Field Guide Stops 1-10

 

Travelling in the Altiplano required the team to get used to the elevation.   Over the course of the trip, we climbed from sea level to over 5100 m (17,000 feet)!   For reference, the peak of the highest mountain in the entire lower 48 states (Mount Whitney, California) is only 4,421 m (14,505 ft). 

A guide to the dangers of working at high altitude can be found here.

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Elevation Profile of Northern Chile

Here is a map showing the change in elevation from Calama to Linzor (Click map for a high resolution version)

We have split the trip into four sections - primarily to keep the navigation organized - and some pages will represent multiple waypoint stops at the same general location (aka La Poruna, San Pedro, etc.).   This first section covers from the City of Antofagasta to the Divasaco Ignimbrite seen on the road to Chao.

Satellite Image of Stops 1 through 10

 

City of Antofagasta

Antofagasta

23°38'44"S,  70°23'39"W
Elevation: Sea Level

The first thing you notice when the plane lands in Antofagasta is that there is no vegetation on the landscape that hasn't been planted there.  This is because rain in Antofagasta is extremely rare, averaging less than 4mm a year with recorded rain free droughts of over forty years!!  (Vargas, et.al., 2000)  Instead, it is the brightly colored houses and shops that bring color to the landscape. 

Antofagasta

Antofagasta is a prominant port town and has a population of over a quarter of a million people - the fourth largest in Chile.   Because of it's proximity to the mines, much of the economy in town is in support of the mining industry.

Geology:

The City of Antofagasta is underlain by Jurassic era basaltic andesite lava's known as the La Negra Formation.  (Ferraris and Di Biase, 1978)    These lava's are overlain by sandstone that is often embedded with or covered by dense layers of shells (see photo below) and local pebbles formed from a Pleistocene marine terrace.  (Ortlieb, 1995)

Geologic map of Northern Chile

(Figure from Hartley, et al., Rev. geol. Chile v.28 n.1 Santiago jul. 2001)


La Portada:

Eighteen kilometers north of Antofagasta is the famous La Portada (which means The Portal or Gateway in Spanish).  La Portada is a 140 foot tall archway of sandstone (resting on top of the La Negra) formed from continuous marine erosion of the shorline cliffs. 

La Portada sandstone archway in the sea.

Check out our amazing Photosynth of La Portada HERE

 

Shells layered into the cliff walls

 

 

 

 

 

 

The sandstone cliff walls are layered with an ancient densely packed layer of shells.

 

 

 

 

 

 

 

 

 

 


Some Field Notes:

Our goal in Antofagasta was to get supplies and rent reliable transportation.   Hertz was in town and had two four-wheel drive trucks (a MUST) ready to go and proved to be an excellent choice because of their customer service.    (We had a truck burn a clutch halfway through the trip and they drove a replacement out to meet us in less than a day!)     Renting two cars ensures that you will be able to drive out should something go wrong...  because on the Altiplano, you do not want to break down without another way out.    Also, there are no gas stations past Calama on our journey.    So, we packed in all the gasoline, water, food, cooking equipment, field gear, and camping gear into the two trucks. 

Speaking of water...   there is none.   What naturally occuring fresh water there is has filtered through run-off from the mines and has been known to contain high levels of arsenic.  (Pérez-Carrera et.al, 2010; Borgoño et.al, 1976)   Today, the city gets much of its water from sea water desalinization.   Either way, bottled water is a good idea in the city and an absolute must beyond this point on during the trip.  With the change in elevation and the amount of running around we did each day, staying hydrated was difficult at best.  You cannot have too much water!  (and remember...  Con Gas = with bubbles, Sin Gas = without)Axel, Benigno, and Stephanie

Finally, while we were here, we had the opportunitty to meet with researchers from the Universidad Católica del Norte.  These experts, who regularly work on the Altiplano, included our good friend - the one and only (and all around great guy) Dr (c) Benigno Godoy Neira.

 


Additional Sources:

  • Ferraris, F.; Di Biase, F. 1978. Hoja Antofagasta. Instituto de Investigaciones Geológicas de Chile, Carta Geológica de Chile, No. 30, 48 p.
  • Borgoño, J.M., et al. Environ Health Perspect. 1977 August; 19 : 103–105.
  • Boric, R.; Díaz, F.; Maksaev, V. 1990. Geología y Yacimientos Metalíferos de la Región de Antofagasta. Servicio Nacional de Geología y Minería, Boletín, No. 40, 246 p.
  • Hartley, et al., Rev. geol. Chile v.28 n.1 Santiago jul. 2001
  • Ortlieb, L. 1995. Late Quaternary coastal changes in northern Chile: fieldguide for International Geological Correlation Program Project 367, Late Quaternary records of Coastal Change, Annual Meeting, 1995. Orstom, 175 p. Antofagasta, Chile.
  • Pérez-Carrera, A. and Cirelli, Alicia.  2010.  Arsenic and Water Quality Challenges in South America in Water and Sustainability in Arid Regions, Part 3.   SpringerLink Publishing, Netherlands.  ISBN 978-90-481-2775-7.
  • Shiki, T.; Yamazaki, T. 1996. Tsunami-induced conglomerates in Miocene upper bathyal deposits, Chita Peninsula, central Japan. Sedimentary Geology, Vol. 104, p. 175-188.
  • Vargas, G. et al., Aluviones históricos en Antofagasta y su relación con eventos El Niño/Oscilación del Sur, Rev. geol. Chile vol.27 n.2 Santiago Dec. 2000.

City of Calama

Calama

 22°28'29"S,   68°55'6"W
Elevation: 2268m (7441 ft)


The City of Calama is just south of the mega-copper mine Chuquicamata and primarily serves as a bedroom community for the workers and their families.  This is the prime copper producing province in the world mainly due to the hyper arid environment. (Reich et al, 2009)  

Geology:

From Antofagasta to Calama runs the Antofagasta–Calama Lineament (ACL), a series of Northeast trending strike slip faults which is thought to have controlled the emplacement of the extensive porphyry copper deposits. (Palacios et al, 2007)   The town has consequently had its share of earthquakes including a 7.8 in 2005.  (The town was also completely destroyed in 1870 by an earthquake!)

The stratigraphic succession in the Calama Basin (from Moreno and Gibbons, 2007)

Geology of Calama

Related Info:

Renowned photographer Paula Allen did a photographic story on the Courageous Women of Calama

With a population of almost 150,000, the community has the basic services you might expect in any major city.  This was our last chance to stock up on gasoline, water, and food for some time!

Additional Sources:

  • Latorre C, Betancourt JL, Rylander KA, Quade J. 2002. Vegetation invasions into Absolute Desert: A 45,000-yr rodent midden record from the Calama-Salar de Atacama Basins, northern Chile (22–248 S). Geological Society of America Bulletin 114: 349–366

  • Moreno, T. and Gibbons, W.   The Geology of Chile.   Geological Society of London.  ISBN 186239220X. p. 84.

  • Palacios, C. et.al. (2007)  The role of the Antofagasta–Calama Lineament in ore deposit deformation in the Andes of northern Chile.  Mineralium Deposita; Volume 42, Number 3: 301-308.

  • Reich, M., et al.  2009.  Supergene enrichment of copper deposits since the onset of modern hyperaridity in the Atacama Desert, Chile.   Mineralium Deposita; Volume 44, Number 5: 497-504.

Stop 1: The Upper Rio San Pedro Ignimbrite

 

THE UPPER RIO SAN PEDRO IGNIMBRITE

22°19'1.85"S,  68°38'52.89"W

From Calama, we took the 21 North towards San Pedro which was now clearly visible to the North. We got off at the Village of Chui Chui and headed north along the Rio Loa river valley.

Petroglyphs dot the roadside

 

 

This stop is a tourist attraction as well as a geological stop that is located along the banks of the Loa River on the road from Calama toward San Pedro. There are petroglyphs carved into the Sifon Ignimbrite (8.1 Ma) also referred to as the Upper Rio San Pedro Ignimbrite.

 

 

  

This outcrop represents the most western part of the ignimbrite that continues north to San Pedro. In certain areas of the APVC the deposit is 800 m thick, while here is roughly 300 m thick, indicating that it is relatively proximal to the source or the valley fill. The Sifon is a massive crystal-rich deposit that lacks pumice clasts, and contains abundant biotite and lithics. The deposits underlying the Sifon are Pleistocene lake deposits.

There are also ruins on the opposite side of the petroglyphs that are most likely “Pukará de Lasanna” from Quechua Pukará, signifying “fortress”. Lasanna is a small village located 40 km northeast of the city of Calama and 8 km north of San Francisco de Chiu Chiu in the Antofagasta Region of northern Chile. The main cultural attraction of the village is a pre-Columbian fortress built in the 12th century that was declared a national monument in 1982. Peppercorn trees and desert sage characterize the landscape in the area and camping is possible in the campground adjacent to the ruins. 

Examining the Upper Rio San Pedro 



Stop 2: The Lower Rio San Pedro Ignimbrite

 

THE LOWER RIO SAN PEDRO IGNIMBRITE

21°56'28.36"S, 68°31'50.38"W

A nice outcrop of the Lower Rio San Pedro Ignimbrite is on the road between the San Pedro area and Turi/Chao. 

 

Extracting Pumice from the Lower Rio San Pedro Ig. 

 

The Lower Rio San Pedro Ignimbrite, 9.66 Ma is a dense-micro vesicular dacite with abundant lithics and juvenile pumice. The ignimbrite contains quartz, plagioclase, copper-colored biotite, titanite/sphene, but the pumice is crystal-poor (~ 25%) in relation to the other ignimbrites in the area. The Lower Rio San Pedro is a simple cooling unit of two distinct flow units with an average thickness of 20 m along the Rio San Pedro. 

 

 

Stop 3: La Poruna

   La Poruna

  21°53'33"S,    68°29'55"W
Elevation: 3577m (11733 ft)

 


 

Just about 30 miles north of Chui Chui, lie the San Pedro and San Pablo Volcanoes on the right and the La Poruna cone directly ahead. 

 

La Poruna cone (middle foreground) and the San Pedro Volcano (right) 

(Click for a larger view)  

 

La Poruna is a scoria cone on the western flank of San Pedro Volcano.   Several lava flows from La Poruna extend westerward for almost eight kilometers!  These were mapped in O'Callaghan and Francis, 1986 as part of their work on the San Pedro/Pablo Volcanoes. 

Geologic Map of LaPoruna

The flow is a basaltic andesite with ~59% Silica.   Juvenile block from the flow was dated (via Helium surface-exposure) at 103,000 years  (Worner et al, 2000). 

La Poruna from an aerial photograph

 

 

 

 

 

La Poruna is one of the primary  targets we have been researching as part of a project exploring lava flow morphology in satellite imagery.  

 

More information about that project can be found here.

 

 


Up close, it is spectacular!   

 

La Poruna Cone

 


 

The next three days, we spent measuring the flow margin lobes,

Measuring Lobes at La Poruna 

 

exploring crease structures in the lava,  

 

Axel explores a crease structure   

 

and climbing to the top of the cone for a perspective view of the flows.  

 

The view from the summit of La Poruna   

 

On top, the team stopped for a group picture! 

 

 The team poses for a group shot on top of La Poruna

 

 


 

Additional Sources:

  • O'Callaghan, L.J., and Francis, P.W., 1986. Volcanological and petrological evolution of San Pedro volcano, Provincia El Loa, North Chile. J. Geol. Soc. Lond. 143, 275-286
  • Wörner, G., Hammerschmidt, K., Henjes-Kunst, F., Lezaun, J., Wilke, H. (2000).  Geochronology ( ( 40 40 Ar- 39 39 Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from northern Chile (18°-22°S): Implications for magmatism and tectonic evolution of the Central Andes. Revista Geológica de Chile, v. 27 (02), pp. 205-240.

 

Stop 4: San Pedro Volcano

 

   San Pedro / San Pablo

  21°53'27"S,    68°23'44"W
Elevation: 6145m (20000 ft)

San Pedro Volcano

The San Pedro Volcano with the La Poruna Cone and lava flow in the foreground.   Dark material in the closer foreground is from a debris avalance caused when the older edifice collapsed leaving the horseshoe shaped crater we see today.

San Pedro Volcano Puffing

 

The San Pedro Volcano is a composite volcano and one of the highest active volcanoes in the world.  As we drove up, it was clearly puffing away from a fumerole at the top and continued to do so the entire time we were in view.  (Perhaps a puff around every minute or so)

The San Pedro Volcano at Sunset, taken from our camp in the La Poruna lava's (seen in the foreground).   Click the image for Hi-Rez.

 

   


 

 

Lava Flows at San Pedro

 The lava flows at San Pedro are significantly larger than the flows across the street at La Poruna. 
(Note the tractor trailer in the forground with the lava front just behind.)
 

Additional Sources:

Stop 5: Carcote Ignimbrite

 

CARCOTE IGNIMBRITE

21°53'41.91"S, 68°34'44.01"W

The Carcoté Ignimbrite, 5.6 Ma is a high silica rhyolite that is visible from the road. The ignimbrite flowed from the Aucanquilcha area and overlies the Sifon Ignimbrite, 8.1 Ma. The Carcoté is a pumice-rich rhyolite, typically 5-6 m thick and has a white-gray color.

The pumice clasts show a sillar texture, indicative of vapor phase alteration. The post-depositional texture is created when the matrix recrystallizes and welds together as bubbles are stretched as they ascend up the conduit. This process results in silky pumice clasts. Lithic fragments are small (~ 2 cm) and rare and the matrix is fine-grained, crystal-poor (10-15%) and contains abundant plagioclase and biotite

Baker and Francis, 1978

Stop 6: Sifon Ignimbrite

  

 

THE SIFON IGNIMBRITE

21°54'42.33"S, 68°35'41.92"W

Sifon Ig.

The view of Rio Loa shows exposed ignimbrite and lake deposits. The lowest unit is Sifon Ignimbrite, a crystal-rich dacite deposited 8.1 Ma. In this northern area, the Sifon is a single, non-welded, homogenous deposit with a thickness of roughly 8-10 m (de Silva, 1989). Abundant plagioclase and biotite exist within the Sifon and lithics are rare. Small pumice clasts (~3 cm) have silky textures and contain plagioclase and biotite (de Silva, 1989).

The Sifon is overlain by Carcoté Ignimbrite, ~5.6 Ma along the Rio Loa. The uppermost units are younger lake deposits from Chiu Chiu. In some areas, the Lower Rio San Pedro Ignimbrite, 9.66 Ma outcrops below the Sifon. As the Andes were being uplifted the river was downcutting to form the valley that we see today.  


Stop 7: Salar de Ascotan

 Salar de Ascotan

  21°41'9"S,    68°15'1"W
Elevation: 3735m (12253 ft)

Aucanquilcha Volcanic Cluster with Salar de Ascotan in the foreground

After two days of running around lava flows, we decided to go for a drive.    Our destination was a fall deposit between the Salar de Ascotan and the Salar de Carcote, but we also wanted to go to get a glimpse of the volcanoes Ollagüe and Aucanquilcha.

Salar de Ascotan in the foreground.

The Salar is home to several Boron and Lithium mines as well as the first wildlife we had seen since leaving Antofagasta!  Both Flamingos and Vicuna call the Salar home drinking from the water that remains in the trapped lakes.    These lakes also contain a endangered and very rare species of fish known as Orestias ascotanensis.  

 Astronauts about the International Space Station took this photo of the Salar de Ascotan

Astronauts on board the International Space Station took this picture of the Salar de Ascotan in October 2007.  (Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth.")


 

Additional Sources:

  • Jara, F. et al. 1995.  Reproduction in Captivity of the Endangered Killifish Orestias ascotanensis (Teleostei: Cyprinodontidae). Copeia, Vol. 1995, No. 1 (Feb. 15, 1995), pp. 226-228
  • Johnson, A.W., Behn, F. and Millie, W.   The South American Flamingos.  The Condor, Vol. 60, No. 5 (Sep. - Oct., 1958), pp. 289-299

Stop 8: Salar de Carcote

 Salar de Carcote

  21°25'11"S,    68°23'3"W

Elevation: 3694m (13096 ft)


About 60 km North of San Pedro, we arrived at our destination, the Salar de Carcote.   The Carcote is a salt flat that covers over 100 square kilometers and all that remains of an ancient lake!

Salar de Carcote

Extensive background information on the Carcote is available here.

 Looking out across Carcote towards Aucanquilcha

Looking out across Carcote towards Aucanquilcha

We came there to examine an amazing layered fall deposit from either Aucanquilcha or Ollagüe.

Layered fall deposit

While there, we ran into the two most masochistic bikers on the planet!

Biking the Altiplano!

Stop 9: Chanka

Chanka (aka Pabellón)

21°45'02.5"S, 68°19'09.8"W


 

Returning to the San Pedro/San Pablo area after visiting the salars, we came across the first, of many, major lava dome we would see on our trip. These enormous lava domes dot the APVC and represent a style of volcanism different than we had seen previously on our trip. The large eruptions that created the ignimbrites of the region, seem to have given way to the more gentle, effusive style of volcanism which created these domes. It is possible that the formation of many of these domes may represent the waning stages of the magmatic system that gives rise to the APVC.

 

Chanka

Right off the main road, Chanka was formed on the northwest slopes of Azufre Volcano, and just north of San Pedro.  Like most of the lava domes, Chanka is primarily dacitic in composition, and is extremely crystal rich (30%-40% crystals). The crystal rich nature of the lavas that formed Chanka, along with its dacitic composition, lead to incredibly viscous lavas. Due to this incredible viscosity, many of the domes take on a standard “torta” or cake shape, having steep sides and flat top. 

While the exact date of Chanka is unknown, it is probably post glacial in age.

 

Chanka Satellite Image

Azufre Satellite image with Chanka to the west (Cc)

Petrographic and mineralogic details

Chanka is of dacitic composition and high crystal content, generally over 30% crystals. The phenocryts seen are typically Quartz, Plagioclase, biotite and hornblende. There are frequent, finer grained, mafic enclaves present that show phenocrysts of Plagioclase, hornblende and some Olivine. The host lava also has a friable texture, due to some microvesiculation of the matrix.

Stop 10: Divisaco Ignimbrite

 

THE DIVISACO IGNIMBRITE

22°15'12.29"S, 68°28'26.91"W



This location is noteworthy due to the exposure of the Divisoco Ignimbrite, 10.6 Ma that underlies the Sifon Ignimbrite, 8.1 Ma. The Divisoco is the lowermost unit in the area north of the Rio Salado, and it lies directly above the basement rocks. The deposit has been described as a massive, crystal-rich (~ 60%) dacite containing quartz, plagioclase, biotite and hornblende. The Divisoco has a fine-grained matrix, abundant lithics and a pink color.