1. 
   Isograd
   In geology, an isograd is a plane of constant metamorphic grade in the field; it separates metamorphic zones of different metamorphic index minerals. On geologic maps focusing on metamorphic terranes (or landscapes underlain by metamorphic rocks), the boundaries between rocks of different metamorph...
   Found op http://en.wikipedia.org/wiki/Isograd
   
   
2. 
   isograd
   (from the article `metamorphic rock`) Reactions that introduce new minerals in rocks of a specific bulk composition are referred to as mineral appearance isograds. Isograds can be mapped ... ...significant cooling. Nappe formation is a major process of crustal thickening during continent-continent c...
   Found op http://www.britannica.com/eb/a-z/i/44
   
   

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