Dear metamorphic community,

    We're working on a suite of archean paragneiss (Opinaca subprovince, Superior Craton) that display a barrovian-type sequence of isograds (bt-gt-st-sill). In the field, we have noticed a blueish-greenish mineral in the pressure shadows of early kinematic staurolite, and thought it's either chlorite or cordierite. However, in thin section, the mineral has clearly been altered and shows a heterogeneous chemical composition (see attached document for pictures and probe analyses).

We are looking for ways to confirm or infirm that the altered mineral was once cordierite. 

Any comments/advice/references will be greatly appreciated.

Best regards

Carl and Myriam