First (U–Th)/He Ages of Detrital Zircons From Paleozoic Strata of the Severnaya Zemlya Archipelago (Russian High Arctic)
Friday, 18 December 2015
Poster Hall (Moscone South)
The Severnaya Zemlya Archipelago contains rocks varying in age from late Neoproterozoic to Permian and is a key area for understanding the tectonic evolution of the North Kara and Laptev Sea basins. Here we present the first results of (U–Th)/He dating of detrital zircon collected from Ordovician – Devonian strata of Pioneer and October Revolution islands (Severnaya Zemlya Archipelago) along with Sedov Island. Twelve detrital zircon grains from two samples of Ordovician-Silurian strata yielded (U-Th)/He ages ranging from 583.8 ± 46.7 to 429.0 ± 34.3 Ma with a peak age of ca. 465 Ma. In Devonian strata, 36 detrital zircon grains from four samples yielded (U-Th)/He ages ranging from 1028.9 ± 82.31 to 332.9 ± 26.6 Ma showing major peaks at ca. 375 Ma and a smaller peak at ca. 465 Ma. The (U-Th)/He ages are older than depositional ages of host rocks for all samples from the Ordovician – Devonian strata of Severnaya Zemlya Archipelago, indicating the samples were not buried deep enough (~6-8 km) to reset the (U-Th)/He age, thus the ages indicate the exhumational history of the clastic source region. The (U-Th)/He detrital zircon ages from Ordovician- Silurian strata, with a peak age of ca. 465 Ma, suggest the primary source region was located within the Caledonian Orogen, which is unknown in the vicinity of Severnaya Zemlya. The abundance of Caledonian ages in the studied samples suggests a continuation of Caledonides northeastward across Barents shelf as previously inferred from subsequent Permo-Carboniferous rifting trend illustrated by geophysical data. In contrast to older clastic rocks, (U-Th)/He detrital zircon ages from the Devonian deposits show a mixture of Ellesmerian and Caledonian ages with age peaks at ca. 375 Ma and 465 Ma and the youngest grains nearing the age of sedimentation. The ages suggest the clastic source area of Devonian sandstones likely contained rocks affected by both Caledonian and Ellesmerian orogenies.