O-, Sr-, Nd-isotope, and trace element relationships in lavas from Mount Shasta in northern California

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6453049

Mertzman, S A; Savin, S M

If subducted oceanic material is involved in the genesis of lavas in island arc and continental margin tectonic settings, its influence on the chemical and isotopic composition of orogenic volcanic rocks ought to be greatest on the oceanic side of the arc. Andesites and dacites (58-66% SiO/sub 2/) from Mt. Shasta, the westernmost large composite volcano in the California segment of the Cascade volcanic belt, are characterized by a concave downward curve on a /sup 143/Nd//sup 144/Nd-/sup 87/Sr//sup 86/Sr diagram. This trend begins at 0.70285 and 0.51300 and terminates near 0.70397 and 0.51280 respectively. The shape of the curve, being slightly displaced to the left of the mantle array, precludes involvement of altered oceanic crust in the generation of Shasta andesites and dacties. delta /sup 18/O data concerning these same silicic extrusives range from +7 to +9 per thousands values clearly higher than most orogenic andesites and seemingly incompatible with a mantle source without significant modification. A delta /sup 18/O-/sup 87/Sr//sup 86/Sr diagram of this data produces a curve with some scatter that is convex upward, suggesting crustal contamination with deep-sea or geosynclinal sediments as the causative process. Hf-Ta-Th data are in agreement with this suggestion; however, preliminary Pb isotope data on these silicic lavas is ambiguous. O-, Sr-, and Nd-isotope data from concurrently erupted basalts in the Shasta region clearly indicate they are not parental to any of the andesites or dacites extruded at this volcano.

• Research Organization: Franklin and Marshall College, Lancaster, PA (USA)
• OSTI ID: 6453049
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ANDESITES
CHEMICAL COMPOSITION
PETROGENESIS
CALIFORNIA
VOLCANOES
GEOCHEMISTRY
ISOTOPE RATIO
LAVA
NEODYMIUM ISOTOPES
OCEANIC CRUST
OXYGEN ISOTOPES
STRONTIUM ISOTOPES
SUBDUCTION ZONES
TRACE AMOUNTS
ALKALINE EARTH ISOTOPES
CHEMISTRY
EARTH CRUST
FEDERAL REGION IX
IGNEOUS ROCKS
ISOTOPES
NORTH AMERICA
ROCKS
USA
VOLCANIC ROCKS
580400* - Geochemistry- (-1989)