HR: 14:40h
AN: V43G-05    [Abstracts]
TI: The River Mountains Volcanic Section – Wilson Ridge Pluton, a Long Lived Multiphase Mid- Tertiary Igneous System in Southern Nevada and Northwestern Arizona, USA
AU: * Honn, D K
EM: dkhonn@gmail.com
AF: University of Nevada, Las Vegas, Department of Geoscience, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, United States
AU: Simon, A C
EM: Adam.Simon@unlv.edu
AF: University of Nevada, Las Vegas, Department of Geoscience, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, United States
AU: Smith, E I
EM: Gene.Smith@unlv.edu
AF: University of Nevada, Las Vegas, Department of Geoscience, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, United States
AU: Spell, T L
EM: Terry.Spell@unlv.edu
AF: University of Nevada, Las Vegas, Department of Geoscience, 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010, United States
AB: ²⁰⁶Pb/²³⁸U zircon dates (LA-ICPMS) from 106-40 μm spots on 49 zircons suggest the Wilson Ridge Pluton in northwestern Arizona and its corresponding volcanic cover in the River Mountains of southern Nevada represent a complex multiphase igneous system active for 4.2 million years (based on a zircon core-rim pair) to a maximum of 7.2 million years (from two zircon rim dates 18.9 ± 0.8 to 13.1 ± 0.6 Ma). This period of activity is significantly longer than the 500 thousand year interval (12.99 ± 0.02 to 13.45 ± 0.02) determined by ⁴⁰Ar/³⁹Ar sanidine, biotite, hornblende, and whole rock dates. The ⁴⁰Ar/³⁹Ar dates only reflect the time when the igneous system cooled to mineral closure temperatures during emplacement in the upper crust. Zircon xenocrysts identified in cathodoluminescence images range in age from 1517.5 ± 11.2 Ma to 21.3 ± 0.8 Ma. Inherited zircon cores are as much as 8.9 million years older than their rims. Zircon dates correspond to pluton stratigraphy with late stage dikes at 15.3 Ma (mean age based on 9 dates), quartz monzonite intermediate in composition and age (mean age 15.5 Ma based on 20 dates), and the oldest unit, the Horsethief Canyon diorite (mean age 17.5 Ma based on 6 dates). Although the mean ages correspond to stratigraphy, the spread of ages for each unit overlaps, therefore these correlations are preliminary. The River Mountains volcanic section lies 20 km to the west of the pluton and may have been separated from it by west directed motion along the Saddle Island detachment fault. The River Mountains volcanic section and the Wilson Ridge Pluton are considered a single igneous system as demonstrated by major and trace element geochemistry, whole rock isotopic analyses (Sr and Nd), previous ⁴⁰Ar/³⁹Ar and K-Ar dates, mafic enclave chemistry, extensive magnesio-riebeckite alteration unique to both the River Mountains volcanic and Wilson Ridge Plutonic sections, and the location of the Saddle Island fault. Preliminary zircon dates from the River Mountains stock (18.1 ± 1.3 Ma to 14.1 ± 0.9 Ma) and River Mountains volcanic section (15.2 ± 0.3 to 13.6 ± 0.7 Ma) fall within the range of dates for the Wilson Ridge Pluton. These overlapping zircon ages provide additional evidence of a link between the volcanic and plutonic sections. Ongoing research includes U/Pb dating of zircons from each of the units within the Wilson Ridge Pluton, and River Mountains volcanic section using a sensitive high-resolution ion probe (SHRIMP).
DE: 1040 Radiogenic isotope geochemistry
DE: 1090 Field relationships (3690, 8486)
DE: 3618 Magma chamber processes (1036)
DE: 3640 Igneous petrology
DE: 9350 North America
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting