Trace Elements And Isotopes Flashcards
What is chemical fractionation?
All elements distribute themselves unevenly between any 2 phases at equilibrium
What are the 2 type of incompatible elements?
What distinguishes the difference between the two types?
High Field Strength Elements - higher charge, smaller radius
Large Ion Lithophile Elements - smaller charge, larger radius
What is the bulk distribution coefficient? What is it used for?
The measure of the concentration of each trace element and coexisting minerals from experimental runs.
Useful because trace elements partitions themselves between common minerals in a basaltic - andesitic melt.
What are high field strength elements? What are some elements that are HFSE?
Incompatible elements that have smaller radii and higher charge.
Th, Ce, U, Zr, Ti, Nb
What are large ion lithophile elements? What are some elements that are LILE?
Incompatible elements that have a large radii and less of a charge.
K, Rb, Cs, Sr, Eu
What type of source rock would have lower K/Rb distribution coefficients? What process would the source rock have to go through to create the magma?
Amphibole-bearing source rocks
Partial melting of the amphibole-bearing source rocks would create the magma.
As you crystallize plagioclase, what happens to values of Ba/Sr? How about if you crystallize K-feldspars?
Values of Ba/Sr would increase with crystallization of plag and would level off
Values would decrease with increase in crystallization of K-feldspar
What is significant about the distribution coefficient values for Ni/Cr and/or Ni/Sc?
Can help distinguish the effects of olivine and augite in a partial melt or a bunch of rocks produced by fractional crystallization
What is so significant about Garnet in terms of HREE? How would it be seen on a REE diagram if garnet was in equilibrium with the partial melt?
Garnet concentrates the HREE and fractionates among them.
A steep negative slope would be seen in REE and HREE.
If on a REE diagram an Eu anomaly pops up, what does that suggest in terms of processes and minerals associated?
Shallow partial melting of the mantle resulting with plagioclase in the residuum.
Why are Ni, Co, and Cr useful trace elements?
All are highly compatible elements. Ni and Co concentrate in olivine and Cr in spinel and Cpx. They can suggest a mantle source if there were high enough concentrations.
Why are V and Ti useful trace elements?
Both show strong fractionation into Fe-Ti oxides like ilmenite and could fractionate into accessory phases like rutile or sphene.
Why are Zr and Hf useful trace elements?
Both are very incompatible elements and don’t substitute into major silicate phases.
Why are Ba and Rb useful trace elements?
Both incompatible element that substitute for K in K-spar, mica or hornblende. Rb substitutes less readily in horblende.
Why is Sr a useful trace element?
Substitutes for Ca in plagioclase and behaves like a compatible element at low pressures where plag forms early but as an incompatible at high pressures where plag isn’t stable anymore.
