Very near the contacts of the stocks the sediments have been replaced by sanidine and diopside, through magmatic reaction. An irregular zone of indurated sediments, produced largely by hydrothermal agents, extends outward from the stocks for as much as half a mile. Locally, more intense hydrothermal metamorphism has formed orthoclase and fibrous amphibole with some diopside and locally garnet, phlogopite, spinel, and cordierite.
Along the dikes metamorphism extends out from the contacts for a distance of a few inches up to 5 feet. Thermal metamorphism produced recrystallization of the fine interstitial material of the sandstone. Aegirite, calcite, hematite, and pyrite were deposited by hydrothermal solutions. Magmatic reaction produced diopside.
Reaction between sandstone and the magma of the headed dike caused a progressive replacement of plagioclase and quartz by potash feldspar.
Granitic inclusions in the biotite phonolite dikes have a marginal shell in which plagioclase has been replaced by orthoclase. Surrounding each inclusion is a zone of mixed rock which contains quartz grains much embayed and surrounded by 0.1 mm. prisms of pyroxene.
|Publication Subtype||Journal Article|
|Title||Igneous rocks of the Highwood Mountains, Montana: Part V. Contact Metamorphism|
|Series title||GSA Bulletin|
|Publisher||Geological Society of America|
|Other Geospatial||Highwood Mountains|
|Google Analytic Metrics||Metrics page|