Volcanism at constructive plate margins Flashcards
Name a type constructive plate margin setting.
Mid-ocean ridges.
What type of melting occurs at constructive plate margins?
Adiabatic decompression melting.
What is adiabatic decompression melting?
Where no heat is transferred between the system and the surroundings.
Describe the positions of the geothermal and solidus at constructive plate margins.
The geothermal crosses the solidus at a shallow depth.
Explain how the geothermal crosses the solidus at a shallow depth.
Pressure on the mantle is reduced by lithospheric thinning.
What is the eruption temperature at constructive plate margins?
1,100C.
What type of magma is erupted at constructive plate margins?
Basaltic.
What type of basalt is mid-ocean ridge basalt (MORB)?
Tholeiitic.
Describe tholeiitic basalt.
Al and Mg-rich and K-poor.
How are tholeiitic basalts formed?
Higher degrees of partial melting.
Give two examples of common types of tholeiitic basalts/
Olivine and quartz tholeiites.
What type of mantle rock is melted to produce basaltic magma?
Ultramafic mantle rocks.
Why can’t MORB be a primary melt?
It is not in equilibrium with mantle olivine.
Describe fast spreading ridges.
They have smooth topography, a homogenous crust, and a robust magma supply.
Describe slow spreading ridges.
They have rugged topography with normal faulting, a heterogenous crust, and a variable magma supply.
