Internal structure of the Sierra Nevada batholith based on specific gravity and gravity measurements

Details Internal structure of the Sierra Nevada batholith based on specific gravity and gravity measurements Internal structure of the Sierra Nevada batholith based on specific gravity and gravity measurements

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993georl..20.2179o&link_type=abstract

Geophysical Research Letters (ISSN 0094-8276), vol. 20, no. 20, p. 2179-2182

Mathematics

8

Batholiths, Density (Mass/Volume), Depth Measurement, Dynamic Structural Analysis, Earth Gravitation, Sierra Nevada Mountains (Ca), Silicon Dioxide, Topography, Computer Aided Mapping, Gravity Anomalies, Grid Generation (Mathematics), Relief Maps, Spatial Distribution

Scientific paper

About 6,000 specific-gravity (SG) measurements of samples collected from nearly 200 granitic plutons comprising the central Sierra Nevada batholith yield a SG contour map across the batholith from 36.25 deg to 38 deg north latitude. A good correlation between measured SG and analyzed weight percent SiO2 enables estimation of average silica variations across the batholith. The average SG is 2.69 corresponding to an average of 68 wt. % SiO2 for the 18,000 sq km central part of the batholith. A 1-km gridded version of the SG measurements has been used to generate a series of synthetic gravity maps. The synthetic map computed for a depth of 10 km shows the best correspondence with the isostatic residual gravity map indicating that variations in the observed gravity residuals are largely caused by SG variations of the plutonic rocks exposed at the surface that apparently extend downward to an average depth of about 10 km. Although the 10-km synthetic gravity map gives the best overall fit to the observed gravity data, comparison of indivudual anomalies indicates that the bottoms of the plutons as defined by SG variations at the surface are generally shallower along the west edge of the Sierra Nevada (7 +/- 2 km) and deeper in the younger and more felsic eastern part (12 +/- 3 km). These depths may indicate the depth below which density homogenization occurs, either by igneous, or possibly, structural processes.

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