Paired metamorphic belts

1. PAIRED METAMORPHIC BELTS

2. CONTENTS
 INTRODUCTION
 METAMORPHISH
 TYPES OF METAMORPHISH
 PAIRED METAMORPHISM
 ORIGIN OF THE PAIRED METAMORPHIC BELTS
 PAIRED METAMORPHIC BELTS AND PLATE
TECTONICS
 OCCURRENCE OF PAIRED METAMORPHIC BELT
 CONCLUSION
 REFERENCE

3. METAMORPHISM
• Metamorphism (meta-change,
morphism-form or character)
• The process by which rocks are
altered in composition, texture, or
internal structure by extreme heat,
pressure, and the introduction of
new chemical substances.
INTRODUCTION

4. TYPES OF METAMORPHISM
Contact Metamorphism
Regional Metamorphism
Shock Metamorphism
High Strain Metamorphism
Paired Metamorphism

5. CONTACT METAMORPHISM
• Metamorphism in which the mineralogy and texture of a body of rock are
changed by exposure to the pressure and extreme temperature associated with a
body of intruding magma.
•Contact metamorphism often results in the formation of valuable minerals, such
as garnet and emery, through the interaction of the hot magma with adjacent rock.

6. REGIONAL METAMORPHISM
• A type of metamorphism in which the mineralogy and texture of rocks are
changed over a wide area by deep burial and heating associated with the large-
scale forces of plate tectonics.
• In regional metamorphism, rocks that form closer to the margin of the tectonic
plates, where the heat and pressure are greatest, often differ in their minerals
and texture from those that form farther away.

7. SHOCK METAMORPHISM
• It exclusively occurs locally
around impact craters and possibly
around some diatremes.
• characterized by extremely high
P/T conditions (tens of hundred of
kilobars) over very short time
spans.
• These conditions result from the
passing of a shock wave through
the rocks.

8. HIGH STRAIN METAMORPHISM
• High-strain metamorphism deforms rocks with only minor
thermal effects and occurs when the strain rate exceeds the ability
of the rock to deform plastically.
• It is sometimes also called cataclastic metamorphism.

9. PAIRED METAMORPHIC BELT
• Paired metamorphic belt juxtaposed zones of metamorphic rocks a
high pressure low temperature (Blueschist facies) zones which
was parallel to a low pres-high temp(Greenschist facies)zones.
Paired metamorphic belt were first recognized in Japan.
• In 1961, Miyashiro noted that belts of high-pressure / low-
temperature metamorphism on the oceanic side in the Circum-
Pacific region were associated with belts of high-pressure / high-
temperature metamorphism on the continental side. He termed
such occurrences Paired Metamorphic Belts.

10. ORIGIN OF THE PAIRED METAMORPHIC BELTS
• The origin of the paired structure of metamorphic zones is
interpreted in terms of subduction at the relatively cool rocks of the
oceanic crust beneath the continental crust or at the abduction
(translation of the continental crust on the oceanic)
• A narrow zone of high-pressure facies thus develops in the lower
plate in the thintarland the heat flow increases (in island –arc zone
it amounts of 2.5 cm3 on the average) and descending rocks being
rich in water undergo melting.
• As result of dehydration the volume of rocks is reduced which
accounts for the origin of earthquakes at the plate boundaries.

12. PAIRED METAMORPHIC BELT

13. PAIRED METAMORPHIC BELTS AND PLATE
TECTONICS
• In 1961 , before plate tectonics had been conceived . A . Miyashiro
(1973) recognized that in the mesozoic-cenozoic terranes of the
circum –pacific region.
• The high P/T belt with its associated tectonically juxtaposed
ophiolites and trench sediments generally lies closer to the ocean
and adjacent to the oceanic trench .
• The formation of paired regionally extensive metamorphic belt
with mineral assemblages characteristic of contrasting P/T
gradients can be rationalized in the light of global plate tectonics
• In region of ocean – continental plate convergence there are two,
but not necessarily distinct and separable , region of potential
metamorphism which may be appreciated by examination

15. occurrence
• Paired metamorphic belt occur in many parts of the
circum-pacific regions
• A pair is composed of two contrasting belt running
parallel a high-pressure metamorphic belt which
probably beneath a trench zone
• The former and a low-pressure metamorphic belt which
probably formed a volcanic chain in the adjacent island
arc or continental margin
• the latter belt are accompanied by basic-ultrabasic rocks
and by granitic-andesitic rhyollitic rocks respectively.

16. Conclusion
• The term metamorphism is the changes in
mineralogical composition and structure in
rocks
• In regional metamorphism, rocks that form closer to the
margin of the tectonic plates, where the heat and pressure are
greatest, often differ in their minerals and texture from those
that form farther away.
• high pressure low temperature (Blueschist facies) zones which
was parallel to a low pres-high temp(Greenschist facies)zones.
Paired metamorphic belt were first recognized in Japan.

17. References
• Petrology of igneous and metamorphic rocks
by Donald W. Hyndman, (1985). Page no.27
• Igneous and metamorphic petrology by
Myron G.Best(1986) .page no.432,433,434
• Metamorphic texture by Bhaskar Rao.
• http://earthds.info/pdfs/EDS_19.PDF
• http://www.cms.fu-berlin.de/geo/fb/e-
paired_belts_metamorphism

18. Indian Examples
• Gondwanaland, based on geological arguments,
paleomagnetic data and best fit of continents have
derived two possible models of reassembly
• The most popular places India–Ceylon adjacent to East
Antarctica the other places it next to Western Australia
• That Precambrian granulite facies, paired metamorphic
belts can be traced throughout the basement rocks of
Gondwanaland
• The significance of these paired belts in terms of plate
tectonics during the Precambrian is also discussed.
•