones have _______ slopes than basaltic cones From: Marshak 2001 Andesitic Flow Copyright Greg Finn ERSC 3P21 Brock University Greg Finn 2005 11 Igneous Environments lecture 2a Rhyolitic Lava Flows • Rhyolite lava is the most ______ due to its _____ SiO2 content and _____ overall temperature • Does not flow easily, tends to form a _____ or _____ over the vent Rhyolitic Dome From: Marshak 2001 Rhyolitic Spire ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Lava dome in crater 1984 ERSC 3P21 Brock University Greg Finn 2005 Pyroclastic Debris • Fragmental material _______ at a volcanic vent • Come in a variety of sizes • On a global scale has the largest impact on the planet ERSC 3P21 Brock University Greg Finn 2005 12 Igneous Environments lecture 2a Pyroclastic Debris Wind Direction Stratospheric Haze Rising Column Falling Lapilli Collapsing Column Nuée Ardente • Coarse material falls _______ the vent • Finer material falls ________ from the vent ERSC 3P21 Brock University Greg Finn 2005 Pyroclastic Debris • ______ • powder size • _______________ • marble to plum sized • __________ • basketball to fridge sized • ________ • streamlined blocks ERSC 3P21 Brock University Greg Finn 2005 Pyroclastic Debris • During eruptions lava fountains into the air and freezes into glassy rock before falling to the ground ERSC 3P21 Brock University Greg Finn 2005 13 Igneous Environments lecture 2a Pyroclastic Debris • Basaltic droplets form glassy beads termed Pelé’s tears after the Hawaiian goddess of ____________ • An accumulation of blocks is termed a volcanic _____________ • Andesitic and rhyolitic eruptions eject ________ - sponge like volcanic glass filled with air bubbles ERSC 3P21 Brock University Greg Finn 2005 Pyroclastic Debris Pelé’s Tears Lapilli From: Stromboli on-line Copyright J. Alean Copyright J.Aabech Pumice Volcanic Agglomerate ERSC 3P21 Brock University Greg Finn 2005 Pyroclastic Debris • Unconsolidated pyroclastic material is termed _______ • Cemented pyroclastic material is termed ________ • Ash that falls gently from the air is termed an ________________ • Where ash mixes with air it forms a fast moving _______________ (nuée ardente) ERSC 3P21 Brock University Greg Finn 2005 14 Igneous Environments lecture 2a Mount St. Helens Pyroclastic flow moving from crater at right to valley floor travelling at 60 mph and at 800°C ERSC 3P21 Brock University Greg Finn 2005 Volcanic Gas • Most magmas contain dissolved gases – H2O, CO2, SO2, H2S, etc. • Gases come out of ________ as the magma _______ to the surface and the pressure _________ • Gas bubbles which become frozen in a lava are termed _________ • Vesicles which are eventually filled as a result of secondary processes are termed _____________ ERSC 3P21 Brock University Greg Finn 2005 Igneous Textures • ___________ - trapped air bubbles • ___________ - filled vesicles Vesicles Amygdules ERSC 3P21 Brock University Greg Finn 2005 15 Igneous Environments lecture 2a Volcanic Gas • In low viscosity lavas (basalt), trapped bubbles can generally escape from the liquid before ______________ • In ______ viscosity lavas (andesite and rhyolite) the gas bubbles cannot escape from the lava • As the pressure ____, the gas _______ and may cause the violent eruption of the volcano ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Pre 1980 view - Peak is at 2,950 m elevation ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens May 18, 1980 Eruption ERSC 3P21 Brock University Greg Finn 2005 16 Igneous Environments lecture 2a Mount St. Helens September 1980 peak height now 2,550 m and crater is 1.5 km across following May 18 1980 eruption ERSC 3P21 Brock University Greg Finn 2005 Pre 1980 May 17, 1980 May 18, 1980 From Marshak 2001 ERSC 3P21 Brock University Greg Finn 2005 Immediate Area Effected From: National Geographic, January 1981 ERSC 3P21 Brock University Greg Finn 2005 17 Igneous Environments lecture 2a From: Earth; 15 years later: Mount St. Helen’s Immediate Area Effected ERSC 3P21 Brock University Greg Finn 2005 Extent of Ash cloud/fall From: National Geographic, January 1981 ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens 1982 eruption note ash cloud, and ash fall on surface of snow ERSC 3P21 Brock University Greg Finn 2005 18 Igneous Environments lecture 2a Mount St. Helens Pyroclastic flow moving from crater at right to valley floor. Travelling at 100 km/hr and at a temperature of 800°C. ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Pumice blocks deposited at the edge of a pyroclastic flow ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Lava dome in crater 1981 ERSC 3P21 Brock University Greg Finn 2005 19 Igneous Environments lecture 2a Mount St. Helens Lava dome in crater 1985, Photo taken from same spot as previous photo ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Lava dome 1983. Note geologist at centre right of photo. Ground is actually ash covered snow. ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Mount St Helens from Johnston Ridge May 17, 1980 ERSC 3P21 Brock University Greg Finn 2005 20 Igneous Environments lecture 2a Mount St. Helens Mount St. Helens from Johnston Ridge September 1980 ERSC 3P21 Brock University Greg Finn 2005 Mount St. Helens Mount St. Helens from Johnston Ridge September 1984 ERSC 3P21 Brock University Greg Finn 2005 Important Volcanic eruptions • • • • • • • • Santorini ~1645 BC Vesuvius 79 AD Tambora 1515 Krakatoa 1883 Surtsey 1973 Mount St. Helens 1980 Pinatubo 1991 Olympus Mons (Mars) ERSC 3P21 Brock University Greg Finn 2005 21 Igneous Environments lecture 2a Ejecta Volumes From: National Geographic, January 1981 ERSC 3P21 Brock University Greg Finn 2005 22