Preston Peak ophiolite, Klamath mountains, California, an immature island arc: petrochemical evidence

Book · Fri Dec 31 23:00:00 EST 1976

OSTI ID:6378899

Snoke, A W; Bowman, H R; Hebert, A J

Major and trace element contents (including rare earth elements) were determined on a suite of rocks from the Preston Peak ophiolite, Klamath Mountains, California. These geochemical data combined with field relations and petrography suggest that the Preston Peak ophiolite is a remnant of a Permian-Triassic immature island arc. The lowest unit in the ophiolite is a depleted periodolite tectonite which was subsequently intruded and overlain by mafic rocks as the ophiolite developed. Diabase and diabase breccia, the most common constituents of the mafic complex, have undergone greenschist facies metamorphism and related chemical migration. Nevertheless, low TiO/sub 2/ contents as well as low Cr values suggest similarity with island arc tholeiite rather than obyssal tholeiite. Xenoliths of clinopyroxenite and gabbro, locally common in the diabasic rocks, appear to be cumulates developed in small magma chambers that were later disrupted by intruding younger basaltic magmas. Evidence of extensive differentiation is lacking and apparently much of the fine-grained mafic rocks of the ophiolite represent primary magmas. The most leucocratic and siliceous rock in the suite is a Na-rich quartz diorite which is enriched in light rare earth elements and probably represents an independent magma type rather than a differentiate.

• OSTI ID: 6378899
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
CALIFORNIA
CHALCOGENIDES
CHROMIUM
DATA FORMS
DIAGRAMS
ELEMENTS
GEOCHEMICAL SURVEYS
GEOLOGY
METALS
METAMORPHISM
MOUNTAINS
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
PETROLOGY
ROCKS
STRATIGRAPHY
TABLES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
USA
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