Plate interactions of Laurussia and Gondwana during the formation of Pangaea 鈥?Constraints from U-Pb LA-SF-ICP-MS detrital zircon ages of Devonian and Early Carboniferous siliciclastics of the Rhenohercynian zone, Central European Variscides
文摘
The southern Rheinisches Schiefergebirge, which is part of the Rhenohercynian zone of the Central European Variscides, exhibits several allochthonous units: the Gie脽en-, and the H枚rre nappe, and parts of the Frankenbach imbrication zone. These units were thrust over autochthonous and par-autochthonous volcano-sedimentary complexes of the Lahn and Dill-Eder synclines. This paper reports a representative data set of U-Pb LA-SF-ICP-MS ages of 1067 detrital zircon grains from Devonian and Lower Carboniferous siliciclastic sediments of the autochthonous and the allochthonous areas, respectively. The cluster of U-Pb ages from the allochthonous units points to a provenance in the Saxothuringian zone. Zircon populations from the Saxothuringian zone are representative of a Gondwanan hinterland and are characterized by age clusters of ~ 530-700 Ma, ~ 1.8-2.2 Ga, ~ 2.5-2.7 Ga, and ~ 3.0-3.4 Ga. Further samples were taken from the autochthonous and par-autochthonous units of the Lahn-Dill and Kellerwald areas. A Lower Devonian sandstone sample from the Siegen anticline provides a reference for siliciclastic sediments derived from the Old Red Continent. These samples show a provenance representative of Laurussia with debris primarily derived from Baltica and Avalonia. U-Pb zircon age clusters occur at ~ 400-450 Ma, 540-650 Ma, 1.0-1.2 Ga, ~ 1.4-1.5 Ga, ~ 1.7-2.2 Ga, and 2.3-2.9 Ga. Provenance analysis and geochemical data of the Rhenohercynian zone provide new information on the evolution of magmatic arcs in the Mid-Paleozoic. The data set constrains top-SE and top-NW directed subduction of the oceanic crust of the Rheic Ocean. Subduction-related volcanism lasted from the Early Devonian to the Early Carboniferous and thus confirms the existence of the Rheic Ocean until the Early Carboniferous. The tectonic model outlined for the Rhenohercynian zone suggests a wide Rheic Ocean.
