T73 Assembling Laurentia: Turning Points in Paleoproterozoic Tectonic Evolution I

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

LOCALIZED BACKARC RIFTING DURING THE PALEOPROTEROZOIC ASSEMBLY OF LAURENTIA: GEOCHEMICAL AND ISOTOPIC EVIDENCE FROM MAFIC MAGMATISM, LABRADOR, CANADA

Paper number: T73-12
Program: Technical Sessions
Time: 4:05 PM – 4:20 PM

Authors

  • Alana Hinchey Presenting Author
    Government of Newfoundland & Labrador Natural Resources, St. John's, NF

Abstract

The Paleoproterozoic convergence of southeastern Laurentia documents the assembly of the supercontinent Nuna, featuring a long-lived internal ocean closure as various proto-continents collided. This created an overall compressive regime and localized extension, due to the multiple subducting plates. Evidence for localized extension is preserved in mafic volcanic rocks of a bimodal suite (Aillik Group) of the 1.9-1.7 Ga Makkovik Orogen, developed along the margin of Laurentia. Geochemical and isotopic data, from mafic volcanic rocks, constrain the tectonic setting of the early basin, refining the pre-deformation history of the Aillik Group and defining constraints on the accretion of the Laurentian margin.

Lithogeochemical signatures of the basaltic magmatism define two suites. Suite one basaltic rocks have N-MORB chemical affinities, illustrated by low TiO2 concentrations, and flat REE. These rocks have high εNd(0) values ranging from +2.8 to +4.8. Suite two basaltic rocks plot as a mixture between N-MORB and IAT basalts, with variable LREE enrichment and depletion in HREE. Suite two basalts display moderately developed subduction zone signatures, such as negative Nb and Ti. The suite two rocks have εNd(0) that range from -3.4 to +2.2.

The geochemical variability of the Aillik Group mafic volcanic rocks results from the mixing of depleted mantle components with variable contributions from crustal and subducted-slab sources. Coupled with field-mapping evidence, the geochemical and isotopic signatures of the mafic volcanic rocks support derivation in an extensional, backarc basin setting. This backarc basin formed because of localized extension during Nuna assembly, and was initiated prior to 1883 Ma. There was a switch to a compressional tectonic setting by ca. 1836 Ma, marked by the accretion of part of Cape Harrison Arc. This resulted in the inversion of the backarc basin and subsequent northwestward transport of the Aillik Group, concomitant with regional-scale shearing and folding with associated low-grade metamorphism. The Makkovik Province preserves a complex orogen characterized by multiple diachronous, compressional and extensional tectonic events along a long-lived active margin of Laurentia.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357154

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.