50th meeting New England Intercollegiate Geological Conference: Connecticut, 1958: Trip 

Eaton, Gordon P.

Rosenfield, John L.

English

UNH Scholars' Repository

University of New Hampshire University of New Hampshire Scholars' Repository NEIGC Trips New England Intercollegiate Geological Excursion Collection 1-1-1958 Itinerary for Trip A: 50th Meeting, New England Intercollegiate Geological Conference Rosenfield, John L. Eaton, Gordon P. Follow this and additional works at: https://scholars.unh.edu/neigc_trips Recommended Citation Rosenfield, John L. and Eaton, Gordon P., "Itinerary for Trip A: 50th Meeting, New England Intercollegiate Geological Conference" (1958). NEIGC Trips. 19. https://scholars.unh.edu/neigc_trips/19 This Text is brought to you for free and open access by the New England Intercollegiate Geological Excursion Collection at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in NEIGC Trips by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact nicole.hentz@unh.edu. T R. Mever*ITINERARY FOR TRIP A 50th Meeti nq - New Engl and Intercollegiate Geol ogicaI Conference Trip Leaders: John L. Rosenfeld and Gordon P. EatonOctober II, 1958STOP I. (This stop is north of the northeast corner of the geo logic map. ) New London Turnpike, northwest of Marl borough.The purpose of this stop is to examine the lithologic units and associated structural and metamorphic features that can be seen in crossing the overturned syncline that extends north- northeastward from Great Hill in Portland toward the state line. The field excursion will proceed from the Monson gneiss (?) on the east (normal) limb to the Glastonbury gneiss on the west (overturned) Limb. On the east limb, the three members of the Bolton group display the following thicknesses (including tec­tonic repetition): Great Hill quartzite, 175'; Mine Brook calc-silicate, 600#; Camp Jenkins staurolite schist, 1,450'.STOP 2. (Optional) (E-9). On north side of Carr Brook, just east of Highway 17 near Gil dersleeve. Here one can see the dis­tinctive, highly-aluminous kyanite-rich schist and gneiss that characterize the lower part of the Collins Hill formation. A short distance west, on the east side of Highway 17, is an ex­posure of Maromas microcline gneiss.STOP 3. (C-I I) Exposures of coarse conglomerate of the Triassic Portland formation on west side of Highway 17, about one-third of a mile north of U.S. Highway 6A east of Portland.The clasts in this outcrop are of interest for the light they shed on the nature of the provenance area and its relative loca­tion at the time of deposition. Of particular interest is the contrast in grade of metamorphism between the clasts of schist and their higher grade equivalents at Stop I. In this outcrop, and in nearby exposures, it is possible to find large angular blocks and cobbles of Great Hill quartzite, Mine Brook carbonate rocks, and representative types from units below the Bolton group, including fine-grained garnet quartzites from the Collins Hill formation and anthophylite or cummingtonite rocks of the Middletown formation. Clasts that are believed to have been derived from the Bolton group are not found south of Duck Hill (just south of the Connecticut River). A few miles south of the river, clasts of a type of rock not found today in the Eastern Highlands appear rather abundantly. Boulders of gneissoid garnetiferous quartz porphyry are abundant. Their source, which must have been limited in its areal extent, has been eroded away. It seems logical to expect that feeder dikes will be found in the Eastern Highlands, but they have not, as yet, been discovered.It ine r ar y for T r ip  A - 2 -STOP 4. (N-13,14) South end of Great Hill, about 3 miles east of Portland. This is an area in which plunging structures allow one to prove that the quartzite on the east side of the schists of the Bolton group is the same as that on the west side, thereby proving that the formation is involved in a large fold.The truncation of the unconformity between the Collins Hill forma­tion and older rocks by the basal quartzite of the Bolton group, and the downward convergence of dips in this quartzite in areas to the north, prove that this fold is a syncline. At this locality the Great Hill quartzite is 450' thick, and the Mine Brook calc-silicate, 400', but both units display isoclinal folds.STOP 5. (P-28) Picnic ground north of Hurd Brook and Hubbard Brook syncline, in Hurd State Park, south of Middle Haddam. The rock at this locality is typical Maromas granitic gneiss. To the south, rocks in the lower part of the Collins Hill formation dip gently north in the core of the overturned, i soclinal Hubbard Brook syncline.LUNCH STOP. (R-29) One-half mile beyond Stop 5, on the Hurd Park loop. For those who are interested, just beyond the picnic ground, at the summit of the road, one of the large dia­base dikes that trend quasi-paralleI to the Eastern Border Fault, is exposed. It is possible that this dike, and others like it, represent the feeders for the lava flows in the Triassic lowland. Their composition is similar to that of the lavas. Furthermore, the presence of clasts of vesicular basalt in the Triassic Port­land formation suggests that lavas were present in the Eastern Highlands during its deposition. The orientation of tilted pipe vesicles in the lavas also indicates an eastern source.STOP 6. (R-26) Exposures located northeast of the entrance to Hurd Park. Outcrops of the Middletown formation, with numer­ous sills and cross-cutting dikes of Maromas gneiss, are well exposed here. Although these discordant masses of Maromas gneiss are abundant in the Middletown formation at this locality, they are nowhere found in the Col I ins Hi I I formation in nearby areas. Furthermore, the line of cut-off of these discordant masses is parallel to the strata within the Collins Hill formation. Be­cause of the presence, elsewhere, of coarse conglomerate at the base of the Collins Hill formation, and also because of the above­mentioned termination of dikes, it is believed that the Maromas gneiss and older metasedimentary and metavolcanic rocks lie un- conformably beneath the Collins Hill formation.STOP 7. (S-30) Hill 366, east of White Mountain, just south of Hurd Park: delineation of the Hubbard Brook syncline usingthe Hurd Park member (diopside-hornbIende rocks)of the CollinsItin era ry for T r ip  A -3-Hill formation as a marker horizon. Minor structural features such as folds, boudinage, mineral lineation, and fracture cleavage are we I I exposed. The rocks at this locality are in the sillimanite zone of metamorphism. Tracing the Hurd Park member of the Collins Hill formation across the Hubbard Brook syncline proves the stratigraphic equivalence of the sections mantling the Maromas gneiss and the Killingworth dome.STOP 8. (S-32) This exposure is just west of Alexson Brook, on the road south of Hurd Park: typical exposures of the dis- tinctive anthophylite-bearing and cummingtonite-bearing gneisses and amphi bol ites of the Middletown formation. Some of the an- thophylite here is asbestiform, and is difficult to distinguish from sil l imanite.STOP 9. (F-26) This locality lies along the power line just south of the Hubbard Brook road, about one mile east of Highway 9 in the town of Middletown. The exposure includes the lower highly-aluminous member of the Collins Hill formation and the underlying rocks of the Middletown formation. The Collins Hill formation is distinctive at this point for the coexistence of kyanite and small clots of fibrous sillimanite believed to haveder,ved from_the alteration of the kyanite. The underlying Middletown formation displays large lensoid masses of epidote. These masses also occur in the Glastonbury gneiss near its con­tact with the Coll ins Hill formation, and it has been suggested that they may represent meta-caliche.STOP 10. (Optional) (H-25) This locality is on the north side of Hubbard Brook road, about one-half mile east of Stop 9.The basal conglomeratic gneiss of the Collins Hill formation, characterized by numerous small quartz pebbles, is well exposed. Flattening of the pebbles within the plane of schistosity suggests considerable distention over the northward plunging nose of the Killingworth dome.STRATIGRAPHIC SECTION OF MIDDLE HADDAM AREA-1 XGray non-rustyIntrusive diabasic rocks (Triassic)Portland formation: Feldspathic conglomerate and arkose (Triassic)MAJOR ANGULAR UNCONFORMITY (also Metamorphic "Unconformity")Camp Jenkins formation (Littleton)garnet-staurolite-binary schist; some platy quartz- sericite schist and quartzite particularly in low­er portion (Lower Devonian).Mine Brook formation (Fitch): Laminar calcareous biotite gneiss, diopside granulite, and schist showing deep pits on the weathered surface due to the solution of calcite marble masses. Rusty weathering aluminous schist in upper part. (Middle Sil urian)Great Hill formation (Clough): quartzite in the lower portion granulr quartzite and Lower Sil urian)UNCONFORMITYformation: Rusty-weathering graphitic binary schist commonly containingConglomeratic overlain by wel quartz sericitebanded granular schist (late _ ANGULAR Collins Hill garneti feroussillimanite and/or kyanite. In its lowest portion this formation commonly contains a basal conglom­erate gneiss associated with an overlying well- banded unit, consisting of: fine-grained quartz­ite, containing manganiferous garnet and cumming- tonite; and laminar amphibolite, occasionally containing relatively large garnets. Interbedded caIc-sil i cate bands and fine-grained biotite-Muscovite gneiss are increasingly abundant to west. Horizons consist of persistent amphibolites and c a lc-silicate bands in lower part of formation (Middle Ordovician?).^  UNCONFORMITYGlastonbury and Maromas gneisses: Biotite and hornblende granitoid gneiss of probable igneous origin showing intrusive relationships into the Middletown formation and a sedimentary contact with the overlying Collins Hill formation (Lower Ordovician?).INTRUSIVE CONTACT Middletown formation: Amphibolites and heterogen­eous biotite-oligoclase gneiss, commonly well- banded and characterized by the presence in many places of cummingtonite, hornblende, and antho- phyllite (cambio-Ordovician =an?)Monson or Haddam gneiss: Well-banded oligoclase-rich gneisses with subordinate amphibolite bands (probably of sedimentary origin). This unit is separated with difficulty from the overlying Middletown formation to which it appears to be related (age questionable; pre-Ordovician?)72°37 30't»JL£ i t*/L£72°JO'GS Ol Oe /C M A P  O P  77/S M I D D L E  H A D D A M  Q U A D R A N G L EB y  J oh ri L. R osen feld &  G o r d o n/suraS t r u c t u r a l  S e c t i o n s  o f  t h eMIDDLE HADDAM AREA4I°30'C.72030*00'Metamorphism Middle Haddam Area

Itinerary for Trip A: 50th Meeting, New England Intercollegiate Geological Conference

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Itinerary for Trip A: 50th Meeting, New England Intercollegiate Geological Conference

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