1. Igneous rocks form when melted rocks cool and crystallize. This is simple enough except that, when rocks melt and crystallize, different chemical species within the rock melt or crystallize at different temperatures and so the very process of melting or crystallizing changes the residual liquid and subsequent crystallization/melting products.
2. On the melting end of things, almost all melt comes from the upper mantle where the pressure, temperature, or composition has deviated from "normal" as some given location. The upper mantle is composed of an ultramafic rock called a 4-phase lherzolite and when this melts, the result is not melted lherzolite- it is of a mafic (basaltic) composition.
3. On the crystallization side of things, a familiarly with the research of N. L. Bowen is particularly useful... In a basaltic melt at surface pressure, olivine is the first silicate mineral to crystallize and contains considerably more Mg and considerably less Si than the melt. As a result, the melt will become progressively depleted in Mg and relatively enriched in all of the other major elements (such as Si). The remaining melt will eventually evolve to the point that olivine is no longer the thermodynamically most stable mineral and orthopyroxene (OPX) will begin to crystallize instead. As a result of this compositional melt evolution, igneous rocks or any composition (ultrmafic, mafic, intermediate, and felsic) can form from basaltic melt.
4. Elements that tend to enter the solid (mineral phase) during crystallization are called "compatible" and those that tend to remain in the liquid are called "incompatible." The ratio of the abundance of an element in the melt vs. its abundance in the crystallizing mineral is called the partition coefficient. For instance, the element nickle (Ni) is highly compatible in the mineral olivine (the partition coefficient = 10) and the element aluminum is incompatible (partition coefficient = 0.01). This means that a melt with 0.1% Ni and 10% Al will crystallize with 1% Ni and 0.1% Al. We will revisit these concepts later when discussing ore body formation.
5. The igneous rock types that are important four our discussions include granite, pegmatite, basalt, and peridotite. You should be able to loosely describe these rocks based on their grain size, elemental, and mineralogical composition.
6. Sedimentary rocks can be divided into clastic, chemical, biochemical, and organic based on how they formed. Clastic rocks are classified based on their grain size and there is no systematic mechanism for classification of the other sedimentary rocks
7. The sedimentary rock types that are important four our discussions include sandstone (clastic), shale (clastic), limestone (chemical and geochemical), rocksalt (chemical), rock gypsum (chemical), and coal (organic). You should be able to loosely describe these rocks based on their grain size, elemental, and mineralogical composition.
Your next treading assignments will be for Wednesday:
1. is an excerpt from the chapter of Stephen Marshak's other introductory physical geology textbook, Earth: Portrait of a Planet, 3rd edition on the formation of oil and gas reservoirs that is available as a .pdf on our Sakai website and the and,
2. is an article from the website "Stuff You Should Know" called "How Oil Refining Works" by Craig Freudenrich.
Please have both read by the beginning of class on Wednesday.
Slides from today's lecture are on Sakai. Monday, we will finish up with the rock cycle and introduce plate tectonics and sedimentary basins.
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