The mantle plume centre of the 1270 Ma Mackenzie large igneous province (LIP) is located at the focus of the giant radiating Mackenzie dyke swarm, on the west side of Victoria Island in northern Canada. The Amundsen Basin, an intracratonic sedimentary basin, partially surrounds the plume centre region, suggesting a genetic link with the Mackenzie plume. This study conducts 2D gravity and magnetic modelling using Oasis Montaj GM-SYS software, of the circumferential gravitational low of the Amundsen Basin. Radial narrow gravity highs (modelled as wide 'macro'-dykes) connecting an inner ring of mid-crustal intrusions (circumscribing an apical graben) with an outer ring of smaller (potentially shallower) intrusions, are also modelled. The outer ring includes the Ni-Cu-PGE mineralized Muskox intrusion; other outer ring intrusions may have similar economic potential. We propose that the Mackenzie plume caused the Amundsen Basin subsidence (and initiation of sedimentation at ca. 1070 Ma) through three mechanisms: thermal decay of the plume occurring over approximately 200 Ma (1270-1070 Ma), lateral redistribution of large volumes of magma (80,000 km(3)) away from the plume centre through the radiating dyke swarm, and crustal loading in the plume centre due to the emplacement of massive mafic/ultramafic intrusions and regionally extensive eclogitized ultramafic underplating.

Plate tectonics is a unique feature of Earth, but its proposed time of initiation is still controversial, with published estimates ranging from ca. 4.2 to 0.7 Ga. Paleomagnetic data can provide a robust argument for one essential aspect of plate tectonics: large-scale relative lateral motions of distinct, rigid crustal blocks. Previously, the oldest relative horizontal motion between two or more blocks was constrained to a broad age interval of ca. 2.7-2.17 Ga using paleomagnetic data. In this study, we obtain a robust ca. 2.48 Ga paleomagnetic pole from Wyoming craton. Combining this result with the ca. 2.7-2.17 Ga apparent polar wander paths from Wyoming and Superior cratons, we suggest that they assembled during ca. 2.7-2.5 Ga and remained directly juxtaposed until ca. 2.17 Ga. Tectonostratigraphic data and geological proxies also suggest Wyoming and Superior collided at ca. 2.6 Ga. The results provide strong evidence for relative horizontal motion between crustal blocks during the Neoarchean. Together with other tectonic proxies, the data suggest plate mobilism in operation prior to 2.5 Ga.

LIP printing is a term adapted from forensic science to describe the use of geochemical proxies for tectonic and petrogenetic fingerprinting of Large Igneous Provinces (LIPs). Here, we investigate in detail the LIP printing of basic lavas, sills and dykes using two immobile element proxies: Th/Nb, a crustal input proxy, to monitor subduction-metasomatism and crustal assimilation and Ti/Yb, a residual garnet proxy, to monitor depth and degree of melting. The LIP printing diagram, a plot of Th/Nb against Ti/Yb for intraplate, plume-derived magmas, is characterised by two distinct arrays: a subduction-modified lithospheric mantle (SZLM) array and a MORB-OIB-OPB (plume) array (where OPB = oceanic plateau basalt). LIP basalt suites divide into three categories on this diagram: Type I plots entirely within the MORB-OIB-OPB array indicative of a significant plume source; Type II plots entirely within the SZLM array indicative of a significant sub-continental lithospheric mantle source, and Type III plots on a variety of trends between the two arrays indicative of significant plume-lithosphere interactions. Modelling demonstrates how the three LIP types, and the observed trends within and between individual LIPs, can be explained by differences in the compositions and relative contributions of lithospheric and asthenospheric (plume) mantle, in temperature and depth of melting and in the extent and nature of magma-crust interactions. This large genetic, and hence compositional, variability within and between LIPs relates to differences in geological and geodynamic setting and supports the forensic concept that ‘no two LIP prints are alike’. The potential applications of the LIP printing diagram are demonstrated here using four types of examples that highlight temporal and spatial LIP print diversity: flood basalt terranes related to Atlantic breakup (NAIP, Parana-Etendeka and CAMP); giant dyke swarms (Superior Craton Late Archean to Early Proterozoic dyke swarms and the Mackenzie dyke swarm); mineralization-related LIP terranes (Bushveld and Noril’sk); and early (c. 3.5 Ga) Earth and extraterrestrial lavas (terrrestrial Paleoarchean basalts and komatiites, lunar mare basalts and Martian shergottites).

A c. 1450 Ma, east-west-oriented suite of Proterozoic mafic intrusions in eastern Canada, located between Labrador City and coastal Labrador near Rigolet, has been divided into two groups: the Shabogamo Gabbro, which is exposed west of Churchill Falls, and the Michael Gabbro, which crops out east of Churchill Falls. Both suites of gabbro are within-plate tholeiites that range from sub-alkaline basalt to basaltic andesite in composition and are enriched in P2O5 and K2O. Collectively, the two suites are better interpreted as a single magmatic event, termed the Michael- Shabogamo Gabbro (MSG), with ages ranging from 1425 to 1450 Ma, based on new U-Pb isotope dilution thermal ionization mass spectrometry baddeleyite ages of 144963, 143764 and 1435610 Ma, along with previously published ages. Within the MSG, two geochemical groups are evident. Most notably, each is characterized by differing P2O5/Zr (P/Zr) ratios: (1) a high P/Zr group, c. 1425-1437 Ma; (2) a low P/Zr group, c. 1435-1450 Ma. The positive slope of P2O5 versus Zr data arrays for each group indicates that melting of apatite was pivotal in influencing the rare earth element concentrations of the MSG magmas and their secular changes in geochemistry. K2O is enriched in the MSG relative to enriched mid-ocean ridge basalts and is correlated with P2O5, Ba and Rb. Multiple origins for the enrichment of P2O5 and K2O in the MSG are considered and the available evidence is most consistent with melting of a metasomatized subcontinental lithospheric mantle source interpreted to originate by infiltration of partial melts of phosphate-rich sediments. A slab window is proposed to have facilitated lithospheric melting at c. 1425-1450 Ma. (Less)

Three new U-Pb ID-TIMS isotopic ages confirm previous evidence for two geochemically distinct, early Mesoproterozoic pulses of mafic magmatism along the western margin of Laurentia. The first is a U-Pb baddeleyite age of 1590 +/- 5 Ma from a dyke swarm in the Tobacco Root Mountains of western Laurentia. It is the first evidence for magmatism of this age in west-central Laurentia. The second is a U-Pb baddeleyite age of 1592.4 +/- 2.5 from the Western Channel Diabase, 2000 km to the north in NW Laurentia, which supports two previous U-Pb baddeleyite ages of ca. 1590 Ma for these intrusions. The third is a U-Pb baddeleyite age of 1551 +/- 5 Ma, also from the Tobacco Root Mountains, and provides evidence for a distinct younger pulse of mafic magmatism. We propose that the ca. 1590 Ma mafic intrusions in northwestern and west-central Laurentia represent components of a large igneous province (LIP), which we name the "ca. 1590 Ma Mammoth-Western Channel LIP." This 1590 Ma LIP is geochemically similar to the contemporaneous volcanic rocks in the Gawler Craton and Curnamona Province of Australia. Furthermore, the 1599 Ma Wernecke Breccias near the Western Channel Diabase are geologically similar to the 1590 Ma Olympic Dam Breccias on the South Australian craton. We propose that a mantle plume at ca. 1590 Ma centered between the Laurentian and Southern Australian cratons, located by converging dyke swarms, fed the intrusions on Laurentia plus the Gawler Range Volcanics, the Hiltaba Suite granites and the Ninnerie Supersuite on the South Australian craton. Additionally, magmatic underplating from the plume set up the hydrothermal system responsible for the formation of the Wernecke and Olympic Dam Breccias. The younger 1551 Ma magmatism in the Tobacco Root Mountains, which shows less contamination of a metasomatized subcontinental lithospheric mantle than the older 1590 Ma pulse, may represent an early stage of rifting that pre-dates the ca. 1470 Ma Belt-Purcell Basin extension of western Laurentia. Felsic magmatism, hypothesized to have accompanied the 1590-1550 Ma LIP magmatism, could be a potential source for detrital zircon, thereby reducing the requirement for a non-Laurentian source for detrital zircon ages within the 1610-1490 Ma "North American Magmatic Gap." Additionally, the 1590 Ma and 1550 Ma ages on western Laurentia dykes provide tighter constraints for previous paleomagnetic studies. Crown Copyright (C) 2018 Published by Elsevier B.V. All rights reserved.

Proterozoic mafic magmatic rocks exposed along the western side of North America, or western Laurentia, from Kimberley, British Columbia, through to northwestern Wyoming have been previously divided into two large igneous provinces: the ca. 1460 Ma Moyie-Purcell and the ca. 780 Ma Gunbarrel large igneous provinces. New geochemical analysis from this study demonstrates that there are additional intraplate mafic magmatic rocks present. Distinguishable by variable normalized rare earth element patterns combined with differing slopes on a binary Ti versus V plot, there are 17 identifiable geochemical signatures in the 307 whole-rock and trace-element analyses from this study. Only seven of these signatures can be linked to the ca. 1460 Ma Moyie-Purcell large igneous province, and one signature to the 780 Ma Gunbarrel large igneous province. This study has identified two groups of intrusions with distinct geochemical signatures previously linked with the ca. 1460 Ma Moyie-Purcell large igneous province but now recognized to be separate events, a single unique geochemical signature with a U-Pb age correlative with the Moyie-Purcell large igneous province and seven other heretofore unidentified signatures interpreted to belong to additional undated events.

A new large igneous province (LIP), the 1501 +/- 3 Ma Kuonamka LIP, extends across 700 km of northern Siberia and is linked with coeval dikes and sills in the formerly attached Sao Francisco craton (SFC)-Congo craton to yield a short-duration event 2000 km across. The age of the Kuonamka LIP can be summarized as 1501 +/- 3 Ma (95% confidence), based on 7 U-Pb ID-TIMS ages (6 new herein) from dolerite dikes and sills across the Anabar shield and within western Riphean cover rocks for a distance of 270 km. An additional sill yielded a SIMS (CAMECA) age of 1483 +/- 17 Ma and sill in the Olenek uplift several hundred kilometers farther east, a previous SIMS (SHRIMP) age of ca. 1473 Ma was obtained on a sill; both SIMS ages are within the age uncertainty of the ID-TIMS ages. Geochemical data indicate a tholeiitic basalt composition with low MgO (4-7 wt%) within-plate character based on trace element classification diagrams and source between E-MORB and OIB with only minor contamination from crust or metasomatized lithospheric mantle. Two subgroups are distinguished: Group 1 has gently sloping LREE ((La/Sm)(PM) = 1.9) and HREE ((Gd/Yb)(PM) = 1.8) patterns, slightly negative Sr and moderate TiO2 (2.2 wt%), and Group 2 has steeper LREE ((La/Sm)(PM) = 2.3) and HREE ((Gd/Yb)(PM) = 2.3), strong negative Sr anomaly, is higher in TiO2 (2.7 wt%), and is transitional from tholeiitic to weakly alkaline in composition. The slight differences in REE slopes are consistent with Group 2 on average melting at deeper levels. Proposed reconstructions of the Kuonamka LIP with 1500 Ma magmatism of the SFC-Congo craton are supported by a geochemical comparison. Specifically, the chemistry of the Chapada Diamantina and Curaca dikes of the SFC can be linked to that of Groups 1 and 2, respectively, of the Kuonamka LIP and are consistent with a common mantle source between EMORB and OIB and subsequent differentiation history. However, the coeval Humpata sills and dikes of the Angola block of the Congo craton represent a different magma batch. (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The Toodoggone-McConnell Project was inititated in 1996 to map and evaluate a tract of Early Jurassic plutons and surrounding arc volcanic successions of Paleozoic to Jurassic age for base and precious metal mineralization. Bedrock mapping during the first year of the program focussed on a region south of the Finlay River and east of Thutade Lake, documenting local geology near known copper-gold porphyry targets the Kemess South deposit and Kemess North and Pine prospects (Diakow and Metcalfc, 1997). The current 1:ZOOOO scale mapping program expands this geology to the east and south into the McConnell Range, between latitudes 57’06’ and 56”39’ north, and longitudes 126’39’ and 126”25’ east (Figure I). The McConnell Range was divided into two contiguous map areas along the drainage line of Jensen and Theme creeks. The northern map segment, described in this report, ties into geological work completed in 1996 in the vicinity of the t&mess South mine. It illustrates the extent of older, Paleozoic strata as far south as Jensen Creek, and also provides a glimpse of strata low in the overlying Upper Triassic succession. Geology in the southern map segment of the McConnell Range between Jensen and Johanson creeks is reported by Legun (1998). The southern region is underlain by Upper Triassic strata that are progressively younger towards the south, which affords stratigraphic comparison to correlative rocks that host important stratabound copper deposits in the Upper Triassic Takla Group in the type-area to the west. Staging for this program was the Kemess South minesite. It is situated along the northwestern periphery of the study area, and requires only a short helicopter ferry into the McConnell Range.