(U‐Th)/He Thermochronology and Zircon Radiation Damage in the South American Passive Margin: Thermal Overprint of the Paraná LIP?

Abstract

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.

Differential Phanerozoic evolution of cratonic and non-cratonic lithosphere from a thermochronological perspective: São Francisco Craton and marginal orogens (Brazil)

“…The onset of the break-up was approximately coeval with the emplacement of the Paraná-Etendeka flood basalts in the Paraná Basin (Fig. 2: 15, Hueck et al, 2018;Krob et al, 2020;Rocha et al, 2020). Krob et al (2020) combined stratigraphic records and thermochronological data sets to suggest a possible thermal effect of this mantle plume in the intraplate environment adjacent to its emplacement.…”

Zircon (U-Th)/He Thermochronologic Constraints on the Long-Term Thermal Evolution of Southern New Mexico and Western Texas

“…The red dashed lines in each plot are the best-fit forward models from each location. 16 Lithosphere…”

“…The large ZHe temperature sensitivity window makes it possible to constrain more complete and continuous thermal histories, offering an opportunity to bridge the gap between higher and lower temperature methods. Previous studies have relied on this intrasample spread in ZHe dates to investigate a wide range of geologic processes, such as the Proterozoic thermal history of rocks (e.g., [14]), timing of Laramide exhumation [15], and development of the South American passive margin [16]. However, additional studies are needed to further assess the efficacy of this method.…”

Low-temperature thermochronology of the South Atlantic margin along Uruguay and its relation to tectonic events in West Gondwana

“…Published data suggest that an important limit between pre-and post-rift cooling and exhumation is located in the Florianópolis region, southern Brazil (Fig. 1), where a very complex thermal history has been reported (Jelinek et al 2003;Karl et al 2013;Hueck et al 2018a). Further south of this region, thermochronometry studies have reported mainly pre-rift Paleozoic cooling phases in southernmost Brazil (Borba et al 2002(Borba et al , 2003Oliveira et al 2016;Machado et al 2019), Uruguay (Kollenz 2015;Hueck et al 2017;Gomes & Almeida 2019) and Argentina (Kollenz et al 2017).…”