Mantle Xenoliths

Chondritic Meteorite

+ IronMetal

Iron

basalt orgranite crust

peridotite mantle

olivine

feldspar

= Sun

oliv

opx

cpx

Mantle Xenoliths

nephelinite

Refractory Mantle Residues

Chondritic Meteorites

Solar Composition

chondrules

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 orgranite crust

Fe-Nimetallic

core

peridotite mantle

SiO2 + MgO + FeO ~ 91%

Sun - Chondritic Meteorites - Earth’s Mantle

~

Igneous Petrology Lab 3:

The Mantle Source and Primary Magmas

Apatite = P5+ / 3

 

Cpx (XYT2O6) = X = (Ca2+ + Na+ + K+) - 5 x Apatite

Spinel (Y2+Y3+2O4) = Y3+/2 = Cr3+/2 + (Al3+ - 2Ti4+ - Na+)/2

.

Opx* (Y2T2O6) = Y/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*

Si* = 00.00

Opx = Opx* - Oliv

 

If Si* is positive:

Qtz = Si*

Oliv = 0.0

Opx = Opx*

In order to plot your points, orthopyroxene must be recalculated as a mixture of olivine and quartz.

Calculation for plotting in Olivine – Clinopyroxene – QuartzLiquidus Projection

Solid Source Refractory Solid + Liquid Restite

Refractory Mantle + Oceanic Crust

Cpx-rich PeridotiteLherzolite

Olivine-rich Peridotite + Basalt Harzburgite

Partial Melting of the Mantle

Fertile Mantle

Whole = Σ Parts

Lever Rule: p/R = x/y

y

x

R

amount of basalt (P) infertile mantle = x/(x+y)

~ 15-20%

opx

cpx

Calculate an ideal Cpx formula: XYT2O6: cations sum to 4

 

Al(1V) = 2 – Si

Al(VI) = Al - Al(1V)

CrCaTs (CaCrAlSiO6) = Cr

AlCaTs (CaAl2SiO6) = Al(VI) – CrCaTs – Na

Jadeiite (NaAlSi2O6) = Na

Wo (CaSiO3) = (Ca - AlCaTs – CrCaTs)/2

En (MgSiO3) = (1-Wo-Jd) × XMg where XMg = Mg/(Fe+Mg)

Fs (FeSiO3) = (1-Wo-Jd) × (1-XMg)

Clinopyroxene component calculation

opx

cpx

Estimation of Pressure or Depth of Origin