Paleoproterozoic volcano-sedimentary series in the ca. 2.27-1.96 Ga Birimian Orogen of the southeastern West African Craton

摘要

The ca. 2270-1960 Ma accretionary-collisional Birimian Orogen in the southern West African Craton (sWAC) contain a number of volcano-sedimentary series, which were deposited in basins that developed during the regional Eburnean collisional orogeny (ca. 2160-1960 Ma). Understanding their spatiotemporal distribution is thus crucial for constraining the tectonic evolution of the orogenic system. This study presents new LA-ICPMS data on detrital zircon from volcano-sedimentary series in southeastern sWAC, which indicate maximum depositional ages between ca. 2160-2130 Ma. The detrital zircon population is predominantly composed of grains with ages compatible with derivation from local Birimian crust, but older Paleoproterozoic and Archean components are also present. These may have been derived from crustal domains now present in South American cratons and terranes, and which would have been located to the present east or southeast of the sWAC. The deposition of the volcano-sedimentary series also coincided with the onset of the Eburnean collisional orogeny in eastern sWAC, which suggest a dynamic coupling between compression on one hand and extension on the other, where the latter controlled the establishment of the depocentres in which the series were deposited. The data in this study support previous observations that sedimentation across sWAC was diachronous during the course of the Eburnean orogeny, and that an early pulse occurred primarily in the east between ca. 2165-2125 Ma while a later pulse occurred in the west around ca. 2115-2080 Ma, followed by limited volcanism and sedimentation at ca. 2065 Ma. This diachroneity is also reflected in the lithostratigraphy, with areally extensive shallow water deposits being more frequent in the east, whereas carbonates are only present in the younger successions to the west. This may reflect a hinterland-foreland style relationship between eastern and western sWAC, respectively, where sedimentation occurred progressively d