Middle Jurassic U-Pb crystallization age for Siniktanneyak Mountain ophiolite, Brooks Range, Alaska

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

OSTI ID:5024136

Moore, T E ^[1]; Aleinikoff, J N; Walter, M ^[2]

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1. Geological Survey, Menlo Park, CA (United States)
2. Geological Survey, Denver, CO (United States)

The authors report here a U-Pb age for the Siniktanneyak Mountain Ophiolite klippe in the west-central Brooks Range, the first U-Pb ophiolite age in northern Alaska. Like klippen of mafic and ultramafic rocks in the Brooks Range, the Siniktanneyak Mountain klippe is composed of a lower allochthon of Devonian and younger( ) diabase and metabasalt with trace-element characteristics of seamount basalts and an upper allochthon of ophiolite. The ophiolite is partial, consisting of (1) abundant dunite and subordinate harzburgite and wehrlite; (2) cumulate clinopyroxene gabbro, and (3) minor noncumulate clinopyroxene gabbro and subordinate plagiogranite; no sheeted dikes or volcanic rocks are known in the ophilitic allochthon. The plagiogranite forms small dikes and stocks that intrude the noncumulate gabbro and consists of zoned Na-rich plagioclase + clinopyroxene with interstial quartz and biotite. Five fractions of subhedral, tan zircon from the plagiogranite yield slightly discordant U-Pb data with an upper intercept age of 170 [+-] 3 Ma. The U-Pb data indicate that the Siniktanneyak Mountain ophiolite crystallized in the Middle Jurassic and was emplaced by thrusting onto mafic accretionary prism rocks within about 10 m.y. of crystallization. The U-Pb data provide an upper limit to the age of initiation of the Brookian orogeny.

• OSTI ID: 5024136
• 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
ACTINIDE ISOTOPES
AGE ESTIMATION
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BASALT
DEVELOPED COUNTRIES
GABBROS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
JURASSIC PERIOD
LEAD ISOTOPES
MESOZOIC ERA
NORTH AMERICA
PETROLOGY
PLUTONIC ROCKS
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URANIUM ISOTOPES
USA
VOLCANIC ROCKS