This is a massive problem set that is meant to take you a month to complete. Start it right away and work on it regularly; if you wait until the last few days, you will crash and burn. It is due on Sept. 27.
The Hawaii Scientific Drilling Project pilot hole was set in lavas of the lower flanks of Mauna Loa volcano. It quickly penetrated the Mauna Loa section, entered the youngest lavas of Mauna Kea, and penetrated into the shield-building phase of Mauna Kea. Because I want to look at the entire life of a volcano, we’ll stick to the Mauna Kea lavas.
The problem set presumes your acumen with computers. If you don’t understand some of the computer procedures, you can receive help from the helpdesk. Realize that the following instructions are purposely vague, because I want you to figure out how to do these things on your own. In the following, stuff I’ll want you to turn in is in bold and mundane instructions in regular type. You may have to refer to a petrology text (e.g. McBirney or Winter) to complete parts of the exercise.
- Provide thorough petrographic descriptions of the thin sections.
They can be checked out from Rachel. Keep in mind that if you damage one, you will be sacrificed. In addition to mere description (e.g. mode, habit, texture, etc.), see whether you can assess the following issues:
- Could the rocks be related by fractionation of the observed phenocrysts?
- Is there any evidence that some of the crystals may not have formed by crystallization from a liquid like that of the groundmass? Could some of them be xenocrysts? Are some in reaction with the liquid?
- What is the crystallization order in the entire suite?
- Download the geochemical data via anonymous log in from my ftp site (backdoor.mines.uidaho.edu/pub/geist/HSDP data.hqx). It is in binhex format, so you may need to decompress it with winzip if your computer does not do it automatically.
- Calculate the "magnesium number" (or Mg#, which is the molar MgO/(MgO+FeO*)) for each sample.
- You were probably taught that SiO2 is the best indicator of the degree of evolution of an igneous rock. This is not true of basalts, where SiO2 is mostly unrelated to temperature. MgO is a much stronger function of temperature for basalts. Plot each of the major elements, Nb, Nb/Zr, Ni, Ba, La, La/Sm, Sc, and Sc/Yb against MgO.
- Calculate the effects of fractionating each of the silicate mineral phases from the lava with the highest MgO on each of the diagrams you constructed for part 4.
You can do this by plotting mineral compositions on the diagrams you made above and adding vectors showing the effects of subtracting each of the minerals. Use representative mineral compositions from a basalt from a resource such as Deer, Howie and Zussman for the major element compositions. For the trace elements, simply calculate whether each element will increase or decrease, using the Rayleigh equation for fractional crystallization, an average phenocryst mode, and distribution coefficients from the GERM web site (via
