Connecticut Valley-Gaspe Research Articles

Silurian-Devonian age and tectonic setting of the Connecticut Valley-Gaspe trough in Vermont based on U-Pb SHRIMP analyses of detrital zircons

U-Pb SHRIMP ages of detrital zircons from metasedimentary rocks of the Connecticut Valley-Gaspé trough in Vermont corroborate a Silurian-Devonian age of deposition for these strata and constrain their provenances. Ages of randomly selected detrital zircons obtained from quartzites within the Waits River and Gile Mountain Formations range from Archean to Devonian with Mesoproterozoic, Neoproterozoic, Ordovician, and Silurian age populations suggesting both eastern and western sources of the sediments. The two youngest single-grain detrital zircon ages from samples collected in the Waits River Formation are 418 ± 7 and 415 ± 2 Ma. The youngest single-grain detrital zircon age from the eastern part of the Gile Mountain Formation is 411 ± 8. The youngest detrital zircons from the western portion of the Gile Mountain Formation comprise an age population with a weighted average of 409 ± 5 Ma. These ∼409 Ma zircons are likely of volcanic origin, perhaps derived from the Piscataquis magmatic belt to the east. The absence of younger volcanic zircons in the coarser-grained eastern facies of the Gile Mountain Formation suggests the eastern sediments are older and were buried during Piscataquis volcanism and deposition in the west. The shift in protoliths from calcareous silts and muds of the Waits River Formation to quartzo-feldspathic sands of the Gile Mountain Formation implies a change from a continental slope-like depositional environment to a near-shore or terrestrial environment of deposition. This change supports a transition in the nature of the basin from an intercontinental back-arc extensional setting to a foreland basin setting. Maximum depositional ages of sediments above and below this facies boundary constrain the timing of transition in basin style between about 415 and 411 Ma. Given the timing of the approaching Acadian wedge, this shift in basin style likely reflects westward migration of thrust sheets during the Acadian orogeny. The fine-grained nature of the youngest silts, muds and turbidites suggests that sedimentation occurred in increasingly deeper water. The implied basin subsidence was likely caused by lithospheric flexure as the Acadian wedge approached from the east. The timing of this subsidence is constrained to be younger than the youngest zircons at about 409 Ma.

Metallogeny of the Mont-de-l’Aigle IOCG deposit, Gaspé Peninsula, Québec, Canada

The Mont-de-l’Aigle deposit is located in the northern part of Dome Lemieux, in the Connecticut Valley-Gaspe Synclinorium, Gaspe Peninsula, Quebec. The Dome Lemieux is a subcircular antiform of Siluro–Devonian sedimentary rocks that is cut by numerous mafic and felsic sills and dikes of Silurian to Late Devonian age. Plutonism occurred in a continental within-plate extensional setting typical of orogenic collapse. The Cu−Fe (± Au) mineralization of Mont-de-l’Aigle occurs in veins, stockworks, and breccias. Mineralization is located near or within N−S and NW−SE faults cutting sedimentary rocks. IOCG mineralization postdates intrusions, skarns, hornfels, and epithermal mineralization typical of the southern part of the Dome Lemieux. The paragenetic sequence comprises: (1) pervasive sodic, potassic, chlorite, and silica alteration, (2) hematite, quartz, pyrite, magnetite, and chalcopyrite veins, stockworks and breccias and, (3) dolomite ± hematite veins and veinlets cutting the earlier mineralization. Intrusions display proximal sodic and potassic alteration, whereas sedimentary rocks have proximal decalcification, silicification, and potassic alteration. Both intrusive and sedimentary rocks are affected by a pervasive distal chlorite (± silica) alteration. The sulfur isotope composition of pyrite and chalcopyrite (δ34S=−1.5 to 4.8‰) suggests that sulfur was derived mainly from igneous rocks. Fluid δ18O (−0.4 to 2.65‰) indicates meteoric or seawater that reacted with the country rocks. Mixing of hot magmatic fluids with a cooler fluid, perhaps meteoric or seawater is suggested for mineral deposition and alteration of the Mont-de-l’Aigle deposit. The mineralogy, alteration, and sulfur isotope composition of the Mont-de-l’Aigle deposit compare well with IOCG deposits worldwide, making the Mont-de-l’Aigle deposit a rare example of Paleozoic IOCG mineralization, formed at shallow depth, within a low metamorphic grade sedimentary rock sequence.

Geophysical modeling of the northern Appalachian Brompton-Cameron, Central Maine, and Avalon terranes under the New Jersey Coastal Plain

A regional terrane map of the New Jersey Coastal Plain basement was constructed using seismic, drilling, gravity and magnetic data. The Brompton-Cameron and Central Maine terranes were coalesced as one volcanic island arc terrane before obducting onto Laurentian, Grenville age, continental crust in the Taconian orogeny [Rankin, D.W., 1994. Continental margin of the eastern United States: past and present. In: Speed, R.C., (Ed.), Phanerozoic Evolution of North American Continent-Ocean Transitions. DNAG Continent-Ocean Transect Volume. Geological Society of America, Boulder, Colorado, pp. 129–218]. Volcanic island-arc rocks of the Avalon terrane are in contact with Central Maine terrane rocks in southern Connecticut where the latter are overthrust onto the Brompton-Cameron terrane, which is thrust over Laurentian basement. Similarities of these allochthonous island arc terranes (Brompton-Cameron, Central Maine, Avalon) in lithology, fauna and age suggest that they are faulted segments of the margin of one major late Precambrian to early Paleozoic, high latitude peri-Gondwana island arc designated as “Avalonia”, which collided with Laurentia in the early to middle Paleozoic. The Brompton Cameron, Central Maine, and Avalon terranes are projected as the basement under the eastern New Jersey Coastal Plain based on drill core samples of metamorphic rocks of active margin/magmatic arc origin. A seismic reflection profile across the New York Bight traces the gentle dipping (approximately 20 degrees) Cameron's Line Taconian suture southeast beneath allochthonous Avalon and other terranes to a 4 sec TWTT depth (approximately 9 km) where the Avalonian rocks are over Laurentian crust. Gentle up-plunge (approximately 5 degrees) projections to the southwest bring the Laurentian Grenville age basement and the drift-stage early Paleozoic cover rocks to windows in Burlington Co. at approximately 1 km depth and Cape May Co. at approximately 2 km depths. The antiformal Shellburne Falls and Chester domes and Chain Lakes-Pelham dome-Bronson Hill structural trends, and the synformal Connecticut Valley-Gaspe structural trend can be traced southwest into the New Jersey Coastal Plain basement. A Mesozoic rift basin, the “Sandy Hook basin”, and associated eastern boundary fault is identified, based upon gravity modeling, in the vicinity of Sandy Hook, New Jersey. The thickness of the rift-basin sedimentary rocks contained within the “Sandy Hook basin” is approximately 4.7 km, with the basin extending offshore to the east of the New Jersey coast. Gravity modeling indicates a deep rift basin and the magnetic data indicates a shallow magnetic basement caused by magnetic diabase sills and/or basalt flows contained within the rift-basin sedimentary rocks. The igneous sills and/or flows may be the eastward continuation of the Watchung and Palisades bodies.

Turbidite Channel/Overbank Deposition in a Lower Devonian Orogenic Shale Basin, Fortin Group of Gaspe Peninsula, Northern Appalachians, Canada

ABSTRACT The Lower Devonian Fortin Group, one of the major stratigraphic units in Connecticut Valley-Gaspe Synclinorium of the Gaspe Peninsula, and its stratigraphic equivalent, the Temiscouata Formation in northwestern New Brunswick and southeastern Quebec, are interpreted as a base-of-slope to deep-basin turbidite succession sandwiched between shallow-marine to nonmarine Siluro-Devonian sediments. The deep-water interpretation is based on a comparison with modern deep-sea turbidite depositional environments and the lower-slope to deep-basinal settings established by previous investigators for equivalent rocks in New England. The monotonous sequences of largely unfossiliferous, well-bedded dark slate, phyllite, and siltstone with intercalated sandstone packets of the Fortin Group and Temiscou ta Formation in the Matapedia and Madawaska/St. John Valley regions, respectively, are interpreted as submarine overbank and channel-fill facies associations. Seven lithofacies have been distinguished: (1) Associations of massive sandstone beds up to 13 m thick and (2) associations of sandstone beds of intermediate (0.5-2.0 m) thickness forming isolated sandstone packets encased in slate and siltstone are the equivalent of modern deep channel-fill deposits. (3-5) Laterally continuous, largely nonbioturbated thin siltstone layers with climbing-ripple lamination (turbidite c division) and parallel lamination (turbidite d division) followed by slate (turbidite e division and hemipelagite) are analogous to muddy spill-over turbidites with interbedded hemipelagites on modern natural levees th t accompany deep channels. Among the fine-grained sediments, a proximal-to-distal facies succession (with respect to presumed lateral distance from channels) consists of (3) siltstone-slate, (4) banded slate, and (5) laminated slate, if found in lateral succession. The same succession may reflect spill-over from progressively deeper channels. The channel/levee interpretation is supported by field observations of (i) a partly exposed channel wall, (ii) truncation of siltstone and slate layers at sandstone contacts, (iii) lag material at the base of massive sandstone layers, and (iv) the chevron pattern of nearly opposing paleocurrent directions in the spill-over facies. (6) Syndepositionally deformed and diamictite facies comprise fine-grained rocks of Facies 3-5. (7) Volumetrically subor inate conglomerates are the coarsest of the redeposited sediments. Siegenian (Praguian)-Emsian turbidite deposition occurred in a deep basin of the Connecticut Valley-Gaspe Trough that developed in response either to wrench tectonics or back-arc spreading related to a volcanic island arc (Piscataquis volcanic belt)/deep-sea trench system (Merrimack-Fredericton Trough).

Lead-isotopic evidence for distinct sources of granite and for distinct basements in the northern Appalachians, Maine

Lead-isotopic compositions of feldspars in plutons of the coastal lithotectonic block (Avalonian basement), central Maine (Merrimack) synclinorium, and Connecticut Valley-Gaspe synclinorium in northern Maine (Granville basement) indicate the presence of three fundamentally different sources of Devonian granitic rocks in Maine. Plutons in the coastal lithotectonic block have the most radiogenic values ( 206 Pb/ 204 Pb: 18.25–19.25; 207 Pb/ 204 Pb: 15.59–15.67; 208 Pb/ 204 Pb: 38.00–38.60); plutons in northern Maine are the least radiogenic ( 206 Pb/ 204 Pb: 18.00–18.50; 207 Pb/ 204 Pb: 15.51–15.55; and 208 Pb/ 204 Pb: 37.80–38.38). Intermediate lead-isotope values characterize the plutons in central Maine ( 206 Pb/ 204 Pb: 18.20–18.40; 207 Pb/ 204 Pb: 15.56–15.60; and 208 Pb/ 204 Pb: 38.00–38.30). All plutons show relatively radiogenic lead values for their ages and suggest the imprint of continental crustal sources especially in the coastal block and in central Maine. Plutons from the Connecticut Valley–Gaspe synclinorium allow for a more significant isotopic input from the subcontinental mantle. The three distinct lead-isotope groups probably identify plutons formed in different crustal fragments in a continental collisional environment that were juxtaposed after emplacement of the granites.

Structural analysis of the Silurian-Devonian rocks of the Royalton area, Vermont

Structural analysis of Silurian-Devonian schists of the Waits River and Gile Mountain Formations in the Royalton area, Vermont, provides clear evidence of three Acadian deformational phases and polymetamorphism. Structurally, the Royalton area lies within the Connecticut Valley–Gaspe synclinorium. The Gile Mountain Rocks are part of the western band of the formation, which has its southern termination in the study area and extends northward to join the eastern band around the northern end of the calcareous Waits River Formation of the Strafford-Willoughby arch. The earliest deformation (D 1 ), is recognized by a pervasive schistosity (S 1 ) generally parallel to bedding (S 0 ) and by rarely identified folds (F 1 ). The second deformation (D 2 ) has left the most widespread imprint, with an S 2 cleavage or schistosity and open to moderately flattened folds (F 2 ) in schistosity, parallel to bedding (S 0 /S 1 ). Least easily recognized is the third deformation (D 3 ), with sparse open folds in S 2 . The western band of the Gile Mountain Formation is interpreted as the westward- and downward-facing nose — the Royalton synform — of a large D 1 recumbent fold — the eastern Vermont nappe. D 2 structures have generally been regarded as synchronous with and genetically related to formation of domes and the Strafford-Willoughby arch. However, the D 2 structures are interpreted here as pre-doming, with D 3 structures related to the doming deforming them. Compressive buckling and variable flattening imposed during D 2 upon a variably oriented S 0 /S 1 may have been the result of emplacement of higher nappes (now removed by erosion), which increased the depth of burial promoting prograde metamorphism.

Geology of the Connecticut Lakes-Parmachenee Area, New Hampshire and Maine

The Connecticut Lakes-Parmachenee area, in northernmost New Hampshire and northwesternmost Maine, is underlain principally by Lower to Middle Paleozoic clastic sediments, and felsic and mafic volcanic rocks, all of low metamorphic grade. The area includes a section of the entire northwest flank of the Boundary Mountains anticlinorium (the southeast flank of the Connecticut Valley-Gaspe synclinorium) and part of the axial region of the latter synclinorium. Approximately 23,000 feet of Ordovician, and perhaps some Cambrian, strata are represented. These include, from oldest to youngest, the Aziscohos, Albee, and Dixville formations, the last containing the coarse, clastic Magalloway Member in the Maine part of the area. These rocks were folded during the Taconic orogeny. Along the Taconic unconformity are very local, thin Upper Silurian limestones, and to the northwest lie about 20,000 feet of Devonian strata, constituting the Seboomook and overlying Frontenac formations. The Compton Formation, believed to be equivalent to the Seboomook across a synclinal axis, may appear at the northwest corner of the area. The stratified rocks are intruded by a granodiorite stock of probable Taconic age, and by two granitic stocks and many microgranite lenses, a gabbro and a tonalite stock, many gabbro sills, and a few small serpentinites and peridotites, all of Acadian age. Study of the minor structures shows that the Cambro-Ordovician rocks were deformed and strengthened by recrystallization at low temperatures during the Taconic orogeny, but the principal metamorphism and regional deformation were Acadian.

STRATIGRAPHIC AND GEOTECTONIC RELATIONSHIPS IN NORTHERN VERMONT AND SOUTHERN QUEBEC

Research Article| May 01, 1960 STRATIGRAPHIC AND GEOTECTONIC RELATIONSHIPS IN NORTHERN VERMONT AND SOUTHERN QUEBEC WALLACE M CADY WALLACE M CADY U. S. GEOLOGICAL SURVEY, MONTPELIER, VT. Search for other works by this author on: GSW Google Scholar Author and Article Information WALLACE M CADY U. S. GEOLOGICAL SURVEY, MONTPELIER, VT. Publisher: Geological Society of America Received: 03 Feb 1958 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1960, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1960) 71 (5): 531–576. https://doi.org/10.1130/0016-7606(1960)71[531:SAGRIN]2.0.CO;2 Article history Received: 03 Feb 1958 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WALLACE M CADY; STRATIGRAPHIC AND GEOTECTONIC RELATIONSHIPS IN NORTHERN VERMONT AND SOUTHERN QUEBEC. GSA Bulletin 1960;; 71 (5): 531–576. doi: https://doi.org/10.1130/0016-7606(1960)71[531:SAGRIN]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Stratified rocks of early and middle Paleozoic age form a belt of northeast-trending anticlinoria and synclinoria of middle Paleozoic age, in northern Vermont and adjacent parts of southern Quebec. The foreland margin of this belt, in the Champlain and St. Lawrence valleys to the west, is cut by eastward-dipping thrust faults of middle Paleozoic age and by later northeast-trending normal faults. The Green Mountain anticlinorium, which is the dominant structure of the region, is flanked to the west, on the foreland, by the St. Albans-Hinesburg-Middlebury synclinorium and to the east, in the midst of the folded belt, by the Connecticut Valley-Gaspe synclinorium. The principal thrust faults, notably the Champlain and Philipsburg thrusts, are in the west limb of the St. Albans-Hinesburg-Middlebury synclinorium. East of the Connecticut Valley-Gaspe synclinorium is the Boundary Mountain anticlinorium, in eastern Vermont and adjacent New Hampshire and along the international boundary between Quebec and Maine.Two contrasting intergradational lithic assemblages, the graywacke-shale assemblage and the carbonate-quartzite assemblage, characterize the protolith of the bedded rocks. The graywacke-shale assemblage includes thick sections of lower Paleozoic strata, portions of which lap both gradationally and unconformably westward on the foreland, particularly in Quebec; it also includes middle Paleozoic strata that offlap eastward away from the foreland. The carbonate-quartzite assemblage laps both unconformably and gradationally eastward over the graywacke-shale assemblage in sections of the middle Paleozoic east of the axis of the Green Mountain anticlinorium.Stratigraphic correlation has become well established in the foreland belt where numerous distinctive and fossiliferous strata, chiefly of the carbonate-quartzite assemblage, have escaped metamorphism. It is also fairly clear in sections in the eastern foreland and western part of the Green Mountain anticlinorium, where the strata of the carbonate-quartzite assemblage extend eastward and interfinger with rocks of the graywacke-shale terrane. Rocks that are entirely of the graywacke-shale assemblage have been correlated in the present study.The stratified rocks west of the axis of the Green Mountain anticlinorium are of Cambrian(?), Cambrian, and Ordovician age; those to the east range in age from Cambrian to Devonian.The geotectonic setting of the region is the once mobile belt of the Appalachian orthogeosyncline, which is at the southeastern margin of the stable continental block, or craton, of North America. The orthogeosyncline was a belt, chiefly of subsidence, that embraced two parallel and adjoining longitudinal zones: the eugeosynclinal zone, which was more mobile, and the miogeosynclinal zone, which was less mobile. Second- and third-generation geosynclines are superimposed not only on the orthogeosyncline but also on adjoining parts of the craton.Uplift, and finally folding, gradually superseded subsidence in the orthogeosyncline. Local uplift, chiefly within the eugeosynclinal zone, provided most of the clastic sediments, principally those of the graywacke-shale assemblage. General stabilization of the western part of the orthogeosyncline at the end of the Ordovician was accompanied by eastward migration of the miogeosynclinal zone. Localized uplift within the eastern part of the orthogeosyncline at this time is marked by unconformities referred to the Taconic disturbance. Folding and uplift after the Early Devonian is shown by angular unconformities referred to the Acadian and Appalachian orogenies.The interpretation of the geotectonic relations of the bedded rocks is aided by critical features of the magmatic activity that began with, accompanied, and followed the diastrophism. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.