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Geology topics

J. F. Evernden

Publications and source records attributed to J. F. Evernden.

11 recordsLinked to original sources
USGS1983

Intensity patterns in eastern Asia.

Investigation of the intensity patterns of earthquakes of E Asia indicates a strong regional pattern of attenuation parameter k and systematic correlation of this pattern with topography, P residuals, and level of seismicity as in the USA.-Author

Chinese Geophysics↗
USGS1971

Sierra Nevada plutonic cycle: Part I, origin of composite granitic batholiths

Intrusion of Mesozoic batholiths in California and the western North America Cordillera began in the Late Triassic 210 m.y. ago and ended in the Late Cretaceous 80 m.y. ago. Emplacement of granitic rocks was apparently not continuous but was accomplished during five major epochs of intrusion at approximately 30 m.y. intervals, each epoch taking 10 to 20 m.y. to complete. A progressive transgression of epicontinental seas onto the midcontinent occurred during the same interval of time as the batholithic emplacement to the west. A penecontemporaneous deformation near the loci of granitic emplacement and a temporary regression during the major progressive transgression of seas onto the midcontinent are correlated with each intrusive epoch. The locus of Mesozoic granitic rocks was a source of sediments during most of the period of time required to emplace the batholiths; the origin of the batholithic magmas cannot be related only to localized down-warping of geosynclines. The source of the major proportion of the mobile granodioritic magmas of the Sierra Nevada was within the mantle, as is indicated by Sr isotope data. All plutons now exposed in the Sierra Nevada, whether of Cretaceous age or older, were emplaced at depths of a very few kilometers, the shallowest having been emplaced at depths of 4 km or less. The spatial relationships among these synchronous geologic phenomena and the geochemical and geophysical data from the same region are accounted for by a northwestward drift of North America in the region of the western Cordillera of the United States onto and across a Mesozoic feature that had characteristics like present-day oceanic rises.

California↗
USGS1971

Sierra Nevada plutonic cycle: Part II, tidal energy and a hypothesis for orogenic-epeirogenic periodicities

The dissipative power of the solid earth tides is the order of 10 19 ergs/sec, or a few percent of terrestrial heat flow. It is proposed that this energy is concentrated along oceanic ridge systems and in the asthenosphere by mechanisms of viscous dissipation involving shear melting. Tidal energy localizes and sustains sources of sea-floor spreading through the melting mechanism, convection and magmatic transfer. Components of this energy enter the continent as magmatic heat either where ridge type sources and continents interact or where lateral motions induce shear zones and viscous dissipation within the continent. Temporal maxima of igneous intrusion into continental crust and related epeirogenic oscillations, spaced at intervals of about 30 m.y., are explained in terms of periodic thermal instabilities in the process of shear melting in the mantle. That is, maxima in rates of magma production in the mantle are relieved by vertical magmatic transfer. This process is coupled with lateral motions of the continent in a way analogous to episodic creep episodes of much shorter period in motions of active fault systems. Calculated periodicities are found to be simultaneously compatible with (l) the Sierra Nevada intrusive epochs of Part I, (2) oscillations in the eustatic curve during the Mesozoic Era, (3) concepts of sea-floor spreading, and (4) the magnitude of tidal power. More profound epeirogenic oscillations, having periods of about 200 m.y., are induced by variations in proportioning of tidal energy dissipation between the solid earth and the epicontinental seas. Thus, the tidal deformations of the earth provide information that leads to a general dynamic theory where magmatism, orogency, epeirogeny, sea-floor spreading and continent migration are systematically interrelated.

California↗