Middle Tertiary near-trench volcanism from ridge-trench collisions along west-central California: Implications from Nd, Sr-isotopic and REE data

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6137539

Cole, R B; Basu, A R ^[1]

---

1. Univ. of Rochester, NY (United States). Dept. of Geological Sciences

Early Miocene near-trench bimodal volcanism in the Santa Maria Province (SMP) of west-central California occurred when segments of the East Pacific Rise collided with a subduction zone along western North America. These ridge-trench interactions resulted in the transition from subduction to transform tectonic regimes along the California continental margin. The Nd, Sr-isotopic and trace element geochemical data for the SMP volcanic rocks indicate a depleted mantle (mid-ocean ridge basalt/MORB) source of magma. The basalts are mildly enriched in light rare earth elements (LREE) with La/Ce (n) = 0.9 to 1.2 and Ce/Yb (n) = 1.8 to 2.6. Basaltic andesites show moderate LREE enrichment with La/Ce (n) = 1.0 to 1.4 and Ce/Yb (n) = 2.2 to 3.4, and rhyolites/dacites exhibit strong LREE enrichment of La/Ce (n) = 1.1 to 1.3 and Ce/Yb (n) = 3.8 to 7.1. These data for the SMP volcanic rocks are analogous to MORB isotopic signatures from modern and young oceanic spreading ridges, including the East Pacific Rise, and indicate a MORB source of magma. This magma erupted to form basalts and also assimilated and partially melted local Jurassic-Cretaceous sedimentary and metasedimentary basement rocks to form rhyolites and dacites. The data indicates that SMP volcanism occurred when a depleted mantle reservoir of MORB was juxtaposed beneath the continental margin with the approach of the East Pacific Rise and was rapidly erupted during a phase of crustal extension/transtension and basin development. The results of this study clearly document that mid-ocean ridge and trench interactions can provide a unique tectonomagmatic setting for plate margin volcanism.

• OSTI ID: 6137539
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
BASALT
CALIFORNIA
CENOZOIC ERA
CHEMISTRY
DATA
DEVELOPED COUNTRIES
ELEMENTS
EXPERIMENTAL DATA
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
IGNEOUS ROCKS
INFORMATION
ISOTOPES
MAGMA
METALS
NEODYMIUM ISOTOPES
NORTH AMERICA
NUMERICAL DATA
PLATE TECTONICS
RARE EARTHS
ROCKS
STRONTIUM ISOTOPES
TECTONICS
TERTIARY PERIOD
USA
VOLCANIC ROCKS
VOLCANISM