Geology of Albuquerque Geology of Albuquerque The geology

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, 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/s 1 index. 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/s 1 index. 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/s 1 index. html

Great Unconformity Photo: http: //geoinfo. nmt. edu/ images/NMMag_la_luz_trail 3. jpeg

Alluvial Fans • Fan shaped deposits of sediment, called alluvial fans, 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 valley 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. up

Albuquerque's Environmental Story. 2006. http: //www. cabq. gov/aes/s 1 index. 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/o 4/75/47975/1/57914168. Albuquerque. Volcano_32483. jpg