|
Article |
Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK
In the Appalachian Orogen of NE Newfoundland, the Gander and Avalon zones are separated by the 1–2 km wide, dextral, Dover Fault Shear Zone. This structure overprints sinistral transpressive deformations that affect broad regions either side of the Gander-Avalon boundary and is post-dated by ?Alleghenian (or younger) brittle dextral faults that are not thought to record large regional displacements. In ?Lower Palaeozoic sedimentary rocks of the Gander Lake Subzone, a steeply dipping sinistral shear zone (up to 20 km wide) was the focus of syn-tectonic sillimanite grade metamorphism, migmatization and granitic plutonism. In lower greenschist facies late Precambrian sedimentary and volcanic rocks of the Avalon Zone, early sinistral displacements were focused into a high strain zone (c. 2km wide) along the boundary. Although developed at different metamorphic grades, these early sinistral transpressive shear zones can be correlated and are thought to record the main phase of sinistral-oblique accretion and regional orogenesis during the mid-Silurian (c. 415-435 Ma). The switch to dextral displacements forming the Dover Fault Shear Zone appears to have initiated during later stages of syntectonic plutonism in the Gander Lake Subzone, suggesting that it may also be Silurian in age.
No evidence links the Gander and Avalon zones prior to sinistral transpression. Sinistral fabrics overprint flat-lying structures in the Gander Lake Subzone that are thought to be related to mid-Ordovician accretion of the superjacent Exploits (Dunnage) arc-ophiolite terrane to the west. The Gander and Dunnage allochthons were probably accreted to the Laurentian margin prior to the sinistral-oblique collision of Western Avalonia during the Silurian and they overlie the suture that separates Laurentia from the Central Lower Crustal Block of Avalonian affinities. The Gander-Avalon boundary in NE Newfoundland would then form the steeply-dipping surface expression of a collision-linked sinistral shear zone that allowed lateral decoupling of the Avalon and Central Lower Crustal Blocks during or following oblique collision.
Along the margin of the Gander Lake Subzone, the shear zone-hosted belt of sheeted granites and melting increasingly became the focus of deformation during the later stages of sinistral transpression. This suggests significant rheological softening of the crust that would account for the ability of transpressive terrane boundaries to accommodate large displacements. Furthermore, the estab-lishment of a thermal anomaly would have a long-lived weakening effect that could explain why such terrane boundaries are prone to reactivation.
This article has been cited by other articles:
 |
|
 |
|
  C.R. van Staal, K.L. Currie, G. Rowbotham, N. Rogers, and W. Goodfellow Pressure-temperature paths and exhumation of Late Ordovician-Early Silurian blueschists and associated metamorphic nappes of the Salinic Brunswick subduction complex, northern Appalachians Geological Society of America Bulletin, 2008; 120: 1455 - 1477. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. R. Jones, R. E. Holdsworth, M. Hand, and B. Goscombe Ductile extrusion in continental collision zones: ambiguities in the definition of channel flow and its identification in ancient orogens Geological Society, London, Special Publications, 2006; 268: 201 - 219. [Abstract] [PDF]
|
|
|
|
 |
|
 P. Clegg and R.E. Holdsworth Complex deformation as a result of strain partitioning in transpression zones: an example from the Leinster Terrane, SE Ireland Journal of the Geological Society, 2005; 162: 187 - 202. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. J. van der Velden, C. R. van Staal, and F. A. Cook Crustal structure, fossil subduction, and the tectonic evolution of the Newfoundland Appalachians: Evidence from a reprocessed seismic reflection survey Geological Society of America Bulletin, 2004; 116: 1485 - 1498. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. E. Holdsworth, R.E. Holdsworth, E. Tavarnelli, P. Clegg, R.V.L. Pinheiro, R.R. Jones, and K.J.W. McCaffrey Domainal deformation patterns and strain partitioning during transpression: an example from the Southern Uplands terrane, Scotland Journal of the Geological Society, 2002; 159: 401 - 415. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Malo and M. Malo Late Silurian-Early Devonian tectono-sedimentary history of the Gaspe Belt in the Gaspe Peninsula: from a transtensional Salinic basin to an Acadian foreland basin Bulletin of Canadian Petroleum Geology, 2001; 49: 202 - 216. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. B. Allen, M. B. ALLEN, G. I. ALSOP, and V. G. ZHEMCHUZHNIKOV Dome and basin refolding and transpressive inversion along the Karatau Fault System, southern Kazakstan Journal of the Geological Society, 2001; 158: 83 - 95. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. E. Holdsworth, M. Stewart, J. Imber, and R. A. Strachan The structure and rheological evolution of reactivated continental fault zones: a review and case study Geological Society, London, Special Publications, 2001; 184: 115 - 137. [Abstract] [PDF]
|
|
|
|
|
|
B. Tikoff, P. Kelso, C. Manduca, M. J. Markley, and J. Gillaspy Lithospheric and crustal reactivation of an ancient plate boundary: the assembly and disassembly of the Salmon River suture zone, Idaho, USA Geological Society, London, Special Publications, 2001; 186: 213 - 231. [Abstract] [PDF]
|
|
|
|
|
|
R. D. Hatcher Jr Rheological partitioning during multiple reactivation of the Palaeozoic Brevard Fault Zone, Southern Appalachians, USA Geological Society, London, Special Publications, 2001; 186: 257 - 271. [Abstract] [PDF]
|
|
|
|
|
|
P.-A. Bourque, M. Malo, and D. Kirkwood Paleogeography and tectono-sedimentary history at the margin of Laurentia during Silurian to earliest Devonian time: The Gaspe Belt, Quebec Geological Society of America Bulletin, 2000; 112: 4 - 20. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. F. Dewey, R. E. Holdsworth, and R. A. Strachan Transpression and transtension zones Geological Society, London, Special Publications, 1998; 135: 1 - 14. [Abstract] [PDF]
|
|
|
|
|
|
R. R. Jones and R. E. Holdsworth Oblique simple shear in transpression zones Geological Society, London, Special Publications, 1998; 135: 35 - 40. [Abstract] [PDF]
|
|
|
|
|
|
C. R. Van Staal, J. F. Dewey, C. M. Niocaill, and W. S. McKerrow The Cambrian-Silurian tectonic evolution of the northern Appalachians and British Caledonides: history of a complex, west and southwest Pacific-type segment of Iapetus Geological Society, London, Special Publications, 1998; 143: 197 - 242. [Abstract] [PDF]
|
|
|
|
|
|
R. E. HOLDSWORTH, C. A. BUTLER, and A. M. ROBERTS The recognition of reactivation during continental deformation Journal of the Geological Society, 1997; 154: 73 - 78. [Abstract] [PDF]
|
|
|
|
|
|
R. S. D'LEMOS, D. I. SCHOFIELD, R. E. HOLDSWORTH, and T. R. KING Deep crustal and local rheological controls on the siting and reactivation of fault and shear zones, northeastern Newfoundland Journal of the Geological Society, 1997; 154: 117 - 121. [Abstract] [PDF]
|
|
