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The geology of Peru includes ancient Proterozoic rocks, Paleozoic and Mesozoic volcanic and sedimentary rocks, and numerous basins and the Andes Mountains formed in the Cenozoic.

Geological history, stratigraphy & tectonics

The oldest rocks in Peru date to the Precambrian and are more than two billion years old. Along the southern coast, granulite and charnockite shows reworking by an ancient orogeny mountain building event. Situated close to the Peru-Chile Trench, these rocks have anomalously high strontium isotope ratios, which suggest recent calc-alkaline volcanism.^[1]

In the Eastern Cordillera of Peru, Precambrian magmatism in the Huanuco region produced ultramafic, mafic and felsic rocks, including serpentinite, meta-diorite, meta-gabbro, meta-tonalite and diorite and granite that intruded after the first phase of orogenic tectonic activity.^[2]

The basement of the Central Andean orogeny includes the rocks of the Arequipa Massif, which reach granulite grade on the sequence of metamorphic facies and formed around 1.9 billion years ago. Zircon grains in these rocks match those in Labrador, Greenland and Scotland, indicating that much of western South America originated as a promontory of the proto-North American continent Laurentia.^[3]

Paleozoic (541-251 million years ago)

In the Paleozoic, Peru was on the western margin of the supercontinent Gondwana. Analysis of Ordovician and Devonian sandstones in the Eastern Cordillera (spanning into Bolivia) indicates eroded zircon grains formed to the east in Brazil during the Brasiliano orogeny. By contrast, Altiplano and Coastal Cordillera sandstones seem to have originated from the Arequipa Massif.^[4]

Plutonic and volcanic rocks in the Inner Arc domain (later uplifted in the Central Andean orogeny) include the high-grade, low-pressure metamorphic gabbro-granite of the San Gaban Complex and early Permian Mitu Group alkali basalts. Rocks, such as those in the Mitu Group, formed during pulses of magmatism in back-arc basins.^[5]^[6] Parts of central North America were adjacent to western South America during the late Paleozoic, helping to drive folding and metamorphism.^[7]

The region was affected by the Hercynian orogeny from 550 to 220 million years ago, leading to granitoid intrusion, nepheline syenite, syntectonic granites and calc-alkaline volcanism.

Along the coast, subduction produced basins on land and volcanic activity, that resulted in the two kilometer thick Yamayo Group and the overlying one to six kilometer volcanic and volcaniclastic Yura Group.

Mesozoic (251-66 million years ago)

The Andean orogeny began in the late Triassic. In the south, the two kilometer Chocolate Formation formed with sedimentary rocks into the late Triassic.^[8] Central Peru experienced less magmatic activity than during the Hercynian orogeny, but acid plutonic rocks emplaced in the center of the country.^[9]

The Pucara Basin subsided on the landward side of a structural high from the Triassic into the early Jurassic. The basin filled first with carbonates and then with argillite followed by shallow water carbonates. Some carbonates were later transformed to dolomite and the basin's rocks show signs of Mississippi Valley Type lead-zinc mineralization, common in basin-forming shear zones.^[10]

In the area of Puno-Santa Lucia, which was slowly being uplifted as the Andes, two kilometer Paleozoic Cabanillas Group quartzite and shale is overlain by the 1.5 kilometer Jurassic Lagunillas Group. The Huancane and Moho groups include red beds and limestone, formed in closed basin.^[11]

The 1600 kilometer Coastal Batholith of Peru formed in an ensialic marginal basin in the early Cretaceous, with the emplacement of pillow lavas, gabbro and volcaniclastic rocks. In the north, it formed as new continental crust with no older continental crust beneath it, while to the south it spans thick Precambrian rocks.^[12]

Cenozoic (66 million years ago-present)

As the Andean orogeny accelerated from the Albian, rock deformation shifted toward the Amazonian foredeep. The Marañón fold and thrust belt formed in the Eocene, bounding the Western Cordillera. Crustal shortening produced a sialic root to the Andes.^[13]^[14]^[15]^[16]

Marine transgressions swept the region starting in the Eocene, emplacing conglomerate, sandstone, siltstone, mudstone and diatomite in the Sechura Basin and Pisco Basin—a pair of forearc basins in the north.^[17]

The Miocene-aged Cordillera Blanca Batholith intrudes the Coastal Batholith over 50 kilometer thick crust, with S-type peraluminous granites produced by deformation and uplift. The majority of rocks in the batholith are high-sodium, high-silica I-type granites, with characteristics that have been interpreted as subducted oceanic crust melts. However, it does not have positioning consistent with subduction and geologists have interpreted it as underplating leading to partial melting, the formation of trondhjemitic magmas rich in clinopyroxene, garnet and amphibole.^[18] Intense volcanism, deformation and plutonism was common in the Miocene and Pliocene in central Peru.^[19]

In the last 2.5 million years of the Quaternary, andesite lavas erupted, forming the Arequipa and Barosso groups in the south, including partially melted Precambrian granulite gneiss, with a high lead concentration.^[20]

References

^ Dalmayrac, B.; Lancelot, J. R.; Leyreloup, A. (7 October 1977). "Two-Billion-Year Granulites in the Late Precambrian Metamorphic Basement Along the Southern Peruvian Coast". Science. 198 (4312): 49–51. Bibcode:1977Sci...198...49D. doi:10.1126/science.198.4312.49. PMID 17741896.
^ "Vista do The Upper Precambrian of South America". www.periodicos.usp.br.
^ Wasteneys, Hardolph A.; Clark, Alan H.; Farrar, Edward; Langridge, Robert J. (1 May 1995). "Grenvillian granulite-facies metamorphism in the Arequipa Massif, Peru: a Laurentia-Gondwana link". Earth and Planetary Science Letters. 132 (1–4): 63–73. Bibcode:1995E&PSL.132...63W. doi:10.1016/0012-821X(95)00055-H.
^ Reimann, C.R.; Bahlburg, H.; Kooijman, E.; Berndt, J.; Gerdes, A.; Carlotto, V.; López, S. (1 September 2010). "Geodynamic evolution of the early Paleozoic Western Gondwana margin 14°–17°S reflected by the detritus of the Devonian and Ordovician basins of southern Peru and northern Bolivia". Gondwana Research. 18 (2–3): 370–384. Bibcode:2010GondR..18..370R. doi:10.1016/j.gr.2010.02.002.
^ Jel, Reitsma, Martje (9 November 2018). "Reconstructing the Late Paleozoic : Early Mesozoic plutonic and sedimentary record of south-east Peru : Orphaned back-arcs along the western margin of Gondwana".{{cite web}}: CS1 maint: multiple names: authors list (link)
^ Kontak, D.J.; Clark, A.H.; Farrar, E.; Archibald, D.A.; Baadsgaard, H. (1 January 1990). "Late Paleozoic-early Mesozoic magmatism in the Cordillera de Carabaya, Puno, southeastern Peru: Geochronology and petrochemistry". Journal of South American Earth Sciences. 3 (4): 213–230. Bibcode:1990JSAES...3..213K. doi:10.1016/0895-9811(90)90004-K.
^ Ross, Charles A. (9 November 1979). "Late Paleozoic collision of North and South America". Geology. 7 (1): 41. Bibcode:1979Geo.....7...41R. doi:10.1130/0091-7613(1979)7<41:LPCONA>2.0.CO;2.
^ Boekhout, F.; Sempere, T.; Spikings, R.; Schaltegger, U. (1 November 2013). "Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: Temporal evolution of sedimentation along an active margin". Journal of South American Earth Sciences. 47: 179–200. Bibcode:2013JSAES..47..179B. doi:10.1016/j.jsames.2013.07.003.
^ Carlier, G.; Grandin, G.; Laubacher, G.; Marocco, R.; Mégard, F. (1 November 1982). "Present knowledge of the magmatic evolution of the Eastern Cordillera of Peru" (PDF). Earth-Science Reviews. 18 (3–4): 253–283. Bibcode:1982ESRv...18..253C. doi:10.1016/0012-8252(82)90040-X.
^ Rosas, Silvia; Fontboté, Lluís; Tankard, Anthony (1 June 2007). "Tectonic evolution and paleogeography of the Mesozoic Pucará Basin, central Peru". Journal of South American Earth Sciences. 24 (1): 1–24. Bibcode:2007JSAES..24....1R. doi:10.1016/j.jsames.2007.03.002.
^ Jorge a. Portugal (2) (1974). "Mesozoic and Cenozoic Stratigraphy and Tectonic Events of Puno-Santa Lucia Area, Department of Puno, Peru". AAPG Bulletin. 58. doi:10.1306/83d915e7-16c7-11d7-8645000102c1865d.{{cite journal}}: CS1 maint: numeric names: authors list (link)
^ Atherton, M. P. (1984). "The Coastal Batholith of Peru". Andean Magmatism. pp. 168–179. doi:10.1007/978-1-4684-7335-3_12. ISBN 978-1-4684-7337-7.
^ Mégard, F. (1 September 1984). "The Andean orogenic period and its major structures in central and northern Peru". Journal of the Geological Society. 141 (5): 893–900. Bibcode:1984JGSoc.141..893M. doi:10.1144/gsjgs.141.5.0893.
^ Noble, Donald C.; McKee, Edwin H.; Mourier, Thomas; Mégard, François (1990). "Cenozoic stratigraphy, magmatic activity, compressive deformation, and uplift in northern Peru". Geological Society of America Bulletin. 102 (8): 1105–1113. Bibcode:1990GSAB..102.1105N. doi:10.1130/0016-7606(1990)102<1105:CSMACD>2.3.CO;2.
^ Tosdal, Richard M.; Clark, Alan H.; Farrar, Edward (1984). "Cenozoic polyphase landscape and tectonic evolution of the Cordillera Occidental, southernmost Peru". Geological Society of America Bulletin. 95 (11): 1318. Bibcode:1984GSAB...95.1318T. doi:10.1130/0016-7606(1984)95<1318:CPLATE>2.0.CO;2.
^ Kulm, LaVerne D. (1 January 1981). Nazca Plate: Crustal Formation and Andean Convergence : a Volume Dedicated to George P. Woollard. Geological Society of America. ISBN 9780813711546 – via Google Books.
^ Dunbar, Robert B.; Marty, Richard C.; Baker, Paul A. (1 April 1990). "Cenozoic marine sedimentation in the Sechura and Pisco basins, Peru". Palaeogeography, Palaeoclimatology, Palaeoecology. 77 (3–4): 235–261. Bibcode:1990PPP....77..235D. doi:10.1016/0031-0182(90)90179-B.
^ Petford, Nick; Atherton, Michael (1996). "Na-rich Partial Melts from Newly Underplated Basaltic Crust: The Cordillera Blanca Batholith, Peru". Journal of Petrology. 37 (6): 1491–1521. Bibcode:1996JPet...37.1491P. doi:10.1093/petrology/37.6.1491.
^ Noble, Donald C.; McKee, Edwin H.; Farrar, Edward; Petersen, Ulrich (1 January 1974). "Episodic Cenozoic volcanism and tectonism in the Andes of Peru". Earth and Planetary Science Letters. 21 (2): 213–220. Bibcode:1974E&PSL..21..213N. doi:10.1016/0012-821X(74)90057-0.
^ Tilton, George R.; Barreiro, Barbara A. (12 December 1980). "Origin of Lead in Andean Calc-Alkaline Lavas, Southern Peru". Science. 210 (4475): 1245–1247. Bibcode:1980Sci...210.1245T. doi:10.1126/science.210.4475.1245. PMID 17810771.