No description available.

No description available.

No description available.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1976. / Microfiche copy available in Archives and Science / Bibliography: leaves 232-239. / by Rudolph Hon. / Ph.D.

Metasediments from portions of two of the six lithologic terranes in the Penobscot Bay area of coastal Maine, the Late Precambrian (?) to Ordovician(?) Copeland Formation and the Rider Bluff member of the Copeland Formation at the eastern margin of the Passagassawakeag (PGW) terrane and the Silurian (?) to Devonian (?) Bucksport Formation of the adjacent Bucksport terrane, shared a common history of four phases of ductile deformation (D₁, D₂, D₃, and D₄) and interdeformational metamorphism and granitic plutonism. D₁ (early Acadian ?) produced tight to isoclinal folds and an axial plane foliation that deform all three metasedimentary units and contacts between these units. These units and therefore the PGW and Bucksport terranes must have been together by the time of D₁ at the latest. No observed structural or metamorphic gradient coincides with this terrane boundary in the Penobscot Bay area, but in southeast Maine it is mapped as a pre-metamorphic thrust fault. Intrusion of the 412± 14 Ma Stricklen Ridge granite and amphibolite facies metamorphism occurred between D₁ and D₂ . D₂ (Acadian) produced open, upright folds and a strong, hinge-parallel mineral elongation lineation under upper greenschist to lower amphibolite conditions. D₃ ductile strike-slip shear zones formed under upper greenschist to lower amphibolite conditions, and D₄ open, steeply-reclined folds formed under greenschist facies conditions. D₃ and D₄ are probably related to the same stress system as the dextral strike-slip Norumbega Fault Zone (Alleghanian) and probably represent a continuum of deformation. Brittle faults exploit D₃ shear zones and may also be related to the same stress system. / M.S.

The Bottle Lake Complex is a Paleozoic composite granite emplaced near the core of the Merrimack synclinorium in east-central Maine. The two plutons exposed within the Complex are reversely zoned in their mineralogy, major and trace element compositions. Each intrusive exhibits characteristic features including the abundance of amphibole and mafic xenoliths as in the Passadumkeag River granite, and relative abundance of biotite, aplites, and pegmatites in the granite of Whitney Cove. Both display geochemical variations identifying the respective core facies as the least differentiated zones compared to the rims. On the basis of field relations the relative sequence of intrusion is established between the two intrusives, but geochronologic studies using Pb-Pb zircon ages do not display a clear age difference. The granite of Passadumkeag River is, as judged by the field relations, the youngest pluton in the Complex. This granite is also the most heterogeneous body as expressed by petrography, mineral chemistry, and bulk composition. The numerous mafic xenoliths enclosed by the Passadumkeag River pluton display textural, mineralogical, and geochemical variations distinct from those found in the host granitoid rocks. The source of the Bottle Lake Complex was heterogeneous in composition as suggested by the petrology of the granites and xenoliths, and by the wide range in ²³⁸U/²⁰⁴Pb of the batholith. Fractional crystallization accounts for most of the variation within each pluton, although other processes such as mixing of liquids must also be postulated. In the case of the Whitney Cove pluton, mixing occurred prior to the major stage of fractionation. The granite of Passadumkeag River, however, records the mixing of a different batch of liquid during fractionation. Comparison of the geologic relations in the granites of east-central Maine, emplaced across the Merrimack synclinorium indicates that a major discontinuity in the sources of granitic liquid exists on either side of the Norumbega fault system. The Bottle Lake Complex is a distinctive batholith representative of the plutons emplaced in the core of the synclinorium. Together with the nearby Center Pond granite they form a distinct subgroup in comparison to the rest of the plutons on the northside of the Norumbega fault. The lead isotopic compositional variation across the synclinorium is unlike the documented changes present in complex subduction systems such as the Sierra Nevada. This is in agreement with previous geologic studies which suggested an absence of features characteristic of destructive tectonic margins in this area of New England. Granite generation across the synclinorium occurred in a short time interval probably by melting volcaniclastic materials on the north side of the fault, and by melting cratonic detritus on the opposite side. / Ph. D.

The Lucerne pluton intrudes rocks of the Penobscot formation Ordovician-Silurian (?)), a quartz-rich sulfidic pelite that contains muscovite, biotite, cordierite, andalusite, plagioclase, pyrrhotite and graphite outside the thermal aureole; and the Bucksport formation (=Vassalboro, Silvian-Devonian (?)), a calcareous, quartzofeldspathic pelite that contains chlorite, biotite, celadonitic muscovite, albite, and ilmenite outside the Lucerne aureole. Within the aureole, the Penobscot formation contains K-feldspar plus andalusite as the result of muscovite reaction with quartz. Corundum occurs at the immediate contact of the granite from the. reaction of the remaining muscovite. The Bucksport formation is recrystallized within the aureole to a purple and green gneiss. The gneissic banding is not present in the low grade calcareous rocks, and represents the segregation of biotite-rich and calc-silicate-rich bands. Vertical or sleepy dipping, the banding parallels both the regional strike and the intrusive contact, and is probably the result of both mechanical and chemical effects. The following sequence of assemblages (+ quartz) is found in the calcareous portions of the Bucksport formation as the Lucerne contact is approached: a) chl + bio + musc + cc + albite; b) bio + cc + plag (An₂₅₋₃₃); c) actinolite + cc + K-feldspar + plag (An₄₀); d) diopside + zoisite + sphene +cc+ plag (An₈₅₋₉₀). Interbedded pelites contain biotite + quartz + plagioclase + pyrite with corundum occurring at the igneous contact in quartz free beds. The mineral assemblages in the Lucerne aureole indicate a lithostatic pressure between 1000 and 3000 bars during metamorphism with temperatures between 700°C and 450°C. Isobaric univariant assemblages in the calc-silicate beds indicate buffering of H₂O/CO₂ fluids produced by prograde reactions. H₂O rich fluids that produced zoisite were probably associated with late stage crystallization of the Lucerne. / Master of Science