Abstract Fossil trackways in the Jura-Triassic rift basin of the Connecticut River Valley are important to geoheritage for their quality, preservation, and role in the history of geology, especially of ichnology. Discovered in the early 1800s, these trackways of small to large, bipedal, three-toed animals came to the attention of Edward Hitchcock, a prolific geologist and natural theologian. His first publication on the subject was in January 1836 and, in the same year, William Buckland included parts of the report, with illustrations, in his Bridgewater Treatise. Hitchcock and Buckland are credited with establishing the field of ichnology, the study of track and trails. Within the first decade, other traces documented include four-footed tracks, fish fossils, invertebrate burrows, plant impressions, ripple marks and raindrop impressions; few bones have ever been discovered in the valley. Early fossil-track collectors included Hitchcock, James Deane, Dexter Marsh and Roswell Field. Specimens quickly made their way to Europe, and publications brought the tracks to international attention, in both science and literature. In nineteenth-century discussions, the three-toed trackway makers – birds or dinosaurs? – were particular subjects of interest and debate. These fossil trackways remain well known and studied today, with several preserved field sites and museum collections.

Abstract Geoparks and the valorization of sites with a strong geoheritage component is a new frontier for sustainable tourism. A UNESCO special recognition was established in 2015, and much work has been undertaken in establishing sites in Europe and Asia, yet only five localities have been recognized by UNESCO in North America. This paper discusses three sites relevant to geoheritage – Pulpit Rock in Massachusetts, Montmorency Falls in Quebec and Niagara Falls in New York and Ontario – which were visited in 1863 by the newly appointed professor of geology at Bologna University, Giovanni Capellini. During his four-month journey across northeastern North America, he made sketches, took notes and collected more than 2000 specimens that together provide a depth of perspective on the importance of the geoheritage of the sites he visited. We chose these sites, among the many visited by Capellini, because Niagara Falls is now seeking UNESCO recognition, and the other two, though no longer fully accessible, remain important tourist sites and areas of geological interest.

Abstract Avalonia, defined by its distinctive uppermost Ediacaran–Ordovician overstep sequence, extends from New England through Atlantic Canada to Wales. It unconformably overlies: (1) parts of one cratonic Neoproterozoic arc that which records several pulses at: 760–730 Ma, 680–600 Ma and 580–540 Ma; (2) an 800–760 Ma passive margin sequence; and (3) c. 976 Ma isolated plutons, possibly basement. Comparisons with modern arc dimensions suggest the dip of the Benioff Zone ranged from c. 22° W in Newfoundland to c. 52–67° elsewhere. A 600–580 Ma hiatus in arc magmatism in Cape Breton Island is attributed to overriding an oceanic plateau, leading to a 15° decrease in the dip of the Benioff Zone. The Collector magnetic anomaly along the Grand Banks and the Minas Fault is inferred to mark the Neoproterozoic southern margin of the Avalon Plate consisting of leaky transform faults and trench segments characterized by magnetite serpentinite mantle wedge beneath forearcs. The Minas Fault/Collector Anomaly connects similar arc units in Cape Breton Island and southern New Brunswick, suggesting that they were already offset by the Minas transform fault in the late Neoproterozoic. Similar tectonic, palaeomagnetic and isotopic data in the Timan Orogen of Baltica suggest that Avalonia may correlate with the Kipchak arc.

Abstract The pre-accretionary shapes of cratonic margins form successions of promontories and re-entrants inherited from the rifting of supercontinents. In accretionary orogens, the extent of deformation related to a collision with a continent characterized by an irregular margin is obfuscated through the partitioning of deformation along pre-existing structures. In the Northern Appalachians, the extent of the deformation related to the oblique collision of the Meguma terrane with the composite Laurentian margin is disputed. Herein, we use a framework based on modern collisional settings to investigate the Late Devonian to Mississippian deformation inboard of the Avalonia–Meguma boundary and evaluate the regional tectonic setting. We combine published shear zone kinematic interpretations, deformation ages and regional 40 Ar/ 39 Ar cooling ages with structural interpretation of aeromagnetic and gravimetric depth slices covering the Northern Appalachians. We find that the deformation related to the collision of the Meguma terrane, attributed to the Neoacadian orogeny, has a larger structural footprint than previously documented. While this deformation is partitioned in multiple structures in the Canadian Appalachians, northern New England is characterized by rapid crustal deformation, high palaeoelevation and fast erosional exhumation, similar to modern syntaxis structures.

ABSTRACT The Appalachian Mountains in northern Vermont host a complex rock record of the tectonic evolution of eastern Laurentia, from the opening of the Iapetus Ocean to the subsequent formation of a convergent Paleozoic margin involving multiple phases of orogenesis. Prior 40 Ar/ 39 Ar studies in Vermont and northern Massachusetts have generally interpreted two major events associated with a dominantly Ordovician Taconic orogeny and a Devonian Acadian orogeny; intermediate ages were considered to reflect Taconic metamorphism and/or deformation that was “partially reset” during the Acadian orogeny. However, recent studies have documented Salinic ages in northern Vermont, aligning with multiple lines of evidence in southern Quebec for an intervening Salinic orogeny during the Silurian. This study reports integrated microstructural and 40 Ar/ 39 Ar geochronological analyses of samples collected across the Green Mountain anticlinorium in northern Vermont. The dominant S 2 and S 3 foliations are defined in thin section by predominantly white mica/quartz microlithons and aligned mica cleavage domains in schist to graphitic schist that formed under greenschist-facies conditions. Correlation of microstructures across the field area and associated 40 Ar/ 39 Ar plateau ages reveal a spatial pattern associated with microstructural development across the anticlinorium. In the eastern limb, the oldest plateau age, 457.6 ± 2.0 Ma (1σ), is interpreted to reflect the timing of formation of S 2 . The youngest plateau age, 419.0 ± 2.4 Ma, comes from the western limb of the anticline near the trace of the Honey Hollow fault, where S 2 is completely transposed by S 3 . Intermediate ages were obtained across the axis of the anticline, where S 3 is a crenulation cleavage. While the Green Mountain anticlinorium has been previously interpreted to have formed in the Devonian during the Acadian orogeny, the typical ca. 386–355 Ma ages are notably absent in the data set, except in locally disturbed spectra. The results of this work are closely aligned with published results of 40 Ar/ 39 Ar dating in southern Quebec that reflect deformation during Taconic and Salinic orogenesis. These new data, together with recently reported ages of west-directed transport on Taconic thrusts along the western Green Mountain front at ca. 420 Ma, suggest a phase of mountain building in the New England Appalachians that has been previously unreported in Vermont. The formation of the Green Mountain anticlinorium coincided with a complex tectonic interval that overlapped temporally with (1) the transition from Salinic thrusting to normal faulting, (2) magmatism attributed to slab breakoff, and (3) syntectonic deposition in the Connecticut Valley–Gaspé Basin.

ABSTRACT The Appalachian Mountains were formed through multiple phases of Paleozoic orogenesis associated with terrane accretion. The timing, tempo, and significance of each event in New England are obscured by overprinting, the limits of geochronologic tools, and differences between lithotectonic domains. We present new monazite and xenotime geochronology, 40 Ar/ 39 Ar thermochronology, and major- and trace-element thermobarometry from major tectonic domains in southern New England and across multiple structural levels. These data show contrasting pressure-temperature-time (P-T-t) paths across tectonic domains and highlight eastward metamorphic overprinting associated with younger tectonic events. Our data and geochemical proxies suggest two major periods of crustal thickening, ca. 455–440 Ma and 400–380 Ma, and a heterogeneous record of thinning/exhumation. Ordovician (Taconic) crustal thickening postdates the interpreted accretion of the Moretown terrane by ~20 m.y. and may have been related to shallow subduction after subduction polarity reversal. Subsequent cooling and exhumation (440–430 Ma) may have been related to the end of the Taconic orogeny and opening of the Connecticut Valley basin. (Neo)Acadian tectono-metamorphism is recognized in accreted terranes of New England and is absent in the Taconic block. Amphibolite- to (high-pressure) granulite-facies metamorphism, slow cooling, and protracted anatexis ca. 400–340 Ma support the existence of a long-lived orogenic plateau in southern New England. Exhumation, which began at 340–330 Ma, may have involved ductile (channel) flow. The boundary between continental Laurentia and accreted terranes has been reactivated at multiple times and is presently manifested as a 12–15 km Moho step. At the latitude of our samples, Alleghanian-age tectonism (ca. 310–285 Ma) was limited to retrograde metamorphism, and relatively minor loading and exhumation in the vicinity of the Pelham dome. Our results highlight the sensitivity of the integrative petrochronologic approach and the transition of the eastern margin of Laurentia from terrane accretion to the formation of a high-elevation plateau.