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New detrital zircon sensitive high-resolution ion microprobe (SHRIMP) geoch...
New detrital zircon sensitive high-resolution ion microprobe (SHRIMP) geochronology and published framework geology of Neoproterozoic to Silurian strata are integrated to reexamine tectonic models of the Pearya terrane and the Franklinian margin at Ellesmere Island, Arctic Canada. Compared to Cambrian detrital zircon reference spectra, Neoproterozoic sandstones from the Pearya terrane contain Laurentian detrital zircon ages. In fact, they compare very well with Neoproterozoic strata of Greenland. Ultramafic, tholeiitic, and andesitic basalts of the Maskell Inlet complex, inferred to have an age of ca. 481 Ma, predate the M'Clintock orogeny at ca. 475 Ma. Ordovician granitoid ages within the Pearya terrane span ca. 475-463 Ma. A K-Ar cooling age of 452 Ma records post-tectonic exhumation. Deposited at ca. 450 Ma, new data show that the Cape Discovery Formation contains mainly ca. 500-450 Ma detrital zircon ages, but also older ages of 660-620 Ma. Upper Ordovician sandstones indicate that the Pearya terrane platform continued to receive near-syndepositional zircon. The Pearya terrane platform was submerged at ca. 435 Ma and overlain by Silurian flysch fed by sources similar to detrital zircon within Proterozoic to Ordovician strata of the Pearya terrane. Ties between the Pearya terrane and the Franklinian shelf include: similar Proterozoic-Cambrian stratigraphy; detrital zircon ages from the Lower Cambrian Grantland Formation that appear to be a combination of recycled Marinoan strata of Pearya terrane and Franklinian shelf strata; and profound unconformities on the Franklinian shelf that correlate temporally to the M'Clintock orogeny. A pericratonic model is a straightforward solution to the tectonic history of the Pearya terrane and the Franklinian shelf. We hypothesize that the Pearya terrane was part of the Franklinian margin in the Neoproterozoic and that the intervening deep water basin, or Hazen Trough, originated as a failed rift. The Maskell Inlet complex records ca. 481 Ma volcanism as a response to mantle upwelling beneath a subducting slab, shortly before or as the continent-ocean transition zone of the Franklinian margin was overridden. Continued convergence and crustal thickening during arc-continent collision drove the M'Clintock orogeny at ca. 475 Ma and resulted in the unconformities on the Franklinian shelf. After arc-continent collision, magmatism between ca. 475 and 438 Ma was related to subduction on the outboard margin, and the Pearya terrane was overlain by a low-accommodation retroarc foreland basin. A subsequent collisional event led to progressive drowning of the Pearya terrane and Franklinian platforms between 435 and 425 Ma. Silurian flysch then blanketed the Pearya terrane and entered the axis of the foreland basin, which also received sediment from cratonic sources of the flexural basin margin. Limited deformation at northern Axel Heiberg Island was associated with a ca. 390 Ma granitoid within the Pearya terrane. After a Devonian pulse of subsidence, infilling of the basin to form the Devonian clastic wedge overlapped in age with small ca. 368 Ma granitic intrusions within the Pearya terrane and was followed by extensive foreland deformation of the Late Devonian-Mississippian Ellesmerian orogeny.
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