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 | |
| Publication status | Published - 2004 Sep 1 |
| Externally published | Yes |
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Keywords
- Correlation of metamorphism
- Effect of homogenization on inclusion trail geometry
- FIAs
- Homogenization of compositional zoning
- Porphyroblasts
- Shear heating
ASJC Scopus subject areas
- Geology
Cite this
Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing. / Bell, Tim H.; Kim, Hyeong-Soo.
In: Journal of Structural Geology, Vol. 26, No. 9, 01.09.2004, p. 1591-1613.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Preservation of Acadian deformation and metamorphism through intense Alleghanian shearing
AU - Bell, Tim H.
AU - Kim, Hyeong-Soo
PY - 2004/9/1
Y1 - 2004/9/1
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.
KW - Correlation of metamorphism
KW - Effect of homogenization on inclusion trail geometry
KW - FIAs
KW - Homogenization of compositional zoning
KW - Porphyroblasts
KW - Shear heating
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UR - http://www.scopus.com/inward/citedby.url?scp=3242740464&partnerID=8YFLogxK
U2 - 10.1016/j.jsg.2004.01.006
DO - 10.1016/j.jsg.2004.01.006
M3 - Article
VL - 26
SP - 1591
EP - 1613
JO - Journal of Structural Geology
JF - Journal of Structural Geology
SN - 0191-8141
IS - 9
ER -