Paper No. 5
Presentation Time: 8:00 AM-12:00 PM
INVESTIGATION OF POLYPHASE MINERAL/”MELT” INCLUSIONS FROM ADIRONDACK GARNETS
High-grade metamorphic rocks including migmatites and granulites have recently begun to be examined more carefully by geochemical analyses of melt inclusions that have devitrified during cooling (Cesare et al., 2009). Older work by Darling et al., (1997) found multiphase mineral inclusions containing cristobalite, albite, and minor ilmenite within garnet crystals from granulite-facies metagabbros from Gore Mountain in the Adirondacks of New York that they interpreted as hydrous Na-aluminosilicate melt inclusions. Other than these “melt” inclusions, there is no evidence for the presence of anatectic melts within the metamorphic rocks of the Adirondacks. The goal of this study was to re-examine the Gore Mountain samples and trying to expand their study to other garnet localities within the Adirondacks for comparison. Samples were collected from four different locations in the Adirondacks, including Gore Mountain, Warrensburg, Ruby Mountain, and the Old Hooper Mine. Polyphase mineral inclusions were found in both Gore Mountain and the Warrensburg location, both of which are metagabbros. No polyphase inclusions have been found in either the Ruby Mountain or Old Hooper Mine locations, both of which are meta-anorthosites. The proportions of the different mineral phases were not consistent from one “melt” inclusion to the next for either Gore or Warrensburg. Melt inclusions that have devitrified will have consistent volumetric percentages of daughter phases. Additionally, the polyphase mineral inclusions were unable to be homogenized when taken to 1100°C using a 1 atmosphere furnace. These two lines of evidence suggest that these inclusions represent trapped mineral phases and not melt inclusions that devitrified.