Serpentine Mine, Cyprus, 2007 What is an ophiolite? Simply: - - PowerPoint PPT Presentation

Serpentine Mine, Cyprus, 2007

What is an ophiolite?

• Simply: Ophiolites are pieces of
• ceanic crust found on land
• The international ophiolite conference

restricted the term “ophiolite” to only include the following rock types/assemblages

• This definition has been challenged

recently due to recent discoveries made by the IODP

New Mineral you need to know: Serpentine Mg3 Si2 O5 (OH)4

Fibrous/Fine grained mat like Habit 1st order interference colours Pale Green-yellow pleochroism Serpentine group of minerals (chrysotile, lizardite, and antigorite)

New Mineral you need to know: Talc Mg3 Si4 O10 (OH)2

Colourless in PPL 2nd order birefringence Fibrous-bladed habit May be difficult to distinguish from muscovite in thin section easy in hand sample

New Mineral you need to know:

Pumpellyite Ca4 (Mg,Fe2+)(Al,Fe3+)5 O(OH)3 [Si2 O7 ]2 [SiO4 ]2.2H2 O

Green Yellow-pleochroism Bladed-radiating habit *most useful Anomalous blue birefringence and yellow-brown birefringence Prehnite Ca 2 Al 2 Si 3 O 12 (OH) commonly associated with pumpellyite NOTE: higher birefringence and more fibrous h bit

New texture you need to know: mesh texture

Mesh Texture: Hydrothermal alteration produces a network

• r serpentine

interlaced with

• riginal igneous

minerals

Particulars…

• Full rock description of

KHAB 2

OR

331/88/1 (worth ½ the lab!) Good Luck!

Amphibole

Amphibole Anxiety…

Ortho-amphiboles Vs. Clino-amphiboles

Amphibole Anxiety: Ortho-amphiboles

• There are two common forms of orthoamphibole:

Anthophyllite: (Mg,Fe)2 (Mg,Fe)5 SiO22 (OH)2 Gedrite: (Mg,Fe)5 Al2 [Al2 Si6 O22 (OH)2 ]

• Orthoamphibole occurs in metamorphic rock of medium-high grade, but

not in igneous rocks. Amphiboles are hydrous minerals which break down in anhydrous environments.

• They are not found in mafic and ultramafic igneous rocks because these

magmas have little dissolved water. The amphiboles will break down to form pyroxenes instead.

• Helpful Hints

– Orthoamphiboles have parallel extinction – Maximum interference colours of first order red and second order blue – Brown color of orthoamphibole may be useful in distinguishing it from hornblende, which usually has a green-black color

Amphibole Anxiety: Clino-Amphiboles

• Hornblende (Na,K)0-1

(Ca,Na,Fe,Mg)2 (Mg,Fe,Al)5 (Si,Al)8 O22 (OH)2

Name given to an amphibole with an indeterminate composition Ubiquitous mineral in intermediate igneous rocks and amphibolite facies metamorphism

• Actinolite Series

Ca-rich amphiboles are most common in greenschist-amphibolite facies metamorphism (i.e. meta-carbonates)

Tremolite: Ca2 Mg5 Si8 O22 (OH) 2

White colour in HS; maximum interference colours are upper 1st order; inclined extinction; large 2V (75-88)

Actinolite: Ca2 (Mg,Fe)5 Si8 O22 (OH)2

Pale-deep green; negative optic sign

• Cummingtonite Series

Commonly found in mafic metamorphic rocks at intermediate pressures and temperatures

Cummingtonite: (Mg,Fe)7 Si8 O22 (OH)2

Inclined extinction, twins and higher birefringence distinguish from orthoamphiboles; positive optic sign and

• ccurrence distinguish from actinolite series

Grunerite: Fe7 Si8 O22 (OH)2

Subtle pleochroism when compared to cummingtonite

• Glaucophane series: Na2

Mg3 Al2 Si8 O22 (OH)2

Only found in metamorphic rocks (i.e. Blueschist facies) Distinct pleochroism (colourless-medium blue)