Structural reconstruction and zonation of a tilted mid-crustal magma chamber: the felsic Chemehuevi Mountains plutonic suite
Structural relief resulting from middle Tertiary extensional deformation in the Chemehuevi Mountains of California exposes a unique cross section through an extensive (> 280 km/sup 2/) calc-alkalic, compositionally zoned, sill-like granitic intrusion of Late Cretaceous age. Minimum estimates for emplacement pressure, 4 to 6 kbar, imply that the Chemehuevi Mountains plutonic suite was initially intruded at mid-crustal depths and has undergone 10/sup 0/ to 15/sup 0/ of post emplacement tilting, tectonic denudation, and erosion. Reconstruction of the pre-Tertiary (pre-tilt) configuration suggests that this metaluminous to peraluminous granitic suite exhibits crude normal, vertical, and temporal zonation from granodiorite to granite. The zonation involves a decrease in age and an increase in silica away from the walls and roof, the youngest and most evolved members being concentrated toward the center and floor of the intrusion. The lower part of the intrusion had a flat floor, which was penetrated by at least three feeder dikes providing magma to the chamber. Structural reconstruction indicates that the roof is less than 1 km above the exposed top of the intrusion. The magma apparently ponded along the contact between undeformed Proterozoic basement above and subhorizontally foliated mylonitic gneisses below. This reconstruction provides opportunity to observe crosscutting relations between different types of mid-crustal structures (thick mylonitic shear zones, granitic intrusions, and temporally unrelated detachment faults), the geometry of which emphasizes the need for careful evaluation of seismic reflection profiles across complexly deformed and intruded continental crust.
- Research Organization:
- Univ. of California, Santa Barbara (USA)
- OSTI ID:
- 7183336
- Journal Information:
- Geology; (United States), Journal Name: Geology; (United States) Vol. 16:7; ISSN GLGYB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
CALIFORNIA
CONTINENTAL CRUST
CRETACEOUS PERIOD
DEFORMATION
EARTH CRUST
EROSION
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOMETRY
GEOPHYSICAL SURVEYS
GEOTHERMAL SYSTEMS
GRANITES
IGNEOUS ROCKS
INTRUSION
MAGMA
MAGMA SYSTEMS
MATHEMATICS
MESOZOIC ERA
MOUNTAINS
NORTH AMERICA
PLUTONIC ROCKS
ROCKS
SEISMIC SURVEYS
SURVEYS
TECTONICS
USA