University of New Hampshire University of New Hampshire Scholars' Repository New England Intercollegiate Geological NEIGC Trips Excursion Collection 1-1-1970 Geology of the Lower Paleozoic Rocks in the Boundary Mountain Anticlinorium Harwood, David S. Green, John C. Guidotti, Charles V. Follow this and additional works at: https://scholars.unh.edu/neigc_trips Recommended Citation Harwood, David S.; Green, John C.; and Guidotti, Charles V., "Geology of the Lower Paleozoic Rocks in the Boundary Mountain Anticlinorium" (1970). NEIGC Trips. 133. https://scholars.unh.edu/neigc_trips/133 This Text is brought to you for free and open access by the New England Intercollegiate Geological Excursion Collection at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in NEIGC Trips by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. A-3 1 Geology of the Lower Paleozoic Rocks in the Boundary Mountain Anticlinorium By David S. Harwood .^John C. Greenland Charles V. Guidotti^ Introduction The Boundary Mountain anticlinorium (Albee, 1961) in northern New Hampshire, west-central Maine, and adjacent Quebec consists of a core of pre-Silurian rocks overlain to the northwest and southeast, respectively, by Silurian and Devonian rocks in the Connecticut Valley- Gaspd synclinorium (Cady, 1960) and the Merrimack synclinorium (Osberg, Moench, and Warner, 1968). This trip will examine the highlights of the stratigraphy, structure, and metamorphism of the rocks in the anti­ clinorium, beginning in the Silurian rocks on its southeast flank near Rangeley, Maine, and proceeding westward across its core to a synclinal inlier of Silurian rocks near Parmachenee Lake (fig. 1). Emphasis will be given to the basal Silurian clastic rocks in two widely separated parts of the region and to some of their possible source rocks in the core of the anticlinorium. Before the mid-1950Ts, the geology of this remote woodland area, shown in figure 1 , was known only through the reconnaissance studies of Hitchcook (1877) and Logan (1863). During the past 15 years, however, detailed mapping in the Errol, Second Lake, and Moose Bog quadrangles by Green (1964, 1968), in the Dixville quadrangle by Hatch (1963), in the Oquossoc quadrangle by Guidotti (Maine Geol. Survey, open-file report), and in the Cupsuptic and Arnold Pond quadrangles by Harwood (1966, 1968) has extended the classical New Hampshire stratigraphic sequence worked out by Billings (1937, 1956), into northernmost New Hampshire and west-central Maine. McGerrigle (1935) and Marleau (1957, 1959, 1968) have mapped the rocks in the adjacent part of Québec. Stratigraphy The stratigraphy of the field-trip area is briefly summarized be­ low; more detailed descriptions of the rocks are available in the ref­ erences cited: Aziscohos Formation: (Green, 1964). Lower part is predominantly car­ bonaceous rusty-weathering schist and phyllite composed of quartz, pla­ gioclase, muscovite, biotite, and chlorite with garnet, staurolite, andalusite, and sillimanite present in certain rocks at the appropriate grades of metamorphism. Upper part is green, silvery-green to gray phyllite and schist characterized by abundant stringers and pods of milky-white quartz. In addition to these principal rock types, the formation contains about 10 percent of biotite-quartz-plagioclase gneiss, carbonaceous quartzite, calc-silicate rock, and quartz-spessartite rock. ^Publication authorized by the Director, U. S. Geological Survey. ^U. S. Geological Survey, Washington, D.C. ^University of Minnesota, Duluth. ^University of Wisconsin. Figure 1 - Generalized geologic map of the southwestern part of the Boundary Mountain anticlinorium EXPLANATION A-3 3 c Devonian rocks •Hcd Dr-gray slate and quartzite of Gile Mountain, Seboomook., d o Frontenac, and Compton formations; contains mafic meta > volcanic rocks, Drv P0 d d cd 0 -H a . d Unnamed Silurian rocks Sis-calcareous slate and limestone P •H<H CQ Sc -quartz-pebble and polymict conglomerate S r u S r d 3 ^ ^ — •Hcd d d --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- •— i Rangeley Formation •H - CQ Sr-parts A,B, and C and small amount of Perry Mountain Formation d 0 south of 45th parallel (see Trip A-l) £ O Sru-gray slate, quartzite, and minor polymict conglomerate lenses P Src-quartz-pebble conglomerate and quartzite Srp-polymict conglomerate aid quartzite ___________ UNCONFORMITY ______________ o- d cd 0d -HO a. *h Quimby and Greenvale Cove formations; a > P O undivided TJ od Dixville Formation Odm-Magalloway member; feldspathic graywacke and subordinate slate, d granule conglomerate, and metavolcanic rocks •Hcd a Od -black slate, feldspathic quartzite, and layers of predominantly •H mafic metavolcanic rock > o T3 Odv-predominantly mafic metavolcanic rock Od 0 Albee Formation <73•H Oad-green, gray, black, and purplish-gray slate with minor arenaceous beds Oap-green, gray, and red slate or silvery-gray schist with "pinstripe" quartzite beds d cd d Aziscohos Formation of Green (196A) •Hd •Hcd O OGz-green to silvery-gray phyllite and schist with quartz pods and P •H > stringers O T3 O 0€zr-black to dark gray carbonaceous phyllite and schist, minor d t j U cd d arenaceous and metavolcanic rocks Cu0 o P d P 0 £ o p Devonian intrusive rocks Ordovician intrusive rocks Orodovician serpentinite and related mafic rocks 0-1 X _ Fossil locality Fault . ___________ .k___________ . _____________ . _____ Field trip route showing stops A-3 4 Albee Formation: (Billings, 1937, 1956; see also Green 1964, 1968; Hatch, 1963; Harwood, 1966). South of the 45th parallel the Albee is primarily silvery-gray to greenish- or brownish-gray schist that contains distinctly laminated "pinstripe" quartzite and feldspathic quartzite beds. North of the 45th parallel it is predominantly green to gray-green slate and phyllite with the same diagnostic arenaceous rocks interbedded in variable proportions. In the Cupsuptic quadran­ gle and adjacent parts of the Oquossoc quadrangle, the Albee contains red slate with interbedded "pinstripe" quartzite and green, gray and purplish-gray slate with abundant quartz stringers and scarce arena­ ceous beds. Dixville Formation: (Green, 1964, 1968; Hatch, 1963, Harwood, 1966; Harwood and Berry, 1967). The Dixville consists predominantly of black to dark-gray carbonaceous rusty-weathering schist, phyllite, and slate with interbeds of feldspathic metasandstone and locally calcareous lithic graywacke and minor conglomerate. Mappable patches and layers of mafic and felsic metavolcanic rocks are present at dif­ ferent stratigraphic levels within the black slate. In the northern part of the Second Lake and Cupsuptic quadrangles the upper part of the formation is a heterogeneous collection of feldspathic graywacke, arkosic conglomerate lenses, black, green, and purplish-gray slate, and lenticular patches of metavolcanic rocks mapped as the Magalloway Member (Green, 1968; Harwood 1966). The Magalloway Member is contin­ uous across the international boundary with the Arnold River Forma­ tion of Marleau (1968). Quimby Formation: (Moench, 1969). This formation consists of a lower metagraywacke member that contains interbedded conglomeratic metagraywacke, gray to black slate, and felsic metavolcanic rocks and an upper metashale member that contains cyclically bedded metagray­ wacke and metashale interlayered in equal proportions. Greenvale Cove Formation: (Moench, 1969). Light- and dark-gray meta­ morphosed shale, siltstone, and sandstone are interlayered on a fine scale to produce a characteristically banded rock. The formation locally contains calc-silicate rock and biotite granofels (see Moench and Boudette, Trip A-l, this volume). Rangeley Formation: (Osberg, Moench, and Warner, 1968; Moench and Boudette, this volume). According to R. H. Moench (written commun., 1970) the polymict conglomerate at stop 1 contains well-rounded clasts of felsic and mafic metavolcanic rocks, metamorphosed lamprophyric rocks, vein quartz, metashale, metasiltstone, quartzite, crinoid- bearing limestone, and various granitic rocks, including distinctive medium-grained granodiorite and quartz diorite with blue quartz. In the Cupsuptic quadrangle the polymict conglomerate contains abundant platy fragments of black slate, minor amounts of green slate, boulders of coral-bearing limestone, as well as the clasts listed above for stop 1. Fossil fragments in the matrix and in the limestone boulders in the Cupsuptic area suggest a Silurian age (Harwood and Berry, 1967). Quartz-pebble conglomerate that overlies the polymict conglomerate in the Cupsuptic quadrangle is considered equivalent to similar rocks that contain Early Silurian (C^ -C5 of the Late Llan­ dovery) fossils in the Kennebago Lake quadrangle, reported by E. L. Boudette (U. S. Geol. Survey, 1965, p. A-74). (See Moench and Boudette, this volume). Unnamed Silurian rocks at Parmachenee Lake: (Harwood, 1966, Harwood and Berry, 1967). Gray argillite and tuff interfingers with and un­ derlies quartz-pebble conglomerate containing interbedded purple slate, gray feldspathic quartzite, and one lens of polymict conglomerate. The conglomerate is succeeded by tan-weathering, mottled gray and white well-bedded argillaceous limestone which, in turn, is overlain by tan to greenish-tan pit-weathering fossiliferous