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TitleThe Paleoproterozoic Otish Gabbro suite and coeval dyke swarms of the Superior Province: Probing the ca. 2.17 Ga mantle
AuthorMilidragovic, DORCID logo; Beaudoin, G; Hamilton, M A; King, J J
SourcePrecambrian Research vol. 278, 2016 p. 126-144,
Alt SeriesEarth Sciences Sector, Contribution Series 20160316
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
NTS22M/13; 22M/14; 22M/15; 22M/16; 23D/01; 23D/02; 23D/03; 23D/04; 32P/16; 33A/01
AreaCamie River
Lat/Long WENS -72.8333 -70.0000 53.0000 52.0000
Subjectsgeochronology; general geology; dykes, mafic; uranium lead dating; sills; uranium deposits; mineral deposits; lithogeochemistry; Superior Province; Otish Gabbro; Precambrian
Illustrationslocation maps; geological sketch maps; tables; photomicrographs; plots; Concordia diagrams; magnetic anomaly maps
ProgramTargeted Geoscience Initiative (TGI-4)
Released2016 06 01
AbstractThe uraniferous, Proterozoic Otish Basin of the southeastern Superior Province hosts shallow-dipping sills and northeast to northwest-trending dykes of the Otish Gabbro suite and the north-trending Matoush dyke. Otish Gabbro sills comprise two distinct geochemical groups that reflect different degrees of crystal accumulation in a common olivine-tholeiitic parental magma. Group 1 Otish gabbros approach liquid compositions, whereas Group 2 gabbros are crystal cumulates of olivine + plagioclase + clinopyroxene. The high Nb/Yb, La/Yb, Th/Yb and low Zr/Nb ratios of the Otish Gabbro sills reflect trace elementenriched, mantle-derived parental liquids, modified by the addition of a crustal component. A northtrending Matoush dyke records a second magmatic event in the Otish Basin, genetically unrelated to the emplacement of the Otish Gabbro sills. In contrast to the gabbros, the strongly altered Matoush dyke has more fractionated trace element patterns and strong enrichments in light rare earth elements (LREE) that are indicative of a lamprophyric affinity. The Otish Gabbro sills are part of a large ca. 2.17 Ga magmatic event that also generated the extensive Biscotasing and Payne River dyke swarms in the south-central and northeastern Superior Province, respectively. The contemporaneous mafic dyke swarms experienced relatively minor crustal contamination and their high Nb/Zr and Nb/Yb ratios suggest derivation from fertile mantle sources. Furthermore, the low Ti/Yb ratios of the ca. 2.17 Ga magmas are consistent with melting at relatively shallow depths (<100 km), implying removal of the depleted Archean lithosphere from a large portion of the Superior Province and replacement by a more fertile Proterozoic mantle. The variable geochemical composition of the ca. 2.17 Ga mafic magmas indicates melting of a compositionally heterogeneous mantle and
appears inconsistent with a common distal mantle plume source. A more suitable petrogenetic model for the ca. 2.17 Ga dyke swarms of the Superior Province is vertical rise of mantle-derived magmas in a rifting environment.

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