MORB And Ophiolites Flashcards
In MORBs, what minerals undergo fractional crystallization?
Olivine, plagioclase, Cpx
Why can’t MORBs be primary magmas?
The MORB has Mg # = 0.55 - 0.68 which is way less than the Mg # classified for primary magmas (70-74).
What are the incompatible-rich and incompatible-poor mantle source regions for MORB magmas? What are the criteria’s for that region?
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
Why are alkaline basalts favoured over tholeiites?
By deeper melting and low % of partial melting
What is N-MORB?
“Normal” MORB that taps the depleted upper mantle source
What is E-MORB?
“Enriched” MORB that tap the deeper mantle
What are the 2 types of ocean island basalts?
- Ocean island tholeiitic basalt
- Ocean island alkaline basalt
What is the pre-shield stage of the eruption building cycle?
Submarine eruptions of alkaline basalt, highly alkaline basanites followed by tholeiitic basalts
What is the shield-building stage of the eruption building cycle?
Outpour of tholeiitic basalts
What is the post-shield stage in the eruption building cycle?
Episodic, violent alkaline activity with shallow fractionation producing hawaiites and trachytes
What is the post-erosional stage in the eruption building cycle?
Alkaline and silica undersaturated magmas with xenoliths present