Detrital zircon U-Pb geochronology of modern Andean rivers in Ecuador: Fingerprinting tectonic provinces and assessing downstream propagation of provenance signals

Abstract

Recognizing detrital contributions from sediment source regions is fundamental to provenance studies of active and ancient orogenic settings. Detrital zircon U-Pb geochronology of unconsolidated sands from modern rivers that have source catchments with contrasting bedrock signatures provides insight into the fidelity of U-Pb age signatures in discriminating tectonic provenance and downstream propagation of environmental signals. We present 1705 new detrital zircon U-Pb ages for 15 samples of unconsolidated river sands from 12 modern rivers over a large spatial extent of Ecuador (∼1°N–5°S and ∼79°–77°W). Results show distinctive U-Pb age distributions with characteristic zircon age populations for various tectonic provinces along the Andean convergent margin, including the forearc, magmatic arc, and internal (hinterland) and external (foreland) segments of the fold-thrust belt. (1) Forearc and magmatic arc (Western Cordillera) river sands are characterized by Neogene–Quaternary age populations from magmatic sources. (2) Rivers in the hinterland (Eastern Cordillera) segment of the Andean fold-thrust belt have substantial populations of Proterozoic and Paleozoic ages, representing upper Paleozoic–Mesozoic sedimentary and metasedimentary rocks of ultimate cratonic origin. (3) River sands in the frontal fold-thrust belt (Subandean Zone to Oriente Basin) show distinctive bimodal Jurassic age populations, a secondary Triassic population, and subordinate Early Cretaceous ages representative of Mesozoic plutonic and metamorphic bedrock. Detrital zircon U-Pb results from a single regional watershed (Rio Pastaza) spanning the magmatic arc to foreland basin show drastic downstream variations, including the downstream loss of magmatic arc and hinterland signatures and abrupt introduction and dominance of selected sources within the fold-thrust belt. Disproportionate contributions from Mesozoic crystalline metamorphic rocks, which form high-elevation, high-relief areas subject to focused precipitation and active tectonic deformation, are likely the product of focused erosion and high volumes of local sediment input from the frontal fold-thrust belt, leading to dilution of upstream signatures from the hinterland and magmatic arc.

Flow‐process controls on grain type distribution in an experimental turbidity current deposit: Implications for detrital signal preservation and microplastic distribution in submarine fans

“…Autogenic modulation of signal preservation is comparatively well‐studied in terrestrial and shallow‐marine environments compared to submarine fans (Capaldi et al, 2019; Covault et al, 2007; Garzanti et al, 2015; Jackson et al, 2019). Here, a known composition of mixed grain types was diluted at the scale of a single turbidity current (Figure 11).…”

Neogene Retroarc Foreland Basin Evolution, Sediment Provenance, and Magmatism in Response to Flat Slab Subduction, Western Argentina

“…Detrital zircon (DZ) U-Pb analyses of modern river sands help define regional magmatic and metamorphic histories (Ducea et al, 2018;Finzel, 2019;Link et al, 2005;Pepper et al, 2016) and identify the impact of erosion, zircon fertility, and lithologic erodibility on provenance signatures (e.g., Amidon et al, 2005;Horton et al, 2015;Jackson et al, 2019;Malkowski et al, 2020). Zircon U-Pb ages for Andean rivers draining the Principal Cordillera, Frontal Cordillera, Precordillera, and Sierras Pampeanas (Capaldi et al, 2017(Capaldi et al, , 2019 help characterize provenance variations across hinterland, wedge-top, foreland, and broken foreland basin settings ( Figure 6), providing an opportunity to track Cenozoic erosional unroofing and sediment routing patterns.…”

Detrital zircon geochronology of modern river sediment in south-central Alaska: Provenance, magmatic, and tectonic insights into the Mesozoic and Cenozoic development of the southern Alaska convergent margin

“…This study is one of a growing number that utilize detrital zircon geochronology of modern river sediment for provenance studies (e.g., Cawood et al, 2003;Saylor et al, 2013;Bradley et al, 2015;Lease et al, 2016;Pepper et al, 2016;Capaldi et al, 2017;Ducea et al, 2018;Jackson et al, 2019). The application of detrital zircon ages in modern Research Paper river sediment to characterize major magmatic and provenance trends along a convergent margin is useful in that (1) the potential source areas and tectonic setting of a given watershed are better defined relative to ancient basinal settings, allowing for more efficient characterization of zircon age distributions; and (2) in regions that have an extensive and long-lived history of magmatism, a temporal felsic magmatic record of the tectonic development of the margin may be documented.…”