Nappes, Gneiss Domes and Plutonic Sheets
of West-Central New Hampshire

by
Tim Allen, Geology Dept., MS 2001, Keene State College, Keene, NH 03435-2001,
tallen@keene.edu

Originally published in: Timothy W. Grover, Helen N. Mango, and Edward J. Hasenohr, editors, Guidebook to Field Trips in Vermont and Adjacent New Hampshire and New York, New England Intercollegiate Geologic Conference, 89th Annual Meeting. pp. A2.1 - A2.19.

This document is also available as an Adobe Acrobat PDF file .

Introduction

The area between Keene and Hanover in west-central New Hampshire (NH; Figure 1) is home to some "classic" geology of the Acadian Appalachians. This geology includes (1) fold nappes which transported highly metamorphosed deep-basin sediments over less-metamorphosed shelf sediments, (2) gneiss domes which subsequently deformed (and metamorphosed) these nappes, and (3) large anatectic plutonic sheets, whose emplacement may have been intimately involved with the formation of the nappes. These rocks are encompassed within the Central Maine Terrane (CMT; Eusden & Lyons, 1993), and astride the Bronson Hill Anticlinorium (BHA; Billings, 1956). On this trip, we are primarily interested in the relationships between and among rocks on the BHA and those further east in central NH. The relationship of these rocks (NH sequence) with those to the west (Vermont sequence) is the subject of other trips at this conference (A6, Armstrong et al, 1997.; and C1, Thompson et al., 1997).

Metasedimentary and Metavolcanic Stratigraphy

An important part of understanding the geology in any region is the ability to recognize the relative sequence in which the rock units were deposited or intruded, from principles of super-position and cross-cutting relationships, but also from fossil assemblages and radiometric dates. On the basis of fossils discovered in the Littleton area, Billings and others (1934, 1935, 1937) were able to define a stratigraphic sequence for the metavolcanic and metasedimentary rocks of the BHA (Figure 2). Once a sequence is established, mapping in adjacent areas can commence by making correlations back to the known rocks. Billings, his students and others proceeded to map much of the rest of NH, with reference to the Littleton section, leading to the publication of a NH state geologic map in 1956. Most of the rocks throughout NH (with a few notable exceptions) are, however, devoid of the fossils needed to corroborate one's position in the stratigraphic sequence, thus correlations must be made primarily on the basis of lithologic characteristics. Given a high degree of structural complexity, a wide range of metamorphic changes and degrees of weathering, large expanses of intervening plutonic rocks, and significant original sedimentological variations, such correlations (upon which structural and tectonic interpretations hinge) are often problematic.

As the state map was being compiled, Thompson (1954, 1956) discovered structural complications on the BHA, arising from the recognition of distinct stratigraphic units (based on fossil occurrences) in rocks that had previously been mapped as belonging to one formation. This lead to a second round of mapping in the region, still referencing the Littleton section, that culminated in the oft-cited 1968 paper by Thompson and others, establishing the current paradigm outlined above.

Meanwhile, Lyons, his students, and others working in central NH found that the BHA stratigraphy didn't fit very well with rocks exposed there, and developed a new informal lithostratigraphy for their work (c.f. Duke et al., 1988). Billings and others (1941, 1946, 1975) had earlier wrestled with this problem in the Mount Washington-Gorham area further north, and in revisiting this area Hatch and others (1983; Duke et al., 1988) extended to central NH a stratigraphic sequence established in the Rangeley area of Maine (Figure 2; Boone et al., 1970). A key component of this interpretation is the recognition of a change in depositional environments, from a shelf-type on the BHA to a deep closed basin in the CMT. A third generation of mapping was undertaken in western NH to determine the relationship between the stratigraphy of rocks on the BHA and that to the east in central NH (Chamberlain et al., 1988). While the rocks themselves have remained essentially unchanged for several hundred million years, their exposures (too often too few and far between) and our interpretations of them seem to change continuously. The release of a new NH state geologic map is imminent (Lyons et al., 1997), but many interesting problems persist.

Intrusive Igneous Rocks

Billings' state map (1956) also showed several suites of intrusive igneous rocks in this region (Figure 1), including the Oliverian magma series and the New Hampshire Plutonic Series (NHPS), including the so-called Kinsman Quartz Monzonite (KQM), Bethlehem Gneiss, Spaulding Group and Concord Group. At that time, the details of age relationships, the sources of these magmas, and their modes of emplacement were uncertain. Since then, the application of radiometric dating techniques, petrologic and isotopic studies, geophysical and structural investigations, and thermal modelling have vastly improved our understanding of the Oliverian and NHPS rocks.

The Oliverian suite is comprised of granites, tonalites and trondjhemites ranging in age from 442-456 Ma (Naylor, 1969; Zartman & Leo, 1985; Aleinikoff c.f. Lyons et al., 1996) which form the core rocks of the en echelon mantled gneiss domes making up the BHA, as well as a few discordant intrusions just off the axis of the BHA to the west. These rocks have an internal gneissic foliation paralleling their contacts with wall rocks, giving rise to their (sometimes asymmetric) domal structures. Structures within the mantling strata, including Silurian and Devonian rocks substantially younger than the core gneisses, also exhibit this doming. In addition, metamorphic isograds in these strata commonly wrap around the domes, with the grade of metamorphism increases toward the center of the dome. It is thought that the domes might have been created by diapiric rise (Thompson et al., 1968), resulting from a density inversion between the core materials and the mantling strata (Fletcher, 1972), during the early Devonian Acadian orogeny. Such a model has been demonstrated by scaled gravity tectonic experiments (Ramberg, 1973). Lyons and others (1996) used gravity measurements to confirm the geometry of these domes, and their mushroom- shaped models support reactivated diapiric rise of the core rocks. The metamorphic patterns might be the result of focussed heat flow due to contrasts in thermal conductivity (Allen & Chamberlain, 1989). The cores of the domes may also represent relict volcanic islands of an oceanic island arc (Hitchcock, 1883, 1890 c.f. Thompson et al., 1968) -- an interpretation which is not incompatible with diapiric rise. One school of thought suggests that the docking of the Bronson Hill island arc with the Laurentian continent was responsible for the Taconic orogeny.

The NHPS were emplaced during and after the early Devonian Acadian orogeny. Of these, the Mount Clough pluton and the Cardigan pluton are the most voluminous. Both of these plutons are heterogeneous granitoids, ranging from granite (sensu stricto) to quartz diorite but being predominately granodiorite. Although compositionally very similar (Billings & Wilson, 1964), the rocks of the these plutons do differ in texture and mineralogy and have been identified as separate units, the Mount Clough pluton being comprised of Bethlehem Gneiss, and the Cardigan pluton of KQM (although no longer considered a quartz monzonite).

Characteristic of the KQM are abundant potassium feldspar megacrysts in a course groundmass of quartz, plagioclase, biotite, muscovite and garnet. In some places, garnet becomes the dominant mineral suggesting zones of restite entrained within the magma. The Bethlehem Gneiss is a more homogeneous micaceous granodiorite distinguished from the KQM by a prominent gneissic foliation and the lack of potassium feldspar megacrysts and restites.

Lathrop and others (1994, 1996) made detailed Sr, Nd and O isotopic studies of the Mount Clough and Cardigan plutons to address questions about the nature of origin and source for these rocks. Their results show that, while isotopically heterogeneous and complex, the Bethlehem Gneiss and KQM magmas formed from anatectic melting of the adjacent metasedimentary rocks found in the BHA and the CMT, with very little if any contribution from the mantle. The original sedimentary material in the CMT was enriched in heat producing elements, which when the crust was thickened during the Acadian orogeny, would have provided a sufficient heat source for melting in situ (Chamberlain & Sonder, 1990). However, the rocks of the BHA are not so enriched, and so would have required an external heat source or deeper burial for melting.

In addition to the Mount Clough and the Cardigan plutons, several smaller satellite plutons of Bethlehem Gneiss (or KQM) have also been mapped, for example the Bellows Falls pluton. Geophysical investigations, combined with geologic structural constraints, indicate that these plutons are floored by metasedimentary rocks and were probably emplaced as large sill-like bodies, not much thicker than about 2000 meters (Nielson et al., 1976; Kruger & Linehan, 1941). It is thought that several of these plutons may have at one time been connected, covering the entire area; the Bellows Falls Pluton perhaps being an outlier of the Mount Clough Pluton, for example.

It should further be noted that the Bethlehem Gneiss and the KQM cannot be distinguished from one another on the basis of Nd, Sr, or O isotope compositions (Lathrop et al., 1996), nor their major element compositions (Billings & Wilson, 1964). Thus it has been suggested that these two magmas were originated from the same parent material, with their mineralogical differences the result of different metamorphic conditions during their crystallization, or perhaps post- crystallization metamorphism (Chamberlain & Lyons, 1983). Differences in texture could be related to the degree to which the plutons were involved in nappe-stage deformation, the Mount Clough pluton of Bethlehem Gneiss being the further west on the eastern flanks of the BHA, while the Cardigan pluton is within the CMT. Allen proposed (1984, 1985) that the upper-most Fall Mountain nappe may have been aided in its transport to the west by the intrusion of Bethlehem Gneiss as a sheet along its sole, such that the Fall Mountain outlier and the Bellows Falls pluton are a package. To the east, the Huntley Mountain Spur of the Cardigan pluton is mapped along the sole of the Fall Mountain nappe (Chamberlain et al., 1988).

The Spaulding Group rocks, also syn-orogenic, and the post-orogenic Concord Group, may be associated with migmatite zones (Allen & Chamberlain, 1992; Allen, 1994, 1996a, b) found extensively along the axis of the Central NH Anticlinorium (Eusden et al., 1987; Eusden & Lyons, 1993). Thermal relaxation following the crustal thickening of the Acadian orogeny could have lead to melting of CMT rocks to produce the post-orogenic Concord Group plutons (Chamberlain & England, 1985).

Structure and Metamorphism

Thompson and others (1968) mapped a series of several west-vergent isoclinal fold nappes lying on and lapping over the BHA. These were recognized on the basis of repeats and inversions of the stratigraphy as well as structural features. The nappes were then deformed and backfolded by the subsequent diapiric-rise of the Oliverian domes (Robinson & Hall, 1979), greatly complicating the structure of the region. Further to the south, thrust faulting was recognized as an intermediate stage between emplacement of the fold nappes and subsequent doming (Thompson et al., 1987). Clearly, not all of the nappes are strictly fold nappes, the upper-most Fall Mountain nappe probably being more of a thrust structure (Allen, 1984, 1985, Chamberlain et al., 1988), with intimate involvement of rocks from the NHPS, as discussed above. On the eastern flanks of the CMT, to the east of the Central NH Anticlinorium, a somewhat similar set of early nappes are recognized, there being east-vergent (Eusden et al., 1987). The Central NH Anticlinorium is interpreted as a "dorsal zone" or "pop-up" structure forming the core of the Acadian orogeny (Eusden et al., 1987; Eusden & Lyons, 1993).

The succession of nappes emplaced over the BHA explained the inversion of metamorphic isograds observed in the region (Chapman, 1953). Each nappe, rooted to the east of the BHA in the CMT, brought deeper, hotter rocks westward with it, over colder previous nappes and autochthonous rocks. Thus rocks of high metamorphic grade were correlated to high tectonic level, in this case later nappes (Thompson et al., 1968). Spear and others (1990, 1992; Kohn et al., 1992) have correlated this scenario with pressure-temperature-time (P-T-t) histories of metamorphism found in rocks from the various nappes, wherein the nappe or thrust emplacement of hot rocks drives metamorphism of underlying colder rocks as the nappe cools. Indeed, they have gone on to postulate the existence of additional nappes (or thrust sheets), that are not exposed anywhere, on the basis of P-T-t histories. Certainly, within the CMT east of the BHA, the metamorphic pattern shows localized regions of high- or low-grade metamorphism (Chamberlain & Lyons, 1983). Chamberlain (1986) has explained these as the result of metamorphism enhanced by sequential episodes of intersecting folds.

Conclusion

The geology seen here in west-central NH appears to be characteristic of many orogenic belts. Thompson and others (1968) drew analogies between their interpretation of nappes and gneiss domes with similar structures observed in the western Alps, as further developed by Thompson and others (1990, 1993). Mantled gneiss domes are present in many deeply eroded mountain belts, including the Alps, Caledonides, Canadian Cordillera and the Appalachians (Eskola, 1949; Allen & Chamberlain, 1989), as well as the Himalaya and Karakorum (Allen & Chamberlain, 1991; Searle et al., 1989; Kundig, 1989). Perhaps their previous experience in west-central NH influenced their thinking, but Allen & Chamberlain (1991) recognized in the Karakorum of Pakistan a very similar scenario to that outlined here: fold-and-thrust nappes inverting the crust and thus metamorphic isograds, with subsequent deformation by gneiss domes of re-mobilized earlier granitic intrusives (Allen, Smith, Zeitler & Chamberlain, unpublished data).

Acknowledgements

I would like to express my sincere appreciation to C. Page Chamberlain, James B. Thompson, Jr., and John B. Lyons for first showing me these outcrops, and introducing me to and involving me in the study of the geology of my home stomping grounds. Any errors or omissions are mine alone. I'm sure that I have overlooked some important references, and haven't adequately represented all of those cited.

Road Log

We will depart at 8:00 AM from the intersection of Routes 12 and 12A (Maple Avenue) in northwest Keene, NH. Please carpool, bring a lunch, and have a full tank of gas -- enough for at least 150 miles of driving. The best reference map I can suggest would be a NH state highway map -- we're going to cover a lot of ground!

Mileage

0.0 Set trip meter to zero at the Rt. 12 overpass over Rt. 12A.
0.7 Stoplight, continue on Rt. 12A towards Surry.
4.6 roadside outcrops of Oliverian granite in the Keene Dome, view of Surry Mountain (see stops 1 & 2 below) to the east.
7.0 Park on the right side, as far over as possible. Leave hazard indicators flashing.

7.2 Turn right onto River or Gilsum road
7.4 Park on the right side, as far over as possible. Leave hazard indicators flashing.

STOP 2: Surry Mountain Septum (10 minutes) Exposed here are some of the metavolcanic and metasedimentary rocks of the Surry Mountain septum (see stop 1 above). We may find gedrite- cordierite assemblages in a "garbenschiefer" texture (better exposed up on Surry Mountain); the rock is also reported to contain Na-micas with talc intergrowths (J. B. Thompson, Jr., pers. comm., 1992). Return to the vehicles and continue east.

11.4 Stop sign across stone arch bridge, turn left onto Rt. 10 north through Gilsum
15.0 Park on the right side, as far over as possible. Leave hazard indicators flashing. Take care in crossing the highway.

18.6 Turn left onto Rt. 123 west at Marlow
19.9 Park on the right side, as far over as possible. Leave hazard indicators flashing.

23.1 Flashing yellow light, East Alstead. Continue straight through on 123 west
24.3 Mill Hollow. Continue through on 123 west
27.2 Rt. 12A comes in from the left, continue on 123 west
28.0 Rt. 123A comes in from the right, continue on 123 & 12A through Alstead village
28.6 Rts. 12A and 123 diverge, turn left staying on 123 west
30.6 Stop sign, Rt. 123 turns left, continue straight across onto Cold River Road
31.2 (optional stop) outcrops in the river are of a window to the floor of the Bellows Falls pluton
31.9 outcrop on far bank of the river are of the Bellows Falls pluton
32.5 another river outcrop of the floor under the Bellows Falls pluton, Fall Mountain looms to the right.
33.3 Stop sign, intersection with Rt. 123, bear right on 123 west
33.5 Stop sign, intersection with Rt. 12, turn right onto 12 north
34.5 Stop lights, continue through to just past the railroad yard
34.6 Park on the right side, as far over as possible. Leave hazard indicators flashing. Take care in crossing the highway and scrambling down to the outcrops in the river.

35.1 Stop light, turn left and cross the bridge to Vermont
35.3 Stop sign at end of bridge, turn left onto Rt. 5 south
35.6 Downtown Bellows Falls, continue south on 5
35.9 Stoplight, bear right uphill on Rt. 121 west
36.9 Turn left around monument onto Gage St.
37.1 Continue straight ahead onto dirt road
37.3 Park on the right or left sides, as far over as possible.

37.9 Rejoin Rt. 121 headed back into town
38.4 Stoplight at bottom of hill, turn 90 degrees to the left onto Rt. 5 North (to I-91) -- not back through downtown
39.2 Stop sign, continue north on 5
42.0 Rt. 5 turns off to the right, Rt. 103 ahead to the left -- go straight up the on-ramp to I-91 north
46.2 first view of Mount Ascutney, a remnant volcano associated with the White Mountain Magma Series, straight ahead For more information, see Schneiderman (1988).
48.6 Exit at Springfield
48.9 Stop sign at end of ramp, turn left to go north on Rt. 5 & east on Rt. 11
49.3 Turn left onto Rt. 5 north, just before the toll bridge
50.6 Park in the fork on the right.

54.7 Rt. 143 comes in from the left, continue north on 5
60.3 Yield sign, turn right towards Claremont
61.2 Stoplight at intersection with Rt. 12A, continue straight towards Claremont
63.6 Turn left, following sign for Newport and Sunapee (not downtown)
64.2 Stoplight, continue straight through
64.6 Park in turnout to the right, just before the stoplight at intersection with Rt. 120. This may well be our Lunch Stop. Take care in crossing the highway to roadcuts at the intersection.

64.8 Stoplight, turn left onto Rts. 11 & 103 east (Washington Street, Claremont). Continue through all the stoplights along this strip.
71.7 outcrops of Bethlehem Gneiss
73.7 Stoplight, go straight
74.1 Stoplight at intersection with Rt. 10 (Main Street, Newport), turn left to follow Rts. 11 & 103 east
74.2 Turn right following sign for Rts. 11 & 103 east
74.4 Yield sign, continue onto Rts. 11 & 103 east
77.3 Rts. 11 & 103 diverge (Guild), bear right to stay on Rt. 11 east toward Sunapee
79.7 Rt. 103B on the right, continue straight
79.8 Flashing yellow for Sunapee Harbor, continue straight
80.0 Turn left onto Sargent Road, park on dirt track by Sunapee Fire Station. Take care in crossing the highway.

80.3 Flashing yellow for Sunapee Harbor, continue straight
80.4 Turn left onto Rt. 103B south
81.0 small quarry operation, with antique steam tractor on left
82.8 View of Mount Sunapee Ski Area ahead through trees.

The ridge extending south-southwest from Mount Sunapee to Lempster Mountain, and north from Sunapee to Mount Cardigan, represents a septum of metasediments (interdigitated with the Huntley Mountain Spur) caught between the Cardigan pluton to the east and the Mount Clough pluton to the west. Mapped by Dean (1976) based on the BHA stratigraphy, a new look at these rocks with insights from the CMT and other areas, may help tie together the stratigraphy and structure of southwestern NH with that to the north and west, as well as furthering our understanding of the relationships between the Cardigan and Mount Clough plutons.

83.8 Stop sign, proceed across and around the Mount Sunapee Traffic Circle, leaving on Rt. 103 east.
84.7 outcrops of KQM injected with multiple dikes of aplite
85.1 outcrops of KQM with rafts of metasediment
86.2 Newbury Harbor
86.3 Intersection with Rt. 103A

Alternate Route (shortcut, skipping stops 10 and 11):
86.3 Turn left onto R.t 103A north
88.7 Pull off on the LEFT side of the road to park just before Ramblewood Circle. Leave hazard indicators flashing, and take care in crossing the highway. Across the road is an interesting outcrop of the KQM.
89.2 Rt. 103A bears to the left, continue following it to the north.
91.3 Turn right onto King Hill Road, towards I-89 southbound
92.3 Bog Road takes off the left, continue on King Hill Road
92.5 The author's childhood home is on the left
93.0 View of Mount Kearsarge ahead (see comments at mile 99.0).
93.7 Under the highway, turn left on to entrance ramp for I-89 northbound. Pick up the road log at mile 109.7, and subtract about 16 miles from subsequent mileage readings.

Original Route (the long way):
86.3 Rt. 103A goes off to the left, continue east on Rt. 103
86.8 more outcrops of KQM
87.1 Mountain Road on the right, continue on 103 east. K-Ar dating of kaolinite gouge from the Newbury Fault zone exposed here yielded an age of 160 Ma (J. B. Lyons, pers. comm., 1988)
89.1 Flashing yellow, South Newbury
91.4 Park on right side of road, as far over as possible. Leave hazard indicators flashing. Take care in crossing the highway.

91.7 Stoplight at intersection with Main Street, Bradford. Continue straight on Rt. 103 east
92.4 Stoplight at intersection with Rt. 114, continue straight on Rt. 103 east to Warner
98.7 Park on right just before onramp to I-89 south, as far over as possible. Leave hazard indicators flashing. Take care in crossing the highway.

99.0 Turn left on to ramp for I-89 north, and take in the view of Mount Kearsarge

Mount Kearsarge (Lyons, 1988), Mount Monadnock to the south (P. J. Thompson, 1988) and Mount Washington to the north (Eusden et al., 1996a, b), are all composed of highly erosion- resistant members of the Littleton formation, noted on each summit for the occurrence of "turkey track" sillimanite pseudomorphs after andalusite and dramatic cyclic graded bedding of quartzites and schists. These peaks essentially mark the trace of the Kearsarge-Central Maine synclinorium.

105.9 View of Mount Kearsarge over right shoulder (exit 10, continue N on I-89)
109.7 outcrop of abundant pegmatite (exit 11, continue N on I-89)
111.0 Slow down and look out the vehicle to the left.

111.3 overpass over Bog Road
113.0 Slow down and look out the vehicle to the right.

114.3 outcrop of Bethlehem Gneiss
115.6 Take Exit 12A for Georges Mills
115.8 Stop sign at end of ramp, turn left under highway
116.0 Turn right onto Stoney Brook Road
116.5 Park on left, just under the highway.

118.3 View ahead of the white ledges over Grantham

These ledges, well-viewed from the interstate, are outcrops of the Clough Quartzite in the mantle of the Croydon dome. Samples from these outcrops contain well preserved brachiopod and other fossils (J.B. Thompson, Jr., pers. comm., 1984). Contained within the boundaries of the private Blue Mountain hunting reserve, they are now essentially inaccessible.

120.9 Stop sign, bear to the left on the Grantham-Springfield Road
122.0 Stop sign, turn right onto Rt. 10 north
122.6 Pass under I-89, continue straight ahead on Old Route Ten
122.9 View to the left of the gray ledges, opposite the entrance to the Eastman development
125.1 Turn left onto Miller Pond Road, under the highway
125.2 Park just past the underpass in class VI road.

125.3 Turn left to continue north on Old Route Ten
127.7 Turn right and pass under highway
127.9 Turn left up on ramp to I-89 north
128.1 outcrops on the right of Bethlehem Gneiss
128.4 outcrops on the right of Bethlehem Gneiss
128.7 outcrop on the right of the core of the Skitchewaug Nappe
130.0 Exit off I-89 at Montcalm
130.2 Stop sign at end of ramp, turn left under highway
130.3 T-intersection, turn left (now heading south)
131.4 Park in turnaround at dead end by the Humane Society

STOP 14: Skitchewaug Nappe (30 minutes). This is Stop 1 of J.B. Thompson, Jr. (1988), and your are referred to that source for detailed information about these rocks. We'll make a traverse along the bike path, looking at outcrops of the BHA stratigraphic sequence (Figure 3). The outcrops of Bethlehem Gneiss where we got onto I-89 at Exit 14 are an outlier of the Mount Clough pluton, separated by the Grantham Fault. It appears to be folded into the core of the Skitchewaug Nappe. With a sharp eye, fossils can be observed in the glacially polished surface at the top of northernmost outcrop of the Clough (Stop 14-A in Figure 3). No hammering please! Return to the vehicles and head back the way we came.

132.6 Turn right to pass under the highway
132.7 Turn left on to the ramp to I-89 north, park on right side (as far over as possible) before merging with highway. Leave hazard indicators flashing.

STOP 15: Littleton Formation (10 minutes) This is Stop 2 of J. B. Thompson, Jr. (1988). A thick section of Littleton schist (Figure 3), rich with staurolite crystals -- some with cruciform twins -- giving the rock a lumpy appearance. Few of the crystals are very fresh, most showing incipient alteration. Bedding is obscure, although the rock has good foliation and a dome-stage mineral lineation. Continue onto I-89 northbound.

Original Route:
138.2 Exit off I-89 for Lebanon & Hanover
138.5 Yield sign at end of ramp, bear right onto Rt. 120 north
138.7 Stoplight, continue straight on 120 north
139.1 Stoplight, continue straight on 120 north
140.0 Park on right side of road, as far off as possible, or just ahead at the tire dealer. If on Rt. 120, leave hazard indicators flashing and beware of traffic.

140.5 Stoplight at top of hill (entrance to DHMC), continue straight on 120 north
141.4 Stoplight (entrance to DHMC and Jesse's), continue straight on 120 north
141.8 Stoplight, bear to the left staying on 120 into Hanover
142.6 Stoplight at the Hanover Food Coop, bear to the right staying on 120 north
143.1 Stoplight, turn left onto Rt. 10 south (East Wheelock St)
143.2 Turn right up Dartmouth driveway
143.4 Dartmouth Observatory
143.5 Park wherever there is a spot. Climb down to outcrops alongside building housing Dartmouth College's Department of Earth Sciences and the Kresge Physical Science Library.

End of Trip

To get to Pico from here, go down and around the Dartmouth Green to the head of Main Street. Turn right onto West Wheelock Street and follow this across the Ledyard Bridge to Norwich. Take I-91 south to I-89 north to Route 4 west. It is approximately 45 miles.

References Cited

Allen, T, 1984. The Fall Mountain Outlier, a piece of the Fall Mountain Nappe, North Walpole, New Hampshire. Undergraduate Thesis, Harvard University.

Allen, T, 1985. "A reinterpretation of the Fall Mountain Nappe, as seen from Fall Mountain, North Walpole, New Hampshire, (abstract)." GSA Abstracts with Program 17(1): 2.

Allen, T, 1994. "New Hampshire Migmatites: Oxygen Isotope Fractionation During Partial Melting, and Suggestions of Structurally Enhanced Magma Migration." (abstract), EOS, Transactions of the American Geophysical Union 75(16): 360-361.

Allen, T, 1996a. "A Stratigraphic and Structural Traverse of Mount Moriah, New Hampshire." in Guidebook to Field Trips in Northern New Hampshire and Adjacent Regions of Maine and Vermont, Mark Van Baalen, editor, NEIGC 88: 155-169.

Allen, T, 1996b. "Petrology and Stable Isotope Systematics of Migmatites in Pinkham Notch, New Hampshire." in Guidebook to Field Trips in Northern New Hampshire and Adjacent Regions of Maine and Vermont, Mark Van Baalen, editor, NEIGC 88: 279-298.

Allen, T and CP Chamberlain, 1989. "Thermal consequences of mantled gneiss dome emplacement." Earth and Planetary Science Letters 93: 392-404.

Allen, T and CP Chamberlain, 1991. "Metamorphic evidence for an inverted crustal section, with constraints on the Main Karakorum Thrust, Baltistan, northern Pakistan." Journal of Metamorphic Geology 9: 403-418.

Allen, T and CP Chamberlain, 1992. "Pluton Migration Through Crust Leaves Migmatites Behind." GSA Abstracts with Program 24(7): A338.

Armstrong, TR, GJ Walsh and FS Spear, 1997. "A Transect across the Connecticut Valley Sequence in East- Central Vermont," this volume (NEIGC 89).

Barreiro, B and JN Aleinikoff, 1985. "Sm-Nd and U-Pb isotopic relationships in the Kinsman quartz monzonite, New Hampshire." GSA Abstracts with Program 17: 3.

Billings, MP, 1956. The Geology of New Hampshire, Part II - Bedrock Geology. Concord, State of New Hampshire Planning and Development Commission.

Billings, MP, 1935. Geology of the Littleton and Moosilauke Quads, New Hampshire. Concord, State of New Hampshire Planning and Development Commission.

Billings, MP, 1937. "Regional Metamorphism of the Littleton-Moosilauke area, New Hampshire." GSA Bulletin 48: 463-566.

Billings, MP, 1941. "Structure and metamorphism in the Mount Washington area, New Hampshire." GSA Bulletin 52: 863-936.

Billings, MP, and AB Cleaves, 1934. "Paleontology of the Littleton area, New Hampshire." American Journal of Science 28(5): 412-438.

Billings, MP, CA Chapman, RW Chapman, K Fowler-Billings and FB Loomis, 1946. "Geology of the Mount Washington Quadrangle, New Hampshire." GSA Bulletin 57: 261-273.

Billings, MP and JR Wilson, 1964. Chemical analyses of rocks and rock minerals from New Hampshire, Part XIX, Mineral Resources Survey. Concord, NH Department of Resources and Economic Development.

Billings, MP, and K Fowler-Billings, 1975. The Geology of the Gorham Quadrangle, New Hampshire and Maine. Concord, State of New Hampshire Department of Resources and Economic Development.

Boone, GM, EL Boudette and RH Moench, 1970. "Bedrock geology of the Rangeley Lakes - Dead River basin region, western Maine." Guidebook for Field Trips, NEIGC 62: 1-24.

Boucot, AJ and JB Thompson, Jr, 1958. "Late Lower Silurian fossils from sillimanite zone near Claremont, New Hampshire." Science 128: 362-363.

Boucot, A J and JB Thompson, 1963. "Metamorphosed Silurian brachiopods from New Hampshire." GSA Bulletin 74: 1313-1334.

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