Geochemistry of Early Devonian calc-alkaline plutons in the Merrimack Belt: implications for mid-Paleozoic terrane relationships in the New England Appalachians

Abstract

A series of northeast-trending plutons extending from northeastern Massachusetts to southeastern Maine intruded the metasedimentary rocks of the Merrimack belt. The Early Devonian Dracut, Sweepstakes, Island Pond, Exeter, and Webhannet plutons are metaluminous and, with the exception of the granitic Webhannet pluton, are dominantly mafic to intermediate in composition. The plutons are calc-alkaline in character and have major, minor, and trace element compositions typical of magmas generated at destructive plate margins. These characteristics include mid-to high-K contents, enrichment of LILE, LREE, Ba, and Sr, and negative Nb and Ta anomalies. Whole-rock chemical data indicate that the plutons of the Merrimack belt are similar in every measured geochemical parameter to ca. 400 Ma mafic to intermediate rocks of the New Hampshire Plutonic Suite. These similarities suggest that both groups of plutons were emplaced within the same magmatic arc and belong to the same magmatic suite. A magmatic suite common to both the Merrimack belt and Central Maine terrane suggests that the two lithotectonic zones were proximal to each other at ca. 400 Ma. Trace element differences between Merrimack belt and Sharpners Pond rocks suggest that the Putnam-Nashoba terrane represents a separate arc. Located in the Central Maine terrane of New Hampshire, the Rochester pluton is geochemically distinct from the Siluro-Devonian plutons of the Merrimack belt and New Hampshire Plutonic Suite. The Rochester pluton has alkaline affinities but retains overall calc-alkaline features. High concentrations of incompatible elements (K, Ti, P, Ba, Rb, Zr) in the Rochester pluton are markedly similar to those observed in the 360 Ma Hardwick Tonalite of Massachusetts. The strong geochemical correlation between the Rochester and Hardwick plutons implies derivation from the same magmatic event and a common, Late Devonian origin. We suggest that these plutons may have originated in response to pull-apart rifting related to late-stage Acadian transpression. Une serie de plutons orientee vers le nord-est s'etendant du nord-est du Massachusetts au sud-est du Maine, fait intrusion dans les roches metasedimentaires de la ceinture de Merrimack. Les plutons du Devonien inftrieur Dracut, Sweepstakes, Island Pond, Exeter et Webhannet constituent des intrusions metalumineuses et, mis k part le pluton granitique Webhannet, ils ont une composition en predominance mafique a intermediate. Les plutons ont une conformation calcoalcaline et leur composition du point de vue des principaux elements presents, de ceux presents en quantite restreinte et des elements traces est representative des magmas produits aux fronti6res de plaques destructives. Leurs caracteristiques component notamment une teneur moyenne a elevee en potassium, un enrichissement en LILE, en elements de terres rares ldgeres, en BA et en SR, de meme que des anomalies negatives de Nb et Ta. Les donnees de la roche totale revelent que les plutons de la ceinture de Merrimack sont semblables, sous le rapport de...

Age and tectonic setting of the Quinebaug-Marlboro belt and implications for the history of Ganderian crustal fragments in southeastern New England, USA

“…28) and its less voluminous extension into southern New England (van Staal and Barr, 2012;Pinan-Llamas and Hepburn, 2013;Wilson et al, 2017). The Silurian to Early Devonian calc-alkaline rocks are related to subduction prior to closure and collision in the Salinic or early part of the Acadian orogeny (Wones and Goldsmith, 1991;Watts et al, 2000;van Staal et al, 2009;Hussey et al, 2010;Barr et al, 2011;Pinan-Llamas and Hepburn, 2013;Hepburn et al, 2014). In Massachusetts, the Newbury Volcanic Complex (Zen et al, 1983) at the northern end of the Putnam-Nashoba terrane (Fig.…”

“…Trace-element geochemical data suggest that late Silurian to Early Devonian arc-related calcalkaline plutons in the Putnam-Nashoba terrane and adjacent overriding Merrimack belt developed in different settings as indicated by mid-to high-K, enrichment of LILE, LREE, Ba, and Sr, and negative Nb and Ta anomalies in the latter (Hepburn et al, 1995;Watts et al, 2000). The slightly younger plutonic rocks in the overlying Merrimack belt show an overlap in age with rocks in the underlying Putnam-Nashoba terrane rocks.…”

Characterizing the Southwestern Extent of the Norumbega Fault System, a Mid-Paleozoic Crustal-Scale Strike-Slip Fault System in the New England Appalachians

“…Zircon ages suggest dual sources for the MB from Ganderia and Laurentia with decreasing Ganderian input with decreasing depositional age (Sorota, 2013). The metamorphic grade in the MB increases westward from lower-greenschist facies to amphibolite facies (Lyons et al, 1997;Robinson, 1981;Wintsch et al, 1992;Watts et al, 2000). The MB underwent multiple folding events beginning with several generations of m-to km-scale, east-verging isoclinal folds, followed by local north-trending horizontal recumbent chevron folds (Robinson, 1978(Robinson, ,1981Goldstein, 1994;Kopera and Walsh, 2014;Kuiper et al, 2014;Charnock, 2015).…”