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Episodic caldera volcanism in the Miocene southwestern Nevada volcanic field; revised stratigraphic framework, (super 40) Ar/ (super 39) Ar geochronology, and implications for magmatism and extension

David A. Sawyer, R. J. Fleck, M. A. Lanphere, R. G. Warren, D. E. Broxton and Mark R. Hudson
Episodic caldera volcanism in the Miocene southwestern Nevada volcanic field; revised stratigraphic framework, (super 40) Ar/ (super 39) Ar geochronology, and implications for magmatism and extension
Geological Society of America Bulletin (October 1994) 106 (10): 1304-1318

Abstract

The middle Miocene southwestern Nevada volcanic field (SWNVF) is a classic example of a silicic multicaldera volcanic field in the Great Basin. More than six major calderas formed between g15 and 7.5 Ma. The central SWNVF caldera cluster consists of the overlapping Silent Canyon caldera complex, the Claim Canyon caldera, and the Timber Mountain caldera complex, active from 14 to 11.5 Ma and centered on topographic Timber Mountain. Locations of calderas older than the Claim Canyon caldera source of the Tiva Canyon Tuff are uncertain except where verified by drilling. Younger peralkaline calderas (Black Mountain and Stonewall Mountain) formed northwest of the central SWNVF caldera cluster. We summarize major revisions of the SWNVF stratigraphy that provide for correlation of lava flows and small-volume tuffs with the widespread outflow sheets of the SWNVF. New laser fusion (super 40) Ar/ (super 39) Ar isotopic ages are used to refine and revise the timing of eruptive activity in the SWNVF. The use of high-sensitivity mass spectrometry allowed analysis of submilligram-sized samples with analytical uncertainties of approximately 0.3% (1), permitting resolution of age differences as small as 0.07 Ma. These results confirm the revised stratigraphic succession and document a pattern of episodic volcanism in the SWNVF. Major caldera episodes (Belted Range, Crater Flat, Paintbrush, Timber Mountain, and Thirsty Canyon Groups) erupted widespread ash-flow sheets within 100-300 k.y. time spans, and pre- and postcaldera lavas erupted within 100-300k.y. of the associated ash flows. Peak volcanism in the SWNVF occurred during eruption of the Paintbrush and Timber Mountain Groups, when over 4500 km (super 3) of metaluminous magma was erupted in two episodes within 1.35 m.y., separated by a 750 k.y. magmatic gap. Peralkaline and metaluminous magmatism in the SWNVF overlapped in time and space. The peralkaline Tub Spring and Grouse Canyon Tuffs erupted early, and the peralkaline Thirsty Canyon Group tuffs and Stonewall Flat Tuff erupted late in the history of the SWNVF, flanking the central, volumetrically dominant peak of metaluminous volcanism. Magma chemistry transitional between peralkaline and metaluminous magmas is indicated by petrographic and chemical data, particularly in the overlapping Grouse Canyon and Area 20 calderas of the Silent Canyon caldera complex. Volcanism in the SWNVF coincided with the Miocene peak of extensional deformation in adjoining parts of the Great Basin. Although regional extension was concurrent with volcanism, it was at a minimum in the central area of the SWNVF, where synvolcanic faulting was dominated by intracaldera deformation. Significant stratal tilting and paleomagnetically determined dextral shear affected the southwestern margin of the SWNVF between the Paintbrush and Timber Mountain caldera episodes. Larger magnitude detachment faulting in the Bullfrog Hills, southwest of the central SWNVF caldera cluster, followed the climactic Timber Mountain caldera episode. Postvolcanic normal faulting was substantial to the north, east, and south of the central SWNVF caldera cluster, but the central area of peak volcanic activity remained relatively unextended in postvolcanic time. Volcanism and extension in the SWNVF area were broadly concurrent, but in detail they were episodic in time and not coincident in space.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 106
Serial Issue: 10
Title: Episodic caldera volcanism in the Miocene southwestern Nevada volcanic field; revised stratigraphic framework, (super 40) Ar/ (super 39) Ar geochronology, and implications for magmatism and extension
Affiliation: U. S. Geological Survey, Denver, CO, United States
Pages: 1304-1318
Published: 199410
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 95
Accession Number: 1994-048490
Categories: Igneous and metamorphic petrologyGeochronologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N36°45'00" - N37°19'60", W116°45'00" - W116°00'00"
Secondary Affiliation: Los Alamos National Laboratory, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199422
Program Name: USGSOPNon-USGS publications with USGS authors
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