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ERSC 3P21 Metamorphic Petrology II 03/11/2005 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 granitic and/or ultramafic masses intruded into the terranes generally, but not always near the thermal axis. ERSC 3P21 - Brock University Greg Finn 1 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Regional Metamorphism At point A temperature = 400°C, pressure = 3.5 kbars ERSC 3P21 - Brock University Greg Finn From: Marshak 2001 Sugluk Superior Province Cape Smith Belt Subprovince Types Minto La or ad br Hudson Bay ou Tr i to ba ar io Trans - Hudson Orogen M Ashuanipi Bienville O Volcanic nt an Thompson Belt gh High Grade Pikwitonei La Grande R. Plutonic Winisk Sachigo James Bay Opinica R. N Metasedimentary Berens River Uchi Bird River Nemiscau R. English River Wabigoon Opatica Quetico Wawa Quetico sin g Winnipeg River Ka pus ka Canada U.S.A. Abitibi Pontiac Grenville Province Wawa Quebec Southern Province Ontario Minnesota 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 II 03/11/2005 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 II 03/11/2005 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. • Rich ore deposits are often formed as a result of hydrothermal metamorphism. ERSC 3P21 - Brock University Greg Finn 4 03/11/2005 http://www.pbs.org/wgbh/nova/abyss/frontier/images/chron10.jpeg ERSC 3P21 Metamorphic Petrology II http://earthsci.org/energy/geomin/kuroko.gif ERSC 3P21 - Brock University http://www.nmm.ac.uk/uploads/jpg/black_smoker.jpg 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 From: Marshak 2001 Greg Finn 5 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Compositional Groups • Loose groupings of metamorphic rocks based on the original ________ composition – Mudstones Î – Basic Rocks Î – Ultramafics Î – Calcareous Î – Granites Î Pelites Metabasites Ultramafics Marbles Granites 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 low temp pelites – Biotite - common in higher temp 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 garnet biotite schist biotite schist Garnet muscovite schist ERSC 3P21 - Brock University Greg Finn 6 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Pelite mu st mu q q bi bi st mu mu a st q gt q gt q b 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 p op p a b p p op 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 II 03/11/2005 Barrovian Metamoprhism Dalradian Moinian Lewisian and Torridonian N 50 0 Moin e Th rust Scale, km Buchan Zones Fa ult Inverness re a tG len Aberdeen G • Named for _______ __________, who first mapped these lithologies in the 19th century • Rocks are the _______ sequence that outcrop in the Scottish Highlands • The Dalradian sequence consists of Precambrian and early Cambrian _________, overlain by unmetamorphosed Upper Devonian Sandstones. r da un Bo nd hla Hig yF lt au Area investigated by Barrow ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism • Within the Dalradian sequence, Barrow recognized the existence of unmetamorphosed shale (pelite) which subsequently underwent metamorphism. • Barrow recognized a series of zones of progressive 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 II 03/11/2005 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 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 II 03/11/2005 ERSC 3P21 - Brock University Greg Finn Dalradian Metamorphic Zones Newer Granite Chlorite Biotite Almandine Andalusite Kyanite Sillimanite Moinian G re at G le n Fa ul t Buchan Zones Extension of Barrow’s Zones along the extent of the Dalradian in Scotland Hi gh ar y nd ou B d lan 0 Fa ult N km 50 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 _________ (line of equal grade). Isograds can be drawn for each index mineral. • Barrow's work led to our present concept of metamorphic grade, although the interpretation of the significance of the zones varies. ERSC 3P21 - Brock University Greg Finn 10 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Barrovian Metamoprhism • Barrow believed the zones resulted from the heat from the small granitic intrusives found in the high grade zones - Contact Metamorphism • Another geologist, (C.E. Tilley) working on the same rocks in a different area suggested that the temperature of each zone was largely determined by the depth of burial (geothermal gradient), modified at depth by heat from the intruded granites – Regional Metamorphism. • Tilley (1924) suggested that the isograds mark rocks originating under closely similar physical conditions of temperature and pressure - not greatly different from what we believe today. ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism P-T Grid for Dalradian Upper limit of staurolite Pressure Staurolite Zone Lower limit of staurolite Temperature ERSC 3P21 - Brock University Greg Finn Barrovian Metamoprhism Pressure Lower limit of biotite Garnet Zone Upper limit of staurolite Staurolite Zone Lower limit of staurolite Kyanite Zone Lower limit of sillimanite Path followed by Dalradian sequence during metamorphism Chlorite Zone Biotite Zone Lower limit of almandine P-T Grid for Dalradian Upper limit of kyanite Sillimanite Zone Temperature Water saturated granite solidus ERSC 3P21 - Brock University Greg Finn 11 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Barrovian Metamoprhism • The first appearance of an index or zone mineral indicates a ________ metamorphic grade, as long as the rocks were of an appropriate ___________ for that mineral to grow. • The appearance of a particular mineral depends on the following variables: – Conditions under which the _____________ occurred, i.e., temperature, water pressure, load pressure. – Rates of _________ and _______ involved in formation of the mineral. – ____________ of the rock. • The last variable is the most important factor in the production of a given mineral under different metamorphic conditions. ERSC 3P21 - Brock University Greg Finn Facies • An isograd mapped within a single, homogeneous layer closely approaches the idealized concept of a line of equal grade. • Correlation of an isograd from one area with one mapped in a widely separated area, can in rocks of similar composition, be hazardous as each rock may have formed under different conditions at different times. ERSC 3P21 - Brock University Greg Finn Facies • A Finnish geologist, Eskola, was the first to attempt to correlate metamorphic zones between widely separated areas. • Working in Finland, Eskola found that contact metamorphic assemblages were related to grade and composition. • When he compared his results to others he found that some mineral assemblages were the same between areas, while others in rocks of similar composition were quite different. ERSC 3P21 - Brock University Greg Finn 12 ERSC 3P21 Metamorphic Petrology II 03/11/2005 Facies • Led Eskola to speculate that if rocks from the two different areas were metamorphosed under different conditions, e.g., P & T, they would respond differently • This prompted him to propose a classification of metamorphic rocks: – ________ - an association of metamorphic rocks, each consisting of a mineral assemblage consistently related to the composition of the rock. ERSC 3P21 - Brock University Greg Finn Facies Mineral assemblages for different facies of metamorphism, i.e. each facies represents the same T and P conditions, for three common lithologies Unmetamorphosed Rock Shale - Mudstone Facies A chlorite muscovite albite quartz Slate or Phyllite Andesitic Volcanic Tuff actinolite albite epidote chlorite quartz Sandy Limestone or Siliceous Dolomite dolomite calcite quartz Facies B biotite chlorite muscovite albite quartz Facies C garnet biotite muscovite albite* quartz staurolite garnet biotite plagioclase* quartz Phyllite or Schist actinolite albite epidote chlorite quartz tremolite calcite quartz Facies E sillimanite garnet biotite plagioclase quartz Schist or Gneiss hornblende albite epidote Quartz hornblende plagioclase quartz tremolite calcite Quartz diopside calcite quartz Chlorite or Actinolite Schist Marble Facies D hornblende plagioclase quartz Amphibolite Tremolite Marble diopside calcite quartz Diopside Marble ERSC 3P21 - Brock University Greg Finn * - plagioclase composition changes from albite ( <An10) to oligoclase-andesine (An20 to An 40) Facies • Table shows the relationship between metamorphic zones and metamorphic facies. Not only for pelitic rocks as mapped by Barrow, but also for Basic and Calcareous rocks. • If all the rock types in the table were interbedded correlation of the mineral assemblages within each rock type would be very simple. • Such a correlation, for several rock types within a single metamorphic grade, defines the metamorphic facies for that grade. ERSC 3P21 - Brock University Greg Finn 13