Transcript Geology of Albuquerque - Geology - mr. gentry ehs

Geology of Albuquerque
Geology of Albuquerque
• The geology of Albuquerque, is a diverse
group of features, formed in different
ways.
For Example:
• To the east are the
–
Sandia Mountains.
• To the west are the
–
Albuquerque Volcanoes.
• Directly under your feet is the
– Rio Grande Rift, filled in by almost 4 miles of
sediment.
Sandia Mountains
•
The Sandias are
made up of mainly
two different types
of rock:
1. The Sandia Granite
2. The Madera
Limestone
Photo: L. Brown 10-03-10
Sandia Granite
• This pinkish colored rock makes up the
bulk of the Sandias.
• It is an igneous rock that formed 1.5 Ga
(billion years ago) when 950 C magma
was injected into the bedrock deep below
the Earth’s surface and then slowly
cooled.
Albuquerque's Environmental Story. 2006. http://www.cabq.gov/aes/s1index.html
Madera Limestone
• This is the white rock on top of the
Sandias.
• It formed 330 Ma (million years ago) from
sediment deposited on the bottom of a
shallow sea (the seas retreated from NM
~250 Ma).
• If you look closely at the Madera
Limestone, you will see many marine
fossils.
Madera Limestone
Photo: L. Brown 8-6-11
• How did rock that formed in an ocean get
up on top of the mountains?
Sandia Fault
• There is a fault at the base of the Sandias
which began to move around 7 – 10 Ma.
• The Sandias slowly rose along the fault to
their present height of 10,678 feet.
• The total vertical movement on the fault is
equal to about 5 miles (25,000 – 26,000
feet).
• The same rocks we see on top of Sandia
Crest lay buried beneath Albuquerque at
about 15,000 feet below sea level.
Albuquerque's Environmental Story. 2006. http://www.cabq.gov/aes/s1index.html
The Great Unconformity
• An unconformity is a surface that
separates two beds (or layers) of rock.
• It represents a time during which
deposition of sediment stopped &/or
erosion removed rock.
The Great Unconformity
• The great unconformity represents a huge
break in the geologic record.
• It is located between the Sandia Granite
(1.5 billion years old) and the Madera
Limestone (330 million years old).
• During the time between 330 Ma and 1.5
Ga, rock was not deposited or was eroded
away.
• The total amount of time missing from the
geologic record at this unconformity is
1.1 billion years.
Albuquerque's Environmental Story. 2006. http://www.cabq.gov/aes/s1index.html
Great
Unconformity
Photo: http://geoinfo.nmt.edu/
images/NMMag_la_luz_trail3.jpeg
Alluvial Fans
• Fan shaped deposits of sediment, called
alluvial fans, spread out from the base of
the Sandias, and extend all the way to the
river.
• Alluvial fans form when sediment is
deposited by water runoff from the
mountains.
Alluvial Fans
The Rio Grande Rift
• This is the long valley-like depression
through which the Rio Grande river flows,
and in which the city of Albuquerque is
located.
• A rift is a tear in the crust.
• It is a place where tensional stresses are
pulling the crust apart.
The Rio Grande Rift
• Rifting began here about 25 Ma.
• The Rio Grande Rift is >600 miles long
(from northern Colorado to Mexico) and 30
miles wide at Albuquerque.
The Rio Grande Rift
• The western margin of the rift is along the
Rio Puerco (about 20 miles west of
downtown) and the eastern edge is at the
base of the Sandias (along the Sandia
Fault).
• The rift is bounded by faults along these
two margins.
• The middle of the rift drops down along
the faults and the margins rise up.
Albuquerque's Environmental Story. 2006. http://www.cabq.gov/aes/s1index.html
Albuquerque Basin
• Albuquerque sits in a basin that is filled in
by sediments.
• The sediments that fill this basin eroded
from the Sandias to the east and from the
mesa to the west.
• Sediments have also been deposited in
the basin by rivers flowing from the north.
Albuquerque Basin
• The Albuquerque Basin contains >20,000
feet (3.8 miles) of young (less than 25 my
old) sediment.
Albuquerque Volcanoes
• The volcanoes located on the west side
of Albuquerque erupted 150,000 years
ago.
• They formed along a fracture zone in the
Rio Grande Rift.
• This fracture is well defined by the 6+
volcanoes that are aligned in a N-S
direction.
Albuquerque Volcanoes
• Rifting caused fractures in the crust that
acted as a conduit (kind of like plumbing)
for the magma to rise to the surface.
• The eruption was active along the whole
length of the fissure (~6 miles) at the same
time.
Albuquerque volcanoes
Photo: http://i.pbase.com/o4/75/47975/1/57914168.AlbuquerqueVolcano_32483.jpg