A mantle plume origin for the Palaeoproterozoic Circum-Superior Large Igneous Province

The Circum-Superior Large Igneous Province (LIP) consists predominantly of ultramafic-mafic lavas and sills with minor felsic components, distributed as various segments along the margins of the Superior Province craton. Ultramafic-mafic dykes and carbonatite complexes of the LIP also intrude the more central parts of the craton. Most of this magmatism occurred 1880 Ma. Previously a wide range of models have been proposed for the different segments of the CSLIP with the upper mantle as the source of magmatism. New major and trace element and Nd-Hf isotopic data reveal that the segments of the CSLIP can be treated as a single entity formed in a single tectonomagmatic environment. In contrast to most previous studies that have proposed a variety of geodynamic settings, the CSLIP is interpreted to have formed from a single mantle plume. Such an origin is consistent with the high MgO and Ni contents of the magmatic rocks, trace element signatures that similar to oceanic-plateaus and ocean island basalts and eNd-eHf isotopic signatures which are each more negative than those of the estimated depleted upper mantle at 1880 Ma. Further support for a mantle plume origin comes from calculated high degrees of partial melting, mantle potential temperatures significantly greater than estimated ambient Proterozoic mantle and the presence of a radiating dyke swarm. The location of most of the magmatic rocks along the Superior Province margins probably represents the deflection of plume material by the thick cratonic keel towards regions of thinner lithosphere at the craton margins. The primary magmas, generated by melting of the heterogeneous plume head, fractionated in magma chambers within the crust, and assimilated varying amounts of crustal material in the process

The geochemistry and petrogenesis of the Paleoproterozoic du Chef dyke swarm, Quebec, Canada

The du Chef dyke swarm in southern Québec, Canada is composed of numerous northeast trending, greenschist-amphibolite facies, gabbronoritic dykes that crop out either side of the Grenville Front. The age of the du Chef swarm (2408 ± 3 Ga) has led previous authors to suggest a genetic link between the du Chef dykes and coeval swarms (including the Ringvassøy, Scourie, Widgemooltha and Sebanga) preserved on other Archean cratons. These now disparate dyke swarms are proposed to have formed in response to mantle plume-induced continental breakup during the early Proterozoic. This work represents the first geochemical study of the du Chef dykes and shows that the swarm evolved through fractional crystallisation of a tholeiitic parent magma that remained largely uncontaminated during its residence in, and ascent through, the crust. We also show that the primary magma for the du Chef swarm was derived through partial melting of an enriched region of the mantle, with a similar trace element composition to the modern-day HIMU reservoir and that the magma produced was significantly hotter than the ambient mantle at the time. We contend that the du Chef dykes are the product of early Proterozoic mantle plume magmatism and may help pinpoint an ancient hotspot centre that initiated continental break up along the margin of the Superior Craton at ∼2.4 Ga. Other dyke swarms proposed to be genetically linked with the du Chef dykes record a distinctly different petrogenetic history to that of the du Chef dykes, as evidenced by their more volcanic arc-like geochemical signature. These contrasting geochemical signatures in supposedly cogenetic continental tholeiitic rocks may be evidence of early Proterozoic mantle heterogeneity sampled by the rising du Chef mantle plum

The Early Proterozoic Matachewan Large Igneous Province: Geochemistry, Petrogenesis, and Implications for Earth Evolution

The Matachewan Large Igneous Province (LIP) is interpreted to have formed during the early stages of mantle plume-induced continental break-up in the early Proterozoic. When the Matachewan LIP is reconstructed to its original configuration with units from the Superior Craton and other formerly adjacent blocks (Karelia, Kola, Wyoming and Hearne), the dyke swarms, layered intrusions and flood basalts, emplaced over the lifetime of the province, form one of the most extensive magmatic provinces recognized in the geological record. New geochemical data allow, for the first time, the Matachewan LIP to be considered as a single, coherent entity and show that Matachewan LIP rocks share a common tholeiitic composition and trace element geochemistry, characterized by enrichment in the most incompatible elements and depletion in the less incompatible elements. This signature, ubiquitous in early Proterozoic continental magmatic rocks, may indicate that the Matachewan LIP formed through contamination of the primary magmas with litho-spheric material or that the early Proterozoic mantle had a fundamentally different composition from the modern mantle. In addition to the radiating geometry of the dyke swarms, a plume origin for the Matachewan LIP is consistent with the geochemistry of some of the suites; these suites are used to constrain a source mantle potential temperature of c. 1500-1550 degrees C. Comparison of these mantle potential temperatures with estimated temperatures for the early Proterozoic upper mantle indicates that they are consistent with a hot mantle plume source for the magmatism. Geochemical data from coeval intrusions suggest that the plume head was compositionally heterogeneous and sampled material from both depleted and enriched mantle. As has been documented with less ancient but similarly vast LIPs, the emplacement of the Matachewan LIP probably had a significant impact on the early Proterozoic global environment. Compilation of the best age estimates for various suites shows that the emplacement of the Matachewan LIP occurred synchronously with the Great Oxidation Event. We explore the potential for the eruption of this LIP and the emission of its associated volcanic gases to have been a driver of the irreversible oxygenation of the Earth

The geochemistry and petrogenesis of the Blue Draw Metagabbro

The Blue Draw Metagabbro (BDM) in western South Dakota, is an 800 m thick, layered intrusion, which is interpreted to have been intruded as a rift-related subvolcanic sill during the Palaeoproterozoic. The age and tectonic setting of the BDM are similar to those recorded by the East Bull Lake Suite of layered intrusions in Southern Ontario. These similarities have led previous authors to suggest that the two sets of intrusions are cogenetic. The East Bull Lake Suite intrusions are relatively well studied and are known to host significant contact-type Ni–Cu–PGE sulphide mineralisation, however, prior to this work, relatively little was known of BDM both in terms of its geochemistry and mineralisation potential. Chemostratigraphic profiles through the BDM show that the intrusion is the product of at least two magma pulses which fractionated to produce a sequence of rocks which grade from peridotitic at the base of the intrusion to gabbronoritic at the upper margin. Closed-system fractionation following the intrusion of the second magma pulse caused the magma to become saturated in sulphur and precipitate Ni–Cu–PGE bearing sulphides—now preserved in a low-grade 50 m thick zone near the top of the intrusion. Petrological modelling shows that the parental melt of the BDM was a low-Ti tholeiite, with a trace element chemistry defined by enrichments in large-ion lithophile and light rare-earth elements and prominent negative Nb, Ta, and Ti anomalies. This ‘arc-like’ geochemistry recorded by the BDM parent magma is shared with parent magmas of the East Bull Lake Suite and may suggest that the BDM and its potential Canadian relatives share a common magmatic source. However, the relative ubiquity of such geochemical signatures in Archaean–Palaeoproterozoic intracontinental magmatic rocks coeval with the BDM suggests that the geochemical similarities recorded by the BDM and East Bull Lake Suite are non-unique and hence, are not definitive evidence of a genetic link between the two sets of intrusions. Instead, this geochemical signature that is common to many ancient igneous provinces may indicate the presence of a transient and (currently) poorly understood Archaean–Palaeoproterozoic mantle reservoir which was a globally significant magma source

A mantle plume origin for the Palaeoproterozoic Circum-Superior Large Igneous Province

The Circum-Superior Large Igneous Province (LIP) consists predominantly of ultramafic-mafic lavas and sills with minor felsic components, distributed as various segments along the margins of the Superior Province craton. Ultramafic-mafic dykes and carbonatite complexes of the LIP also intrude the more central parts of the craton. Most of this magmatism occurred ∼1880 Ma. Previously a wide range of models have been proposed for the different segments of the CSLIP with the upper mantle as the source of magmatism

The northern and southern sections of the western ca. 1880 Ma Circum-Superior Large Igneous Province, North America: The Pickle Crow dyke connection?

The ca. 1880 Ma Circum-Superior Large Igneous Province (LIP) consists of a number of discontinuous segments known to cover a significant portion of the margin of the Superior Province craton in North America. New geochemical and isotopic data from western segments of this LIP support a common origin for the these segments and suggest that magmatism in the Lake Superior region may have been fed through the ~ 600 km long Pickle Crow dyke from a source north of the Fox River Belt in northeastern Manitoba. The Fox River Belt, Pickle Crow dyke and sections of the Hemlock Formation in the Lake Superior region possess trace element signatures which are similar to those of more recent oceanic plateaux. The Hemlock Formation displays a heterogeneous geochemical signature. This chemical heterogeneity can in part be explained by lithospheric contamination and possibly by source heterogeneity. The tectonomagmatic setting in which these igneous rocks were formed could have involved a mantle plume. Evidence supporting a plume origin includes high MgO volcanic rocks, high calculated degrees of partial melting and geochemical signatures similar to those of oceanic plateaux

The early proterozoic matachewan large igneous province: geochemistry, petrogenesis, and implications for earth evolution

The Matachewan Large Igneous Province (LIP) is interpreted to have formed during the early stages of mantle plume-induced continental break-up in the early Proterozoic. When the Matachewan LIP is reconstructed to its original configuration with units from the Superior Craton and other formerly adjacent blocks (Karelia, Kola, Wyoming and Hearne), the dyke swarms, layered intrusions and flood basalts, emplaced over the lifetime of the province, form one of the most extensive magmatic provinces recognized in the geological record. New geochemical data allow, for the first time, the Matachewan LIP to be considered as a single, coherent entity and show that Matachewan LIP rocks share a common tholeiitic composition and trace element geochemistry, characterized by enrichment in the most incompatible elements and depletion in the less incompatible elements. This signature, ubiquitous in early Proterozoic continental magmatic rocks, may indicate that the Matachewan LIP formed through contamination of the primary magmas with litho-spheric material or that the early Proterozoic mantle had a fundamentally different composition from the modern mantle. In addition to the radiating geometry of the dyke swarms, a plume origin for the Matachewan LIP is consistent with the geochemistry of some of the suites; these suites are used to constrain a source mantle potential temperature of c. 1500-1550 degrees C. Comparison of these mantle potential temperatures with estimated temperatures for the early Proterozoic upper mantle indicates that they are consistent with a hot mantle plume source for the magmatism. Geochemical data from coeval intrusions suggest that the plume head was compositionally heterogeneous and sampled material from both depleted and enriched mantle. As has been documented with less ancient but similarly vast LIPs, the emplacement of the Matachewan LIP probably had a significant impact on the early Proterozoic global environment. Compilation of the best age estimates for various suites shows that the emplacement of the Matachewan LIP occurred synchronously with the Great Oxidation Event. We explore the potential for the eruption of this LIP and the emission of its associated volcanic gases to have been a driver of the irreversible oxygenation of the Earth