Research Article| August 01, 1977 Structural analysis of the Silurian-Devonian rocks of the Royalton area, Vermont BERTRAM G. WOODLAND BERTRAM G. WOODLAND 1Department of Geology, Field Museum of Natural History, Chicago, Illinois 60605 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1977) 88 (8): 1111–1123. https://doi.org/10.1130/0016-7606(1977)88<1111:SAOTSR>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BERTRAM G. WOODLAND; Structural analysis of the Silurian-Devonian rocks of the Royalton area, Vermont. GSA Bulletin 1977;; 88 (8): 1111–1123. doi: https://doi.org/10.1130/0016-7606(1977)88<1111:SAOTSR>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 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–Gaspé 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 (D1), is recognized by a pervasive schistosity (S1) generally parallel to bedding (S0) and by rarely identified folds (F1). The second deformation (D2) has left the most widespread imprint, with an S2 cleavage or schistosity and open to moderately flattened folds (F2) in schistosity, parallel to bedding (S0/S1). Least easily recognized is the third deformation (D3), with sparse open folds in S2.The western band of the Gile Mountain Formation is interpreted as the westward- and downward-facing nose — the Royalton synform — of a large D1 recumbent fold — the eastern Vermont nappe. D2 structures have generally been regarded as synchronous with and genetically related to formation of domes and the Strafford-Willoughby arch. However, the D2 structures are interpreted here as pre-doming, with D3 structures related to the doming deforming them.Compressive buckling and variable flattening imposed during D2 upon a variably oriented S0/S1 may have been the result of emplacement of higher nappes (now removed by erosion), which increased the depth of burial promoting prograde metamorphism. 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.
High-grade metamorphic rocks in the Burke area include staurolite-, andalusite-staurolite-, sillimanite-andalusite-staurolite-, sillimanite-garnet-staurolite-, sillimanite-garnet-potash feldspar (rare)-, kyanite-sillimanite-staurolite-, and kyanite-sillimanite-andalusite-staurolite-bearing assemblages. These rocks are interpreted as having been formed from low-grade schist and phyllite under load conditions higher than those characterizing normal hornfels aureoles. The various assemblages indicate the metamorphic trends produced as a result of increasing temperature. The one occurrence of a kyanite-sillimanite-andalusite-bearing assemblage suggests that these polymorphs were probably formed under closely similar conditions during thermal metamorphism but not necessarily simultaneously. Change of temperature is easier to envisage than change of pressure during the crystallization of this assemblage. Temperature and pressure conditions must have hovered near to the assumed triple point of the alumino-silicates.
ABSTRACT Irregular and discontinuous coalified objects, here termed rhizomorphs, occur above the Summum (No. 4) Coal Member (Carbondale Formation) at one locality in La Salle County, Illinois. These vitrinite structures, varying between 3 mm and 4 cm in diameter, occur in a blocky to structureless mottled claystone characterized by numerous carbonaceous streaks and small‐scale slickensides. The rhizomorphs twist and bend in a tightly coiled and kinked pattern, and may extend laterally through the claystone for 40 cm or more before bifurcating or terminating. The rhizomorphs display little or no evidence of compressive distortion. They are composed of two types of material: structureless bright conchoidal collinite; and cellular woody structure. One or more vascular bundles occur as discrete steles within a groundmass of collinite gel; these are generally aligned longitudinally within the coal except where steles diverge laterally as offshoots. The rhizomorphs are believed to be a diagenetic derivative of rooting structures; this is based on their occurrence in an underclay‐like sediment and on their irregular, kinked form, which differs from that of most vertical supportive plant stems. Non‐compressive coalification of the plant material may have occurred through: (1) aerobic alteration of cell walls to non‐compressive inertinite; (2) centripetal contraction and selective degradation of plant tissue; and (3) impregnation of more resistant stelar elements by organic gel derived from degradation of thin‐walled tissue.
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