Stop 3
Greenschist Facies
Stop 3 is northwest of Stop 2
(Google Earth)
Temperature and
depth of burial for the greenschist facies. Greenschist is on
the continental/typical geothermal gradient.
Stop
3
The greenschist facies can have a wide variety of burial depths and temperatures, on the island it is thought to have burial depths of 20 to 30 km +/- and temperatures around 400°C. The age of this unit is 113 +/-3 MYO (Grove M., Bebout G.E. 2008). The schistosity (metamorphic layering) is well developed in these outcrops, and the beds range from horizontal to vertical. Index minerals for the greenschist facies are epidote, chlorite, and actinolite, which give it the green color. They can also contain serpentine, talc and tremolite if ultramafic rocks like peridotite are in the protolith.
Outcrops of greenschist along airport road. Note the
variety of orientations found in the schistose fabric. In the 1st picture
its near vertical and the remaining pictures its
close to horizontal.
Photo 1 is greenschist, photo 2 has some weak schistose fabric, and the
last photo is greenstone so no schistosity/layering.