Unlock the Mystery of The Green Vein

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Unlock the Mystery of The Green Vein

By Kim Zenon Kristen Collier RET
2003-NHMFL Geochemistry-Dr. Vince Salters
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Our Project

• Our task this summer was to investigate why a
  mysterious green vein is visible in several
  xenolith samples here at the lab.

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What is a xenolith?

• Xenoliths are rocks that are carried by magma to
  the surface.
• The xenoliths from this study are from the mantle
  and are called peridotites.

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So why study xenoliths?

• Geochemists believe that studying xenoliths will
  further their understanding of the make-up of
  Earths mantle.

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Our particular samples

• The rock samples we are studying are mantle
  samples exposed in the volcanic field of San
  Carlos, Arizona.
• They are believed to be recent, about 100,000
  years old!
• The mantle samples contain veins of
  clinopyroxene.

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Samples included these minerals

• Clinopyroxene Ca(MgFe)Si2O6 (grassy green)
• Orthopyroxene (MgFe)2Si2O6 (dark green)
• Olivine (MgFe)SiO4 (yellow to pale green)
• Spinel MgAlO4 (black)

Our goal is determine the chemical differences
and similarities between the clinopyroxene from
the vein and the clinopyroxene from the host
peridotite.
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Just Four Easy Steps-

• Separate the clinopyroxene from the rock sample.
• Dissolve the clinopyroxene with hydrofluoric
  acid.
• Take the dissolved sample up in a dilute nitric
  acid solution.
• Analyze the samples using the ICP Mass
  Spectrometer.
• To Unlock the Mystery!

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Step One
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• Chisel samples of the minerals from three
  different areas of the rock
• Right of the vein
• The vein
• Left of the vein

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We also had to

• Separate the tiny pieces of clinopyroxene from
  the samples using a stereoscope and fine tip
  tweezers.

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Step Two
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• The individual samples of clinopyroxene were
  weighed.
• Samples were cleaned by leaching in acid for one
  hour, rinsing with distilled water, and drying
  over night.

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After the samples dried

• The samples were weighed again to record how much
  was leached by the acid.
• Then we added hydrofluoric acid to the samples to
  begin the 72 hour dissolving process.

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More Dissolving!

• After dissolving in hydrofluoric acid, we dried
  the samples
• After the samples were dried down, we dissolved
  and dried them with hydrochloric acid.

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Step Three
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Nitric Acid Solutions

• Samples were redissolved in nitric acid.
• Finally, the solutions were diluted through
  accurate weighing to produce a solution with 500
  parts per million rock.

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Step Four
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The ICP mass spectrometer!

• ICP Inductively Coupled Plasma

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How it works
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Rare Earth Elements
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The Results . . . .
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The Data
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Melting
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REE in basalts
Clinopyroxene melts
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Metasomatized Peridotites
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Conclusions

• Clinopyroxenes are not simply related to bulk
  silicate earth by melting.
• No melts observed on the Earths surface are in
  equilibrium with these mystery veins.
• Although they have been at high temperature the
  samples are all different.
• The veins are the most fractionated, the slope of
  the pattern is the steepest.
• Patterns are indicative of interactions between a
  fluid and the host peridotite.

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A Special Thanks to

• Dr. Vincent Salters-
• Director of Geochemistry Science here at NHMFL.

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We would also like to thank

• National High Magnetic Field Laboratory
• National Science Foundation
• Center for Integrating Research and Learning
• Dr. Pat Dixon, Director-CIRL
• Ms. Gina LaFrazza-Hickey, Education
  Specialist-CIRL
• The Geochemistry Department