W8L2 Metamorphic Facies

Question 1

Metamorphic Facies definition

Answer 1

A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. … The boundaries between facies (and corresponding areas on the temperature v. pressure graph) are wide because they are gradational and approximate

Question 2

Metamorphic Grade ablauf

Answer 2

Lithification
low temp, low pressure
Low Grade Metamorphism → intermediate → metamorphic grade

Question 3

Pete Envelope

Answer 3

bordered by partial melting in wet rock and partial melting in dry rock
water has big effect on melting in metamorphic rocks!
in this area very high grade dry rock or partial melting of wet rock
in presence of water can melt at much lower temps!

Question 4

Prograde

Answer 4

prograde: increase burial path, into high grade

most metamorphic reactions are prograde

Question 5

Retrograde

Answer 5

retrograde: return path, back to low grade bcs slow uplift of the crust
minerals can grow anywhere on this path
but time as key component, the faster the less “memory” so doesnt show record if this stage

Question 6

Peak metamorphism

Answer 6

Peak metamorphism: maximum metamorphic condition which the system/ rock experiences

Question 7

Zeolite . Facies on graph

Answer 7

upper left corner
lithification area
low temp low pressure

Question 8

PP on graph

Answer 8

just below Zeolite and above Blueschist
left bordeer is “notpossible in nature”
right border is greenschist

Question 9

greenschist on graph

Answer 9

further right so about 200-200 T zone
left border: blueschist and PP
right bordeer: Amphibolite
bottom border: Eclogite
goes down to like 8 Pa

Question 10

Blueschist on graph

Answer 10

below PP and greenschist on graph
bottom border: Eclogite
stays by “not possible in nature” border on left
goes to about 8 Pa then eclogite, starts . at about 6Pa

Question 11

Eclogite on graph

Answer 11

has highest pressure . at cold temp
so runs along bottom of graph till Granulite
top border amphibolite and greenschist

Question 12

Amphibolite on graph

Answer 12

kinda the middle of the graph 
under hornfels
above eclogite
left broder greenschist 
right border granulite

Question 13

Granulite

Answer 13

furthest right of the graph
almost takes up whole right bottom sectrion
kinda borders Hornfels at top
startsin hotter temp, all Pressure fields and depth

Question 14

Hornfels on Graph

Answer 14

stretched along top of the graph as this like think layer till 900 Temo then Granulit etakes over
never lower than 2 Pa

Question 15

Pathway 1 on graph

Answer 15

Conditions of thermal metamorphism

runs thru hornfels , stays at top till 10km at granulite

Question 16

Pathway 2 on graoh

Answer 16

Condition beneath mountain belts
could almost say it goes straigh thru diagram from top left to bottom right
with lsight ciurve

Question 17

pathway 3 on graph

Answer 17

conditions beneath stable continental interior
starts top left, then pretty stable fall
ends shortly after wet melting line

Question 18

pathway 4 on graph

Answer 18

Condition in an accretionary plane

goes from top left steep down, kinda stays along left side, just off “not possible” zone

Question 19

Moderate to high temp and high pressure . Facies

Answer 19

Regional Metamorphic Rocks
• produced during mountain building episodes
• result of burial & deformation
• affect large portions of the Earth’s cr
With increasing T & P …
• greenschist facies
• amphibolite facies
• granulite facies
metamorphosed rocks in mountain belts

Question 20

Metamoprhic Index Materials

Answer 20

how to tell which grade a mineral is in
different minerals are stable at different T & P
index minerals are common minerals with well understood P & T stabilities

Question 21

Barrovian Zones

Answer 21

By mapping the occurrences of index minerals in regionally metamorphosed rock zones of equal grade can be determined, separated by isograds

Question 22

Areas of maximum grade

Answer 22

Areas of maximum grade indicate areas which have been most deeply buried
can reconstruct how crust ect have formed

Question 23

High pressure - low temp facies

Answer 23

Subduction Zone Metamorphism
• associated with subducting slabs
• preserved in subduction trench environments
• require rapid uplift for preservation
With increasing P …
• blueschist facies
• eclogite facies (very HP, HT)
 low temperature facies

Question 24

Low presure to high temp facies

Answer 24

Thermal (Contact) Metamorphic Rocks
• produced as a result of magmatic heating
• affect rocks local to the intrusion only

Question 25

textures in thermally metamorphosed rocks

Answer 25

In lower grade parts of the aureole slatey rocks are formed
These often contain porphyroblasts of cordierite and/or andalusite
“spotted slates”