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

Abstract

The São Francisco Craton (SFC) and its marginal Araçuaí and Brasília orogens exhibit a significant diversity in their lithospheric architecture. These orogens were shaped during the Neoproterozoic-Cambrian amalgamation of West Gondwana. The rigid cratonic lithosphere of the SFC and the relatively weak lithosphere of the Araçuaí Orogen were disrupted during the Cretaceous opening of the South Atlantic Ocean, whereas the Brasília Orogen remained in the continental hinterland. In earlier research, the thermal effects of the Phanerozoic reactivations in the shallow crust of the Araçuaí Orogen have been revealed by low-temperature thermochronology, mainly by apatite fission track (AFT) analysis. However, analyses from the continental interior are scarce. Here we present new AFT data from forty-three samples from the Brasília Orogen, the SFC and the Araçuaí Orogen, far from the passive margin of the Atlantic coast (~150 to 800 km). Three main periods of basement exhumation were identified: (i) Paleozoic, recorded both by samples from the SFC and Brasília Orogen; (ii) Early Cretaceous to Cenomanian, recorded by samples from the Araçuaí Orogen; and (iii) Late Cretaceous to Paleocene, inferred in samples from all domains. We compare the differential exhumation pattern of the different geotectonic provinces with their lithospheric strengths. We suggest that the SFC likely concentrated the Meso-Cenozoic reactivations in narrow weak zones while the Araçuaí Orogen displayed a far-reaching Meso-Cenozoic deformation. The Brasília Orogen seems to be an example of a stronger orogenic lithosphere, inhibiting reworking, confirmed by our new AFT data. Understanding the role of the lithosphere rigidity may be decisive to comprehend the processes of differential denudation and the tectonic-morphological evolution over Phanerozoic events.

Exhumation of the passive margin of the DR Congo during pre- and post- Gondwana breakup: Evidence from low-temperature thermochronology, geology and geomorphology

“…3) and reveals significant basement cooling (>100 °C, c. 2-4 km) during the Cenozoic (e.g. Fonseca et al, 2021;Jelinek et al, 2014;Van Ranst et al, 2020b). This observation implies important tectonic activity posterior to the late Cretaceous rifting that separated South America and Africa.…”

“…Track length distributions are all similar for south-eastern Brazil, showing unimodal distributions with slightly negative skewness (Van Ranst et al, 2020a). Therefore, there is a consensus that this area of the AWCO suffered intense erosion due to post-rift uplift pulses constrained to the Late Cretaceous to Palaeogene (Fonseca et al, 2021). The uplift in south-eastern Brazil is commonly ascribed to restraining intracontinental stress resulting from both the Andean orogeny and the Mid-Atlantic ridge-push (max.…”

“…Other published data on passive margins already pointed to weak thermal effects of rifting and opening of new ocean basins in the nearby passive margins (e.g. Fonseca et al, 2021;de Borba et al, 2003;Morón et al, 2020). Firstly, it has already been shown that the upper crust is hardly affected by thermal effects, i.e.…”

“…Passive margins with no clear reset of the AFT system during the rifting phase have indeed been associated to cratonic rheology (e.g. Fonseca et al, 2021;de Borba et al, 2003;Morón et al, 2020). In this case, epirogenic uplift or flexural isostasy during the ocean opening are mitigated along with the erosional response to these processes, resulting in an almost stable thermal structure.…”

“…Larger amounts of AFT (and other low-T thermochronological) data are available on the conjugate Brazilian passive margin, such as from the Araçuaí counterpart of the WCB (Fig. 3; Amaral-Santos et al, 2019;Fonseca et al, 2021;Jelinek et al, 2014;Van Ranst et al, 2020b). Before Gondwana breakup, the south-eastern Brazilian highlands, which are underlain by the litho-tectonic units of the Araçuaí Orogen, were directly juxtaposed to the Lower Congo region (Fig.…”