|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA
2 Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557, USA
3 U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA
The Caetano Tuff is a late Eocene, rhyolite ash-flow tuff that crops out within an 
90-km-long, east-west–trending belt in north-central Nevada, previously interpreted as an elongate graben or "volcano-tectonic trough." New field, petrographic, geochemical, and geochronologic data show that: (1) the east half of the "trough" is actually the Caetano caldera, formed by eruption of the Caetano Tuff at 33.8 Ma and later structurally dismembered during Miocene extension; (2) the west half of the trough includes both the distinctly younger and unrelated Fish Creek Mountains caldera (ca. 24.7 Ma) and a west-trending paleovalley partly filled with outflow Caetano Tuff; and (3) the Caetano Tuff as previously defined actually consists of three distinct units, two units of the 33.8 Ma Caetano Tuff and an older (34.2 Ma) tuff, exposed north of the Caetano caldera, herein named the tuff of Cove Mine.
Miocene extensional faulting and tilting has exposed the Caetano caldera over a paleodepth range of >5 km, from the caldera floor through post-caldera sedimentary rocks, providing exceptional constraints on an evolutionary model of the caldera that are rarely available for other calderas. The Caetano caldera filled with more than 4 km of intracaldera Caetano Tuff, while outflow tuff flowed west and south of the caldera, primarily down Eocene paleovalleys. Caldera fill consists of two units of Caetano Tuff. The lower compound cooling unit is as much as 3600 m thick and is separated by a complete cooling break from a 500–1000-m-thick upper unit that consists of multiple, thin, ash flows interbedded with sedimentary deposits. Multiple granite porphyries, including the 25-km2 Carico Lake pluton, intruded and domed the center of the caldera within 0.1 Ma of caldera formation; one of these porphyries is associated with pervasive argillic and advanced argillic alteration of the western half of the caldera. All exposed caldera-related rocks are rhyolites or granites (71–77.5 wt% SiO2). Caldera collapse was significantly greater than the thickness of caldera fill and created a topographic depression that served as a depocenter until at least 25 Ma, filling with nearly 1 km of sediments and distally derived, ash-flow tuffs.
The caldera is presently exposed in a series of 40–50°, east-tilted blocks bounded by north-striking, west-dipping normal faults that formed after 16 Ma. Slip on these faults accommodated 100% E-W extension, making the restored Caetano caldera 20 km east-west by 10–18 km north-south. The estimated volume of intracaldera Caetano Tuff is, therefore, 840 km3, and the minimum estimated total eruptive volume is 1100 km3. Although the Caetano magmatic system was probably too young to supply heat for nearby Carlin-type gold deposits in the Cortez district, earlier nearby magmatic activity may have contributed to formation of these deposits. Reconstruction of the late Eocene, pre-Caetano caldera geologic setting, immediately prior to caldera formation, indicates that the Cortez Hills and Horse Canyon Carlin-type deposits formed at 
1 km depths.
Keywords: calderas • ash-flow tuff • magma resurgence • Basin and Range Province • extensional tectonics • Carlin-type gold deposit
This article has been cited by other articles:
|
|
 |
|
  J.C. Fosdick and J.P. Colgan Miocene extension in the East Range, Nevada: A two-stage history of normal faulting in the northern Basin and Range GSA Bulletin, September 1, 2008; 120(9-10): 1198 - 1213. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. J. Gonsior and J. H. Dilles Timing and evolution of Cenozoic extensional normal faulting and magmatism in the southern Tobin Range, Nevada Geosphere, August 1, 2008; 4(4): 687 - 712. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. W. Lipman and W. C. McIntosh Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from? GSA Bulletin, July 1, 2008; 120(7-8): 771 - 795. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. D. Henry Ash-flow tuffs and paleovalleys in northeastern Nevada: Implications for Eocene paleogeography and extension in the Sevier hinterland, northern Great Basin Geosphere, February 1, 2008; 4(1): 1 - 35. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. P. Colgan, D. A. John, C. D. Henry, and R. J. Fleck Large-magnitude Miocene extension of the Eocene Caetano caldera, Shoshone and Toiyabe Ranges, Nevada Geosphere, February 1, 2008; 4(1): 107 - 130. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
