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532889 
Journal Article 
Geology and geochronology of the Spirit Mountain batholith, southern Nevada: Implications for timescales and physical processes of batholith construction 
Walker, BA; Miller, CF; Claiborne, LL; Wooden, JL; Miller, JS 
2007 
1 
Journal of Volcanology and Geothermal Research
ISSN: 0377-0273 
167 
1-4 
239-262 
English 
The Spirit Mountain batholith (SMB) is a similar to 250 km(2) composite silicic intrusion located within the Colorado River Extensional Corridor in southernmost Nevada. Westward tilting of 40-50 degrees has exposed a cross-section from the roof through deep levels of the batholith. Piecemeal construction is indicated by zircon geochronology, field relations, and elemental geochemistry. Zircon U/Pb data (SHRIMP) demonstrates a similar to 2 million year (17.4-15.3 Ma) history for the SMB. Individual samples contain zircons with ages that span the lifetime of the batholith, suggesting recycling of extant zircon into new magma pulses. Field relations reveal several distinct intrusive episodes and suggest a common injection geometry of stacked horizontal sheets. The largest unit of the SMB is a gradational section (from roof downward) of high-silica leucogranite through coarse granite into foliated quartz monzonite. Solidification of this unit spans most of the history of the batholith. The 25 kin x 2 km leucogranite was emplaced incrementally as subhorizontal sheets over most or all of the history of this section, suggesting repeated fractional crystallization and melt segregation events. The quartz monzonite and coarse granite are interpreted to be cumulate residuum of this fractionation. Age data from throughout this gradational unit show multiple zircon populations within individual samples. Subsequent distinct intrusions that cut this large unit, which include minor populations of zircons that record the ages of earlier events in construction of the batholith, preserve a sheeted, sill-on-sill geometry. We envision the SMB to have been a patchwork of melt-rich, melt-poor, and entirely solid zones throughout its active life. Preservation of intrusion geometries and contacts depended on the consistency of the host rock, Zircons recycled into new pulses of magma document remobilization of previously emplaced crystal mush, suggesting the mechanisms by which evidence for initial construction of the batholith became blurred. (c) 2007 Published by Elsevier B.V. 
magma chamber; batholith construction; zircon geochronology; granite; Colorado River Extensional Corridor; silicic magma chambers; exposed cross-section; coso volcanic field; long valley; residence times; northwestern arizona; eldorado mountains; range province; united-states; new-zealand