HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Brem, A. G. Articles by Mcnicoll, V. J. Search for Related Content Articles by Brem, A. G. Articles by Mcnicoll, V. J. GeoRef GeoRef Citation

The Middle Ordovician to Early Silurian voyage of the Dashwoods microcontinent, West Newfoundland; based on new U/Pb and ⁴⁰Ar/³⁹Ar geochronological, and kinematic constraints

Arjan G. Brem^*,, Shoufa Lin^*, Cees R. Van Staal^**, Donald W. Davis^*** and Vicki J. Mcnicoll^****

^* Department of Earth Sciences, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
^** Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada
^*** Department of Geology, University of Toronto, Ontario, M5S 3B1, Canada
^**** Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada

Corresponding author: E-mail: agbrem{at}uwaterloo.ca

The Dashwoods microcontinent is an important tectonic segment in the peri-Laurentian setting of the Newfoundland Appalachians. In order to better understand the tectonic history of Dashwoods during the Ordovician Taconic orogeny, we have undertaken field mapping, microscopic studies, and U-Pb and ⁴⁰Ar/³⁹Ar geochronological studies along the northern (Little Grand Lake Fault; LGLF) and western (Baie Verte Brompton Line - Cabot Fault Zone; BCZ) boundaries.

Oblique-dextral ductile deformation in the BCZ occurred from late Middle Ordovician into the Early Silurian, based on the presence of a late syn-tectonic pegmatite dike (455 ± 12 Ma) and a foliated granodiorite sheet (445.8 ± 0.6 Ma). Deformation is coeval with oblique-sinistral accretion along the eastern margin of Dashwoods, which means that Dashwoods and its Notre Dame Arc had a southward translation with respect to the Laurentian margin and the then-present Iapetus Ocean during the Late Ordovician. Dextral movement along the BCZ continued after the collision of Dashwoods with the Laurentian margin. Deformation along the Little Grand Lake Fault is bracketed between 463 ± 5 Ma and 440 ± Ma. These ages combined with other geological arguments indicate that motion probably took place during the Late Ordovician to earliest Silurian contemporaneous with the southward translation of Dashwoods. A possible explanation is that the Snooks Arm arc moved independently from and faster southwards than the Notre Dame Arc with its Dashwoods infrastructure, thereby underthrusting the Dashwoods along the Little Grand Lake Fault.

Our new U-Pb geochronological data, including a muscovite granite (463 ± 5 Ma), a schistose muscovite granite (459 ⁺¹⁷/_-21 Ma), and a tectonized tonalite (458 ± 20 Ma), add to the geochronological database of the voluminous second phase of the Notre Dame Arc. Additionally, in all-but-one of our U-Pb samples, inherited grains of Mesoproterozoic (circa 1.0 Ga) age have been obtained. Their regional presence fortifies the possible relationship of the Dashwoods microcontinent with the Long Range Inlier in western Newfoundland. Furthermore, it introduces a potential link with the Blair River Inlier in Cape Breton Island.