Origin of mafic and potassic to ultrapotassic rocks, Manicouagan area, central Grenville Province: geochemical and geochronological constraints on the evolution of the Mesoproterozoic SE Laurentian margin and the Grenvillian LHO
The southeastern margin of Laurentia preserves evidence for a long episode of juvenile crustal growth and recycling extending from the late Paleoproterozoic and throughout the Mesoproterozoic (~1.9–1.2 Ga). This was terminated by the onset of the Grenvillian continental collision (~1.1–0.98 Ga), for...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
2019
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| Online Access: | https://research.library.mun.ca/14257/ https://research.library.mun.ca/14257/1/thesis.pdf |
| Summary: | The southeastern margin of Laurentia preserves evidence for a long episode of juvenile crustal growth and recycling extending from the late Paleoproterozoic and throughout the Mesoproterozoic (~1.9–1.2 Ga). This was terminated by the onset of the Grenvillian continental collision (~1.1–0.98 Ga), forming a large, hot, long-duration orogen (LHO), comparable in scale to the modern day Himalayan-Tibet LHO. The Grenvillian LHO has been subdivided into the ca. 1090-1020 Ma Ottawan phase for which evidence is preserved in allochthonous rocks in the orogenic hinterland, and the ca. 1005-980 Ma Rigolet phase for which evidence is mainly preserved in the parautochthonous foreland (Rivers et al. 2012). Mesoproterozoic to early Neoproterozoic metamorphosed mafic and unmetamorphosed potassic to ultrapotassic rocks from the Canyon domain, part of the polycyclic allochthonous, medium-pressure (aMP) belt of the Grenville Orogen in the Manicouagan area, central Grenville Province, were investigated using integrated petrographic, geochronological, isotopic, and geochemical methods. The principal results of the thesis, presented as three Chapters (2 - 4), are summarized below. In Chapter 2, U-Pb TIMS geochronology of zircon, and whole-rock geochemical and Sm-Nd isotopic analyses of two granulite-facies mafic tholeiitic suites, provide constraints on: (i) the emplacement of crust-contaminated, depleted to enriched MORB-type, high Fe-Ti-P mafic sills at 1439⁺⁷⁶₋₆₈ Ma within a ca. 1.5 Ga supracrustal sequence that was under limited extension at that time, probably in a back-arc setting; and (ii) emplacement of a crust-contaminated, enriched MORB to arc-type mafic intrusive suite, previously dated at 1410 ± 16 Ma, in a transitional back-arc to arc setting. Integrated with published information, these results support the existing model of a long-lived continental margin arc on the southeastern margin of Laurentia, with intermittent back-arc opening and closure during Geons 15-14. In Chapter 3, U-Pb TIMS geochronology of zircon from two ... |
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