121-666: The Purico complex is a Pleistocene volcanic complex in Chile close to Bolivia, formed by an ignimbrite , several lava domes and stratovolcanoes and one maar . It is in the Chilean segment of the Central Volcanic Zone , one of the four volcanic belts which make up the Andean Volcanic Belt . The Central Volcanic Zone spans Peru, Bolivia, Chile and Argentina and includes 44 active volcanoes as well as
242-405: A decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of the fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into
363-860: A plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or the Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are
484-517: A sill -like body and has been named the "Altiplano-Puna magma body". Ignimbritic activity in such systems is episodic, being interrupted by periods with lower volume "steady state" volcanism. The eruption of the Purico ignimbrite is the youngest large ignimbrite eruption in the Altiplano-Puna volcanic complex; the Altiplano-Puna volcanic complex presently is in such a "steady state" stage, but
605-611: A change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years. However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere . Glaciation in the Pleistocene
726-551: A change in the nature of the magma supply, from large volume flow that heavily interacted with the crust and gave rise to the ignimbrites to smaller volume flows in a colder and thus brittler crust and did not accumulate or interact with it in a significant way. Thus the later eruption products appear to be more primitive and less affected by crustal contamination. Macon stratovolcano is considered to be of Holocene age, and Alitar maar displays active fumaroles and hot springs . There are no know historical eruptions of Alitar and there
847-574: A deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another isotope ratio versus time. Ratios are converted to a percentage difference from the ratio found in standard mean ocean water (SMOW). The graph in either form appears as a waveform with overtones . One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials. According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in
968-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving
1089-410: A fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing the seismic shaking and tsunami hazard to infrastructure and people in
1210-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
1331-421: A few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from
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#17327732238521452-533: A surface area of 1,500 square kilometres (580 sq mi) over the whole complex, and its volume has been estimated to be 80–100 cubic kilometres (19–24 cu mi) with an additional 0.4 cubic kilometres (0.096 cu mi) contributed by tephra fall deposits. The ignimbrite is 250 metres (820 ft) thick and becomes thinner westward, with more distal sectors reaching thicknesses of 25 metres (82 ft). Potassium-argon dating has yielded ages between 1,380,000 ± 70,000 and 870,000 ± 520,000 years ago for
1573-578: A team of Russian scientists in collaboration with Princeton University announced that they had brought two female nematodes frozen in permafrost , from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet. The evolution of anatomically modern humans took place during the Pleistocene. At the beginning of the Pleistocene Paranthropus species were still present, as well as early human ancestors, but during
1694-494: Is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and
1815-427: Is cold, with annual mean temperatures of −3 – −4 °C (27–25 °F); during summer it hovers around 0 °C (32 °F) and during winter it can decrease to −6 °C (21 °F). Because of the high altitude, the air is thin and ultraviolet radiation is high. Llano del Chajnantor features the world's highest insolation , which under particular meteorological conditions can approach that at Venus . There
1936-426: Is considered to be of Plio-Pleistocene age. The eruptive episode that formed these centres is thus more recent than the Purico ignimbrite and may have been triggered by mafic magma being injected into the Purico system. It is also much smaller, with volumes ranging 0.36–4 cubic kilometres (0.086–0.960 cu mi). This change in the pattern of eruptive activity from large ignimbrites to smaller domes reflects
2057-521: Is constructed by lava flows and has a well preserved summit crater , while Cerro Purico is a stratovolcano and also known as Cerro Toco ( 22°57′0″S 67°47′0″W / 22.95000°S 67.78333°W / -22.95000; -67.78333 ). Additional more subdued structures in the principal complex are 5,058 metres (16,594 ft) high Cerro Agua Amarga ( 23°1′0″S 67°43′0″W / 23.01667°S 67.71667°W / -23.01667; -67.71667 ) just southwest of El Chascon and
2178-585: Is due to the combined effects of the subtropical ridge , the Humboldt Current in the Pacific Ocean and the rain shadow exercised by the Andes , but it was in the past interrupted by wet periods. The dry climate and high elevation mean that vegetation is scarce in the region, with cacti such as Echinopsis atacamensis and grasses occurring at lower elevations. The little vegetation that
2299-781: Is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America , and several hundred in Eurasia . The mean annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F). Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over
2420-543: Is known as the Chajnantor Plateau, and which contains further flat areas such as Llano de Chajnantor, Pampa El Vallecito and Pampa La Bola. There is no evidence that a caldera exists there, unlike in many other volcanoes of this type. To the west, close to the margin of the Salar de Atacama , the shield drops down to a bajada . A north-south trending system of fractures and conspicuous normal faults cuts across
2541-488: Is little precipitation in the area (about 200 millimetres per year (7.9 in/year) on the upper parts of the shield, decreasing to less than 10 millimetres per year (0.39 in/year) close to the Salar de Atacama ), which mainly happens during the summer months as a consequence of the South American monsoon . Snow also falls during winter but winter snow mainly evaporates while summer snow melts. This dry climate
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#17327732238522662-477: Is no indication of seismic activity in the Purico area. Renewed activity at Alitar would likely be in the form of phreatic eruptions of only local significance. The fumaroles of Alitar are concentrated in the northern and eastern parts of Alitar, while the hot springs occur in the Quepiaco creek area about 250 metres (820 ft) southwest of Alitar and consist of six separate small vents. The temperatures of
2783-459: Is no systematic correspondence between pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined. The sum of transient factors acting at
2904-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of
3025-520: Is part of the Central Volcanic Zone (CVZ), a belt of volcanoes that runs along the western margin of South America between 14° and 28° southern latitude. This 1,500 kilometres (930 mi) long belt is one of four separate volcanic belts that make up the Andean Volcanic Belt . They are separated from each other by gaps where no recent volcanism occurs. The CVZ segment includes 44 active systems, 18 minor volcanic centres and over 6 large ignimbrite or caldera systems. One of these volcanoes, Ojos del Salado ,
3146-443: Is present displays an altitudinal zonation with a lower "Prepuna" with shrubs and succulents , a middle "Puna" with grasses and shrubs and a "high Andean steppe" with bunch grass . A report in 1993 stated that red-brown cacti and brown grass grew around the foot of Purico. Conversely, the soils on the Purico complex contain a diverse population of microbes which have to tolerate extreme environmental conditions. Among these are
3267-434: Is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas the brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when
3388-496: Is responsible for volcanism in the Andean Volcanic Belt . Volcanic activity in the region of the Central Volcanic Zone has been ongoing for 200 million years, but with temporal and local variations; 25 million years ago for example it was centered farther east and later moved west. About 23 million years ago, large scale ignimbritic activity commenced in the region with the emplacement of the Oxaya Formation , followed by
3509-522: Is the geological epoch that lasted from c. 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations . Before a change was finally confirmed in 2009 by the International Union of Geological Sciences , the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of
3630-505: Is the highest volcano in the world. The largest historical eruption in the CVZ occurred in 1600 at Huaynaputina in Peru while Lascár is its most active member, with a major eruption in 1993. Purico is a circular shield with a diameter of 15–25 kilometres (9.3–15.5 mi), whose slopes descend away from a centre at an elevation of 5,000 metres (16,000 ft). This shield forms a plateau, which
3751-571: Is the source of the major Purico ignimbrite , which was emplaced at the time of the Jaramillo geomagnetic reversal . It was originally called Cajon ignimbrite and attributed to an area northwest of Purico known as Chaxas. Also, the Toconao ignimbrite was originally attributed to the Purico complex, but now the La Pacana caldera is considered to be its source. The Purico ignimbrite itself covers
Purico complex - Misplaced Pages Continue
3872-481: Is volumetrically the largest part. The Lower Purico Ignimbrite covers a surface of 800 square kilometres (310 sq mi) primarily on the western side of the Purico complex. Finally, the Upper Purico Ignimbrite is a moderately to densely welded flow that occurs particularly close to the summit of the Purico complex, where it forms six flow units that contain fiamme textures. Characteristic for
3993-659: The Alpine ice sheet on the Alps . Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were ice-covered. South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide Ice Sheet retreated, north-central North America was completely covered by Lake Agassiz . Over a hundred basins, now dry or nearly so, were overflowing in
4114-466: The Altiplano–Puna volcanic complex , a system of large calderas and ignimbrites of which Purico is a member. Licancabur to the north, La Pacana southeast and Guayaques to the east are separate volcanic systems. The Purico complex consists of a shield shaped volcanic structure consisting of the Purico ignimbrite and a number of secondary volcanoes that are emplaced on this volcanic shield. During
4235-463: The Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in
4356-529: The ICS timescale, the Pleistocene is divided into four stages or ages , the Gelasian , Calabrian , Chibanian (previously the unofficial "Middle Pleistocene"), and Upper Pleistocene (unofficially the "Tarantian"). In addition to these international subdivisions, various regional subdivisions are often used. In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for
4477-657: The Isthmus of Panama , causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia . The end of the Early Pleistocene is marked by
4598-677: The Laurentide Ice Sheet . Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch , which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ('most new' or 'newest') from the Greek πλεῖστος ( pleīstos ) 'most' and καινός ( kainós ( Latinized as cænus ) 'new'). This contrasts with
4719-615: The Mid-Pleistocene Transition , with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans also spread to the Australian continent and the Americas for the first time, co-incident with
4840-662: The Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and to the west in the Atlas Mountains . In the northern hemisphere, many glaciers fused into one. The Cordilleran Ice Sheet covered the North American northwest; the east was covered by the Laurentide . The Fenno-Scandian ice sheet rested on northern Europe , including much of Great Britain;
4961-489: The Salar de Pujsa . The 5,130 metres (16,830 ft) high Macon stratovolcano ( 23°2′0″S 67°49′0″W / 23.03333°S 67.81667°W / -23.03333; -67.81667 ), Alitar maar ( 23°9′0″S 67°38′0″W / 23.15000°S 67.63333°W / -23.15000; -67.63333 ) and 5,346 metres (17,539 ft) high Alitar volcano ( 23°09′S 67°38′W / 23.150°S 67.633°W / -23.150; -67.633 ) lie to
Purico complex - Misplaced Pages Continue
5082-413: The ice ages caused the development of glaciers on Purico; at times, an ice cap with outlet glaciers covered an area of 200 square kilometres (77 sq mi)-250 square kilometres (97 sq mi) at 5,000 metres (16,000 ft) elevation on Purico. Apparently three different stages of glaciation occurred, the third between 30,000–25,000 years ago, the second between 50,000–60,000 years ago and
5203-418: The ice ages , the shield was in part covered by glaciers which have left moraines . Purico is the source of the Purico ignimbrite, which has a volume of about 80–100 cubic kilometres (19–24 cu mi). After the emplacement of the Purico ignimbrite, a number of lava domes and stratovolcanoes developed on the ignimbrite shield. The maar of Alitar is still fumarolically active. In historical times, sulfur
5324-477: The last glacial period ended about 10,000 years ago. Over 11 major glacial events have been identified, as well as many minor glacial events. A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials". These events are defined differently in different regions of
5445-461: The tripoint between Argentina , Bolivia and Chile . The arid climate of this region means that most volcanic systems are well preserved with little erosion. This complex is underpinned by a magma body at depths of 15–35 kilometres (9.3–21.7 mi), where arc magmas interact with the crust to form the secondary magmas later erupted by the volcanoes of the Altiplano-Puna volcanic complex. This magma body has been imaged with seismic tomography as
5566-599: The woolly rhinoceros , various giraffids , such as the Sivatherium ; ground sloths , Irish elk , cave lions , cave bears , Gomphotheres , American lions , dire wolves , and short-faced bears , began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice , migratory birds, and swifter animals like whitetail deer had replaced
5687-532: The 5,262 metres (17,264 ft) high Cerro Aspero ( 23°5′0″S 67°42′0″W / 23.08333°S 67.70000°W / -23.08333; -67.70000 and the 5,462 metres (17,920 ft) high Cerro Putas ( 23°6′0″S 67°43′0″W / 23.10000°S 67.71667°W / -23.10000; -67.71667 ) to the south. All these domes (with the exception of the pancake-like "dacite dome D") have conical shapes, and Aspero, El Cerillo and El Chascon appear to be post-glacial in age. The Chascon dome
5808-610: The Alitar vents range between 54–57 °C (129–135 °F). Fumarolic gases are mostly water vapour , with lesser amounts of carbon dioxide , and sulfur deposition takes place. They appear to originate from both magmatic and precipitation water, with a large contribution from atmospheric air and an important role for a hydrothermal system. Purico has been quarried for building materials, and many buildings in San Pedro de Atacama were built from rocks quarried there. As of 1984, Alitar
5929-656: The Altos de Pica Formation 17-15 million years ago. However, effusive activity of andesitic composition dominated volcanism until the late Miocene . Purico appears to be part of a group of large, caldera -forming volcanic centres that erupted dacitic ignimbrites , a group that is known as the Altiplano-Puna volcanic complex . This group includes the Cerro Guacha , Cerro Panizos , Coranzulí , La Pacana , Pastos Grandes and Vilama centres that cluster around
6050-529: The Atana ignimbrite. Occasionally Purico is considered part of the La Pacana system. The Purico complex has erupted various different magmas, ranging from the dacitic Purico ignimbrite over rhyolitic pumices contained in the ignimbrite to the andesitic -dacitic post-ignimbrite volcanics. Dacite is the dominant component and forms a crystal-rich potassium -rich suite. Varying amounts of phenocrysts occur in
6171-468: The Cordon Honor with Cerro Purico Sur in the "opening" of the semicircle. Lahars and debris flows from the volcanoes have covered parts of the ignimbrite shield with gravels. A meltwater-fed spring on Cerro Toco is known as Aguada Pajaritos, and a small lake Laguna de Agua Amarga is found south of Chascon. Presently, the Purico complex forms the drainage divide between the Salar de Atacama and
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#17327732238526292-569: The Early Pleistocene Gelasian . Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced. By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number and interglacials receive an odd number. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16. The warmest interglacials were 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under
6413-409: The Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors. The Mid-Pleistocene Transition , approximately one million years ago, saw
6534-479: The North American west. Lake Bonneville , for example, stood where Great Salt Lake now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided . African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation. It has been estimated that during
6655-434: The Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. Radiocarbon dating is considered to be inaccurate beyond around 50,000 years ago. Marine isotope stages (MIS) derived from Oxygen isotopes are often used for giving approximate dates. Pleistocene non-marine sediments are found primarily in fluvial deposits , lakebeds, slope and loess deposits as well as in
6776-496: The Pleistocene's overall climate could be characterised as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru , warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It
6897-503: The Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP . The start date has now been rounded down to 2.580 million years BP. The IUGS has yet to approve a type section , Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary ( i.e.
7018-805: The Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka. During the 2.5 million years of the Pleistocene, numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of
7139-411: The Pleistocene, the plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period. In glacial periods, the sea level would drop by up to 120 m (390 ft) lower than today during peak glaciation, exposing large areas of the present continental shelf as dry land. According to Mark Lynas (through collected data),
7260-482: The Purico complex rocks; the minerals they are formed of include augite , biotite , clinopyroxene , hornblende , hypersthene , iron oxides , oligoclase , orthopyroxene , plagioclase , quartz and titanium oxides . Additionally, mafic xenoliths are found in the Purico ignimbrite; such xenoliths are a common finding in volcanic arc rocks. They are even more common in Chascon rocks, where they might reflect
7381-509: The Purico ignimbrite is the so-called "banded" pumice , which consist of alternating darker mafic and brighter components, in the upper 33% of the ignimbrite. The extrusion of the Purico ignimbrite was accompanied by the eruption of large amounts of tephra , some of which fell as far as the Coastal Cordillera west of Purico. After emplacement, the ignimbrites were modified by fluvial erosion, which formed curvilinear channels in
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#17327732238527502-405: The Purico ignimbrite. The 2 cubic kilometres (0.48 cu mi) large "dacitic dome D" has an age of 980,000 ± 50,000 and may thus have formed at the same time as the ignimbrites. The emplacement of the Purico ignimbrite was part of a pulse of activity in the Altiplano-Puna volcanic complex 1 million years ago. The Purico ignimbrite contains three flow units, the two Lower Purico Ignimbrites and
7623-492: The Upper Purico Ignimbrite. Their thicknesses differ; the Upper ignimbrite is 10–12 metres (33–39 ft) thick while the two lower ones together reach an average thickness of 30 metres (98 ft), with a maximum of 80 metres (260 ft). The lowermost Lower Purico Ignimbrite is one single flow. The upper Lower Purico Ignimbrite is more heterogeneous, starting with a base surge , a pumice layer and then another flow unit, which
7744-706: The appearance of Homo sapiens about 300,000 years ago. Artifacts associated with modern human behavior are unambiguously attested starting 40,000–50,000 years ago. According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciation in the Middle Palaeolithic during the Eemian Stage , spreading all over the ice-free world during the late Pleistocene. A 2005 study posits that humans in this migration interbred with archaic human forms already outside of Africa by
7865-527: The articles for those names. Both marine and continental faunas were essentially modern but with many more large land mammals such as Mammoths , Mastodons , Diprotodons , Smilodons , tigers , lions , Aurochs , short-faced bears , giant sloths , species within Gigantopithecus and others. Isolated landmasses such as Australia , Madagascar , New Zealand and islands in the Pacific saw
7986-425: The bacteria Amycolatopsis vastitatis , Lentzea chajnantorensis , Micromonospora acroterricola , Micromonospora arida , Micromonospora inaquosa , Modestobacter altitudinis , Modestobacter excelsi , Nocardiopsis deserti and Streptomyces aridus which were first isolated at the Purico complex. Some of these yield pharmacologically interesting compounds. Increased moisture availability during
8107-473: The complex as well. The existence of the Purico complex was established on the basis of Landsat images. Licancabur volcano was constructed on ignimbrites from Purico just north of the complex. Guayaques lies east of Purico, the La Pacana caldera is located southeast of the complex, and La Pacana's Filo Delgado ignimbrite has buried part of the Purico ignimbrite. The known volcanoes Lascár and El Tatio are found at larger distances from Purico. Purico
8228-414: The crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of a hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through
8349-487: The dacite, causing the eruption to become a violent Plinian eruption with the development of an eruption column . This phase then drew onto denser dacitic magma, causing the column to collapse and the Upper Purico Ignimbrite and the "dacite dome D" to form. Volcanic activity after the eruption of the ignimbrite has been subdivided into the older andesitic Purico group and the younger Chascon group. The first includes Cerro Negro, Cerro Purico, Putas and Cerro Toco which assume
8470-433: The direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as
8591-618: The entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania . The current decaying glaciers of Mount Kenya , Mount Kilimanjaro , and
8712-782: The evolution of large birds and even reptiles such as the Elephant bird , moa , Haast's eagle , Quinkana , Megalania and Meiolania . The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major extinction event of large mammals ( megafauna ), which included mammoths , mastodons , saber-toothed cats , glyptodons ,
8833-703: The existence of a ring fault on which the individual centres were emplaced. Clockwise starting from the west this semicircle includes 5,016 metres (16,457 ft) high Cerro Negro ( 23°1′0″S 67°51′0″W / 23.01667°S 67.85000°W / -23.01667; -67.85000 ), Cerro Purico, "dacite dome D" and 5,639 metres (18,501 ft) high El Cerillo which is also known as Cerro Chajnantor ( 22°59′0″S 67°44′0″W / 22.98333°S 67.73333°W / -22.98333; -67.73333 ), 5,703 metres (18,711 ft) high Cerro El Chascon ( 23°1′0″S 67°41′0″W / 23.01667°S 67.68333°W / -23.01667; -67.68333 ),
8954-444: The extinction of most large-bodied animals in these regions. The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by
9075-409: The fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of a non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body,
9196-459: The fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of
9317-413: The fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on the direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and
9438-656: The first over 100,000 years ago. Moraines associated with Lake Tauca appear to be either small or nonexistent. These glaciations have left moraines on Purico which extend for many kilometres at altitudes of 4,400–4,600 metres (14,400–15,100 ft), sometimes descending as far down as 4,200 metres (13,800 ft). The moraines reach heights of 10 metres (33 ft) on the eastern side of Purico and 2–5 metres (6 ft 7 in – 16 ft 5 in) on its western side. These moraines are covered with boulders and accompanied by striated surfaces and erratics . Penitentes still occur on Purico to this day. The Purico complex
9559-428: The footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms
9680-531: The footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other, is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near
9801-429: The geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in the gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of
9922-414: The glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another. For most of the 20th century, only
10043-547: The highest in the world. In 1998, the Cerro Chascón Science Preserve was established on Purico, which among other things disallows mining in the area of the preserve. This Science Preserve covers most of the Purico complex. Pleistocene The Pleistocene ( / ˈ p l aɪ s t ə ˌ s iː n , - s t oʊ -/ PLY -stə-seen, -stoh- ; referred to colloquially as the Ice Age )
10164-450: The historical terminology was established. Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: pluvia , rain). A pluvial is a warmer period of increased rainfall; an interpluvial is of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread. There
10285-400: The ignimbrite has been explained by magma chamber processes. Prior to the Purico ignimbrite eruption, a dacitic magma chamber already existed beneath the volcano. Probably after an injection of andesitic magma, dacitic contents of the magma chamber escaped upwards and formed the lowermost Lower Purico Ignimbrite. This injection of mafic magma rapidly increased the temperature and gas content of
10406-404: The ignimbrites. In contrast to other ignimbrites in the region, there is little evidence of eolian erosion of the Purico ignimbrite. Eolian erosion takes much longer than fluvial erosion and it is possible that the Purico ignimbrite is too young to have been modified by wind action. Some surfaces of the ignimbrite have been affected by glaciation , giving them a smooth surface. This structure of
10527-445: The immediately preceding Pliocene ("newer", from πλείων ( pleíōn , "more") and kainós ) and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος ( hólos , "whole") and kainós ) epoch , which extends to the present time. The Pleistocene has been dated from 2.580 million (±0.005) to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of
10648-491: The implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering ,
10769-622: The large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometres of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred metres. The modern continents were essentially at their present positions during
10890-464: The largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where
11011-401: The largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line
11132-457: The late Pleistocene, incorporating archaic human genetic material into the modern human gene pool. Ring fault In geology , a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with
11253-540: The latest period of repeated glaciation , up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9700 BCE (11,700 calendar years BP). The end of the Younger Dryas is the official start of the current Holocene Epoch . Although it is considered an epoch, the Holocene is not significantly different from previous interglacial intervals within the Pleistocene. In
11374-470: The lower Palaeolithic they disappeared, and the only hominin species found in fossilic records is Homo erectus for much of the Pleistocene. Acheulean lithics appear along with Homo erectus , some 1.8 million years ago, replacing the more primitive Oldowan industry used by A. garhi and by the earliest species of Homo . The Middle Paleolithic saw more varied speciation within Homo , including
11495-478: The megafauna and migrated north. Late Pleistocene bighorn sheep were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed. The extinctions hardly affected Africa but were especially severe in North America where native horses and camels were wiped out. In July 2018,
11616-408: The miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of
11737-435: The most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to the original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to
11858-526: The occurrence of mafic magma in the feeder system prior to the formation of Chascon. Some physical properties of the Purico magmas have been inferred from the chemistry and petrology of the erupted rocks. The dacites had temperatures of about 750–810 °C (1,380–1,490 °F) while the andesites and rhyolites reached higher temperatures, up to 800–880 °C (1,470–1,620 °F). Water contents ranged from 3.2 to 4.8% by weight, while carbon dioxide concentrations were low throughout. The climate at Purico
11979-494: The opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and
12100-593: The origin of the sulfur deposits at Purico. Aspero, Cerro El Chascon, Cerros El Negro and Putas are younger and show no evidence of glaciation. El Chascon especially may be only tens of thousands of years old, seeing as it displays both a summit crater and pristine lava flow structures. Aspero was once considered to be of Holocene age in light of it and Chascon overlying moraines; later, dates of 180,000 ± 20,000 years ago were obtained on Aspero and Chascon. Apart from these, there are no radiometric dates for post-ignimbrite volcanic structures at Purico. The Alitar volcano
12221-478: The period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology . The name is a combination of Ancient Greek πλεῖστος ( pleîstos ) 'most' and καινός ( kainós ; Latinized as cænus ) 'new'. At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by
12342-497: The presence of active geothermal system indicates that magmatic activity is still ongoing. Outcrops in the region range in age from Paleozoic to Holocene . The Purico complex formed on top of older ignimbrites such as the Puripicar ignimbrite in the north, the Atana and the La Pacana ignimbrites farther south. The neighbouring La Pacana caldera between 4.5 and 4.1 million years ago erupted some of these ignimbrites including
12463-417: The ratio of O to O (two isotopes of oxygen ) by mass (measured by a mass spectrometer ) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in O , which is included in the tests of the microorganisms ( foraminifera ) contributing the calcite. A more recent version of
12584-461: The recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy. However, the revised definition of the Quaternary , by pushing back the start date of
12705-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
12826-423: The rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along a fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy
12947-407: The sampling process makes use of modern glacial ice cores. Although less rich in O than seawater, the snow that fell on the glacier year by year nevertheless contained O and O in a ratio that depended on the mean annual temperature. Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of
13068-649: The sole factor responsible for the variations in climate since they explain neither the long-term cooling trend over the Plio-Pleistocene nor the millennial variations in the Greenland Ice Cores known as Dansgaard-Oeschger events and Heinrich events. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores. In oxygen isotope ratio analysis, variations in
13189-665: The south of the main complex. Alitar maar is located is 500 metres (1,600 ft) wide and 50 metres (160 ft) deep. [REDACTED] West of South America, the Nazca Plate subducts beneath the South America Plate at rates of 9–7 centimetres per year (3.5–2.8 in/year). This subduction process along with that of the Antarctic Plate beneath the South American Plate farther south
13310-404: The strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of the fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of
13431-416: The stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in the fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form
13552-650: The structure of polygenetic volcanoes , while the latter is taken to include Aspero, El Cerillo/Chajnantor and El Chascon which are lava dome - lava flow structures. The Chascon group of domes is also the only one which contains mafic xenoliths. The Cerro Purico and Macon volcanoes formed a short time after, and possibly even before, the ignimbrites. They are thus old volcanic centres and deeply eroded, displaying moraine deposits from glaciation and rocks which have been subject to hydrothermal alteration from fumarolic activity. Such hydrothermal alteration processes, together with desublimation of fumarolic sulfur, are also
13673-421: The study of cyclical climate changes. The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since
13794-400: The surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in a manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along
13915-648: The upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W. The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone , isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils : Discoaster pentaradiatus and Discoaster surculus . The Pleistocene covers
14036-526: The vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
14157-419: The western margin of the Purico complex. On top of this shield, a complex of lava domes and lavas reaches elevations of over 5,800 metres (19,000 ft) above sea level; the vent of the ignimbrite may be buried beneath this complex. This complex forms approximately a 10 by 20 kilometres (6.2 mi × 12.4 mi) wide semicircle open to the southwest around the centre of the shield, which may reflect
14278-543: Was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes. The main factor at work in climate cycling is now believed to be Milankovitch cycles . These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion. The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's albedo. Milankovitch cycles cannot be
14399-541: Was mined on Purico and transported by truck to San Pedro de Atacama where it was processed. In 1993, production of sulfur amounted to 200 tonnes per month (2,400 t/a). The Purico complex is the site of a number of astronomical observatories , including but not limited to the Llano de Chajnantor Observatory and the Atacama Large Millimeter Array , and an atmospheric observatory that is among
14520-466: Was mined on Purico. Today, the Llano de Chajnantor Observatory lies on the ignimbrite shield. The Purico complex lies in Chile close to the border between Bolivia and Chile, east of the town of San Pedro de Atacama and northeast of Toconao . The volcanic complex can be seen from San Pedro de Atacama. A road runs along the northern and eastern margin of the Purico complex, and a gas pipeline crosses
14641-411: Was under investigation as a potential source of geothermal power . Two sulfur deposits occur at Purico, the first southeast of Cerro Toco and the second at Alitar. The Purico deposit in 1968 was estimated to feature 4 million tons of caliche with a grade of 50%, while the Alitar deposit in that year amounted to 1.5 million tons of caliche with a grade of 60%. In the 1950s and as recently as 1993, sulfur
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