Lithosphere-scale thrusting in the western US Cordillera as constrained by Sr and Nd isotopic transitions in Neogene volcanic rocks

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0063:LSTITW>2.3.CO;2· OSTI ID:6951798

Leeman, W P; Oldow, J S ^[1]; Hart, W K ^[2]

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1. Rice Univ., Houston, TX (United States)
2. Miami Univ., Oxford, OH (United States)

The western Idaho suture zone juxtaposes continental and oceanic terranes with distinctive Sr and Nd isotopic signatures across a sharp isotopic transition coincident with the Mesozoic {sup 87}Sr/{sup 86}Sr = 0.706 line (MSL). Late Cretaceous to Eocene granitic plutons that define the MSL are allochthonous and were transported eastward by {approximately}150 km during late Mesozoic to Tertiary (ca. 100-55 Ma) thrusting. Sr and Nd isotopic compositions of Neogene rhyolites and basalts from southwestern Idaho, southeastern Oregon, and northern Nevada define isotopic transitions coincident with the MSL; there are continental affinities east of long 116{degree}30minutesW and oceanic affinities west of 119W. Between these longitudes, intermediate isotopic compositions imply derivation of magmas from both continental and oceanic mantle (basalts) and crustal (rhyolites) sources. It is inferred that the basal decollement of the Mesozoic and Tertiary contractional orogen dips westward below depths of segregation of basaltic magmas, and that oceanic lithospheric mantle was thrust eastward over a shelf of old, isotopically evolved continental lithospheric mantle that now protrudes {approximately}150 km west of the MSL.

• OSTI ID: 6951798
• Journal Information: Geology; (United States), Journal Name: Geology; (United States) Vol. 20:1; ISSN GLGYB; ISSN 0091-7613
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
CENOZOIC ERA
CONTINENTAL CRUST
CRETACEOUS PERIOD
DEVELOPED COUNTRIES
EARTH CRUST
FEDERAL REGION IX
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
IDAHO
IGNEOUS ROCKS
ISOTOPES
MESOZOIC ERA
NEODYMIUM ISOTOPES
NEVADA
NORTH AMERICA
OCEANIC CRUST
OREGON
PETROCHEMISTRY
PETROGENESIS
PLATE TECTONICS
ROCKS
STRONTIUM ISOTOPES
TECTONICS
TERTIARY PERIOD
USA
VOLCANIC ROCKS