|Cordilleran Section - 106th Annual Meeting, and Pacific Section, American Association of Petroleum Geologists (27-29 May 2010)|
|Paper No. 10-4|
|Presentation Time: 2:35 PM-2:55 PM|
DEVELOPMENT OF A VERTICALLY-STRATIFIED DACITE-RHYOLITE MAGMATIC SYSTEM WITHIN THE MOUNT WHITNEY INTRUSIVE SUITE, SIERRA NEVADA, CALIFORNIA
HIRT, William H., Natural Sciences, College of the Siskiyous, 800 College Avenue, Weed, CA 96094, email@example.com|
Some ash-flow tuffs that preserve dacite-rhyolite compositional transitions are interpreted as the erupted contents of stratified reservoirs in which rhyolitic magmas overlie the dacitic “mushes” from which they segregated. The youngest member of the Mount Whitney Intrusive Suite (MWIS) may preserve a plutonic record of such a compositionally-stratified system.
The MWIS was emplaced between 90 and 83 Ma near the eastern edge of the Sierra Nevada batholith and its youngest member, the Whitney pluton, intrudes both older members and wall rocks warmed by them. The pluton grades from marginal granodiorite at low elevations to granite in its upper central part, and mass balance calculations indicate the granite can derived from the granodiorite by modest fractionation of hb + pl + mt. Alkali-feldspar megacrysts comprise 6-11% of the body and are coarser towards its center. Evidence of repeated resorption and growth of Ba-rich zones in the megacrysts indicates open-system behavior during which influxes of hotter magma are inferred to have selectively dissolved small alkali-feldspar crystals and led to coarsening. The inward coarsening of megacrysts suggests that the longest history of recharge occurred near the center of the Whitney pluton where it would have promoted differentiation by episodically raising temperature and lowering crystallinity.
Cordilleran Section - 106th Annual Meeting, and Pacific Section, American Association of Petroleum Geologists (27-29 May 2010)
General Information for this Meeting
|Session No. 10|
Debating the Connections Between the Plutonic and Volcanic Rock Record
Marriott Anaheim Hotel: Platinum 2
1:30 PM-5:00 PM, Thursday, 27 May 2010
Geological Society of America Abstracts with Programs, Vol. 42, No. 4, p. 52
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