The Geology of Pacific Northwest Volcanoes, Mountains and Earthquakes
Lab 4: Accreted Terranes Lab
NAME_________________________ DATE _______________
In this lab you will be creating a map based on the major accreted terranes of the
Western coast of North America, mainly in Oregon. The thing about accreted terranes is
that, geologically, they are a mess. They have everything you could possibly imagine in
them, sedimentary rocks, igneous rocks, metamorphic rocks, continental rocks, oceanic
rocks, fossils, etc. In fact, they are so messy the crazy geology is usually called a mélange
(the French word for mixture). So, today you are going to create your own map of these
accreted terranes and you are going to decipher what type of accreted terrane they are
based on their rock assemblage.
PART 1:
I. You will need to assemble your map by cutting out your accreted terranes and
gluing them to the map based on the borders shown and the cities on both the
terranes and the main map.
II. Once your terranes are glued onto the main map you will color them based on
their age and names:
a. IMT—Intermontane Terrane: Middle to late Jurassic Accretion BLUE
b. OB—Omineca Belt: Middle to late Jurassic Accretion RED
c. KT—Klamath Terrane: Late Jurassic to Early Cretaceous GREEN
d. CPC—Coast Plutonic Complex: Middle Cretaceous YELLOW
e. EOT—Eastern Oregon Terranes: Middle Cretaceous PURPLE
f. INT—Insular Super Terrane: Middle to late Cretaceous LIGHT BLUE
g. OT—Olympic Terrane: Tertiary ORANGE
h. CT—Coastal Terrane: Tertiary to present BROWN
III. Now, using the attached geologic timeline, tell me the approximate ages of each of
the terranes and volcanic arcs:
a. Intermontane Terrane: __________________
b. OB—Omineca Belt: __________________
c. KT—Klamath Terrane: __________________
d. CPC—Coast Plutonic Complex: __________________
e. EOT—Eastern Oregon Terranes: __________________
f. INT—Insular Super Terrane: __________________
g. OT—Olympic Terrane: __________________
h. CT—Coastal Terrane: __________________
The Geology of Pacific Northwest Volcanoes, Mountains and Earthquakes
Lab 4: Accreted Terranes Lab
PART 2:
Use the following rock assemblages to tell me what type of terrane each of the 7
Terranes are mapped above. A description is given for each type of terrane first, named
A, B, C, or D. After each rock assemblage for the 7 Terranes there is a blank space to list
the type of terrane(s) related to it. (Know that sometimes these terranes occur together,
so there can be more than one answer.)
A. Ophiolite: a section of oceanic crust that contains from top to bottom:
ultramafic rocks, gabbro, sheeted dikes, pillow basalts, silicious ooze
B. Volcanic Island Arc: Erupted volcanic rocks intruded by numerous diorite,
granodiorite, and granite bodies that intruded into the island arcs.
C. Oceanic Plateaus: Some of the rocks are limestone formed from coral
reefs in a marine environment Also contains submarine fans similar to
those currently being formed on the continental slope off the west coast.
D. Continental Volcanic Arc: Extensive folding, faulting, and metamorphism
due to convergence of a oceanic plate, widespread intrusion by granites.
I. Intermontane Terrane contains erupted volcanic rocks and intruded by granitic
rocks and packets of limestone and coral fossils.__________________
II. Omineca Belt consists of a wide spread area of mainly of granite and gneiss (a
metamorphic rock consisting of dark and light mineral bands).
_________________
III. Klamath Terrane Ryolite and andesite intruded by granites. Limestone pockets
and coral fossils. Also contains sheeted dikes and pillow lavas. _______________
IV. Coast Plutonic Complex: Massive amounts of molten granite injected in this area
metamorphosing local country rock into a glittering medium-grade metamorphic
rock called schist. __________________
V. Eastern Oregon Terranes consists of volcanic rocks like andesite, intruded by
numerous diorite, granodiorite, and granite bodies . Laos contains sequences of
volcanic sediments with limestone and fossils of coral reefs. These aforementioned
sequences are sandwiched pillow basalts, gabbros and sheeted dikes.
__________________
VI. Insular Super Terrane: contains erupted volcanic rocks and intruded by granitic
rocks and packets of limestone and coral fossils. __________________
VII. Olympic Terrane contains a lot of basalt and pillow basalts. Also contains Also
contains submarine fans similar to those currently being formed on the
continental slope off the west coast.: __________________
VIII. Coastal Terrane contains gabbro and a large amount of basalt. Also contains
submarine fans similar to those currently being formed on the continental slope
off the west coast.__________________
The Geology of Pacific Northwest Volcanoes, Mountains and Earthquakes
Lab 4: Accreted Terranes Lab
Geological Society of America Time Scale:
http://www.geosociety.org/science/timescale/timescl.pdf