Pete Loader 2011. GL4: Q1 June 2010 Partial melting can be achieved when the temperature of the...
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Transcript of Pete Loader 2011. GL4: Q1 June 2010 Partial melting can be achieved when the temperature of the...
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)
Geotherm is below melting point curve for mantle peridotite (solidus)
Credit: Dougal Jerram
Subduction zone
By adding water at a subduction zone (convergent boundary) – decreasing the melting point of mantle peridotite (wet solidus)
Credit: U S Geological Survey
Credit: Dougal Jerram
Student copyS Student copy
Credit: http://geosun.sjsu.edu/~jmiller/Geo1_Lec5_IgRocks.html
Mid-Ocean Ridge Divergent plate
boundaryA rising convection current at a divergent boundary crosses the solidus and causing rapid decompression melting.
Credit: Dougal Jerram
Credit: U S Geological Survey
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. 1. Partial melting of Partial melting of
lithospherelithospheresubducted mafic subducted mafic crust,crust,peridotite mantle peridotite mantle wedge,wedge,continental crustcontinental crust
2. Gravity settling -2. Gravity settling -Fractional Fractional crystallisation crystallisation (cumulates)(cumulates)
3. Magma mixing3. Magma mixing
4. Contamination - 4. Contamination - XenolithsXenoliths
Based on Loader et al .(in prep)
In fact the processes of magma formation and evolution can
generate igneous rocks with a variety of compositions regardless
of the plate environment