Detrital zircon U-Pb-Hf isotope signatures of Old Red Sandstone strata constrain the Silurian to Devonian paleogeography, tectonics, and crustal evolution of the Svalbard Caledonides

Abstract

Abstract Detrital zircon provenance studies of Mesoproterozoic basement and overlying Old Red Sandstone strata in northwestern Svalbard, Arctic Norway, were conducted to test competing models for Caledonian paleogeography and tectonics and constrain the magnitude of orogen-parallel, Silurian to Devonian strike-slip faulting following the Laurentia-Baltica collision. Mesoproterozoic basement strata, cut by earliest Tonian orthogneiss units, mostly yielded 1640–1050 Ma detrital zircon populations that are consistent with pre-Caledonian locations near northeast Greenland. Basal Old Red Sandstone deposits that filled pull-apart basins showed basement-derived signatures but also contained 530–450 Ma and 670–570 Ma populations with slightly subchondritic (ε Hf[t] = –4 to –2) Hf isotope compositions. These results are consistent with late Silurian–Early Devonian proximity to the northeast Greenland Caledonides and Pearya, which indicates limited (<200 km) strike-slip displacement of Svalbard’s Caledonian allochthons after the Laurentia-Baltica collision. Previously interpreted connections between the Svalbard Old Red Sandstone and British Caledonides are incompatible with these detrital zircon results. Lochkovian Old Red Sandstone strata were deposited after a second episode of strike-slip faulting and show recycled basement signatures. The lack of 530–450 Ma and 670–570 Ma populations suggests that the second deformation episode reorganized local drainages. Pragian–Givetian strata have provenance from local Old Red Sandstone sources that were uplifted during a third and final episode of strike-slip deformation. The results indicate that northern Caledonian (Svalbard, Pearya) crustal evolution was characterized by the reworking of Mesoproterozoic–Paleoproterozoic sources and mostly <600 m.y. crustal residence times, whereas the southern Caledonides (UK, Ireland) show evidence for the reworking of older basement and mostly >600 m.y. crustal residence times.