Abstract
Evidence for separate hydration and thermal pulses during M3 regional-contact metamorphism in western Maine
Abstracts with programs - Geological Society of America, Vol.32(7), p.54
Geological Society of America, 2000 annual meeting
2000
Abstract
Polymetamorphic textures produced by regional-contact metamorphism in western Maine indicate that the thermal maximum during M3 metamorphism was preceded by a widespread re-hydration event. Workers in the region have long recognized evidence for the re-hydration event in lower grade rocks because of the spectacular muscovite+chlorite pseudomorphs after staurolite in the M3 lower staurolite and garnet zones. Evidence for re-hydration of higher grade rocks is more subtle because the temperature increase that followed the hydration event caused partially pseudomorphed porphyroblasts to re-grow, obliterating the pseudomorphs and producing porphyroblasts with little indication of a complex history. However, microprobe Ca maps of garnet porphyroblasts allow recognition of garnet dissolution and re-growth because the zoning pattern in the portion of the garnet produced by M2 is distinct from the portion of the garnet produced by M3. Ca maps of garnets from the M3 lower sillimanite zone in the Rangeley area show evidence for garnet dissolution and re-growth, suggesting the region was affected by widespread hydration of M2 assemblages followed by a temperature increase that produced the peak M3 textures. Further evidence of these two events is provided by textures that indicate M3 staurolite grew after M2 staurolite had been replaced by M3 muscovite+chlorite pseudomorphs. In some cases, M3 staurolite re-grew on a partially pseudomorphed M2 staurolite in a manner similar to the garnet re-growth described above. In other cases, M3 pseudomorphs after M2 staurolite are cross cut by later M3 staurolite crystals that do not appear to have grown on remnants of M2 staurolite. This texture developed in rocks where the M2 staurolite was entirely consumed by the pseudomorphing reaction so that completely new staurolites nucleated and grew when the rock re-entered the staurolite stability field. The extensive distribution of textures indicating early re-hydration followed by a temperature increase suggests that M3 is characterized by an early pulse of fluid that migrated through the country rock ahead of the thermal pulse that produced the peak M3 assemblages.
Details
- Title: Subtitle
- Evidence for separate hydration and thermal pulses during M3 regional-contact metamorphism in western Maine
- Creators
- C. T Foster - University of Iowa, Department of Geoscience Iowa City, IA USA United StatesBarbara L Dutrow - Louisiana State University
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.32(7), p.54
- Conference
- Geological Society of America, 2000 annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2000 annual meeting
- Language
- English
- Date published
- 2000
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240903502771
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