Late-Orogenic Potassic to Ultrapotassic Dykes from the Central Grenvillian Hinterland: Trace Element and Sr-Nd-Pb-O Isotopic Perspective

Abstract

New whole-rock Sr-Nd-Pb-O isotope data are combined with previously published results for Sr and Nd isotopes and major and trace element chemistry to examine the petrogenetic and tectonic environments of a suite of ca. 980 Ma potassic to ultrapotassic dykes (PUD) from the Canyon domain, central Grenville Province. The PUD suite can be divided into two geochemically distinct groups that exhibit characteristic source mineralogy, depth of partial melting, and multi-stage metasomatism of heterogeneous mantle sources. Major and trace element data suggest involvement of both fertile and depleted peridotite sources involving spinel and garnet, while trace element and isotope data indicate long-term LREE and LILE enrichments and HFSE depletions in ancient subduction settings. Low time-integrated Rb/Sr, Sm/Nd, and U/Pb ratios suggest enriched mantle EM-I metasomatized by ancient subduction of continental upper crust and/or carbonate sediments. A latest phase of fluid/melt metasomatism is attributed to a late-Grenvillian intracontinental subduction and limited lithospheric extension. The late-Grenvillian tectonic setting is proposed here to be characterized by shallow-angle underthrusting of the foreland beneath the Grenvillian hinterland, where SCLM, initially of Proterozoic age and eventually of Late Archean age, became transported beneath the orogenic core. The intracontinental collision was short-lived and probably terminated because of buoyancy constraints related to the refractory character of the subducted Archean lithospheric mantle.

Keywords: Orogenic magmatism, Grenville Province, Geochemistry, subcontinental lithospheric mantle, ultrapotassic dykes, mantle metasomatism