Architecture and Internal Geometry of a Giant Intrusive-Extrusive Complex, Panoche Hills - Central Coastal Range, CA, USA

Vigorito, Mario¹, Andrew Hurst¹, Anthony Stephen John Scott¹, J. A. Cartwright² (1) Aberdeen University, Aberdeen, United Kingdom (2) Cardiff University, Cardiff, United Kingdom

The Panoche Giant Injection Complex (PGIC) is an analogue for large scale injectition complexes. It extends for more than 54km in length and consists of an intrusive network extending vertically for more than 800m and connected to sand extrusions and carbonate cold-seeps. The lower portion of the intrusive network is characterised by the presence of irregular, laterally discontinuous sills and by a large amount of relatively short and narrow dykes displaying a scattered distribution pattern. Dykes become wider, more organised and less abundant upwards and are seen to feed into, depart from or cross cut laterally continuous sills up to 15m thick. The medial and upper portions of the injection complex are dominated by dykes. The latter may be up to 20m thick and may be arranged to form “conical” intrusions up to 1.5km wide and more than 250m thick. Two main architectural styles have been identified: 1) Conical-injections formed by a single 12-20m thick asymmetric, V-shaped low-angle dyke bordered at the periphery by thinner high-angle dykes. 2) Conical injections formed by multiple stepping dykes arranged as petals of a rose. Individual dykes are characterised by a curved to crescent plan-geometry and range from 1 to 8m in thickness. In both cases the host-rock included within the conical intrusion is commonly devoid of injections or cut by a few narrow high-angle dykes. Multiple bioturbated sand-mounds, locally exhibiting a single or multiple venting conduits, occur at the top of the intrusive network and are interpreted as sand extrusions.