ABSTRACT
Continuous outcrop mapping (1:240) along coastal exposures in
southern Maine has led to the recognition of a complex brittle
structural history that established the pre-existing structural
grain for, and culminated in, the intrusive development of several
Mesozoic dike swarms. The structural grain within the Rye
Formation of the southern part of the field area consists of a
dominant NE-trending near-vertical gneissic (mylonitized)
foliation on which is superimposed the intense brittle shear
fracturing of the pseudotachylyte-bearing Fort Foster Brittle
Zone. This brittle shear fracturing was responsible for the later
localization of explosive igneous breccias and felsic melts above
the largely unexposed Gerrish Island Igneous Complex. The later
emplacement of the dominant N25E-trending dike swarm, possibly
Late Jurassic to Early Cretaceous in age, was primarily
independent of the pre-existing structural grain and directly
related to a system of late rusty-weathering open brittle
fractures. The structural grain within the Kittery Formation of
the northern part of the field area consists of a prominent
N60E-trending vertical planar bedding-anisotropy as limbs of
Acadian fold structures and a second N45E-trending vertical planar
cleavage anisotropy related to a late Z-shaped asymmetric fold and
dextral shear zone development. These bedding-cleavage
anisotropies are responsible for the structural localization of a
prominent N60-45E trending dike swarm, possibly Early Triassic to
Early Jurassic in age, associated with the alkaline syenite
complex at Agamenticus. The bedding-anisotropy is found to play an
important role in determing the character of strain accommodation
between en echelon dike terminations. A younger NNW-NNE trending
secondary dike swarm is interpreted as a termination structure for
the prominent N25E-trending dike swarm exposed farther south at
Gerrish Island. The emplacement of this N25E-trending dike swarm
and the development of the related late brittle fracture system
involves a N65W-S65E, Late Jurassic-Early Cretaceous, crustal
extension and its interaction with the prominent N60E-trending
vertical bedding-anisotropy and the large rigid cylindrical
Agamenticus intrusion. Finally, a regional synthesis of Mesozoic
structural developments in eastern North America results in a
model for a complex decoupling history during central Atlantic
rifting. This model incorporates the varied interaction between
dextral shear, extension, sinistral shear and final crustal
separation along a wide, arcuate, near-pole, small-circle
transform system and the linear belt of pre-existing Appalachian
structural grain. The N60-45E and N25E trending dike swarms
studied in southern Maine would most likely be related to the
Triassic-Jurassic extensional phase and final Jurassic-Cretaceous
crustal separation phase, respectively, within the proposed model.
Swanson, M.T., 1982. The structure and tectonics of Mesozoic dike
swarms in eastern New England. Unpublished PhD dissertation,
State University of New York at Albany. 278pp., +xxiii; 10 folded
plates (maps)
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1982 S92
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.8MB pdf
file
Photo pages in dissertation
(greyscale
photos with captions): - 3.4MB pdf file
Plate 1 - Pattern
of Mesozoic dike intrusion and igneous brecciation above the
Gerrish Island Igneous Complex (1:1200) 1.2MB pdf file
Plate 2 - Pattern
of Mesozoic dike intrusion about the Cretaceous Cape Neddick
Gabbroic Complex (1:2400 and 1:1,200) 1.2 MB pdf file
Plate 3 - Pattern
of Mesozoic dike intrusion: Bald Head north to Perkins Cove
(1:2400) 0.3MB pdf file
Plate 4A - Pattern
of Mesozoic dike intrusion: Bald Head north to Perkins Cove
(1:600)
Plate 4B - Pattern
of Mesozoic dike intrusion: Bald Head north to Perkins Cove
(1:600)
Plate 5 - Pattern
of Mesozoic dike intrusion: Bald Head south to Pond Rocks
(1:2400)
Plate 6 - Pattern
of Mesozoic dike intrusion: Bald Head south to Pond Rocks
(1:600)
Plate 7 - Distribution
of late brittle fractures in the York 15' Quadrangle
(1:62,500)
Plate 8 - Distribution
of late topographic lineaments in the York 15' Quadrangle
(1:62,500)
Plate 9 - Shear
fracture pattern in thicker quartzite unit, York Cliffs
layer-parallel sinistral brittle shear structure (1:2)
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