Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing

Tim H. Bell; Hyeong Soo Kim

doi:10.1016/j.jsg.2004.01.006

Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing

Tim H. Bell, Hyeong Soo Kim

Research output: Contribution to journal › Article › peer-review

14 Citations (Scopus)

Abstract

The Northfield syncline in Massachusetts, USA, preserves the same Acadian succession of FIA trends (foliation intersection axes preserved in porphyroblasts) as that in Southeast Vermont, in spite of the overprinting effects of intense Alleghanian deformation and metamorphism resulting from this syncline being thrust southwards over the Pelham gneiss dome. Therefore, both regions were multiply tectonized about the same succession of directions of shortening prior to the Alleghanian, but all relics of Acadian metamorphism were obliterated in the matrix of the Northfield syncline rocks during southwards thrusting. Within the most intensely foliated rocks at the contact between the Northfield syncline and the Pelham gneiss dome, the compositional zoning within the garnet porphyroblasts was homogenized. The 55 °C increase in the rims of these garnet porphyroblasts against the matrix appears to be a product of shear heating that occurred when these rocks were thrust over the Avalonian rocks of the Pelham dome. The lack of equivalent intense Alleghanian shearing in Vermont suggests north central Massachusetts marks the upper contact of the northwest extremity of Avalon. This extremity was less than 10 km thick if it reached SE Vermont suggesting that these rocks were tectonically wedged into North America rather than simply underthrust, and that some delamination of the upper part of this portion of Avalon occurred in Alleghanian times.

Original language	English
Pages (from-to)	1591-1613
Number of pages	23
Journal	Journal of Structural Geology
Volume	26
Issue number	9
DOIs	https://doi.org/10.1016/j.jsg.2004.01.006
Publication status	Published - 2004 Sept 1
Externally published	Yes

Bibliographical note

Funding Information:
Bell acknowledges the Australian Research Council for providing the funds that enabled the research to be done. Bell and Kim acknowledge the facilities for research at JCU. The Departamento de Geodinamica at the Universidad de Granada provided facilities that allowed a major revision of this manuscript to be made. We thank Peter Welch for preparing some of the garnet compositional zoning maps and taking some of the photos and Peter Robinson for use of his maps of the NE margin of the Pelham Dome. We also acknowledge a review by Bob Tracy that improved the manuscript immensely.

Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.

Keywords

Correlation of metamorphism
Effect of homogenization on inclusion trail geometry
FIAs
Homogenization of compositional zoning
Porphyroblasts
Shear heating

ASJC Scopus subject areas

Geology

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10.1016/j.jsg.2004.01.006

Cite this

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title = "Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing",

abstract = "The Northfield syncline in Massachusetts, USA, preserves the same Acadian succession of FIA trends (foliation intersection axes preserved in porphyroblasts) as that in Southeast Vermont, in spite of the overprinting effects of intense Alleghanian deformation and metamorphism resulting from this syncline being thrust southwards over the Pelham gneiss dome. Therefore, both regions were multiply tectonized about the same succession of directions of shortening prior to the Alleghanian, but all relics of Acadian metamorphism were obliterated in the matrix of the Northfield syncline rocks during southwards thrusting. Within the most intensely foliated rocks at the contact between the Northfield syncline and the Pelham gneiss dome, the compositional zoning within the garnet porphyroblasts was homogenized. The 55 °C increase in the rims of these garnet porphyroblasts against the matrix appears to be a product of shear heating that occurred when these rocks were thrust over the Avalonian rocks of the Pelham dome. The lack of equivalent intense Alleghanian shearing in Vermont suggests north central Massachusetts marks the upper contact of the northwest extremity of Avalon. This extremity was less than 10 km thick if it reached SE Vermont suggesting that these rocks were tectonically wedged into North America rather than simply underthrust, and that some delamination of the upper part of this portion of Avalon occurred in Alleghanian times.",

keywords = "Correlation of metamorphism, Effect of homogenization on inclusion trail geometry, FIAs, Homogenization of compositional zoning, Porphyroblasts, Shear heating",

author = "Bell, {Tim H.} and Kim, {Hyeong Soo}",

note = "Funding Information: Bell acknowledges the Australian Research Council for providing the funds that enabled the research to be done. Bell and Kim acknowledge the facilities for research at JCU. The Departamento de Geodinamica at the Universidad de Granada provided facilities that allowed a major revision of this manuscript to be made. We thank Peter Welch for preparing some of the garnet compositional zoning maps and taking some of the photos and Peter Robinson for use of his maps of the NE margin of the Pelham Dome. We also acknowledge a review by Bob Tracy that improved the manuscript immensely. Copyright: Copyright 2011 Elsevier B.V., All rights reserved.",

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doi = "10.1016/j.jsg.2004.01.006",

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PY - 2004/9/1

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N2 - The Northfield syncline in Massachusetts, USA, preserves the same Acadian succession of FIA trends (foliation intersection axes preserved in porphyroblasts) as that in Southeast Vermont, in spite of the overprinting effects of intense Alleghanian deformation and metamorphism resulting from this syncline being thrust southwards over the Pelham gneiss dome. Therefore, both regions were multiply tectonized about the same succession of directions of shortening prior to the Alleghanian, but all relics of Acadian metamorphism were obliterated in the matrix of the Northfield syncline rocks during southwards thrusting. Within the most intensely foliated rocks at the contact between the Northfield syncline and the Pelham gneiss dome, the compositional zoning within the garnet porphyroblasts was homogenized. The 55 °C increase in the rims of these garnet porphyroblasts against the matrix appears to be a product of shear heating that occurred when these rocks were thrust over the Avalonian rocks of the Pelham dome. The lack of equivalent intense Alleghanian shearing in Vermont suggests north central Massachusetts marks the upper contact of the northwest extremity of Avalon. This extremity was less than 10 km thick if it reached SE Vermont suggesting that these rocks were tectonically wedged into North America rather than simply underthrust, and that some delamination of the upper part of this portion of Avalon occurred in Alleghanian times.

AB - The Northfield syncline in Massachusetts, USA, preserves the same Acadian succession of FIA trends (foliation intersection axes preserved in porphyroblasts) as that in Southeast Vermont, in spite of the overprinting effects of intense Alleghanian deformation and metamorphism resulting from this syncline being thrust southwards over the Pelham gneiss dome. Therefore, both regions were multiply tectonized about the same succession of directions of shortening prior to the Alleghanian, but all relics of Acadian metamorphism were obliterated in the matrix of the Northfield syncline rocks during southwards thrusting. Within the most intensely foliated rocks at the contact between the Northfield syncline and the Pelham gneiss dome, the compositional zoning within the garnet porphyroblasts was homogenized. The 55 °C increase in the rims of these garnet porphyroblasts against the matrix appears to be a product of shear heating that occurred when these rocks were thrust over the Avalonian rocks of the Pelham dome. The lack of equivalent intense Alleghanian shearing in Vermont suggests north central Massachusetts marks the upper contact of the northwest extremity of Avalon. This extremity was less than 10 km thick if it reached SE Vermont suggesting that these rocks were tectonically wedged into North America rather than simply underthrust, and that some delamination of the upper part of this portion of Avalon occurred in Alleghanian times.

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Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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