Deep crustal growth of quartz, kyanite and garnet into large‐aperture, fluid‐filled fractures, north‐eastern Connecticut, USA

Deep crustal growth of quartz, kyanite and garnet into large‐aperture, fluid‐filled... Abstract A petrographic and petrological analysis of exceptionally well‐preserved hydrothermal veins from the Merrimack synclinorium, north‐eastern Connecticut, has been carried out in order to place new field‐based constraints on fracture aperture dimensions and porosity in the lower continental crust. The veins preserve substantial open space today in outcrop, and contain mineral assemblages including subhedral to euhedral crystals of quartz, kyanite and almandine‐rich garnet. Textural evidence indicates unequivocally that the vein minerals grew into macroscopic (mm‐ to cm‐scale) open space between the vein walls. The veins are interpreted to have been large‐aperture fractures along which significant advective fluid infiltration and chemical reaction occurred. The porosity of the rock mass due to open space between fracture walls today is c. 0.3%, but it could have been as large as several percent when the flow system was active. Quantitative thermobarometry results from vein mineral assemblages indicate that the fractures formed at pressures and corresponding crustal depths of c. 0.8 GPa and c. 30km, and temperatures of 550–600° C. The depth of fracture formation corresponds to published estimates of the maximum burial depth of the Merrimack synclinorium during the Acadian orogeny. The formation of large‐aperture fractures could increase significantly the transient permeability of the deep crust, and therefore influence metamorphic heat and mass transfer. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Metamorphic Geology Wiley

Deep crustal growth of quartz, kyanite and garnet into large‐aperture, fluid‐filled fractures, north‐eastern Connecticut, USA

Journal of Metamorphic Geology, Volume 13 (2) – Mar 1, 1995

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Publisher
Wiley
Copyright
Copyright © 1995 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0263-4929
eISSN
1525-1314
DOI
10.1111/j.1525-1314.1995.tb00220.x
Publisher site
See Article on Publisher Site

Abstract

Abstract A petrographic and petrological analysis of exceptionally well‐preserved hydrothermal veins from the Merrimack synclinorium, north‐eastern Connecticut, has been carried out in order to place new field‐based constraints on fracture aperture dimensions and porosity in the lower continental crust. The veins preserve substantial open space today in outcrop, and contain mineral assemblages including subhedral to euhedral crystals of quartz, kyanite and almandine‐rich garnet. Textural evidence indicates unequivocally that the vein minerals grew into macroscopic (mm‐ to cm‐scale) open space between the vein walls. The veins are interpreted to have been large‐aperture fractures along which significant advective fluid infiltration and chemical reaction occurred. The porosity of the rock mass due to open space between fracture walls today is c. 0.3%, but it could have been as large as several percent when the flow system was active. Quantitative thermobarometry results from vein mineral assemblages indicate that the fractures formed at pressures and corresponding crustal depths of c. 0.8 GPa and c. 30km, and temperatures of 550–600° C. The depth of fracture formation corresponds to published estimates of the maximum burial depth of the Merrimack synclinorium during the Acadian orogeny. The formation of large‐aperture fractures could increase significantly the transient permeability of the deep crust, and therefore influence metamorphic heat and mass transfer.

Journal

Journal of Metamorphic GeologyWiley

Published: Mar 1, 1995

References

  • Contrasting styles of Taconian, eastern Acadian, and western Acadian metamorphism, central and western New England
    Armstrong, Armstrong; Tracy, Tracy; Hames, Hames
  • Effects of fluid production on fluid flow during regional and contact metamorphism
    Hanson, Hanson
  • The effect of heterogeneous stress and strain on metamorphic fluid flow, Mary Kathleen, Australia, and a model for large scale fluid circulation
    Oliver, Oliver; Valenta, Valenta; Wall, Wall

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