Compositional diversity of Late Cenozoic basalts in a transect across the southern Washington Cascades: Implications for subduction zone magmatism

Journal Article · Sat Nov 10 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB12p19561· OSTI ID:5263214

Leeman, W P ^[1]; Smith, D R ^[2]; Hildreth, W ^[3]; Palacz, Z; Rogers, N ^[4]

---

1. Rice Univ., Houston, TX (USA)
2. Trinity Univ., San Antonio, TX (USA)
3. Geological Survey, Menlo Park, CA (USA)
4. Open Univ., Milton Keynes (England)

Major volcanoes of the Southern Washington Cascades (SWC) include the large quaternary stratovolcanoes of Mount St. Helens (MSH) and Mount Adams (MA) and the Indian Heaven (IH) and Simcoe Mountain (SIM) volcanic fields. There are significant differences among these volcanic centers in terms of their composition and evolutionary history. The authors conclude that subducted fluids and sediments do not play an essential role in producing these magmas. Rather, they infer that they formed by variable degree melting of a mixed mantle source consisting mainly of heterogeneously distributed OIB and mid-ocean ridge basalt source domains. Relatively minor occurrences of high field strength element (HFSE) depleted arclike basalts may reflect the presence of a small proportion of slab-metasomatized subarc mantle. The juxtaposition of such different mantle domains within the lithospheric mantle is viewed as a consequence of (1) tectonic mixing associated with accretion of oceanic and island arc terranes along the Pacific margin of North America prior to Neogene time, and possibly (2) a seaward jump in the locus of subduction at about 40 Ma. The Cascades arc is unusual in that the subducting oceanic plate is very young and hot. They suggest that slab dehydration outboard of the volcanic front resulted in a diminished role of aqueous fluids in generating or subsequently modifying SWC magmas compared to the situation at most convergent margins. Furthermore, with low fluid flux conditions, basalt generation is presumably triggered by other processes that increase the temperature of the mantle wedge (e.g., convective mantle flow, shear heating, etc.).

• OSTI ID: 5263214
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
VOLCANIC REGIONS
GEOCHEMISTRY
WASHINGTON
AGE ESTIMATION
ANDESITES
BASALT
CASCADE MOUNTAINS
EARTH MANTLE
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOMORPHOLOGY
LAVA
MAGMA
MAGMA SYSTEMS
MAGMATISM
MELTING
MIXING
MT ST HELENS
QUATERNARY PERIOD
RESERVOIR FLUIDS
RHYOLITES
SUBDUCTION ZONES
TECTONICS
VOLCANIC ROCKS
VOLCANOES
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
FEDERAL REGION X
FLUIDS
GEOLOGIC AGES
GEOLOGY
GEOTHERMAL SYSTEMS
IGNEOUS ROCKS
MOUNTAINS
NORTH AMERICA
PHASE TRANSFORMATIONS
ROCKS
USA
580000* - Geosciences