Primary Structures The value of measuring section Measuring
section is the process of making detailed notes about each of the
layers/intrusions found in an outcrop. The process really forces
you to LOOK. We work up or down section as appropriate. Note
rock/sediment type, primary and secondary structures, fossils, note
color, orient surfaces and lineations with the brunton, etc. Slide
2 Slide 3 Slide 4 Munsell Rock Color Charts To note colors, I use
one of these, but they are expensive. In your notes, just use your
own judgment. Also note whether the sample is wet or dry Slide 5
Graded Beds Flysch: old [Alpine] name for thick sequences of
turbidites laid down in a deep trench marking an active plate
boundary (like a subduction zone). PM p17 Slide 6 Graded Bedding
(2) Discuss Younging direction. Slide 7 Cross Beds Ripples, dunes
and deltas in cross section, usually truncated tops (younging
direction) and current direction indicated Notice the lens in the
photo to give scale. Use whatever is the right size and is a known
size, coin, a pencil, a ruler, your notebook, etc. Slide 8 Surface
Markings: Load Casts Sand layer over mud, blobs of sand sink into
mud. Slide 9 Flute Casts Vortices dig into the unconsolidated
sediment. Shallower and wider downstream. Slide 10 Mudcracks They
curl up when they form, and give the younging direction Slide 11
Asymmetrical Ripples Steep face on downstream side. Slide 12 Pillow
Lavas Lava erupted under water (MOR, rift valley lakes), or flowed
into water (Hawaii) Slide 13 Unconformities Angular Unconformity
Nonconformity Disconformity Slide 14 Recognizing Unconformities and
erosional surfaces: Channeling Slide 15 Recognizing Unconformities:
Basal Conglomerate Slide 16 Recognizing Unconformities: Age
discordance
http://www.sciencedirect.com/science/article/pii/S1631071308002800
Ludlow 423- 419 Mya Givetian 392-385 Mya Unc ~30My Slide 17
Recognizing Unconformities: Soil Horizons Root Casts Slide 18
Halokinesis: Salt layer movements Buoyancy Salt density about 2200
kg/m 3 Sedimentary Rock average density 2500 kg/m 3 When the
positive buoyancy [dense sediment over light salt] is sufficient to
upwarp the sediment above, the salt will rise. PM p 26
http://search.datapages.com/data/open/offer.do?target=%2Fspecpubs%2Fmemoir65%2Fch20%2F0413.htm
Slide 19 Halokinesis: Differential loading This may occur when the
downward force on the salt layer varies laterally. PM p.26 Slide 20
Oil traps Salt Diapir Diapir, pierces overlying strata Dome, upward
bulge Slide 21 Igneous Rocks 3 ways of making primary magma, all
basaltic Slide 22 Plutonic and Volcanic Igneous Structures
Laccolith like a sill, but bows up overlying strata to make a dome
Slide 23 Bowens Reaction Series Molten- VERY Hot No solids Molten-
Not so hot 100% Solid First mineral to crystallize out Slide 24
Fine crystals Need a microscope Course crystals Easily seen Low
silica, HOT, fluidHigh silica, warm, viscousIntermediate Slide 25 A
size comparison of the three types of volcanoes Slide 26 A Pahoehoe
lava flow Slide 27 T ypical aa flow Broken, often further from vent
Slide 28 Fluid basalt forms lava tubes Checking Bowens Reaction
Series Slide 29 Materials extruded from a volcano Pyroclastic
materials Tephra Propelled through the Air Types of pyroclastic
debris Dust 0.001 mm and Ash < rice sized Cinders or Lapilli -
pea to walnut-sized material Particles larger than lapilli Bombs -
> 64 mm ejected as hot lava -Surtsey Is. Bombs the size of
busses Slide 30 A nue ardente on Mt. St. Helens Slide 31 A volcanic
bomb Bomb is approximately 10 cm long Some the size of a Bus Slide
32 Tephra forms Tuff Source: Gerald & Buff Corsi/Visuals
Unlimited, Inc. St. Lucia Anecdote Slide 33 Tephra layers fine away
from source Slide 34 Pumice Felsic magmas with high water content
may bubble out of a vent as a froth of lava. Quickly solidifies
into the glassy volcanic rock known as Pumice.
http://volcanoes.usgs.gov/Products/Pglossary/pumice.html Slide 35
Mt Mazama Eruption and Caldera Collapse 4700 BC S Oregon Ngorongoro
Crater in Tanzania similar 2 mya Slide 36 Volcanism on a tectonic
plate moving over a hot spot Slide 37 Hey, the plate changed
direction ! Flood Basalts Hot Spot currently forming Hawaii Slide
38 Flood Basalts Fluid basaltic lava extruded from crustal
fractures called fissures e.g., Columbia River Plateau, Deccan
Traps in India Cover huge areas Plumes from Mantle Slide 39 Flood
Basalt erupted from fissures - Snake River Plain, southern Idaho
Plume Activity Slide 40 Lava Plateau Formation Slide 41 Formation
of a volcanic neck Slide 42 Slide 43 Spanish Peaks and Radiating
Dikes (southern CO) Slide 44 Plutonic igneous activity Types of
intrusive igneous features Dike a sheetlike injection into a
fracture Discordant - cuts across pre-existing Sill a sheetlike
injection into a bedding plane Concordant - lies parallel to
bedding Laccolith A mushroom-shaped concordant Slide 45 A sill in
the Salt River Canyon, AZ Sill: Sediments above and below sill are
baked. Lava Flow, just baked below. Slide 46 Why No C-C collisions
Slide 47 Plate tectonics and igneous activity Igneous activity
along plate margins Mid-Ocean Ridges Basaltic Pillow Lavas Great
volumes of volcanic rock produced along oceanic ridges New ocean
floor Mechanism of spreading or rifting Lithosphere pulls apart and
thins Less pressure results in partial melting in mantle
http://www.archipelago.nu/SKARGARD/ENGELSKA/ICELAND/surtsey.htm
Slide 48
http://volcanoes.usgs.gov/Products/Pglossary/ancientseq.html
Basaltic Pillow Lavas Slide 49 Plate tectonics and igneous activity
Igneous activity along Subduction zones Descending plate partially
melts Magma slowly moves upward Rising magma can form either A
Volcanic Island Arc if ocean-ocean plate collision (Aleutians,
Japan, etc.) A Continental Volcanic Arc if ocean- continent plate
collision (Sierra Nevada) Slide 50 The Cascades, Washington State
Slide 51 Slide 52 Plate tectonics and magmatism Intraplate
volcanism Associated with plumes of heat in mantle Form localized
volcanic regions in the overriding plate called a hot spot Produces
basaltic magma sources in oceanic crust (Hawaii) Produces granitic
magma sources in continental crust (Yellowstone Park) These
differences are predicted by a Crust-Melting model of Granite
generation Slide 53 Slide 54
http://www.mt-fuji.co.jp/Photo/Photo.html Notice the potential for
a huge lahar during the eruption of this big composite volcano
(stratovolcano), Mt. Fugiyama.
