Thickness and spatial distributions of clastic dykes, northwest Sacramento Valley, California

The geometry and distribution of the clastic dv s.es of the Ono district. North Sacramento Valley are examined within stream sections. Five traverses along dry stream beds provide good exposure allowing the spacing, thickness and geometry of the dykes to be reorded. The spatial and thickness distribution of the dykes are considered using cumulative frequency plots, allowing a visual estimation of a best lit distribution. Dyke thickness conforms best to a log-normal distribution. There is also a characteristic minimum dyke thickness in a traverse and this is attributed lo the minimum aperture thai a fluid with sand clasts is able to exploit. Dyke spacing, however, shows a good correlation with a power-law distribution for four traverses, suggesting thai there is a mechanistic control on the spatial dislribulion. Plolting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation. I'nlike veins and igneous dykes, elastic dykes continue lo provide preferential pathways for fluid flow, subsequent lo their intrusion, thus inhibiting intrusion in the area surrounding a pre-existing dyke. Acombination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the Ono district. California.