Neogene basin infilling from cosmogenic nuclides (10Be and 21Ne) in Atacama, Chile: Implications for palaeoclimate and supergene copper mineralization. (21st June 2021)

• Record Type: Journal Article
• Authors: Sanchez, Caroline; Regard, Vincent; Carretier, Sébastien; Riquelme, Rodrigo; Blard, Pierre‐Henri; Campos, Eduardo; Brichau, Stéphanie; Lupker, Maarten; Hérail, Gérard
• Is Part Of: Basin research. Volume 33:Number 5(2021)
• Page Start: 2549
• Page End: 2571
• Publication Date: 2021-06-21
• Subjects: Atacama -- burial dating -- cosmogenic nuclides -- denudation rates -- intramountainous basin -- supergene copper deposits; Sedimentation and deposition -- Periodicals; Sedimentary basins -- Periodicals; 551
• DOI: 10.1111/bre.12568
• Languages: English
• ISSNs: 0950-091X

Abstract

Abstract: Increasing evidence suggests that supergene exotic copper deposits were emplaced during periods of geomorphic quiescence and pulses of humidity in arid environments. We tested this idea in the Centinela Mining District in the Atacama Desert (northern Chile). We collected 14 sand samples at depth (up to 110 m) in two open‐pit mines (Central Tesoro and Mirador) exposing Miocene sediment, and located in the El Tesoro Basin, which hosts two exotic copper‐rich orebodies. We inverted the 10 Be and 21 Ne concentrations by using a two‐box model (IMIS, inversion of multi‐isotopes in a sedimentary basin) composed of an eroding source of sediment and a depositional sedimentary basin, and by selecting denudation and sedimentation rate histories that can explain our data. The ages found demonstrate that the two exotic orebodies were deposited during a narrow period between 14 Ma (10 Ma younger than previously thought) and 9.5 Ma, when an ignimbrite covered the sedimentary sequence. The dated lower exotic copper orebody was deposited during or just before a sharp decrease in the sedimentation rates (from >100 to 0.5–5 m/Ma), which is consistent with published sedimentological and carbonate isotopic data in this district. This confirms the idea that exotic deposits form during a quiescence of the geomorphic activity. Nevertheless, our model suggests that the back‐ground denudation rate providing sediment to these basins between ca. 14 Ma and ca. 9.5 Ma was surprisingly high (>250 m/Ma) for such an arid environment. These denudation rates can be explained by a relatively rapid local back‐scarp retreat providing most of the sediment to these basins and possibly a wetter climate compared to the present. Then, during the period 10–7 Ma, the denudation rates decreased to >50 m/Ma. This decrease may correspond to a local progressive decrease in the slope of the surrounding hills, or to a progressive aridification, or a combination of both phenomena. Abstract : Cosmogenic nuclides 10 Be and 21 Ne measured in a sedimentary basin records the denudation evolution. Around 9.5–14 Ma, thigh denudation rates (>250 m/Ma) were recorded, possibly linked to a scarp retreat. Between 7 and 10 Ma denudation rates were moderate (>50 m/Ma) and very low since then (<10 m/Ma).