SHRIMP U–Pb zircon evidence for age, provenance, and tectonic history of early Paleozoic Ganderian rocks, east-central Maine, USA

Abstract

SHRIMP 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.

Detrital zircon signatures in Precambrian and Paleozoic sedimentary units in southern New Brunswick – more pieces of the puzzle

“…8). Such peaks are characteristic of sedimentary rocks from Gondwanaderived terranes and reflect the widespread pan-African igneous activity related to the assembly of the Gondwanan continent (e.g., Satkoski et al 2010;Pollock et al 2009Pollock et al , 2015Dokken et al 2018;Ludman et al 2018). It is difficult to assess the significance of the variations in the position of the Ediacaran peak or of the spread in Ediacaran ages in terms of specific provenance areas in Gondwana because even samples from a single belt or stratigraphic unit can display significant differences, as has been documented in the Ganderian parts of New Brunswick, Nova Scotia, and Newfoundland (e.g., Fyffe et al 2009;Satkoski et al 2010;Barr et al 2012;van Rooyen et al 2019).…”

“…1a), it provides a comparison dataset for areas to the southeast. Ludman et al (2017Ludman et al ( , 2018 suggested that the Fredericton trough represents an independent basin that was not linked to the more southern New England basins, and interpreted the detrital zircon signatures as being derived from dominantly Gondwanan sources. In contrast, Dokken et al (2018) documented more mixed zircon provenance signature with significant Laurentian contributions.…”

“…In addition, the youngest detrital zircon grains give an indication of maximum depositional age, significant in units where other age constraints are minimal or lacking. All three of these applications have relevance in southern New Brunswick, and this technique has been applied previously to rock units in that area as well as in adjacent parts of New England and Nova Scotia (Barr et al 2003a(Barr et al , 2012Fyffe et al 2009;Satkoski et al 2010;Dokken et al 2018;Ludman et al 2018). The significance of differences in detrital zircon populations between Ganderia and Avalonia is an ongoing debate, and the database of detrital zircon U-Pb data for both pre-and post-Appalachian strata is growing.…”

Terrane history of the Iapetus Ocean as preserved in the northern Appalachians and western Caledonides

“…However, farther NE in Maine, there is a gap between the Liberty-Orrington belt and the Miramichi inlier, where Silurian forearc basin rocks of the Central Maine trough are juxtaposed with Silurian turbidites of the Merrimack-Bucksport-Fredericton (MBF) or "Merribuckfred" (Hussey et al, 2010) belt. The two belts display similar facies and ages, and the boundary between them is difficult to define (Ludman et al, 2018). Most of the sedimentary strata in the Central Maine trough and the northern part of the Fredericton belt are dominated by Laurentian zircon, although some samples show mixed Laurentian and Gondwanan provenance (Dokken et al, 2018;Ludman et al, 2018) The southernmost inlier of pre-Silurian rock in the belt that separates the Merrimack and Central Maine troughs is the Massabesic Gneiss complex of New Hampshire (MSB; Fig.…”

“…The two belts display similar facies and ages, and the boundary between them is difficult to define (Ludman et al, 2018). Most of the sedimentary strata in the Central Maine trough and the northern part of the Fredericton belt are dominated by Laurentian zircon, although some samples show mixed Laurentian and Gondwanan provenance (Dokken et al, 2018;Ludman et al, 2018) The southernmost inlier of pre-Silurian rock in the belt that separates the Merrimack and Central Maine troughs is the Massabesic Gneiss complex of New Hampshire (MSB; Fig. 7).…”