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.
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]
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.
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]
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]
The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico, with the easternmost extent of the mountain-building represented by the Black Hills of South Dakota. The phenomenon is named for the Laramie Mountains of eastern Wyoming. The Laramide orogeny is sometimes confused with the Sevier orogeny, which partially overlapped in time and space.
The Andean orogeny is an ongoing process of orogeny that began in the Early Jurassic and is responsible for the rise of the Andes mountains. The orogeny is driven by a reactivation of a long-lived subduction system along the western margin of South America. On a continental scale the Cretaceous and Oligocene were periods of re-arrangements in the orogeny. Locally the details of the nature of the orogeny varies depending on the segment and the geological period considered.
The geology of Bolivia comprises a variety of different lithologies as well as tectonic and sedimentary environments. On a synoptic scale, geological units coincide with topographical units. The country is divided into a mountainous western area affected by the subduction processes in the Pacific and an eastern lowlands of stable platforms and shields. The Bolivian Andes is divided into three main ranges; these are from west to east: the Cordillera Occidental that makes up the border to Chile and host several active volcanoes and geothermal areas, Cordillera Central once extensively mined for silver and tin and the relatively low Cordillera Oriental that rather than being a range by its own is the eastern continuation of the Central Cordillera as a fold and thrust belt. Between the Occidental and Central Cordillera the approximately 3,750-meter-high Altiplano high plateau extends. This basin hosts several freshwater lakes, including Lake Titicaca as well as salt-covered dry lakes that bring testimony of past climate changes and lake cycles. The eastern lowlands and sub-Andean zone in Santa Cruz, Chuquisaca, and Tarija Departments was once an old Paleozoic sedimentary basin that hosts valuable hydrocarbon reserves. Further east close to the border with Brazil lies the Guaporé Shield, made up of stable Precambrian crystalline rock.
Arequipa-Antofalla is a basement unit underlying the central Andes in northwestern Argentina, western Bolivia, northern Chile and southern Peru. Geologically, it corresponds to a craton, terrane or block of continental crust. Arequipa-Antofalla collided and amalgamated with the Amazonian craton about 1000 Ma ago during the Sunsás orogeny. As a terrane Arequipa-Antofalla was ribbon-shaped during the Paleozoic, a time when it was bounded by the west by the Iapetus Ocean and by the east by the Puncoviscana Ocean.
The East Antarctic Shield or Craton is a cratonic rock body that covers 10.2 million square kilometers or roughly 73% of the continent of Antarctica. The shield is almost entirely buried by the East Antarctic Ice Sheet that has an average thickness of 2200 meters but reaches up to 4700 meters in some locations. East Antarctica is separated from West Antarctica by the 100–300 kilometer wide Transantarctic Mountains, which span nearly 3,500 kilometers from the Weddell Sea to the Ross Sea. The East Antarctic Shield is then divided into an extensive central craton that occupies most of the continental interior and various other marginal cratons that are exposed along the coast.
The Lhasa terrane is a terrane, or fragment of crustal material, sutured to the Eurasian Plate during the Cretaceous that forms present-day southern Tibet. It takes its name from the city of Lhasa in the Tibet Autonomous Region, China. The northern part may have originated in the East African Orogeny, while the southern part appears to have once been part of Australia. The two parts joined, were later attached to Asia, and then were impacted by the collision of the Indian Plate that formed the Himalayas.
The Famatinian orogeny is an orogeny that predates the rise of the Andes and that took place in what is now western South America during the Paleozoic, leading to the formation of the Famatinian orogen also known as the Famatinian belt. The Famatinian orogeny lasted from the Late Cambrian to at least the Late Devonian and possibly the Early Carboniferous, with orogenic activity peaking about 490 to 460 million years ago. The orogeny involved metamorphism and deformation in the crust and the eruption and intrusion of magma along a Famatinian magmatic arc that formed a chain of volcanoes. The igneous rocks of the Famatinian magmatic arc are of calc-alkaline character and include gabbros, tonalites and granodiorites. The youngest igneous rocks of the arc are granites.
Choiyoi Group is a Permian and Triassic-aged group of volcano-sedimentary formations in Argentina and Chile. The group bears evidence of bimodal-style volcanism related to an ancient subduction zone that existed along the western margin of the supercontinent Gondwana.
The Coastal Batholith of Peru is a group of hundreds, if not thousands, of individual plutons that crop out near or at the coast of Peru. The batholith runs a length of ca. 1600 km. Most of the plutons of the batholith were intruded in an elongated coast-parallel extensional basin. The magma that formed the batholith's plutons is thought to have originated from the partial melting of hydrated basaltic rocks at the base of the crust during rifting (extension). Subsequently, the rift basin was inverted. During the ascent the magma followed vertical pathways but emplacement was mostly in the form of tabular bodies.
The Marañón fold and thrust belt is a 1,000 kilometres (620 mi) long, northwest–southeast trending belt of deformed rocks located in the Andes of central Peru. The formation of the belt defines the Incaic Phase of the Andean orogeny.
Patagonia comprises the southernmost region of South America, portions of which lie either side of the Chile–Argentina border. It has traditionally been described as the region south of the Rio Colorado, although the physiographic border has more recently been moved southward to the Huincul fault. The region's geologic border to the north is composed of the Rio de la Plata craton and several accreted terranes comprising the La Pampa province. The underlying basement rocks of the Patagonian region can be subdivided into two large massifs: the North Patagonian Massif and the Deseado Massif. These massifs are surrounded by sedimentary basins formed in the Mesozoic that underwent subsequent deformation during the Andean orogeny. Patagonia is known for their vast earthquakes and the damage.
Hainan Island, located in the South China Sea off the Chinese coast and separated from mainland China by the Qiongzhou Strait, has a complex geological history that it has experienced multiple stages of metamorphism, volcanic and intrusive activities, tectonic drifting and more. The oldest rocks, the Proterozoic metamorphic basement, are not widely exposed, but mostly found in the western part of the Island.
The geology of Somalia is built on more than 700 million year old igneous and metamorphic crystalline basement rock, which outcrops at some places in northern Somalia. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate. The geology of Somaliland, the de facto independent country recognized as part of Somalia, is to some degree better studied than that of Somalia as a whole. Instability related to the Somali Civil War and previous political upheaval has limited geologic research in places while heightening the importance of groundwater resources for vulnerable populations.
The geology of Italy includes mountain ranges such as the Alps, the Dolomites and the Apennines formed from the uplift of igneous and primarily marine sedimentary rocks all formed since the Paleozoic. Some active volcanoes are located in Insular Italy.
The geology of Venezuela includes ancient Precambrian igneous and metamorphic basement rocks, layered with sedimentary rocks from the Paleozoic and Mesozoic and thick geologically recent Cenozoic sediments with extensive oil and gas.
The geology of Ecuador includes ancient Precambrian basement rock and a complex tectonic assembly of new sections of crust from formerly separate landmasses, often uplifted as the Andes or transformed into basins.
The geology of Argentina includes ancient Precambrian basement rock affected by the Grenville orogeny, sediment filled basins from the Mesozoic and Cenozoic as well as newly uplifted areas in the Andes.
The geology of Brazil includes very ancient craton basement rock from the Precambrian overlain by sedimentary rocks and intruded by igneous activity, as well as impacted by the rifting of the Atlantic Ocean.
The geology of Newfoundland and Labrador includes basement rocks formed as part of the Grenville Province in the west and Labrador and the Avalonian microcontinent in the east. Extensive tectonic changes, metamorphism and volcanic activity have formed the region throughout Earth history.