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Week 10: March 20-24 (including
lecture on April 7)
Isotopes and
trace elements in igneous petrology
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Radiogenic, heavy
isotopes
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definitions
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isotope
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radioactive
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radiogenic
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stable
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non-radiogenic
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isotopes of the U-Pb,
Rb-Sr, Sm-Nd systems
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causes of variability
in isotopes (parent-daughter ratio and time)
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causes of variation
in parent-daughter ratios
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distribution of isotopes
between crust and mantle with time
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Example - the Rb-Sr
system
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applications to petrology
- dating and tracers
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isochrons
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Trace elements
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Compatible trace elements
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Incompatible trace elements
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High field strength
elements (HFSE)
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Large ion lithophile
elements (LILE)
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The rare earth elements
(REE) - a special group
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light rare earths
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heavy rare earths
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Spidergrams
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arrangment of elements
from most incompatible to least incompatible
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normalization (usually
by chondritic values)
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spidergrams of "primitive
mantle" - relatively "flat" patterns
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spidergrams of MORBs
- depleted in more incompatible elements
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spidergrams of OIBs
- enriched in more incompatible elements
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spidergrams of arc magmas
- "spiked" pattern: enrichment in fluid-mobile elements; depletion in some
fluid-immobile elements
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interpretation of above
patterns in terms of magma sources and processes
Petrology
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