A2 Metamorphic Processes

Question 1

Relict structures

Answer 1

such as bedding, present in the parent rock, which is partially preserved in a metamorphic rock.

Question 2

Dalradian

Answer 2

a regionally metamorphosed group of rocks originally deposited in the late Precambrian. They are found in Scotland and Ireland.

Question 3

Inclusion

Answer 3

the term used to mean an early formed mineral enclosed by one that grew later.

Question 4

Unfoliated

Answer 4

describes the random orientation of minerals in a metamorphic rock.

Question 5

Hornfels

Answer 5

a fine grained, hard, splintery, granoblastic metamorphic rock formed when shale is completely recrystallised close to the contact with an igneous intrusion.

Question 6

Polymorphs

Answer 6

minerals that have the same composition but occur in different crystal forms.

Question 7

Isograd

Answer 7

the name given to a line on a map joining points of equal metamorphic grade. They join places where the first appearance of an index mineral occurs.

Question 8

Metamorphic zone

Answer 8

the name given to an area between two isograds. The zone is named after the lower grade isograd. All locations within a metamorphic zone experienced the same metamorphic grade.

Question 9

Barrovian zones

Answer 9

are metamorphic zones mapped using index minerals identified by George Barrow.

Question 10

Prograde metamorphism

Answer 10

is the recrystallisation of a rock in response to an increase in the intensity of metamorphism.

Question 11

5 index minerals low grade to high grade

Answer 11

Chlorite, Biotite, Garnet, Kyanite, Sillimanite

Question 12

Crenulation Cleavage

Answer 12

A metamorphic fabric formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions causing the formation of the superimposed foliations

Question 13

Pre-kinematic metamorphic minerals

Answer 13

Describes porphyroblast growth in relation to foliation development. Pre-kinematic refers to minerals that form before deformation and are affected by it.

Question 14

Syn-kinematic metamorphic minerals

Answer 14

Describes porphyroblast growth in relation to foliation development. Syn-kinematic refers to minerals that form during deformation and show similar patterns.

Question 15

Post-kinematic metamorphic minerals

Answer 15

Describes porphyroblast growth in relation to foliation development. Post-kinematic refers to minerals that form after deformation and are therefore not affected by it.

Question 16

Al2SiO5

Answer 16

The chemical formula of polymorphs Kyanite, Andalusite and Sillimanite

Question 17

The AL2SiO5 polymorph that forms at the highest temperature and pressure

Answer 17

Sillimanite

Question 18

The ALSiO5 polymorph that forms at low pressure and medium temperatures

Answer 18

Andalusite

Question 19

The AlSiO5 polymorph that forms at a range of pressures but at low temperatures

Answer 19

Kyanite

Question 20

Boudinage

Answer 20

A geological process that occurs when a rigid layer of rock is stretched and deformed into sausage-shaped structures called boudins.

Question 21

Metamorphic Fabric

Answer 21

Refers to the arrangement and orientation of mineral grains, as well as the presence of foliation or lineation in a metamorphic rock.

Question 22

Examples of metamorphic fabrics

Answer 22

Slaty cleavage, schistosity, gneissose banding, porphyroblastic, granoblastric, crenulation cleavage