Hinged Alleghanian Uplift of the Bronson Hill terrane in Connecticut and Massachusetts

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Hinged Alleghanian Uplift of the Bronson Hill
terrane in Connecticut and Massachusetts

• Elizabeth R. Goeke, Julie L. Boyd, and Robert P.
  Wintsch
• Indiana University, Bloomington, Indiana

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Research support by

• Geological Society of America Student Research
  grants awarded to Elizabeth R. Goeke and Julie L.
  Boyd
• National Science Foundation grants EAR 91-04495
  (R. P. Wintsch) and EAR99-09410 (R. P. Wintsch)
• Department of Geological Sciences, Indiana
  University

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Goals To evaluate the Alleghanian overprint on
rocks previously metamorphosed in the Acadian
Orogeny.
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Why the Bronson Hill terrane?

• The entire terrane was metamorphosed during the
  Acadian Orogeny.
• The terrane extends from the Long Island Sound to
  the New Hampshire/Canadian border.
• Cooling ages from Connecticut in the Bronson Hill
  are indicative of cooling from Alleghanian events.

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Julies horn ages on a map
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Julies musc ages on a map
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Ponder the Difference

• Hornblende ages are cooling from Alleghanian
  heating in the south and the Acadian Orogeny in
  the north.
• Muscovite ages are fairly uniform the length of
  the terrane and indicative of cooling from
  Permian heating.

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Map of ERG samples
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Thermometers and Barometers

• Holland and Blundy, 1994
• hornblende-plagioclase thermometer
• Graham and Powell, 1984
• garnet-hornblende thermometer
• Kohn and Spear, 1989 and 1990
• garnet-hornblende-quartz-plagioclase barometer

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Various P-T paths with gar-hb points, hb-pl
points, and exhumation lines
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Conclusions

• The southern portions of the Bronson Hill were
  buried to greater depths during the Alleghanian
  Orogeny than those in northern Connecticut and
  Massachusetts.
• The Bronson Hill was exhumed quicker in the south
  than to the north.