The Early Silurian–Early Devonian Arisaig Group, in the Avalon terrane of Nova Scotia, consists of a thick (∼1900 m) sequence of unmetamorphosed fossiliferous siliciclastic strata that unconformably overlies the 460 Ma bimodal Dunn Point Formation volcanic rocks and is unconformably overlain by basalts and red clastic rocks of the McArras Brook Formation. The Dunn Point volcanic rocks were deposited when Avalonia was a microcontinent, in a New Zealand–type arc setting ∼1800 km north of Gondwana and 1700–2000 km south of Laurentia. Geochemical, Sm-Nd, and U-Pb (detrital zircon) isotopic data of all Arisaig Group strata show fundamental differences from the underlying Avalonian rocks, indicating that they were not derived from Avalonian basement. These data are instead compatible with derivation from Baltica, implying that Avalonia had accreted to Baltica by the earliest Silurian and that the Arisaig Group is part of a clastic sequence that has overstepped Appalachian-Caledonide terrane boundaries. The lack of penetrative deformation and the approximately concordant nature of the contact between the Dunn Point Formation and the Arisaig Group suggest that this portion of Avalonia was located on the trailing edge of the Avalonia plate during the collision. Regional syntheses suggest that the basin was initiated by local transtension during oblique sinistral collision between Avalonia and Baltica. An overall trend toward increasingly negative ϵ Nd values in the clastic rocks toward the top of the Arisaig Group is thought to reflect increasing input from Laurentia by the time of deposition of the Early Devonian strata. The basin also preserves evidence of loading in the Late Silurian, which is thought to reflect the development of a foreland basin and the ongoing shortening across the orogen associated with the onset of the Acadian orogeny. The unconformity between the Arisaig Group and the overlying McArras Brook Formation is the local expression of the deformation associated with Acadian orogeny in the Antigonish Highlands. The orientation and style of Acadian deformation preserved in the Arisaig Group is compatible with dextral movement along major northeast-trending faults, consistent with evidence of regional dextral shear along the northern margin of the Rheic Ocean in the Middle Devonian. Late Devonian–early Carboniferous deposition of the predominantly continental clastic rocks of the Horton Group occurred around the Antigonish Highlands in a series of grabens and half-grabens, most notably represented by the St. Mary's basin, which originated by dextral shear along the boundary between the Meguma and Avalon terranes. Continued episodes of dextral shear in the late Carboniferous resulted in localized regions of transtension and basin development, and also in episodes of transpression, manifested by intense deformation, thrusting, and S-C fabric development. Taken together, Middle Devonian–late Carboniferous episodes of dextral shear reflect the local accommodation of oblique convergence and eventual collision between Gondwana and Laurussia.

Abstract New Rb–Sr isotopic data from South Portuguese Zone (SPZ) turbidites show that the 87 Sr/ 86 Sr(t) ratio increases from the basal Mértola Formation (Visean–Serpukhovian: 0.706–0.707), through the Mira Formation (Serpukhovian–Bashkirian: 0.706–0.712) to the uppermost Brejeira Formation (Bashkirian–Moscovian: 0.713–0.715). In addition, estimated Nd T DM model ages for the Mértola (1.29–1.09 Ga), Mira (1.58–1.1 Ga) and Brejeira (1.73–1.37 Ga) formations indicate inverted stratigraphy for their isotopic sources. The isotope geochemical data indicate significant changes in the sources from which the SPZ Carboniferous turbidites are derived, consistent with the progressive denudation of a continental magmatic arc built on the Laurussian margin. Mértola turbidites inherited their geochemical and isotopic characteristics from an adjacent dissected Middle–Late Devonian continental magmatic arc with an intermediate–felsic composition: that is a Laurussian (Rheic magmatic arc)-type source. The progressive erosion of its plutonic roots and older host continental basement rocks are indicated in the Mira and Brejeira formations by the increasing contribution of recycled ancient continental crust. The pronounced similarity between the Nd T DM model ages and the detrital zircon populations of the Mira and Brejeira formations (SW Iberia) suggest that they share a common Laurussian (West Avalonia/Meguma terrane)-type source but a contribution from Gondwanan (Ossa-Morena)-type sources cannot be discarded.

Abstract Granitic plutons dominated by felsic-intermediate compositions are commonly spatially and temporally associated with mafic intrusions; however, the genetic relationship between the apparently coeval but compositionally dissimilar magmas is controversial. To better understand this relationship, we present new lithogeochemical and isotopic data from coeval late Neoproterozoic plutonic rocks in the Antigonish Highlands of Nova Scotia where the regional context is well documented. The predominantly mafic Greendale Complex contains lamprophyre, appinites and leucocratic dykes. The appinites are remarkably variable in their textures, and consist of hornblende pegmatites, hornblende cumulates, porphyritic hornblende gabbro and coarse-grained, equigranular hornblende gabbro. Geochemical data show enrichment in large-ion lithophile elements and depletion in the high field strength elements suggesting an arc setting. ε Nd (607) values from the Greendale Complex range from +3.2 to +5.0 and are on average slightly more juvenile than coeval granitic rocks which have petrological characteristics typical of continental arc magmas. Hydrous mafic magmas were likely contaminated by subducted sediments and their ascent was facilitated by lithospheric-scale faults. Felsic magmas were derived by anatexis of heterogeneous Avalonian crust that oscillated between fluid-saturated to fluid-deficient (dehydration) melting, consistent with the evolution from arc to intra-arc rift environment.

Abstract Following the collision of Gondwana and Laurussia to form Pangaea, a large system of regional-scale strike-slip faults developed which resulted in the formation of transtensional syncollisional basins. One such basin, the Antigonish Basin, contains late Devonian fluvial, marine and lacustrine sedimentary rocks, including sandstone, conglomerate and shale. LA-ICP-MS U–Pb detrital zircon data from three samples from the lower and middle of the McIsaacs Point section have a strong Silurian–Devonian ( c. 440–380 Ma) population whereas the top of the section lacks these age populations and is instead dominated by Neoproterozoic ( c. 630–550 Ma) grains. Detritus was derived from a mix of local Avalonian and more distal Meguma terrane sources. Detrital zircon and field data show that sediments were deposited in a braided to meandering fluvial system transitional to a proximal braided stream environment followed by evolution to a more distal braided stream environment. As the basin evolved, the source of detritus shifted from a dominantly Meguma terrane source to a more local Avalonian source. This temporal evolution in provenance and depositional environment attests to the complex depositional processes associated with syntectonic basin evolution during the formation of Pangaea.