Geochemistry and U-Pb Geochronology of the 1450-1425 Ma Large Igneous Province of Eastern Laurentia and 2480-780 Ma Large Igneous Provinces of Western Laurentia

Abstract

Mesoproterozoic magmatism that is exposed on the eastern and western margins of Laurentia (North America) are interpreted to be parts of large igneous provinces (LIP). The western margin between Kimberley (British Columbia) and Yellowstone National Park (Wyoming), and the eastern margin between Labrador City and coastal Labrador are herein referred to as western Laurentia (WL) and eastern Laurentia (EL), respectively. WL intraplate magmatism was previously divided into two LIPs the: 1) ca. 1460 Ma Moyie-Purcell LIP (MPL) which consists of the i) Purcell lavas in the USA, ii) Moyie sills of the Belt-Purcell basin iii) dykes of the Tobacco Root Mountains and 2) the ca. 780 Ma Gunbarrel LIP. The MPL is composed of tholeiitic basalts, and associated with the world class Sullivan Pb-Zn deposit. EL consists of basalts of the non-mineralized Michael-Shabogamo Gabbros (MSG). This research demonstrated that at least 17 geochemical groups are present in WL of which some belong to additional previously unrecognized events. Seven geochemical groups belong to the ca. 1460 Ma MPL; 1 with the ca. 780 Ma Gunbarrel LIP, 2 with a 1590-1550 Ma Mammoth-Western Channel LIP (MWCL); 2 with ages of 2480, and 1420 Ma; and 5 undated mafic pulses. The MWCL is similar to contemporaneous volcanic rocks within the South Australia craton, which was adjacent to NW Laurentia ca. 1590 Ma. This study proposes a shared 1590 Ma plume and LIP magmatism between Laurentia, and South Australia cratons. The MSG of EL are subalkaline basalts enriched in P2O5 and K2O and are shown to represent a single event with 2 pulses based on new U-Pb ages. Each pulse is defined by a distinct [P2O5*1000]/Zr (P/Zr) ratio: 1) a high P/Zr group at ca. 1425-1435 Ma; and 2) a low P/Zr group at ca. 1435-1450 Ma. Enrichment of P2O5 and K2O is due to melting of a metasomatized subcontinental lithospheric mantle with melting facilitated by a slab window.