Engineering topics

Dokka, R. K.

Publications and source records attributed to Dokka, R. K..

3 records

NASA NTRS1994

Paleomagnetic and structural evidence for localized tectonic rotation associated with fault drag in the northeastern Mojave Desert: Implications for the late Cenozoic tectonic evolution of the Eastern California shear zone

Paleomagnetic data, coupled with detailed geological analysis of the southeastern Goldstone Lake region, indicate that lower Miocene volcanic and epiclastic rocks of the Pink Canyon area have been folded, faulted and tectonically rotated approximately 28.4 + or - 9.0 deg clockwise about a vertical axis. The Coyote Canyon Fault is locally folded about a vertical axis approximately 25 deg in a clockwise sense in the Pink Canyon area. Timing relationships indicate that rotation is post-early Miocene; regional relationships imply that deformation is late Miocene to Holocene in age. These relationships imply that tectonic rotation is local rather than regional in extent as proposed by some tectonic models. The results of this study are generally consistent with the Dokka and Travis model and the subsequently revised Dokka model of strain partitioning in the northeastern Mojave Desert block.

Macconnell, D. F.↗

NASA NTRS1990

Faults in the Mojave Desert, California, as revealed on enhanced Landsat images

Landsat TM images, subjected to four-component processing through which lithologies can be discriminated by their contrasting absorption and reflection at IR wavelengths, have revealed previously unsuspected strike-slip and normal faults in the central and eastern Mojave Desert. These discriminations, which extend to ferric and ferrous iron and to hydroxyl content without compromise of landform depiction, represent a novel type of geophysical display for geologic mapping in regions of well-exposed bedrock; the faults thus discovered form part of an extensive regional network of right shear which connects Death Valley region faults with those in the San Andreas system.

Ford, J. P.↗

NASA NTRS1985

Thermal history of a metamorphic core complex

Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

Dokka, R. K.↗