Joseph P. Colgan Christopher D. Henry 2017 Vector Digital Data Set (Point) Denver, CO USGS https://doi.org/10.5066/F7JD4TX8 Joseph P. Colgan Christopher D. Henry 2017 Publication (Other) Professional Paper 1832 Denver, CO USGS https://doi.org/10.3133/pp1832 The magmatic, tectonic, and topographic evolution of what is now the northern Great Basin remains controversial, notably the temporal and spatial relation between magmatism and extensional faulting. This controversy is exemplified in the northern Toiyabe Range of central Nevada, where previous geologic mapping suggested the presence of a caldera that sourced the late Eocene (34.0 mega-annum [Ma]) tuff of Hall Creek. This region was also inferred to be the locus of large-magnitude middle Tertiary extension (more than 100 percent strain) localized along the Bernd Canyon detachment fault, and to be the approximate location of a middle Tertiary paleodivide that separated east and west-draining paleovalleys. Geologic mapping, 40Ar/39Ar dating, and geochemical analyses document the geologic history and extent of the Hall Creek caldera, define the regional paleotopography at the time it formed, and clarify the timing and kinematics of post-caldera extensional faulting. During and after late Eocene volcanism, the northern Toiyabe Range was characterized by an east-west trending ridge in the area of present-day Mount Callaghan, probably localized along a Mesozoic anticline. Andesite lava flows erupted around 35?34 Ma ponded hundreds of meters thick in the erosional low areas surrounding this structural high, particularly in the Simpson Park Mountains. The Hall Creek caldera formed ca. 34.0 Ma during eruption of the approximately 400 cubic kilometers (km3) tuff of Hall Creek, a moderately crystal-rich rhyolite (71?77 percent SiO2) ash-flow tuff. Caldera collapse was piston-like with an intact floor block, and the caldera filled with thick (approximately 2,600 meters) intracaldera tuff and interbedded breccia lenses shed from the caldera walls. The most extensive exposed megabreccia deposits are concentrated on or close to the caldera floor in the southwestern part of the caldera. Both silicic and intermediate post-caldera lavas were locally erupted within 400 thousand years of the main eruption, and for the next approximately 10 million years sedimentary rocks and distal tuffs sourced from calderas farther west ponded in the caldera basin surrounding low areas nearby. Patterns of tuff deposition indicate that the area was characterized by east-west trending paleovalleys and ridges in the late Eocene and Oligocene, which permitted tuffs to disperse east-west but limited their north-south extent. Although a low-angle fault contact of limited extent separates Cambrian and Ordovician strata in the southwestern part of the study area, there is no evidence that this fault cuts overlying Tertiary rocks. Total extensional strain across the caldera is on the order of 15 percent, and there is no evidence for progressive tilting of 34?25 Ma rocks that would indicate protracted Eocene?Oligocene extension. The caldera appears to have been tilted as an intact block after 25 Ma, probably during the middle Miocene extensional faulting well documented to the north and south of the study area. New geologic mapping and 40Ar/39Ar ages from key volcanic units document formation of the Hall Creek caldera and clarify the timing and kinematics of extensional faulting in the northern Toiyabe Range. New mapping was focused on caldera-related rocks and structures—caldera margins, caldera floor, intracaldera tuff, post-caldera volcanic units—and on the Bernd Canyon detachment and related faults in the southwestern part of the caldera. 2017 Date of Publication Complete None planned -117.11785 -116.78124 39.98363 39.53394 None Argon Geochronology USGS Metadata Identifier USGS:583f4cfbe4b04fc80e3c57b4 None Nevada Lander County Toiyabe Range None. Please see 'Distribution Info' for details. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. U.S. Geological Survey, Southwest Region Joseph P Colgan Research Geologist mailing address

Denver Federal Center, Mail Stop 980, W 6th Ave Kipling St

Lakewood CO 80225 303-236-1021 303-236-5601 jcolgan@usgs.gov Environment as of Metadata Creation: Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1; Esri ArcGIS 10.3.1 (Build 4959) Service Pack N/A (Build N/A) No formal attribute accuracy tests were conducted. No formal logical accuracy tests were conducted. Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. Handheld GPS accurate to 3-4 meters. A formal accuracy assessment of the vertical positional information in the data set has either not been conducted, or is not applicable. Minerals were separated from crushed, sieved samples by standard magnetic and density techniques. Sanidine and plagioclase were leached with dilute HF to remove adhering matrix. All samples were hand-picked under a binocular microscope. Samples and neutron flux monitor Fish Canyon Tuff sanidine were irradiated in Al disks for 7 hours at the Nuclear Science Center in College Station, Tex., or at the USGS reactor in Denver, Colo. Individual sanidine crystals were fused with a CO2 laser at 5W. Biotite, plagioclase, and hornblende were step heated with a diode laser at progressively higher powers. Analyses of extracted gases of samples collected during or before 2011 (H11- and H08-) were performed on a Mass Analyzer Products model 215-50 single-collector mass spectrometer operated in static mode, according to methods summarized in McIntosh and others (2003). Samples collected more recently (H12- and JC13-) were analyzed on an ARGUS VI multi-collector mass spectrometer. All ages are calculated for an age of 28.201 Ma (Kuiper and others, 2008; Min and others, 2000) on Fish Canyon Tuff sanidine. Ages determined on the ARGUS VI mass spectrometer are significantly more precise and accurate than ages determined on the MAP 215-50 (Heizler, 2011; Heizler and others, 2014). However, methodology is evolving, and final calculations of uncertainties may differ slightly from those reported here. Weighted mean 40Ar/39Ar ages of sanidine calculated by the method of Samson and Alexander (1987). Decay constants after Min et al. (2000); total = 5.463 x 10-10 yr 1. Isotopic abundances after Steiger and Jäger (1977); 40K/K = 1.167 x 10-4. Isotopic ratios corrected for blank, radioactive decay, and mass discrimination, not corrected for interfering reactions. Errors quoted for individual analyses include analytical error only, without interfering reaction or J uncertainties. Mean age is weighted mean age of Taylor (1982). Mean age error is weighted error of the mean (Taylor, 1982), multiplied by the root of the MSWD where MSWD>1, and also incorporates uncertainty in J factors and irradiation correction uncertainties. Decay constants and isotopic abundances after Steiger and Jäger (1977). # symbol preceding sample ID denotes analyses excluded from mean age calculations. Ages calculated relative to FC-2 Fish Canyon Tuff sanidine interlaboratory standard at 28.201 Ma Decay Constant (LambdaK (total)) = 5.463e-10/a Correction factors: (39Ar/37Ar)Ca = 0.0007 ± 5e-05 (36Ar/37Ar)Ca = 0.00028 ± 2e-05 (38Ar/39Ar)K = 0.013 (40Ar/39Ar)K = 0.0072 ± 0.00016 Heizler, M.T., 2011, Introducing the ARGUS VI mass spectrometer to geo and thermochronology: American Geophysical Union, Fall Meeting 2011, abstract V51A–2508. Heizler, M.T., McIntosh, W.C., Ross, Jake, and Hamilton, Doug, 2014, 10e13 Ohm Faraday multi-collection: Striving for accuracy to match ultrahigh precision 40Ar/39Ar measurements: Sacramento, Calif., Goldschmist 2014 Abstracts, p. 957. Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R., and Wijbrans, J.R., 2008, Synchronizing rock clocks of Earth history: Science, v. 320, p. 500–504. McIntosh, W.C., Heizler, M., Peters, L., and Esser, R., 2003, 40Ar/39Ar geochronology at the New Mexico Bureau of Geology and Mineral Resources: New Mexico Bureau of Geology and Mineral Resources Open File Report OF-AR-1, 10 p. Min, K., Mundil, R., Renne, P.R., and Ludwig, K.R., 2000, A test for systematic errors in 40Ar/39Ar geochronology through comparison with U/Pb analysis of a 1.1 Ga rhyolite: Geochimica et Cosmochimica Acta, v. 64, p. 73–98. Samson, S.D., and Alexander, E.C., Jr., 1987, Calibration of the interlaboratory 40Ar/39Ar dating standard, MMhb-1: Chemical Geology Isotope Geoscience, v. 66, p. 27–34. Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p. 359–362. 2015 0.0197494333 0.0255704112 Decimal degrees D_North_American_1927 Clarke_1866 6378206.4 294.9786982 ID ID number of individual sanidine grain or heating step Power (watts) Laser power of individual heating steps 40Ar/39Ar 40Ar to 39Ar ratio 38Ar/39Ar 38Ar to 39Ar ratio 37Ar/39Ar 37Ar to 39Ar ratio 36Ar/39Ar (x 10 E-3) 36Ar to 39Ar ratio 39ArK (x 10 E-15 mol) 39Ar produced from potassium K/Ca Potassium to Calcium ratio Cl/K Chlorine to Potassium ratio 40Ar* (percent) Radiogenic argon 39Ar (percent) Cumulative 39Ar released at each heating step Age (Ma) Age of individual analyses or heating steps ±1s (1-sigma) Uncertainty on individual analyses or heating steps Quantity ID Power 40Ar/39Ar 38Ar/39Ar 37Ar/39Ar 36Ar/39Ar 39ArK K/Ca Cl/K 40Ar* 39Ar Age ±1s Min Value 0.30 3.48 -0.02 0.00 -0.02 0.02 0.03 -0.01 3.68 0.16 11.79 0.00 Max Value 35.00 257.69 0.06 19.86 840.22 69.91 315.21 0.03 100.69 100.00 38.68 3.08 The entity and attribute information was generated by the individual and/or agency identified as the originator of the data set. Please review the rest of the metadata record for additional details and information. U.S. Geological Survey - ScienceBase" mailing

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Denver CO 80225 USA 888-275-8747 sciencebase@usgs.gov Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also contains copyrighted materials as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Microsoft Excel https://doi.org/10.5066/F7JD4TX8 None. No fees are applicable for obtaining the data set. 20220829 Joseph Colgan mailing

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Denver CO 80225 USA 303-236-1021 jcolgan@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998