Download Partial melting Tutorial

Pete Loader 2011
GL4: Q1 June 2010
Partial melting can be achieved when the temperature of
the mantle (indicated by the local geotherm) exceeds
the melting point of peridotite.
This can occur in a number of ways and in different
geological environments as shown by the following :
1. By adding water at a subduction zone (convergent
boundary) – decreasing the mantle melting point.
2. By rapid decompression at a divergent boundary.
3. By locally increasing the geotherm (hot spot)
Credit: Dougal Jerram
Geotherm is below melting point curve for mantle peridotite (solidus)
Credit: Dougal Jerram
Credit: U S Geological Survey
Subduction zone
By adding water at a subduction zone (convergent boundary)
– decreasing the melting point of mantle peridotite (wet solidus)
Student
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Student
S
Credit: http://geosun.sjsu.edu/~jmiller/Geo1_Lec5_IgRocks.html
Credit: Dougal Jerram
Credit: U S Geological Survey
Mid-Ocean Ridge
Divergent plate boundary
A rising convection current at a divergent boundary crosses the solidus and
causing rapid decompression melting.
Student copy
Credit: http://geosun.sjsu.edu/~jmiller/Geo1_Lec5_IgRocks.html
Partial melting at plate margins
summary
GL4: Q1 June 2003
GL4: Q4 June 2005
Basalt
Andesite
Credit: US Geological Survey
Magmatic model
at subduction
zones
1. Partial melting of
lithosphere
subducted mafic crust,
peridotite mantle
wedge,
continental crust
2. Gravity settling Fractional crystallisation
(cumulates)
3. Magma mixing
Based on Loader et al .(in prep)
4. Contamination Xenoliths
In fact the processes of magma
formation and evolution can generate
igneous rocks with a variety of
compositions regardless of the plate
environment