Geology topics

Research about Andes Mountains

Source-linked reports with geographic coverage including Andes Mountains.

4 recordsLinked to original sources

USGS2022

Porphyry copper: Revisiting mineral resource assessment predictions for the Andes

A mineral resource assessment of porphyry copper deposits in the Andes Mountains of South America was done in 2005 in cooperation with geological surveys in South America. The study identified 590 million metric tons (Mt) of copper in identified resources. Continued exploration and development in the region over a 15-year period provide an opportunity to compare the predicted assessment results with new discoveries and resource growth in previously known deposits. The 2005 assessment estimated that 145 undiscovered deposits could contain a mean of 750 Mt of copper. The actual number of deposits increased (2005 to 2020) from 69 to 120 and the amount of identified copper resources increased from 590 Mt to 1600 Mt. Although most of the new deposits and copper resources are concentrated in Miocene-Pliocene and Eocene-Oligocene mineral belts, new deposits have been discovered in Jurassic and Cretaceous mineral belts. Resource growth in porphyry copper deposits known in the Andes in 2005 (1100 Mt copper) exceeds copper resources in new discoveries since 2005 (490 Mt copper) by a factor of 2.

Andes Mountains↗

USGS2015

Lake formation, characteristics and evolution in retroarc deposystems: A synthesis of data from the modern Andean orogen and its associated basins

Lake deposystems are commonly associated with retroarc mountain belts in the geological record. These deposystems are poorly characterized in modern retroarcs, placing limits on our ability to interpret environmental signals from ancient deposits. To address this problem, we have synthesized our existing knowledge about the distribution, morphometrics, and sedimentary geochemical characteristics of tectonically formed lakes in the central Andean retroarc. Large, active mountain belts such as the Andes frequently create an excess of sediment, to the point that modeling and observational data both suggest their adjacent retroarc basins will be rapidly overfilled by sediments. Lake formation, requiring topographic closure, demands special conditions such as topographic isolation and arid climatic conditions to reduce sediment generation, and bedrock lithologies that yield little siliciclastic sediment. Lacustrine deposition in the modern Andean retroarc has different characteristics in the six major morphotectonic zones discussed. (1) High-elevation hinterland basins of the arid Puna-Altiplano Plateau frequently contain underfilled and balanced-filled lakes that are potentially long-lived and display relatively rapid sedimentation rates. (2) Lakes are rare in piggyback basins, although a transition zone exists where basins that originally formed as piggybacks are transferred to the hinterland through forward propagation of the thrust belt. Here, lakes are moderately abundant and long-lived and display somewhat lower sedimentation rates than in the hinterland. (3) Wedge-top and (4) foredeep deposystems of the Andean retroarc are generally overfilled, and lakes are small and ephemeral. (5) Semihumid Andean back-bulge basins contain abundant small lakes, which are moderately long-lived because of underfilling by sediment and low sedimentation rates. (6) Broken foreland lakes are common, typically underfilled, large, and long-lived playa or shallow systems.

Book chapter↗

USGS1970

Macusanite occurrence, age, and composition, Macusani, Peru

Macusanite, originally believed to be a type of tektite because of its sculpture, is shown to be related to sillar of the Macusani region, Peru. K-Ar measurements establish identical Pliocene ages (4.2 m.y.) for macusanite and sillar and relate these deposits to the extensive ash flows of the southern Andes. These rocks are unique for glassy rocks in that lithium, boron, and arsenic contents are very high; cesium, rubidium, tellurium, fluorine, and tin are higher than normal; zinc, copper, chromium, and zirconium are lower than normal; and high-alumina minerals such as andalusite are present.

Macusani↗

USGS1961

Local evidence of Pleistocene to recent orogeny in the Argentine Andes

Deformed continental sedimentary rocks are exposed in the province of Salta, northwestern Argentina, in one of many intermontane basins of the Puna, a high desert region of subparallel north-trending block-fault ranges. These rocks, formerly thought to be Tertiary but recently dated by fossil diatoms as Pleistocene or younger, comprise several thousand feet of elastics and evaporites interpreted as having accumulated in a structural basin under geologic and climatic conditions much like those of today. They are overlain unconformably by sedimentary rocks and sediments of three distinct depositional periods. The stratigraphic section is as follows: Fan gravels and playa deposits ( Recent ) - Disconformity - Flat-lying lacustrine sandstones and siltstones, minor salines - Angular unconformity - Gently folded conglomerates and sandstones - Angular unconformity - Folded and faulted conglomerate, sandstone, shale, evaporites, and tuffs The basin rocks are folded along north-trending axes and are cut by northeast- to southeast-trending normal faults and by a north-trending reverse fault; the next younger conglomerates and sandstones are gently folded; the two youngest units are undisturbed. The three unconformities, the faults and folds in the older beds, and post-lake-bed faulting of an erosion surface on an adjacent block all indicate intermittent late Pleistocene to Recent local deformation. Neither regional tension nor regional compression can explain both the Pleistocene to Recent movements on the regional block faults and the contemporaneous compressional structures within the basin. The mechanism of horst-wedging, suggested by a current explanation of the analogous ranges of the Great Basin, is proposed as a solution to the dilemma; the horst blocks, forced directly upward along Miocene normal faults, acted as wedges and compressed the sediments accumulating in the graben, creating the pattern of faults and folds now observed. If such structures are ever discovered in the North American Great Basin, as seems reasonable, they should offer new insight into the understanding of basin-and-range structure.

Andes Mountains↗