Central New York Association of Professional Geologists

February Dinner Meeting and Speaker: Joe Gonzales (Syracuse Univ) "Pressure-temperature-time histories across the Burgess Branch Fault Zone, northern Vermont" and Mariana Rhoades (St. John Fisher College), "Historic Quarries and the Stone Industry..."

  • Wednesday, February 21, 2018
  • 5:00 PM - 8:30 PM
  • Spaghetti Warehouse

Registration

  • Dinner and talk
  • Dinner and Talk
  • Dinner and Talk
  • Dinner and Talk for any student who is not a Student-member of the organization
  • Pay at the door on the day of the event with no prior registration.
  • Pay at the door on the day of the event with no prior registration.
  • Pay at the door on the day of the event with no prior registration.
  • Pay at the door on the day of the event with no prior registration.

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Joe Gonzales (2017 CNYAPG Student Scholarship recipient), "Pressure-temperature-time histories across the Burgess Branch Fault Zone, northern Vermont"

Abstract

Metamorphic rocks in the Tillotson Peak Complex, northern Vermont, provide evidence for subduction processes during the Taconic Orogeny (470-450 Ma). Previously documented metamorphic fabrics and 40Ar/39Ar data were interpreted to record deformation from multiple orogenies. A glaucophane total fusion 40Ar/39Ar age constrains the timing of Taconic high-pressure (HP) metamorphism as 468 ± 6.4 Ma (Laird et al., 1984). The Burgess Branch Fault Zone (BBFZ), a polydeformed steep eastward dipping normal fault (present day), separates Tillotson Peak (footwall) blueschists and metapelites from Ottauquechee Formation metapelites (hanging wall). P-T-t histories were derived from samples collected along a transect across the Tillotson Peak Complex and into the BBFZ. Total fusion 40Ar/39Ar geochronology on phengite and K white mica-chlorite thermobarometry were used to constrain P-T-t. Chemically homogeneous phengites in garnet mica schist from the Hazen’s Notch Formation within the Tillotson Peak Complex yielded pressures of 16-20 kbar assuming 450oC and an 40Ar/39Ar age 480 ± 1.3 Ma (1). Another garnet mica schist yielded an age of 468 ± 1.8 Ma. A Hazen’s Notch Formation mica schist farther east yielded pressures of 9-12 kbar at 450oC and an age of 478 ± 1.3 Ma. Within the BBFZ, petrographic observations reveal chemical zoning and intergrowth of different composition phengites suggesting partial to complete recrystallization. A BBFZ Hazen’s Notch Formation phengite yielded recrystallization P-T as 6-8.5 kbar at 370oC and an age of 407 ± 1.3 Ma. BBFZ Ottauquechee Formation phengites yielded ages of 417 ± 1.2 Ma and 415 ± 1.8 Ma. A Stowe Formation phengite yielded an age of 436.7 ± 1.2 Ma. P-T data indicate that Hazen’s Notch schists may have formed at greater depths than previously known. The 40Ar/39Ar total fusion ages are concordant with those of previous studies, and 468-480 Ma ages in Hazen’s Notch schist are possibly related to exhumation of HP metamorphic rocks. In contrast, 407-417 Ma recrystallized BBFZ phengites appear to be unrelated to exhumation of HP lithologies, instead they are possibly related to the late-reactivation deformation.

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Mariana Rhoades will introduce her new book "HISTORIC QUARRIES & THE STONE INDUSTRY ERIE COUNTY, NY, 1820-1930"




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