THE PALEOZOIC EUREKA PEAK INTRUSION OF SIERRA-NEVADA (NORTHERN CALIFORNIA) - A MAGMA CHAMBER OF A CALC-ALKALINE ARC FEEDING THE MILLS PEAK PERMIAN SEAMOUNT

The Paloezoic Eureka Peak intrusion of Sierra Nevada, which is associated with several basic dykes, consists of ultramafic rocks, gabbros and diorites. The plutonic and basic rocks intrude the Famennian Sierra Buttes rhyolites and are affected by the thermal metamorphism of the Jurassic Nevadan batholiths. This intrusion is regarded as the magma chamber of the Permian Mills Peaks submarine volcano because: (1) its associated mafic dykes share with the Mills Peak pillow-basalts and dykes the same mineralogy and chemistry; (2) its plutonic rocks show also a calc-alkaline affinity; and (3) both intrusive and extrusive rocks are affected by the same polyphase tectonism.