ERTH 3020: LABS 47

1
ERTH 3020 LABS 4-7

• Progressive metamorphism of specific
• compositional groups
• Lab 4 Metabasites and metamorphic facies
• Lab 5 Pelites and Barrovian zones
• Lab 6 Calcareous and other rocks
• Lab 7 Gneisses and migmatites (various
  compositions)
• systematic changes in mineralogy and texture
• determination of metamorphic grade

2
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
1. Mineralogy
Metabasites - Mg-Ca-Fe-rich rocks derived from
basalts, andesites, and their pyroclastic or
intrusive equivalents Actinolite
Garnet Orthopyroxene Biotite
Glaucophane Plagioclase Carbonate
Hornblende Prehnite Chlorite
Lawsonite Pumpellyite Clinopyroxene Fe-Ti
Oxides Quartz Epidote Omphacite Titanite
(Sphene)
most metabasites contain amphibole
plagioclase look for changes in composition of
amph plag changes in associated
minerals
3
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
2. Metamorphic facies sets of mineral
assemblages, repeatedly associated in space and
time, considered characteristic of a range of
P-T conditions about a dozen metamorphic
facies recognized span complete range of
crustal metamorphic conditions many facies
names come from metabasites, but the concept
applies to any bulk composition some names apply
both to the facies and to rock types within that
facies (potential confusion!)
4
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
3 facies series distinguished based on P
range (technically, dT/dP)
Lab 4 focuses on medium and high P facies series
5
MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2 where A Na,K X
Ca,Na,Fe,Mg Y Mg,Fe,Mn,Al T Al,Si root
formula tremolite Ca2Mg5Si8O22(OH)2
several different families of amphibole can be
recognised depending on X-site occupancy
calcic amphiboles X mostly Ca (e.g.,
actinolite, hornblende) sodic amphiboles X
mostly Na (e.g., glaucophane) Fe-Mg amphiboles X
mostly Fe,Mg (e.g., anthophyllite)
(ortho-) (etc...)
6
MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
TOT groups linked by other cations (A, X)
A
SiO44- double chain (T-site)
chains linked by octahedral Y-sites (M1, M2)
I-beam
T O T
relationship between structure and cleavage
7
MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
biaxial ve mod biref pale green
biaxial ve or ve mod biref green to brown
act hbl
interference colour range
8
MoW 5 Amphibole (Nesse, Ch. 14, p. 277-289)
double-chain silicate, general formula
A0-1X2Y5T8O22(OH)2
clear distinction among various amphibole
groups requires working out pleochroic scheme
biaxial ve or ve mod biref green to brown
biaxial ve mod biref pale green
act hbl
interference colour range
9
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
high P glaucophane barroisite (Na-amphiboles)
medium low P actinolite --gt green hornblende
--gt brown hornblende (Ca-amphiboles)
10
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
CC
CCGS-02 (2.5 mm) actinolite in greenschist
TMS-AM (2.5 mm) hornblende in amphibolite
1513 (2.5 mm) glaucophane in blueschist
11
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
A) Very Low-Grade Metamorphism (low T, low
P) Zeolite facies a variety of Ca- and Na-
zeolites Prehnite-Pumpellyite facies prehnite
pumpellyite chlorite albite quartz
hematite leucoxene (no particularly good
Reference Collection samples for these facies)
12
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
B) Low- to Medium-Grade Metamorphism (low to
moderate T, low to moderate P medium P
series) Greenschist facies chlorite epidote
albite actinolite quartz titanite Epidote
amphibolite (sub)facies (transitional) epidote
hornblende plagioclase (An0-20) quartz
titanite Amphibolite facies hornblende
plagioclase (An20-40) quartz titanite (or
ilmenite)

amphibole pale green --gt blue-green --gt green
13
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
Greenschist --gt Amphibolite Facies
TMS-AM (amphibolite)
CCGS-02 (greenschist)
LONG-1 (transitional)
14
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
C) High-Grade Metamorphism (high T, moderate P
medium P/T series) Granulite facies
orthopyroxene clinopyroxene plagioclase
(An30-50) quartz ilmenite rutile garnet
hornblende biotite high-grade metabasites
may also include gneisses and migmatites (Lab 7)
amphibole green --gt green-brown --gt brown
15
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
Amphibolite --gt Granulite Facies
TMS-AM (amphibolite)
RJ97-2 (granulite)
Q45A (garnet amphibolite)
16
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
D) High-Pressure Metamorphism (low-moderate T,
high P high P series) Blueschist
facies lawsonite glaucophane quartz albite
omphacite epidote or zoisite Eclogite
facies omphacite garnet (Fe-poor) quartz
rutile amphibole zoisite phengite
kyanite
amphibole blue-violet --gt pale blue-green
17
ERTH 3020 LAB 4 Metabasites and metamorphic
facies
Blueschist and Eclogite Facies
PM85-2 (blueschist)
BVE-02 (eclogite)
18
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
1. Mineralogy
A) Pelites - Al-rich rocks derived from sediments
rich in clay minerals (shales, mudstones,
etc.) Andalusite Garnet
Plagioclase Alkali feldspar Graphite
Quartz Biotite Kyanite
Sillimanite Chlorite Muscovite
Sulphides Chloritoid Fe-Ti Oxides
Staurolite Cordierite Paragonite
Stilpnomelane
most pelites contain quartz muscovite look for
changes in associated mineral assemblage
Al2SiO5 loss of muscovite at high grade
Barrovian index minerals
19
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
2. Barrovian zones

• systematic change in mineral assemblage with
• increasing grade (inferred by Barrow (1915) from
• rocks in southern highlands of Scotland)
• for convenience, can be summarised in terms of
• first appearance of characteristic "index"
  minerals
• and corresponding "Barrovian" zones
• index minerals generally persist into other
  zones
• (may not disappear when next index mineral
  appears)
• index minerals alone insufficient to define
  grade
• (need full assemblage assessment of
  stability)

chlorite ? biotite ? garnet ? staurolite ?
kyanite ? sillimanite (I ? II)
20
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
2. Barrovian zones
chlorite ? biotite ? garnet ? staurolite ?
kyanite ? sillimanite (I ? II)
stability range of index minerals depends
strongly on bulk composition (X, esp Al, Fe/Mg)
as well as P,T Barrovian zones can be related to
facies by comparing assemblages in interlayered
metabasites and pelites note that facies apply
to all bulk compositions including pelites
Barrovian zones restricted to pelites
21
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Very Low-Grade (sub-greenschist facies) clay
minerals (various) chlorite quartz (rocks are
very-fine-grained mineral identification
requires XRD or microprobe analysis) Greenschist
Facies Chlorite zone chlorite muscovite
quartz albite Biotite zone biotite
muscovite chlorite albite quartz
chloritoid Garnet zone biotite muscovite
garnet sodic plagioclase quartz chlorite
chloritoid (transition from greenschist to
amphibolite facies occurs within the garnet zone
albite (An0-7) ? oligoclase (An15-25) but change
in plag composition may not be optically
detectable)
22
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Biotite zone PHYL-1 (6.25 mm)
Chlorite zone BRS-1 (0.5 mm)
Garnet zone BVS-1 (0.5 mm) (chlorite is
retrograde)
23
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Amphibolite Facies Staurolite zone biotite
muscovite garnet quartz staurolite
plagioclase (An20-30) kyanite Kyanite zone
biotite muscovite garnet kyanite
plagioclase (An25-45) quartz
staurolite Sillimanite zone I biotite
muscovite garnet quartz sillimanite
plagioclase (An30-45) staurolite
kyanite Sillimanite zone II biotite garnet
sillimanite plagioclase (An30-45) K-feldspar
quartz leucosome (note loss of muscovite,
appearance of K-feldspar, and first
appearance of leucosome within Sill zone II)
24
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Kyanite zone CON-JK (6.25 mm)
Staurolite zone 75-13 (6.25 mm)
Sillimanite zone (I or II?) BAF01-S (2.5 mm)
25
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Granulite Facies (not part of standard Barrovian
sequence) garnet sillimanite plagioclase
(An30-45) quartz K-feldspar biotite
orthopyroxene cordierite leucosome (pelitic
rocks in upper amphibolite to granulite facies
are generally migmatitic mesoscopic and
microscopic textures suggest in situ partial
melting)
26
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
BAF01-23 (2.5 mm)
BAF01-23 (6.25 mm)
Granulite facies garnet cordierite
sillimanite ( leucosome)
27
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones

• at low pressure (P lt 5 kb), pelites contain
  some
• characteristic minerals not typical of the
  Barrovian
• sequence
• sometimes referred to as the "Buchan" sequence,
  
• or more commonly the "Low Pressure Facies
  Series"
• in a P-sensitive isograd scheme ("bathograds"
• Carmichael, 1978) these correspond to
  bathozones 1-3
• low P facies names are not widely used mineral
  
• assemblages depend on P, T, X reference to
• mineral assemblage is more useful.

28
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
MEDIUM P Barrovian sequence
29
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Albite-epidote hornfels facies biotite
muscovite chlorite albite quartz
andalusite cordierite Hornblende hornfels
facies biotite muscovite andalusite
cordierite albite quartz chlorite biotite
muscovite andalusite cordierite oligoclase
quartz staurolite garnet biotite
andalusite cordierite intermediate
plagioclase K-feldspar quartz staurolite
garnet Pyroxene hornfels facies biotite
cordierite sillimanite intermediate
plagioclase K-feldspar quartz garnet
orthopyroxene Sanidinite facies orthopyroxene
spinel sanidine cordierite mullite quartz
30
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
Low P Facies Series
JF-1 (6.25 mm)
71-111 (6.25 mm)
all contain cordierite and/or andalusite
KM-CM (6.25 mm)
31
ERTH 3020 LAB 5 (Meta)pelites and Barrovian zones
MEDIUM P Barrovian sequence