HR: 1400h
AN: V53B-08    [Abstracts]
TI: Redefining an Igneous System: Volcanic-Plutonic Links Between the Wilson Ridge Pluton and River Mountains Volcanic Section, Nevada USA
AU: Honn, D K
EM: dkhonn@gmail.com
AF: University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, United States
AU: * Smith, E I
EM: gsmith@ccmail.nevada.edu
AF: University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, United States
AB: The study of an igneous system is often limited by the extent of exposure. Rarely are both the plutonic and volcanic segments of a single igneous system preserved and recognized. Just east of Las Vegas Nevada, both the volcanic (River Mountains) and plutonic (Wilson Ridge) parts of a single igneous system are exposed. The River Mountains volcanic section (12.6 to 13.4 Ma) and the Wilson Ridge Pluton (12.5 to 13.4 Ma) are linked by similarities of geochronology, structure, and geochemistry. The River Mountains volcanic section was separated from the Wilson Ridge pluton by the mid-Tertiary (~13.4 Ma) west-dipping Saddle Island detachment fault and now lies 20 km to the west of the pluton. Normal faulting and stratal rotation have exposed much of the volcano in cross section including a porphyritic quartz monzonite plug in its conduit. The Wilson Ridge Pluton is tilted to the north (~5º to 20º) resulting in nearly 20 km of continuous exposure with its base to the south and roof to the north. The connection between the the pluton and volcanic section is indicated by the tight clustering of relatively immobile trace elements Th (4.2 to 25.1 ppm), Hf (3.3 to 6.6 ppm), and Ta (0.9 to 1.7 ppm) from 88 samples from the pluton and 32 samples from the volcanic section. Furthermore, Nd and Sr isotopes indicate a single cogenetic system. The upper part of the pluton is a dike complex composed of fine-grained monzonite to granite. The largest volume of the pluton is relatively homogeneous quartz monzonite. Near its base, mafic to dioritic enclaves locally compose as much as 75% of the rock. Diorite enclaves are interpreted as xenoliths incorporated into Wilson Ridge magma during ascent. Basaltic enclaves are synplutonic mafic dikes physically disrupted by flow within the more felsic Wilson Ridge magma. The River Mountains volcanic section ranges from basalt to dacite. Mafic enclaves are present locally in dacite and may be the volcanic equivalent of those in the pluton. Chemical similarities between the mafic enclaves in the pluton and the basalt flows of the River Mountains support the link between the Wilson Ridge Pluton and River Mountains volcanic section. Ongoing research aims to model the evolution of the integrated Wilson Ridge - River Mountains igneous system by studying magma residence times from diffusion profiles in phenocrysts, U-Pb dating of Zircons, open system petrogenetic modeling, as well as a chemical and petrographic comparison of the enclaves in the pluton and volcanic section.
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8486 Field relationships (1090, 3690)
DE: 9350 North America
DE: 9604 Cenozoic
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly