Provenance of Albian sandstones in the São Luís–Grajaú Basin (northern Brazil) from evidence of Pb–Pb zircon ages, mineral chemistry of tourmaline and palaeocurrent data

Abstract

Provenance of Albian sandstones in the southern margin of the São Luís–Grajaú Basin, northern Brazil, is documented for the first time. Palaeocurrent patterns, mineral chemistry of tourmaline and 207Pb/ 206Pb zircon dating, were used to define potential source areas for these deposits. The studied quartz-sandstones were sourced from different areas, discriminated essentially by palaeocurrent patterns and provenance-sensitive heavy mineral indices that suggest changes in provenance. Based on palaeocurrent patterns and RuZi, the studied sedimentary succession was subdivided into four heavy mineral zones, generically named A, B, C and D, in ascending stratigraphic order. Chemical analysis of tourmaline indicates provenance from metasedimentary rocks as metapelites and metapsammites, with lesser amounts of granites, pegmatites and aplites. 207Pb/ 206Pb ages from detrital zircon reveal a direct fingerprint of Archean and Proterozoic terrains in the source. Three major zircon populations were defined: Archean (3103–2545 Ma), Paleoproterozoic (2460–1684 Ma) and Neoproterozoic (993–505 Ma). Small groups of Mesoproterozoic (1570–1006 Ma) and Paleozoic (535–441 Ma) grains are also present. The potential source terrains for these stratigraphic zones were deduced on the basis of the overlap of probability density of zircon ages from the studied quartz-sandstones, with U–Pb and Pb–Pb zircon data from the basement of the São Luis–Grajaú Basin that includes the Amazonian and São Luís cratons, Araguaia and Gurupi belts, Borborema Province and Parnaiba Basin. The sediments of the Zone A were supplied from the São Luís Craton and Gurupi Belt and from the northwestern portion of the Borborema Province. The main source areas for the Zones B, C and D were the eastern portion of the Amazonian Craton and Araguaia Belt, and the Borborema Province. Zircons with ages of ca. 1000 Ma were attributed to the Cariris Velho Event, widely recognized in Borborema Province. The predominance of zircon and tourmaline grains with high textural maturity supports a strong contribution from sedimentary and metasedimentary rocks form Parnaiba Basin and Araguaia Belt, respectively. A more specific evaluation of these source regions is not yet possible due to the limited number of detrital zircon ages from these regions, mainly from the Parnaiba Basin. However this Paleozoic basin was one of the most important source of sediment for the Albian sandstones in the São Luís–Grajaú Basin.