Joint Meeting Pacific Section, AAPG & Cordilleran Section GSA April 29–May 1, 2005, San José, California

Geometry versus Genesis, Structure of Central California

Ronald C. Crane
Danville, CA 94526, [email protected]

Geologic interpretation requires considering all four dimensions rather than a two dimensional map view. Data acquisitions starts with accurate field mapping which then determines the structural form or geometry of the rocks. The geometry then determines the genesis of the structures. Starting with a genetic viewpoint and fitting the data to that model is an invalid approach.

One hundred twenty two (122) quadrangles were remapped and 234 cross sections were prepared. The geometry of the structures shows conclusively that the basic geology of Central California is due to compressive forces which form thrust faults and folds.

Unfolding of cross sections shows the development of the area over time. The interaction of the eastward moving Pacific Plate and the westward moving North American Plate is the dominant force. Individual, areally restricted microplates encountered the continent at different times and in different places leading to an overll shortening of several hundred percent. The misidentified strike-slip major features are the loci of several thrust faults where different terranes collided.

Posted with permission of The Geological Society of America; abstract also online (http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_84638.htm). © Copyright 2005 The Geological Society of America (GSA).