Dextral transpression at the Casco Bay restraining bend, Norumbega fault zone, coastal Maine

Swanson, Mark T.

doi:10.1130/0-8137-2331-0.85

Cited by 12 publications

(14 citation statements)

References 31 publications

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“…Harpswell Neck lies within the Casco Bay shear‐zone system of Swanson (), a structurally complex, ~30 km wide region of late Palaeozoic deformation that constitutes the southwestern continuation of the Norumbega fault zone (Fig. ).…”

Section: Geological Settingmentioning

confidence: 99%

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Controls on metamorphic equilibration: the importance of intergranular solubilities mediated by fluid composition

Carlson

Hixon

Garber

et al. 2014

Journal Metamorphic Geology

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A dramatic demonstration of the role of intergranular solubility in promoting chemical equilibration during metamorphism is found in the unusual zoning of garnet in pelitic schist exposed at Harpswell Neck, Maine, USA. Many garnet crystals have irregular, patchy distributions of Mn, Cr, Fe and Mg in their inclusion-rich interiors, transitioning to smooth, concentric zoning in their inclusion-poor outer rims; in contrast, zoning of Ca and Y is comparatively smooth and concentric throughout. We re-assess the disputed origin of these zoning features by examining garnet growth in the context of the thermal and structural history of the rocks, and by evaluating the record of fluid-rock interaction revealed in outcrop-scale veining and fluid-inclusion assemblages. The transition in the character of garnet zoning correlates with the onset of a synkinematic, simple-shear-dominated phase of garnet growth and with a shift in the composition of the intergranular fluid from CO 2 -rich to H 2 O-rich. Compositional variations in garnet are therefore best explained by a two-stage growth history in which intergranular diffusive fluxes reflect differences in the concentration of dissolved species in these two contrasting fluids. Interiors of garnet crystals grew in the presence of a CO 2 -rich fluid, in which limited solubility for Mn and Cr (and perhaps Fe and Mg) produced patchy disequilibrium overprint zoning, while appreciable solubility for Ca and Y permitted their rock-wide equilibration. Rims grew in the presence of an H 2 O-rich fluid, in which high intergranular concentrations for all elements except Cr enabled diffusion over length scales sufficient for rock-wide equilibration. This striking example of partial chemical equilibrium during reaction and porphyroblast growth implies that thermal effects may commonly be subsidiary in importance to solubilities in the intergranular medium as determinants of length scales for metamorphic equilibration.

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Section: Geological Settingmentioning

confidence: 99%

“…Swanson () recognized that because the Casco Bay area occupies a regional restraining bend along the main fault in the shear‐zone system (Fig. ), it experienced dextral transpression that generated a sequence of folding, thrusting and strike‐slip events with systematic geographical distribution (cf.…”

Section: Geological Settingmentioning

confidence: 99%

Controls on metamorphic equilibration: the importance of intergranular solubilities mediated by fluid composition

Carlson

Hixon

Garber

et al. 2014

Journal Metamorphic Geology

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“…1), Carboniferous right-lateral strike-slip faulting associated with the Norumbega fault system is pervasive (West and Hubbard 1997;Swanson 1999;West 1999). We propose that a likely northern Appalachian tectonic equivalent for the origins of the alkalic magmatism at Litchfield, Maine can be found in the Cobequid Highlands of Nova Scotia.…”

Section: Regional Tectonic Significancementioning

confidence: 83%

The Litchfield Pluton in South-Central Maine: Carboniferous Alkalic Magmatism in northern New England, USA

West

Bradley

Coish

2016

atgeol

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The Litchfield pluton is a poorly exposed 7 km 2 composite alkalic intrusive complex that cuts previously deformed and metamorphosed Silurian turbidites in south-central Maine. The pluton includes a variety of alkaline syenites, including the type locality of "litchfieldite, " a coarse-grained cancrinite-, sodalite-, and lepidomelane-bearing nepheline syenite first recognized over 150 years ago and common in many petrologic collections. A new U-Pb zircon age of 321 ± 2 Ma from the nepheline syenite is interpreted to represent the crystallization age of the plutonic complex. A new biotite 40 Ar/ 39 Ar age of 239 ± 1 Ma from the syenite is similar to previously published mica ages from the surrounding country rocks and dates the time of regional cooling in the area below ~ 300°C. Whole-rock chemical analyses of rocks of the Litchfield pluton reveal silica-undersaturated alkaline compositions that are consistent with formation in a within-plate tectonic setting. The age and geochemical characteristics of the alkalic igneous rocks near Litchfield are consistent with a model that invokes the generation of a small volume of alkalic magma beneath south-central Maine during a period of Carboniferous transcurrent tectonism in the northern Appalachian orogen. RÉSUMÉLe pluton de Litchfield est un complexe intrusif alcalin composite de sept kilomètres carrés peu affleurant qui recoupe des turbidites siluriennes précédemment déformées et métamorphisées dans le centre-sud du Maine. Le pluton inclut diverses syénites alcalines, notamment la localité type de la « litchfieldite », une syénite néphélinique renfermant de la cancrinite, de la sodalite et de la lépidomélane à grain grossier identifiée pour la première fois il y a plus de 150 ans et répandue dans maintes collections pétrologiques. Une nouvelle datation U-Pb sur zircon de 321 ± 2 Ma de la syénite néphélinique est interprétée comme une représentation de l'âge de la cristallisation du complexe de roches plutoniques. Une nouvelle datation de la syénite par biotite et The Litchfield pluton in south-central Maine: Carboniferous alkalic magmatism in northern New England, USA nepheline syenite (Fig. 2) that was assigned the name "litchfieldite" by Bayley (1892), is part of a composite alkalic plutonic complex (Barker 1965) that occupies an area of approximately 7 km 2 (Fig. 3). While these unusual rocks have attracted the interest of mineral collectors for over a century and a half, extremely poor exposure has discouraged detailed study; thus the age and tectonic INTRODUCTIONSince the mid-1800s (Jackson 1845; Clarke 1886), the small village of Litchfield in south-central Maine (Fig. 1) has been known as a collecting locality for specimens of cancrinite, sodalite, nepheline, and lepidomelane (Fe-rich biotite). The host rock to these minerals, a coarse-grained of the Litchfield pluton, Barker (1965) suggested that they are associated with the Mesozoic White Mountain magma series. However, limited major element geochemical data are available from these rocks, and ...

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“…Merrimack Trough and Putnam-Nashoba are thought to be Ganderian. and Hussey 1999;Swanson 1999). Felsic plutonic bodies and abundant associated pegmatite, both variably sheared into near-parallelism with highly mylonitized host rocks, led Lyons et al (1997) to coin the name Rye Complex.…”

Section: Geologic Settingmentioning

confidence: 99%

The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA: geochronological and chemical evidence for the affinity of an enigmatic terrane

Dorais

Bothner

Buchwaldt

2014

atgeol

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The Rye Complex of coastal New Hampshire and Maine is a peri-Gondwanan terrrane that up to now had an uncertain origin. An offshore portion of the complex, Appledore Island of the Isles of Shoals, hosts a mainly dioritic intrusion that yielded an U-Pb zircon age of 361.09 ± 0.14 Ma, allowing comparison of its geochemical characteristics with mafic rocks of similar age across the northern Appalachian orogen. The Appledore Island diorite has similar major, trace, and isotopic compositions as continental rift tholeiite in the Narragansett Basin in southern New England and in the Maritimes Basin of Canada. These intraplate volcanic rocks range from 375 to 330 Ma, bracketing the age of the Appledore Island diorite. Their intraplate tectonic setting reflects regional extension during the Late Devonian to Early Carboniferous which produced successor basins after the Acadian orogeny. The geochemical and age similarities of the Appledore Island diorite and the mafic rocks of the successor basins suggest that the Rye Complex is a basement fragment of a successor basin block. Further evidence of the identity of the Rye Complex is provided by the isotopic composition of intermingled, comagmatic granitic rocks associated with the Appledore Island diorite. The granite has a Ganderian isotopic signature, suggesting that the Rye Complex is a Ganderian basement block that was transposed by movement along the Norumbega Fault System to its position adjacent to the Merrimack Trough of New Hampshire and Maine.

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Dextral transpression at the Casco Bay restraining bend, Norumbega fault zone, coastal Maine

Cited by 12 publications

References 31 publications

Controls on metamorphic equilibration: the importance of intergranular solubilities mediated by fluid composition

Controls on metamorphic equilibration: the importance of intergranular solubilities mediated by fluid composition

The Litchfield Pluton in South-Central Maine: Carboniferous Alkalic Magmatism in northern New England, USA

The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA: geochronological and chemical evidence for the affinity of an enigmatic terrane

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