Recent expansion in the demand for clean-energy and efficient technologies has led to demand for a variety of exotic, rare, or “strategic” metals. Some of these are physically rare, while others are economically or politically unavailable. In order to fill the gap between supply and demand, and to ensure future resources, various unconventional resources are being examined. This chapter discusses deep-ocean and industrial ecology–based solutions for providing these materials and provides considerations of how such resources can be considered within a framework of sustainable development. Specifically, this chapter addresses the importance of the social elements of the rare metals supply chain, examining the elements of local stakeholder impact and the broader, global public interest represented by the technologies utilizing such metals. The chapter also considers how technical and environmental knowledge derived from geosciences can have an impact on stakeholder support for alternative resources.

Integrated magmatic, structural, and geophysical data provide a basis for modeling the Neogene lithospheric evolution of the high Central Andean Puna-Altiplano Plateau. Reconstruction of three transects south of the Bolivian orocline in the Altiplano and Puna Plateau shows processes in common, including subduction characterized by relatively shallow and changing slab dips, crustal shortening, delamination of thickened lower crust and lithosphere, crustal melting, eruption of giant ignimbrites, and deep crustal flow. Temporal similarities in events in the three transects can be correlated with changes in the rate of westward drift of South America and slab rollback. Temporal differences between the three transects can be attributed to variations in Nazca plate geometry in response to southward subduction of the aseismic Juan Fernandez Ridge. Subduction of the north-south arm of the ridge can explain an Oligocene flat slab under the Altiplano, and subduction of a northeast arm of the ridge can explain a long period of relatively shallow subduction characterized by local steepening and shallowing. Major episodes of ignimbrite eruption and delamination have occurred over steepening subduction zones as the ridge has passed to the south. Late Miocene to Holocene delamination of dense lithosphere is corroborated by published seismic images. The southern Altiplano transect (17°S–21°S) is notable for high, structurally complex Western and Eastern Cordilleras flanking the Altiplano Basin, the eastern border of which is marked by late Miocene ignimbrites. The broad Subandean fold-and-thrust belt lies to the east. The Neogene evolution can be modeled by steepening of a shallowly subducting plate, leading to mantle and crustal melting that produced widespread volcanism including large ignimbrites. Major uplift of the plateau at 10–6.7 Ma was dominantly a response to crustal thickening related to Subandean shortening and peak lower-crustal flow into the Altiplano from the bordering cordilleras as the ignimbrites erupted, and partly a response to delamination along the eastern Altiplano border. A smaller ignimbrite volume than in the northern Puna suggests the Altiplano lithosphere never reached as high a degree of melting as to the south. An Oligocene flat-slab stage can explain extensive Oligocene deformation of the high plateau region. The northern Puna transect at ~21°S–24°S is notable for voluminous ignimbrites (>8000 km 3 ) and a narrower Subandean fold-and-thrust belt that gives way southward to a thick-skinned thrust belt. The evolution can be modeled by an early Miocene amagmatic flat slab that underwent steepening after 16 Ma, which led to mantle melting that culminated in widespread ignimbrite eruptions beginning at 10 Ma, peaking in the backarc at ca. 8.5–6 Ma, restricted to the near arc by 4.5 Ma, and ending by 3 Ma. The formation of eclogitic residual crust caused periodic lower-crustal and lithospheric mantle delamination. Late Miocene uplift was largely due to crustal thickening in response to crustal shortening, magmatic addition, and delamination. Crustal flow played only a minor role. The high degree of mantle and crustal melting can be explained as a response to steepening of the early Miocene flat slab. The southern Puna transect at ~24°S–~28°S is notable for eastward frontal arc migration at 8–3 Ma, intraplateau basins bounded by high ranges, long-lived Miocene stratovolcanic-dome complexes, voluminous 6–2 Ma ignimbrites, 7–0 Ma backarc mafic flows, and the latest Miocene uplift of the reverse-faulted Sierras Pampeanas ranges to the east. Its evolution can be modeled by a moderately shallow slab producing widespread volcanism with subsequent steepening by 6 Ma, leading to delamination of dense lithosphere culminating in the eruption of the voluminous Cerro Galan ignimbrite at 2 Ma.

Abstract This seven-day field trip is designed to examine the distinctive magmatic, structural, and sedimentological features of the late Oligocene to Recent evolution of the southern part of the high central Andean Puna plateau and the southern Central Volcanic Zone magmatic arc. The stops for Days 1–5 between 23° and 27°S latitude in Argentina emphasize the distinctive magmatic and structural features of the Puna region, which comprises the southern half of the central Andean Puna–Altiplano plateau. Differences between the northern and southern Puna are highlighted. Among the features to be observed are (1) giant Miocene ignimbrites of the northern Puna, (2) distinctive normal and strike-slip faults and associated shoshonitic lavas of the central Puna, (3) the intraplate and calc-alkaline lavas of the southern Puna, (4) the silicic calderas of the southern Puna, and (5) internally drained salar basins. The stops for Days 6 and 7 between 26.5° and 27.5°S latitude in Chile present a view of the Miocene to Recent frontal arc region on the western side of the plateau. The stops particularly highlight the late Miocene to Pliocene displacement of the magmatic arc front from the Maricunga Belt on the western edge of the plateau to its present position in the Central Volcanic Zone. Evidence for the timing of plateau uplift, changes in the angle of the underlying subduction zone, delamination of the underlying continental crust and mantle lithosphere, and forearc subduction erosion are examined throughout the course of the trip. DISCLAIMER: This is not a geologic field guide to be used in the traditional sense of a detailed road log, but rather a survey of the southern Puna region that can be done with the use of Google Earth. Latitude and longitude coordinates are given for all stops in WGS84 (world geodetic system) coordinates that can be used with Google Earth (downloadable from the Web) or any other georeferenced imagery. Driving instructions are given where access is possible by paved or high-quality unpaved roads that are present on road maps that are generally available in the region. Due to the lack of information on available road maps, changing driving conditions, and the need for caution in accessing the sites, precise instructions are not given for others. A significant number of these stops are on primitive, unmaintained roads or tracks that require a serious four-wheel drive vehicle, an experienced off-road driver, and supporting equipment (winch, spare tires, jack, etc.) to navigate safely. Many of the stops are in the Atacama Desert, where there is almost no water. The majority of the stops are at high elevations—most are between 3500 and 4500 m (~11,500–14,750 ft); all are over 2000 m (6500 ft). Attention needs to be paid to the potential for altitude sickness (called the Puna in Argentina). There are no cell phone towers, no service stations, or towing facilities in most of the region to bail you out! The availability of fuel can be questionable at times. Contact a knowledgeable guide to the region before attempting to use this field guide in the more isolated parts of the area.

This paper integrates new field observations to summarize the evolution of the 37–39°S segment of the Andean margin during the Neogene period. The western Neuquén Andes represent a transitional segment between the high, broad Central Andes and the low, narrow Patagonian Andes. The Main Cordillera at this latitude was uplifted between 11 and 6 Ma. Since then, extension and transtension has dominated the area. South of 38°S, deformation concentrates along the Liquiñe-Ofqui fault zone, a crustal-scale dextral strike-slip system that accommodates part of the margin-parallel component of oblique subduction. The architecture of the volcanic arc is strongly controlled by this fault zone. We differentiate four main tectonic phases: (1) late Oligocene–middle Miocene extension and development of a segmented intra-arc continental rift basin and broad volcanic zone; (2) late Miocene shortening, resulting in uplift, exhumation, and inversion of the former basins and a volcanic gap in the Main Cordillera; (3) Pliocene–early Pleistocene extension of the orogenic structure, reestablishment of the volcanic arc, and transtension along the intra-arc zone; and (4) late Pleistocene–Holocene narrowing of the arc and localized extension-transtension along the axial intra-arc zone. In the Central Andes, shortening has been more or less continuous since the Miocene, whereas in the Neuquén Andes, shortening stopped at ca. 6 Ma, probably related to the increase of the slab angle triggering the extension of the former orogenic structure and the onset of arc-parallel strike-slip faulting. The episodic evolution and migration of volcanism are related to changes in dip of the subducting plate.

The Neuquén Embayment, which developed along the eastern foothills of the southern Central Andes, has a complex history of intraplate deformation. The Paleozoic basement fabrics exerted a major influence in Mesozoic and Cenozoic deformation. The most important feature is an E-W–striking fault system that is related to a late Paleozoic fabric and is associated with the Huincul basement high, which truncates the basin. This fabric is interpreted as being the result of the accretion of the Patagonia terrane with Gondwana during the Early Permian. Two-dimensional (2D) and three-dimensional (3D) seismic coverage and subsurface information identify different sectors in the Neuquén Embayment that record alternating episodes of contraction and extension during the Jurassic and Cretaceous. The deformation history east of the thrust front of the Agrio fold-and-thrust belt is characterized by periods of (1) transpression and almost orthogonal contraction to the continental margin, (2) extension, and (3) relative quiescence, which alternates in different sectors. The earliest shortening occurred in the Early Jurassic when the main stress was oriented in the N-NW sector. The stress rotated to the northwest up to Valanginian times, when a more orthogonal orientation to the continental margin became dominant and prevailed after the Cenomanian. After a period of quiescence in the Neuquén Embayment associated with very oblique subduction during the Paleogene, the final contractional deformation took place in the late Miocene, with a west-east orientation of the main stress, and was followed by Pliocene extension. The changing stress patterns correlate with differences in convergence vectors between the Aluk, Farallon, and Nazca oceanic plates and the Gondwana or South American continental plates. The Aluk stage from the Jurassic to the Valanginian was characterized by tectonic inversion that is shown by shortening and right-lateral strike-slip structures that are concentrated in the Huincul system and more subtle deformation in the Chihuidos and Entre Lomas systems. The early Farallon stage was distinguished by reduced inversion and displacement in the Huincul system and a general retreat of deformation after the Valanginian. The change to late Farallon stage was characterized by a prominent tectonic inversion of the Entre Lomas system, which resulted from the inception of the formation of the Agrio fold-and-thrust belt in the retroarc area. This belt developed during most of the Late Cretaceous, when the embayment showed a general quiescence. The Nazca stage was characterized by the main episode of uplift, tectonic inversion of the older half-grabens, and important strike-slip faulting that was followed by local collapse of some structures during the Pliocene.

The southern Central Andes of Argentina between 35° and 39°S latitude can be divided into two sectors with contrasting geological histories. The boundary between the sectors coincides with the Cortaderas lineament. North of the Cortaderas lineament, the Andes record a foreland expansion of arc magmatism that is associated with contractional deformation in the Malargüe fold-and-thrust belt, and subsidence of the Río Grande foreland basin between 15 and 5 Ma. The peak expansion of deformation into the foreland occurred as late Miocene magmatic arc rocks erupted more than 500 km east of the trench and the San Rafael basement block was uplifted in central Mendoza. This stage was followed by the collapse of the basement uplift by normal faulting, the retreat of the magmatic arc, and the eruption of widespread late Pliocene to early Pleistocene within-plate lava flows in the Payenia region. Extensive Quaternary calderas and rhyolitic domes along the axis of the main Andes reflect crustal melting associated with basaltic underplating. In contrast, the structural evolution of the sector south of the Cortaderas lineament is dominated by the Late Cretaceous development of the Agrio fold-and-thrust belt, which underwent minor reactivations in the Eocene and the late Miocene. The post-Miocene Guañacos fold-and-thrust belt that has since developed along the axis of the main Andes concentrates neotectonic contraction. Arc magmatism in this sector is largely restricted to the axial area of the Andes. Both the sectors north and south of the Cortaderas lineament show evidence of an important episode of extension during the Oligocene to early Miocene, and for renewed extension in the Pliocene and the Pleistocene. The contrasting geological histories north and south of the Cortaderas lineament reflect differences in the geometry of the subducting plate, variations in crustal rheologies inherited from a more restricted distribution of Mesozoic rifts in the northern than the southern segment, and variations in the trench roll-back velocity through time.