MORB And Ophiolites Flashcards

1
Q

In MORBs, what minerals undergo fractional crystallization?

A

Olivine, plagioclase, Cpx

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2
Q

Why can’t MORBs be primary magmas?

A

The MORB has Mg # = 0.55 - 0.68 which is way less than the Mg # classified for primary magmas (70-74).

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3
Q

What are the incompatible-rich and incompatible-poor mantle source regions for MORB magmas? What are the criteria’s for that region?

A

N-MORB (normal) taps the depleted upper mantle source. Mg# < 65%, K2O < 0.1and TiO2 < 1.0

E-MORB (enriched) taps the deeper, fertile mantle. Mg# < 65, K2O > 0.10 and TiO2 > 1.0

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4
Q

Why are alkaline basalts favoured over tholeiites?

A

By deeper melting and low % of partial melting

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5
Q

What is N-MORB?

A

“Normal” MORB that taps the depleted upper mantle source

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6
Q

What is E-MORB?

A

“Enriched” MORB that tap the deeper mantle

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7
Q

What are the 2 types of ocean island basalts?

A
  1. Ocean island tholeiitic basalt
  2. Ocean island alkaline basalt
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8
Q

What is the pre-shield stage of the eruption building cycle?

A

Submarine eruptions of alkaline basalt, highly alkaline basanites followed by tholeiitic basalts

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9
Q

What is the shield-building stage of the eruption building cycle?

A

Outpour of tholeiitic basalts

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10
Q

What is the post-shield stage in the eruption building cycle?

A

Episodic, violent alkaline activity with shallow fractionation producing hawaiites and trachytes

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11
Q

What is the post-erosional stage in the eruption building cycle?

A

Alkaline and silica undersaturated magmas with xenoliths present

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