Formation Conditions of Marble in Devil’s Canyon

Event Center BC

Marble and Calc-silicate pods included within the Gneiss of Devil Canyon represent a broad range of compositions that correspond to formation conditions of varying metamorphic grade and concentrations of H2O and CO2. Mineral assemblages from a thirty-mile long sample area along the western San Bernardino Mountains were determining using optical microscopy and X-ray powder diffraction, and split into eight different compositions based on stable minerals phases present within the sampled rocks. Based off these compositions, the reactions that likely formed the assemblages along with the temperature and pressure of metamorphism were determined for each assemblage from a T-XCO2 phase diagram for siliceous carbonates. The results of correlating compositions to temperature and pressure show that marble and calc-silicate rock formed within gneiss and schist as a result of primary greenschist to amphibolite metamorphism from tectonically driven regional metamorphism of Cordilleran miogeocline aged sedimentary rocks. In some areas, these rocks were secondary metamorphosed to upper amphibolite facies, were serpentinized through CO2 poor fluids, or were newly formed at lower greenschist facies through fluid interactions in fractures as Cretaceous and Jurassic plutons intruded the vast sequence of sedimentary rocks that were deposited during the Paleozoic era.