Composition of the Haines and Klukwan zoned ultramafic complexes, southeastern Alaska

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

OSTI ID:5291405

Burns, L E ^[1]; Newberry, R J ^[2]

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1. Div. of Geological and Geophysical Survey, Fairbanks, AK (United States)
2. Univ. of Alaska, Fairbanks, AK (United States). Dept. Geology

Zoned ultramafic complexes in southeastern Alaska have particular compositional characteristics, both major and mineral composition, that allows differentiation of these ultramafic rocks from ophiolitic rocks. The Haines and Klukwan ultramafic bodies fit these distinctive compositional trends. Major oxide differentiation between suites is based on TiO[sub 2], Al[sub 2]O[sub 3], CaO, and MgO. Mineral compositions can be distinguished by Al[sub 2]O[sub 3]-MgO contents of cpx. Haines and Klukwan bodies are fairly evolved for zoned complexes and consist of clinopyroxenite, magnetite clinopyroxenite, and hornblendite. Cpx compositions show that the rocks fit the same trend as the ultramafic sills adjacent to the Treadwell Au mine near Juneau. The Haines and Klukwan bodies consist of multiple generations of dikes and metasomatic veining. Due to the abundant diking by hornblende gabbro, fine-grained clinopyroxenite, and hornblendite, only remnants of the early-formed, coarse-grained clinopyroxenites are exposed in the Haines body. Klukwan contains more coarse-grained clinopyroxenites. Haines and Klukwan also differ in that Klukwan contains abundant magnetite, while Haines contains more biotite. The analyses suggest that the rocks intruded at moderate pressure, possibly from an alkalic magma, and that at least part of the Haines ultramafic is slightly more differentiated, and probably more alkalic/lower fO[sub 2] than the Klukwan body. Roof pendants 1 km sq of ultramafic rocks in younger plutons north of Klukwan indicate many more small bodies associated with zoned ultramafic complexes are probably present in southeast. The authors that these bodies are sills or laccoliths above Duke Island type bodies.

• OSTI ID: 5291405
• 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
DEVELOPED COUNTRIES
GABBROS
GEOLOGIC DEPOSITS
GEOLOGY
IGNEOUS ROCKS
MINERALOGY
NORTH AMERICA
PETROCHEMISTRY
PETROGENESIS
PETROLOGY
PLUTONIC ROCKS
ROCKS
USA