Crystals settling to the bottom due to gravity are removed from further reaction with the melt - silica poor minerals at bottom of chamber, silica rich minerals at top 17 CHAPTER 3 IGNEOUS ROCKS CRYSTALLIZATION OF MAGMA Processes responsible for diversity of igneous rocks: 3) Continuous Reaction of the Melt and Early Formed Minerals - early formed crystals keep in contact with the melt, continuing to react with the melt forming minerals of different composition (BRS) 4) Crystallization of the Melt in a New Location - some of the melt can be squeezed into fracture surrounding the magma chamber - the minerals formed is lacking in early formed minerals giving rise to rocks of different composition 18 CHAPTER 3 IGNEOUS ROCKS CRYSTALLIZATION OF MAGMA Processes responsible for diversity of igneous rocks: Other mechanisms 5) Assimilation : incorporation of pre-existing country rocks (and reaction) into a magnetic melt - unmelted country rocks are called XENOLITHS 6) Mixing of magmas : two magmas of different composition merge e.g. basaltic + granitic = andesitic 7) Partial melting : produces magma with composition different from that of the parent rock (this the reverse of the Bowen's reaction series) 19 CHAPTER 3 IGNEOUS ROCKS NAMING OF IGNEOUS ROCKS 1) From BRS, the first minerals to crystallize are: Ca-Plagioclase , Olivine and Pyroxene - these minerals are high in Fe, Mg, Ca and low in Si -
(Crystals; settling; to the bottom due to gravity) (fracture; surrounding; the magma chamber) (early formed minerals; giving; rise; to rocks of different composition) (early; formed; minerals giving rise to rocks of different composition) (the minerals formed; is lacking; in early formed minerals) (magnetic melt - unmelted country rocks; are called; XENOLITHS 6) Mixing of magmas) (the minerals; formed; ) (the melt; forming; minerals of different composition) Context(the melt forming,List([415, 431))):(4) Crystallization of the Melt in a New Location; can be squeezed; into fracture) (these minerals; are; high; L:in Fe, Mg, Ca and low) Context(these minerals are,List([1357, 1375))):(the first minerals to crystallize; are; Ca-Plagioclase , Olivine and Pyroxene - these minerals are high in Fe, Mg, Ca and low in Si)
the melt forming,List([415, 431)) these minerals are,List([1357, 1375))
Crystals fracture early formed minerals early the minerals formed magnetic melt - unmelted country rocks the minerals the melt 4) Crystallization of the Melt in a New Location these minerals the first minerals to crystallize
settling surrounding giving formed is lacking are called formed forming can be squeezed are are
to the bottom due to gravity
the magma chamber
rise to rocks of different composition
minerals giving rise to rocks of different composition
in early formed minerals
XENOLITHS 6) Mixing of magmas
minerals of different composition
into fracture
high L:in Fe, Mg, Ca and low
Ca-Plagioclase , Olivine and Pyroxene - these minerals are high in Fe, Mg, Ca and low in Si