|Titre||Is the formation of the Appalachian Silurian/Devonian volcano-sedimentary troughs controlled by delamination?|
|Auteur||Pinet, N; Tremblay, A|
|Source||The history of convergent and passive margins in the polar realm: Sedimentary and tectonic processes, transitions and resources; 2006 p. 56|
|Séries alt.||Secteur des sciences de la Terre, Contribution externe 20090159|
|Réunion||Québec 2006: ILP task force on sedimentary basins; Quebec City; CA; Septembre 18-22, 2006|
|Province||Nouveau-Brunswick; Nouvelle-Écosse; Québec|
|Sujets||roches sédimentaires; sédiments marins; carbonates; caractéristiques structurales; failles; sediments; milieux sédimentaires; milieu sédimentaire; interprétations tectoniques; milieux tectoniques;
sédimentologie; géologie structurale; tectonique; Dévonien; Silurien; Paléozoïque|
|Résumé||(disponible en anglais seulement)|
In the Appalachians of Canada and New England, Silurian/Devonian rocks are found in continental-scale troughs, and rest unconformably or in fault contact with
older rocks belonging to Laurentia and to Gander/Avalon. The Silurian/Devonian series consist of marine clastic deposits with subordinate carbonates, lava flows and terrestrial deposits.
Key geological parameters to constrain the geodynamic
setting of these troughs are: 1) sediments deposited on the various early Paleozoic terranes share common characteristics suggesting that they correspond to an overlapping sequence; 2) some conglomerates found at the base of the sequence include
clasts of different early Paleozoic domains and attest of the sedimentary linkage of terranes; 3) paleomagnetic constraints suggest that early Paleozoic terranes were already docked at the inception of the sedimentary troughs. Points 1 to 3 indicate
that Middle Paleozoic troughs are 'intra-continental' basins; 4) structures in pre-Silurian rocks of Laurentia argue for significant crustal extension during deposition; 5) the troughs are discontinuously separated by outliers of pre-Silurian rocks
which may be interpret as basement horsts, buried in Devonian; 6) volcanic rocks are widely distributed in time and space, and are mostly subalkaline within-plate tholeiites, which is consistent with a tectonic setting involving crustal extension
Points 4 to 6 suggest that extension was predominant at a regional scale; 7) the geochemical signature of Late Silurian to Devonian volcanics discards subduction processes; 8) Silurian-Devonian plutons are abundant in the southeasten (Merrimack)
trough and attest for high-temperatures at mid-crustal levels.
We suggest that delamination, probably located at the boundary between early Paleozoic terranes is responsible of the heating of the lower crust during the Silurian. Delamination and
the upwelling of asthenosphere would have been followed by isostatic uplift and formation of basement highs, extensive magmatism in the lower crust and regional-scale contact metamorphism in the upper crust, the collapse of adjacent metamorphic
terranes and the formation of subsiding sedimentary basins. The Middle Paleozoic Appalachian troughs are comparable to Neogene Mediterranean extensional basins in the following sense, (i) elongated troughs along continents that have suffered orogenic
shortening, (ii) an internal geometry characterized by buried basement uplifts, (iii) extensional structures preserved as syn-sedimentary normal faults or as detachments within the adjacent continents, (iv) volcanism occurring at various
stratigraphic levels and characterized by coexisting calc-alkaline and alkaline trends, (v) anomalous heat flow, and (vii) basin development in a timeframe of 10 to 20 m.y. following crustal shortening.