Northeastern Section - 44th Annual Meeting (2224 March 2009)
Paper No. 54-14
Presentation Time: 8:00 AM-12:00 PM

FLUID INCLUSION MICROTHERMOMETRY OF QUARTZ VEINS FROM THE WEPAWAUG SCHIST, SOUTHERN CONNECTICUT

DABROWSKI, Daniel, Physics and Earth Science, Central Connecticut State University, New Britain, CT 06050, dabrowskidar@ccsu.edu and EVANS, Mark, Department of Physics and Earth Sciences, Central Connecticut State University, New Britain, CT 06050

Fluid inclusion microthermometry of quartz in syn- to post-metamorphic veins is used to infer the post-peak metamorphic fluid history and deformation conditions of the Wepawaug Schist in southern Connecticut. Veins were sampled across the steep Barrovian metamorphic gradient, from the chlorite zone, biotite-garnet zone, and staurolite-kyanite zone.

Most fluid inclusions are two-phase, typically less than 10 microns in size, have a vapor bubble occupying <10- 20% volume % of the inclusion, and contain NaCl-rich fluids with less than 6.0 wt. % NaCl equivalent salinity. They occur as primary and pseudosecondary inclusions in chlorite zone veins; and as pseudosecondary and secondary inclusion in the biotite-garnet and staurolite-kyanite zones. In the higher grade zones, most primary inclusions exhibit re-equilibration textures. Primary inclusions in a NE-striking vein in the chlorite-zone have homogenization (Th) values of 144 - 177C and 2.9 to 3.5 % salinity, while inclusions in a NW-striking vein have Th values of 220 - 228C and 5.7 to 6.0 % salinity. Both veins post-date foliation. The NE-striking vein gives trapping conditions (based on lithostatic [25C km-1 and 26 MPa km-1]) of 320 - 460C and 315 450 MPa (12.1 17.3 km) and the NW-striking vein gives conditions of 415 - 425C and 405 420 MPa (15.6 16.2 km).

A folded quartz vein in the biotite-garnet zone has pseudosecondary inclusions that have Th) values of 201 - 236C and 5.0 % salinity, corresponding to trapping conditions of 390 - 450C and 380 445 MPa (14.6 17.1 km). A foliation-parallel vein in the biotite-garnet zone has coeval pseudosecondary CH4-CO2) and two-phase brine inclusions (Th) of 217 - 249C and 4.0 to 4.7 % salinity) that were trapped at 505C and 340 MPa (13.0 km). Secondary inclusions in a recrystallized foliation-parallel vein from the staurolite-kyanite zone has Th) values of 132 - 145C and 1.2 % salinity, giving trapping conditions of 295 - 315C and 290 310 MPa (11.2 11.9 km).

In general, fluid inclusions were trapped at 300 - 500C and <450 MPa, significantly less than 400 - 600C and 600 900 MPa at peak metamorphism as determined by Ague (1994). Therefore, fluid inclusions in veins reflect post-peak metamorphic conditions in the Wepawaug Schist, and were probably trapped as the system opened during unroofing and was at a depth of 12-17 km.

Northeastern Section - 44th Annual Meeting (2224 March 2009)
General Information for this Meeting
Session No. 54--Booth# 34
Igneous/Metamorphic Petrology, Geochemistry, Mineralogy (Posters)
Holiday Inn By the Bay: Casco Bay Hall
8:00 AM-12:00 PM, Tuesday, 24 March 2009

Geological Society of America Abstracts with Programs, Vol. 41, No. 3, p. 110

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