| dc.description.abstract | The Sara’s Lust Gneisses are a recently separately named formation adjacent to the Marowijne Greenstone Belt in the Guiana Shield, Suriname. They comprise granitoids, amphibolites, mafic volcanics and plutons, and greywackes, which all underwent metamorphism up to amphibolite facies. Contact relationships between these gneisses and the lower grade metamorphic Marowijne Greenstone Belt are not well constrained and as a result, the geological relationship between the two is unknown. In this study emphasis is placed on the petrogenesis and metamorphic history of the Sara’s Lust Gneisses. New petrographical data, bulk rock major and trace element chemistry data, mineral chemistry data and metamorphic peak conditions of the Sara’s Lust Gneisses are presented in this report. Pseudosections, modelled with Perple_X, and geothermometric calculations yield peak pressures of 4.6 - 5.5 (± 1) kbar and temperatures 617 - 688 (± 50) °C. Further, the mafic suite of the Sara’s Lust Gneisses exhibits a high content of incompatible elements, which is construed with a plume-derived petrogenesis. The granitoids in the Sara’s Lust Gneisses are A-type and their chemistry implies that they were generated in an ocean ridge. As their magmatic age (2.156 ± 12 Ga) is coeval with the subduction event of the Transamazonian Orogeny (2.18 - 2.13 Ga), these granitoids are interpreted to have formed in a back-arc basin setting. This is in contrast with other granitoids in the Marowijne Greenstone Belt, as these are mainly associated with arc-volcanism. Consequently, due to this spatial difference in the former subduction zone, it is likely that the Sara’s Lust Gneisses neither represent the lower crustal equivalent, nor the basement of the Marowijne Greenstone Belt. Rather, they were situated adjacently to one another. During collision (2.11 - 2.08 Ga) the Marowijne Greenstone Belt was likely thrusted onto the Sara’s Lust Gneisses. This event resulted in metamorphism of the Sara’s Lust Gneisses (2.084 ± 18 Ga). The provenance of the metagreywackes does not show a detectable influence of TTG material, which is in agreement with deposition in a back-arc basin setting. Hence, the petrogenetic history of the Sara’s Lust Gneisses, and on a larger scale the Guiana Shield, is consistent with a shift in tectonic style from a mantle-plume upwelling style from the earliest part of Earth history towards modern-day horizontal tectonics. | |
