Diverse midMiocene silicic volcanism associated w

Authors: Matthew E Brueseke William K Hart Matthew T Heizler

Publish Date: 2007/06/20

Volume: 70, Issue: 3, Pages: 343-360

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Abstract

The Santa Rosa–Calico volcanic field SC of northern Nevada is a complex multivent midMiocene eruptive complex that formed in response to regional lithospheric extension and flood basalt volcanism Santa Rosa–Calico volcanism initiated at ∼167 Ma concurrent with regional Steens–Columbia River flood basalt activity and is characterized by a complete compositional spectrum of basalt through highsilica rhyolite To better understand the relationships between upwelling mafic magmatism coeval extension and magmatic system development on the Oregon Plateau we have conducted the first comprehensive study of Santa Rosa–Calico silicic volcanism Detailed stratigraphicbased field sampling and mapping illustrate that silicic activity in this volcanic field was primarily focused along its eastern and western margins At least five texturally distinct silicic units are found in the western Santa Rosa–Calico volcanic field including abundant lava flows near vent deposits and shallow intrusive bodies Similar physical features are found in the eastern portion of the volcanic field where four physically distinct units are present The western and eastern Santa Rosa–Calico units are characterized by abundant macro and microscopic disequilibrium textures reflecting a complex petrogenetic history Additionally unlike other midMiocene Oregon Plateau volcanic fields eg McDermitt the Santa Rosa–Calico volcanic field is characterized by a paucity of calderaforming volcanism Only the Cold Springs tuff which crops out across the central portion of the volcanic field was calderaderived Major and trace element geochemical variations are present within and between eastern and western Santa Rosa–Calico silicic units and these chemical differences coupled with the observed disequilibrium textures illustrate the action of opensystem petrogenetic processes and melt derivation from heterogeneous source materials The processes and styles of Santa Rosa–Calico silicic magmatism are linked to three primary factors local focusing of and thermal and material contributions from the regional flood basalt event lithospheric extension within the northern portion of the Northern Nevada rift and interaction of midMiocene silicic magmas with preSanta Rosa–Calico lithosphere Similar processes and styles of midMiocene silicic volcanism likely occurred across the Oregon Plateau in regions characterized by both focused lithospheric extension and localized mafic magmatismWe thank Stan Mertzman for XRF trace element analyses John Morton for his assistance with DCP analyses Alan Wallace and Peter Vikre for their continued discussions on the evolution of the Northern Nevada rift and local mineralization and Wes LeMasurier for his detailed field map of the Hinkey Summit region We thank Charles Bruce Minturn III Lauren Gilbert Amy Maloy Jacob Knight and Steve Pasquale for their valuable assistance in the field and for work on related subprojects We also thank Katharine Cashman Craig White and Chris Henry for providing constructive and thoughtful reviews and Mike McCurry for handling this manuscript Primary financial support for this research was provided by the National Science Foundation EAR0106144 to Hart and a 2001 Geological Society of America Student Research Grant Brueseke

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