Sedimentary provenance of Mid-Devonian clastic sediments in the Tepla-Barrandian Unit (Bohemian Massif): U-Pb and P-Pb geochronology of detrital zircons by laser ablation ICP-MS

摘要

The provenance of the Mid-Devonian clastic sediments in the Tepla-Barrandian Unit (TBU) of the Bohemian Massif was investigated by laser ablation ICP-MS U - Pb zircon dating, bulk sediment geochemistry and mineralogical study of the heavy mineral fraction. In contrast to the island arc provenance of the TBU Neoproterozoic sediments, the Early Palaeozoic sediments contain significant amounts of differentiated crustal material. The detrital zircon populations in the Barrandian Mid-Devonian siltstones and sandstones show ages ranging from Archaean ( similar to 3.0 Ga) to Early Palaeozoic ( similar to 0.39 Ga). Major age maxima are at similar to 2.6 Ga, 2.0 - 2.25 Ga, 0.62 and 0.51 Ga. The youngest identified zircons so far correspond to Lower and Mid-Devonian ages. The extensive mechanical abrasion of zircons having Archaean ( 3.0, 2.8 and 2.6 Ga) to Paleoproterozoic ages ( 2.25 - 2.0 Ga) suggest their provenance from recycled old sedimentary sequences. The relatively large number of zircons with ages between similar to 2.0 and 3.0 Ga may indicate the presence of relicts of the Archaean/Paleoproterozoic crust in the source areas of the studied Mid-Devonian sediments. The absence of detrital zircon ages between similar to 0.9 and 1.2 Ga and the presence of zircon ages of similar to 2.0 - 2.25 and 0.5 - 0.8 Ga correspond to the zircon age pattern from the Gondwana-related North African, rather than Gondwana-related South American and Baltic terranes. The material was entering the basin predominantly from the west and consisted primarily of detrital material of Cambrian granitoids and recycled material of Neoproterozoic meta-sedimentary sequences.