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Tectonic Setting and Structural Analysis of Mt. Diablo and Vicinity

It has long been recognized that many of the geologic features exposed in the eastern Coast Ranges of the San Francisco Bay Area are due to a component of Pacific-plate-boundary contraction. This study uses regional cross sections, constrained by surface geology, petroleum wells, and map analysis, to infer the geometry and kinematics of the contractional and strike-slip fault systems responsible for the observed topographic and structural geometry. Insights from this research are: Uplift of the Mount Diablo anticline is generated by slip transfer from the here-defined Subsurface Greenville fault to the Franklin Canyon fault via Unruh et al.’s (2007) Mount Diablo blind thrust. Exposure of the Franciscan Complex and Coast Range Ophiolite at Mount Diablo anticline is due to the north-dipping, southwest-verging, Diablo Thrust (Dibble, 2005) that largely lies above the anticline and links the Concord fault and the Greenville fault system.

  • The anomalous topographic height of Mt Diablo results from the superposition of structures and the exposure of resistant basement rocks at the surface.
  • Slip from the regional wedge thrust that generates the boundary of the Eastern Coast Ranges daylights along the Concord and Franklin Canyon faults and their lateral equivalents.
  • The Calaveras fault terminates northward by slip transfer to thrusts to the west, thus generating the anomalous structural relief in the East Bay Hills which culminates with exposure of the Coast Range Ophiolite, known locally as the San Leandro Gabbro.
  • Geologic and active seismic fault are aligned in some locations and disparate in others.
  • Development of a retro-deformable, three-dimensional geological model is required to evaluate the magnitude and timing of strike-slip versus dip-slip motion on East Bay faults.

Speaker: Donald Medwedeff

Wednesday, 02/26/20

Contact:

Website: Click to Visit

Cost:

$5 General, $1 Students & Teachers

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Northern California Geologic Society

9 Altarinda Rd
Masonic Center
Orinda, CA 94563