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Types of Metamorphism Regional Metamorphism ERSC 3P21 Metamorphic Petrology III 24/08/2011 Types of Metamorphism • _________________________ • _________________________ • _________________________ • _________________________ • _________________________ ERSC 3P21 - Brock University Greg Finn Regional Metamorphism • Corresponds to changes, _________, in Temperature & Pressure, due to _____ • Commonly associated with _________ events and processes • Regionally metamorphosed rocks occur in very large belts 10-100's km wide x 100-1000's km long. ERSC 3P21 - Brock University Greg Finn Regional Metamorphism • Within each belt will be preserved at least ______________, representing the ________ temperature of metamorphism within the belt. • Temperatures will __________ towards the thermal axis. • Associated ________ and/or __________ masses intruded into the terranes generally, but not always near the thermal axis. ERSC 3P21 - Brock University Greg Finn 1 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Regional Metamorphism At point A temperature = 400°C, pressure = 3.5 kbars From: Marshak 2001 ERSC 3P21 - Brock University Greg Finn Sugluk Superior Province Cape Smith Belt Subprovince Types Minto L a b ra d o Hudson Bay r T ro u g h High Grade Thompson Trans - Hudson a b Belt Orogen o it io n r a ta M n Ashuanipi Volcanic O Bienville Pikwitonei La Grande R. Plutonic James Winisk Sachigo Bay Opinica R. N Metasedimentary Berens River Uchi Bird River English River Nemiscau R. Opatica Canada Winnipeg River Quetico g Abitibi U.S.A. n Wabigoon i Grenville s a Pontiac Province Wawa k s u p Quetico a K Wawa Quebec Southern Province Minnesota Ontario River Valley St. Catharines 0 250 Km ERSC 3P21 - Brock University Greg Finn Modified from Percival 1989 Contact Metamorphism • Recrystallization, production of metamorphic mineral assemblages, within the ______________ surrounding an intrusive body • Generally held that P remains _______ and metamorphism results from temperature _________, due to conduction of heat away from intrusive ERSC 3P21 - Brock University Greg Finn 2 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Contact Metamorphism ERSC 3P21 - Brock University Greg Finn From: Marshak 2001 An example of contact metamorphism on I-25 just north of Las Vegas, New Mexico. The mafic intrusion cooked the sedimentary strata (shale and chalk). The width of the zone of contact metamorphism is about 20 feet. From: http://www-class.unl.edu/geol101i/07_metamorphic.htm ERSC 3P21 - Brock University Greg Finn http://www.gpc.edu/~janderso/images/metafaci.jpg ERSC 3P21 - Brock University Greg Finn 3 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Pyro-metamorphism • Recrystallization at high __________ of xenolith fragments in volcanic rocks or small intrusions • Melting of the xenolith may occur ERSC 3P21 - Brock University Greg Finn Hydrothermal Metamorphism • Recrystallization associated with and influenced by a hydrothermal solution - _________________ • Rocks that are altered at _______ temperatures and ________ pressures by hydrothermal fluids are hydrothermally metamorphosed. • This is common in basaltic rocks that generally lack hydrous minerals. ERSC 3P21 - Brock University Greg Finn Hydrothermal Metamorphism • Hydrothermal metamorphism results in alteration to such _______ rich hydrous minerals as talc, chlorite, serpentine, actinolite, tremolite, zeolites, and clay minerals. • __________________are often formed as a result of hydrothermal metamorphism. ERSC 3P21 - Brock University Greg Finn 4 ERSC 3P21 Metamorphic Petrology III 24/08/2011 er/images/chron10.jpeg yss/fronti gbh/nova/ab http://www.pbs.org/w http://earthsci.org/energy/geomin/kuroko.gif http://www.nmm.ac.uk/uploads/jpg/black_smoker.jpgERSC 3P21 - Brock University Greg Finn Cataclastic Metamorphism • Cataclastic metamorphism occurs as a result of __________________________ – eg. when two bodies of rock slide past one another along a fault zone. • Heat is generated by the ________ of sliding along such a shear zone, and the rocks tend to be mechanically deformed, being _______ and __________, due to the shearing. • Cataclastic metamorphism is not very common and is restricted to a ________ zone along which the shearing occurred. ERSC 3P21 - Brock University Greg Finn Cataclastic Metamorphism ERSC 3P21 - Brock University Greg Finn From: Marshak 2001 5 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Compositional Groups • Loose groupings of metamorphic rocks based on the original ________ composition – Mudstones Î ___________ – Basic Rocks Î ___________ – Ultramafics Î ___________ – Calcareous Î ___________ – Granites Î ___________ ERSC 3P21 - Brock University Greg Finn Pelites • Derived from ________ sediments (mudstones) • Characterized by high _____ and ______ contents, which result in abundant _______ produced during metamorphism – Muscovite - common in _____ _______ pelites – Biotite - common in ______ _____ pelites • Pelites often display a well developed ___________, defined by parallel alignment of micas – Mica schists • Also have minerals rich in _____ in pelites, e.g., – Kyanite, andalusite, sillimanite - Al2SiO5 – Staurolite - Fe2Al9O6(SiO4)4(OH)2 – Cordierite - Mg2Al3(AlSi)5O18 – Garnet - (Fe,Mg)3Al2(SiO4)3 ERSC 3P21 - Brock University Greg Finn kyanite muscovite schist biotite schist garnet biotite schist Garnet muscovite schist ERSC 3P21 - Brock University Greg Finn 6 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Pelite mu mu q q st bi bi mu st mu q st gt q gt a b q Plate 4: Sample 88-2 - Pelite (metamorphosed mudstone) the minerals present in this rock are produced as a result of metamorphism, increased Temperature and Pressure. Minerals: garnet (gt), staurolite (st), muscovite (mu), biotite (bi) and quartz (q). (FOV = 13.5mm) ERSC 3P21 - Brock University Greg Finn Metabasites • Equivalent to _________ rocks with . 50 wt % SiO2 • Basalts are often included in sedimentary piles within orogenic belts, thus mineral assemblages in metabasites can be _________ with assemblages in associated pelites as both formed under similar P &T. • Basic rocks rich in MgO, FeO, CaO and Al2O3, metamorphic minerals produced include: – Chlorite, actinolite, epidote, at low temp greenschist – Hornblende, plagioclase in amphibolite – Hornblende, plag & garnet, opx & cpx in granulite ERSC 3P21 - Brock University Greg Finn Metabasite hb hb cpx cpx hb hb p p cpx cpx op p op p p p a b Sample 99-3 - Amphibolite (metamorphosed gabbro) under (a) plane light and (b) crossed polars. Minerals present include plagioclase (p), clinopyroxene (cpx) (note the variable colour (pleochroism) of the cpx brown and green), hornblende (hb) and opaques (op). (FOV = 8.5mm) ERSC 3P21 - Brock University Greg Finn 7 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Barrovian Metamoprhism • Named for _______ Dalradian Moinian __________, who first Lewisian and N Torridonian mapped these 0 50 lithologies in the 19th Scale, km t s century u r h T e n i • Rocks are the _______ o M Buchan Inverness sequence that outcrop Zones lt u in the Scottish a F Aberdeen n le G t Highlands a re • The Dalradian sequence G t ul consists of Precambrian Fa y Area investigated ar nd by Barrow ou and early Cambrian B nd la gh _________, overlain by Hi unmetamorphosed From: Turner 1968 Upper Devonian Sandstones. ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism • Within the Dalradian sequence, Barrow recognized the existence of unmetamorphosed _____ (______) which subsequently underwent metamorphism. • Barrow recognized a series of zones of ___________ metamorphism ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism • Each zone is based on the first appearance of a distinctive ____________ as the highest metamorphic grade, along the thermal axis, was approached. • Thermal axis has abundant ________ bodies along its length. • Index mineral is one which is __________ of that zone - any mineral within the zone may be the index mineral. ERSC 3P21 - Brock University Greg Finn 8 ERSC 3P21 Metamorphic Petrology III 24/08/2011 Barrovian Metamoprhism The following zones were recognized by Barrow: • Zone of _________________________ – now termed chlorite zone - characterized by first appearance of chlorite – assemblage - qtz-chlorite-muscovite-albite • ____________ Zone – marked by the first appearance of red-brown biotite from muscovite & chlorite • ____________ Zone – assemblage - qtz-musc-biotite-almandine (Fe,Mg)3Al2Si3O12)-ab or oligoclase ERSC 3P21 - Brock University Greg Finn From: Turner 1968 ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism • ___________ Zone – qtz-misc-bio-almandine-staurolite-(oligoclase) • ___________ Zone – qtz-bio-misc-oligoclase-almandine-kyanite • ___________ Zone – qtz-bio-misc-oligoclase-almandine-sillimanite • Zones were mapped in a small portion of Aberdeenshire and latter extended across the full length of the Highlands. ERSC 3P21 - Brock University Greg Finn 9 ERSC 3P21 Metamorphic Petrology III 24/08/2011 From: Turner 1968 ERSC 3P21 - Brock University Greg Finn Dalradian Metamorphic Zones Newer Granite Extension of Chlorite Biotite Barrow’s Zones Almandine along the extent Andalusite Kyanite Buchan of the Dalradian Sillimanite Zones in Scotland lt u a F n le G t a e Moinian Gr t ul Fa y ar N nd ou B nd la km gh Hi 0 50 From: Turner 1968 ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism • Some minerals, e.g., biotite, _______through the higher grade zones, however others, e.g., staurolite, __________ in the next zone. • A line on a map that corresponds to the first appearance of an index mineral is called an _________
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