Presentation on theme: "Kinds of metamorphism Lecture based on"— Presentation transcript:
1 Kinds of metamorphismLecture based onAnd PowerPoint lecture of Dr. J.D. Winter
2 The Types of Metamorphism Different approaches to classification1. Based on principal process or agentDynamic MetamorphismThermal MetamorphismDynamo-thermal Metamorphism
3 2. Based on setting (P-T conditions/tectonic) Contact MetamorphismPyrometamorphismRegional MetamorphismOrogenic MetamorphismBurial MetamorphismOcean Floor MetamorphismHydrothermal MetamorphismFault-Zone Metamorphism (cataclastic or mylonitic in your text)Impact or Shock Metamorphism
4 Types of metamorphism based on pressure and temperature conditions
5 Blueschist metamorphism Geothermal gradient: Indicates the average increase of temperature with depthHIGH pressure/Low temperatureTypically associated with subduction zonesExample: Blueschist (from glaucophane)
6 Glaucophane in a blueschist (ppl). 1mmGlaucophane in a blueschist (ppl).
7 Eclogite metamorphism VERY HIGH pressure/moderate temperatureHappens in the mantleExample: Eclogite (pyroxene/garnet)
9 Hydrothermal metamorphism Low pressure/low temperatureHot, chemically active waters react with the surrounding rocksExample: Serpentinite, soapstone
10 Hydrothermal metamorphism Usually involves METASOMATISM (metamorphism plus exchange of ions from an external source)Difficult type to constrain: hydrothermal effects often play some role in most of the other types of metamorphism
11 Contact metamorphism Low pressure/HIGH temperature “Country” rocks baked by igneous intrusion (pluton)Example: Hornfels, skarn (baked carbonate rocks), quartzite, marble
13 Contact MetamorphismMost easily recognized where a pluton is introduced into shallow rocks in a static environment(Pluton=intrusive igneous body, like a batholith)® Hornfelses (granofelses) commonly with relict textures and structures
15 Pyrometamorphism A minor type of contact metamorphism Very high temperatures at very low pressures, generated by a volcanic or subvolcanic bodyAlso developed in xenoliths (pieces of solid rocks carried up by magma)Pyrometamorphism may be accompanied by various degrees of partial melting
16 Barrovian metamorphism Also referred to as “regional” metamorphismIntermediate pressure/Low-high temperatureExample: Slate-phyllite-schist-gneiss, also quartzite and marble
17 Regional Metamorphism sensu lato: metamorphism that affects a large body of rock, and thus covers a great lateral extentThree principal types:Orogenic metamorphismBurial metamorphismOcean-floor metamorphismThe term, “regional metamorphism” is often used synonymously with “orogenic metamorphism” (OROGENY=mountain building)
18 Orogenic Metamorphism is the type of metamorphism associated with convergent plate margins Dynamo-thermal: one or more episodes of orogeny with combined elevated geothermal gradients and deformation (differential stress)Foliated rocks are a characteristic product
23 Burial metamorphism = low-grade metamorphism in sedimentary basins Metamorphic effects attributed to increased temperature and pressure due to burialOccurs in areas that have not experienced significant deformation or orogenyMild deformation, no igneous intrusions discovered
24 Restricted to large, relatively undisturbed sedimentary piles away from active plate margins Term coined by Coombs (1961) based on Southland Syncline in New Zealand: thick pile (> 10 km) of Mesozoic volcaniclasticsModern examples:The Gulf of Mexico?Bengal Fan?
25 Ocean-Floor Metamorphism affects the oceanic crust at ocean ridge spreading centers A wide range of temperatures at relatively low pressureSeawater penetrates down fracture systems, where it becomes heated, and leaches metals and silica from the hot basaltsConsiderable metasomatic alteration, notably loss of Ca and Si and gain of Mg and Na
26 Highly altered chlorite-quartz rocks- distinctive high-Mg, low-Ca composition Black smokers - Another example of hydrothermal metamorphism
27 Fault-Zone and Impact Metamorphism High rates of deformation and strain with only minor recrystallization(a) Shallow fault zone with fault breccia(b) Slightly deeper fault zone (exposed by erosion) with some ductile flow and fault mylonite
29 Fault-Zone and Impact Metamorphism High rates of deformation and strain with only minor recrystallizationImpact metamorphism at meteorite (or other bolide) impact cratersBoth correlate with dynamic metamorphism, based on process
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