Compositional and textural variety in microgranitoid enclaves within the granite of Cadillac Mountain, Mount Desert Island, Maine

Seaman, Sheila; Ramsey, Patrick

'The granite of Cadillac Mountain is a Devonian alkali feldspar-hornblende-granite which comprises approximately one-half of the exposed area of Mount Desert Island, Maine. It intrudes the Cambro-Ordovician Ellsworth Schist and the Siluro-Devonian Bar Harbor Formation (Gilman, et al. 1988; Chapman, 1970). The Granite of Cadillac Mountain contains microgranitoid enclaves (2-8 cm in diameter) that vary in texture and composition. The enclaves are fine-grained and appear darker in color than the host Granite of Cadillac Mountain. Although most enclaves are spherical to ellipsoidal, some have subangular to angular edges.' 'Some enclaves are fine-grained compositional equivalents of the host granite. Others are composed of clinopyroxene and calcic plagioclase, a more mafic mineral assemblage than that represented by the host Cadillac Mountain Granite. Enclave-within-enclave textures occur in several samples. These textures consist of either single coarse quartz or alkali feldspar crystals or clusters of crystals of size and composition similar to Granite of Cadillac Mountain enclosed in microgranitoid enclave. Enclaves differing in composition from the surrounding granite have been observed to display mineral rims, interpreted as reaction textures. These rims typically consist of hornblende and quartz. Similar relationships are associated with coarse crystal clusters inside microgranitoid enclaves.' 'The fine grain size and the presence of acicular apatite and skeletal hornblende crystals in microgranitoid enclaves attest to their quenching as liquid droplets against cooler granitic magma. The presence of crystals and clusters of crystals of granitic affinity within microgranitoid enclaves suggests that the host granite was not solid at the time of compositional mingling. Compositional variety of enclaves may indicate repeated episodes of magma mingling (Vernon et al. 1988). Based on compositional similarity of some enclaves to the enclosing granite, the origin of the enclaves seems more likely to have been in a deeper zone of the Cadillac Mountain magma chamber than a separate magma body.' /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/Cadillac Mountain

Compositional and textural variety in microgranitoid enclaves within the granite of Cadillac Mountain, Mount Desert Island, Maine

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