GSCI 1050 Lecture 9: 02.14.2017
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Department
Geoscience
Course
GSCI 1050
Professor
Jennifer Cooper Boemmels
Semester
Fall

Description
GSCI1050-002 02.14.17 Session 8 watch mini-lectures (snow day) In-Class Quiz Tuesday 2/21 - can bring notes again, same format (Sessions 6-9) Journal 2 due by Tuesday 2/21 by 11:59PM Midterm Exam 3/2! Review • silica content, temperature control viscosity
 • high silica content (felsic) traps volatiles, builds pressure and creates explosive eruptions • low silica content (mafic) is representative of Hawaiian lavas that have relatively low viscosity • Extremely slow/viscous magma slow doesn’t look like typical lava flow, but rather a steaming slope with some rock fall/increasing instability (it’s going down very slowly and solidifying along the edge of the slope, so you don’t see it) Mt. St. Helens • May 18, 1980 • geologically significant because could study it • plume of ash being violently ejected ◦ in this form because high silica content, volatiles trying to get released, pressure builds and explosive eruption occurred • magma flowing up from deep reservoirs started to pool beneath the surface, creating a dome (cryptodome) - summit started to bulge • slope became oversteepened, landslide occurred, pressure lowered and that triggered the lateral blast • destroyed everything in 230 square miles in 5-9 min • Mt. St. Helens is stratovolcano • part of Cascades (which represents volcanic arc) • on convergent boundary • generated by flux melting (subducting slab releasing volatiles, partial melting) Metamorphic Rocks Hard Rocks including Metamorphic Rocks -Metamorphic Definition and Classification -Metamorphic Grade and Facies -Hard Rock: Provinces -Hard Rock: Terranes • Which of the following is NOT a metamorphic process? Melting
 ◦ Recrystallization, Neocrystallization are metamorphic processes ◦ Neocrystallization - growth of new minerals ◦ Recrystallization - existing crystals recrystallize, grow larger • Metamorphism is significant transformation of rock by heat, pressure and motion without pervasive melting
 ◦ Ex: fossils in limestone (sedimentary form of calcium carbonate) ◦ Ex: Pure marble (calcite crystals that have been crystallized) • Texture and composition are important for any rock type ◦ Texture - size, shape ◦ Composition - based largely on original/parent rock (protolith) • Metamorphic rocks are classified by 2 dichotomies: “regional” vs contact, and foliated vs. unfoliated ◦ regional metamorphism —> foliated ▪ ex: Appalachain mts, metamorphic roc
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