SHRIMP U–Pb zircon evidence for age, provenance, and tectonic history of early Paleozoic Ganderian rocks, east-central Maine, USA
AbstractSHRIMP U–Pb zircon ages from Ganderia in eastern Maine clarify the ages and provenance of basement units in the Miramichi and St. Croix terranes and of cover rocks in the Fredericton trough and Central Maine/Aroostook-Matapedia basin (CMAM). These new data constrain timing of orogenic events and help understand the origin of the cover rock depocenters.
Detrital zircon data generally confirm suggested ages of the formations sampled. Zircon grains with ages of ca. 430 Ma in both depocenters, only slightly older than their host rocks, were probably derived from the earliest volcanic eruptions in the Eastport-Mascarene belt. Their presence indicates that unnamed CMAM sandstone units may be as young as Pridoli and their absence from the Appleton Ridge and Digdeguash formations suggests that these formations are older than initial Eastport-Mascarene volcanism. Detrital and volcanic zircon ages confirm a Late Cambrian to Middle Ordovician age for the Miramichi succession and date Miramichi volcanism at 469.3 ± 4.6 Ma. In the St. Croix terrane, zircon grain with an age of 477.4 ± 3.7 Ma from an ashfall at the base of the Kendall Mountain Formation and age spectra and fossils from overlying quartz arenite suggest that the formation may span Floian to Sandbian time. The main source of CMAM and Fredericton sediment was recycled Ganderian basement from terranes emergent after Late Ordovician orogenesis, supplemented by Silurian tephra. Zircon barcodes and lithofacies and tectonic models suggest little, if any, input from Laurentia or Avalonia.
Zircon- and fossil-based ages indicate coeval Upper Ordovician deformation in the St. Croix (ca. 453 to 442 Ma) and Miramichi (ca. 453 to 446 Ma) terranes. Salinic folding in the southeastern Fredericton trough is bracketed between the 421.9 ± 2.4 Ma age of the Pocomoonshine gabbro-diorite and 430 Ma detrital zircons in the Flume Ridge Formation. Zircon ages, lithofacies analysis, and paleontological evidence support the origin of the Fredericton trough as a Salinic foredeep. The CMAM basin cannot have been an Acadian foreland basin, as sedimentation began millions of years before Acadian subduction.
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