Silurian-Early Devonian mafic rocks of the Piscataquis volcanic belt in northern Maine

Authors

  • R. Hon Department of Geology and Geophysics, Boston College, Chestnut Hill, Massachusetts 02167, U.SA.
  • J. P. Fitzgerald Department of Geology and Geophysics, Boston College, Chestnut Hill, Massachusetts 02167, U.SA.
  • S. L. Sergent Department of Geology and Geophysics, Boston College, Chestnut Hill, Massachusetts 02167, U.SA.
  • W. D. Schwartz Department of Geology and Geophysics, Boston College, Chestnut Hill, Massachusetts 02167, U.SA.
  • J. Dostal Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada
  • J. D. Keppie Nova Scotia Department of Mines and Energy, P.O. Box 1087, Halifax, Nova Scotia B3J 2X1, Canada

DOI:

https://doi.org/10.4138/1858

Abstract

The Silurian-Early Devonian eruptive rocks at selected sites in the Piscataquis volcanic belt in northern Maine are composed of mafic and felsic rocks with rare intermediate types. The mafic rocks are mainly basalts that are commonly strongly fractionated and have the characteristics of intraplate continental tholeiites. The mantle-normalized incompatible trace element patterns of the rocks display negative Nb-Ta anomalies that were probably inherited from sub-continental lithosphere modified by pre-Silurian subduction processes. However, they do not have Ti depletion typical of subduction-related magmas. On the other hand, the youngest (late Early Devonian) Edmunds Hill Formation is composed of calc-alkali andesites that exhibit features typical of arc-related magmas. The Silurian-Early Devonian volcanic rocks were primarily erupted in a within-plate extensional environment that terminated with limited subduction. This extensional environment is inferred to be associated with the sinistral accretion of the Avalon Composite Terrane that produced an oblique pull-apart rift in adjacent Laurentia. R᳧SUM᳧ Les roches ᳻rutives du Silurien et du D᳻vonien pr᳻coce provenant de sites choisis dans la ceinture volcanique de Piscataquis du Maine septentrional sont compos᳻es de roches mafiques et felsiques avec de rares termes interm᳻diates. Les roches mafiques sont principalement des basaltes qui sont commun᳻ment diff᳻renc᳻s et qui pr᳻sentent les caract᳻ristiques des thol᳻iites continentales intraplaques. Les patrons d'᳻l᳻ments traces normalis᳻s par le manteau pour les roches mafiques montrent des anomalies n᳻gatives en Nb et Ta qui furent probablement h᳻rit᳻es de la lithosphere sous-continentale modifi᳻e par des processus de subduction pr᳻-siluriens. Cependant, elles ne pre᳻entent pas d'appauvrissement en Ti typique des magmas reli᳻s ᳲ la subduction. Par ailleurs, la Formation d'Edmunds Hill, qui est la plus jeune (fin du D᳻vonien pr᳻coce), est compos᳻e d'and᳻sites calco-alcalines pr᳻sentant des caract᳻ristiques typiques des magmas reli᳻s aux arcs. Les roches volcaniques du Silurien et du D᳻vonien pr᳻coce firent ᳻ruption dans un environnement intraplaque extensionnel qui se termina par une composante mineure de subduction. On deduit que cet environnement extensionnel est associ᳻ ᳲ l'accr᳻tion senestre du terrain composite d'Avalon qui produisit un rift de d᳻crochcment oblique dans le terrain de Laurentia adjacent. [Traduit par le journal]

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Published

1992-07-01

How to Cite

Hon, R., Fitzgerald, J. P., Sergent, S. L., Schwartz, W. D., Dostal, J., & Keppie, J. D. (1992). Silurian-Early Devonian mafic rocks of the Piscataquis volcanic belt in northern Maine. Atlantic Geoscience, 28(2). https://doi.org/10.4138/1858

Issue

Vol. 28 No. 2 (1992)

Section

Articles

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