Andalusite, Kyanite, and Sillimanite from the Mount Moosilauke Region, New Hampshire

DOUGLAS RUMBLE III Department of Geology, University of California, Los Angeles, California 90024

ABSTRACT of andalusite is wedge-shaped and terminates with increasing pressure. A number of prob- Andalusite, kyanite, and sillimanite occur lems important to the interpretation of the in regionally metamorphosed rocks of the Al2SiOo distribution, such as metamorphic Mount Moosilauke region, New Hampshire. chronology and postmetamorphic tectonics, Andalusite and sillimanite are found together were raised in their paper; however, in a frequently in the same thin sections. Kyanite report of such scope these questions could not appears once in the same thin section with be answered in detail. Furthermore, there sillimanite but never with andalusite. were then no systematic data available on the Andalusite and sillimanite mica schists chemical compositions of the aluminum were subjected to multiple episodes of recrys- silicates; therefore, the trace-element contents tallization that resulted in the reaction se- of the polymorphs could not be used to test quence andalusite —» sillimanite —» andalusite. the hypothesis of attainment of chemical Kyanite crystallized in an adjacent area during equilibrium. the same time period. Kyanite from quartzite The purpose of this paper is to present the containing hematite is enriched in Fe203 but the results of a detailed study of the distribu- andalusite. and sillimanite from rutile and tion, metamorphic chronology, and chemical ilmenite—or graphite-bearing mica schists— compositions of the aluminum-silicate minerals are relatively impoverished in Fe2Os. The occurring in the Mount Moosilauke region, Al2Si05 minerals crystallized during post- New Hampshire. The Mount Moosilauke Lower Devonian, pre-Triassic regional meta- region is one of the New England localities morphism under conditions approaching chem- where the trace of the "fossil isobaric surface" ical equilibrium. (Thompson and Norton, 1968, p. 324) cross- cuts middle-grade metamorphic rocks. In such INTRODUCTION an area, occurrences of all three polymorphs Thompson and Norton (1968) published a are to be expected (see Billings, 1937, p. 482, synthesis of Paleozoic regional metamorphism 493); therefore, the most favorable conditions of New England in which they distinguish be- are afforded for testing the hypothesis of tween the andalusite-sillimanite terrane of Thompson and Norton. northeastern New England and the kyanite- sillimanite terrane of southwestern New England. A line was drawn across the map of METHOD OF STUDY New England "such that all occurrences of andalusite believed to have formed during The initial phase of the work was facilitated regional metamorphism lie to the east or by the comprehensive petrographic collections northeast of it" (Thompson and Norton, 1968, of the Department of Geological Sciences, p. 324). Assuming the mapped Al2Si03 Harvard University. One thousand thin sec- distribution to be due to local equilibration in tions of rock samples from the Moosilauke, a rock volume subjected to continuous pres- Littleton, Franconia, and Woodsville quad- sure and temperature gradients, they inferred rangles (all collected by M. P. Billings), the the line so drawn to be the approximate trace Mount Cube quadrangle (collected by J. B. of the isobaric surface representing the pres- Hadley), and the Plymouth quadrangle sure of the invariant point in the system (collected by C. B. Moke) were studied with Al2SiOs. This is so because the stability field the petrographic microscope. Two-thousand

Geological Society of America Bulletin, v. 84, p. 2423-2430, 1 fig., July 1973 2423

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rock samples and 800 thin sections were col- folded and refolded into north-northeast- lected and studied by me. trending anticlinoria and synclinoria (Rumble, Two important sampling biases affect the 1971b; Thompson and others, 1968). mapped distribution of Al2Si05 polymorphs The kyanite-bearing rocks located on Black (Fig. 1). In order to avoid the problem of Mountain and to the southwest were meta- interpreting relic mineral assemblages of pre- morphosed during the penetrative deforma- Silurian age, sampling efforts were concentrated tion that accompanied recumbent folding and on rocks of Silurian and Devonian age. All the developement of the anticlinoria (Rumble, major outcrop areas of Silurian or Devonian 1971b). The growth of porphyroblastic min- mica schist and quartzite, whose bulk com- erals in the andalusite and sillimanite mica positions favored the crystallization of alumi- schists found east and northeast of Black num silicates, were sampled thoroughly. Out- Mountain continued after penetrative de- crop areas of amphibolite, quartz-feldspar formation had ceased. gneiss, and calc-silicate rock received cursory Outcrop belts of Bethlehem Gneiss occur- attention only. ring on either side of the Bronson Hill anti- Minor-element contents of aluminum-silicate clinorium are erosional remnants of a large minerals were measured using an ARL-EMX nappelike body whose root zone lies east of microprobe located in the Department cf the anticlinorium and whose leading edge lies Geology, UCLA. Wavelength scans carried ou: to the west (Billings, 19156, Fig. 13, p. 126; at 15 kv and 0.04 pa. sample current revealed Thompson and others, IS68, PI. 15-lb). The Fe as the only detectable impurity (the Kinsman Quartz Monzorite may also occupy detectability limit for transition metals is a similar structural position (Thompson and estimated to be 0.1 weight percent). Quantita- others, 1968, PI. 15-lb). The origin of these tive analyses of Fe content were made at 15 rocks has been interpreted in a variety of kv and 0.03 jua specimen current with Elba ways (Thompson and others, 1968, p. 208; hematite (provided by A. L. Albee) as standard. Page, 1968, p. 377-378; Billings, 1937, p. 537). Individual grains were analyzed using 100-sec Most workers would agree that their emplace- counting times such that the number of mea- ment did not significantly change the thermal surements on the Fe Ka x-ray peak equalled regime imposed during regional metamorphism. the number of measurements of background The French Pond Granite is similar in x-radiation. Counting statistics were calculated mineralogical and chemical composition to using the data reduction scheme of Boyd the Bethlehem and Kinsman rocks but it was (Boyd and others, 1969) and Hadidiacos intruded after regional metamorphism. It (Hadidiacos and others, 1971); matrix cor- superimposed a contact aureole containing rections were calculated by the Bence-Albee fibrolitic sillimanite ori its staurolite- and method (Bence and Albee, 1968). Calculated garnet-bearing country rocks (White and detectability limit of Fe in the quantitative Billings, 1951, p. 692). The White Mountain analyses is 0.01 weight percent. plutonic-volcanic series, is Jurassic in age (Lyons and Faul, 1968, p. 312) and was em- GEOLOGICAL HISTORY placed subsequent to folding and regional The pre-Silurian metamorphosed sedimen- metamorphism of the .Silurian and Devonian tary and igneous rocks exposed in the Bronson rocks. Contact metamorphic effects, including Hill anticlinorium (Fig. 1) are probably the formation of anddusite, have been ob- Ordovician in age (Thompson and others, served adjacent to the stock exposed in the 1968, p. 206); they may have experienced northeast corner of the: Plymouth quadrangle metamorphism and deformation before deposi- (Moke, 1946, quoted by Billings, 1956, p. tion of Silurian sediments but evidence for ':he 142). In the discussion that follows, only those pre-Silurian orogeny has been almost com- aluminum silicates formed during regional pletely erased by post-Lower Devonian, pre- metamorphism will be considered. Triassic metamorphism and deformation (Nay- The Ammonoosuc fault developed after lor, 1969; Rumble, 1969). Metamorphosed regional metamorphism of the Silurian- and sedimentary and igneous rocks of Silu ian Devonian-age rocks. Neither geology nor and Devonian age overlie unconformably the mineral occurrences are shown on Figure 1 for pre-Silurian rocks (Billings, 1937). The entire the area lying west cf the fault (see Albee, stratigraphic succession has been recumbently 1968, Fig. 25-1). The fault is the locus of

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j White Mountoin plutonic-volcanic series, I Jurassic, post-regionol metomorphism

French Pond Granite, Devonian, post- regional metamorphism.

1 Bethlehem Gneiss and Kinsman Quartz Monzon- ] ite, Devonian, syn-regional metamorphism • Silurion and Devonion metamorphic rocks

I Ordovician metamorphic rocks

Locotion of Figure I ond >5' quadrangles Stourotite isograd defined by first oppeorance of Is WoodsviHe, 2 = Moos'louke, 3= Fronconia, X staurohte, tick morks on high grade side Rocks on 4s Mt. Cube, 5 s Rumney,6s Plymouth x low grade side of isogrod are m garnet zone

Figure 1. Aluminum-silicate distribution of the Mount Moosilauke region, New Hampshire. Geology A Andolusite occurrence and mineral distribution after Billings (1937, 1956), f Fibrohtic silhmonite occurrence Hadley (1942), Moke (1946), Page (in Fowler-Billings and Page, 1942), Rumble (1969, 1971b), Williams and K Kyamte occurrence Billings (1938), White and Billings (1951), and new S Prismatic siilimanite occurrence observations by me. S f A ^ssemblageof pnsmotic siliimonite.fibrolitic silli- * ' manite and ondalus»te occurs m one thin section

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TABLE 1. FE2O8 CONTENTS OF ALUMINUM-SILICATE MINERALS AND MINERAL ASSEMBLAGES FROI/ THE MOOSILAUKE QUADRANGLE

Sample 71-31 71-32 71-59 71-60 71-96 68- no.* 68-44 B B 71-33 71-35 B D G 302A

quartz + + + + + + + + + muscovite + + + + + + + + + andalusite + kyanite + + + + + + + + prismatic sillimanite fibrolitic sillimanite + staurolite + + + chloritoid + + + garnet + chlorite + biotite + tourmaline + + + + rutile + + hematite + + + + + + ilmenite + + + magnetite + + + + pyrite pyrrhotite t + Fe203 0.5- 0.8- 0.3- 0.5- 0.5- 0.3- 0.3- 0.3- wt percent 0.7 1.0 0.6 0.9 0.9 0.7 0.6 0.6 0.30 in Al2Si06 (0.64) (0.85) (0.51) (0.74) (0.75) (0.59) (0.55) (0.58)

'The first eight samples listed were collected near Black Mountain; the remainder of the samples were collected near Mount Moosilauke. t Total Fe content assumed to be present as FeiOs; figure in parenthesis gives average Fe2C>3 content.

kink-banding and intense retrograde meta- particular chemical reaction. The sillimanite morphism (Hadley, 1942, p. 171-173; White isograd lies in the east limb of the Bronson and Billings, 1951, p. 689-690). Shear zones Hill anticlinorium (Fig. 1). Staurolite persists showing kink-banding and retrograde meta- in the part of the sillimanite zone that is ad- morphism are scattered throughout the area jacent to the kyanite zone; no staurolite is shown in Figure 1; they cannot be mapped for known from the Plymouth or adjacent areas more than a few hundred yards along strike. of the Rumney quadrangle. The sillimanite- Retrograde metamorphism associated with potash feldspar isograd (Guidotti, 1963) is faulting has doubtless destroyed many alumi- located in the southeast corner of the Ply- num-silicate occurrences but the relative mouth quadrangle. disposition of the remaining aluminum silicates has not been significantly affected. DISTRIBUTION OF ALUMINUM- SILICATE MINERALS DISTRIBUTION OF REGIONAL Four distinctive areas of aluminum-silicate METAMORPHIC MINERAL ISOGRADS mineral occurrence are shown in Figure 1: (1) The staurolite isograds shown on Figure 1 The northwestern section including the Salmon divide the area into a band of staurolite- Hole Brook syncline has no aluminum silicates; bearing rocks in the extreme west and a (2) the southwestern section located in the central region of staurolite-bearing rocks Mount Cube quadrangle and the southwest separated by a medial outcrop belt of garnet- ninth of the Moosilauke quadrangle contains mica schists that lack staurolite. The staurolite kyanite only; (3) the northeastern section isograds are defined on the basis of the presence contains andalusite, with or without sillimanite; or absence of staurolite in rocks of appro- and (4) sillimanite alone occurs throughout the priate bulk composition. The isograds do not southeastern section in Figure 1. Although it represent the outcrop trace of an isothermal is convenient to divide the mapped region surface or of the equilibrium surface of one in this way, the reader must bear in mind that

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TABLE 1. (Continued)

Sample 70- 70- 71- 71-92 no.* 178 185 71-82 71-83B 146D L-569 A LH-57 LH-58 LM-83

quartz + + + + + + + + + + muscovite + + + + + + + + 4- + andalusite 4- + + + + + kyanite prismatic sillimanite + + + + + + fibrolitic sillimanite + + 4- + + 4- 4- staurolite + + + + + + 4- + 4- chloritoid garnet + 4- 4- 4- + + + chlorite 4- + + + + + + biotite + + + + + + + + + tourmaline + + + + + + 4- + rutile + + + + + + hematite ilmenite + + + + + + + + + + magnetite pyrite 4- pyrrhotite 4- + + Fe2(V 0.36(A) wt percent 0.30 0.33 0.42(A) 0.17(S) 0.31 0.33 0.12 0.17 0.27 0.12 in AljSiOs

* The first eight samples listed were collected near Black Mountain; the remainder of the samples were collected near Mount Moosilauke. t Total Fe content assumed to be present as Fe2C>3; figure in parenthesis gives average Fe20s content.

the four areas are elements of a regional rences in the west limb of the Bronson Hill metamorphic continuum, continuously vary- anticlinorium. The effective bulk composition ing spatially in its mineralogical and textural of the oxidized rocks is improverished in ferrous properties. iron because of the stability of hematite; in Rocks of the aluminum-silicate-free zone consequence, kyanite is the only silicate, apart located in the northwest corner of Figure 1 from quartz and muscovite, that occurs in contain the lower grade assemblages (plus them. Kyanite is found with biotite in reduced quartz and muscovite) chloritoid-chlorite- rocks located in the Mount Cube quadrangle, garnet-tourmaline-ilmenite and chloritoid- just east of the Ammonoosuc fault. The char- chlorite-garnet-biotite-ilmenite; higher-grade acteristic assemblage is quartz-muscovite- assemblages include staurolite-chlorite-biotite- kyanite - staurolite - garnet - biotite - ilmenite- graphite-ilmenite and staurolite-garnet-biotite- rutile with or without graphite. graphite-ilmenite. Textural evidence suggests The Lower Devonian mica schists of the many of the porphyroblastic minerals cry- northeastern section of the area shown in stallized following deformation rather than Figure I contain mineral assemblages of during it. Aluminum-silicate minerals are andalusite, fibrolitic sillimanite, prismatic silli- known to be stable at this metamorphic grade manite, and staurolite that have been subject in rocks of highly aluminous bulk composition. to repeated episodes of recrystallization. Despite diligent searching, rocks of such bulk Staurolite occurs throughout these schists in composition have not been found. two characteristic textures: (1) Clusters of The mineral assemblages of kyanite-bearing randomly oriented staurolite euhedra (max- quartzite from the Black Mountain area are imum length 1/16 in.) are embedded in a listed in Table 1; note the conspicuous absence mesh of randomly oriented muscovite grains; of the coexistence of kyanite and biotite. The the staurolite + muscovite aggregates are highly oxidized nature of these assemblages pseudomorphs after a former porphyroblastic is characteristic of most of the kyanite occur- mineral which had a parallelepiped shape and

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dimensions of 1 in. X 1/4 in. X 1/4 in.; and CHEMICAL COMPOSITIONS OF (2) staurolite euhedra also occur in discon- ALUMINUM-SILICATE MINERALS tinuous rims around prismatic sillimanite Fe203 contents of aluminum-silicate minerals (Billings, 1937, p. 551-552). Andalusite in the are given in Table 1 (total Fe has been recal- area north of Mount Moosilauke occurs as culated as Fe20s). Analyzed kyanites are porphyroblasts 1/8 to 1/4 in. in diameter that uniformly enriched in Fe2C>3 relative to anda- poikiloblastically enclose quartz, biotite, and lusite and sillimanite. The kyanites are in- staurolite. The andalusite occurrences just homogeneous with respect to FeîOs content; south of Hurricane Mountain are quite dif- andalusite and sillimanite are not. The kyanites ferent from any of the other known occur- occur in relatively oxidized rocks and their rences. Here clusters of subhedral andalusite (1/16 in. maximum length) are embedded in Fe203-rich contents reflect rock bulk composi- a mesh of biotite and muscovite grains. Sub- tion (see, for example, Chinner and others, hedral andalusite is also found rimming 1969, Fig. 1; Okrusch aid Evans, 1970). prismatic sillimanite; the similarity of these Coexisting aluminum silicates have been textures to those of staurolite, described above, analyzed from only one sample, 71-83B; is striking. Fibrolitic sillimanite usually occurs andalusite is enriched in Fe203 relative to in association with biotite and muscovite (see, sillimanite (see Okrusch and Evans, 1970, for example, Chinner, 1961); however, it also Fig. 1; Chinner and others, 1969, Table 7; occurs independently in quartz grains. All of Albee and Chodos, 1969, Fig. 2). the prismatic sillimanite in the vicinity of Mount Moosilauke and Hurricane Mountain occurs as porphyroblasts 1/4 to 1/3 in. in INTERPRETATION OF REPEATED diameter which consist of a mosaic of small RECRYSTALLIZATION OF MOUNT grains slightly misoriented with respect to each MOOSILAUKE MICA SCHISTS other; viewed under crossed nicols, the porphyroblasts show a patchy extinction. The The minerals and textures, of the mica schists prismatic sillimanite is divided into four sec- exposed in the Hurricane Mountain—Mount tions by inclusions of quartz, biotite, and Moosilauke belt are believed to have originated ilmenite that are identical in appearance to during a single metamorphic: episode of gradual those found in chiastolitic andalusite. Speci- dehydration followed by partial rehydration. mens of prismatic sillimanite photographed by The aluminum-silicate minerals crystallized Rosenfeld (1969, PI. 3) and Hollister (1969, within their respective equilibrium stability PI. 2F) are identical to those of the Mount fields. Once crystallized, however, they per- Moosilauke area. sisted metastably. The initial assemblage formed in the mica schists was quartz-musco- The occurrences of andalusite and fibro- vite-andalusite-staurolite-garnet- biotite-ilmen- litic sillimanite located in the outcrop areas of ite, with or without plagiodase, graphite, and metamorphic rock included within the rocks pyrrhotite. This assemblage was then sub- of the White Mountain plutonic-volcanic jected to a prograde metamorphism involving series (northeast quarter of Franconia quad- the following reactions: andalusite = prismatic rangle) are associated with cordierite-bearing sillimanite in the southern part of the belt, and rocks in which garnet is very rare, in striking 6 staurolite + 4 muscovite 7 quartz contrast to the rocks of the Mount Moosilauke = 31 fibrolitic sillimanite -f- 4 biotite + 3 H2O area. These mica schists lie within a ring dike of the White Mountain plutonic-volcanic (Billings, 1937, p. 552; Thompson and Norton, series; Williams and Billings (1938, p. 1019) 1968, p. 323). believed them to have subsided 10,000 ft or The mica schists were then subjected to a more following their metamorphism under slight rétrogradation according to the follow- low confining pressure. ing reactions: The southeastern section shown in Figure 1 prismatic sillimanite = andalusite contains both fibrolitic and prismatic silli- and manite in the assemblage quartz-muscovite- fibrolitic sillimanite = andalusite sillimanite-garnet-biotite-plagioclase-ilmenite- rutile. No chiastolitic inclusions are found in in the Hurricane Mountain area, and the the prismatic sillimanite. reactions:

31 andalusite -(- 4 biotite -)- 3 H2O = 6 staurolite The distribution of chloritoid-staurolite -f- 4 muscovite 7 quartz quartzites with respect to outcrops of alumi- and num-silicate minerals in the Moosilauke quad- 31 prismatic sillimanite -{- 4 biotite 3 H2O rangle confirms Ganguly's inference that the = 6 staurolite -)- 4 muscovite + 7 quartz Al2Si05 invariant point lies within the thermal produced the staurolite-muscovite pseudo- stability range of chloritoid (Rumble, 1971a, morphs (Billings, 1937, p. 552). p. 290-294; Ganguly, 1969, p. 939-942). That different retrograde reactions operated It is concluded that the rocks of the southern in different areas may be attributed to variable part of the Mount Moosilauke quadrangle were access of aqueous fluid to the already de- recrystallized under the pressure-temperature hydrated rocks. The reader will readily recog- conditions of the AUSiOs invariant point dur- nize that the sequence of reactions outlined ing post-Lower Devonian, pre-Triassic regional above is largely ad hoc, a deficiency that can metamorphism. The hypothesis of Thompson only be eliminated by acquiring modal and and Norton (1968, p. 324) regarding the chemical-composition data on the minerals in location of the invariant point isobar in the question in order to set up mass balance con- Mount Moosilauke area is confirmed. This im- straints that the proposed reactions must plies the rocks of the Mount Moosilauke were satisfy. buried beneath 7 mi of overburden during regional metamorphism. The geological validity CONCLUSIONS of such a thickness of overlying strata is dif- The variation of Fe203 contents of alumi- ficult to evaluate because the Silurian-Devon- num-silicate minerals with rock bulk composi- ian stratigraphic section has been truncated by tion (Table 1) is a necessary but not sufficient erosion and because of the difficulty in esti- condition that must be satisfied in order to mating the amount of secondary thinning or demonstrate the minerals attained heteroge- thickening of strata produced by deformation. neous chemical equilibrium during recrystallization (Zen, 1963, p. 941). The chemical ACKNOWLEDGMENTS inhomogeneity of kyanite proves it was unable This paper has been improved through dis- to attain homogeneous equilibrium. The cussion with W. G. Ernst, J. Ganguly, ). L. Fe203 contents reported in Table 1 are not Rosenfeld, and E. Stoddard. The critical large enough to significantly change the comments of A. Heitanen and J. B. Lyons are stability fields of the aluminum silicates (Strens, gratefully acknowledged. M. P. Billings gave 1968; Holdaway, 1971). The distribution of access to his field notebooks and rock-specimen Al2Si05 minerals approaches that predicted collections for the Moosilauke, Woodsville, from the appearance of the AI2S1O5 equilibrium and Franconia quadrangles. The study was phase diagram especially when allowance is supported initially by a National Science made for the repeated recrystallization of the Foundation graduate fellowship and the re- mica schists of the Mount Moosilauke-Hur- sources of the Department of Geological ricane Mountain belt. A one-phase field of Sciences, Harvard University. Field work was kyanite in the southwest is in contact with a completed during the summers of 1970 and field of andalusite to the northeast and a field of 1971, while I held a postdoctoral fellowship sillimanite to the east. The mere fact of coexis- from the Carnegie Institution of Washington, tence of two aluminum silicates, as in the D.C. Microprobe analyses and manuscript Mount Moosilauke-Hurricane Mountain belt, preparation have been supported by National cannot be taken as a priori evidence of dis- Science Foundation Grant GA 31202. equilibrium (Thompson, 1970, p. 532-533). Although the metastable behavior of fibrolitic sillimanite relative to andalusite has been demonstrated in short-term laboratory exper- REFERENCES CITED iments (Holdaway, 1971, p. 112-114), only Albee, A. L., 1968, Metamorphic zones in northern one example of the conversion of fibrolitic Vermont, in Zen, E-an, and others, eds., sillimanite to andalusite has been found in the Studies of Appalachian geology: New York, Mount Moosilauke area and it is accompanied John Wiley, p. 329-341. by textures suggesting the simultaneous con- Albee, A. L„ and Chodos, A. A., 1969, Minor element content of coexistent Al Si0 poly- version of prismatic sillimanite to andalusite 2 6 morphs: Am. Jour. Sci., v. 267, p. 310-316. (Hurricane Mountain). Bence, A. E., and Albee, A. L., 1968, Empirical

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Ganguly, J., 1969, Chloritoid stability and related Strens, R.G.J., 1968, Stability of AljSi06 solid parageneses: theory, experiments, and applica- solutions: Mineralog. Mag., v. 36, p. 839-849. tions: Am. Jour. Sci., v. 267, p. 910-944. Thompson, J. B., Jr., 1970, Geochemical reaction Guidotti, C. V., 1963, Metamorphism of the and open systems: Geochim. et Cosmochim. pehtic schists in the Bryant Pond quadrangle, Acta, v. 34, p. 529-551. Maine: Am. Mineralogist, v. 48, p. 772-791. Thompson, J. B., Jr., and Norton, S. A., 1968, Hadidiacos, C. G., Finger, L. W„ and Boyd, F. R., Paleozoic regional metamorphism in New 1971, Computer reduction of electron probe England and adjacent areas, in Zen, E-an, and data: Annual Rept. of the Director, Geophys. others, eds., Studies of Appalachian geology: Lab., 1969-1970, Carnegie Inst. Washington, New York, John Wiley, p. 319-327. p. 294. Thompson, J. B., Jr., Robinson, P., Clifford, T. N., Hadley, J. B., 1942, Stratigraphy, structure, and ar_d Trask, N. J., 1968, Nappes and gneiss petrology of the Mt. Cube area, New Hamp- domes in west-central New England, in Zen, shire: Geol. Soc. America Bull., v. 53, p. 113- E-an, and others, eds., Studies of Appalachian 176. geology: New York, John Wilev, p. 203-218. Holdaway, M. J., 1971, Stability of andalusite and White, W. S., and Billings, M. P., Ì951, Geology the aluminum silicate phase diagram: Am. of the Woodsvillc: quadrangle, Vermont-New Jour. Sci., v. 271, p. 97-131. Hampshire: Geol. Soc. America Bull., v. 62, Hollister, L. S., 1969, Metastable paragenetic p. 647-696. sequence of andalusite, kyanite, and silli- Williams, C. R., and Billings, M. P., 1938, Petrol- manite, Kwoiek area, British Columbia: Am. ogy and structure of the Franconia quadrangle, Jour. Sci., v. 267, p. 352-370. New Hampshire: Geol. Soc. America Bull., Lyons, J. B., and Faul, H., 1968, Isotope geo- v. 49, p. 1011-1044. chronology of the northern Appalachians, Zen, E-An, 1963, Components, phases, and in Zen, E-an, and others, eds., Studies of c-iteria of chemical equilibrium in rocks: Am. Appalachian geology: New York, John Wiley, Jour. Sci., v. 261, p. 929-942. p. 305-318. Moke, C. B., 1946, Geology of the Plymouth Quadrangle: Concord, New Hampshire, New MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST Hampshire State Planning and Development 30, 1972 Commission, 21 p. REVISED MANUSCRIPT RECEIVED JANUARY 10,1973

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