Abstract Achieving net-zero carbon emissions goals will increasingly rely on critical mineral resources while simultaneously decreasing the extraction, processing and use of hydrocarbons as the primary provider of energy. Canada is well positioned to contribute to this effort through a series of innovative policy and research initiatives, and it is Canada's goal to be a stable supplier of critical minerals into the future. To this end, Natural Resources Canada and the Geological Survey of Canada invest financial resources into critical mineral research initiatives. This research aims to generate precompetitive baseline geological, geochemical and geophysical data for large, underexplored regions within Canada, whereas targeted studies focus on mineral systems science and improved exploration models for the large variety of critical mineral resources distributed throughout Canada. These research approaches can be combined, digitally, to generate mineral potential models. These ongoing efforts by the Geological Survey of Canada enhance the viability of Canada being (or maintaining its status as) a hub for critical mineral resource development and processing well into the future.

The southwestern Grenville Province in Ontario consists of Paleoproterozoic and Mesoproterozoic rocks that formed along the southeastern margin of Laurentia during a significant period of growth of the North American continent. The area investigated consists of high-grade ortho- and paragneisses whose protoliths formed between 1500 and 1350 Ma. Geochemical and geochronological data from the rocks investigated point to a period of arc and back-arc magmatism along the Laurentian margin between ca. 1500 and 1450 Ma. A-type charnockites and granites are temporally and spatially associated with the arc rocks, and have compositions interpreted to indicate derivation from a tholeiitic basaltic underplate and from crustal melting, respectively. This interpretation implies that the arc underwent extension during part of its history. Between ca. 1450 and 1430 Ma, magmatism apparently ceased in the study area and was temporally associated with high-grade metamorphism in the back-arc region, possibly suggesting a change from an extensional to a compressional tectonic regime, although other interpretations are equally likely. Few data exist for the period after ca. 1430 Ma; however, a number of geochronological studies from nearby parts of the Grenville Province suggest that arc magmatism may have moved to a more outboard position on the continental margin. At ca. 1360 Ma, bimodal rhyolitic and basaltic magmatism suggests a return to an extensional tectonic regime. The geochemical data generally support, but suggest refinements to, previously proposed models for the evolution of the southeastern Laurentian margin in the Grenville Province that may be applicable to other parts of the margin.

The Pine Mountain window contains the southernmost Grenville basement massif to be found in the Appalachians. Granulite- and upper-amphibolite-facies granitic gneisses that form the basement complex are isotopically dated at 1.1–1.0 Ga. Locally, the gneisses contain rare mafic injections and supracrustal and plutonic xenoliths. The Pine Mountain Group cover sequence nonconformably overlies Grenville basement and is interpreted to correlate with Blue Ridge units as follows: Halawaka/Sparks Schist = Ocoee Supergroup (Late Proterozoic, rift), Hollis Quartzite = Chilhowee Group (Late Proterozoic-Cambrian, rift-to-drift), and Chewacla Marble = Shady Dolomite (Cambro-Ordovician, drift). Facies variations within the sedimentary cover units were cited as evidence for a southward decrease in the extent of the Ocoee rift basins, but new mapping documents the continuity of thick packages of Halawaka (i.e., Ocoee) rocks extending southward beneath the Gulf Coastal Plain. In contrast to upper amphibolite- and granulite-facies metamorphism of the basement during the Grenville event, cover rocks contain staurolite and staurolite-kyanite zone assemblages reflecting Paleozoic Appalachian metamorphism. Sensitive high-resolution ion microprobe (SHRIMP) and conventional single-grain U-Pb datings of detrital zircons from the basal Hollis Quartzite document a distinct population of clear, subrounded zircons of ca. 1.09 Ga, which were most likely derived from underlying Grenville-age gneiss. An older, white/gray population found in the lowermost Hollis is ca. 2.4–2.3 Ga, an age restricted to Gondwanan continents and very limited occurrences in northern Laurentia. Tectonic reconstructions of Unrug (1997) and others depict southeast Laurentia proximal to the Amazonia and Rio de la Plata cratons during the Neoproterozoic, offering the possibility that they may be the source for 2.4–2.3-Ga zircons in Hollis sediments. Alternatively, the AUSWUS (Australia/Western United States) reconstruction (Karlstrom et al., 2001) places east Antarctica and the Australian Gawler craton, both of which contain abundant 2.4 Ga granites, proximal to the southwestern United States during this time. Depending on the stream systems present during the Neoproterozoic, zircons from the Gawler may have been transported to the vicinity of the Pine Mountain window. In addition, three clear zircons yield ages of 1.4 Ga, and may have been derived from either the Laurentian Mid-continent granite-rhyolite province or the Rondonian Province of South America. A Chilhowee Group sandstone sample contains a similar mixture of Grenville and Mid-continent/Rondonian-age zircons, but none with ages of 2.4–2.3 Ga.

The Mars Hill terrane (MHT), a lithologically diverse belt exposed between Roan Mountain, North Carolina–Tennessee, and Asheville, North Carolina, is distinct in age, metamorphic history, and protoliths from the structurally overlying Eastern Blue Ridge and underlying Western Blue Ridge. MHT lithologies include diverse granitic gneisses, abundant mafic and sparse ultramafic bodies, and mildly to strongly aluminous paragneisses. These lithologies experienced metamorphism in the granulite facies and are intimately interspersed on cm to km scale, reflecting both intrusive and tectonic juxtaposition. Previous analyses of zircons by high-resolution ion microprobe verified the presence of Paleoproterozoic orthogneiss (1.8 Ga). New data document a major magmatic event at 1.20 Ga. Inherited and detrital zircons ranging in age from 1.3 to 1.9 Ga (plus a single 2.7 Ga core), ubiquitous Sm-Nd depleted mantle model ages ca. 2.0 Ga, and strongly negative ε Nd during Mesoproterozoic time all attest to the pre-Grenville heritage of this crust that was suggested by previous whole-rock Pb and Rb-Sr isotope studies. A single garnet amphibolite yielded a magmatic age of 0.73 Ga, equivalent to the Bakersville dike swarm, which cuts both the MHT and the adjacent Western Blue Ridge. Zircons from this sample display 0.47 Ga metamorphic rims. Zircons from all other samples have well-developed ca. 1.0 Ga metamorphic rims that date granulite-facies metamorphism. Silica contents of analyzed samples range from 45 to 76 wt%, reflecting the extreme diversity observed in the field and the highly variable protoliths. The MHT contrasts strikingly with basement of the adjacent Eastern and Western Blue Ridge, which comprise relatively homogeneous, 1.1 to 1.2 Ga granitic rocks with initial ε Nd values near 0. It appears to have more in common with distant Paleoproterozoic crustal terranes in the Great Lakes region, the southwestern United States, and South America.

Sedimentary and metasedimentary rocks within the southern Appalachian Blue Ridge and Inner Piedmont contain a valuable record of Late Proterozoic Laurentian margin evolution following the breakup of Rodinia. Paleogeographic reconstructions and increasing amounts of geochronologic and isotopic data limit the derivation of these paragneisses to the Laurentian and/or west Gondwanan craton(s). Southern Appalachian crystalline core paragneiss samples have ε Nd values between –8.5 and –2.0 at the time of deposition and contain abundant 1.1–1.25 Ga zircon cores with Grenville 1.0–1.1 Ga metamorphic rims. Less abundant detrital zircons are pre-Grenvillian: Middle Proterozoic 1.25–1.6 Ga, Early Proterozoic 1.6–2.1 Ga, and Late Archean 2.7–2.9 Ga. Blue Ridge Grenvillian basement has almost identical ε Nd values and displays the same dominant magmatic core and metamorphic rim zircon ages. Based on our data, nonconformable basement-cover relationships, and crustal ages in eastern North America, we contend that the extensive sedimentary packages in the southern Appalachian Blue Ridge and western Inner Piedmont are derived from Laurentia. ε Nd values from Carolina terrane volcanic, plutonic, and volcaniclastic rocks are isotopically less evolved than southern Appalachian paragneisses and Blue Ridge Grenvillian basement, easily separating this composite terrane from the mostly Laurentian terranes to the west. Neoproterozoic and Ordovician, as well as Grenvillian and pre-Grenvillian, zircons in eastern Inner Piedmont paragneisses indicate that these samples were deposited much later and could have been derived entirely from a Panafrican source or possibly a mixture of Panafrican and recycled Laurentian margin assemblages.

The Carthage-Colton mylonite zone is a major geothermochronological discontinuity across the northwest Adirondack Mountains of New York, a southern extension of the Grenville Province. A large syenitic gneiss body, the Diana syenite, occurs along most of the southern Carthage-Colton mylonite zone. The present study examined petrofabrics and magnetofabrics of oriented cores and accurately oriented thin- sections to investigate the sources of anisotropy of magnetic susceptibility (AMS) within a central portion of the Diana syenite. Three petrographic foliations, a petrographic lineation, and a magnetic intersection lineation were clearly distinguished. Two of the foliations appear to represent axial planar foliations of the second- and third-phases of regional folding as defined by Wiener (1983). The youngest foliation and the magnetic intersection lineation have not been previously described. This research suggests that folding identified in the Adirondack Lowlands can be traced to at least the southwest margin of the Diana syenite with no obvious discontinuity. Significant implications of this research suggest that: (1) the Adirondack Lowlands deformation likely includes some folding events associated with Ottawan orogen compression, and (2) the kinematics and style of deformation within the Carthage-Colton mylonite zone remain cryptic and cannot conclusively be connected to the fabrics explored in this research.

The western Blue Ridge Province of the southern Appalachians contains a rich record of the Mesoproterozoic Grenville orogeny, but subsequent Paleozoic metamorphic events have variably overprinted Grenville rocks, and Paleozoic thrusting has telescoped Grenville rock units. Effects of Paleozoic orogenesis must be unraveled to decipher the Grenville record. The Grenville rocks in the Blue Ridge of northwestern North Carolina and eastern Tennessee reside in a stack of Alleghanian thrust sheets that lie above the Grandfather Mountain and Mountain City windows. The composite Fries thrust sheet is the structurally highest unit in the stack and contains rocks of the eastern Blue Ridge juxtaposed against Grenville basement rocks (Pumpkin Patch Metamorphic Suite) along the Devonian Burnsville fault, which is the only identifiable Acadian structure in the thrust stack. West of the Grandfather Mountain window, the Sams Gap–Pigeonroost thrust splays off the Fries fault. Only the Fries and Sams Gap–Pigeonroost sheets appear to have been affected by Ordovician Taconic metamorphism. Below the Fries and Sams Gap–Pigeonroost sheets, Grenville basement rocks in the Fork Ridge and Linville Falls–Stone Mountain thrust sheets display widespread greenschist-facies metamorphism and deformation associated with Alleghanian thrusting. The lowest basement sheet is the Little Pond Mountain thrust sheet, which experienced only Late Paleozoic chlorite-grade metamorphism. Palinspastic restoration of the Grenville rocks to their pre-Paleozoic relative positions places rocks of the Pumpkin Patch Metamorphic Suite outboard of western Blue Ridge Grenvillian rocks.

The Chicoutimi Gneiss Complex was previously considered to host the huge 1160–1140 Ma Lac St. Jean anorthosite suite (20,000 km 2), the 1082 ± 3 Ma Chicoutimi Mangerite, and the 1067 ± 3 Ma La Baie Granite. New geological mapping and geochronological data from the Chicoutimi Gneiss Complex now demonstrate clear correlations among some gneissic units and the partially deformed Chicoutimi Man-gerite and La Baie Granite. The remaining gneissic units in the Chicoutimi Gneiss Complex have been grouped into six new lithodems. The three oldest were generated during two distinct events. The Saguenay Gneiss Complex, which is one of these lith-odems and includes the Cap de la Mer Amphibolite unit dated at 1506 ± 13 Ma, is related to a widespread Pinwarian event. It was followed, 100 Ma later, by the 1391 +7/−8 Ma Cap à l'Est Gneiss Complex and the 1383 ± 16 Ma Cyriac Rapakivi Granite. Two younger lithodems are the 1155–1135 Ma Kénogami Charnockite and the 1150 ± 3 Ma Baie à Cadie Mafic-Ultramafic Suite, which are genetically related to the Lac St. Jean Anorthosite Suite. Finally, the 1045 ± 5 Ma Simoncouche Gabbro is the youngest Grenvillian igneous unit dated so far in the Saguenay region. The Lac St. Jean Anorthosite Suite, the Chicoutimi Mangerite, the La Baie Granite, and their host rocks (the Saguenay Gneiss Complex, the Cap à l'Est Gneiss Complex, and the Cyriac Rapakivi Granite) are everywhere in tectonic contact with each other. These contacts are part of the St. Fulgence shear zone, which is over 400 km long and several kilometers wide. Since the Simoncouche Gabbro outcrops within the St. Fulgence shear zone and is weakly deformed, it can be concluded that 1045 ± 5 Ma marked the end of the final movement along the St. Fulgence shear zone in the Saguenay region.

The Mount Eve granite suite is a postorogenic, A-type granitoid suite that consists of several small plutonic bodies occurring in the northwestern New Jersey–Hudson Highlands. Mount Eve granite suite rocks are equigranular, medium- to coarse-grained, quartz monzonite to granite, consisting of quartz, microperthite, and oligo-clase, with minor hornblende, biotite, and accessory zircon, apatite, titanite, magnetite, and ilmenomagnetite. Whole-rock analyses indicate that Mount Eve granite is meta-luminous to slightly peraluminous (ASI or aluminum saturation index, A/CNK or Al 2 O 3 /(CaO + Na 2 O + K 2 O) = 0.62 to 1.12) and has A-type compositional affinity defined by high K 2 O/Na 2 O (1.4 to 2.8), Ba/Sr (3 to 12), FeO t /(FeO t +MgO) (0.77 to 0.87), Ba (400 to 3000 ppm), Zr (200 to 1000 ppm), Y (30 to 130 ppm), Ta (2.5 to 6 ppm), total rare earth elements or REE (300 to 1000 ppm), low MgO (<1 wt%), Cr and Ni (both <5 ppm); and relatively low Sr (200 to 700 ppm). Variably negative Eu anomalies (Eu/Eu* = 0.13 to 0.72, where Eu/Eu* is the chondrite-normalized ratio of measured Eu divided by the hypothetical Eu concentration required to produce REE pattern with no Eu anomaly) and systematic decreases in Sr, Ba, Zr, Hf, Nb, and Ta, with constant total REE content and increasing Ce/Yb and SiO 2 contents, suggest crystallization of feldspars + zircon + titanite ± apatite. Possible modes of origin include dry melting of charnockitic gneisses or Fe-rich mafic to intermediate diorites within the Mesoproterozoic basement. Two possible tectonic mechanisms for generation of Mount Eve granite include (1) residual thermal input from a major lithospheric delamination event during or immediately after peak Ottawan orogenesis (1090–1030 Ma) or (2) broad orogenic relaxation between peak Ottawan and a late (1020–1000 Ma) high-grade, right-lateral transpressional event.

40 Ar/ 39 Ar incremental-heating measurements of Grenville metamorphic rocks from the Adirondack Lowlands, New York, constrain a ca. 1100–900 Ma history of uplift, exhumation, and cooling in the eastern Frontenac terrane following the ca. 1200–1170 Ma Elzevirian orogeny and the ca. 1080–1070 Ma peak of the subsequent Ottawan orogeny. Four hornblende-biotite pairs yield a time-integrated post-Ottawan cooling rate of 1.6 ± 0.2 °C/m.y. and an inferred exhumation rate of 0.06 ± 0.02 km/m.y. between ca. 1100 Ma (oldest hornblende, northwest Lowlands) and ca. 900 Ma (youngest biotite, southeast Lowlands), based upon closure temperatures of 500 and 300 °C and a 30 ± 10 °C/km geotherm. Moreover, these and ∼20 additional cooling ages for hornblende and biotite define parallel northwest-to-southeast younging trends of ∼3 m.y./km across ∼45 km between the St. Lawrence River and the Carthage-Colton shear zone, which separates the Lowlands and the Adirondack Highlands domains. Two end-member models potentially explain the age trends: (1) ca. 1100–900 Ma cooling of the Lowlands through subhorizontal isotherms, followed by ca. 900–520 Ma regional tilting (∼9° ± 3°NW); or (2) ca. 1100–900 Ma cooling of the Lowlands against a warm Highlands footwall, through gently northwest-dipping inclined isotherms that flattened out by ca. 900 Ma. On balance, the regional tilting model is the favored explanation of observed trends in the hornblende and biotite ages. Differential uplift during regional extension most likely tilted the Lowlands, and the ca. 900–520 Ma time frame suggests that breakup of the supercontinent Rodinia was ultimately responsible for these tectonic events and the resultant trends in cooling age.