New Mexico Bureau of Geology and Mineral Resources

The axial basins of the northern and central Rio Grande rift evolved since late Oligocene as a chain of half grabens between the Colorado Plateau on the west and the interior of the craton on the east. The basins range from 80 to 240 km in length and from 5 to 95 km in width, with an average width of approximately 50 km. Basin-fill sedimentary deposits range up to 5 to 6 km in thickness. The oldest dated volcanic rocks interbedded with syn-rift sediments are about 26 Ma. Extension in the rift was left oblique and increases southward from 8...

Research Article| March 01, 1998 Sequence, age, and source of silicic fallout tuffs in middle to late Miocene basins of the northern Basin and Range province Michael E. Perkins; Michael E. Perkins 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Search for other works by this author on: GSW Google Scholar Francis H. Brown; Francis H. Brown 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Search for other works by this author on: GSW Google Scholar William P. Nash; William P. Nash 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Search for other works by this author on: GSW Google Scholar S. K. Williams; S. K. Williams 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Search for other works by this author on: GSW Google Scholar William McIntosh William McIntosh 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico, 87801 Search for other works by this author on: GSW Google Scholar Author and Article Information Michael E. Perkins 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 Francis H. Brown 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 William P. Nash 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 S. K. Williams 1Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112 William McIntosh 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico, 87801 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1998) 110 (3): 344–360. https://doi.org/10.1130/0016-7606(1998)110<0344:SAASOS>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Michael E. Perkins, Francis H. Brown, William P. Nash, S. K. Williams, William McIntosh; Sequence, age, and source of silicic fallout tuffs in middle to late Miocene basins of the northern Basin and Range province. GSA Bulletin 1998;; 110 (3): 344–360. doi: https://doi.org/10.1130/0016-7606(1998)110<0344:SAASOS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The latest Cenozoic (<6 Ma) ash beds in the western United States have been intensively studied for several decades. The more widespread of these ash beds are well-documented event horizons that are of great value in studies of the timing and pace of geological, climatological, and biological events throughout the region. Because explosive volcanism was not restricted to latest Neogene time in this region, many older ash beds are likely to prove as useful as younger beds as event horizons, once they are located, characterized, and dated. As a first step in developing a useful chronology of older Cenozoic ash beds in the western United States, we have sampled and analyzed silicic fallout tuffs in middle to late Miocene sedimentary basins across the northern Basin and Range province.The northern Basin and Range basins, ideally situated in the vicinity of major coeval silicic volcanic centers, contain numerous relatively unaltered, silicic fallout tuffs. We have correlated tuffs between all sampled sections on the basis of glass shard composition. The composite stratigraphic sequence established by the correlations contains more than 200 individual tuffs, including 59 widely distributed tuffs termed correlative tuffs. The tuffs vary widely in composition, but most are in one of two compositional groups: gray metaluminous vitric tuffs (Gm tuffs) or white metaluminous vitric tuffs (Wm tuffs). Distribution patterns, compositional characteristics, and correlation with ash-flow tuffs show that the source for most Gm tuffs was the Snake River Plain volcanic province along the northern edge of the northern Basin and Range, and the source for most Wm tuffs was the southwestern Nevada volcanic field in the southern part of the northern Basin and Range.The northern Basin and Range tuffs range in age from ca. 16–6 Ma. The ages of individual tuffs are determined variously by direct isotopic dating, by correlation to previously dated fallout and ash-flow tuffs, or by interpolation age estimation. Ages for most tuffs are known to within 0.25 m.y. (1σ) or less and for many tuffs to within 0.1 m.y. or less. The sequence and ages of tuffs established in this study provide insights into the evolution of the northern Basin and Range basins and patterns of explosive volcanism in coeval volcanic centers, and contribute to the development of a high-resolution stratigraphy and chronology of coeval sedimentary deposits throughout the western United States. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| January 01, 1984 New K-Ar dates from basalts and the evolution of the southern Rio Grande rift W. R. SEAGER; W. R. SEAGER 1Earth Science Department, New Mexico State University, Las Cruces, New Mexico 88003 Search for other works by this author on: GSW Google Scholar M. SHAFIQULLAH; M. SHAFIQULLAH 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar J. W. HAWLEY; J. W. HAWLEY 3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar R. F. MARVIN R. F. MARVIN 4U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information W. R. SEAGER 1Earth Science Department, New Mexico State University, Las Cruces, New Mexico 88003 M. SHAFIQULLAH 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721 J. W. HAWLEY 3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 R. F. MARVIN 4U.S. Geological Survey, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1984) 95 (1): 87–99. https://doi.org/10.1130/0016-7606(1984)95<87:NKDFBA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation W. R. SEAGER, M. SHAFIQULLAH, J. W. HAWLEY, R. F. MARVIN; New K-Ar dates from basalts and the evolution of the southern Rio Grande rift. GSA Bulletin 1984;; 95 (1): 87–99. doi: https://doi.org/10.1130/0016-7606(1984)95<87:NKDFBA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract In the southern Rio Grande rift, two extensional regimes of different origin (but transitional with each other through the Miocene) can be interpreted from structures and rocks formed within the past 28 to 29 m.y. The earlier regime, which began about 28 to 29 m.y. B.P., is characterized by emplacement of "basaltic andesite" flows with relatively high strontium isotope ratios; formation of broad, relatively deep, northwest-trending basins; and incipient uplift of some of the region's fault-block mountains. This regime appears to have developed in a back-arc setting, perhaps behind a rapidly steepening slab and a westward-sweeping arc system.The younger episode seemingly represents a renewal or acceleration of block faulting and volcanism during the latest Miocene and Pliocene, 9 to 3 m.y. B.P., after a long transitional period during the early and mid-Miocene when volcanism was absent and tectonism was less vigorous. The latest Miocene-Pliocene episode produced the modern northerly-trending rift basins and uplifts, regional uplift of the rift 1 to 2 km above sea level, and renewal of volcanism, this time dominated by relatively primitive alkali-olivine basalt. New basalt dates reveal that in the southern rift, modern ranges and basins were almost fully developed and that near-modern drainage ways were established across uplifts into bolsons by about 5.0 m.y. B.P. An ancestral Rio Grande had extended itself southward into the southern rift by 3 to 4 m.y. B.P., and the river entrenched itself into its modern valley between 0.7 and 0.5 m.y. B.P.Horst-graben development of the southern Basin and Range province, as well as associated basaltic volcanism, swept progressively eastward from southeastern California in the past 20 m.y., culminating in formation of the Rio Grande rift and other fault-block terrane in west Texas, New Mexico, and northern Chihuahua in the latest Miocene and Pliocene. Late Quaternary Basin and Range fault scarps increase in density eastward, which also suggests that more easterly parts of the province are youngest. These relationships support a previous model of an eastward-expanding, slab-free triangle (related to growth of the San Andreas transform), through which mantle upwelling triggers eastward-younging patterns of tectonism, volcanism, and uplift and promotes lithospheric thinning and increased heat flow. Across most of the southern Basin and Range and Rio Grande rift, the horst-graben structures related to growth of this triangle are superimposed on somewhat older (late Oligocene-middle Miocene) extensional terrane that appears to have formed in a back-arc or arc setting. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abstract Research on the Precambrian basement of North America over the past two decades has shown that Archean and earliest Proterozoic evolution culminated in suturing of Archean cratonic elements and pre-1.80-Ga Proterozoic terranes to form the Canadian Shield at about 1.80 Ga (Hoffman, 1988,1989a, b). We will refer to this part of Laurentia as the Hudsonian craton (Fig. 1) because it was fused together about 1.80 to 1.85 Ga during the Trans-Hudson and Penokean orogenies (Hoffman, 1988). The Hudsonian craton, including its extensions into the United States (Chapters 2 and 3, this volume), formed the foreland against which 1.8- to 1.6-Ga continental growth occurred, forming the larger Laurentia (Hoffman, 1989a, b). Geologic and geochronologic studies over the past three decades have shown that most of the Precambrian in the United States south of the Hudsonian craton and west of the Grenville province (Chapter 5) consists of a broad northeast to east-northeast-trending zone of orogenic provinces that formed between 1.8 and 1.6 Ga. This zone, including extensions into eastern Canada, comprises or hosts most rock units of this age in North America as well as extensive suites of 1.35- to 1.50-Ga granite and rhyolite. This addition to the Hudsonian Craton is referred to in this chapter as the Transcontinental Proterozoic provinces (Fig. 1); the plural form is used to denote the composite nature of this broad region. The Transcontinental Proterozoic provinces consist of many distinct lithotectonic entities that can be defined on the basis of regional lithology, regional structure, U-Pb ages from zircons, Sr-Nd-Pb isotopic signatures, and regional geophysical anomalies.

Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO 2 ‐rich gas (CO 2 /S total &gt; 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur‐rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8–10 km deep, whereas the shallow magmatic gas source is at ~3–5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H 2 S/SO 2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (&gt;3000 T/d SO 2 and H 2 S/SO 2 &gt; 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H 2 S/SO 2 &lt; 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high‐temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.

Research Article| February 01, 2003 Controls on architecture of the Late Cretaceous to Cenozoic southern Middle Magdalena Valley Basin, Colombia Elías Gómez; Elías Gómez 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Search for other works by this author on: GSW Google Scholar Teresa E. Jordan; Teresa E. Jordan 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Search for other works by this author on: GSW Google Scholar Richard W. Allmendinger; Richard W. Allmendinger 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Search for other works by this author on: GSW Google Scholar Kerry Hegarty; Kerry Hegarty 2Geotrack International, 37 Melville Road, Brunswick West, Victoria 3055, Australia Search for other works by this author on: GSW Google Scholar Shari Kelley; Shari Kelley 3New Mexico Tech, Department of Earth and Environmental Sciences, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Matthew Heizler Matthew Heizler 4New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Elías Gómez 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Teresa E. Jordan 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Richard W. Allmendinger 1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Kerry Hegarty 2Geotrack International, 37 Melville Road, Brunswick West, Victoria 3055, Australia Shari Kelley 3New Mexico Tech, Department of Earth and Environmental Sciences, Socorro, New Mexico 87801, USA Matthew Heizler 4New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Publisher: Geological Society of America Received: 09 Jul 2001 Revision Received: 09 May 2002 Accepted: 13 May 2002 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (2): 131–147. https://doi.org/10.1130/0016-7606(2003)115<0131:COAOTL>2.0.CO;2 Article history Received: 09 Jul 2001 Revision Received: 09 May 2002 Accepted: 13 May 2002 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Elías Gómez, Teresa E. Jordan, Richard W. Allmendinger, Kerry Hegarty, Shari Kelley, Matthew Heizler; Controls on architecture of the Late Cretaceous to Cenozoic southern Middle Magdalena Valley Basin, Colombia. GSA Bulletin 2003;; 115 (2): 131–147. doi: https://doi.org/10.1130/0016-7606(2003)115<0131:COAOTL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Maastrichtian–Cenozoic southern Middle Magdalena Valley Basin of Colombia contains a unique record of unconformities, strata, and structure, from which we extract the histories of exhumation of the Central Cordillera, to the west, and evolution of the Eastern Cordillera fold-and-thrust belt, to the east. This study integrates field-based analyses of stratigraphy, laboratory analyses of provenance, fission-track thermochronology, vitrinite-reflectance data, volcanic-ash geochronology, and studies of synorogenic geometries and structure displayed in seismic data. A major unconformity, the Middle Magdalena Valley unconformity, formed by eastward migration of Central Cordillera uplift during Late Cretaceous to early Eocene time, which transformed a Maastrichtian marine basin into a Paleocene depositional piedmont area. This transformation is recorded by a coarsening-upward sequence of marine shales to alluvial-fan conglomerates, which was partly eroded during further early Eocene propagation of Central Cordillera deformation. Cessation of this phase of uplift led to formation of a pediment surface, the Middle Magdalena Valley unconformity, which was buried by westward-onlapping middle Eocene to Neogene alluvial deposits. Middle Eocene to Neogene facies, paleoflow, and unconformities were controlled by Eastern Cordillera deformation. In the Eastern Cordillera foothills, growth strata and thermal history reveal two phases of folding of middle Eocene–Oligocene and late Miocene ages, prior to intense Pliocene–Pleistocene uplift. Two unconformities of early late Miocene and Pliocene–Pleistocene ages occur to the west of the Eastern Cordillera and record flexural tilting related to episodes of Eastern Cordillera loading. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The exposed top of the conduit system at Mount Erebus Volcano, Ross Island, Antarctica, is a convecting lava (magma) lake hosting Strombolian eruptions caused by the explosive decompression of large (up to 5 m radius) gas slugs. Short‐period (SP; f ≥1 Hz) seismoacoustic eruption seismograms are accompanied by oscillatory very long period (VLP) signals observed in the near field by broadband seismometers 0.7 to 2.5 km from the lava lake. A variable VLP onset, preceding eruptions by several seconds, is followed by a repeatable VLP coda that persists for several minutes until the lava lake recovers to its preeruptive level. VLP signals are dominated by distinct decaying nonharmonic modes, the largest at periods of 20.7, 11.3, and 7.8 s, with respective source Q values of approximately 11, 18, and 4. Particle motions indicate a temporally evolving source producing increasingly vertical posteruptive displacements as the signal decays. VLP scalar moments, up to ∼5×10 11 N m, exceed SP moments by an order of magnitude or more, suggesting distinct, though genetically related, SP and VLP source mechanisms. We conclude that VLP signals arise from excitation of a quasi‐linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent, eruption, and magma recharge. VLP signal stability across hundreds of eruptions spanning 5 years, the persistence of the lava lake, and the rapid posteruptive lava lake recovery indicate a stable near‐summit magma reservoir and VLP source process.

Research Article| July 01, 2001 Upper Cenozoic chronostratigraphy of the southwestern Amazon Basin Kenneth E. Campbell, Jr.; Kenneth E. Campbell, Jr. 1Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007, USA Search for other works by this author on: GSW Google Scholar Matt Heizler; Matt Heizler 2New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Carl D. Frailey; Carl D. Frailey 3Johnson County Community College, Overland Park, Kansas 66210, USA Search for other works by this author on: GSW Google Scholar Lidia Romero-Pittman; Lidia Romero-Pittman 4Instituto Geológico, Minero y Metalúrgico (INGEMMET), San Borja, Apartado 889, Lima 41, Peru Search for other works by this author on: GSW Google Scholar Donald R. Prothero Donald R. Prothero 5Department of Geology, Occidental College, Los Angeles, California 90041, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kenneth E. Campbell, Jr. 1Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007, USA Matt Heizler 2New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Carl D. Frailey 3Johnson County Community College, Overland Park, Kansas 66210, USA Lidia Romero-Pittman 4Instituto Geológico, Minero y Metalúrgico (INGEMMET), San Borja, Apartado 889, Lima 41, Peru Donald R. Prothero 5Department of Geology, Occidental College, Los Angeles, California 90041, USA Publisher: Geological Society of America Received: 03 Nov 2000 Revision Received: 01 Mar 2001 Accepted: 09 Mar 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2001) 29 (7): 595–598. https://doi.org/10.1130/0091-7613(2001)029<0595:UCCOTS>2.0.CO;2 Article history Received: 03 Nov 2000 Revision Received: 01 Mar 2001 Accepted: 09 Mar 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Kenneth E. Campbell, Matt Heizler, Carl D. Frailey, Lidia Romero-Pittman, Donald R. Prothero; Upper Cenozoic chronostratigraphy of the southwestern Amazon Basin. Geology 2001;; 29 (7): 595–598. doi: https://doi.org/10.1130/0091-7613(2001)029<0595:UCCOTS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The lack of numerical age dates for upper Cenozoic strata of the Amazon Basin has prevented resolution of its geologic history and accurate dating of important paleofaunas. Here we present results of magnetostratigraphy and 40Ar/39Ar dating of two volcanic ash deposits from the Madre de Dios Formation of eastern Peru. The two ash ages, 9.01 ± 0.28 Ma and 3.12 ± 0.02 Ma, provide the first numerical age data necessary for accurate interpretation of late Tertiary sedimentation in Amazonia and establish approximate time constraints for the last major cycle of Cenozoic deposition within the southwestern Amazon Basin. The older ash age also provides a minimum age for numerous Amazonian paleofaunas, which allows a more definitive correlation of these paleofaunas with those in other regions of South America. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| March 01, 2005 Timing and development of the Heise volcanic field, Snake River Plain, Idaho, western USA Lisa A. Morgan; Lisa A. Morgan 1U.S. Geological Survey, Federal Center, Box 25046, MS 966, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar William C. McIntosh William C. McIntosh 2New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2005) 117 (3-4): 288–306. https://doi.org/10.1130/B25519.1 Article history received: 07 Nov 2003 rev-recd: 29 Apr 2004 accepted: 10 Jun 2004 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Lisa A. Morgan, William C. McIntosh; Timing and development of the Heise volcanic field, Snake River Plain, Idaho, western USA. GSA Bulletin 2005;; 117 (3-4): 288–306. doi: https://doi.org/10.1130/B25519.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Snake River Plain (SRP) developed over the last 16 Ma as a bimodal volcanic province in response to the southwest movement of the North American plate over a fixed melting anomaly. Volcanism along the SRP is dominated by eruptions of explosive high-silica rhyolites and represents some of the largest eruptions known. Basaltic eruptions represent the final stages of volcanism, forming a thin cap above voluminous rhyolitic deposits. Volcanism progressed, generally from west to east, along the plain episodically in successive volcanic fields comprised of nested caldera complexes with major caldera-forming eruptions within a particular field separated by ca. 0.5–1 Ma, similar to, and in continuation with, the present-day Yellowstone Plateau volcanic field. Passage of the North American plate over the melting anomaly at a particular point in time and space was accompanied by uplift, regional tectonism, massive explosive eruptions, and caldera subsidence, and followed by basaltic volcanism and general subsidence.The Heise volcanic field in the eastern SRP, Idaho, represents an adjacent and slightly older field immediately to the southwest of the Yellowstone Plateau volcanic field. Five large-volume (>0.5 km3) rhyolitic ignimbrites constitute a time-stratigraphic framework of late Miocene to early Pliocene volcanism for the study region. Field relations and high-precision 40Ar/39Ar age determinations establish that four of these regional ignimbrites were erupted from the Heise volcanic field and form the framework of the Heise Group. These are the Blacktail Creek Tuff (6.62 ± 0.03 Ma), Walcott Tuff (6.27 ± 0.04 Ma), Conant Creek Tuff (5.51 ± 0.13 Ma), and Kilgore Tuff (4.45 ± 0.05 Ma; all errors reported at ± 2σ). The fifth widespread ignimbrite in the region is the Arbon Valley Tuff Member of the Starlight Formation (10.21 ± 0.03 Ma), which erupted from a caldera source outside of the Heise volcanic field. These results establish the Conant Creek Tuff as a distinct and widespread ignimbrite in the Heise volcanic field, eliminating former confusion resulting from previous discordant K/Ar and fission-track dates.New 40Ar/39Ar determinations, when combined with geochemical, lithologic, geophysical, and field data, define the volcanic and tectonic history of the Heise volcanic field and surrounding areas. Volcanic units erupted from the Heise volcanic field also provide temporal control for tectonic events associated with late Cenozoic extension in the Snake Range and with uplift of the Teton Range, Wyoming. In the Snake Range, movement of large (≥0.10 km3) slide blocks of Mississippian limestone exposed 50 km to the east of the Heise field occurred between 6.3 and 5.5 Ma and may have been catastrophically triggered by the caldera eruption of the 5.51 ± 0.13-Ma Conant Creek Tuff. This slide block movement of ∼300 vertical meters indicates that the Snake Range had significant relief by at least 5.5 Ma. In Jackson Hole, the distribution of outflow facies of the 4.45 ± 0.05-Ma Kilgore Tuff related to eruption from the Kilgore caldera in the Heise volcanic field on the eastern SRP indicates that the northern Teton Range was not a significant topographic feature at this time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abstract The Holocene portion of the Siple Dome (Antarctica) ice core was dated by interpreting the electrical, visual and chemical properties of the core. The data were interpreted manually and with a computer algorithm. The algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the GISP2 (Greenland Ice Sheet Project 2) ice core, 10 Be stratigraphic ties to the dendrochronology 14 C record and the dated volcanic stratigraphy. The algorithm interpretation is more consistent and better quantified than the tedious and subjective manual interpretation.

Research Article| August 01, 1993 Architecture of the Sierra Ladrones Formation, central New Mexico: Depositional controls on the permeability correlation structure J. MATTHEW DAVIS; J. MATTHEW DAVIS 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar RUTH C. LOHMANN; RUTH C. LOHMANN 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar FRED M. PHILLIPS; FRED M. PHILLIPS 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar JOHN L. WILSON; JOHN L. WILSON 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar DAVID W. LOVE DAVID W. LOVE 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar Author and Article Information J. MATTHEW DAVIS 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 RUTH C. LOHMANN 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 FRED M. PHILLIPS 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 JOHN L. WILSON 1Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 DAVID W. LOVE 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1993) 105 (8): 998–1007. https://doi.org/10.1130/0016-7606(1993)105<0998:AOTSLF>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation J. MATTHEW DAVIS, RUTH C. LOHMANN, FRED M. PHILLIPS, JOHN L. WILSON, DAVID W. LOVE; Architecture of the Sierra Ladrones Formation, central New Mexico: Depositional controls on the permeability correlation structure. GSA Bulletin 1993;; 105 (8): 998–1007. doi: https://doi.org/10.1130/0016-7606(1993)105<0998:AOTSLF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Statistical models of hydrogeological heterogeneity are often used in aquifer and reservoir characterization. The number of data required to estimate objectively the spatial correlation structure of permeability, however, is often prohibitive. The objective of this study was to develop a better understanding of how information about depositional processes can be used to characterize hydrogeological heterogeneity. An outcrop of the fluvial/interfluvial Sierra Ladrones Formation of New Mexico was studied for this purpose. On the basis of previous studies of paleogeography and our own field observations, deposits of the Sierra Ladrones Formation are interpreted as marginal ancestral Rio Grande flood-plain and tributary deposits. Architectural elements were mapped over a 0.16-km2 peninsular outcrop of Pliocene-Pleistocene deposits of the central Albuquerque Basin. Geostatistical analysis of the architectural-element map data indicates non-orthogonal anisotropy in the horizontal direction. The orientations of the strongest (N30°W) and weakest (N90°E) correlation correspond to the orientation of the tributary system and the ancestral Rio Grande flood plain, respectively. In the vertical direction, the correlation structure exhibits exponential behavior corresponding to the average-element thicknesses. The results demonstrate that information about depositional environment can be used to help to quantify statistically subsurface heterogeneity. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

An 40Ar / 39Ar age of 451Ma determined for lavas from northern Saipan confirms that these high-silica rhyolites erupted during the ‘proto-arc ’ stage of volcanism in the Izu^Bonin^Mariana system, which is characterized elsewhere by eruption of boninitic lavas. Incompatible trace element concentrations and Sr, Hf, Nd, and Pb isotope ratios for these rhyolites are transitional between those of c. 48Ma boninitic lavas and post-38 Ma ‘first-arc ’ andesites and dacites from Saipan and Rota that have typical subduction-related compositions.These transitional compositions are modeled by crystal fractionation of parental tholeiitic basalt combined with assimila-tion of young boninitic crust. A second stage of Rayleigh fractiona-tion in the upper crust is required by SiO2 concentrations that exceed 77 wt % and near-zero compatible element concentrations. First-arc magma compositions are consistent with fractionation of basalt and assimilation of crust similar in composition to the first-arc magmas

When compared to a database of modern foliar physiognomy and climate, the physiognomy of a new collection of dicotyledonous leaves from the 10.66±0.06 Ma Jakokkota flora, Bolivian Altiplano, implies a mean annual temperature (MAT) of 18.6–21.0±2.5°C. Similarly, a literature-derived sample of the early-middle Miocene Potosı́flora, Cordillera Oriental, implies a MAT of 21.5–21.7±2.1°C. We estimate that both floras experienced a growing season precipitation of 50±40 cm. The paleoclimate thus appears considerably warmer than the current highland climate, with MATs of 8–9°C; the paleoprecipitation is indistinguishable from modern levels. A comparison of the Miocene MATs with the modern MATs, with the effects of latitudinal continental drift and global climate change subtracted, suggests that the Jakokkota flora grew at an elevation of 590–1610±1000 m, and the Potosı́flora grew at an elevation of 0–1320±1000 m. Both paleoelevation estimates are significantly lower than the present elevations of 3940 and 4300 m, respectively, requiring a substantial component of Andean uplift since 10.7 Ma. This uplift history is consistent with two-stage tectonic models of Andean orogeny. La fisiognomı́a de una nueva colección de hojas dicotiledoneas de la flora Jakokkota, Altiplano de Bolivia, de 10.66±0.06 Ma de edad, implica un promedio anual de temperatura (PAT) de 18.6–21.0±2.5°C, si la compara a un base de datos de fisiognomı́a moderna y el clima. Similarmente, una muestra derivada de la literatura de la flora Potosı́, Cordillera Oriental, de edad Mioceno temprano o medio, implica un PAT de 21.5–21.7±2.1°C. Estimamos que las dos floras experimentaron una precipitación durante la estación de crecimiento de las plantas de 50±40 cm. Entonces, parece que el paleoclima era mas caliente que el clima actual de terreno montañoso, con PATs de 8–9°C; la paleoprecipitación no era muy diferente de los niveles actuales. Una comparación de los PATs Miocenos con los PATs modernos, con los efectos de la deriva de los continentes y el cambio global de clima sustraidos, sugiere que la flora Jakokkota crecióa una altura de 590–1610±1000 m, y la flora Potosı́crecióa una altura de 0–1320±1000 m. Las dos estimaciones son significativamente mas bajas que las alturas actuales de 3940 y 4300 m, respectativamente, requiriendo un componente substancial de solevantamiento desde 10.7 Ma. Esta historia de solevantamiento estáde acuerdo con los modelos tectonicos de la orogenia Andina de dos etapas.

Abstract Soils at some prehistoric agricultural sites in New Mexico were investigated to study agricultural adaptation in a semi‐arid mountainous region, evaluate soil productivity, and determine long‐term effects of agriculture on the physical environment. The sites, farmed during the Mimbres Classic period (about AD 1000 to 1150), occur within certain geomorphic settings, implying a strategy to optimize climatic and hydrologic conditions for runoff agriculture. The landscape was modified by terracing, which probably served to reduce runoff velocity, increase soil moisture, and thicken the naturally thin A horizon. Comparisons of prehistoric agricultural soils with nearby, similarly developed, uncultivated soils indicate significant differences in soil properties over eight centuries after farming ceased. Soil changes resulting from the prehistoric agriculture were mostly degradative, including accelerated erosion, compaction, and reduced concentrations of nutrients such as nitrogen and phosphorus. Despite soil degradation, study of maize growth in the soils suggests favourable productivity with fertilization and improved soil conservation.

Research Article| July 01, 2008 Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from? Peter W. Lipman; Peter W. Lipman † 1MS 910, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA †E-mail: plipman@usgs.gov Search for other works by this author on: GSW Google Scholar William C. McIntosh William C. McIntosh 2New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2008) 120 (7-8): 771–795. https://doi.org/10.1130/B26330.1 Article history received: 20 Sep 2007 rev-recd: 26 Dec 2007 accepted: 12 Jan 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter W. Lipman, William C. McIntosh; Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from?. GSA Bulletin 2008;; 120 (7-8): 771–795. doi: https://doi.org/10.1130/B26330.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The northeastern San Juan Mountains, the least studied portion of this well-known segment of the Southern Rocky Mountains Volcanic Field are the site of several newly identified and reinterpreted ignimbrite calderas. These calderas document some unique eruptive features not described before from large volcanic systems elsewhere, as based on recent mapping, petrologic data, and a large array of newly determined high-precision, laser-fusion 40Ar/39Ar ages (140 samples). Tightly grouped sanidine ages document exceptionally brief durations of 50–100 k.y. or less for individual Oligocene caldera cycles; biotite ages are more variable and commonly as much as several hundred k.y. older than sanidine from the same volcanic unit. A previously unknown ignimbrite caldera at North Pass, along the Continental Divide in the Cochetopa Hills, was the source of the newly distinguished 32.25-Ma Saguache Creek Tuff (~400–500 km3). This regionally distinctive crystal-poor alkalic rhyolite helps fill an apparent gap in the southwestward migration from older explosive activity, from calderas along the N-S Sawatch locus in central Colorado (youngest, Bonanza Tuff at 33.2 Ma), to the culmination of Tertiary volcanism in the San Juan region, where large-volume ignimbrite eruptions started at ca. 29.5 Ma and peaked with the enormous Fish Canyon Tuff (5000 km3) at 28.0 Ma. The entire North Pass cycle, including caldera-forming Saguache Creek Tuff, thick caldera-filling lavas, and a smaller volume late tuff sheet, is tightly bracketed at 32.25–32.17 Ma. No large ignimbrites were erupted in the interval 32–29 Ma, but a previously unmapped cluster of dacite-rhyolite lava flows and small tuffs, areally associated with a newly recognized intermediate-composition intrusion 5 × 10 km across (largest subvolcanic intrusion in San Juan region) centered 15 km north of the North Pass caldera, marks a near- caldera-size silicic system active at 29.8 Ma. In contrast to the completely filled North Pass caldera that has little surviving topographic expression, no voluminous tuffs vented directly from the adjacent Cochetopa Park caldera, which is morphologically beautifully preserved. Instead, Cochetopa Park subsided passively as the >500 km3 Nelson Mountain Tuff vented at 26.9 Ma from an "underfit" caldera (youngest of the San Luis complex) 30 km to the SW. Three separate regional ignimbrites were erupted sequentially from San Luis calderas within an interval of less than 50–100 k.y., a more rapid recurrence rate for large explosive eruptions than previously documented elsewhere. In eruptive processes, volcanic compositions, areal extent, duration of activity, and magmatic production rates and volumes, the Southern Rocky Mountains Volcanic Field represents present-day erosional remnants of a composite volcanic field, comparable to younger ignimbrite terranes of the Central Andes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The 40Ar/39Ar ages of 10 magmatic and hydrothermal micas from the Grasberg Igneous Complex range from 3.33 ± 0.12 to 3.01 ± 0.06 Ma. The ages of intrusive rocks and the paragenetic relationships between intrusive rocks and hydrothermal alteration and mineralization indicate that the Grasberg Igneous Complex formed during several cycles of intrusion and hydrothermal alteration. These include the Dalam and Main Grasberg intrusion and alteration cycles (3.33 ± 0.12–3.19 ± 0.05 Ma), a Kali intrusion and alteration cycle (3.16 ± 0.06–3.06 ± 0.03 Ma), and a post-Kali intrusion and Grasberg mineralization cycle (3.06 ± 0.03 and 3.01 ± 0.06 Ma). Each cycle of intrusion and alteration appears to have lasted around 0.1 m.y. or less and indicates that the huge size and high grade of Grasberg did not result from an unusually prolonged period of hydrothermal activity. A sample of phlogopite predating magnetite from the Kucing Liar Cu-Au deposit adjacent to Grasberg has an age of 3.41 ± 0.03 Ma. This is within error of the age of a Dalam intrusive rock from the Grasberg Igneous Complex and suggests formation of the calc-silicate skarn part of Kucing Liar at an early stage in the development of the complex. The ages of the equigranular diorite from the Ertsberg intrusion (2.67 ± 0.03 Ma), phlogopite from an endoskarn vein in the intrusion (2.71 ± 0.04 Ma), and phlogopite from the Ertsberg Cu-Au deposit (2.59 ± 0.15 Ma) indicate that intrusion and alteration and/or mineralization at Ertsberg are younger than the intrusions and mineralization in the Grasberg Igneous Complex. The Ertsberg therefore represents at least one additional cycle of approximately 0.1 m.y. of intrusion and alteration and/or mineralization in the district. The intrusions that make up the Grasberg Igneous Complex and Ertsberg and the hydrothermal fluids responsible for much of the alteration and mineralization appear to have been derived from a deeper level magma chamber. The youngest dated intrusive phase in the Grasberg Igneous Complex is a post-Kali diorite dike that is more basic than the preceding Kali quartz monzodiorite intrusions. This, together with the presence of mafic xenoliths in the Kali and Ertsberg intrusions, suggests that the magma chamber from which the intrusions and fluids were sourced was periodically replenished by basic magma. This process may also have triggered release of magma to form the shallow-level intrusions now exposed at the surface. The basic magmas also may have contributed components including fluids, metals, and/or sulfur to the Cu-Au deposits in the Ertsberg district.

Research Article| October 01, 1999 Late Quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar-dated time horizons in West Antarctic ice and marine cores T. I. Wilch; T. I. Wilch 1Department of Geological Sciences, Albion College, Albion, Michigan 49224 Search for other works by this author on: GSW Google Scholar W. C. McIntosh; W. C. McIntosh 2Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar N. W. Dunbar N. W. Dunbar 3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1999) 111 (10): 1563–1580. https://doi.org/10.1130/0016-7606(1999)111<1563:LQVAIM>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. I. Wilch, W. C. McIntosh, N. W. Dunbar; Late Quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar-dated time horizons in West Antarctic ice and marine cores. GSA Bulletin 1999;; 111 (10): 1563–1580. doi: https://doi.org/10.1130/0016-7606(1999)111<1563:LQVAIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Late Quaternary volcanic activity at three major alkaline composite volcanoes in Marie Byrd Land, West Antarctica, is dominated by explosive eruptions, many capable of depositing ash layers as regional time-stratigraphic horizons in the West Antarctic Ice Sheet and in Southern Ocean marine sediments. A total of 20 eruptions at Mount Berlin, Mount Takahe, and Mount Siple are recorded in lava and welded and nonwelded pyroclastic fall deposits, mostly peralkaline trachyte in composition. The eruptions, dated by the 40Ar/39Ar laser-fusion and furnace step-heating methods, range in age from 571 to 8.2 ka.Tephra from these 40Ar/39Ar-dated Marie Byrd Land eruptions are identified by geochemical fingerprinting in the 1968 Byrd Station ice core. The 74 ka ice-core record contained abundant coarse ash layers, with model ice-flow ages ranging from 7.5 to 40 ka, all of which were previously geochemically correlated to the Mount Takahe volcano. We identify a one-to-one geochemical and age correlation of the youngest (ca. 7.5 ka) tephra layer in the Byrd ice core to an 8.2 ± 5.4 ka (2sigma uncertainty) pyroclastic deposit at Mount Takahe. We infer that the 20–30 ka tephra layers in the Byrd ice core actually were erupted from Mount Berlin, on the basis of age and geochemical similarities. If products of these youngest, as well as the older 40Ar/39Ar-dated eruptions are identified by geochemical fingerprinting in future ice and marine cores, they will provide the cores with independently dated time horizons.More than 12 40Ar/39Ar-dated tephra layers, exposed in bare ice on the summit ice cap of Mount Moulton, 30 km from their inferred source at Mount Berlin, range in age from 492 to 15 ka. These englacial tephra layers provide a minimum age of 492 ka for the oldest isotopically dated ice in West Antarctica. This well-dated section of locally derived glacial ice contains a potential "horizontal ice core" record of paleoclimate that extends back through several glacial-interglacial cycles. The coarse grain size and density of the englacial tephra (mean diameters 17–18 mm, densities 540–780 kg/m3), combined with their distance from source, indicate derivation from highly explosive Plinian eruptions of Mount Berlin. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| May 01, 1996 Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado Kathryn M. Gregory; Kathryn M. Gregory 1Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964-8000 Search for other works by this author on: GSW Google Scholar W. C. McIntosh W. C. McIntosh 2New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1996) 108 (5): 545–561. https://doi.org/10.1130/0016-7606(1996)108<0545:PAPOTO>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Kathryn M. Gregory, W. C. McIntosh; Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado. GSA Bulletin 1996;; 108 (5): 545–561. doi: https://doi.org/10.1130/0016-7606(1996)108<0545:PAPOTO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Angiosperm leaves from the Oligocene Pitch-Pinnacle flora, which grew between 32.9 and 29 Ma, are described for the first time. This flora is especially interesting because it grew in a tectonically active region around the time of the precipitous Oligocene temperature drop and thus provides important constraints on paleoclimate and paleoelevation. New multiple regression models are developed from the modern vegetation leaf physiognomy data set of J. A. Wolfe and, when applied to the Pitch-Pinnacle flora, suggest a mean annual temperature (MAT) of 12.7 ± 1.5°C, with cold month and warm month means of 4.5 ± 2.2°C and 20.4 ± 2.5°C, respectively, and a mean annual range of temperature of 18.5 ± 3.8°C. Growing season precipitation is estimated to have been 101 ± 16 cm, with this rain falling mostly during the nongrowing season. When the MAT estimate for the Pitch-Pinnacle flora is combined with MAT estimates for coeval floras from the coast, the implied elevation is either 2–3 km if the flora is pre-Oligocene deterioration, or around 1 km if post-deterioration. Paleodrainage reconstructions suggest the former, but more data are needed to resolve this issue. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The 40 Ar/ 39 Ar ages for rocks from the Valles caldera, New Mexico, imply that resurgent uplift of the caldera floor occurred within 27 ± 27 ka of caldera collapse. The structural resurgent dome of the Valles caldera was uplifted approximately 1000 m above the surrounding caldera floor during resurgence. The upper Bandelier Tuff, which yields an age of 1.256 ± 0.010 Ma (2 σ ; ages relative to Fish Canyon tuff sanidine at 28.02 Ma), is the lower constraint on the timing of resurgence. The oldest postcollapse ring fracture dome, Cerro del Medio, is the upper time constraint and yields an age of 1.229 ± 0.017 Ma for one of its oldest flow lobes. Therefore resurgent uplift probably occurred within 54 ka, at a minimum rate of 1.9 cm/yr. Sanidine phenocrysts from rhyolites of the postcollapse intracaldera Deer Canyon and Redondo Creek members yield 40 Ar/ 39 Ar single‐crystal laser fusion ages ranging from 1.229 ± 0.013 Ma to 1.283 ± 0.017 Ma (Deer Canyon Member; n = 8) and 1.208 ± 0.017 Ma to 1.239 ± 0.017 Ma (Redondo Creek Member; n = 4). With one exception from each unit, these ages are statistically indistinguishable from the upper Bandelier Tuff, indicating that eruption of these postcollapse rhyolites probably commenced shortly after caldera formation. Melt inclusion hosted excess argon was not found to have a measurable effect on the age of sanidine from the upper Bandelier Tuff or the Deer Canyon Member.

Research Article| July 01, 1992 Time-stratigraphic framework for the Eocene-Oligocene Mogollon-Datil volcanic field, southwest New Mexico WILLIAM C. McINTOSH; WILLIAM C. McINTOSH 1New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar CHARLES E. CHAPIN; CHARLES E. CHAPIN 1New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar JAMES C. RATTÉ; JAMES C. RATTÉ 2U.S. Geological Survey, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar JOHN F. SUTTER JOHN F. SUTTER 3U.S. Geological Survey, 981 National Center, Reston, Virginia 20222 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1992) 104 (7): 851–871. https://doi.org/10.1130/0016-7606(1992)104<0851:TSFFTE>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation WILLIAM C. McINTOSH, CHARLES E. CHAPIN, JAMES C. RATTÉ, JOHN F. SUTTER; Time-stratigraphic framework for the Eocene-Oligocene Mogollon-Datil volcanic field, southwest New Mexico. GSA Bulletin 1992;; 104 (7): 851–871. doi: https://doi.org/10.1130/0016-7606(1992)104<0851:TSFFTE>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A time-stratigraphic framework for discontinuously exposed regional ignimbrites in the Eocene-Oligocene Mogollon-Datil volcanic field has been established using correlations aided by 40Ar/39Ar age determinations and paleomagnetic analyses. 40Ar/39Ar age spectra from sanidine separates (25 regional ignimbrites, 85 samples, 97 spectra) yield well-defined plateau ages that are precise (within-sample and within-unit 1σ < ± 0.5%) and agree closely with independently established stratigraphic order. Paleomagnetic remanence directions (404 sites) from individual ignimbrite outflow sheets are generally vertically and horizontally uniform throughout facies ranging from thick (100-500 m), densely welded, proximal ignimbrites to thin (1.5-30 m), unwelded, distal fringes. Between-unit differences in paleomagnetic directions provide useful correlation criteria, particularly for units having ages too close to be resolved using 40Ar/39Ar dating.The Mogollon-Datil time-stratigraphic framework clarifies ignimbrite history and provides improved age control for intercalated lavas and sedimentary rocks. Ignimbrite activity was strongly episodic; outflow sheets were primarily erupted in four discrete pulses representing synchronized activity of two separate cauldron complexes. Activity in the southern complex began at 36.2 Ma near Las Cruces, New Mexico, and subsequently migrated 220 km northwest, culminating in the 28.0 Ma Bursum cauldron. Activity in the northern complex, located west of Socorro, New Mexico, underwent a less defined and more modest 40-km westward migration over its 32.0 to 24.3 Ma life span. The four pulses of ignimbrite activity were (1) 36.2-24.3 Ma, 12 major units, >1,500 km3 total volume; (2) 32.0-31.4 Ma, three major units, >1,500 km3 volume; (3) 29.1-27.4 Ma, nine major units, >6,000 km3; and (4) 24.3 Ma, one major unit. The third and largest ignimbrite pulse was accompanied by extensive rhyolitic dome and flow eruptions in the area between the two main cauldron complexes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.