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Isochemical! - Minerals are transformed

Texturally or mineralogically distinct

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:N ote Th e rocks exp osedin B o u ld e r C an yo n w e st o f

to w n a re a llre g io n a llym etam orp h osed

.Pre C a m b ria n ro cks T h e

ag e of m etam orp h ismd e te rm in e d fro mra d io m e tric d a tin g is

.a b o u t 1 8 b illio n y e a rs

1. regional: burial, transformation, and exhumation of entire

regions

2. contact: transformed by contactwith an igneous intrusion.

ontact and RegionalMetamorphism

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Contact metamorphism

Locally and adjacent to igneous

intrusions Along fractures in contact with hot

fluids (hydrothermal)

Mineral crystals precipitate alongfractures

Caused by low P, high T (from magmaor fluids)

Time scale: days kyr Intensity greatest at contact between

parent and intrusive magma orfluids

Decreases rapidly over short distances

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RegionalMetamorphism

Large intrusions,tectonism,widespreadhydrothermal

fluids High P, Lower T

Usually results inrocks that arestrongly foliated

Widespreadhydrothermal

migration -

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ineralogical Composition- Kinds and abundances within the rock- Composition can change OR stay the same

( )texture changes-=Recrystallization crystals of one mineral

, !fewer larger crystals of same mineral

= !Neomorphism changes mineral compositionRecrystallizes minerals and form different

!minerals from same elements

= ,Metasomatism Chemicals are added or lost! (can gain new elements Minerals of a totally)different composition

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Textures Foliated layering, parallel alignment

of platy mineral crystals (i.e. micas) From pressure and shearing of

crystals

1. Slaty (low grade) closely spacedshear planes, flat foliated 2. Pyllite texture (intermediate) wavy

foliation, metallic luster 3. Schistosity (intermediate-high) -

glittery layering or linear alignment ofcrystals, breaks on wavy foliations

4. Gneissic Banding layers of light anddark, medium-coarse rained

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Slaty

Phyllite Texture

Schistosity

Gneissic Banding

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Nonfoliated no obvious layering

1.Crystalline texture (nonfoliated)

intergrown, usually equal sizevisible crystals

2.Microcrystalline texture fine-

grained, intergrown microscopicminerals (i.e. sugar cube)

3.Sandy texture medium-coarse

grained, resemble sandstone,fused sand

4.Glassy texture no visible grains orstructures, breaks along glossysurfaces

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