ANALYZING CONTACT METAMORPHISM OF THE STANLEY SHALE IN THE MAGNET COVE IGNEOUS INTRUSIVE COMPLEX

It is evident by visiting Magnet Cove that the zone of metamorphism exceeds limitations put forth by previous studies since rocks >2,500 feet from the intrusion were observed to display characteristics of hornfels. To investigate this observation, samples collected from Jones Mill Quarry were made into thin sections and examined under a petrographic microscope. Porphyro-blastic nonfoliated subhedral biotite growing inside a cryptocrystalline quartz matrix alongside medium-grained quartz, or perhaps andalusite, was observed in the sample 100 feet from the intrusion. The granoblastic biotite crystals observed in the nearest sample were not present in any other samples taken farther from the intrusion, thus indicating a clearly defined biotite isograd. Thus, while it is clear from the texture of the first sample that the biotite formed through contact metamorphism, thereby indicating exposure to temperatures of approximately 400° to 500° C, it is difficult to distinguish whether the surrounding chlorite zone rocks were altered due to contact or regional metamorphism. Future studies could address this by using an SEM to better resolve the mineralogy of the cryptocrystalline samples.