40 Mesozoic Magmatism, Postrift Tectonics, and Passive Margin Development of Northeastern North America (Posters)

The northeastern region experienced protracted Mesozoic (Triassic-Cretaceous) magmatism associated with continental rifting and subsequent passive margin development. We welcome contributions related to the occurrence, tectonics, or driving mechanisms of these syn- and postrift events.

Tuesday, 24 March 2026
8:00 AM - 12:00 PM
CCC, Ballroom C

Examination of Mineralization Along Fault Zones in the Mesozoic Pomperaug Basin, Western Connecticut

Paper number: 40-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Mesozoic Pomperaug Basin iin west-central Connecticut contains three basalt layers and intervening sedimentary rocks. The faulting within this basin consists of a series of small North-oriented normal faults. Mineralized fractures and faults were sampled from the Southbury Quarry and are cemented with multiple stages of calcite. Four samples of the calcite mineralization were analyzed for δ13C and δ18O stable Isotopes to constrain the history of the fractures, faults, and fluids within the rock.

 

Sample A has euhedral crystals with a clear center core and a yellow rim, and with isotopic values ranging from -7.9 to -11.0 δ13C and -8.2 to -12.3 δ18O. This sample is undeformed, unlike other samples which show twinning. Sample C has 12 layers of calcite that have a symmetrical distribution of isotope values to the center to the rim. The center values range from -6.3 to -6.4 δ13C and -12.8 to -13.2 δ18O, the outer rim values range from -7.4 to -8.6 δ13C and -9.1 to -10.3 δ18O. Sample B consists of blocky calcite and hematite, while sample D has two layers of blocky calcite with a thin layer of hematite. Samples B and D have isotopic values that mirror the core and the rim of Sample C, sample B: -7.6 to -8.4 δ13C and -9.9 to -11.5 δ18O, and sample D: -7.9 to -8.1 δ13C and -9.1 to -10.0 δ18O. 

 

Preliminary fluid inclusion microthermometry of two-phase aqueous inclusions from Sample A gives Th values of 59.6C to 117.8C ( ~7.0 % NaCl equiv. salinity). Sample B has Th values ranging from 81.2C to 106.1C ( 7.6-20.9 % NaCl equiv. salinity). Sample C has Th values ranging from 61.0C to 112.5C (3.87-8.55 %NaCl equiv. salinity) The low salinity values from samples indicate possible fluid mixing with meteoric water. The Th values from sample A indicate burial depths of 2.8km - 3.8km; for sample B, burial depths of 1.0km - 2.5km; and  sample C, burial depths of 1.0km - 3.0km. Sample D did not yield any viable fluid inclusions for analysis, likely due to the greater deformation present in this sample.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411293

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