Transcript Slide 1

basalt or
granite crust
feldspar
peridotite
mantle
Iron
olivine
Chondritic
Meteorite
+ Iron
Metal
Mantle
Xenoliths
= Sun
Chondritic
Meteorites
Mantle Xenoliths
chondrules
cpx
oliv
opx
Solar Composition
Refractory Mantle Residues
Sun - Chondritic Meteorites - Earth’s Mantle
Sun
~
BulkSilicateEarth (~68 wt.%) + Fe-metal core (~31 wt.%)
The Earth’s upper mantle is similar
in composition to BSE, and is
composed of a rock called
peridotite, which consists largely of
the
minerals
olivine
and
orthopyroxene
basalt or
granite crust
peridotite
mantle
Fe-Ni
metallic
core
SiO2 + MgO + FeO
~ 91%
Igneous Petrology Lab 3:
The Mantle Source and
Primary Magmas
Calculation for plotting in Olivine – Clinopyroxene – Quartz
Liquidus Projection
Apatite
= P5+ / 3
Cpx (XYT2O6) = X
= (Ca2+ + Na+ + K+) - 5 x Apatite
Spinel (Y2+Y3+2O4) = Y3+/2
Opx* (Y2T2O6) = Y/2
= Cr3+/2 + (Al3+ - 2Ti4+ - Na+)/2
.
= ((Mg2+ + Fe2+ + Mn2+ + Ni2+ + Co2+) - Spin - Cpx)/2
Si*
= Si4+ - 2 x Cpx - 2 x Opx* + Ti4+
If Si* is negative:
Oliv (Y2TO4)
Si*
Opx
= - Si*
= 00.00
= Opx* - Oliv
If Si* is positive:
Qtz
Oliv
Opx
= Si*
= 0.0
= Opx*
In order to plot your points, orthopyroxene must be recalculated as a mixture of olivine and
quartz.
Partial Melting of the Mantle
Solid Source
Fertile Mantle
Refractory Solid
Restite
+
Refractory Mantle
+
Cpx-rich Peridotite
Lherzolite
Olivine-rich Peridotite
Harzburgite
Whole = Σ Parts
Lever Rule: p/R = x/y
amount of basalt (P) in
fertile mantle = x/(x+y)
y
~ 15-20%
x
R
Liquid
Oceanic
Crust
+
Basalt
opx
cpx
Clinopyroxene component calculation
Calculate an ideal Cpx formula: XYT2O6: cations sum to 4
2 – Si
Al - Al(1V)
Cr
Al(VI) – CrCaTs – Na
Na
Al(1V)
Al(VI)
CrCaTs (CaCrAlSiO6)
AlCaTs (CaAl2SiO6)
Jadeiite (NaAlSi2O6)
=
=
=
=
=
Wo (CaSiO3)
En (MgSiO3)
Fs (FeSiO3)
= (Ca - AlCaTs – CrCaTs)/2
= (1-Wo-Jd) × XMg
where
= (1-Wo-Jd) × (1-XMg)
XMg = Mg/(Fe+Mg)
opx
cpx
Estimation of Pressure or Depth of Origin