QA

 What processes must take place to transform rocks into sediment? o Exposed rock ->weathering ->fragments  What processes normally take place in the transformation of sediments to sedimentary rock? o Sediments compact due to increased pressure, warmth can create minerals between grains  What are the processes that lead to the formation of a metamorphic rock? o Geothermal gradient creates instability leading to transformation of minerals  What is the significance of the term reaction in the name of the Bowen reaction series? o As temp decreases, older minerals react w remaining magma  Why is it common for plagioclase crystals to be zoned from relatively calcium-rich in the middle to more sodium-rich on the outside? o Plagio = calcium rich. As temp drops, sodium increases surrouding  What must happen within a magma chamber for fractional crystallization to take place? o Denser minerals sink & separate from remaining magma which becomes more felsic  Explain the difference between aphanitic and phaneritic textures. o Phaneretic = larger  Explain the difference between porphyritic and pegmatitic textures. o Porphyritic = 2 stage cooling, variation in crystal size  Name the following rocks: o 1. An extrusive rock with 40% Ca-rich plagioclase and 60% pyroxene  Basalt o 2. An intrusive rock with 65% plagioclase, 25% amphibole, and 10% pyroxene  Diorite o 3. An intrusive rock with 25% quartz, 20% orthoclase, 50% feldspar, and minor amounts of biotite  granite  With respect to tabular intrusive bodies, what is the difference between a concordant body and a discordant body? o Concordant = parallel (sill). Discordant = cuts across (dyke)  Why does a dyke commonly have a fine-grained margin? o Dyke only forms once rock has cracked, which only takes place after it cools. Hot magma flooding in cools quickly on edges = fine grains  What is the difference between a batholith and a stock? o Batholith = larger area exposed  Describe two ways in which batholiths intrude into existing rock. o Melting through, collapsing rock falls through magma, push aside  Why is compositional layering a common feature of mafic plutons but not of felsic plutons? o Felsic magma = more viscous; mafic = less viscous, material sinks and creates layers