Trace element and isotopic constraints on magmatic evolution at Lassen volcanic center
- Geological Survey, Menlo Park, CA (USA)
Magmatic evolution at the Lassen volcanic center (LVC) is characterized by a transition from predominantly andesitic to predominantly silicic volcanism with time. Magmas of the adesitic, or Brokeoff phase of volcanism range in composition from basaltic andesite to dacite, whereas those of silicic, or Lassen phase range in composition from basaltic andesite to rhyolite. The distinctive mixing-dominated arrays for each volcanic phase manifest the generation and evolution of two physically distinct, but genetically related magma systems. The LVC magmas have Sr, Nd, and Pb isotope characteristics that approximate two-component mixing arrays. One isotopic component is similar in composition to that of NE Pacific Ocean ridge and seamount basalts (MORB component), the other to mafic Mesozoic granitoids sampled from the neighboring Klamath and Sierra Nevada provinces (KSN component). The lack of a correlation between the major element and isotopic compositions of LVC magmas seriously limits any model for magmatic evolution that relies on assimilation of old middle to upper crust by isotopically homogeneous mafic magmas during their ascent through the crust. Alternatively, the isotopic and geochemical uniformity of the most silicic magmas of the Brokeoff and Lassen phases suggests that they are well-homogenized partial melts. The likely source region for these silicic melts is the lower crust, which the authors envision to consist primarily of mafic igneous rocks that are similar in geochemical and isotopic diversity to the regional mafic lavas.
- OSTI ID:
- 5319882
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B12; ISSN JGREA; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ANDESITES
CALIFORNIA
CHALCOGENIDES
CHEMISTRY
CONTINENTAL CRUST
CRYSTALLIZATION
DEVELOPED COUNTRIES
EARTH CRUST
ELEMENTS
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC HISTORY
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
LEAD ISOTOPES
MAGMA
MAGMATISM
MINERALS
MIXING
NEODYMIUM ISOTOPES
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RHYOLITES
ROCKS
SILICA
SILICON COMPOUNDS
SILICON OXIDES
STRONTIUM ISOTOPES
TRACE AMOUNTS
USA
VOLCANIC REGIONS
VOLCANIC ROCKS
VOLCANISM