Stratigraphy and ductile structure of the , : Tectonic implications for the Acadian orogeny

J. Dykstra Eusden Jr. John M. Garesche Aaron H. Johnson Jenna-Marie Maconochie Department of , Bates College, Lewiston, 04240 Steven P. Peters Jonathan B. O’Brien Beth L. Widmann }

ABSTRACT mation is interpreted as an olistostromal fected by the Early Devonian Acadian melange and has been subdivided into three orogeny. These rocks are extremely well ex- The Presidential Range of New Hamp- different members and six submembers on posed, thus offering a rare opportunity to shire with its unique high relief contains ex- the basis of lithologic variations in the accurately and clearly describe the complex ceptionally well exposed rocks of the Aca- gneiss and subordinate units. stratigraphic and structural features in this dian orogenic hinterland. These rocks are The Presidential Range preserves three part of the northern Appalachians. Though within the Central Maine terrane, a belt of phases of ductile folding (F1, F2, and F3) the Acadian orogeny has been comprehen- complexly metamorphosed and deformed and a single phase of thrust faulting (T1). sively studied by numerous geologists, Aca- Silurian and Devonian metasedimentary Well-constrained southeast-, east- or north- dian tectonic models remain controversial rocks. The Presidential Range lies between east-facing directions and consistent asym- due to the lack of distinctive lithotectonic regions to the south dominated by refolded metry of F1 nappe limbs suggest that nappe assemblages. Notably absent from the nappes and synkinematic high-grade re- vergence was easterly. Severe refolding of Acadian orogen is obducted ocean crust, gional and regions to the some nappes resulted during F2 collapse accretionary melange, or unequivocal arc northeast dominated by overlapping multi- of the nappe pile. The west-vergent (?) volcanics. Additionally, effects of the Aca- ple deformation and contact metamorphism Greenough Spring thrust truncated F1 dian orogeny vary considerably along the produced by late- and post-Acadian plu- and F2 structures and juxtaposed nonmig- length of the orogen. For example, the Pres- tons. To better understand these complex matized and migmatized rocks. F3 east-ver- idential Range lies between regions to the tectonic variations and, in particular, to gent folding dominates the alpine zone and south dominated by refolded nappes and clearly and accurately determine the effects represents the final tightening of Acadian synkinematic high-grade regional metamor- of the Devonian Acadian orogeny in a well- structures, which occurred after early gra- phism and regions to the northeast domi- exposed region, the bedrock geology in the nitic plutonism and prior to the emplace- nated by overlapping multiple deformation alpine zone of the Presidential Range was ment of postkinematic granitic sheets. and contact metamorphism produced by mapped in great detail. The results of the The structural and sedimentological evi- late- and post-Acadian plutons. Our ap- stratigraphic and ductile structural analy- dence supports the existence of a subduc- proach toward a better understanding of the ses are presented here. tion system that was active beginning in the Acadian orogeny is a combined analysis of Five metasedimentary formations have early Silurian on the east flank of the Bron- the and ductile deformation been recognized and constitute a conform- son Hill Anticlinorium with a west-dipping and the relationship of these geologic ele- able stratigraphy, which, from oldest to subducting slab geometry. This system per- ments to possible tectonic models. We have youngest, are the Silurian (?) Rangeley, sisted throughout the Acadian. done this at a detailed scale to reveal with Perry Mountain, Smalls Falls, and Madrid clarity the nature of deformation in the Ap- Formations, and the Devonian (?) Littleton INTRODUCTION palachian hinterland. Formation. The Littleton Formation has The Presidential Range is located near been subdivided into fifteen different mem- This paper details the results of a five-year the axis of the Central Maine Terrane bers and three submembers based on vari- project to map the bedrock geology in the (Fig. 1; Zen et al., 1986; Rankin, 1994; ations in bedding style of the schists and alpine zone of the Presidential Range, New Thompson et al., 1993; Stewart et al., 1993) quartzites and other lithologic peculiarities. Hampshire. The Presidential Range is an and is near the center of the large area of The Madrid, Smalls Falls, and Perry Moun- important region for geologic study as it Acadian high-grade metamorphism. To the tains Formations are extremely thin, con- contains Silurian and Devonian metasedi- south and east, the Central Maine Ter- sistent with their deposition near the mentary cover rocks that postdate the Tac- rane is bounded by the Massabesic Gneiss Silurian tectonic hinge. The Rangeley For- onic orogeny and have been significantly af- Complex, an outlier of late Precambrian

GSA Bulletin; April 1996; v. 108; no. 4; p. 417–436; 17 figures; 2 inserts.

417 Figure 1. Simplified structural map of New Hampshire showing the location of the study area.

418 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE

Avalonian (?) basement, and the Merri- , the highest wind speed These stratigraphic correlations are used on mack-Harpswell terrane, composed of meta- ever recorded in the world gusted at 231 the bedrock geologic map of New Hamp- sedimentary rocks of uncertain age (possibly mph. Gusts of over 100 mph have been re- shire by Lyons et al. (1992). Silurian to Precambrian) (Rankin, 1994; corded every month of the year (AMC, The Silurian metasedimentary rocks of Thompson et al., 1993; Stewart et al., 1993). 1988) and were frequent throughout the the Presidential Range represent the middle To the west and northwest, the Central field seasons. to distal portion (Moench and Pankiwskyj, Maine Terrane abuts the Bronson Hill An- The Presidential Range, with its unique 1988) of a depositional basin, the Kronos ticlinorium, which represents a magmatic natural environment, has always been a ha- Ocean (Berry and Osberg, 1989), that was arc of Ordovician age, with a cover of thin ven for scientific exploration. Many topo- flanked by the Bronson Hill Volcanic Arc on Silurian and somewhat thicker Devonian graphical features have been named after the west and the microcontinent, Avalon, on sediments. The Central Maine Terrane is re- scientific researchers. Jackson, Huntington, the east (Berry and Osberg, 1989; Bradley, garded as an eastward-thickening succession Hitchcock, and Agassiz were among the re- 1983). Within the deepest portions of the of deep-water turbidites, adjacent to the searchers who worked in the Presidential basin, Silurian deposition accounted for up Bronson Hill Anticlinorium, filled with Si- Range during the 1800s. Many geologists to 3.5 km of siliciclastic and lesser carbonate lurian shales and conglomerates (Rangeley have since studied various aspects of the ge- turbidites, which are covered by up to 2.5 km Formation), quartzose turbidites (Perry ology, and research continues today. We dis- of Devonian turbidites (Hatch et al., 1983; Mountain Formation), anoxic shales (Smalls cuss more recent studies done during this Hatch and Moench, 1984; Moench and Falls Formation), and calcareous turbidites century, including the classic works of Bill- Pankiwskyj, 1988). (Madrid Formation), and topped by early ings and Fowler-Billings. The Silurian Rangeley, Perry Mountain, Devonian turbidites and minor volcanics and Smalls Falls Formations are believed to from an eastern source (Littleton Forma- Previous Work have a southeast sediment transport direc- tion) (Moench and Pankiwskyj, 1988; Han- tion, shed from the eroding Bronson Hill arc son and Bradley, 1989). This basin, together Stratigraphy. Billings (1941) originally (Hanson and Bradley, 1989). The sediments with the Bronson Hill Anticlinorium, was correlated the metamorphic rocks of the of the Madrid Formation were transported multiply deformed and metamorphosed Mount Washington to Silurian and Devo- along the axis of the basin, toward the south- during the large-scale crustal shortening and nian formations 40.2 km (25 mi) to the west west (Hanson and Bradley, 1989). The De- thickening of the Acadian orogeny. in the Littleton– area of vonian Littleton sediments had an overall New Hampshire. Billings et al. (1946), Bill- northwesterly transport direction, toward THE PRESIDENTIAL RANGE ings and Fowler-Billings (1975), and Billings the margin of the pre-Acadian North Amer- et al. (1979) subsequently reassigned all of ican continent (Hanson and Bradley, 1993). The Presidential Range of New Hamp- these metamorphic rocks to the Devonian The basin discussed above essentially de- shire is one of the most popular recreational Littleton Formation, by introducing the scribes an extensional or passive tectonic areas in the Northeast. Culminating with Boott member and splitting the Littleton setting throughout the deposition of the Si- Mount Washington, elevation 1916.5 m Formation into upper and lower members. lurian and Devonian sediments. Although (6288 ft; the highest peak in the Northeast), Hatch et al. (1983) correlated the meta- this model has been widely accepted, it is the Range has an extensive alpine zone sedimentary rocks in the often difficult to rationalize tectonically, as which is criss-crossed by miles of hiking area with a stratigraphic section described the Acadian orogeny occurred immediately trails, an automobile road, and a cog rail- by Moench (1971) in the Rangeley, Maine after the deposition of the Littleton (Naylor, road. The main ridge of the Presidential area, along strike, 80.5 km (50 mi) north- 1971), suggesting that an active convergent Range extends 22.5 km (14 mi) from the east. Hatch et al. (1983) extended the use of plate tectonic setting was most likely in northeast to the southwest and contains the Silurian formational names, Rangeley, place prior to the main collision and during eleven major peaks. Timberline occurs any- Perry Mountain, Smalls Falls, and Madrid, deposition. In fact, recent studies by Bradley where from 1219 to 1585 m (4000 to 5200 ft), southwest into New Hampshire. The Devo- and Hanson (1989) and Hanson and Brad- depending on exposure, and marks the be- nian Littleton Formation was retained in ley (1989) have suggested that the upper ginning of the largest alpine zone in the east- New Hampshire and is approximately cor- Madrid and the Carrabassett Formations in ern United States, extending 14 km (8.5 mi) relative to the Devonian Carrabassett, Hil- central Maine were deposited in an active along the ridge from to dreth, and Seboomook Formations of Maine trench system where these formations broke (Fig. 3,1 below). (Hatch and Moench, 1984). Minor modifi- up into fragments enveloped by a finer- The climate of the Range is similar to that cations to this correlation have subsequently grained matrix. Bradley and Hanson (1989) of northern Labrador. The summits are been made by Hatch and Moench (1984), have termed the broken formations me- cloudy 305 days of the year and socked in by Hatch and Wall (1986), Wall (1988), Lyons langes and/or olistostromes. fog 55% of the time (AMC, 1988). As an et al. (1992), and Allen (1992). Structural Geology. Since Marland Bill- example of the severe weather, hail and near The Silurian and Devonian formations of ings’s (1956) first detailed analysis of the freezing temperatures were not uncommon the stratigraphic section mapped in Range- structural geology in much of New Hamp- throughout the summer field seasons during ley, Maine, have been mapped continuously, shire, including the Presidential Range, this research. On April 12, 1934, atop except where interrupted by plutons, from there has been a significant amount of work Maine through New Hampshire, Massachu- done to devise a structural model that would setts, and into (Hatch et al., explain Acadian structures observed in en- 1Loose insert: Figure 3 is on a separate sheet 1983) and represent the cover sequence tire Central Maine Terrane. However, for- accompanying this issue. stratigraphy for the Central Maine Terrane. mulating a single structural model has

Geological Society of America Bulletin, April 1996 419 EUSDEN ET AL.

Figure 2. Evolution of geologic maps in the Presidential Range. (A) Billings (1941), Billings et al. (1946), and Henderson et al. (1977). (B) Lyons et al. (1992). (C) This study. Abbreviations: big, binary ; D1g, Littleton gneiss; D1s, Littleton schist; D1b, Littleton Boott member; Smsf, Madrid and Smalls Falls. Other symbols and abbreviations explained in Figures 3 and 4 on the loose inserts.

proved to be a difficult task. As an illustra- minates in a major asymmetric anticline, Allen (1992) working in the Pinkham tion of the difficulty in reaching consensus without any large-scale overturning or Notch area suggested that the original struc- on the regional sequence of deformations, nappe-like recumbent structures (Fig. 2). ture of the metasedimentary rocks, now the reader is referred to four significantly Hatch and Moench (1984) and Hatch and migmatized, appears to have been one of different models that have been proposed Wall (1986) recognized multiple phases of large-scale, east-vergent isoclinal fold for the Central Maine Terrane of New deformation in the metasedimentary rocks nappes (F1), refolded by tight, upright an- Hampshire and Maine, all purported to be exposed in the Presidential Range. A per- ticlinal and synclinal folds (F2), with axes applicable to the rocks exposed in the Pres- vasive schistosity, in many cases axial planar plunging shallowly alternately to the north- idential Range (Moench and Pankiwskyj, to early isoclines, is characteristically re- east and to the southwest. Within the mig- 1988; Robinson et al., 1991; Osberg et al., folded by open folds with north-striking, matites, however, this earlier structure is 1989; and Eusden and Lyons, 1993). Gen- steeply dipping, axial plane cleavage sur- disrupted, skewing F1 fold axes. erally, these models consist of sequences of faces (Hatch and Moench, 1984). As the focus of this paper is on the stratig- superposed folding and faulting associated In a regional compilation for the state of raphy and structural geology of the Acadian intimately with syn- and/or postkinematic New Hampshire’s bedrock geologic map, orogeny, no detailed summary of the meta- metamorphism. There appears to be signif- Lyons et al. (1992) further modified the morphic and plutonic history is given here. icant across- and along-strike variations in maps of Hatch and Moench (1984) and Bill- The reader is referred to summaries by Os- these sequences. ings (1941). The contact between the Smalls berg et al. (1989), Rankin (1994), Thompson Billings (1941) and Billings et al. (1979) Falls/Madrid and Rangeley Formations is et al. (1993), Guidotti (1989), Lux et al. described the structure of the Presidential shown as a normal fault with the Littleton/ (1986), De Yoreo et al. (1989), Tracy and Range as being the product of a single phase Smalls Falls/Madrid stratigraphy in the up- Robinson (1980), Robinson et al. (1989), of both major and minor asymmetrical, per plate. Figure 2 shows the evolution of Chamberlain and Robinson (1989), and plunging, en echelon folding (Fig. 2). In Bill- the various geologic maps made of the Pres- Carmichael (1978). In the Presidential ings’s (1941) model, Mount Washington cul- idential Range. Range, Allen (1992), Billings (1941), Bill-

420 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE ings et al. (1979), Fowler-Billings (1944), when reading the subsequent sections of this bedding style of the schists and quartzites Henderson (1949), and Wall (1988) have all paper. The geologic map (Fig. 3), cross sec- and any other lithologic peculiarities (see examined various aspects of the metamor- tions (Fig. 4), and structural maps (Figs. 5 Figs. 7 and 4). Representative, typical litho- phism and plutonism. and 6) are the essence of the results of this logic types used to subdivide the Littleton project. are, in no particular order, (1) massive METHODS The mapping done in the alpine zone de- schist; (2) rhythmically bedded, thin-bedded lineated four different geographic domains, schist and quartzite, the couplet being Mapping of the alpine zone in the Presi- each with distinctive stratigraphy, structure, ϳ3–10 cm in thickness; (3) well-bedded dential Range took place during the months and petrology. From north to south the do- schist and quartzite with graded bedding of July and August from 1989 to 1993. A mains are (1) the northern Presidential preserved, and quartzites generally between total of ten months were spent in the field. Range, (2) the Clay klippe, (3) the Mount 10 and 50 cm in thickness; (4) well-bedded Mapping was done at a scale of 1:3048 using Washington area, and (4) the southern Pres- schist and quartzite with graded bedding the maps of Washburn (1988). Approxi- idential Range. We present the stratigraphy preserved, and quartzites generally between mately 85% of the exposed bedrock was sur- and structural geology of the area first, 50 and 100 cm in thickness; and (5) massive veyed in the alpine zone. The remaining followed by a discussion of possible quartzites at least 1 m, and up to several 15% was either only accessible through correlations. meters, in thickness, with thin, up to 10 cm technical climbing (which was not at- thick, interbeds of schist and occasional tempted) or essentially ‘‘guarded’’ by steep Stratigraphy graded bedding. Outcrop photographs of slopes covered by virtually impenetrable these lithologic units and examples of krumholtz. General Statement. Five metasedimen- graded beds are shown in Figure 8. Other Standard equal area stereographic projec- tary formations have been recognized in the unique, generally rare lithologic types found tions of the field measurements were gen- alpine zone. They constitute a conformable in the Littleton Formation throughout the erated for all data using the program Ste- stratigraphy, which, from oldest to youngest, alpine zone are (6) 1- to 5-cm-thick, discon- reonet (see Acknowledgments). The final consists of the Silurian (?) Rangeley, Perry tinuous stringers and lenses, up to a meter map, Figure 3,1 was digitally drawn over Mountain, Smalls Falls, and Madrid Forma- long, of pink garnet and quartz layers, re- Washburn’s topographic map at a scale of tions, and the Devonian (?) Littleton For- ferred to hereafter as garnet coticules; (7) 1:15 000. The reduction in size was done to mation. The stratigraphy is unfossiliferous, moderately rusty brown weathering lenses in make the map more manageable for publi- and assigned ages are based on lithologic the massive quartzites; (8) very rare calc- cation. During the transfer of scale from correlations; thus, queries are given after silicate lenses; and (9) an extremely rare 1:3048 to 1:15 000, approximately 35% of the age assignments. Within the northern quartz pebble conglomerate horizon. All the data collected had to be omitted, as it Presidential Range and Clay klippe, only contacts between the members and sub- would otherwise be too crowded. All of the partial sections of the stratigraphy are pre- members of the Littleton shown in Figure 3 structural data are, however, incorporated served. The missing sections are cut out by a are gradational. Stratigraphic order of the in the stereographic projections. discontinuity interpreted to be a thrust fault. Littleton members is exceptionally well con- Five cross sections were constructed (see The Mount Washington area and southern trolled by the graded bedding. Fig. 4).2 All sections not perpendicular to Presidential Range are stratigraphically Madrid Formation. The Madrid Forma- the strike have been corrected for apparent contiguous. A description of the five forma- tion is a fine-grained, thinly laminated, dip. Stations not on the sections were pro- tions and stratigraphic columns for each do- granofels with well-defined alternating lay- jected parallel to strike until they inter- main is given below (Fig. 7). ers of biotite-rich, schistose granofels and sected the section line. Shapes of folds, Littleton Formation. The Littleton For- calc-silicate-rich granofels. The individual drawn using field observations as a guide, mation consists of dark gray schists com- layers of granofels are from 1 to 5 cm thick. are based on similar fold theory. There is no monly with interbedded, fine-grained, light No graded beds were found. The formation vertical exaggeration to the sections. To gray, and granoblastic quartzite layers of weathers to a dark greenish-gray and is char- fully assess the effects of the multiple phases varying thickness and abundance. Andalu- acteristically broken into platy fragments, of deformation in the range, separate maps site, generally completely pseudomorphed giving it a flaggy appearance. Total thickness were constructed for the D1 (Fig. 52) and by muscovite, sillimanite, and sericite, is of the formation varies between 10 and 50 D3 (Fig. 62) phases of deformation. As in common in the schists forming lumps, ϳ1–3 m. The contact between the Littleton and the case for the bedding and foliation data cm in diameter, and elongate aggregates, Madrid is abrupt and marked by the first plotted in Figure 3, not all of the collected from 1 to 15 cm in length, with rare relict appearance of the granofels. Within the data related to D1 and D3 could be plotted cores of fresh pink andalusite and/or chias- granofels are one or two predominately on the reduced scale. tolite crosses. Schistosity is well developed schistose horizons, up to 2 m thick, that re-

RESULTS and is usually parallel to bedding. In F1 fold semble the Littleton. hinges, bedding and schistosity become Smalls Falls Formation. The Smalls Falls The reader is encouraged to have Fig- oblique to each other. Graded beds, re- Formation is a well-foliated schist with dis- ures 3, 4, 5, and 6 (on loose inserts) at hand versed in grain size by high-grade metamor- tinct red-brown rusty weathering. The for- phism, are common throughout the mation has a dark gray to black fresh sur- formation. face, is highly susceptible to weathering, as a 1Loose inserts: Figures 3, 4, 5, and 6 are on two separate sheets accompanying this issue. The Littleton Formation has been subdi- result is often poorly exposed, and breaks 2Loose insert: Figures 4, 5, and 6 are on sepa- vided into fifteen different members and into platy fragments generally smaller then rate sheets accompanying this issue. three submembers based on variations in those of the Madrid. Quartzite makes up

Geological Society of America Bulletin, April 1996 421 Figure 7. Representative stratigraphic columns in the study area. Formation abbreviations explained in Figure 3.

422 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE



Figure 8. Photographs of the principal lithologic variations in the Littleton Formation. A. Massive pseudo-andalusite schist, L1 and S1 well developed. B. Thin, rhythmically bedded schist and quartzite. C. Well-bedded, poorly graded schist and quartzite. D. Thickly bedded schist and quartzite showing an inverted graded bed. E. Thick, massive quartzites with thin schist beds showing an inverted graded bed. E

Ͻ5% of the unit, with layers up to 5 cm in about 10 m: the rusty schist giving way to quartzites that are commonly 4–10 cm in thickness. These beds are generally weakly progressively less rusty weathering, schis- thickness. Quartzites make up 30% to magnetic due to the presence of pyrrhotite. tose granofels, and then ultimately to non- 40% of the unit and can be up to 60 cm No graded beds are found. Total thickness rusty granofels of the Madrid. thick. The contact between the Smalls of the formation varies between 10 and 50 Perry Mountain Formation. The Perry Falls and Perry Mountain is abrupt. The m. The contact between the Smalls Falls and Mountain Formation is a dark gray schist unit is discontinuous ranging between 0 Madrid Formations is gradational over with interbedded light gray to white and 75 m in thickness. It is only exposed in

Geological Society of America Bulletin, April 1996 423 EUSDEN ET AL.



Figure 9. Photographs of olistostromal facies in the Range- ley Formation. A. Rectangular, well-bedded calc-silicate granofels lens in migmatite. B. Ellipsoidal, concentrically zoned calc-silicate lens in migmatite. C. Nonmigmatized olistostromal facies. D. Complete disaggregation in nonmigmatized facies; pelitic clasts in psammitic matrix. E. Complete disaggregation in nonmigmatized facies; psammitic clasts in pelitic matrix. E

the and lenses (clasts?), 0.5–2 m–long, of well-bed- in these rare locations no graded bedding is region. ded calc-silicate granofels, and ellipsoidal found. In places, the gneiss is extensively in- Rangeley Formation. The Rangeley For- lenses (clasts?), 10–50 cm long, of concen- jected by pegmatites, aplites, and granite. mation is a gray migmatitic paragneiss with trically mineralogically zoned calc-silicate The calc-silicate lenses are most often abundant calc-silicate lenses. Angular to granofels without bedding are common aligned parallel to schistosity, but some are subrounded quartz and/or feldspar segrega- throughout the Rangeley. A few beds of at slight angles or, in the extreme, perpen- tions (clasts?) between 2 and 8 cm in diam- schist and quartzite are sometimes pre- dicular to schistosity. Figures 9A and 9B eter are common. Elongate, rectangular served, having escaped migmatization, and show two examples of calc-silicate lenses in

424 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE outcrop. The Rangeley Formation has been Northern Presidential Range is separated verely refolded. This is seen clearly in Fig- subdivided into three different members and from the Mount Washington area by the ure 3 and especially cross section C–CЈ. This six submembers based on lithologic varia- Clay klippe, it is impossible to correlate fold is further complicated by a bifurcation tions in the gneiss and subordinate units of these two sections of the Littleton in the vicinity of the Alpine Garden (Fig. 3). rusty gneiss, rusty schist, calc-silicate grano- Formation. The main branch of the syncline trends fels, and amphibolite. Because the Rangeley south and a subsidiary branch trends east. is devoid of graded beds throughout the Structural Geology At the bifurcation, the Raymond Cataract Presidential Range, stratigraphic order is nappe intervenes and trends southeast. This based on the uninterrupted juxtaposition of General Statement. The alpine zone of unusual geometry represents one possible the younger Smalls Falls, Madrid, and the Presidential Range preserves three solution to the available data, which include Littleton Formations. Where this juxtaposi- phases of ductile folding (F1, F2, and F3) fold facing directions, the locations of F1 tion is not available, as is the case for the and a single phase of thrust faulting (T1). hinge zones, and topping indicators. The Clay klippe, the internal stratigraphic order An analysis of the brittle structures, consist- southern Presidential Range is dominated of the Rangeley is indeterminate. The con- ing of abundant joints and rare, brittle, nor- by the Mount Washington nappe. The axial tact with the Perry Mountain is gradational, mal faults with negligible offset, was not trace of this F1 nappe is drawn on marked by the first appearance of calc-sili- done for this study. The phases of folding the basis of stratigraphic repetition with- cate lenses. The contact with the Smalls and the thrust faulting are treated as dis- in the migmatized Rangeley Formation and Falls, when the Perry Mountain is missing, is crete, distinct phases of deformation, each is the F1 fold with the least control. abrupt. with a unique set of fabrics or geometric Bedding, as shown on the equal-area con- The southeast-facing, unnamed cirque be- characteristics. This method of data presen- toured poles to S0 of Figure 10A, has an tween Mounts Franklin and Monroe has ex- tation does not rule out the possibility that average orientation of 178Њ,34ЊW. A cylin- posures of nonmigmatized Crawford Mem- the phases of folding and faulting may rep- drical best fit of the data yields a calculated ber of the Rangeley Formation. It is shown resent a continuum of deformation that was fold axis of 272, 29. This fold axis is similar in Figure 3 enclosed by a dashed line with time transgressive. The sequence of defor- to the orientations of many of the F1 and F3 gray teeth on the migmatized side. This mations will be discussed from oldest to folds measured in the study area, suggesting boundary represents a migmatite front, with- youngest. that S0 was considerably reoriented by both in which are nonmigmatized, intact beds of D1 Deformation. According to field ob- D1 and D3. schist, quartzite, and calc-silicate of the servations, the first phase of deformation is The axial surface schistosity of the F1 Crawford Member that gradually disaggre- characterized by reclined to recumbent, iso- folds, S1, is defined by aligned muscovite, gate and become separated into isolated clinal, similar, cylindrical F1 folds. Meso- biotite, and sillimanite in the pelitic schists blocks within a pelitic matrix. Some areas scopic F1 folds have amplitudes of up to sev- and gneisses and by aligned biotite and ac- also show a psammitic matrix with pelitic eral meters and wavelengths of up to 10 m. tinolite in the calc-silicates. S1 has an aver- blocks. Figures 9C, 9D, and 9E show out- Macroscopic F1 folds have amplitudes of age orientation of 185Њ,36ЊW (Fig. 10B). crop photographs of the broken formation. ϳ1 km, and wavelengths of up to 3 km (es- The similarity of this orientation to the av- The blocks within the nonmigmatized zone timates based on cross sections of Fig. 4). erage orientation of S0 is evidence for the have sharp, angular edges. Bedding in the Five F1 anticlines or nappes have been isoclinal nature of the F1 folds; S1 is parallel calc-silicates is truncated by the matrix. mapped: (1) the King Ravine nappe, (2) the to S0 in the vast majority of outcrops mea- Stratigraphic Summary. The northern Edmonds Col nappe, (3) the Mount Wash- sured. A cylindrical best fit of the data yields Presidential Range consists entirely of the ington nappe, (4) nappe, and (5) a fold axis of 220, 23. This fold axis is similar Littleton Formation and has been subdi- the Raymond Cataract nappe. Four F1 syn- to the orientations of the majority of F3 vided into seven members and two submem- clines have also been mapped: (1) the hinges measured in the study area. It ap- bers (Fig. 7). The total minimum thickness is Mount Madison syncline, (2) the Israel pears that F3 folding is responsible for the ϳ1250 m. The Clay klippe consists entirely Ridge syncline, (3) the Mount Jefferson syn- present distribution of the S1 data. of the Rangeley Formation. The total min- cline, and (4) the Tuckerman Ravine syn- The locations of the F1 axial traces imum thickness is ϳ550 m. One member cline. These folds deform bedding, SO. No (Fig. 3) are well constrained by multiple ex- and two submembers are recognized in this earlier fabric (schistosity or cleavage) has posures of the F1 hinge zones. The only ex- domain. The stratigraphic order is uncertain been observed to be folded by the F1 struc- ception to this is the Mount Washington due to lack of graded beds. Figure 7 shows tures. As a result, we are confident that the nappe in the southern Presidential Range. the stratigraphic column of this domain ar- F1 folds represent the earliest phase of duc- All of the remaining F1 folds have a remark- ranged from the structurally highest to low- tile deformation in the study area. ably consistent fabric geometry in the hinge est. The Mount Washington area and the The distribution of the F1 folds in each of zones; the bedding, SO, is perpendicular, or southern Presidential Range are stratigraph- the geographic domains is unique. In the at least, nonparallel to the axial planar schis- ically connected (Fig. 7) and consist of the northern Presidential Range the five mac- tosity, S1, of the folds. In these regions, Littleton Formation (subdivided into eight roscopic F1 folds are shown as discrete axial joined strike and dip symbols (for S1 folia- members and one submember), the Madrid traces in Figure 3. An examination of cross tion and S0 bedding), indicative of outcrops Formation, the Smalls Falls Formation, the section A–AЈ shows minor refolding of these containing two nonparallel fabrics, are seen Perry Mountain Formation, and the Range- structures without severe reorientation. No (Fig. 3). Figure 11 shows several outcrop ley Formation (subdivided into two mem- F1 folds have been recognized in the Clay photographs of F1 hinge zones. Within the bers and four submembers). The total min- klippe. In the Mount Washington area, the F1 fold limbs, bedding, SO, is consistently imum thickness is ϳ2900 m. Because the Tuckerman Ravine syncline has been se- parallel to the axial planar schistosity, S1,

Geological Society of America Bulletin, April 1996 425 Figure 10. Equal area stereographic projections. (A) Contoured poles to bedding, S0. (B) Contoured poles to schistosity, S1. (C) L1 pseudo-andalusite lineations. (D) F1 fold axes. (E) F3 fold axes. (F) Contoured poles to S3 axial plane cleavage. C.I., contour interval; n, number of samples.

426 Geological Society of America Bulletin, April 1996 Figure 11. Photographs of F1 hinge zones in the Littleton For- mation showing the relationships between bedding (S0), foliation (S1), and facing direction (TOPS). A. The Horn nappe hinge zone. B. The Horn nappe closer to the F1 limb. C. Tuckerman Ravine syn- cline hinge zone.

Geological Society of America Bulletin, April 1996 427 EUSDEN ET AL.

Littleton Formation, and within the Little- ton Formation there exist members where L1 is well developed and other members where only lumpy, unaligned, pseudo-anda- lusites are found. Figure 13 shows a typical outcrop photograph of the L1 lineation. Most of the lineations are large, up to 10 cm long, 0.5–1 cm in diameter, chiastolitic an- dalusite, replaced by sericite, muscovite, and/ or sillimanite. A minority of lineations, prin- cipally in the Bigelow Lawn member of the Littleton in the vicinity of Lakes of the Clouds Hut, are composed of smaller, 1–5 cm long, no greater than 0.5 cm in diameter, aggregates of sericite, muscovite, and/or sil- limanite, replacing former andalusite. As no relict chiastolite crosses are seen in these smaller lineations, it is possible that they were once sillimanite and not andalusite. The lineations define a girdle or lineation Figure 12. Photograph of recumbent F1 mesoscopic fold hinge in The Horn nappe hinge plane that has an orientation of 8Њ,34ЊW zone, showing bedding (S0), foliation (S1), and facing direction (TOPS). (Fig. 10C). The maximum along this linea- tion plane is oriented 231, 2; we interpret this to be the average orientation of L1 in and upright on the upright limb, and in- moderately to steeply west-dipping inverted the alpine zone. Whenever L1 lineations are verted on the inverted limb. limbs. This asymmetry, when linked with the observed together with F1 fold axes, the two Mesoscopic F1 folds are only found in the predominant easterly facing direction of the fabrics are parallel (see Figs. 5 and 10D). As macroscopic F1 hinge zones, and, even in F1 hinge zone, strongly suggests that the such, the lineations are best classified as b- these localities, mesoscopic folds are rare. In vergence of these F1 structures was toward type lineations. Figure 5 the few localities where they are the east. More specifically, F1 folds have D2 Deformation. The second phase of found are shown by double-lined arrow sym- northeast, east, or southeast vergence. We folding is based on the map pattern (Fig. 3) bols. Figure 12 shows one of the rare F1 interpret the west- and southwest-facing F1 and systematic variations in the attitude of mesoscopic folds in outcrop. There are no portions of the Tuckerman Ravine syncline S0 and S1 fabrics. Only three mesoscopic F2 mesoscopic F1 folds in the F1 limbs. These to have been reoriented by the second phase fold hinges have been observed in the study observations suggest that the ductility of the of folding, D2, which is discussed in more area. The general style of folding is charac- D1 phase of deformation was not great detail below. terized by open, moderately to gently south- enough for minor folds to develop within the Another fabric associated with F1 folds is west- or south-plunging, moderately to F1 limbs and also not sufficient for abundant abundant L1 pseudo-andalusite lineations steeply inclined folds, without an axial pla- mesoscopic folds to develop in the macro- (Fig. 5). L1 lineations are restricted to the nar foliation. The mesoscopic and macro- scopic hinges. This is in apparent contrast to the majority of F1 recumbent nappe struc- tures in the Central Maine Terrane where minor F1 folds are not restricted to the fold hinges. When the appropriate well-bedded schist and quartzite lithologic units with graded bedding are exposed in the hinge zones of the macroscopic F1 folds, facing directions of the folds can be established. The facing direction of the beds in these hinge zones is consistently northeast, east, or southeast. Only in the region between the four-mile post on the Mount Washington Auto Road and the Nelson Crag Trail at treeline are there west- and southwest-facing F1 hinge zones in the Tuckerman Ravine syncline. The asymmetry of the F1 folds, as typified by the northern Presidential Range cross section, A–AЈ, shows long, gently to moder- Figure 13. Photograph of L1 pseudo-andalusite coarse-grained lineations within massive ately west-dipping upright limbs, and short, schist block.

428 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE scopic F2 folds always deform both S0 and sively injected by two-mica , within west margin of the klippe. The nature of this S1 fabrics. the klippe. (4) As the boundary is ap- refolding will be discussed below. The most significant and obvious F2 struc- proached, the pseudo-andalusites in the D3 Deformation. D3 deformation is the tures are macroscopic F2 folds that are best Littleton Formation become flattened. (5) most common and abundant phase of fold- seen in Figure 3. There are three areas There is a significant stratigraphic disconti- ing seen in the alpine zone. F3 folds are where these folds have been observed. In nuity across the boundary: the Smalls Falls characterized as mesoscopic, moderately in- the northern Presidential Range, an unusual and Madrid Formations are cut out. Though clined to overturned, generally gently but of- contortion of the west limb of the Israel these criteria strongly support the existence ten moderately plunging, asymmetric folds Ridge F1 syncline (see Figs. 3 and 4, cross of a fault, no exposures of the fault have (Fig. 14). The F3 folds have no, or only a section A–AЈ) is believed to be an F2 fold been found. The lack of shear zones re- weakly developed, axial planar S3 cleavage. pattern. This is a region where rare easterly lated to the fault precluded any kinematic Fractures often develop parallel to the S3 dips of S0 and S1 fabrics have been ob- analysis. axial plane. Despite the widespread, readily served, which we attribute to F2 folding. The position of the interpreted thrust observed, mesoscopic effects D3 has on the Within the Clay klippe, macroscopic F2 fault shown in Figure 3 is well controlled by rocks, F3 folds are relatively poorly repre- anticlinal axial traces are shown in Figures 3 abundant exposures on the ridge and the sented at the macroscopic scale (Fig. 6). and 4, cross section B–BЈ. These are based east faces of separating Little- S3 is remarkably consistent in orientation on a consistent variation of S0 and S1 fabrics ton schists from Rangeley gneisses. In the throughout the alpine zone. Figure 10F within the Rangeley Formation. Within the region and west flank of Mount shows the contoured poles to S3. The aver- steep gullies on the east flank of Mount Clay, the thrust is drawn based on mapping age S3 orientation is 8Њ,40ЊW. Clay, these fabrics change frequently from a of the large blocks in the alpine felsenmeer Although S3 surfaces are consistent in northeast strike with a northwest dip to an or block field, and on reconnaissance map- orientation, F3 axes are clearly not east strike and south dip. The calculated ping along the floor of Great Gulf, out of the (Fig. 10E). They define a girdle following fold axis, based on a cylindrical best fit of study area. the average S3 surface. The distribution of poles to S0 of the Rangeley, has a trend and It is possible that this discontinuity is a F3 axes along the S3 surface can be inter- plunge of 247, 33. This is consistent with the normal fault and not a thrust fault. The cross preted as either a sheath-fold geometry, or a geometry of rare mesoscopic F2 folds found section B–BЈ could be redrawn and still obey geometry created by the superposition of F3 in the same region, near Spaulding Lake. the available data. In so doing, the main por- cylindrical folds on the earlier F1 nappe- The most spectacular F2 macroscopic tion of the fault would become antiformal, stage folds. The latter possibility is favored structure is in the region that includes Hun- the Clay region would be a fenster, and the because only mesoscopic, cylindrical folds tington Ravine, the auto road, and the Nel- discontinuity would become a normal fault. are seen in the alpine zone. Furthermore, in son Crag Trail. A broad partial dome, the The thrust option is preferred here because the vicinity of some of the F1 axial traces, F3 Chandler Ridge dome, ϳ2 km wide, can be this fault developed in the midst of the Aca- axes rotate as they cross the F1 fold hinges. seen in Figure 3 and in cross section C–CЈ of dian compression, after peak metamor- A good example of this rotation can be seen Figure 4. The dome is defined by the con- phism and F2 folding but before F3 folding in Figure 6 in the northern Presidential tacts of the Littleton members, the reorien- and static contact metamorphism. Dropping Range, near Mounts Adams and Madison. tation of S0 and S1 fabrics, and F1 fold axial down the younger, cooler Littleton schists On Mount Madison, the F3 folds trend traces. The northwestern margin of the and quartzites, on top of the older, hotter south-southwest and plunge moderately. dome is out of the alpine zone and was not Rangeley Formation gneisses, via a low-an- They progressively rotate in trend from mapped. Available data indicate the domal gle detachment fault, would be geologically southwest to west to northwest as Mount axis trends and plunges to the south-south- less likely than bringing the hot Rangeley Adams is approached. This zone of rotation east. A reversal of plunge to the north- rocks up on top of the cooler Littleton with is related to a noncoaxial phase of D3 re- northwest in the unmapped portion of the a thrust fault. Certainly, if this fault were folding of the King Ravine F1 nappe. There dome cannot be ruled out. premetamorphic, and pre-F1 in age, a nor- are, in addition, many other regions of com- T1 Thrusting, Greenough Spring Fault. mal fault or gravity slide active in the Silu- plete or partial F3 axis rotation throughout The area including Mount Clay and Great rian and Devonian depositional basin would the alpine zone (Fig. 6). Gulf is interpreted to be a klippe (the Clay be a distinct possibility. F3 mesoscopic folds are not uniformly klippe) composed of Rangeley Formation The discontinuity dips northwesterly on distributed throughout the study area. All gneisses, separated from the Littleton For- both the northwest and southeast flanks of areas show some F3 folding, but in places it mation to the north and south by the the klippe. A nontraditional symbol (invert- is distinctly more pervasive than in others. Greenough Spring thrust fault. We believe ed teeth) is used for the thrust fault along The distribution of F3 folds can be seen in this to be a thrust fault and klippe for the the northwest flank of the Clay klippe (see Figure 6, and zones of intense F3 folding are following reasons. (1) The F1 folds in the Fig. 3) to indicate that the fault is inverted indicated in Figure 3 where minor asymmet- northern Presidential Range and Mount there. The fault eventually becomes upright ric folds are shown along the mapped Washington area are truncated at the on the southeast flank of the klippe (the contacts. boundary. (2) The F2 folds within the klippe usual thrust fault symbology is shown there) This distribution appears to be related to are also truncated at the boundary. (3) The as it is severely refolded by an F3 synform. lithologic variations in the Littleton and boundary separates different metamorphic On the west edge of cross section B–BЈ, the Rangeley Formations and the propensity of grades: sillimanite zone metamorphism in fault is hypothesized to become upright certain members to develop F3 folds. For the northern Presidential Range and Mount again based on the discovery of an F3 anti- example, F3 folds are rare in the Edmonds Washington regions, and migmatites, exten- form located immediately beyond the north- Col massive schist, all exposures of Littleton

Geological Society of America Bulletin, April 1996 429 EUSDEN ET AL.


Figure 14. Photographs of mesoscopic F3 folds. A. F3 fold in well-bedded schist and quartzite of the Littleton Formation on J. Q. Adams south face; isolated patch of snow on steep face -is about 10 ؋ 10 m. B. F3 folds with characteristic west-over east asymmetry, folding both bedding (S0) and foliation (S1); Cragway Spring on the Auto Road. C. F3 folds of an aplite sill injected into Littleton Formation schists, below Cragway Spring.


Formation massive quartzites, and the Thus, D3 deformation, and the F3 folds cre- diately northwest of the klippe is only Mounts Clay, Crawford, and Eisenhower ated by it, is east vergent throughout the al- slightly better controlled. In this region member migmatites. On the other hand, F3 pine zone. (Sphinx Col, see Fig. 4) S1 fabrics show re- folds are superbly developed in the thinly Pegmatite and alpite veins, dikes, and sills orientation that is consistent with folding by bedded Mount Madison member, the pri- seen throughout the alpine zone are folded F3. Topping direction of graded beds is also marily schistose Bigelow Lawn member that by F3 (Fig. 14C). These small plutonic consistent with the refolding of the Ed- has thin interbeds of quartzite, and the apophyses are presumably related to the monds Col nappe as shown in cross section thinly laminated Crawford and Eisenhower larger plutons mapped in the alpine zone. B–BЈ. calc-silicate granofels members of the Therefore, these granitic rocks must have In the Chandler Ridge dome, as seen in Rangeley. It is interesting to note that the been emplaced prior to D3 deformation. cross section C–CЈ, an F3 antiform and syn- areas with well-developed F3 folds also have There is a nonuniform distribution of form wrinkle the crest of the dome. The lo- well-developed L1 lineations. Though these macroscopic F3 folds in the alpine zone. F3 cations of the axial traces of these folds are two fabrics developed at different times in macroscopic folds are largely absent in the entirely based on the mapped contact and the structural sequence, the rheological na- northern and southern Presidential Range, consistent variation in attitude of S0 and S1 ture of the bedrock where F3 folds and L1 significantly affect the Clay klippe, and mod- fabrics. The timing relationship between D3 lineations are well developed must have erately affect the Chandler Ridge dome and and the formation of the dome can be been roughly the same. Tuckerman Ravine syncline in the Mount readily observed in Figure 4. The D2 dome F3 folds typically have long, moderately Washington area (see Figs. 3 and 4). pattern is clearly folded by the F3 folds. dipping west limbs and short, steeply dip- In the Clay klippe, an F3 synform folds In the Bigelow Lawn region, some of the ping east limbs. In some instances, the east the Greenough Spring thrust fault and the map pattern (Fig. 3) is controlled by F3 meso- limbs are overturned. This asymmetry gives klippe. The position of this axial trace is only scopic folding. The isolated patches of a west-over-east sense of rotation, a pattern loosely delimited, based entirely on the Smalls Falls and Madrid Formations and the that is seen in all F3 folds in the alpine zone. mapped pattern of the fault and the inter- Great Gulf member occupy the core of an We interpret this rotation sense to be re- pretation that the fault is folded. The posi- F3 synform and antiform respectively (see lated to the tectonic vergence of these folds. tion of the macroscopic F3 antiform imme- cross section D–DЈ).

430 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE

Anomalous F3 folds with east-dipping ax- variations exhibited by the members of the er-parallel extension with progressive frag- ial surfaces were found on the south side of Littleton Formation in the alpine zone, we mentation of intact sandstone turbidite the Mount Washington summit cone (see interpret these rocks to have formed as ma- beds. In the southeast-facing, unnamed cir- Fig. 4). The reason for the peculiar orien- rine turbidites in a slope/rise environment. que between Mounts Franklin and Monroe tation of these F3 folds is not clear. Though Because turbidite facies transitions are rou- (Fig. 3), exposures of nonmigmatized Craw- they have the same fold form as most F3 tinely documented in most marine sedimen- ford member show the beginning stages of folds, they record opposite asymmetry (east tary successions, it is extremely difficult to disruption where intact schist, quartzite, and over west). It is possible these are F3 folds make anything but ambiguous correlations calc-silicate layers are preserved. The stiff that have been reoriented by a later phase of between the Littleton members that are layers gradually become fragmented and deformation. Alternatively these folds may physically separated by the Clay klippe. His- then completely broken and isolated (see define a region of relatively minor antithetic torically, the Littleton has been divided into Figs. 9C–9E). The same process can be in- F3 folding. The latter interpretation is a lower (massive schist) and upper (well- voked for the migmatized Rangeley, where favored. bedded schist and quartzite) members evidence for severe disruption is manifest by (Lyons et al., 1992). However, such a simple isolated calc-silicate lenses, containing well- DISCUSSION subdivision is clearly not the case in the preserved bedding, surrounded by gneisses Presidential Range. As seen in Figure 7, (see Fig. 9A). Stratigraphic Correlations abundant quartzites and well-bedded units The Eisenhower member amphibolites of and Implications are generally well distributed throughout the Rangeley Formation consist of exotic the stratigraphic column. blocks incorporated into the gneisses, per- The metasedimentary rocks of the Presi- haps by one of the following mechanisms: dential Range have been correlated to the Madrid, Smalls Falls, and Perry (1) a diapiric melange (Orange, 1990) bring- Silurian and Devonian Central Maine Ter- Mountain Formations ing the blocks up through the stratigraphy rane cover sequence. Based on estimates from the underlying Ordovician Ammo- from the cross sections (Fig. 4), the maxi- The relatively thin 20–100 m total thick- noosuc volcanics; (2) the intrusion of a small mum total thickness of the highly strained ness of Madrid and Smalls Falls Formations basalt flow or sill through the gneisses and Silurian and Devonian metasedimentary in the alpine zone is likely due to the prox- its subsequent breakup; or (3) the incorpo- rocks in the alpine zone is in the range of imity of this region to the Silurian tectonic ration of Ammonoosuc volcanics from chan- 3500 Ϯ 500 m (see also Fig. 7). The Range- hinge. The depositional setting for these two nel walls during rapid turbidite deposition. ley is the thickest formation at ϳ2000 m, but formations has been well described by Regardless of the mechanism invoked, the it must be even thicker, as the base is not Moench and Pankiwskyj (1988). They envi- presence of exotic blocks is consistent with observed. Because bedding is only rarely sion a euxinic basin with a reducing envi- the interpretation that the Rangeley Forma- preserved in the Rangeley, this thickness is ronment as the site of Smalls Falls deposi- tion is an olistostromal melange (Cowan, a structural not a stratigraphic thickness. tion. This was followed by an abrupt change 1985; Hsu¨, 1968; Orange, 1980; Lash, 1987). The estimated total thickness of the Perry marked by the arrival of the calc-silicate We also believe that the wispy biotite-rich Mountain, Smalls Falls, and Madrid Forma- granofels (more oxygenated, ‘‘energetic’’ schist layers and quartz- and feldspar-rich tions is 175 m. The Littleton Formation is clastic rocks) of the Madrid Formation. In layers of the gneisses are the migmatized ϳ1500 m thick, but it also must be thicker, the Presidential Range only the lower, thinly equivalent of the olistostromal, nonmigma- as the top is not seen. Based on estimates of bedded, calcareous clastic rocks were depos- tized outcrops shown in Figures 9D and 9E. the Silurian marine basin geometry by ited; an upper, thick-bedded, slightly calcar- With the exception of the rare outcrops Moench and Pankiwskyj (1988), the thick- eous sandstone member is identified by where intact bedding is preserved in the nesses reported above would place the strat- Moench and Pankiwskyj (1988) in western Rangeley, we interpret all of the Rangeley igraphic section of the Presidential Range Maine. The thin or absent section of the mapped in the Presidential Range to be a slightly seaward of the Silurian tectonic Perry Mountain Formation in the Presiden- metamorphosed, variably migmatized, olis- hinge, the paleo-shelf-slope break. tial Range suggests incomplete deposition tostromal melange. The depositional model of Moench and of this formation in the study area, consist- One possible tectonic process responsible Pankiwskyj (1988) would predict that Silu- ent with the location near the tectonic hinge. for the Rangeley olistostromal melange is rian conglomerates of the Rangeley Forma- subduction related to the closure of the Kro- tion would be at this position. No such rocks Rangeley Formation nos ocean. The sediments were deposited on have been found in the Silurian of the Pres- a shelf/slope transition of an accretionary idential Range. The discrepancy is probably The calc-silicate lenses in the Rangeley complex. The slope became unstable due to due to either overestimation of the Silurian can be broadly characterized as mappable thrusting, earthquakes, and/or other dis- sedimentary basin thickness by Moench and units of rock fragments enveloped by a mud- turbing mass movements associated with Pankiwskyj (1988), underestimation by us, stone-rich rock which has been metamor- plate movements acting as a triggering mech- or regional facies variations in Silurian phosed into a gneiss. The lithologic descrip- anism. Alternatively, the Rangeley olisto- sedimentation. tion of the Rangeley corresponds with the stromal melange may be a result of regional Type I melange defined by Cowan (1985), extension in the Early Silurian as the Cen- Littleton Formation what Hsu¨ (1968) terms a broken formation, tral Maine Terrane basin developed. Mar- and which are analogous to Rast and Hor- vinney et al. (1992) suggested that the meta- On the basis of the differing lithologic ton’s (1989) olistostromal melange. This sedimentary and volcanic rocks of northern types, bedding characteristics, and facies type of rock-stratigraphic unit displays lay- New Hampshire in the Second Lake rift,

Geological Society of America Bulletin, April 1996 431 EUSDEN ET AL.

Figure 15. Region within which migmatitic Rangeley Formation with calc-silicate lenses is found in New Hampshire and Maine. This region is interpreted to be a highly metamorphosed olistostrome. Sources of information: Eusden and Lyons, 1993; Lyons et al., 1993; Moench and Pankiwskyj, 1988; and J. D. Eusden and J. B. Lyons, unpub. mapping. which include the Silurian Rangeley through The interpretation of the Rangeley For- ny. Though we cannot rule out the possibil- Madrid and Frontenac Formations, were mation as an olistostromal melange may ex- ity that these olistostromal facies were deposited in an extensional sub-basin (the tend well beyond the Presidential Range. formed in an extensional setting, we suggest Second Lake rift) northwest of the Bronson Figure 15 shows areas in New Hampshire they were formed in a west-dipping subduc- Hill Anticlinorium. It could be argued that and a small portion of Maine within which tion system located against the east margin the Rangeley Formation olistostromes in migmatized Rangeley Formation with calc- of the Bronson Hill Anticlinorium. Further- the Presidential Range were formed simi- silicate lenses has been mapped. The area more, we contend that the lack of olistostro- larly. However, we propose that the exten- shown is the broadest possible outline of mal facies in the remaining Silurian Forma- sion in the Second Lake rift was in a back- what may be a regionally significant zone tions and all of the Littleton Formation in arc basin to the Bronson Hill arc and that of highly metamorphosed olistostromal New Hampshire suggests that this subduc- the Rangeley Formation olistostromes in melange. tion system became less active as the enor- the Presidential Range, southeast of the The existence of a region of large-scale mous volume of clastic sediment derived Bronson Hill, were part of a fore-arc/accre- stratal disruption, possibly linked to an ac- from the Avalon continent overwhelmed it. tionary wedge sequence associated with a tively subducting margin, provides critical This model is considerably different from west-dipping subducting slab. tectonic constraints for the Acadian oroge- that proposed by Hanson and Bradley

432 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE

(1989) for the late Silurian to early Devo- Maine Terrane with deeper levels exposed T1 nian in Maine, in which much of the Madrid in southern and shallower lev- and Carrabassett (correlative to the lower els in the north (Tracy and Robinson, 1980; Because the Greenough Spring thrust Littleton in New Hampshire) consist of dis- Robinson et al., 1989). The west-verging fault developed after D1 and D2 deforma- rupted strata that they relate to an accre- nappes may be structurally below the east- tion and after peak metamorphism, it is tionary complex in front of Avalon. verging ones as previously speculated by unlike any other faults identified in the Bradley (1983). Central Maine Terrane. Generally the Structural Geology Another possibility is that the change in faults fall into two categories. There are strike of the Bronson Hill Anticlinorium premetamorphic faults chiefly recognized The sequence of ductile structures ob- from N10ЊE in southern and central New in western Maine, for example, the Plum- served in the Presidential Range more Hampshire to N50ЊE in northern New bago Mountain and Hill 2808 faults closely matches the structural models of Hampshire may have controlled the direc- (Moench and Pankiwskyj, 1988) and the Eusden and Lyons (1993) and Robinson et tions of nappe vergence. The Bronson Hill Foster Hill sole fault of the Piermont al- al. (1991) in New Hampshire and Massa- probably acted as a rigid buttress during the lochthon (Moench, 1990). There are also chusetts than the structural model of collision of the North American and Avalo- synmetamorphic faults chiefly recognized Moench and Pankiwskyj (1988) in western nian plates. Nappe vergence was likely de- in southern New Hampshire that devel- Maine. Apparently structures related to the pendent on the complex interactions be- oped during nappe-stage folding, for ex- emplacement of Devonian plutons (Moench tween the directions of plate movements ample, the Chesham Pond and Brennan and Pankiwskyj, 1988) do not extend west and the orientation of the buttress. into the Presidential Range. The transition Hill thrusts of Robinson et al. (1991). On the basis of the premise that primary Transport direction of the Greenough between the regime of nappe-dominated de- fold-thrust vergence in collisional zones is formation and that of deformation caused Spring thrust is equivocal. In cross section generally opposite that of the dip of the sub- B–BЈ it is shown with northwest-directed by plutons must be east of the Presidential ducting slab, we speculate that the easterly Range in the vicinity of the Maine–New transport. This is based on the presence of vergence of F1 nappes indicates that the Hampshire border. migmatized Rangeley Formation in Pink- subduction system along the western edge of ham Notch, immediately to the east of the the Central Maine Terrane was dipping to D1 klippe. Allen (1992) has mapped a thrust the west under the Bronson Hill Anticlino- fault there that cuts F1 and F2 fold struc- rium. One could alternatively argue that The interpreted east vergence of D1 tures and is controlled by the migmatites. As these nappes are east-verging backfolds an- nappes suggests several things: (1) the dor- the timing of this faulting is essentially the tithetic to the principal west direction of ver- sal zone model (Eusden and Lyons, 1993) same as that for the Greenough Spring gence that was linked to an east-dipping sub- should be restricted to central New Hamp- thrust, these may be of the same generation. duction zone under the Avalon margin (see shire, and the Central New Hampshire an- We speculate that the Greenough Spring discussions by Osberg et al., 1989). How- ticlinorium dies out south of the White fault represents a phase of backthrusting in ever, the point is moot because one could Mountain batholith; (2) the model calling the west-dipping subduction system along for west-directed thrust nappes that are argue equally well that the west-verging nappes are antithetic to the principal east the Bronson Hill Anticlinorium following backfolded and domed adjacent to the the collapse of the nappe pile. Bronson Hill Anticlinorium (Robinson et direction of vergence. Because of both struc- al., 1991) should be restricted to the south- tural and sedimentological evidence, we fa- vor the interpretation that the Acadian tec- western portion of the Central Maine Ter- D3 rane; and (3) a revised regional model for tonic architecture involved a west-dipping subducting system on the east flank of the Acadian deformations is needed to account The final phase of ductile folding in the for the D1 deformation in the Presidential Bronson Hill Anticlinorium. Presidential Range, D3, is similar to most Range as well the structural transitions final phases of folding described for the along the length of the Central Maine Central Maine Terrane. There is agreement Terrane. D2 in style of folding, orientation, and vergence It appears likely that the D1 nappes along with the last phases of deformation pro- the length of the Bronson Hill Anticlino- In comparison to the regional models of rium recorded both east and west vergence. deformation in the Central Maine Terrane, posed by Robinson et al. (1991), Eusden and In such a geometry, the and the second phase of deformation in the Lyons (1993), and us. These folds developed southern New Hampshire portion of the Presidential Range is quite unusual. It is during the waning stages of regional meta- Central Maine Terrane would record west poorly represented mesoscopically, yet it morphism when P-T conditions were such vergence of D1 nappes, whereas the Central significantly affects the macroscopic map that only a weak axial planar cleavage de- Maine Terrane in northern New Hampshire pattern, but only in the Clay klippe and veloped. Because these folds also deform records east vergence of the same genera- Chandler Ridge dome. Furthermore, there two-mica granite sills in the Presidential tion of structures. are no D2 fabrics, lineations, or foliations Range, they postdate the earliest phases of This hypothetical transition in structural developed in the rocks. We can only spec- granite plutonism. We interpret the east ver- vergence along the Bronson Hill east flank ulate that these structures may be related to gence of D3 to be representative of the final may be associated with the variation in a collapse of the nappe pile after D1 defor- pulse of Acadian convergence as Avalon un- crustal depths throughout the Central mation and peak metamorphism. derplated North America.

Geological Society of America Bulletin, April 1996 433 EUSDEN ET AL.

Figure 16. Schematic portrayal of the sequence of tectonic events in the alpine zone of Presidential Range. (A) Rangeley deposition; (B) Rangeley disruption; (C) Perry Mountain, Smalls Falls, Madrid, and Littleton deposition; (D) D1 nappe stage folding; (E) D2 collapse of nappe pile; (F) T1 Greenough Spring thrust fault; (G) D3 final pulse of Acadian folding. Patterns: random dashes, Bronson Hill basement; crosses, Avalonian basement; black, Kronos crust; dot with radial dashes in B, triggering seismic event to disrupt Rangeley. All sections are oriented west (left) to east (right).

SUMMARY mountain range in the Appalachian orogen- vide for new insights into Acadian tectonism ic belt, has revealed a complex stratigraphic in a critical region between well-studied re- Geologic mapping of the Presidential section and a complex sequence of ductile gions in southern New Hampshire and west- Range, perhaps the most well exposed structural events. These observations pro- ern Maine. Figures 16 and 17 present the

434 Geological Society of America Bulletin, April 1996 STRATIGRAPHY AND STRUCTURE OF THE PRESIDENTIAL RANGE

Figure 17. Sequence of depositional, deformational, metamorphic, and plutonic events in the Presidential Range.

proposed sequence of sedimentation, struc- ACKNOWLEDGMENTS Washington area, New Hampshire: Geological Society of America Bulletin, v. 52, p. 863–936. tural events, and metamorphic and plutonic Billings, M. P., 1956, Bedrock geology: Geology of New Hamp- shire, Part 2: Concord, New Hampshire State Planning and events in the alpine zone of the Presidential We thank Bradford Washburn, Howard Development Commission, 203 p. Range. Estimates for the timing of peak met- Weans, Kenneth Kimball, Walter Graff, Billings, M. P., and Fowler-Billings, K., 1975, The geology of the Gorham quadrangle, New Hampshire and Maine: Concord, amorphism range from 390 to 360 Ma as Bruce Hill, and the hut crews and caretakers State of New Hampshire Department of Resources and Economic Development, Bulletin 6, 120 p. delimited by geochronology done in New of Appalachian Mountain Club and Ran- Billings, M. P., Chapman, C. A., Chapman, R. W., Fowler-Billings, Hampshire and Maine by Eusden and Bar- dolph Mountain Club huts for offering in- K., and Loomis, F. B., 1946, Geology of the Mount Wash- ington quadrangle, New Hampshire: Geological Society of reiro (1989) and Smith and Barreiro (1990), sight, advice, and/or assistance during the America Bulletin, v. 57, p. 261–273. Billings, M. P., Fowler-Billings, K., Chapman, C. A., Chapman, respectively. The ages of middle to late Aca- project. We thank Edward C. Beutner, Wal- R. W., and Goldthwait, R. P., 1979, The geology of the dian two-mica granites, part of the Concord lace A. Bothner, Dwight C. Bradley, John B. Mount Washington quadrangle, New Hampshire: Concord, State of New Hampshire Department of Resources and Group, are between 380 and 320 Ma (Lyons Lyons, and an anonymous reviewer for pro- Economic Development, 56 p. Bothner, W. A., Gaudette, H. E., Fargo, T. G., Bowring, S. A., and et al., 1982; Harrison et al., 1987; Lyons et viding critical reviews of the manuscript. Isachsen, C. E., 1993, Zircon and sphene U/Pb ages of the al., 1992; Osberg et al., 1989). Supported by American Chemical Society– Exeter Pluton: Constraints on the Merrimack Group and part of the Avalon Composite Terrane: Geological Society The sedimentology gleaned from these Petroleum Research Fund grant 24269-B2, of America Abstracts with Program, v. 25, no. 6, p. A-485. Bradley, D. C., 1983, Tectonics of the Acadian orogeny in New highly metamorphosed rocks and the pre- National Science Foundation grant EAR- England and adjacent Canada: Journal of Geology, v. 91, served ductile structures suggest tectonism 9105390, and various Bates College grants p. 381–400. Bradley, D. C., and Hanson, L. S., 1989, Turbidites and me´langes in a convergent plate setting with a west- to Eusden. Many thanks to Rick Allmendin- of the Madrid Formation, central Maine, in Berry, A. W., ger for creating and distributing Stereonet Jr., ed., New England Intercollegiate Geological Confer- dipping subduction zone beneath the east ence guidebook for field trips in southern and west-central flank of the Bronson Hill Anticlinorium. version 4.7. Maine: Farmington, University of Maine, p. 183–199. Carmichael, D. M., 1978, Metamorphic bathozones and batho- The absence of critical lithotectonic facies, grads: A measure of the depth of post-metamorphic uplift missing perhaps because of the natural va- REFERENCES CITED and on the regional scale: American Journal of Sci- ence, v. 278, p. 769–797. garies of tectonic processes and preserva- Allen, T., 1992, Migmatite systematics and geology, Carter Chamberlain, C. P., and England, P. C., 1985, The Acadian ther- Dome—Wild River region, White Mountains, New Hamp- mal history of the Merrimack Synclinorium in New Hamp- tion in the rock record, motivated us to re- shire [Ph.D. thesis]: Hanover, New Hampshire, Dartmouth shire: Journal of Geology, v. 93, p. 593–602. construct the Acadian through an analysis of College, 249 p. Chamberlain, C. P., and Lyons, J. B., 1983, Pressure, temperature AMC, 1988, AMC guide to Mount Washington and the Presiden- and metamorphic zonation studies of pelitic schists in the the sedimentation and ductile deformation. tial Range (fourth edition): Boston, Massachusetts, Appa- Merrimack Synclinorium, south central New Hampshire: lachian Mountain Club, 219 p. American Mineralogist, v. 68, p. 530–540. Much more work is needed to continue piec- Barreiro, B., and Aleinikoff, J. N., 1985, Sm-Nd and U-Pb isotopic Chamberlain, C. P., and Robinson, P., eds., 1989, Styles of met- ing the Acadian tectonic puzzle together. relationships in the Kinsman quartz monzonite, New Hamp- amorphism with depth in the Central Acadian High, New shire: Geological Society of America Abstracts with Pro- England: Amherst, University of Massachusetts, Depart- Our stratigraphic and structural approach grams, v. 17, no. 1, p. 3. ment of Geology and Geography, Contribution Number 63, Berry, H. N., IV, and Osberg, P. H., 1989, A stratigraphic synthesis 82 p. would be improved by fully incorporating ig- of eastern Maine and western New Brunswick, in Tucker, Chamberlain, C. P., and Rumble, D., 1988, Thermal anomalies in neous and metamorphic petrology and de- R. D., and Marvinney, R. G., eds., Studies in Maine geology: a regional metamorphic terrane: An isotopic study of the Maine Geological Survey, v. 2, p. 1–32. role of fluids: Journal of Petrology, v. 29, p. 1215–1232. tailed geochronology. Billings, M. P., 1941, Structure and metamorphism in the Mount Chamberlain, C. P., and Sonder, L. J., 1990, Heat producing ele-

Geological Society of America Bulletin, April 1996 435 EUSDEN ET AL.

ments and the thermal and baric patterns of metamorphic New Hampshire: American Journal of Science, v. 283, Society of America, Geology of North America, v. F-2, belts: Science, v. 250, p. 763–769. p. 739–761. p. 179–232. Clark, R. G., and Lyons, J. B., 1986, Petrogenesis of the Kinsman Henderson, D. M., 1949, Geology and petrology of the eastern Rankin, D. W., 1994, Continental margin of the eastern United intrusive suite peraluminous granitoids of western New part of the Quadrangle, Hew Hampshire States: Past and present, in Speed, R. C., ed., Phanerozoic Hampshire: Journal of Petrology, v. 27, p. 1365–1393. [Ph.D. thesis]: Cambridge, Massachusetts, Harvard Univer- evolution of the North American continent-ocean transi- Cowan, D. S., 1985, Structural styles in Mesozoic and Cenozoic sity, 128 p. tions: Boulder, Colorado, Geological Society of America, me´langes in the western Cordillera of North America: Ge- Henderson, D. M., Billings, M. P., Creasy, J., and Wood, S. A., Summary Volume to Accompany DNAG Continent-Ocean ological Society of America Bulletin, v. 96, p. 451–462. 1977, Geology of the Crawford Notch quadrangle, New Transect Series, p. 129–218. DeYoreo, J. J., Lux, D. R., Guidotti, C. V., Decker, E. R., and Hampshire: Concord, State of New Hampshire Department Rast, N. R., and Horton, J. W., Jr., 1989, Me´langes and olisto- Osberg, P. H., 1989, The Acadian thermal history of western of Resources and Economic Development, 29 p. stromes in the Appalachians of the United States and main- Maine: Journal of Metamorphic Geology, v. 7, p. 169–190. Hitchcock, C. H., 1874–1878, Geology of New Hampshire: Vol- land Canada; An assessment, in Horton, J. W., Jr., and Rast, Duke, E. F., 1978, Petrology of the Spaulding Group tonalites, ume 1, 1874; Volume 2, 1877; Volume 3, 1878; atlas 1878, N. R., eds., Me´langes and olistostromes of the U.S. Appa- Penacook quadrangle, New Hampshire [Master’s thesis]: Concord, New Hampshire. lachians: Geological Society of America Special Paper 228, Hanover, New Hampshire, Dartmouth College, 117 p. Hsu¨, K. J., 1968, Principles of me´langes and their bearing on the p. 1–15. Eusden, J. D., Jr., 1988, Stratigraphy, structure and metamorphism Franciscan-Knoxville paradox: Geological Society of Amer- Robinson, P., 1993, Acadian magmatism and metamorphism in of the ‘‘dorsal zone,’’ central New Hampshire, in Bothner, ica Bulletin, v. 79, p. 1063–1074. New England: A product of mantle-lithosphere delamina- W. A., ed., New England Intercollegiate Geological Con- Kilbourne, F. W., 1978, Chronicles of the White Mountains: tion in front of an east-dipping subduction zone?: Geolog- ference, 80th Annual Meeting; Guidebook for field trips in Bowie, , Heritage Books, 437 p. ical Society of America Abstracts with Programs, v. 25, southwestern New Hampshire, southeastern , and Lash, G. G., 1987, Diverse me´langes of an ancient subduction p. A-179. north-central Massachusetts: Durham, University of New complex: Geology, v. 15, p. 652–655. Robinson, P., Tracy, R. J., Hollocher, K., Berry, H. N., and Thom- Hampshire, p. 40–59. Lathrop, A. S., Blum, J. D., and Chamberlain, C. P., 1993, Nd-Sr son, J. A., 1989, Basement and cover in the Acadian met- Eusden, J. D., Jr., and Barreiro, B. A., 1988, The timing of peak isotopic study of Acadian metasediments and granitoids amorphic high of central Massachusetts, in Chamberlain, high-grade metamorphism in central-eastern New England: from New England: Provenance and evidence for anatexis: C. P., and Robinson, P., eds., Styles of Acadian metamor- Maritime Sediments and Atlantic Geology, v. 24, p. 241–255. Geological Society of America Abstracts with Programs, phism with depth in the central Acadian high, New England: Eusden, J. D., Jr., and Lyons, J. B., 1993, The sequence of Acadian v. 25, no. 6, p. A-42. Amherst, Department of Geology and Geography, Univer- deformations in central New Hampshire, in Roy, D. C., and Lux, D. R., DeYoreo, J. J., Guidotti, C. V., and Decker, E. R., sity of Massachusetts, Contribution Number 63, p. 69–140. Skehan, J. W., eds., The Acadian orogeny: Recent studies in 1986, The role of plutonism in low-pressure metamorphic Robinson, P., Thompson, P. T., and Elbert, D. C., 1991, The nappe New England, Maritime Canada and the autochthonous belt formation: Nature, v. 323, p. 794–797. theory in the Connecticut Valley region: Thirty-five years foreland: Geological Society of America Special Paper 275, Lyons, J. B., and Livingston, D. E., 1977, Rb-Sr age of New Hamp- since Jim Thompson’s first proposal: American Mineralo- p. 51–66. shire Plutonic Series: Geological Society of America Bulle- gist, v. 76, p. 689–712. Eusden, J. D., Jr., Bothner, W. A., and Hussey, A. M., 1987, The tin, v. 88, p. 1808–1812. Smith, H. A., and Barreiro, B., 1990, Monazite U-Pb dating of Kearsarge–Central Maine Synclinorium of southeastern Lyons, J. B., Boudette, E. L., and Aleinikoff, J. N., 1982, The staurolite grade metamorphism in pelitic schists: Contribu- New Hampshire and southwestern Maine: Stratigraphic and Avalonian and Gander zones in central eastern New En- tions to Mineralogy and Petrology, v. 105, p. 602–615. structural relations of an inverted section: American Journal gland, in St. Julien, P., and Beland, J., ed., Major structural Stewart, D. B., Wright, B. E., Unger, J. D., Philips, J. D., and of Science, v. 287, p. 242–264. zones and faults of the northern Appalachians: Geological Hutchinson, D. R., compilers, 1993, Global geoscience Fowler-Billings, K., 1944, Igneous and metasedimentary dikes of Association of Canada Special Paper 24, p. 44–66. transect 8, –Gulf of Maine Transect, southeastern the Mt. Washington area: Geological Society of America Lyons, J. B., Bothner, W. A., Moench, R. H., and Thompson, J. B., Canada, northeastern United States of America: U.S. Ge- Bulletin, v. 55, p. 1255–1278. 1992, Bedrock geologic map of New Hampshire: Concord, ological Survey Miscellaneous Investigations Map I-2329, Guidotti, C. V., 1989, Metamorphism in Maine: An overview, in State of New Hampshire Department of Environmental scale 1:1 000 000. Tucker, R. D., and Marvinney, R. G., eds., Igneous and Services Open-File Report. Thompson, J. B., 1954, Structural geology of the Skitchewaug metamorphic geology: Augusta, Maine Geological Survey, Marvinney, R. G., Bothner, W. A., Moench, R. H., and Pollack, Mountain area, Claremont quadrangle, Vermont–New Studies in Maine Geology, v. 3, p. 1–17. S. G., 1994, Silurian stratigraphic succession of northern NH Hampshire: New England Intercollegiate Geological Con- Guthrie, G. D., and Burnham, C. W., 1985, Petrology and origin and western ME: Evidence for extensional sub-basin devel- ference, 46th Annual Meeting, Hanover, New Hampshire, of calc-silicate bodies from the Rangeley Formation, New opment: Geological Society of America Abstracts with Pro- Guidebook, p. 93–174. Hampshire: Geological Society of America Abstracts with grams, v. 26, p. 59. Thompson, J. B., Robinson, P., Clifford, T., and Trask, N., 1968, Programs, v. 17, no. 1, p. A-22. Moench, R. H., 1971, Geologic maps of the Rangeley and Phillips Nappes and gneiss domes in west-central New England, in Hanson, L. S., and Bradley, D. C., 1989, Sedimentary facies and quadrangles, Franklin and Oxford Counties, Maine: U.S. Zen, E., White, G., Hadley, J., and Thompson, J. B., eds., tectonic interpretation of the Lower Devonian Carrabassett Geological Survey Miscellaneous Geologic Investigations Studies of Appalachian geology: Northern and Maritime: Formation, North-Central Maine, in Tucker, R. D., and Map I-605, scale 1:62 500. , John Wiley and Sons, p. 203–218. Marvinney, R. G., eds., Studies in Maine geology: Augusta, Moench, R. H., 1990, The Piermont allochthon, northern Con- Thompson, J. B., Bothner, W. A., Robinson, P., Isachsen, Y. W., Maine Geological Survey, v. 2, p. 101–126. necticut valley area, New England—Preliminary description and Klitgord, K. D., 1993, E-1, Adirondacks to Georges Hanson, L. S., and Bradley, D. C., 1993, Late Silurian to Early and resource implications, in Slack, J. F., ed., Summary re- Bank: Boulder, Colorado, Geological Society of America, Devonian paleogeography of the Kearsarge–Central Maine sults of the Glens Falls CUSMAP Project, New York, Ver- Centennial Continent-Ocean Transect, no. 17, 55 p., 2 Basin revealed by paleocurrents and sedimentary facies: Ge- mont, and New Hampshire: U.S. Geological Survey Bulle- sheets, scale 1:500 000. ological Society of America Abstracts with Programs, v. 25, tin 1887, p. J1–J23. Tracy, R. J., and Robinson, P., 1980, Evolution of metamorphic no. 6, p. A-360. Moench, R. H., and Pankiwskyj, K. A., 1988, Geologic map of belts: Information from detailed petrologic studies, in Ske- Harrison, T. M., Aleinikoff, J. N., and Compston, W., 1987, Ob- western interior Maine: U.S. Geological Survey Miscella- han, J. W., and Osberg, P. H., eds., The Caledonides in the servations and controls on the occurrence of inherited zir- neous Investigations Map I-1692, scale 1:250 000. USA—Geological excursions in the northeast Appalachi- con in Concord-type granitoids, New Hampshire: Geo- Naylor, R. S., 1971, The Acadian orogeny: An abrupt and brief ans: Weston, Massachusetts, Weston Observatory, p. 189–193. chimica et Cosmochimica Acta, v. 51, p. 2549–2558. event: Science, v. 172, p. 558–560. Wall, E. R., 1988, The occurrence of staurolite and its implications Hatch, N. L., Jr., and Moench, R. H., 1984, Bedrock geologic map Nielson, D. L., Clark, R. G., Lyons, J. B., Englund, E. J., and for polymetamorphism in the Mt. Washington area, NH of the wilderness and roadless areas of the White Mountain Borns, D. J., 1976, Gravity models and mode of emplace- [Master’s thesis]: Orono, Maine, University of Maine, 124 p. National Forest, Coos, Carroll, and Grafton Counties, New ment of the New Hampshire Plutonic Series: Geological Washburn, B., 1988, Mt. Washington and the heart of the Presi- Hampshire: U.S. Geological Survey Miscellaneous Field Society of America Memoir 146, p. 301–318. dential Range, New Hampshire: Boston, Massachusetts, Ap- Studies Map 1594-a, scale 1: 250 000. Orange, D. L., 1990, Criteria helpful in recognizing shear-zone and palachian Mountain Club, scale 1:20 000. Hatch, N. L., Jr., and Wall, E. R., 1986, Stratigraphy and meta- diapiric me´langes: Examples from the Hoh accretionary Zen, E-an, Stewart, D. B., and Fyffe, L. R., 1986, Paleozoic tectono- morphism of the Silurian and Lower Devonian rocks of the complex, Olympic Peninsula, Washington: Geological Soci- stratigraphic terranes and their boundaries in the mainland western part of the Merrimack synclinorium, Pinkham ety of America Bulletin, v. 102, no. 7, p. 935–951. Northern Appalachians: Geological Society of America Ab- Notch area, east-central New Hampshire, in Newberg, Osberg, P. H., Hussey, A. M., and Boone, G. M., 1985, Bedrock stracts with Programs, v. 18, p. 800. D. W., ed., New England Intercollegiate Geological Con- geologic map of Maine: Augusta, Maine Geological Survey, ference, 78th Annual Meeting; Guidebook for field trips in scale 1:500 000. southwestern Maine: Durham, University of New Hamp- Osberg, P. H., Tull, J. F., Robinson, P., Hon, R., and Butler, J. R., shire, p. 138–163. 1989, The Acadian orogen, in Hatcher, R. D., Jr., Thomas, MANUSCRIPT RECEIVED BY THE SOCIETY FEBRUARY 21, 1995 Hatch, N. L., Moench, R. H., and Lyons, J. B., 1983, Silurian– W. A., and Viele, G. W., eds., The Appalachian-Ouachita REVISED MANUSCRIPT RECEIVED AUGUST 25, 1995 Lower Devonian stratigraphy of eastern and south central orogen in the United States: Boulder, Colorado, Geological MANUSCRIPT ACCEPTED SEPTEMBER 25, 1995

Printed in U.S.A.

436 Geological Society of America Bulletin, April 1996