Petrology and geobarometry of Admiralty-Revillagigedo belt granitoids near Petersburg, southeastern Alaska

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5099237

Hammarstrom, J M ^[1]; Brew, D A ^[2]

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1. Geological Survey, Reston, VA (United States)
2. Geological Survey, Menlo Park, CA (United States)

The Admiralty-Revillagigedo belt (ARB) of southeastern Alaska is an approximately 400 mile long northwest-trending belt of Late Cretaceous ([approximately]95 Ma) calcalkalic plutons that extends from Juneau to Ketchikan. The ARB is bounded on the east by the younger Coast plutonic complex sill and on the west by the mid-Cretaceous Muir-Chichagof plutonic belt. Near Petersburg, the ARB consists of a variety of plutons that include equigranular and porphyritic quartz diorite, tonalite, quartz monzodiorite, and granodiorite. Minerals in these plutons are: hornblende, biotite, plagioclase, potassium feldspar, quartz, apatite, zircon, titanite, and ilmenite [+-] epidote, minor allanite, magnetite, grossular-almandine garnet, clinopyroxene, and locally trace amounts of sulfide minerals. New geochemical data for six samples from three plutons near Petersburg overlap data for the rest of the ARB, which is metaluminous to slightly peraluminous. The central ARB granitoids are moderately LREE-enriched with slightly negative to slightly positive europium anomalies. High strontium (700 to 800 ppm) and low rubidium contents in central ARB plutons overlap compositions of ARB plutons to the north and south, and magmatic epidote-bearing plutons elsewhere. Pressure estimates for pluton emplacement based on hornblende geobarometry (6 to 9 kbars) are compatible with pressure estimates for plutons to the south and for metamorphic aureole assemblages around ARB plutons elsewhere in the western metamorphic belt of southeastern Alaska. These data support the chemical consanguinity of plutons along the length of the magmatic arc now preserved as the ARB and suggest that the whole ARB has been uplifted and eroded to expose plutons emplaced at relatively deep crustal levels.

• OSTI ID: 5099237
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALASKA
CHEMISTRY
CRETACEOUS PERIOD
DEVELOPED COUNTRIES
GEOBAROMETRY
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
GRANITES
IGNEOUS ROCKS
MESOZOIC ERA
MINERALOGY
NORTH AMERICA
PETROLOGY
PLUTONIC ROCKS
ROCKS
USA