A tour of the geological treasures of The Puna Plateau in northern Argentina and Chile. Continuing Olivier and Caroline’s epic cycle journey through South America.
“What’s the altitude?” I look at the altimeter: 4,840m above sea level. “Higher than Mont Blanc!”, and we burst into tears together. What a surprise: this pass, the highest point of the crossing of the Puna Plateau between San Salvador de Jujuy, Argentina, and San Pedro de Atacama, Chile, is not even indicated on our map! Exhausted, cold and out of breath, we start cycling down the pass toward Atacama, the driest desert in the world.
A lunar landscape opens: a desolate desert stretching between stratovolcano peaks which rise out of the high plateau. In the distance, steam from the Lascar volcano rises through the deep blue sunset, seeming to greet us with an ironic welcome.
Geological Introduction to The Puna Plateau
The Puna Plateau along the asphalted national road N°52. © Olivier Galland.
The Puna Plateau The Puna Plateau is easily accessible via the asphalted national road N°52. The geomorphology of the Puna Plateau consists of a series of flat basins separated by low hills, quite different from the wide, perfectly flat Altiplano Plateau further north. The most spectacular of these high-altitude basins is the Salinas Grandes, a vast salt flat that extends over 120 km2.
The Puna Plateau is itself a geological curiosity. Together with the Altiplano, it is the second largest high plateau after Tibet. It extends over 180,000 km2 between northern Argentina and Chile and has an average altitude of more than 4,200m. This exceptional elevation is due to an anomalously thick crust (~80 km), the result of Cenozoic shortening of the western margin of South America. The detailed geological processes leading to the development of the plateau are not known, but it probably results from complex interactions between tectonics, arc magmatism, and crustal melting, coupled with geomorphological processes specific to dry climates.
The Quebrada de Humahuaca Canyon
The Quebrada de Humahuaca is a deep canyon that extends at the eastern foot of the Puna Plateau, in the Jujuy province in north-western Argentina. It is a UNESCO World Heritage Site, thanks to its spectacular scenery and archeological remnants.
Cerro de los Siete Colores (Hill of the Seven Colors)
The Hill of the Seven Colors at Purmamarca, Quebrada de Humahuaca, Argentina. From background to foreground: (1) light brown mountain – Ordovician sand-clay deposits; (2) green with purple stripes – Precambrian marine sedimentary rocks; (3) red-pink top of the foreground hill – Tertiary sand-clay deposits; (4) striped white, pink and purple bottom of the foreground hill – Upper Cambrian marine sandy deposits, partly quartzitic. © Olivier Galland.
What make the landscape so stunning are the numerous outcrops of colorful red geological formations.
The most spectacular and famous one can be seen at the Cerro de los Siete Colores (Hill of the Seven Colors), behind the village of Purmamarca at the beginning of national road N°52.
There, a combination of sedimentary and tectonic processes have brought into contact geological formations of distinct ages, spanning from Precambrian to Tertiary, and of contrasting colors due to copper oxides (green), copper sulfides (blue) and iron oxides (red).
Paleta del Pintor (Painter’s palette)
Another spectacular locality is the Paleta del Pintor (Painter’s palette) in front of the village of Maimará, a few kilometers north of Purmamarca. The landscape offers a spectacular view over steeply tilted geological formations of contrasting colors, evoking the diversity of a painter’s palette.
Paleta del Pintor (Painter’s palette) in front of the village of Maimará, a few kilometers north of Purmamarca. Steeply tilted geological formations of contrasting colors, evoke the diversity of a painter’s palette.© Olivier Galland.
Here, the north-north-east to south-south-west-trending gorge follows a basement fault that allows the exposure of dark red Upper Cambrian quartzite, covered by yellow to red continental Cretaceous to Paleogene deposits. The interaction between the steeply dipping strata and erosion reveals an astonishing landscape of successive characteristic rule-of-V features.
The Quebrada de Humahuaca hosts numerous archeological treasures that bear witness to more than 10,000 years of human presence. There is evidence that the valley has been a major trading path for successive civilizations, including prehistoric hunter/gatherers, flourishing pre-Hispanic towns and fortresses, the Inca empire, Spanish villages and traces of republican fights for independence. Given that the geological landscapes amaze tourists from all over the world, their esthetical power has doubtless deeply inspired the life, art and spirituality of indigenous populations through time.
The Chuquicamata Copper Mine
The Largest Open Pit Copper Mine in the World (by excavated volume)
The Chuquicamata copper mine, a 4.3-km long, 3-km wide and 1-km deep hole. In the shaded part of the mine, between the white dust cloud and the right flank, a darker steeply-dipping track, ending up in collapse deposits near the bottom of the mine, is visible: it is the trace of the fault that controlled the emplacement of the magmatic intrusions and the ore. © Olivier Galland.
The Chilean flank of the Puna Plateau corresponds to the Atacama region, which displays several remarkable geological sites that can be visited. One of them is the Chuquicamata mine, the largest open pit copper mine in the world by excavated volume. The dimensions of this huge hole are gigantic: 4.3 km long, 3 km wide and 900m deep! Actually, this is the mine of superlatives: it represents one of the largest known copper resources (13%); it is the mine with the largest total production (29 million tons in 2007); and it represents more than one third of Chile’s foreign trade. Chuquicamata is also a significant producer of molybdenum – but it is also probably the largest polluter in South America. Note that Ernesto Guevara visited Chuquicamata when he was young in 1952. This visit opened his eyes to working conditions, and greatly contributed to the development of the revolutionary leader ‘Che’ Guevara.
Geological Formation of the The Chuquicamata Ore Deposit
The Chuquicamata ore deposit is a typical porphyry copper, and is part of the broader Chuqui Porphyry Complex. It consists of a magmatic intrusive complex of dioritic to granodioritic compositions. After their emplacement in the shallow Earth’s crust, these intrusions cooled down and liberated large volumes of fluids rich in dissolved minerals, leading to a kilometer-scale hydrothermal zone where copper and molybdenum minerals, among others, precipitated along veins. The Chuquicamata porphyry was emplaced during the Eocene-Oligocene along a regional north-south striking fault, the trace of which is visible in the open pit mine.
The El Tatio Geyser Field
Part of the El Tatio geyser field.© Olivier Galland.
A journey to the El Tatio geyser field is unforgettable, not only for the beauty of the spectacular manifestations of the active earth, but also for the body: the spectacle is best at the coldest hours of the day, meaning -10°C to -15°C! Indeed, the extreme temperature contrast between the air and the steaming ground give rise to the dramatic view of white steam columns rising over a vast, high altitude (4,300m above sea level) flat plateau surrounded by a string of dormant stratovolcanoes, the peaks of which are illuminated by the burning colors of the sunrise. With a total area of 10 km2, El Tatio is the third largest geyser field in the world, and the largest in the southern hemisphere. It displays boiling water fountains, hot springs (60–80°C), small geysers, mud pools, mud volcanoes and sinter terraces.
Formation of The El Tatio Geothermal Field
The El Tatio geothermal field is located around a large caldera complex, which is part of the regional-scale Altiplano-Puna Volcanic Complex. The collapse of the caldera was coeval with the Quaternary eruption of a large ignimbrite, i.e. an immense volcanic explosion of pyroclastic ash, lapilli and molten blocks flowing down the volcano flanks as pyroclastic density currents. The current geothermal activity strongly suggests that a body of hot magma remains under the caldera, heating up ground water.
Potential for Geothermal Energy
The El Tatio geothermal field represents promising potential for geothermal energy. Geothermal energy projects at El Tatio were initiated as far back as the 1920s, but drilling considerably impacted the natural geyser activity, and several technical and economic challenges prevented the development of profitable geothermal power production. The last attempt was dramatically abandoned after the blow-out of a drilling well in September 2009, generating a 60m-high steam fountain and creating negative publicity for geothermal energy in Chile – much to the satisfaction of tourists and the relief of indigenous populations.
The Atacama Lithium Deposit
Licancabur volcano, the sentinel dominating the Salar de Atacama.© Olivier Galland.
A remarkable geomorphological feature of the Atacama region is a large salt flat, the Salar de Atacama. It lies at an elevation of 2,300m and is confined between the western flank of the Puna Plateau and the moderately high Cordillera de Domeyko. It is covered by a salt crust, where nothing grows, and the sun’s radiation can damage exposed skin in minutes. Humans would keep clear of this hostile area, if it did not hide the precious brine that contains an element that has become more and more essential in our modern world: lithium. The Atacama is one of the largest and purest active sources of lithium, containing 27% of the world’s known reserves. In 2008, Salar de Atacama provided 30% of the world lithium supply, produced as lithium carbonate and lithium chloride salts.
Formation of the Atacama Lithium Deposit
The Salar de Atacama depression is an endorheic basin, i.e. there is no outlet to the sea. Trapped brines from the rivers remain here and as water evaporates, concentrated lithium deposits are precipitated.© Olivier Galland.
This lithium deposit is the result of an optimal geological, geographical and climatic combination. The geothermal fields associated with active volcanism produce waters rich in various salts, including lithium; brines from the El Tatio geyser field are, for instance, considered to be the major source of lithium in Atacama. Once liberated in the rivers, the brines flow down to the Salar, where they remain trapped. Indeed, the Salar de Atacama depression is an endorheic basin, i.e. there is no outlet to the sea. Consequently, the salts brought by the surrounding rivers accumulate through time. Finally, the extremely arid climate evaporates the water, and concentrates the salts in the brines to form the hostile salt crust at the surface. The exceptional lithium concentration of 2 g/L in Atacama is unique.
The production of lithium utilizes the sun as the main processing energy source. The brines are pumped out of their host aquifer into evaporation ponds, where lithium is concentrated by evaporation. During the process, several salts precipitate successively in distinct ponds: calcium sulfate (gypsum), sodium chloride (halite), potassium chloride (sylvite) and eventually lithium chloride and carbonate.
Pachamama: Mother Earth
Contemplating such geological marvels naturally generates a great respect for the planet. Such respect is very much present among indigenous populations through the Pachamama divinity, or Mother Earth in Aymara and Quechua languages. More than a goddess, Pachamama represents a mindset of gratitude to the Earth for fertility over planting and harvesting, and for sustaining life in harmony. People in western countries have been unplugged from this direct connection to the Earth, and a journey to the Puna region has the potential to re-establish it.
Further Reading…
A selection of GEO ExPro articles similar in content or related to topics discussed.
Geothermal in the Future Energy Mix
Marit Brommer; International Geothermal Association
Geothermal energy is still a marginal player in the energy mix, but geoscientists will be needed to help it play its part in the energy transition.
This article appeared in Vol. 15, No. 4 – 2018
Southern Chile’s Ring of Fire
Olivier Galland, University of Oslo, and Caroline Sassier
Southern Chile is the setting for the dramatic snow-covered volcanoes of the Pacific Ring of Fire. This stunning volcanic range is the surface expression of the subduction of the Pacific seafloor under the western margin of South America. The southern Chilean Andes offer a fantastic playground for those who want to experience volcanoes – either peacefully or loaded with adrenaline!
This article appeared in Vol. 12, No. 5 – 2015
