Petrology and geochemistry of selected talc-bearing ultramafic rocks and adjacent country rocks in north-central Vermont

Chidester, A.H.

doi:10.3133/pp345

Cited by 68 publications

(50 citation statements)

References 15 publications

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“…Chidester (1962) and Jahns (1967) have reached a similar conclusion during detailed investigation of the zoned ultramafic bodies of Vermont; they placed the original ultramafic-mafic contact within the steatite zone. Recent work, however, on the Unst, Shetland, occurrence (Curtis & Brown 1969) explains all mineral zones, including the outermost chlorite-and biotite-bearing shells, as derived from serpentinite by a sequential reaction involving Si(OH)4' Ca+ 2 , AJ+3, and K+ gain from the country rock in exchange for Mg+2 and H 2 0.…”

Section: Origin Of Zonesmentioning

confidence: 67%

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Concentrically zoned ultramafic pods from the Haast schist zone, South Island, New Zealand

Cooper

1976

New Zealand Journal of Geology and Geophysics

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Ultramafic pods enclosed within greenschist are described from the Haast River area, South Westland. The largest body, 60 X 800 m in outcrop area, is exposed in Douglas Creek and consists of a central core of serpentinite rimmed successively by concentric, essentially monomineralic or bimineralic shells of talc-magnesite, talc, tremolite, chlorite, biotite, and albite, the last interlaminated with country-rock greenschist. The zones are interpreted as having formed by metasomatic exchange between two masses of dissimilar composition during garnet zone metamorphism-the albite, biotite, and chlorite zones were derived from greenschist, and tremolite, talc, and talc-magnesite rocks from serpentinite. The serpentinite contains a highly magnesian olivine (FjZf'8) interpreted as a metamorphic phase crystallising under conditions of high Po . Relict chromite in the serpentinite suggest a peridotitic parent lithology. Rare 2 harzburgite cobbles occur in float, downstream of the pod.Ultramafic schist occurences elsewhere in western Otago are restricted to linear and arcuate belts wincident with greenschist-rich zones. The serpentinite-bearing greenschist zones are defined magnetically by narrow bands of low amplitude positive anomalies.In the Haast area the distribution of ultramafites coincides with the western boundary of a terrain dominated by macroscopic, isoclinal F, folds. To the west of the ultramafite occurrences F, folds are rare. It is suggested that the ultramafites and possibly some of the associated greenschists represent a slice or slices of the sima tic basement of the Haast Schist Zone, tectonicly emplaced during thrusting of the sYllmetamorphic F2 deformational phase.

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Section: Origin Of Zonesmentioning

confidence: 67%

“…Hess (1933a;1933b);Phillips & Hess (1936);Reed (1934);Chidester (1962);Jahns (1967);and Matthews (1967). Although the zones are petrographically similar, interpretation is varied:…”

Section: I>;'mentioning

confidence: 99%

Concentrically zoned ultramafic pods from the Haast schist zone, South Island, New Zealand

Cooper

1976

New Zealand Journal of Geology and Geophysics

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“…[Chidester, 1962;Frost, 1975]. Bladed amphibole shear zones contain accessory minerals including ilmenite, apatite, zircon, and/or monazite, and may also have small pockets (<1 mm) of plagioclase.…”

Section: Strain History and Strain Fabric Descriptionmentioning

confidence: 99%

Strain localization on an oceanic detachment fault system, Atlantis Massif, 30°N, Mid‐Atlantic Ridge

Schroeder

John

2004

Geochem Geophys Geosyst

153

217

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[1] Microstructural observations, mineral chemistry, and the spatial distribution of deformation fabrics recorded in outcrop samples collected from Atlantis Massif, the active inside corner high at 30°N, MidAtlantic Ridge, suggest that strain is localized near the subhorizontal domal surface hypothesized to be an exposed detachment fault. Deformation textures in peridotite and gabbro indicate that high-temperature (>500°C) strain occurred via crystal-plastic flow and diffusive mass transfer. Low-temperature (<400°C) shear zones containing brittle and semibrittle microboudinage textures in which tremolite, chlorite, and/or talc replace fractured serpentine or hornblende cut earlier formed high-temperature deformation fabrics in peridotite. Textures indicate strain was localized by cataclasis and reaction softening into zones of intense greenschist and subgreenschist grade metamorphism. Gabbro is only weakly deformed below amphibolite facies (<500°C), indicating that strain was partitioned into altered peridotite at low temperature. There is a clear relationship between deformation intensity and structural depth beneath the subhorizontal surface of the Massif. Discontinuous high-intensity crystal-plastic deformation fabrics are found at all structural depths (0-520 m) beneath the surface, indicating that high-temperature, granulite-and amphibolite-grade deformation was not localized in a single shear zone. In contrast, semibrittle and brittle low-temperature shear zones are concentrated less than 90 m structurally beneath the surface, and the most intensely brittlely deformed samples concentrated in the upper 10 m. Localization of brittle deformation fabrics near the upper surface of the massif supports the hypothesis that it is the exposed footwall of a detachment fault. The structural evolution of Atlantis Massif is therefore analogous to a continental metamorphic core complex. Strain was localized onto the fault by reaction-softening and fluid-assisted fracturing during greenschist-and subgreenschist-grade hydrothermal alteration of olivine, clinopyroxene, serpentine, and hornblende to tremolite, chlorite, and/or talc.

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“…Culminations and depressions in the longitudinal fold system, such as the depression marked by the northwest salient of the Stowe formation in the vicinity of Hadley Mountain on the Eden-Lowell township boundary, are of the same age and origin as the longitudinal folds (see also Chidester, 1953). It seems significant that the depression at Hadley Mountain is adjacent to the greatest development of transverse folds in the core of the Gilmore anticline.…”

Section: Structural Synthesismentioning

confidence: 92%

“…Such inferences concerning mutual relationships of the major folds, deduced from interrelationship of the two systems of minor folds, are useful, although supporting data are somewhat obscure (Albee, 1957;Chidester, 1953Chidester, , 1962. Here uncertainty arises from not-too-clear genetic relations between the minor cross folds and larger transverse folds (see p. 63).…”

Section: Structural Synthesismentioning

confidence: 99%

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

Cady¹,

Albee²,

Chidester³

1963

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Petrology and geochemistry of selected talc-bearing ultramafic rocks and adjacent country rocks in north-central Vermont

Cited by 68 publications

References 15 publications

Concentrically zoned ultramafic pods from the Haast schist zone, South Island, New Zealand

Concentrically zoned ultramafic pods from the Haast schist zone, South Island, New Zealand

Strain localization on an oceanic detachment fault system, Atlantis Massif, 30°N, Mid‐Atlantic Ridge

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

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