Effects of magma mingling in the granites of Mount Desert Island, Maine
- Colgate Univ., Hamilton, NY (United States)
Textures and compositional relationships associated with dark-colored, fine-grained enclaves in the Cadillac Mountain and Somesville granites, Mount Desert Island, Maine, preserve abundant evidence for contamination of host granitic magmas by enclave liquids. Fine-grained enclaves, which apparently represent chilled magmatic droplets, have affected the composition and texture of the host granites by three possible mechanisms: (1) crystallization of feldspar-quartz-hornblende pegmatite pods from fluids of enclave origin in the granite surrounding enclaves, and the disaggregation of the pods and dispersion of crystals into the granite; (2) ionic exchange between enclaves and granitic magmas; (3) the generation around enclaves of rinds consisting of an inner alkali feldspar-quartz zone and an outer zone of hornblende-enriched granite. Thermal calculations suggest that the alkali feldspar-quartz zones of the rinds surrounding enclaves may result from resorption of alkali feldspar and quartz crystals in the granitic magma by heat of cooling and crystallization of enclave material. The interaction between the hot enclave and the alkali feldspar-quartz composition liquid may be analogous to that between a pluton and meteoric water in a hydrothermal system. The segregation of alkali feldspar-quartz and hornblende-rich zones may result from the minimum melt composition fluid migrating toward the enclave, leaving behind unmelted hornblende, as part of a convection circuit set up by the enclave. Alternatively, hornblende-rich zones concentric to and outside of the alkali feldspar-quartz rinds may record limit of movement of a front of hydrous fluid driven from the enclave boundary down a thermal gradient.
- OSTI ID:
- 7201889
- Journal Information:
- Journal of Geology; (United States), Vol. 100:4; ISSN 0022-1376
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GRANITES
PETROCHEMISTRY
PETROGENESIS
MAINE
GEOLOGIC FORMATIONS
CRYSTALLIZATION
FELDSPARS
GEOTHERMAL FLUIDS
HYDROTHERMAL ALTERATION
INTERACTIONS
MAGMATISM
MINERALOGY
QUARTZ
DEVELOPED COUNTRIES
FLUIDS
IGNEOUS ROCKS
MINERALS
NORTH AMERICA
OXIDE MINERALS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
USA
580000* - Geosciences