ABSTRACT Examination of 36 Devonian to Pennsylvan- ian plutons within and bordering the Central Maine terrane of north-central New England shows that the plutons display regional varia- tions in mineral and bulk-rock compositions and in oxygen and sulfur isotopic values. These variations principally correspond to the re- gional structural trends of the Central Maine terrane. Plutons located on that terrane’s southeast flank adjacent to the Massabesic Gneiss complex, on the terrane’s northwest flank adjacent to the Bronson Hill anticlino- rium, and in the northeastern part of the Northeast Kingdom batholith of Vermont have biotites with relatively low Al concentrations (≤3.0 cations p.f.u. [per formula unit]), feldspars with higher An contents (up to An 55 ), and lower δ 18 O (7‰–9‰) and higher δ 34 S (av- erage of 0‰) bulk-rock values compared to plutons within the central parts of the Central Maine terrane. These characteristics are most compatible with metaigneous or metavolcani- clastic sources. As shown by others, the plutons of Vermont and northwestern Maine preserve Grenvillian signatures whereas those of south- eastern New Hampshire (specifically, the gran- ite at Milford, New Hampshire) and Maine (Sebago, Phillips) have Avalonian signatures. Within the interior of the Central Maine terrane of New Hampshire and western Maine and in the Connecticut Valley trough of Vermont are distinct regions characterized by peraluminous plutons with high δ 18 O values (>11‰), low δ 34 S values (–25‰), Al-rich bio- tites (>3.3 cations p.f.u.), and An-poor plagio- clases (<An 30 ). These data are most consistent with metasedimentary sources, or, at a mini- mum, the plutons were heavily contaminated by Central Maine terrane or Connecticut Val- ley trough metasedimentary rocks. These peraluminous plutons do not have the unique signatures of the underlying Precambrian basements. Several metaluminous plutons in the Cen- tral Maine terrane along the New Hamp- shire–Maine border separate two regions of peraluminous plutons. These metaluminous plutons have biotite and isotopic compositions that are similar to those of the plutons along the flanks of the Central Maine terrane, in- dicative of less Paleozoic metasedimentary in- put compared to the peraluminous plutons in the interior of the Central Maine terrane. The metaluminous plutons also have trace element characteristics identical to those of plutons in Vermont and northwestern Maine that have a known Grenville basement-terrane source. We suggest that the metaluminous plutons also had sources in the underlying Grenville base- ment and that the Grenville-Avalon boundary cuts diagonally across northern New England. Because the plutons with Grenvillian signa- tures are adjacent to plutons with Avalonian signatures—the Sebago batholith and Phillips pluton—we suggest that there is no Medial New England basement in this region of New England. Some peraluminous, two-mica plutons have trace element and stable isotopic characteris- tics that are compatible with partial melting of metasedimentary rocks, the components of which were deposited in an anoxic basin such as the Smalls Falls Formation of the Central Maine terrane, but many other plutons have compositions that are inconsistent with this model. We suggest that the compositions of many New Hampshire Plutonic Suite plutons indicate greater heat input than that available from U-enriched metasedimentary rocks and instead require emplacement of mafic mag- mas from the mantle or lower crust. Keywords: Avalon, granites, Grenville, New England. INTRODUCTION The collision of fragments of North Africa– Amazonia with North America in the Devonian and again in the Permian resulted in the Acadian and Alleghanian orogenies in New England (Schenk, 1971; Rast et al., 1976; Williams, 1978; Williams and Hatcher, 1982; O’Brien et al., 1983). With subsequent rifting in the Mesozoic of North Africa–Amazonia from North America, a part of North Africa–Amazonia, known as Avalon, remained attached to North America. Avalon is well exposed in southeastern New Eng- land in the states of Rhode Island, eastern Mass- achusetts, and eastern Connecticut (Zen, 1989). North American, Grenville, or Laurentian base- ment rocks are exposed in several domes of west- ern New England and farther west in the Adiron- dack Highlands of New York. Because of the lack of exposure of Avalon and Grenville rocks in northern New England, there is no agreement on the location of the boundary between the Grenville and Avalon basement terranes in this area. Lyons et al. (1982) pro- posed that the Grenville-Avalon boundary fol- lows the Vermont–New Hampshire boundary along the Connecticut River. Thompson et al. (1993) showed essentially the same boundary. In contrast, work by Harrison et al. (1987) demon- strated that the 350 Ma Long Mountain pluton of north-central New Hampshire contains inherited 900 Regional geochemical and isotopic variations of northern New England plutons: Implications for magma sources and for Grenville and Avalon basement-terrane boundaries Michael J. Dorais* Matthew L. Paige † Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA GSA Bulletin; June 2000; v. 112; no. 6; p. 900–914; 11 figures; 1 table. } *Present address: Department of Geology, Brigham Young University, Provo, Utah 84602, USA; e-mail: dorais@byu.edu. † Present address: U.S. Silica Company, P.O. Box 187, Berkeley Springs, West Virginia 25411. Data Repository item 200063 contains additional material related to this article.