The following are thin sections from field trip stops 1, 3, and 8, the only ones from which I took samples.

 

Thin section photos from samples collected at Stop 1. This rock is near the border of the Halifax Pluton, and has numerous metamorphosed sedimentary xenoliths.


Small folded metasedimenary xenolith in the Halifax pluton. The mineralogy is prinicpally biotite, quartz, plagioclase, and K-feldspar, with minor muscovite, garnet, altered cordierite, and opaques.

 

20x, plane polarized light.



Small folded metasedimenary xenolith in the Halifax pluton. The mineralogy is prinicpally biotite, quartz, plagioclase, and K-feldspar, with minor muscovite, garnet, altered cordierite, and opaques.

 

20x, cross polarized light.



Garnet in the small metasedimentary xenolith pictured above.

 

100x, plane polarized light.



Garnet in the small metasedimentary xenolith pictured above.

 

100x, cross polarized light.



Altered cordierite in the small metasedimentary xenolith pictured above.

 

100x, plane polarized light.



Altered cordierite in the small metasedimentary xenolith pictured above.

 

100x, cross polarized light.



Halifax Pluton granite, host to the small metasedimentary xenolith pictured above. Mineralogy is K-feldspar, quartz, plagioclase, biotite, with lesser muscovite and opaques. There was no cordierite or altered cordierite seen in the granite part of this thin section.

 

20x, plane polarized light.



Halifax Pluton granite, host to the small metasedimentary xenolith pictured above. Mineralogy is K-feldspar, quartz, plagioclase, biotite, with lesser muscovite and opaques. There was no cordierite or altered cordierite seen in the granite part of this thin section.

 

20x, cross polarized light.


 

Thin section photos from samples collected at Stop 3. This location is in the pluton interior, and this thin section is from near the center of the large xenolith.

Large metasedimenary xenolith showing poikilitic texture. Lighter large crystals are andalusite, darker patches are mostly altered cordierite. In between is mostly quartz and muscovite with minor biotite and tourmaline.

 

20x, plane polarized light.



Large metasedimenary xenolith showing poikilitic texture. Lighter large crystals are andalusite, darker patches are mostly altered cordierite. In between is mostly quartz and muscovite with minor biotite and tourmaline.

 

20x, cross polarized light.



Fresh cordierite in the center with an altered cordierite rim. The alteration products appear to be a fine-grained mixture of muscovite and chlorite.

 

100x, plane polarized light.



Fresh cordierite in the center with an altered cordierite rim. The alteration products appear to be a fine-grained mixture of muscovite and chlorite.

 

100x, cross polarized light.



Closeup of an andalusite crystal, containing numerous inclusions of quartz, muscovite, opaques, and tourmaline. The andalusite is light-colored and clear, and looks like it is made of many grains but all are optically continuous. Altered cordierite is seen to the upper left and lower right.

 

100x, plane polarized light.



Closeup of an andalusite crystal, containing numerous inclusions of quartz, muscovite, opaques, and tourmaline.The andalusite is light-colored and clear, and looks like it is made of many grains but all are optically continuous. Altered cordierite is seen to the upper left and lower right.

 

100x, cross polarized light.


 

Thin section photos from samples collected at Stop 8. Halifax Pluton granite at Stop 8, a cordierite-bearing locality.

Granite at this locality has weathered pits, including pits in large K-feldspar phenocrysts, that I assumed were weathered out altered cordierite. Though this sample does have altered cordierite (see below), I saw none in thin section in K-feldspar. At least many of the weathered out pits are probably altered calcic cores of plagioclase (like the one in the center).

 

20x, plane polarized light.



Granite at this locality has weathered pits, including pits in large K-feldspar phenocrysts, that I assumed were weathered out altered cordierite. Though this sample does have altered cordierite (see below), I saw none in thin section in K-feldspar. At least many of the weathered out pits are probably altered calcic cores of plagioclase (like the one in the center).

 

20x, cross polarized light.



Probable altered cordierite, represented by a patch of intergrown chlorite and muscovite.

 

100x, plane polarized light.



Probable altered cordierite, represented by a patch of intergrown chlorite and muscovite.

 

100x, cross polarized light.