ROCKY MOUNTAINS
NATIONAL PARK
Front Range north of Boulder, Colorado,
USA (looking west from the Great Plains). Rocky Mountains National Park
(misnamed “Rocky Mountain National Park” by the American federal government) is
part of Colorado's Front Range. The mountains in this area are part of
the true Rocky Mountains (not all mts. in western North America are the
“Rockies”). The American Rockies are subdivided into three physiographic
provinces. This park is part of the Southern Rocky Mountains
Physiographic Province, characterized by the common presence of
Precambrian-aged igneous and metamorphic rocks.
Long's Peak & Beaver
Meadows
(looking ~S) in Rocky Mountains National Park, northern Colorado, USA.
The mountains in the
background are principally composed of Mesoproterozoic-aged (1.42 b.y.)
granites - the Silver Plume Granite (a.k.a. Long's Peak Granite).
The partially forested
valley in the foreground is Beaver Meadows, the site of the now-melted Big
Thompson Glacier. That was an alpine glacier (valley glacier/mountain
glacier) moving downhill (to the left) during the Late Pleistocene (= last Ice
Age). The forested ridge behind the greenish meadow is a lateral moraine
composed of glacial till.
Silver Plume Granite (a.k.a. Long's Peak
Granite) - 1.42 b.y. granite composed of K-feldspar, quartz, biotite mica, and
muscovite mica. This is from a roadcut southeast of Rocky Mountains
National Park.
Silver Plume Granite (a.k.a. Long's Peak
Granite) - 1.42 b.y. granite composed of K-feldspar, quartz, biotite mica, and
muscovite mica. These are outcrop photographs from roadcuts along Trail
Ridge Road (Rt. 34) in Rocky Mountains National Park.
Left: unweathered Silver Plume
Granite - pink speckled granite.
Right: partially weathered Silver
Plume Granite. The orangish-colored rock at left is iron-oxide stained
granite adjacent to a joint (fracture) that acted as a conduit for
groundwater. The whitish-gray speckled granite is bleached granite, again
from the influence of water from the joint at left. The pinkish-colored
rock at right is unaltered and unweathered Silver Plume Granite.
Xenolith in Silver Plume Granite (Mesoproterozoic,
1.42 b.y.). “Xeno” means “foreign”, while “lith” means “rock”. So,
xenoliths are “foreign rocks”. They represent pieces of wall rock that
fell into a cooling magma chamber and did not get melted and incorporated into
the magma before final solidification.
Ypsilon Mountain in the Mummy Range,
northern Rocky Mountains National Park, northern Colorado, USA. The rocks
at this mountain are principally late Paleoproterozoic-aged (1.713 b.y.)
biotite schists and gneisses.
Hagues Peak Granite at Fairchild Mountain
(Mummy Range, northern Rocky Mountains National Park, northern Colorado,
USA). The Hagues Peak Granite is early Mesoproterozoic in age (1.48
b.y.).
Iron Dike Gabbro at Hidden Valley (northern
Rocky Mountains National Park, northern Colorado, USA). This is a true
igneous dike - a planar intrusion that cuts across surrounding country
rock. It is composed of Mesoproterozoic-aged (1.316 b.y.) ferrogabbro.
Silver Plume Granite at Rock Cut (Trail Ridge
Road/Rt. 34), northern Rocky Mountains National Park, northern Colorado, USA.
The pinkish-grayish rock is
pegmatitic granite, a thin injection of Silver Plume Granite (early
Mesoproterozoic, 1.42 b.y.). The host rock is the dark, sparkly material
at top & bottom - it's late Paleoproterozoic-aged (1.713 b.y.) biotite
schist.
Mushroom Rocks - differentially weathered
& eroded outcrops of Silver Plume Granite injected into Precambrian
metamorphics.
Cream-colored rocks in
pedestal of “mushroom” = pegmatitic granite of the Silver Plume Granite
(early Mesoproterozoic, 1.42 b.y.).
Dark-colored rocks in cap of
“mushroom” - gneisses (late Paleoproterozoic, 1.713 b.y.).
Lava Cliffs to the north of Rt. 34
(Trail Ridge Road), northwestern Rocky Mountains National Park, northern
Colorado, USA. The rocks at Lava Cliffs are quite young, compared with
the majority of rocks in this park. The rocks at this cliff (see also the
close-up outcrop photo below) are Oligocene-aged volcanics. The rock is
described in the literature as rhyolitic welded tuff. It's actually a
porphyritic obsidian - large crystals set in a black glassy matrix. This
material originated as volcanic ash that was deposited and self-lithified
("welded") by the heat of the ash. The heat was sufficient to
re-melt most of the material, resulting in black glass.
Geologic Unit & Age: Braddock Peak Volcanic
Complex, Upper Oligocene, 27.7 m.y.
Pink snow & snow algae - this remarkably-colored
snow is often seen in Rocky Mountains National Park. The coloring agent
is biologic. The pink color is from the presence of cryophilic
algae. “Cryo” means “ice” or “cold”. “Philic” means “love”.
So, ice-loving algae are present. Surprisingly, the algae are not
red algae. They're actually green algae (chlorophytes). Dozens of
species of snow algae have been described and named in western America.
The reddish color is from a carotenoid pigment. The green algae also have
chlorophyll, of course.