Docsity
Log inSign up
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Geology 285: Metamorphism & Metamorphic Rocks by Dr. Helen Lang, WVU - Prof. Helen Lang, Study notes of Geology

West Virginia University (WVU)Geology
Prof. Helen Lang

An overview of metamorphism, a geological process that causes changes in mineralogy and texture of rocks due to variations in temperature and pressure. Topics such as diagenesis vs. Metamorphism, metamorphic rocks and textures, agents of change in metamorphism, and different types of metamorphism. It also includes information on isograds and contact vs. Regional metamorphism.

Typology: Study notes

Pre 2010

Uploaded on 09/17/2009

koofers-user-9de
koofers-user-9de 🇺🇸

5

(1)

10 documents

1 / 6

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Geol 285 - Dr. Helen Lang, West Virginia University, Spring 2009
Metamorphism & Metamorphic Rocks
Because the Earth is a dynamic system, rocks, once formed, may be subjected
to very different conditions
Metamorphism means Change
• Changes in conditions cause changes in mineralogy and texture of rocks
• Because minerals that were stable at original conditions are no longer stable at
new conditions
• Changes that take place in the solid state between diagenesis (lower limit) and
melting (upper limit) are called metamorphism
Diagenesis vs. Metamorphism
• Gradational boundary
• Metamorphism begins with the formation of new minerals not observed in any
sediments at Earth’s surface
• (muscovite, chlorite, epidote, albite, paragonite, pyrophyllite)
• Diagenesis/Metamorphism boundary is at about 150o-200oC (~2 kilobars, but P is
not critical)
Metamorphic - Igneous boundary
pf3
pf4
pf5

Partial preview of the text

Download Geology 285: Metamorphism & Metamorphic Rocks by Dr. Helen Lang, WVU - Prof. Helen Lang and more Study notes Geology in PDF only on Docsity!

Geol 285 - Dr. Helen Lang, West Virginia University, Spring 2009

Metamorphism & Metamorphic Rocks

Because the Earth is a dynamic system, rocks, once formed, may be subjected

to very different conditions

Metamorphism means Change

  • Changes in conditions cause changes in mineralogy and texture of rocks
  • Because minerals that were stable at original conditions are no longer stable at new conditions
  • Changes that take place in the solid state between diagenesis (lower limit) and melting (upper limit) are called metamorphism

Diagenesis vs. Metamorphism

  • Gradational boundary
  • Metamorphism begins with the formation of new minerals not observed in any sediments at Earth’s surface
  • (muscovite, chlorite, epidote, albite, paragonite, pyrophyllite)
  • Diagenesis/Metamorphism boundary is at about 150 o^ -200 o^ C (~2 kilobars, but P is not critical)

Metamorphic - Igneous boundary

  • When metamorphic temperature gets very high, the rocks begin to melt
  • Partly melted rocks are called migmatites (mixed rocks) and are considered metamorphic; melting T depends on rock composition
  • granite and shale begin to melt at ~650o^ C
  • basalts begin melting at ~800 o^ C
  • liquid+solid mixture for >200o^ T range
  • If a rock gets mostly or completely melted, it is considered igneous

Protolith

  • Any rock can be changed to become metamorphic
  • Rock from which a metamorphic rock is formed is called its protolith
  • Igneous protolith is indicated by the prefix "ortho-" (metaigneous)
  • Sedimentary protolith is indicated by prefix "para-" (metasedimentary)
  • Protolith is indicated by rock composition, inherited textures, often it’s hard to determine

Textures Characteristic of Metamorphic Rocks

  • Deformation causes anisotropic fabrics
  • foliation - any planar texture or structure in a rock
  • schistosity - alignment of platy minerals (thin, flaky layers)
  • gneissosity - mineral segregation (thicker layers)
  • Burial metamorphism - at the base of a thick sedimentary sequence, very low grade (T (^) max ~300 o^ C, garnet grade) metamorphic conditions may be reached
  • Contact metamorphism - heat from a pluton may raise T of country rocks high enough to cause metamorphism (growth of new metamorphic minerals)
  • Regional metamorphism - crustal scale thrusting, caused by continental collisions, exposes rocks to high pressures and temperatures to cause regional metamorphism
  • Subduction zone metamorphism - when cold rocks are dragged down into a subduction zone, temperatures are lower than normal for a given depth

Define Isograd

  • An isograd is a line on a map marking the first appearance of a new metamorphic mineral
  • Defined by Barrow in 1890s
  • Interpreted to be a line of approximately equal metamorphic grade (or T and P during metamorphism)

Characteristics of Contact Metamorphism

  • Metamorphic effects are localized around a pluton; obvious association with a pluton
  • Isograds are approximately concentric with pluton margin (form contact aureole)
  • Very limited extent; at most a few km wide
  • Mineralogic changes reflect mostly changes in T
  • Minerals are mostly low pressure minerals
  • Minerals lack preferred orientation, rocks are generally undeformed (called hornfels)

Contact Metamorphism of impure Limestone

Characteristics of Regional Metamorphism

  • Metamorphic effects are not clearly associated with a pluton
  • Effects are regional; extending over 10s to 100s of kilometers
  • Rocks contain moderate to high pressure minerals. Like what?
  • Rocks are generally deformed and have strong fabrics (lineation and foliation)
  • Mineral changes reflect changes in both T and P

Regional Metamorphism in Scottish Highlands (see handout)

The Great Glen Fault

Intermediate Cases between Contact and Regional Metamorphism are Common

(Low Pressure Regional or Regional/Contact Metamorphism)

Mineralogic Changes depend on original rock composition, because ingredients

needed to make minerals must be present in the protolith

  • Quartz crystals in a quartz arenite just get bigger (recrystallize), nothing else can grow- Ss becomes quartzite
  • Pure calcite limestone becomes pure calcite marble