East-central Vermont Research Articles

A generalized photon-tracking approach to simulate spectral snow albedo and transmittance using X-ray microtomography and geometric optics

Abstract. A majority of snow radiative transfer models (RTMs) treat snow as a collection of idealized grains rather than an organized ice–air matrix. Here we present a generalized multi-layer photon-tracking RTM that simulates light reflectance and transmittance of snow based on X-ray microtomography images, treating snow as a coherent 3D structure rather than a collection of grains. The model uses a blended approach to expand ray-tracing techniques applied to sub-1 cm3 snow samples to snowpacks of arbitrary depths. While this framework has many potential applications, this study's effort is focused on simulating reflectance and transmittance in the visible and near infrared (NIR) through thin snowpacks as this is relevant for surface energy balance and remote sensing applications. We demonstrate that this framework fits well within the context of previous work and capably reproduces many known optical properties of a snow surface, including the dependence of spectral reflectance on the snow specific surface area and incident zenith angle as well as the surface bidirectional reflectance distribution function (BRDF). To evaluate the model, we compare it against reflectance data collected with a spectroradiometer at a field site in east-central Vermont. In this experiment, painted panels were inserted at various depths beneath the snow to emulate thin snow. The model compares remarkably well against the reflectance measured with a spectroradiometer, with an average RMSE of 0.03 in the 400–1600 nm range. Sensitivity simulations using this model indicate that snow transmittance is greatest in the visible wavelengths, limiting light penetration to the top 6 cm of the snowpack for fine-grain snow but increasing to 12 cm for coarse-grain snow. These results suggest that the 5 % transmission depth in snow can vary by over 6 cm according to the snow type.

Worker Housing in the Vermont Copper Belt: Improving Life and Industry Through Paternalism and Resistance

During the mid-nineteenth century, east-central Vermont supported two major copper mines and their associated villages. In order to wrest thousands of tons of copper from the earth these mines, the Elizabeth and Ely mines, hired and housed thousands of miners, laborers, and their families. Both mines pursued the same resource in the same environment during the same period, but the Ely Mine developed a centralized village, while the Elizabeth Mine housed its workers in isolated housing clusters. The causes of these differences in worker housing can be traced to differences in scale, setting, and managerial philosophy, and can be analyzed within the larger historical context of Improvement and the larger ethnographic context of paternalism in mining communities.

Element mobility and scale of mass transport in the formation of quartz veins during regional metamorphism of the Waits River Formation, east-central Vermont

Veins and adjacent alteration selvages in the Waits River Formation were investigated to determine whether associated mass transfer was due primarily to large-scale advection or small-scale diffusion. Samples of the vein, selvage, and adjacent wall rock were collected from the earliest and most numerous generation of veins in pelite and carbonate hosts from outcrops in the chlorite and the kyanite zones. Bulk compositions of selvages and unaltered wall rocks were compared using a reference frame defined by a combination of Zr, Ti, REEs, and U. Selvages from both outcrops typically exhibit losses of Si, K, Ba, and Rb relative to unaltered wall rock. Kyanite zone selvages show losses in Mg and Cs in addition. Differences in K, Ba, Rb, Cs, and Mg between the vein-selvage system as a whole and adjacent unaltered wall rock are possibly accounted for by development of micas in veins. The addition of Si and Ca to veins is not balanced by removal of Si and Ca from the selvages. Vein-selvage systems contain more Si than wall rock, with an overall addition of ≈40 mg Si/cm3 to the chlorite zone and ≈55 mg Si/cm3 to the kyanite zone. Mass balance of Si at the outcrop scale requires that >90% of the Si in quartz veins was derived externally. Quartz veins studied formed primarily by fluid flow and large-scale advective mass transfer with a relatively minor component of local mass transport by diffusion. The estimated time-integrated fluid flux necessary to produce the observed amount of quartz in veins in an entire outcrop is ≈2-6·106 cm3 fluid/cm2 rock. Mineral inclusions in garnet and fracturing of garnets adjacent to veins indicate that formation of selvages and veins initiated prior to formation of garnet and continued after the end of garnet growth.

Development of spatial variations in reaction progress during regional metamorphism of micaceous carbonate rocks, Northern new England

Progress (ξ) of the infiltration-driven reaction, muscovite + ankerite + quartz + rutile + H₂O = biotite + calcite + plagioclase + CO₂, which occurred during Barrovian and Buchan regional metamorphism in east-central Vermont and south-central Maine, can vary by a factor of ten or more at all spatial scales down to that of adjacent lithologic layers <1 cm thick. Values of proxies for the activity of CO₂ and δ¹⁸O_fluid, K_s(6) ≡ [(a_phl)(a_an)(a_cal)²]/[(a_ms)(a_dol)³(a_qtz)²] and δ¹⁸O_Cal, are uniform within error of measurement over distances up to ≈1 m across layering. The conventional explanation of cm- to dm-scale variations in ξ in terms of layer-parallel channeled fluid flow cannot explain the uniformity in the proxies. Observed cm- to dm-scale variations in ξ are better explained by (a) mineral reactants and products that are solid solutions, (b) layer-by-layer variations in the amounts and compositions of minerals prior to reaction, and (c) uniformity of K_s(6) on a spatial scale larger than the scale of variations in ξ during subsequent infiltration and reaction. The m-scale uniformity in K_s(6) and δ¹⁸O_Cal is interpreted as homogenization of a_CO₂ and δ¹⁸O_fluid caused by the combined effects of intergranular diffusion and hydrodynamic dispersion. Reaction progress therefore was driven by the interplay of layer-parallel advection of chemically-reactive H₂O-rich fluid at decameter and larger scales and cross-layer transport of CO₂ and H₂O by diffusion/dispersion at scales of ≈1 m and less. Regardless of whether mineral reactants and products are solid solutions, the geochemical tracer considered, or the mechanism of fluid-rock reaction, the geometry of fluid flow can never be determined at a scale smaller than the one over which the concentration of the tracer is homogenized in the fluid within error of measurement by diffusion and dispersion.

Partitioning of deformation along an orogen and its effects on porphyroblast growth during orogenesis

An identical succession of foliation inflection/intersection axis trends in porphyroblasts (FIAs) is present in three separate areas affected by Acadian deformation and metamorphism along 130 km of the Appalachians from East Central Vermont to North Central Massachusetts. The FIAs trend successively NW–SE, SW–NE, W–E, NNW–SSE and SSW–NNE and appear to have formed during the same succession of deformations, which have been dated in SE Vermont as follows; not yet dated, pre-425, 425–404, 404–385 and 385–360 Ma, respectively. The two areas that are furthest apart, in east central Vermont and north central Massachusetts, have strikingly similar total distributions of FIAs in garnet porphyroblasts that show a somewhat inverse relationship to those observed in the Chester–Athens dome area of SE Vermont that separates them. That is, the number of samples containing the first formed FIA set is greatest for the two regions lying furthest apart and decreases in younger sets, whereas the number of samples containing the first FIA set is the least in the central region and increases for more recently developed sets. Partitioning of deformation into zones of progressive shearing and shortening has been demonstrated to control the sites of development of differentiated crenulation cleavage versus porphyroblast growth and sites of porphyroblast growth on one limb of a regional fold versus the other. We argue that partitioning of the deformation around competent feldspathic gneiss bodies at an orogen scale produced the variation in the number of samples containing the various FIA sets between the central and outer areas described above. Porphyroblasts most commonly grew during SW–NE directed shortening to the north and south of the Chester–Athens dome region of the Appalachians, but only rarely grew in the latter region. This suggests that deformation at this time partitioned around an outlier of competent basement feldspathic gneiss that underlies the Chester–Athens dome region, and this protected the rocks above and in the strain shadow to the NW and SE from the effects of the great bulk of the deformation that occurred over the period of time during which NW–SE-trending FIAs formed. We attribute the increase in the number of samples containing progressively younger FIAs in the Chester–Athens dome area during subsequent periods of NW–SE-, N–S-, WSW–ENE-, and WNW–ESE-directed shortening to the rise in temperature and pressure recorded in the rocks above the Chester–Athens dome with peak conditions occurring during the development of the NNW–SSE oriented FIA set between 404 and 385 Ma. As the temperature and pressure increased, the gneiss below would have become less competent, allowing the deformation associated with the succession of FIA sets to partition more pervasively through the dome core. This provided more sites for porphyroblast nucleation and growth and hence the number of samples recording these FIA sets increased. The concomitant decrease in the number of samples in which porphyroblasts grew in the rock within the areas to the north and south with successive FIAs possibly resulted from a progressive increase in competency of these rocks as the number of porphyroblasts increased.

Reductive deposition of graphite at lithological margins in East Central Vermont: a Sr, C and O isotope study

AbstractO, Sr and C isotopes from east‐central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross‐layer fluid fluxes of 104−106 moles m−2; absolute values depend on the Sr fluid‐rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ13C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO2 and CH4‐bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO2 released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.

Determination of time-integrated metamorphic fluid fluxes from the reaction progress of multivariant assemblages

An expression is derived for the calculation of time-integrated metamorphic fluid fluxes in two or more dimensions in rocks undergoing multivariant reactions under conditions of varying pressure, temperature and angle of flow. This calcuation requires knowledge of mineral assemblages, modes and compositions, which are obtained from isobaric T-XCO2 pseudosections constructed using the program THERMOCALC and compared with those observed in east central Vermont. THERMOCALC is capable of reproducing peak mineral assemblages, modes, compositions and the observed reaction sequences within the system KCaNaFMASCH for two kyanite grade pelitic carbonate rocks from a Barrovian style regional metamorphic terrain in east central Vermont, U.S.A. Calculation of fluid fluxes for decarbonation reactions under conditions of horizontal, layer-parallel flow produces time-integrated fluid flux figures of the order of 108 moles m−2. Allowance for possible cross-layer flow from adjacent dehydrating pelites reduces this figure significantly, with episodic cross-layer fluxes of the order of 105 moles m−2 being capable of driving the observed decarbonation. Chlorite bearing carbonate protoliths would have initially dehydrated with increasing temperature, a process requiring down-temperature fluid flow to produce the assemblages currently observed.

The timing and direction of metamorphic fluid flow in Vermont

A suite of metabasite dykes, emplaced within the Albee Formation, east-central Vermont, preserves evidence of interaction with a CO2-bearing hydrous fluid during Acadian metamorphism. Coupled advective and diffusive cross-layer fluxes of CO2 are recorded by forwards progress of the hydration-carbonation reaction:

CHEMICAL EVALUATION OF SOIL-SOLUTION IN ACID FOREST SOILS

Soil-solution chemistry is commonly studied in forests through the use of soil lysimeters. This approach is impractical for regional survey studies, however, because lysimeter installation and operation is expensive and time consuming. To address these problems, a new technique was developed to compare soil-solution chemistry among red spruce stands in New York, Vermont, New Hampshire, and Maine. Soil solutions were expelled by positive air pressure from soil that had been placed in a sealed cylinder. Before the air pressure was applied, a solution chemically similar to throughfall was added to the soil to bring it to approximate field capacity. After the solution sample was expelled, the soil was removed from the cylinder and chemically analyzed. The method was tested with homogenized Oa and Bs horizon soils collected from a red spruce stand in the Adirondack Mountains of New York, a red spruce stand in east-central Vermont, and a mixed hardwood stand in the Catskill Mountains of New York. Reproducibility, effects of varying the reaction time between adding throughfall and expelling soil solution (5-65 minutes) and effects of varying the chemical composition of added throughfall, were evaluated. In general, results showed that (i) the method was reproducible (coefficients of variation were generally < 15%), (ii) variations in the length of reaction-time did not affect expelled solution concentrations, and (iii) adding and expelling solution did not cause detectable changes in soil exchange chemistry. Concentrations of expelled solutions varied with the concentrations of added throughfall; the lower the CEC, the more sensitive expelled solution concentrations were to the chemical concentrations of added throughfall. Addition of a tracer (NaBr) showed that the expelled solution was a mixture of added solution and solution that preexisted in the soil. Comparisons of expelled solution concentrations with concentrations of soil solutions collected by zero-tension and tension lysimetry indicated that expelled solution concentrations were higher than those obtained with either type of lysimeter, although there was less difference with tension lysimeters than zero-tension lysimeters. The method used for collection of soil solution should be taken into consideration whenever soil solution data are being interpreted.

Structure and origin of the Ely copper deposit, east-central Vermont : T. W. Offield, J. F. Slack & S. A. Wittinbrink, US Geological Survey Bulletin, 2039, 1993, pp 59–68

Structure and origin of the Ely copper deposit, east-central Vermont : T. W. Offield, J. F. Slack & S. A. Wittinbrink, US Geological Survey Bulletin, 2039, 1993, pp 59–68

Geochronologic studies in central New England I: Evidence for pre-Acadian metamorphism in eastern Vermont

{sup 40}Ar/{sup 39}Ar geochronology on hornblendes from central New England reveals a Grenvillian cooling age (1026 {plus minus} 12 Ma) along the eastern margin of the Green Mountain massif, Acadian ages in east-central Vermont (350-397 Ma) and along the Bronson Hill anticlinorium in New Hampshire and Massachusetts (407-280 Ma), and Late Ordovician to Silurian ages (440-451 Ma) along a belt in eastern Vermont and central Massachusetts. These ages indicate a minimal Acadian overprint in eastern Vermont, the highest degree of Acadian overprint being located along the axis of the domes in the Connecticut Valley synclinorium. These data suggest that the formation of the domes occurred in the Acadian. Moreover, the Late Ordovician to Silurian cooling ages in eastern Vermont suggest that much of the metamorphic mineralogy and fabric observed in the Connecticut Valley synclinorium may be pre-Silurian in age.

A Revision of the Lower Paleozoic Stratigraphy in Eastern Vermont

The rocks between the Northfield slate and the Gile Mountain formation in east-central Vermont can be distinctly divided into three mappable lithologic units. The western two units are continuous with the Barton River and the Westmore formations as denned in the Memphremagog quadrangle to the north. Hitherto these two units have been included within the Waits River formation, a thick sequence of calcareous and non-calcareous rocks in the Barre and East Barre quadrangles. An analysis of the minor folds and cleavage-bedding relations in the area indicates the possibility of correlating the Westmore formation with the Gile Mountain formation across the limbs of a major syncline, the trough of which is occupied by the calcareous unit in the central part of the East Barre quadrangle. If correct, this interpretation makes this calcareous unit the youngest unit in the Paleozoic sequence of Vermont and hence calls for a revision of the stratigraphic sequence in eastern Vermont. It is proposed that the name "Waits River formation" be restricted to this youngest calcareous unit, inasmuch as the type locality-Waits River village-is situated in this unit and excellent outcrops are present nearby. Also, in view of the foregoing subdivision, the total section of rocks included under the "Waits River formation" of Currier and Jahns (1941) may be redefined as the "Barre group," composed of Barton River, Westmore, and the present Waits River formations.

GEOLOGY OF THE HANOVER QUADRANGLE, NEW HAMPSHIRE-VERMONT

The Hanover quadrangle, in west-central New Hampshire and east-central Vermont, is underlain predominantly by three metamorphosed eugeosynclinal formations, all of probable Ordovician age. The Waits River formation, with an exposed thickness of 4000 feet, and the Gile Mountain formation, with a thickness of 7500–8500 feet, are representative of the so-called Vermont sequence. In areas to the north and in part of the Hanover quadrangle, this sequence is separated from the New Hampshire sequence (here represented by the Orfordville formation, with a thickness of 6000 feet) by the Monroe fault. This fault apparently dies out in this quadrangle, and the two sequences are in sedimentary contact. Although the evidence is not unequivocal, it is concluded that Vermont rocks underlie the New Hampshire section and that the Gile Mountain formation is a probable equivalent to the lower part of the Orfordville formation and the upper part of the Waits River formation. A revision of the originally described stratigraphic sequence of the Orfordville formation is necessitated by the geologic relations of the Hanover area. Two pre-metamorphic faults, the Monroe and Northey Hill, and the post-metamorphic Ammonoosuc thrust, disrupt the regional structures. The areal geology is dominated by two domal uplifts, the Lebanon dome and the Pomfret dome. The former is a synkinematic granite intrusive which has been forcibly injected from the northwest toward the southeast, overturning the beds south of the pluton. Considerable granitization has accompanied the intrusion of this massif. The Pomfret dome is a cleavage dome produced by a late-stage or second-deformation upward welling of previously deformed plastic schists. Granite or migmatite working its way upward appears to be the active tectonic element in the formation of the cleavage dome. Most of the minor structures of the Hanover area are tectonically related either to the Lebanon dome or to the Pomfret dome. Regional metamorphism has affected all the rocks, and the intensity of metamorphism increases toward the domal structures. The latter are evidently the major heat sources in the metamorphic reconstitution of the interbedded sedimentary and volcanic rocks. Soaking of quartz, albite, and, to a lesser extent, tourmaline occurs in schists remote from Lebanon granite. Sedaclase tonalites, occasionally in lit-par-lit structures in these metasomatized rocks, possibly represent albitized granites, but their origin is conjectural.

GEOLOGY OF THE WOODSVILLE QUADRANGLE, VERMONT-NEW HAMPSHIRE

The Woodsville quadrangle, in east-central Vermont and west-central New Hampshire, was studied primarily to determine the stratigraphic and structural relations between two contrasting sedimentary sequences, one in western and central New Hampshire, the other in eastern and central Vermont. The Vermont rocks in this quadrangle consist of three formations, probably Middle Ordovician, with a total thickness between 15,000 and 20,000 feet. A fault separates these rocks from the New Hampshire rocks, which are pre-Silurian, Silurian, and Lower Devonian and total approximately 20,000 feet thick. Volcanic rocks, mostly pyroclastic, constitute about 10 per cent of the stratified rocks in the Woodsville quadrangle. Plutonic and hypabyssal rocks, probably late Devonian, occurs as dikes, sills, large intrusive sheets, and small stocks. The quadrangle is divided into four major tectonic units by three faults, which trend north-northeast. The Ammonoosuc fault dips about 36°W. and is younger than the folding and regional metamorphism. The Northey Hill and Monroe faults are steep and are older than most of the metamorphism. Because of the faults the major folds are fragmentary, preserved only as single limbs or as parts of synclines. Countless minor folds are present throughout the region. Progressive metamorphism is well displayed in the quadrangle. Whereas the rocks in a central north-south belt belong in the chlorite zone, the metamorphism increases toward the east and west margins of the quadrangle, where the rocks lie in the staurolite zone. The sillimanite zone has been attained locally around plutonic rocks. Retrograde metamorphism is especially strong along the Ammonoosuc thrust. The folding, thrusting, metamorphism, and igneous intrusions were all phases of the late Devonian Acadian orogeny. Special attention was given to the origin and chronology of the cleavage and minor folds in the Vermont part of the quadrangle, where there is evidence of two stages of deformation. During the earlier stage, schistosity formed parallel to the axial planes of contemporaneous minor folds. Because of the later deformation, these earlier folds are inconspicuous. During the later stage, slip cleavage formed parallel to the axial planes of contemporaneous minor folds. In many places these later folds are very conspicuous and if interpreted as ordinary drag folds may lead to an incorrect interpretation of the stratigraphy and major structure. Toward the west the slip cleavage becomes schistosity. The concept of two stages of deformation has important applications to the geology of New England and other metamorphic terranes.

Structure of Central and East-Central Vermont

The formations of central and east-central Vermont are exposed as a series of parallel belts that strike nearly north. Most of the rocks dip steeply, and many are overturned. With one possible exception, there seem to be no major repetitions within the sequence, and the order of formations from west to east appears to be the same as the order of their deposition. The formations are dominantly schist or phyllite, with varying proportions of arenaceous material. One thin formation, the Shaw Mountain, contains quartz conglomerate, calcareous tuff, and crinoidal limestone. The third-from-highest formation, the Waits River, is very thick and contains a large proportion of calcareous beds. The distance from the base of the lowest formation to the top of the highest, measured normal to bedding, is more than 100,000 feet; this large apparent thickness is believed to be not very much greater than the original thickness. The metasediments have been intruded by granitic dikes and plutons, mafic dikes, and small ultr...