Deposition and tectonic setting of the Palaeoproterozoic Castelo dos Sonhos metasedimentary formation, Tapajos Gold Province, Amazonian Craton, Brazil: age and isotopic constraints

摘要

The Castelo dos Sonhos Formation (CSF) represents a relic of a sedimentary basin located in the southeastern Tapajos Gold Province (TGP), at its boundary with the Iriri-Xingu Domain (IX), south of the Amazonian Craton. The formation comprises mature, coarse-grained metasandstones (quartz-arenites) intercalated with auriferous metaconglomerates with clasts of quartz and subordinately of banded iron formation, quartzite, schist, and felsic metavolcanic rocks. Lithology, planar, channelled, and large-scale cross-bedding suggest deposition in continental setting by the braided fluvial system associated with alluvial fans and subordinate aeolian dunes. The rocks underwent very low metamorphism and gently synformal folding, and were intruded by andesites and granitoids (2011-1918 Ma). U-Pb LA-ICP-MS zircon data indicate maximum depositional ages of 2050 Ma (metaconglomerate) and 2074, 2088, and 2104 Ma (metasandstones). Hence, deposition occurred at 2050-2011 Ma, slightly preceding or being coeval with the onset of the orogenic phase in TGP (2030-1956 Ma). The quartz-arenite composition, zircon U-Pb data, and negative eHf (-1.3 to -13.0) and eNd (-2.9 to -5.3) values indicate: (1) quartzose provenance, (2) prolonged transport and recycling of sedimentary sources, (3) multiple age peaks (2050-3700 Ma), with predominant sources of 2100 and 2750 Ma, and (4) long crustal residence time for the source rocks. Source areas were Rhyacian-Siderian orogenic belts to Mesoarchaean terranes of the Amazonian Craton located to the east, southeast, and northeast of TGP, along with Palaeoarchaean and Eoarchaean detrital zircons recycled from older sedimentary rocks. We interpret CSF as part of a larger foreland system related to the evolution of Rhyacian orogens, currently represented by the Bacaja and Santana do Araguaia domains. The present location of CSF in the easternmost TGP, close to its boundary with IX, is due to rifting (1.89-1.80 Ga) that produced the Uatuma Silicic Large Igneous Province (Uatuma SLIP), and the juxtaposition of the crustal domains is supported by gravity data.