Unlock the Mystery of “The Green Vein”

1. Unlock the Mystery of “The Green Vein” By: Kim Zenon & Kristen Collier RET 2003-NHMFL Geochemistry-Dr. Vince Salters

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

3. 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.

4. So why study xenoliths? • Geochemists believe that studying xenoliths will further their understanding of the make-up of Earth’s mantle.

5. 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.

6. 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.

7. 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!

8. Step One

9. Chisel samples of the minerals from three different areas of the rock… • Right of the vein • The vein • Left of the vein

10. We also had to… • Separate the tiny pieces of clinopyroxene from the samples using a stereoscope and fine tip tweezers.

11. Step Two

12. 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.

13. 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.

14. 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.

15. Step Three

16. 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.

17. Step Four

18. The ICP mass spectrometer! • ICP = Inductively Coupled Plasma

19. How it works…

20. Rare Earth Elements…

21. The Results . . . .

22. The Data…

23. Melting…

24. REE in basalts… Clinopyroxene melts

25. Metasomatized Peridotites…

26. Conclusions • Clinopyroxenes are not simply related to bulk silicate earth by melting. • No melts observed on the Earth’s 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.

27. A Special Thanks to… Dr. Vincent Salters- Director of Geochemistry Science here at NHMFL.

28. 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