Crustal Fluid Evolution and Changes in Deformation Conditions during Regional Syn- to Post-Orogenic Exhumation: Southeastern Piedmont, Southern Appalachians
Fluid inclusion microthermometric data from veins in the southeastern Piedmont province record the changes in fluid composition and deformation conditions during regional exhumation and cooling related to Late Paleozoic syn- to post-orogenic processes and early Mesozoic rifting. In general, the composition of post-metamorphic fluids that were trapped late during the Alleghanian orogeny and during post-orogenic exhumation are remarkably consistent across the southeastern Piedmont, indicating regional fracture connectivity. The first fluids were trapped in veins that formed during the last phases of the Alleghanian. These syn-deformational fluids are CO2-saturated low salinity brines (salinities of 2.6 to 5.7 wt. percent NaCl equivalent) with homogenization temperatures in the range of 200 degrees to 365 degrees C. They were trapped under lithostatic pressures between 240 and 280 MPa, indicating burial depths of 11.2 to 12.7 km. These depths are similar to emplacement depths of post-kinematic plutons, suggesting a period of rapid isobaric cooling. Low-salinity H2O inclusions and rare CO2-rich inclusions are evidence for Early Mesozoic regional decompression as fracturing above the brittle-to-ductile transition allowed regional pore-fluid pressure to drop to hydrostatic levels. Convective circulation of meteoric water resulted in the dilution of 'in-situ' fluids, and ultimately to a system saturated with meteoric water. These fluids continued to be trapped in vein minerals through much of the Mesozoic as rift basins formed during the opening of the Atlantic Ocean. Late Paleozoic through Mesozoic exhumation rates for the eastern Piedmont province average 0.063 km m.y.-1 and cooling rates average approximately 1.9 degrees C m.y.-1. These low rates may be directly related to thinned crust and lithosphere resulting from delamination processes during the late Alleghanian orogeny.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC09-96SR18500
- OSTI ID:
- 837166
- Report Number(s):
- WSRC-MS-2000-00187; TRN: US200505%%153
- Journal Information:
- Geological Society of America Bulletin, Other Information: PBD: 5 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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