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Journal articles on the topic "Orogeny – Vermont"
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Gonzalez, Joseph P., Suzanne L. Baldwin, Jay B. Thomas, William O. Nachlas, and Paul G. Fitzgerald. "Evidence for ultrahigh-pressure metamorphism discovered in the Appalachian orogen." Geology 48, no. 10 (June 19, 2020): 947–51. http://dx.doi.org/10.1130/g47507.1.
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Abstract The Appalachian orogen has long been enigmatic because, compared to other parts of the Paleozoic orogens that formed following the subduction of the Iapetus Ocean, direct evidence for ultrahigh-pressure (UHP) metamorphism has never been found. We report the first discovery of coesite in the Appalachian orogen in a metapelite from the mid-Ordovician (Taconic orogeny) Tillotson Peak Complex in Vermont (USA). Relict coesite occurs within a bimineralic SiO2 inclusion in garnet. In situ elastic barometry and trace-element thermometry allow reconstruction of the garnet growth history during prograde metamorphism. The data are interpreted to indicate garnet nucleation and crystallization during blueschist- to eclogite-facies subduction zone metamorphism, followed by garnet rim growth at UHP conditions of > 28 kbar and > 530 ° C. Results provide the first direct evidence that rocks of the Appalachian orogen underwent UHP metamorphism to depths of > 75 km and warrant future studies that constrain the extent of UHP metamorphism.
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Ratcliffe, Nicholas M., John N. Aleinikoff, William C. Burton, and Paul Karabinos. "Trondhjemitic, 1.35–1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians." Canadian Journal of Earth Sciences 28, no. 1 (January 1, 1991): 77–93. http://dx.doi.org/10.1139/e91-007.
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A newly recognized suite of trondhjemite–tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U–Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crosscutting trondhjemite. Tonalitic plutonism continued until 1.31 Ga.Map-scale contacts between the trondhjemitic–tonalitic–dacitic gneisses and the paragneiss sequence of the Mount Holly Complex are sharp, suggesting that the volcanic rocks of the trondhjemite–tonalite suite underlie the paragneiss units and do not intrude them. These relationships suggest that the trondhjemite–tonalite suite is either considerably older than, and unconformable beneath, the paragneiss cover rocks or represents a volcanic edifice slightly older than the deposition of the sedimentary precursor to the paragneiss units. The paragneiss and tonalite–trondhjemite gneisses are both intruded by younger granitoids that were intruded at about 1.25 Ga during strong dynamothermal metamorphism.The trondhjemitic gneisses of the Mount Holly Complex of Vermont have high Al2O3 and low Yb contents and light rare-earth element enrichment patterns that are more characteristic of continental than oceanic volcanic arcs. The Mount Holly intrusives and volcanics may have formed during 1.35–1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. In Vermont, later deformation and granite intrusion at about 1.25 Ga coincide with the major pulse of the Elzevirian orogeny and associated trondhjemitic plutonism in the Central Metasedimentary Belt of eastern Canada.
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Ratcliffe, Nicholas M., Anita G. Harris, and Gregory J. Walsh. "Tectonic and regional metamorphic implications of the discovery of Middle Ordovician conodonts in cover rocks east of the Green Mountain massif, Vermont." Canadian Journal of Earth Sciences 36, no. 3 (March 25, 1999): 371–82. http://dx.doi.org/10.1139/e99-009.
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Middle Ordovician (late Arenigian - early Caradocian) conodonts were recovered from a dolostone lens in carbonaceous schist 30 m below the base of the Pinney Hollow Formation in the Eastern Cover sequence near West Bridgewater, Vermont. These are the first reported fossils from the metamorphic cover sequence rocks east of the Green Mountain, Berkshire, and Housatonic massifs of western New England. The conodonts are recrystallized, coated with graphitic matter, thermally altered to a color alteration index (CAI) of at least 5, and tectonically deformed. The faunule is nearly monospecific, consisting of abundant Periodon aculeatus Hadding? and rare Protopanderodus. The preponderance of Periodon and the absence of warm, shallow-water species characteristic of the North American Midcontinent Conodont Province suggest a slope or basin depositional setting. The conodont-bearing carbonaceous schist is traceable 3 km southeast to the Plymouth area, where it had been designated the uppermost member of the Plymouth Formation, previously regarded as Early Cambrian in age. The age and structural position of the carbonaceous schist above dolostones of the Plymouth Formation but below the Pinney Hollow Formation (upper Proterozoic and Lower Cambrian?) suggest that this unit may be correlative or time transgressive with the Ira Formation, which underlies the Taconic allochthons in the Vermont Valley. Such a correlation supports the concept of placing the western limit of the root zone of the Taconic allochthons beneath the Pinney Hollow Formation. An approximate absolute age assignment for the conodont-bearing rock is between 470 and 454 Ma. This suggests that dynamothermal metamorphism during the Taconian orogeny on the east flank of the Green Mountains was younger than early Caradocian, which is in accord with the middle Caradocian age of the Ira Formation west of the Green Mountain massif.
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Chew, David M., and Cees R. Van Staal. "The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean." Geoscience Canada 41, no. 2 (May 7, 2014): 165. http://dx.doi.org/10.12789/geocanj.2014.41.040.
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A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé. Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine. Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine. Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve). Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique). La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines. Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments.
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Thompson, Peter J., and Thelma B. Thompson. "The Prospect Rock thrust: western limit of the Taconian accretionary prism in the northern Green Mountain anticlinorium, Vermont." Canadian Journal of Earth Sciences 40, no. 2 (February 1, 2003): 269–84. http://dx.doi.org/10.1139/e02-109.
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This paper presents evidence for an early Taconian, west-directed fault in northern Vermont, the Prospect Rock thrust, which represents the trace of the contact between the Taconian oceanic accretionary prism (Dunnage Zone) and less allochthonous, continental margin rocks (Humber Zone). Mapping at 1 : 24 000 over the last decade has led to reassessment of units within the Camels Hump Group, resulting in newly defined lithotectonic packages: the Green Mountain slice and the Prospect Rock slice. Rocks in these slices may be of similar age, but those in the Green Mountain slice were originally deposited as more proximal sediments and remained on the Humber side of the sub duction zone, whereas those in the Prospect Rock slice were transferred by underplating to the accretionary prism. Both slices contain ultramafics. Motion on the Prospect Rock thrust (D1) preceded Taconian garnet-grade metamorphism and subsequent east-directed back-folding. However, D1 structures were diachronous across the orogen. Late Taconian (D2) structures record a change from east-verging back-folds in northern Vermont and southern Quebec to west-verging folds farther south. The Prospect Rock thrust does not correspond exactly to Cameron's line nor to the Baie Verte Brompton line as originally defined. However, our understanding of the geometry of the Prospect Rock thrust demonstrates that the Dunnage Zone extends farther west than previously recognized and may also explain features farther to the east.
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Lim, Chul, William S. F. Kidd, and Stephen S. Howe. "Late Shortening and Extensional Structures and Veins in the Western Margin of the Taconic Orogen (New York to Vermont)." Journal of Geology 113, no. 4 (July 2005): 419–38. http://dx.doi.org/10.1086/430241.
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LANDING, ED, LISA AMATI, and DAVID A. FRANZI. "Epeirogenic transgression near a triple junction: the oldest (latest early–middle Cambrian) marine onlap of cratonic New York and Quebec." Geological Magazine 146, no. 4 (March 2, 2009): 552–66. http://dx.doi.org/10.1017/s0016756809006013.
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AbstractThe discovery of a fossiliferous interval (Altona Formation, new unit) under the Potsdam Formation requires a new geological synthesis of a large part of the northeast Laurentian craton. Potsdam sandstones can no longer be regarded as the oldest sedimentary unit on the middle Proterozoic Grenville orogen in northern New York and adjacent Quebec and Ontario. The thickest Potsdam sections (to 750 m) in the east Ottawa–Bonnechere aulocogen have been explained by deposition with normal faulting possibly associated with Ediacaran rifting (c. 570 Ma) that led to formation of the Iapetus Ocean. However, sparse trilobite faunas show a terminal early Cambrian–middle middle Cambrian age of the Altona, and indicate much later marine transgression (c. 510 Ma) of the northeast Laurentian craton. Altona deposition was followed by rapid accumulation of lower Potsdam (Ausable Member) sandstone in the middle–late middle Cambrian. The Altona–Ausable succession is probably conformable. The Altona is a lower transgressive systems tract unit deposited on the inner shelf (sandstone, reddish mudstone, and carbonates) followed by aggradation and the deposition of highstand systems tract, current cross-bedded, in part terrestrial(?), feldspathic Ausable sandstone. Unexpectedly late Altona transgression and rapid Ausable deposition may reflect renewed subsidence in the Ottawa–Bonnechere aulocogen with coeval (terminal early Cambrian) faulting that formed the anoxic Franklin Basin on the Vermont platform. Thus, the oldest cover units on the northeast New York–Quebec craton record late stages in a cooling history near an Ediacaran triple junction defined by the Quebec Reentrant and New York Promontory and the Ottawa–Bonnechere aulocogen.
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Brunn, J. H., I. Argyriadis, and J. Braud. "MAGMATIC EMPLACEMENT OF OPHIOLITES IN NORTHERN GREECE." Bulletin of the Geological Society of Greece 36, no. 4 (January 1, 2004): 1618. http://dx.doi.org/10.12681/bgsg.16565.
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Most of the folded mountain ranges of our planet include masses of ophiolites. In accordance with the today 's predominant theory this is explained by obduction of ocean floor masses. Since 1956 Professor Brunn formulated the theory of undersea extrusion of mantel material. Our recent research in the areas of Vourinos, Vermion and Pindos have lead us to the conclusion that: The ophiolites are in normal, no tectonic contact with their supporting layers. This contact shows a typical thermal transformation with layers of homstein, amphibolites and granatites.The directly beneath underlaying series shows progressive and clear evolution from a carbonate platform into a subsea environment with increasing volcanic influences including pillow lava flows. As a conclusion of these observations we can state that we should not automatically interprete ophiolitic findings of the folded ranges to obduction of oceanic floor material. Probably an early compression of the future orogenic areas leads to the creation of rifts with obligue direction to the main axe of compression. Through these rifts hot ultrabasic magma flowed over the sea floor which crystalises in a differencial process.
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Perrot, Morgann, Alain Tremblay, Gilles Ruffet, and Jean David. "Detrital U-Pb and 40Ar/39Ar geochronology of the Connecticut Valley-Gaspé trough, southern Quebec and northern Vermont – Transitional tectonism from Salinic to Acadian orogenic cycles." Tectonophysics 745 (October 2018): 430–52. http://dx.doi.org/10.1016/j.tecto.2018.08.006.
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Brigham, John M., and Suzanne L. Baldwin. "Petrogenesis of arsenic and platinum-group minerals from a partially serpentinized dunite in East Dover, Vermont, USA." GSA Bulletin, September 16, 2022. http://dx.doi.org/10.1130/b36388.1.
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In the Appalachian Mountains of Vermont, USA, variably serpentinized ultramafic rocks mark the Ordovician Taconic orogenic suture zone. These ultramafic rocks provide evidence for several alteration events that occurred during Appalachian orogenesis. The largest of these ultramafic bodies occurs as a partially serpentinized meta-dunite located in East Dover, Vermont. Whole-rock X-ray fluorescence spectroscopy and electron microprobe data on variably serpentinized meta-dunite samples are interpreted with respect to several processes including fluid/melt-rock interaction in the mantle, serpentinization, and subsequent regional metamorphism. We report the first discovery of nickel arsenide minerals hosted in this meta-dunite, as well as rare occurrences of platinum-group mineral inclusions in chromitite. Although the platinum-group minerals and chromitite are rare, their occurrence and chemistry suggest that they formed by fluid/melt-rock interaction during partial melting events that produced the dunite, likely in a supra-subduction zone setting. Arsenic minerals are rare in un-serpentinized samples but are ubiquitous in highly serpentinized samples, which suggests that most of the arsenic was introduced into the ultramafic rocks during serpentinization. Whole-rock geochemical analyses also indicate that highly serpentinized samples contain the highest concentrations of arsenic. The discovery of arsenic minerals identifies a potential source to explain elevated arsenic in groundwater in Vermont, which is a serious health concern in places where wells have been drilled in serpentinite bedrock.
Dissertations / Theses on the topic "Orogeny – Vermont"
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Lagor, Samuel William. "The Relationship Between Magmatism and Deformation During the Acadian Orogeny: A Case Study from Eastern-Central Vermont." ScholarWorks @ UVM, 2016. http://scholarworks.uvm.edu/graddis/566.
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The Silurian-Devonian metasedimentary rocks of the Connecticut Valley-Gaspé trough (CVGT) were subjected to multiple deformational and metamorphic events during the Acadian orogeny in the Middle-Late Devonian. Plutons intruding the Devonian Waits River and Gile Mountain Formations have been considered post-tectonic, but microstructural studies of the intrusions and their metamorphic aureoles indicate some of these plutons intruded syntectonically. This study investigates the relationship between Acadian deformation and intrusion of the Knox Mountain pluton (KMP) of central Vermont. Structural and geochronological data were collected along a c. 15 km transect from the western limit of the CVGT, where the unconformable Richardson Memorial Contact coincides with the Dog River Fault Zone, into the margin of the KMP in the east. Field and microstructural observations indicate the KMP intruded syntectonically. Evidence for Acadian deformation post-dating intrusion includes folded and boudinaged granitic dikes at the margin of the KMP, and microstructures such as flame perthite, myrmekite, deformation twins, and textures associated with grain-boundary migration recrystallization in the granite. In the metamorphic aureole, biotite porphyroblasts overgrow S3, the earliest Acadian secondary foliation, and were deformed during S4 crenulation cleavage development. The KMP intruded at 377±5.2 Ma based on a U-Th-total Pb monazite crystallization age, which is concordant with the published age of the nearby Barre granite. The timing of S4 foliation development in the CVGT is constrained locally by 40Ar/39Ar geochronology at ~365 Ma, consistent with the microstructurally-inferred relative-age relationships. Plateau/weighted mean 40Ar/39Ar ages from across the transect and minimum ages from argon-loss profiles show a general trend of younging towards the east, suggesting these rocks have been affected by Alleghanian and Mesozoic deformation and exhumation.
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Merson, Matthew. "The Progressive Evolution of the Champlain Thrust Fault Zone: Insights from a Structural Analysis of its Architecture." ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/896.
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Near Burlington, Vermont, the Champlain Thrust fault placed massive Cambrian dolostones over calcareous shales of Ordovician age during the Ordovician Taconic Orogeny. Although the Champlain Thrust has been studied previously throughout the Champlain Valley, the architecture and structural evolution of its fault zone have never been systematically defined. To document these fault zone characteristics, a detailed structural analysis of multiple outcrops was completed along a 51 km transect between South Hero and Ferrisburgh, Vermont.
The Champlain Thrust fault zone is predominately within the footwall and preserves at least four distinct events that are heterogeneous is both style and slip direction. The oldest stage of structures—stage 1—are bedding parallel thrust faults that record a slip direction of top-to-the-W and generated localized fault propagation folds of bedding and discontinuous cleavages. This stage defines the protolith zone and has a maximum upper boundary of 205 meters below the Champlain Thrust fault surface. Stage 2 structures define the damage zone and form two sets of subsidiary faults form thrust duplexes that truncate older recumbent folds of bedding planes and early bedding-parallel thrusts. Slickenlines along stage 2 faults record a change in slip direction from top-to-the-W to top-to-the-NW. The damage zone is ~197 meters thick with its upper boundary marking the lower boundary of the fault core. The core, which is ~8 meters thick, is marked by the appearance of mylonite, phyllitic shales, fault gouge, fault breccia, and cataclastic lined faults. In addition, stage 3 sheath folds of bedding and cleavage are preserved as well as tight folds of stage 2 faults. Stage 3 faults include thrusts that record slip as top-to-the-NW and -SW and coeval normal faults that record slip as top-to-the-N and -S. The Champlain Thrust surface is the youngest event as it cuts all previous structures, and records fault reactivation with any top-to-the-W slip direction and a later top-to-the-S slip. Axes of mullions on this surface trend to the SE and do not parallel slickenlines.
The Champlain Thrust fault zone evolved asymmetrically across its principal slip surface through the process of strain localization and fault reactivation. Strain localization is characterized by the changes in relative age, motion direction along faults, and style of structures preserved within the fault zone. Reactivation of the Champlain Thrust surface and the corresponding change in slip direction was due to the influence of pre-existing structures at depth. This study defines the architecture of the Champlain Thrust fault zone and documents the importance of comparing the structural architecture of the fault zone core, damage zone, and protolith to determine the comprehensive fault zone evolution.
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Tam, Evan. "Geochronological Constraints On The Timing Of Deformation: An Examination Of The Prospect Rock Fault Footwall In North-Central Vermont." ScholarWorks @ UVM, 2018. https://scholarworks.uvm.edu/graddis/940.
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The Prospect Rock Fault (PRF) is key to our understanding of the regional tectonic evolution of Vermont during the Taconic, Salinic, and Acadian Orogenies, and may have played an important role in the exhumation of blueschist and eclogite-facies rocks in the Tillotson Peak Complex (TPC) during the Taconic Orogeny. The TPC is in the footwall of the PRF in the eastern limb of the Green Mountain Anticlinorium. In the TPC, the dominant foliation is S2 and E-W trending F2 folds parallel L2 stretching lineations, which trend orthogonal to regional N-S trending folds associated with the Taconic Orogeny. The PRF itself is folded by F2 folds. Presently, there is a lack of consensus about the role of the PRF in the exhumation of the TPC, and studies have not reconciled the formation of the E-W folds and lineations to a regional model.
Oriented samples and structural data were collected from the footwall of the PRF over several transects. Samples were processed into orthogonal thin sections for microstructural analyses and for 40Ar/39Ar step heating of white mica. The dominant foliations in the PRF samples were identified through microstructural analysis and correlating the age of deformation as S2 and S3. These were defined in thin section by mica and quartz microlithons, and oriented mica grains. S1, and in some samples S2, are locally preserved in some mica domains and albite/garnet inclusion trails. S4 appears as crenulations of S3, with no significant new mineral crystallization. In the field, L2 and L3 lineations are defined by mineral and quartz rods, and L4 lineations are defined as intersection lineations on S2 surfaces.
40Ar/39Ar analyses yielded plateau ages ranging from 458.6 ± 2.0 Ma to 419.0 ± 2.4 Ma (1σ). The oldest plateau ages are just slightly younger, yet concordant, with published and new 40Ar/39Ar ages from the TPC and come from the structurally highest portions of the footwall in the northern part of the study area. Virtually all apparent age spectra show age gradients. Results from this study suggest the PRF played a role in exhumation of the TPC and ages obtained are closely aligned with deformation ages constrained from 40Ar/39Ar dating in southern Quebec for the Taconic D2 and Salinian D3 deformation. These dates may aid correlatation of ages and structures regionally and further refining of tectonostratigraphic models describing southern Quebec and New England.
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Ashley, Kyle T. "Titaniq Thermobarometry of Fabric Development in the Strafford Dome, Vermont: Linking Microstructures to Orogenic Processes." ScholarWorks @ UVM, 2011. http://scholarworks.uvm.edu/graddis/11.
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Abstract Geochemical, microstructural and petrological analyses were conducted on metapelites from the Strafford Dome, Vermont. Samples record metamorphic conditions from biotite to peak kyanite/staurolite grade and preserve microstructures related to two Acadian nappe emplacement events. The purpose of this study was to test the validity and application of the Ti-in-quartz (“TitaniQ”) thermobarometer to constraining pressure-temperature-timing-deformation (P-T-t-D) paths in metamorphic tectonites. Due to the nearly ubiquitous presence of quartz in continental rocks, the ability to apply this method would have significant implications for improving our ability to resolve tectonic histories. Cathodoluminescence (CL) imaging on quartz was conducted to qualitatively assess the distribution of Ti in a single grain and/or compare neighboring crystals. X-ray mapping of garnet porphyroblasts was conducted to estimate P-T conditions during garnet growth to provide a framework for included quartz grains. P-T-X contour diagrams (used in P-T calculations for garnet growth) were constructed from data obtained by X-ray fluorescence analysis on bulk-rock chemistries. Secondary ion mass spectrometry analysis was conducted to constrain Ti concentrations in quartz due to the low [Ti] present in the Strafford samples (<10 ppm). Analysis of the samples revealed [Ti] in zoned quartz grains that can be grouped and associated with certain P-T-D conditions. A majority of quartz grains have dark cores in CL images with low [Ti] (~2.5–3.5 ppm) in both matrix quartz and inclusions. Quartz inclusions in garnets that grew syn-tectonically with D2 have bright rims ~5.5 ppm. Matrix quartz, on the other hand, has rims with much higher [Ti] (~7.5–9.5 ppm). Comparing these Ti concentrations to summary P-T paths from previous studies suggests: quartz inclusions have rims recrystallized during the end of D1 deformation, matrix grains have rims re-equilibrated at peak P-T conditions post-D2 deformation, and the dark cores observed in CL images must be from early prograde or relics of the protolith. The evaluation of the TitaniQ thermobarometer’s application to constrain P-T-t-D histories has highlighted some potential problems and significant benefits. To use the thermobarometer, either T or P must be independently constrained, which is often difficult to do given the many microstructural contexts of quartz in a single sample. This study capitalized on the ability to determine the relative timing of quartz (re)crystallization relative to garnet growth. Using another trace element thermobarometer would be ideal (e.g. Zr-in-rutile) for greater precision, although the relevant accessory phases may not be present and constraining the timing of re-equilibration is challenging. The abundance of quartz in continental rocks and the various microstructural occurrences of quartz in a single metamorphic tectonite provides additional opportunities to constrain points on the P-T-D path than conventional thermobarometers. The TitaniQ thermobarometer has the potential to yield deeper insights into the tectonic history of crustal rocks than previously available. These findings further elucidate the potential of the method for use in studies of metamorphic tectonites, continental tectonics and rheology.
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Gavin, Bronwyn Patricia. "The microstructural and metamorphic history preserved within garnet porphyroblasts from southern Vermont and northwestern Massachusetts." Thesis, 2004. https://researchonline.jcu.edu.au/1377/1/01front.pdf.
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Garnet porphyroblasts from southern Vermont and northwestern Massachusetts typically preserve multiple generations of inclusion trails, reflecting a potentially complex deformation and metamorphic growth history. Textural discontinuities, such as inclusion trail truncations or deflection planes, are commonly preserved within these complex inclusion trails and they are dominantly sub-vertically and sub-horizontally oriented. This observation cannot be adequately explained using the rotational model of spiral inclusion trail formation, leading to the conclusion that the trails were formed by the inclusion of multiple sub-vertical and sub-horizontal foliations during episodic garnet growth without porphyroblast rotation. Foliation inflection/intersection axes preserved within porphyroblasts (FIAs) provide important information about the kinematics of deformation, particularly the direction of bulk shortening at the time they formed. Samples from this study preserve a succession of six FIA sets resulting from a progressive change in the direction of bulk shortening through time. The distribution of these FIA sets across the field area indicates that the deformation was heterogeneously partitioned and occurred at different scales throughout orogenesis. Localization of deformation is an important control on garnet growth and repartitioning during successive deformation events resulted in a heterogeneous spatial distribution of garnet growth through time. The episodic nature of garnet growth is reflected in compositional zoning anomalies in garnet porphyroblasts from the Hoosac Formation. Zones of manganese enrichment, accompanied by calcium depletion, reveal pauses in garnet growth that may have been accompanied by fluid infiltration, garnet dissolution-reprecipitation and metasomatism at crystal or greater scales. The metamorphic history of these samples was further investigated using P-T pseudosections constructed via THERMOCALC. The mineral assemblages predicted are in good agreement with the observed mineralogy of the samples and estimates of P-T conditions at the time of garnet core growth were made using compositional isopleths based on microprobe analyses of garnet core composition. The samples do not show a clear relationship between the P-T data and the FIA data, suggesting that the preservation of different FIAs is not simply a function of P-T conditions. In samples where initial garnet appears to have occurred at temperature and/or pressure conditions higher than the minimum P-T conditions predicted for garnet stability, deformation probably played an essential role in garnet nucleation and growth. These “overstepped” samples indicate a progressive increase in pressure through the different phases of orogenesis.
This study reveals that garnet porphyroblasts in southern Vermont and northwestern Massachusetts grew during a complex history of deformation involving the production of multiple sub-horizontal and sub-vertical foliations with garnet growth primarily controlled by deformation partitioning, resulting in a heterogeneous spatial distribution through time. FIAs allow the relative age of different phases of garnet growth to be established and provide a framework for interpreting the relationship between deformation and metamorphism. Compositional zoning anomalies reflect the episodic nature of garnet growth and P-T modelling suggests that deformation took place under conditions of increasing pressure.
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Gavin, Bronwyn Patricia. "The microstructural and metamorphic history preserved within garnet porphyroblasts from southern Vermont and northwestern Massachusetts." 2004. http://eprints.jcu.edu.au/1377/1/01front.pdf.
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Garnet porphyroblasts from southern Vermont and northwestern Massachusetts typically preserve multiple generations of inclusion trails, reflecting a potentially complex deformation and metamorphic growth history. Textural discontinuities, such as inclusion trail truncations or deflection planes, are commonly preserved within these complex inclusion trails and they are dominantly sub-vertically and sub-horizontally oriented. This observation cannot be adequately explained using the rotational model of spiral inclusion trail formation, leading to the conclusion that the trails were formed by the inclusion of multiple sub-vertical and sub-horizontal foliations during episodic garnet growth without porphyroblast rotation. Foliation inflection/intersection axes preserved within porphyroblasts (FIAs) provide important information about the kinematics of deformation, particularly the direction of bulk shortening at the time they formed. Samples from this study preserve a succession of six FIA sets resulting from a progressive change in the direction of bulk shortening through time. The distribution of these FIA sets across the field area indicates that the deformation was heterogeneously partitioned and occurred at different scales throughout orogenesis. Localization of deformation is an important control on garnet growth and repartitioning during successive deformation events resulted in a heterogeneous spatial distribution of garnet growth through time. The episodic nature of garnet growth is reflected in compositional zoning anomalies in garnet porphyroblasts from the Hoosac Formation. Zones of manganese enrichment, accompanied by calcium depletion, reveal pauses in garnet growth that may have been accompanied by fluid infiltration, garnet dissolution-reprecipitation and metasomatism at crystal or greater scales. The metamorphic history of these samples was further investigated using P-T pseudosections constructed via THERMOCALC. The mineral assemblages predicted are in good agreement with the observed mineralogy of the samples and estimates of P-T conditions at the time of garnet core growth were made using compositional isopleths based on microprobe analyses of garnet core composition. The samples do not show a clear relationship between the P-T data and the FIA data, suggesting that the preservation of different FIAs is not simply a function of P-T conditions. In samples where initial garnet appears to have occurred at temperature and/or pressure conditions higher than the minimum P-T conditions predicted for garnet stability, deformation probably played an essential role in garnet nucleation and growth. These “overstepped” samples indicate a progressive increase in pressure through the different phases of orogenesis. This study reveals that garnet porphyroblasts in southern Vermont and northwestern Massachusetts grew during a complex history of deformation involving the production of multiple sub-horizontal and sub-vertical foliations with garnet growth primarily controlled by deformation partitioning, resulting in a heterogeneous spatial distribution through time. FIAs allow the relative age of different phases of garnet growth to be established and provide a framework for interpreting the relationship between deformation and metamorphism. Compositional zoning anomalies reflect the episodic nature of garnet growth and P-T modelling suggests that deformation took place under conditions of increasing pressure.
Book chapters on the topic "Orogeny – Vermont"
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Tam, Evan, Laura E. Webb, Cheyne Aiken, Jonathan Kim, and Keith Klepeis. "Formation of the Green Mountain anticlinorium in northern Vermont at ca. 420 Ma." In Laurentia: Turning Points in the Evolution of a Continent. Geological Society of America, 2022. http://dx.doi.org/10.1130/2022.1220(27).
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ABSTRACT The Appalachian Mountains in northern Vermont host a complex rock record of the tectonic evolution of eastern Laurentia, from the opening of the Iapetus Ocean to the subsequent formation of a convergent Paleozoic margin involving multiple phases of orogenesis. Prior 40Ar/39Ar studies in Vermont and northern Massachusetts have generally interpreted two major events associated with a dominantly Ordovician Taconic orogeny and a Devonian Acadian orogeny; intermediate ages were considered to reflect Taconic metamorphism and/or deformation that was “partially reset” during the Acadian orogeny. However, recent studies have documented Salinic ages in northern Vermont, aligning with multiple lines of evidence in southern Quebec for an intervening Salinic orogeny during the Silurian. This study reports integrated microstructural and 40Ar/39Ar geochronological analyses of samples collected across the Green Mountain anticlinorium in northern Vermont. The dominant S2 and S3 foliations are defined in thin section by predominantly white mica/quartz microlithons and aligned mica cleavage domains in schist to graphitic schist that formed under greenschist-facies conditions. Correlation of microstructures across the field area and associated 40Ar/39Ar plateau ages reveal a spatial pattern associated with microstructural development across the anticlinorium. In the eastern limb, the oldest plateau age, 457.6 ± 2.0 Ma (1σ), is interpreted to reflect the timing of formation of S2. The youngest plateau age, 419.0 ± 2.4 Ma, comes from the western limb of the anticline near the trace of the Honey Hollow fault, where S2 is completely transposed by S3. Intermediate ages were obtained across the axis of the anticline, where S3 is a crenulation cleavage. While the Green Mountain anticlinorium has been previously interpreted to have formed in the Devonian during the Acadian orogeny, the typical ca. 386–355 Ma ages are notably absent in the data set, except in locally disturbed spectra. The results of this work are closely aligned with published results of 40Ar/39Ar dating in southern Quebec that reflect deformation during Taconic and Salinic orogenesis. These new data, together with recently reported ages of west-directed transport on Taconic thrusts along the western Green Mountain front at ca. 420 Ma, suggest a phase of mountain building in the New England Appalachians that has been previously unreported in Vermont. The formation of the Green Mountain anticlinorium coincided with a complex tectonic interval that overlapped temporally with (1) the transition from Salinic thrusting to normal faulting, (2) magmatism attributed to slab breakoff, and (3) syntectonic deposition in the Connecticut Valley–Gaspé Basin.
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Coish, R. A. "Rift and ocean floor volcanism from the late Proterozoic and early Paleozoic of the Vermont Appalachians." In The Nature of Magmatism in the Appalachian Orogen. Geological Society of America, 1997. http://dx.doi.org/10.1130/0-8137-1191-6.129.
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Arth, Joseph G., and Robert A. Ayuso. "The Northeast Kingdom Batholith, Vermont: Geochronology and Nd, O, Pb, and Sr isotopic constraints on the origin of Acadian granitic rocks." In The Nature of Magmatism in the Appalachian Orogen. Geological Society of America, 1997. http://dx.doi.org/10.1130/0-8137-1191-6.1.
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Karabinos, Paul, Elizabeth S. Mygatt, Sean M. Cook, and Matthew Student. "Evidence for an orogen-parallel, normal-sense shear zone around the Chester dome, Vermont: A possible template for gneiss dome formation in the New England Appalachians, USA." In From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region. Geological Society of America, 2010. http://dx.doi.org/10.1130/2010.1206(09).
Full textConference papers on the topic "Orogeny – Vermont"
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Karabinos, Paul, and James L. Crowley. "STRATIGRAPHIC, TECTONIC, AND PALEOGEOGRAPHIC CONSTRAINTS ON THE ACADIAN OROGENY FROM DETRITAL AND IGNEOUS ZIRCON DATING OF ROCKS FROM THE CONNECTICUT VALLEY-GASPE BASIN IN MASSACHUSETTS AND VERMONT." In 54th Annual GSA Northeastern Section Meeting - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019ne-328130.
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Robinson, Jessica, and Jean Crespi. "VARIATION OF GEOMETRY OF STRUCTURES AND STRAIN IN A CURVED OROGENIC BELT: TACONIC ALLOCHTHON, VERMONT AND NEW YORK." In GSA Annual Meeting in Seattle, Washington, USA - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017am-301217.
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Robinson, Jessica, and Jean Crespi. "STRUCTURAL GEOMETRY OF THE TACONIC ALLOCHTHON: A CURVED OROGENIC BELT AND ITS ZONE OF INCLINED TRANSPRESSION, VERMONT AND NEW YORK." In 53rd Annual GSA Northeastern Section Meeting - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018ne-311062.
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