layered mafic intrusions

Question 1

why are intrusions only mafic

Answer 1

due to felsic magma being so viscous, magma just sticks together

Question 2

why study mafic intrusions

Answer 2

most natural and informative examples of crystallization and differentiation

fossil magma chambers - direct observation of intrusive ig rocks as end-product of crystallization and differentiation

Question 3

where do mafic intrusions occur

Answer 3

any tectonic environment where basaltic magma is generated:
-mid-ocean ridges
-continental flood basalts where rifting may be associated with mantle hotspots

Question 4

age of LMI

Answer 4

precambrian

Question 5

size of LMI

Answer 5

range from thin dikes and sill yo 10,000s km2/ kms thick

Question 6

LMI rock types

Answer 6

gabbroic, usually tholeiitic

Question 7

what is a layer

Answer 7

any sheet-like cumulate unit distingushed by its compositional and/or textual features

Question 8

types of layer

Answer 8

uniform layer = crystallization and differentiation

non-uniform = crystallization and differentiation

Question 9

common type of non-uniform layer

Answer 9

graded layer
-shows gradual variation in either mineralogy

Question 10

cumulate texture

Answer 10

ig rocks identified by a framework of touching mineral grains accumulated during magma crystallization and differentiation

Question 11

layering

Answer 11

(stratification)

the structure and fabric of sequences of multiple layers

Question 12

types of layering

Answer 12

modal
phase
cryptic
rhythmic