Resumo

MANTILLA-FIGUEROA, Luis Carlos  e  GARCIA-RAMIREZ, Carlos Alberto. Geology and geochronology of the outcropping lithologies in the Mogotes-San Joaquín section (SW sector of the Santander Massif). bol.geol. [online]. 2018, vol.40, n.1, pp.123-144. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v40n1-2018008.

In the southwestern of the Santander Massif (specifically in the area of Mogotes and San Joaquín towns) outcrop Paleozoic rocks (with and without metamorphism), which have been grouped and mapped as part of the Floresta Formation (Devonian in age). Studies carried out in the framework of this work show that this formation can be divided at least into three members: (a) a basal member with metamorphic foliation (composed mainly of fine-grained and slightly conglomeratic phyllite-like rocks, quart-pelitic in composition) with detrital zircon U-Pb ages of 410 Ma (Early Devonian); (b) a middle member with no evidence of metamorphism (composed mostly of sandstone and mudstone) with detrital zircon U-Pb ages around 372 Ma (Late-Middle Devonian boundary) and; (c) an upper member (predominantly mudstone), which could not be dated by difficulties to find and concentrate their detrital zircons (probably late Devonian in age?). Based on the maximum stratigraphic ages here obtained (derived from the detrital zircon U-Pb ages already mentioned), it is proposed to correlate (in time) the basal member with the Tibet Formation and the middle member with the Floresta Formation. Although the upper member could not be dated, it is inferred that this could be temporarily correlated with the Cuche Formation (units described for the Floresta Massif). Stratigraphically above the Devonian rocks (previously referred), layers of calcareous sandstones (relatively restricted), abundant limestones, calcareous mudstones and mudstones are observed. Based on previous paleontological studies and detrital zircon U-Pb ages here reported (in mudstones of the upper part of this sedimentary record, with a peak age around 288 Ma), it is possible to suggest that these rocks correlate with the unit called ‘Paleozoic of the Nevado River’ (considered Carboniferous-Permian in age).

Palavras-chave : Santander Massif; Mogotes; San Joaquin; Floresta Formation; Paleozoic rocks.

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