New zircon and apatite (U-Th)/He data (AHe and ZHe) from the crystalline basement of the South American passive margin in southern Brazil present a wide distribution of Phanerozoic apparent ages, recording its prerift evolution. Its geological significance can be investigated by modeling the influence of the accumulated radiation damages on the measured crystals in its He ages during a long upper crust residence. Despite the presence of a significant fault in the studied area, the samples essentially constrain a uniform thermal history for the entire study area. Zircon helium ages spread from 472 to 26 Ma and correlate strongly with the radioactive element content of the crystals. Although the region was probably covered by Paleozoic sediments of the Paraná Basin, the ZHe system experienced a more intense thermal overprint, most likely the onset of the Paraná Large Igneous Province (LIP), causing its dispersion. The nearby intrusion of a feeding system of the LIP, the Florianópolis Dyke Swarm, may have contributed for keeping geothermal gradients elevated for a period long enough to promote the observed reset. After the extrusion of the volcanism, the study area was probably covered by up to 2 km of basalt floods, imprinting temperatures above the AHe partial retention zone on the crystalline basement. These were eroded during rapid cooling between 75 and 55 Ma, as indicated by thermal modeling. Additional analyses with Raman spectroscopy were used for calculating radiation damage ages in the zircon crystals measured for (U-Th)/He, resulting in a comparable set of ages.

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Quantifying geological processes has greatly benefited from the development and use of thermochronometric methods over the last fifty years. Among them is the (U-Th)/He dating method, which is based on the production and retention, within a crystal structure, of radiogenic 4He atoms associated with the alpha decay of U, Th and Sm nuclei. While apatite has been the main target of (U-Th)/He studies focusing on exhumation and burial processes in the upper levels of the continental crust (~50–120 °C), the development of (U-Th)/He methods for typical phases of igneous and metamorphic rocks (e.g., zircon and titanite) or mafic and ultramafic rocks (e.g., magnetite) over the last two decades has opened up a myriad of geological applications at higher temperatures (>100–300 °C). Thanks to the understanding of the role of radiation damage in He diffusion and retention for U-Th-poor and rich mineral phases, the application of (U-Th)/He thermochronometry to exhumation processes and continental evolution through deep time is now mainstream. This contribution reviews the (U-Th)/He thermochronometer principle and the influence of radiation damage in modifying the diffusion behavior. It presents applications of (U-Th)/He dating to problems in tectonic and surface processes at shallow to middle crustal depths (>100–300 °C). New and promising applications using a combination of methods will stimulate a research avenue in the future.

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Thick regoliths developed under tropical climate, namely, laterites, resulting from long-term and pronounced geochemical and mineralogical rearrangement of the parent rock in response to environmental changes. Little information is available on the timing of laterite and bauxite formations, especially on the chronology of the main weathering episodes responsible for lateritic cover formation on the Guiana shield. For this purpose, we focused on both lateritic and bauxitic duricrusts developed over the Paleoproterozoic Greenstone Belt in the Brownsberg, Suriname. The duricrust samples have a relatively simple mineralogy (i.e., goethite, gibbsite, hematite, and kaolinite) but reveal, when observed at a microscopic scale, a complex history of formation with multiple episodes of dissolution/reprecipitation. The (U-Th)/He dating of 179 Fe-oxides subsamples shows that duricrusts sampled at the top of the Brownsberg plateau have ages ranging from <0.8 Ma to ∼19 Ma. In contrast, Fe-oxides extracted from detrital duricrust boulders collected downslope indicate formation ages up to 36 Ma. This age discrepancy may indicate that a main episode of physical erosion affected this region between ca. 30 and 20 Ma. Consistently, the bauxite sampled at the mountaintop indicates a younger phase of formation, with Fe-oxides recementing fragments of a preexisting bauxitic material older than ∼15 Ma. Geochronological data also reveal a long-lasting weathering history until the present day, with multiple generations of Fe-oxides in the bauxite and the duricrusts resulting from successive cycles of dissolution and reprecipitation of Fe-oxides associated with redox cycles. This long-lasting weathering history led to geochemical remobilization and apparent enrichment in some relatively immobile elements, such as REE, aluminum, and vanadium, especially in the duricrust sampled at the mountaintop. Our geochronological, mineralogical, and geochemical study of Fe- and Al-crusts from the Brownsberg mountain provide constraints on the evolution of environmental conditions prevailing since the early Oligocene in Suriname.