Chemically diverse, episodic volcanism offshore southern and peninsular California
- Geological Survey, Menlo Park, CA (United States)
- Univ. of California, Los Angeles, CA (United States). Dept. Earth and Space Sciences
Volcanic rocks recovered from eight seamounts offshore southern and peninsular California are chemically diverse. Compositions of lavas from seven small to moderately sized seamounts between 30.5[degree] and 34.0 N latitudes include low-K[sub 2]O tholeiitic, transitional, and mildly to moderately alkalic basalt. Volcanic rocks from the upper part of the much larger and morphologically complex edifice of Rocas Alijos, offshore central Baja California at about 25.0 N latitude, are highly differentiated trachyandesite and trachyte. The low-K[sub 2]O basalts are MORB-like with low abundances of incompatible elements and lower [sup 87]Sr/[sup 86]Sr and higher [sup 143]Nd/[sup 144]Nd ratios than MORB from the East Pacific Rise. The alkalic compositions have higher abundances of incompatible elements and isotopic data indicate more variably enriched mantle sources than those of seamounts near the East Pacific Rise, but the compositions of all samples are within the mantle array defined by other ocean-island basalts. [sup 40]Ar/[sup 39]Ar laser fusion ages for the seamounts span a large range. MORB-like lava from one of the northern edifices is as old as the underlying oceanic crust ([approximately]23 Ma), indicating that it originated at a spreading center. Other seamount lava ages are much younger (16.6--9.1 Ma) than the underlying oceanic crust. The trachytes from Rocas Alijos are less than 300,000 years old, indicating that the last volcanism on this large edifice occurred recently. The region offshore southern and peninsular California is tectonically complex and has many volcanic edifices of varying sizes, shapes, and orientations. The data available for volcanic rocks from this region suggest that the seamounts formed from multiple episodes of chemically diverse volcanism occurring sporadically from early Miocene to Recent.
- OSTI ID:
- 5290700
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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580000* -- Geosciences
AGE ESTIMATION
ARGON ISOTOPES
CALIFORNIA
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPED COUNTRIES
EARTH CRUST
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LAVA
NEODYMIUM ISOTOPES
NORTH AMERICA
OCEANIC CRUST
OFFSHORE SITES
PETROGENESIS
PETROLOGY
QUATERNARY PERIOD
ROCKS
TERTIARY PERIOD
USA
VOLCANIC ROCKS
VOLCANISM