Thickness and spatial distributions of clastic dykes, northwest SacramentoValley, California

The geometry and distribution of the clastic dykes of the Ono district, Nor th Sacramento Valley are examined within stream sections. Five traverses al ong dry stream beds provide good exposure allowing the spacing, thickness a nd geometry of the dykes to be recorded. The spatial and thickness distribu tion of the dykes are considered using cumulative frequency plots, allowing a visual estimation of a best fit distribution. dyke thickness conforms be st to a log-normal distribution. There is also a characteristic minimum dyk e thickness in a traverse and this is attributed to the minimum aperture th at a fluid with sand clasts is able to exploit. Dyke spacing, however, show s a good correlation with a power-law distribution for four traverses, sugg esting that there is a mechanistic control on the spatial distribution. Plo tting dyke thickness against minimum dyke spacing reveals that thin dykes d o not generally intrude in isolation. Unlike veins and igneous dykes, elast ic continue to provide plefel rntial pathways For fluid Aow, subsrqurnt to their intrusion, thus inhibiting intrusion in the area surrounding a pre-ex isting dyke. A combination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of elastic d ykes seen in the Ono district, California. (C) 1998 Elsevier Science Ltd. A ll rights reserved.