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Leah E Morgan, Ph.D.

Leah Morgan is a Research Geologist with the Geology, Geophysics, and Geochemistry Science Center.

I joined the 40Ar/39Ar geochronology lab at the USGS in Denver, Colorado as a research geologist in 2015. I was previously a Marie Curie postdoctoral fellow at the Scottish Universities Environmental Research Center and at the Vrije Universiteit Amsterdam. I received a PhD from the University of California at Berkeley in 2009, and a BA from Carleton College in 2004. I was born and raised in Vermont.

I have worked on a range of applications and method development issues in 40Ar/39Ar geochronology. Applications have largely focused on questions in paleoanthropology and the geologic timescale. Method development projects include developing metrologically traceable systems for measuring absolute quantities of 40Ar and 40K, and the design of a mobile neutron source for the future in situ deployment of 40Ar/39Ar capabilities on planetary surfaces

USGS Service

  • 2020-present, USGS TRIGA Reactor Operating Committee
  • 2017-present, USGS Radiation Safety Committee
  • 2016-present, USGS Rocky Mountain Science Seminar Series Convener
  • 2018-2020 GGGSC Early Career Advisory Team, GGGSC

Professional Experience

  • 2015-present, Research Geologist, U.S. Geological Survey

  • 2014, Visiting Assistant Professor, Geology Department, Carleton College

  • 2011-2014, Marie Curie Postdoctoral Fellow, Scottish Universities Environmental Research Center, University of Glasgow, Scotland

  • 2009-2011, Marie Curie Postdoctoral Fellow, Vrije Universiteit Amsterdam, The Netherlands

Education and Certifications

  • Ph.D. Earth & Planetary Science, University of California at Berkeley, 2009

  • B.S. Geology, Carleton College, 2004

Affiliations and Memberships*

  • 2018-present, Affiliate Faculty, Colorado School of Mines, Golden, CO

  • 2021, co-Chair, Gordon Research Conference on Geochronology

  • 2019, vice-Chair, Gordon Research Conference on Geochronology

  • 2018-2019, Chair and Founder, Geochronology Division of the Geological Society of America

  • 2019-present, Advisory Member, Committee for the Stratigraphy and Chronology Commission, International Union for Quaternary Research

  • 2018-present, Steering Committee Member, EarthRates Research Coordination Network

Honors and Awards

  • 2019, USGS Superior Service Award

Science and Products

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USGS Geochron: A database of USGS geochronological and thermochronological data

The U.S. Geological Survey (USGS) has developed an updated geochronology database (USGS Geochron) to include geochronology summary and analytical data created or funded by the USGS.
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Geosciences and Environmental Change Science Center
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USGS Geochron: A database of USGS geochronological and thermochronological data

The U.S. Geological Survey (USGS) has developed an updated geochronology database (USGS Geochron) to include geochronology summary and analytical data created or funded by the USGS.
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large piece of equipment for argon extraction system and mass spectrometer

Argon Geochronology

This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology...
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center
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Argon Geochronology

This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology...
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Mt. Ouray, Colorado with aspen colors

Geologic Framework of the Intermountain West

The Geologic Framework of the Intermountain West project was launched with the goal of producing a new digital geologic map database and 3D geologic model of a transect from the Rio Grande rift to the Basin and Range, based on a synthesis of existing geologic maps with new targeted new mapping, subsurface data, and other data sets. This database will integrate disparate map data, resolve...
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Geosciences and Environmental Change Science Center
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Geologic Framework of the Intermountain West

The Geologic Framework of the Intermountain West project was launched with the goal of producing a new digital geologic map database and 3D geologic model of a transect from the Rio Grande rift to the Basin and Range, based on a synthesis of existing geologic maps with new targeted new mapping, subsurface data, and other data sets. This database will integrate disparate map data, resolve...
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Serving the U.S. Geological Survey’s geochronological data

Geochronological data provide essential information necessary for understanding the timing of geologic processes and events, as well as quantifying rates and timescales key to geologic mapping, mineral and energy resource and hazard assessments. The USGS’s National Geochronological Database (NGDB) contains over 30,000 radiometric ages, but no formal update has occurred in over 20 years. This proj
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Community for Data Integration (CDI)
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Serving the U.S. Geological Survey’s geochronological data

Geochronological data provide essential information necessary for understanding the timing of geologic processes and events, as well as quantifying rates and timescales key to geologic mapping, mineral and energy resource and hazard assessments. The USGS’s National Geochronological Database (NGDB) contains over 30,000 radiometric ages, but no formal update has occurred in over 20 years. This proj
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Filter Total Items: 24

Argon data for enriched MORB from the 8°20' N seamount chain

This dataset accompanies planned publication 'Near-Ridge Magmatism Constrained Using 40Ar/39Ar Dating of Enriched MORB from the 8°20' N Seamount Chain'. The Ar/Ar data are for samples that record the volcanic history of the area. The geochronology provides time constraints for the eruption of rocks studied in the manuscript. Samples were collected from the 8°20' N seamount chain by Molly Anderson
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Geology, Geophysics, and Geochemistry Science Center

Quetrupillán Volcanic Complex, southern Chile: Argon age data and Pb, Sr, and Nd isotopic data

This dataset accompanies planned publication 'Lava-ice interactions at late Pleistocene trachyte-basaltic andesite fissure eruptions, Quetrupillán Volcanic Complex (39°30′ S, 71°43′ W), southern Chile', as well as planned future publications on this volcanic complex. The Ar/Ar data and the Pb, Sr, and Nd data are for basalt and trachyte lava flows at Quetrupillán volcano. The Ar geochronology and
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

USGS Geochron: A Database of Geochronological and Thermochronological Dates and Data (ver. 2.0, September 2023)

USGS Geochron is a database of geochronological and thermochronological dates and data. The data set contains published ages, dates, analytical information, sample metadata including location, and source citations. The following analytical techniques are represented in the data set: 40Ar/39Ar, K-Ar, U-Th-Pb, Sm-Nd, Rb-Sr, Lu-Hf, fission track, and luminescence. This data set incorporates data prev
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Geosciences and Environmental Change Science Center

Database for the geologic map of the upper Santa Cruz River basin, southern Arizona

This digital publication contains the database, base maps, and style files used to build the geologic map of the upper Santa Cruz River basin in southern Arizona published in U.S. Geological Survey Scientific Investigations Map 3490 (Page and others, 2023). Shapefiles are also included for the user’s convenience. In the database, there are polygon features outlining the map units and data sources;
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Geosciences and Environmental Change Science Center

Argon data for HD-B1 intercalibration

This data release includes 40Ar/39Ar intercalibration data from the U.S. Geological Survey for neutron fluence monitors HD-B1 (Heidelberg biotite) and FCs (Fish Canyon sanidine). Potassium-bearing mineral grains were analyzed by argon geochronology at the U.S. Geological Survey Argon Geochronology Laboratory in Denver, Colorado. These data provide intercalibration information between the two fluen
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Santa Cruz Basin (ver. 1.1, November 2022)

This data release includes 40Ar/39Ar data from the U.S. Geological Survey for samples from the Santa Cruz Basin, Arizona. Mineral samples were collected by Kenzie Turner and William Page from the upper Santa Cruz Basin, Arizona. Potassium-bearing mineral grains were separated from the bulk sample and analyzed by argon geochronology at the U.S. Geological Survey Argon Geochronology Laboratory in De
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Hugub Area, Kesem-Kebena-Dulecha, Ethiopia

Tephra samples were collected by Leah Morgan (now at the U.S. Geological Survey (USGS)) from the Hugub Area, Kesem-Kebena-Dulecha, Afar, Ethiopia. Sanidine grains were separated from the bulk sample and analyzed by argon geochronology at the Scottish Universities Environmental Research Centre, Scotland. The data indicate that the age of the Hugub Bed, which is rich in archarological artifacts, is
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Klamath Mountains

This dataset accompanies planned publication '40Ar/39Ar geochronology of hydrothermal activity related to orogenic gold mineralization in the Klamath Mountains, California, U.S.A.'. The Ar/Ar data are for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Klamath Mountains
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Nepal

This dataset accompanies planned publication 'Determining fault geometry through the transport-parallel distribution of thermochronometer cooling ages'. The Ar/Ar data is for samples that record the thermal history of the area. The geochronology provides time constraints for the thermal histories studied in the manuscript. Samples were collected from Nepal, overseen by Nadine McQuarrie (University
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Amazon Craton

This dataset accompanies planned publication 'Genesis of early Neoproterozoic gold deposits, southwestern Amazon Craton, western Brazil'. The Ar/Ar data is for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Amazon Craton region, and collection was done by Rodrigo Prude
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Central Andes (Domeyko Range, Chile)

This dataset accompanies planned publication 'Gondwanan inheritance on the building of the western Central Andes (Domeyko Range, Chile): Structural and thermochronological approach (U-Pb and 40Ar-39Ar)'. The Ar/Ar data is for samples that record the sedimentation of the area. The geochronology provides time constraints for the sedimentation studied in the manuscript. Samples were collected from th
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Argon data for Yellow Pine

This dataset accompanies planned publication 'Timing of Hydrothermal Alteration and Au-Sb-W Mineralization, Stibnite-Yellow Pine District, Idaho'. The Ar/Ar data is for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Yellow Pine region, and collection was done by numero
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Geologic map and hydrogeologic investigations of the upper Santa Cruz River basin, southern Arizona

This report includes an updated geologic map and cross sections of the upper Santa Cruz River basin, southern Arizona. The map and cross sections describe the geometry, thickness, and structure of the Miocene to Holocene units which form the main aquifers in the basin. The report also includes results of new hydrogeologic studies including (1) mapping and defining depth to bedrock based on geophys
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Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center

Geologic map of the Poncha Pass area, Chaffee, Fremont, and Saguache Counties, Colorado

This report presents a 1:24,000-scale geologic map, cross sections, and descriptive and interpretative text for the Poncha Pass area in central Colorado. The map area is irregular in shape, covering all of one 7 ½' quadrangle (Poncha Pass) and parts of five others (Mount Ouray, Maysville, Salida West, Salida East, and Wellsville). The map boundaries were drawn to cover all of the “Poncha mountain
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National Cooperative Geologic Mapping Program, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center

Geologic map of the San Antonio Mountain area, northern New Mexico and southern Colorado

The geologic map of the San Antonio Mountain area in northern New Mexico and southern Colorado is located along the west-central part of the San Luis Valley. The San Luis Valley is the geomorphic expression of the San Luis Basin, an extensional basin associated with the northern Rio Grande rift. Deposits within the map area record volcanic, sedimentary, and tectonic processes over the last ~33 mil
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National Cooperative Geologic Mapping Program, Geology, Geophysics, and Geochemistry Science Center, Geosciences and Environmental Change Science Center
Filter Total Items: 29

Kesem-Kebena-Dulecha study area, Ethiopia

In 1988 and 1989, the Paleoanthropological Inventory of Ethiopia (PIE) field expedition discovered numerous localities of prehistoric significance across Ethiopia (WoldeGabriel et al., 1992). One of the regions surveyed by the Inventory team was the Dulecha administrative district (Gabi Rasu), Afar Zone (Fig. 1). The surveyed area (geographic reference: 9.407° N, 40.057° E) includes the watershed
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W. Henry Gilbert, V.B. Doronichev, L.V. Golovanova, Leah E. Morgan, Luis Nunez, Laura Rodriguez, Nohemi Sala, D. Cusimano, I. de Gaspar, Paul Mazza, N. Garcia
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Geology, Geophysics, and Geochemistry Science Center

Potassium-39-derived 36Ar production during fission-neutron irradiation and its effect on 40Ar/39Ar ages

Various interference reactions producing unwanted Ar isotopes from K, Ca, Cl and Ar require correction to satisfy the 40Ar/39Ar age equation. Using GEANT4, we design and build a model Cadmium Lined In Core Irradiation Tube (CLICIT) irradiation facility, as used in the Oregon State TRIGA Reactor (OSTR). We illustrate the complexity of the irradiation of geologic samples within this framework and de
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Jack N. Carter, Paul R. Renne, Leah E. Morgan
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Geology, Geophysics, and Geochemistry Science Center

Rare 40K decay with implications for fundamental physics and geochronology

Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts subatomic rare-event searches, nuclear structure theory, and estimated geological ages. A predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The KDK (potassium decay) collaboration reports strong evidence of this rare decay mode. A blinded analysis reveals a nonzero
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M. Stukel, L. Hariasz, P.C.F. Di Stefano, B.C. Rasco, K.P. Rykaczewski, N.T. Brewer, D.W. Stracener, Y. Liu, Z. Gai, C. Rouleau, J. B. Carter, J. Kostensalo, J. Suhonen, H. Davis, E.D. Lukosi, K.C. Goetz, R.K. Grzywacz, M. Mancuso, F. Petricca, A. Fijalkowska, M. Wolinska-Cichocka, J. Ninkovic, P. Lechner, R.B. Ickert, Leah E. Morgan, P.R. Renne, I. Yavin
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

First observation of the ground-state electron-capture of 40K

Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts estimated geological ages spanning billions of years, nuclear structure theory, and subatomic rare-event searches—including those for dark matter and neutrinoless double-beta decay. The decays of this long-lived isotope must be precisely known for its use as a geochronometer, and to account for its presence in lo
Authors
L. Hariasz, M. Stukel, P.C.F. Di Stefano, B.C. Rasco, K.P. Rykaczewski, N.T. Brewer, D.W. Stracener, Y. Liu, Z. Gai, C. Rouleau, J. B. Carter, J. Kostensalo, J. Suhonen, H. Davis, E.D. Lukosi, K.C. Goetz, R.K. Grzywacz, M. Mancuso, F. Petricca, A. Fijalkowska, M. Wolinska-Cichocka, J. Ninkovic, P. Lechner, R.B. Ickert, Leah E. Morgan, P.R. Renne, I. Yavin
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Constraints on near-ridge magmatism using 40Ar/39Ar geochronology of enriched MORB from the 8°20' N seamount chain

Our understanding of the spatial-temporal-compositional relationships between off-axis magmatism and mid-ocean ridge spreading centers is limited. Determining the 40Ar/39Ar ages of mid-ocean ridge basalt (MORB) lavas erupting near mid-ocean ridges (MOR) has been a challenge due to the characteristically low K2O contents in incompatible element-depleted normal MORB (NMORB). High-precision 40Ar/39Ar
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Molly Anderson, Michael Perfit, Leah E. Morgan, Daniel Fornari, Michael A. Cosca, V. Dorsey Wanless
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Geology, Geophysics, and Geochemistry Science Center

Community for data integration 2019 project report

The U.S. Geological Survey Community for Data Integration annually supports small projects focusing on data integration for interdisciplinary research, innovative data management, and demonstration of new technologies. This report provides a summary of the 14 projects supported in fiscal year 2019 and outlines their goals, activities, and accomplishments. Proposals in 2019 were encouraged to addre
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Amanda N. Liford, Caitlin M. Andrews, Aparna Bamzai, Joseph A. Bard, David S. Blehert, John B. Bradford, Wesley M. Daniel, Sara L. Caldwell Eldridge, Frank Engel, Jason A. Ferrante, Amy K. Gilmer, Margaret E. Hunter, Jeanne M. Jones, Benjamin Letcher, Frances L. Lightsom, Richard R. McDonald, Leah E. Morgan, Sasha C. Reed, Leslie Hsu
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Ecosystems Mission Area, Water Resources Mission Area, Science Synthesis, Analysis and Research Program, Science Analytics and Synthesis (SAS) Program, Volcano Hazards Program, Community for Data Integration (CDI), Geology, Geophysics, and Geochemistry Science Center, Geosciences and Environmental Change Science Center, National Wildlife Health Center, Oklahoma-Texas Water Science Center, Southwest Biological Science Center, Volcano Science Center, Western Geographic Science Center, Wetland and Aquatic Research Center , Woods Hole Coastal and Marine Science Center, Science Data Management

First principles calibration of 40Ar abundances in 40Ar/39Ar mineral neutron fluence monitors: Methodology and preliminary results

The accuracy and traceability of geochronometers are of vital importance to questions asked by many Earth scientists. The widely applied 40Ar/39Ar geochronometer relies on the co-irradiation of samples with neutron fluence monitors (reference materials) of known ages; the ages and uncertainties of these monitors are critical to our ability to apply this chronometer. Previously, first principles, a
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Leah E. Morgan, Brett Davidheiser-Kroll, Klaudia F. Kuiper, Darren F. Mark, Noah M. McLean, Jan Wijbrans
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Early Neoproterozoic gold deposits of the Alto Guaporé province, southwestern Amazon craton, western Brazil

The Alto Guaporé gold province, southwestern Amazon craton, contains gold deposits that have been mined since the beginning of the 18th century and these deposits, together, have modern-day, pre-mining gold resources of at least 1.8 Moz. The ore is associated with quartz vein systems along the southeastern part of the Aguapei belt, a ~35-km-wide and ~500-km-long, NNW-trending shear zone formed due
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Rodrigo Prudente de Melo, Marcos Aurélio Farias de Oliveira, Richard J. Goldfarb, Craig A. Johnson, Erin E. Marsh, Roberto Perez Xavier, Leandro Rocha de Oliveira, Leah E. Morgan
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Geology, Geophysics, and Geochemistry Science Center

Late Jurassic-Early Cretaceous orogenic gold mineralization in the Klamath Mountains, California: Constraints from 40Ar/39Ar dating of hydrothermal muscovite

The Klamath Mountains gold province is the second most important historical producer in California, having produced more than 7 Moz of gold from both lode and placer sources. Hydrothermal muscovite grains from gold-bearing veins provide the first 40Ar/39Ar age constraints indicative of a protracted period of mineralization in the Klamath Mountains. The data indicate that the window for orogenic go
Authors
Ryan D. Taylor, Leah E. Morgan, Fred Jourdan, Thomas Monecke, Erin E. Marsh, Richard J. Goldfarb
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Gondwanic inheritance on the building of the western Central Andes (Domeyko Range, Chile): Structural and thermochronological approach (U-Pb and 40Ar-39Ar)

Tectonics inheritance controls the evolution of many orogens. To unravel the role of the Gondwanan heritage (late Paleozoic to Triassic) over the building of the Central Andes in northern Chile (Domeyko Range), we performed detrital U‐Pb zircon and 40Ar/39Ar muscovite geochronology along with structural analyses (kinematics and structural balancing). 40Ar/39Ar dating of detrital muscovite reveals
Authors
Mauricio Espinoza, Veronica Oliveros, Paulina Vasquez, Laura Giambiagi, Leah E. Morgan, Rodrigo Gonzalez, Luigi Solari, Florencia Bechis
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Constraining central Himalayan (Nepal) fault geometry through integrated thermochronology and thermokinematic modeling

Constraining the subsurface structural geometry of the central Himalaya continues to prove difficult, even after the 2015 Gorkha earthquake and the resulting insights into the trajectory of the Main Himalayan thrust (MHT). To this end, we apply a thermokinematic model to evaluate four possible balanced cross section geometries based on three estimates of the MHT in central Nepal. We compare the ef
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Surydoy Ghoshal, Nadine McQuarrie, Delores Robinson, D.P. Adhikari, Leah E. Morgan, Todd A. Ehlers
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Natural Hazards Mission Area, Geology, Geophysics, and Geochemistry Science Center

Conditions and timing of high-grade metamorphism and ductile deformation of the southern segment of the Central Anatolian Ophiolite

Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern,
Authors
Molly S. Radwany, Leah E. Morgan, Donna L. Whitney
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Geology, Geophysics, and Geochemistry Science Center

Non-USGS Publications**

Mark, D.F., P.R. Renne, R. Dymock, V.C. Smith, J.I. SImon, L.E. Morgan, R.A. Staff, and B.S. Ellis, 2017. High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary. Quaternary Geochronology 39, 1-23, https://doi.org/10.1016/j.quageo.2017.01.002.
Morgan, L.E., 2017. 40Ar/39Ar and K-Ar Geochronology, in: A.S. Gilbert (ed.), Encyclopedia of Geoarchaeology. Encyclopedia of Earth Science Series. Springer, Dordrecht, https://doi.org/10.1007/978-1-4020-4409-0.
Morgan, L.E., 2015. Noble Gas Mass Spectrometry, in: W.J. Rink, and J.W. Thompson (eds.), Encyclopedia of Scientific Dating Methods. Encyclopedia of Earth Science Series. Springer, Dordrecht, https://doi.org/10.1007/978-94-007-6304-3_118.
Sahle, Y., L.E. Morgan, D.R. Braun, W.K. Hutchings, 2014. Chronological and behavioral contexts of the earliest Middle Stone Age in the Gademotta Formation, Main Ethiopian Rift, Quaternary International, v. 331, p. 6-19, https://doi.org/10.1016/j.quaint.2013.03.010.
Mark, D.F., M. Petraglia, V.C. Smith, L.E. Morgan, D.N. Barfod, B.S Ellis, N.J. Pearce, J.N. Pal, R. Korisettar, 2014. A high-precision 40Ar/39Ar age for the Young Toba Tuff and dating of ultra- distal tephra: forcing of Quaternary climate and implications for hominin occupation of India, Quaternary Geochronology, v. 21, p. 90-103, https://doi.org/10.1016/j.quageo.2012.12.004.
Sahle, Y., W.K. Hutchings, D.R. Braun, J.C. Sealy, L.E. Morgan, A. Negash, B. Atnafu, 2013. Earliest stone-tipped projectiles from the Ethiopian Rift date to >279,000 years ago. PLOS ONE, v. 8, no. 11, e78092, https://doi.org/10.1371/journal.pone.0078092.
Morgan, L.E., D.F. Mark, J. Imlach, D.N. Barfod, 2013. FCs-EK: A new sampling of the Fish Canyon tuff 40Ar/39Ar neutron flux monitor, in: Jourdan, F., Mark, D., and Verati, C. (eds.), Advances in 40Ar/39Ar Dating: from Archaeology to Planetary Sciences. Geological Society, London, Special Publications, 378, https://doi.org/10.1144/SP378.21.
Renne, P.R., A.L. Deino, F.J. Hilgen, K.F. Kuiper, D.F. Mark, W.S. Mitchell, L.E. Morgan, R. Mundil, J. Smit, 2013. Timescales of critical events around the Cretaceous-Paleogene boundary. Science, v. 339, p. 684-687, https://doi.org/10.1126/science.1230492.
Schoene, B., D.J. Condon, L.E. Morgan, N. McLean, 2013. Precision and accuracy in geochronology. Elements Magazine, v.9, no.1, p. 23-28, http://elementsmagazine.org/past-issue-archive/2013-volume-9/#February2013.
Renne, P.R., S.R. Mulcahy, W.S. Cassata,, L.E. Morgan, S.P. Kelley, L. Hlusko, J. Njau, 2012. Retention of inherited Ar by alkali feldspar xenocrysts in a magma: Kinetic constraints from Ba zoning profiles. Geochimica et Cosmochimica Acta, v. 93, p. 129-142, https://doi.org/10.1016/j.gca.2012.06.029.
Morgan, L.E., P.R. Renne, R. Galotti, G. Kieffer, M. Piperno, J.-P. Raynal, 2012. A chronological framework for a long and persistent archeological record: Melka Kunture, Ethiopia. Journal of Human Evolution, v. 62, no. 1, p. 104-115, https://doi.org/10.1016/j.jhevol.2011.10.007.
Frost, S.R., H.L. Schwartz, L. Giemsch, L.E. Morgan, P.R. Renne, M. Wildgoose, C. Saanane, F. Schrenk, K. Harvati, 2012. Refined age estimates and paleoanthropological investigation of the Manyara Beds, Tanzania. Journal of Anthropological Sciences, v. 90, p. 151-161, https://doi.org/10.4436/jass.90001.
Schwartz, H., P.R. Renne, L.E. Morgan, M.M. Wildgoose, P.C. Lippert, S.R. Frost, K. Harvati, F. Schrenk, C. Saanane, 2012. Geochronology of the Manyara Beds, northern Tanzania: stratigraphy and new magnetostratigraphy and 40Ar/39Ar ages. Quaternary Geochronology, v. 7, no. 1, p. 48-66, https://doi.org/10.1016/j.quageo.2011.09.002.
Morgan, L.E., O. Postma, K.F. Kuiper, D.F. Mark, W. van der Plas, S. Davidson, M. Perkin, I. Villa, J.R. Wijbrans, 2011. A metrological approach to measuring 40Ar* concentrations in K-Ar and 40Ar/39Ar mineral standards, Geochem. Geophys. Geosyst., v. 12, p. A0AA20, https://doi.org/10.1029/2011GC003719.
Renne, P.R., A.L. Deino, W.E. Hames, M.T. Heizler, S.R. Hemming, K.V. Hodges, A.A.P. Koppers, D.F. Mark, L.E. Morgan, D. Phillips, B.S. Singer, B.D. Turrin, I.M. Villa, M. Villeneuve and J.R. Wijbrans, 2009. Data reporting norms for 40Ar/39Ar geochronology. Quaternary Geochronology, v. 4, no. 5, p. 346-352, https://doi.org/10.1016/j.quageo.2009.06.005.
Renne, P.R., W.S. Cassata, and L.E. Morgan, 2009. The isotopic composition of atmospheric argon and 40Ar/39Ar geochronology: time for a change? Quaternary Geochronology, v. 4, no. 4, p. 288-298, https://doi.org/10.1016/j.quageo.2009.02.015.
Renne, P. R., L.E. Morgan, G. WoldeGabriel, W.K. Hart, Y. Haile-Selassie, and T.D. White, 2009. 40Ar/39Ar Ages of the Middle Awash Late Miocene, in: Haile-Selassie, Y., and WoldeGabriel, G. (eds.), Ardipithecus kadabba: Late Miocene evidence from the Middle Awash, Ethiopia. University of California Press, Berkeley, CA.
Morgan, L.E., P.R. Renne, R.E. Taylor, and G. WoldeGabriel, 2009. Archaeological age constraints from eruption ages of obsidian: Examples from the Middle Awash, Ethiopia. Quaternary Geochronology, v. 4, p. 193-203, https://doi.org/10.1016/j.quageo.2009.01.001.
Morgan, L.E. and P.R. Renne, 2008. Diachronous Dawn of Africa’s Middle Stone Age: New 40Ar/39Ar ages from the Ethiopian Rift. Geology, v. 36, no. 12, p. 967-970, https://doi.org/10.1130/G25213A.1.
Gihring, T.M., L.-H. Lin, M. Davidson, T.C. Onstott, L. Morgan, M. Milleson, T.L. Kieft, E. Trimarco, D.L. Balkwill, and M.E. Dollhopf, 2006. The Distribution of Microbial Taxa in the Subsurface Water of the Kalahari Shield, South Africa. Geomicrobiology Journal, v. 23, p. 415-430, https://doi.org/10.1080/01490450600875696.

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

USGS Geochron Database Explorer

This Web Application is a tool for viewing, exploring, and downloading the "USGS Geochron: A Database of Geochronological and Thermochronological Dates and Data" Data Release.

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New online tool serves USGS geochronology data in state-of-the-art way

The U.S. Geological Survey has developed an updated, point and click web application for accessing a geochronology database with sample summary and...

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Science and Products

  • Science
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    USGS Geochron: A database of USGS geochronological and thermochronological data

    The U.S. Geological Survey (USGS) has developed an updated geochronology database (USGS Geochron) to include geochronology summary and analytical data created or funded by the USGS.
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    Geosciences and Environmental Change Science Center
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    USGS Geochron: A database of USGS geochronological and thermochronological data

    The U.S. Geological Survey (USGS) has developed an updated geochronology database (USGS Geochron) to include geochronology summary and analytical data created or funded by the USGS.
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    large piece of equipment for argon extraction system and mass spectrometer

    Argon Geochronology

    This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology...
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    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center
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    Argon Geochronology

    This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology...
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    Mt. Ouray, Colorado with aspen colors

    Geologic Framework of the Intermountain West

    The Geologic Framework of the Intermountain West project was launched with the goal of producing a new digital geologic map database and 3D geologic model of a transect from the Rio Grande rift to the Basin and Range, based on a synthesis of existing geologic maps with new targeted new mapping, subsurface data, and other data sets. This database will integrate disparate map data, resolve...
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    Geosciences and Environmental Change Science Center
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    Geologic Framework of the Intermountain West

    The Geologic Framework of the Intermountain West project was launched with the goal of producing a new digital geologic map database and 3D geologic model of a transect from the Rio Grande rift to the Basin and Range, based on a synthesis of existing geologic maps with new targeted new mapping, subsurface data, and other data sets. This database will integrate disparate map data, resolve...
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    Serving the U.S. Geological Survey’s geochronological data

    Geochronological data provide essential information necessary for understanding the timing of geologic processes and events, as well as quantifying rates and timescales key to geologic mapping, mineral and energy resource and hazard assessments. The USGS’s National Geochronological Database (NGDB) contains over 30,000 radiometric ages, but no formal update has occurred in over 20 years. This proj
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    Community for Data Integration (CDI)
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    Serving the U.S. Geological Survey’s geochronological data

    Geochronological data provide essential information necessary for understanding the timing of geologic processes and events, as well as quantifying rates and timescales key to geologic mapping, mineral and energy resource and hazard assessments. The USGS’s National Geochronological Database (NGDB) contains over 30,000 radiometric ages, but no formal update has occurred in over 20 years. This proj
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  • Data
    Filter Total Items: 24

    Argon data for enriched MORB from the 8°20' N seamount chain

    This dataset accompanies planned publication 'Near-Ridge Magmatism Constrained Using 40Ar/39Ar Dating of Enriched MORB from the 8°20' N Seamount Chain'. The Ar/Ar data are for samples that record the volcanic history of the area. The geochronology provides time constraints for the eruption of rocks studied in the manuscript. Samples were collected from the 8°20' N seamount chain by Molly Anderson
    By
    Geology, Geophysics, and Geochemistry Science Center

    Quetrupillán Volcanic Complex, southern Chile: Argon age data and Pb, Sr, and Nd isotopic data

    This dataset accompanies planned publication 'Lava-ice interactions at late Pleistocene trachyte-basaltic andesite fissure eruptions, Quetrupillán Volcanic Complex (39°30′ S, 71°43′ W), southern Chile', as well as planned future publications on this volcanic complex. The Ar/Ar data and the Pb, Sr, and Nd data are for basalt and trachyte lava flows at Quetrupillán volcano. The Ar geochronology and
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    USGS Geochron: A Database of Geochronological and Thermochronological Dates and Data (ver. 2.0, September 2023)

    USGS Geochron is a database of geochronological and thermochronological dates and data. The data set contains published ages, dates, analytical information, sample metadata including location, and source citations. The following analytical techniques are represented in the data set: 40Ar/39Ar, K-Ar, U-Th-Pb, Sm-Nd, Rb-Sr, Lu-Hf, fission track, and luminescence. This data set incorporates data prev
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    Geosciences and Environmental Change Science Center

    Database for the geologic map of the upper Santa Cruz River basin, southern Arizona

    This digital publication contains the database, base maps, and style files used to build the geologic map of the upper Santa Cruz River basin in southern Arizona published in U.S. Geological Survey Scientific Investigations Map 3490 (Page and others, 2023). Shapefiles are also included for the user’s convenience. In the database, there are polygon features outlining the map units and data sources;
    By
    Geosciences and Environmental Change Science Center

    Argon data for HD-B1 intercalibration

    This data release includes 40Ar/39Ar intercalibration data from the U.S. Geological Survey for neutron fluence monitors HD-B1 (Heidelberg biotite) and FCs (Fish Canyon sanidine). Potassium-bearing mineral grains were analyzed by argon geochronology at the U.S. Geological Survey Argon Geochronology Laboratory in Denver, Colorado. These data provide intercalibration information between the two fluen
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Santa Cruz Basin (ver. 1.1, November 2022)

    This data release includes 40Ar/39Ar data from the U.S. Geological Survey for samples from the Santa Cruz Basin, Arizona. Mineral samples were collected by Kenzie Turner and William Page from the upper Santa Cruz Basin, Arizona. Potassium-bearing mineral grains were separated from the bulk sample and analyzed by argon geochronology at the U.S. Geological Survey Argon Geochronology Laboratory in De
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Hugub Area, Kesem-Kebena-Dulecha, Ethiopia

    Tephra samples were collected by Leah Morgan (now at the U.S. Geological Survey (USGS)) from the Hugub Area, Kesem-Kebena-Dulecha, Afar, Ethiopia. Sanidine grains were separated from the bulk sample and analyzed by argon geochronology at the Scottish Universities Environmental Research Centre, Scotland. The data indicate that the age of the Hugub Bed, which is rich in archarological artifacts, is
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Klamath Mountains

    This dataset accompanies planned publication '40Ar/39Ar geochronology of hydrothermal activity related to orogenic gold mineralization in the Klamath Mountains, California, U.S.A.'. The Ar/Ar data are for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Klamath Mountains
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Nepal

    This dataset accompanies planned publication 'Determining fault geometry through the transport-parallel distribution of thermochronometer cooling ages'. The Ar/Ar data is for samples that record the thermal history of the area. The geochronology provides time constraints for the thermal histories studied in the manuscript. Samples were collected from Nepal, overseen by Nadine McQuarrie (University
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Amazon Craton

    This dataset accompanies planned publication 'Genesis of early Neoproterozoic gold deposits, southwestern Amazon Craton, western Brazil'. The Ar/Ar data is for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Amazon Craton region, and collection was done by Rodrigo Prude
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Central Andes (Domeyko Range, Chile)

    This dataset accompanies planned publication 'Gondwanan inheritance on the building of the western Central Andes (Domeyko Range, Chile): Structural and thermochronological approach (U-Pb and 40Ar-39Ar)'. The Ar/Ar data is for samples that record the sedimentation of the area. The geochronology provides time constraints for the sedimentation studied in the manuscript. Samples were collected from th
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Argon data for Yellow Pine

    This dataset accompanies planned publication 'Timing of Hydrothermal Alteration and Au-Sb-W Mineralization, Stibnite-Yellow Pine District, Idaho'. The Ar/Ar data is for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Yellow Pine region, and collection was done by numero
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center
  • Maps

    Geologic map and hydrogeologic investigations of the upper Santa Cruz River basin, southern Arizona

    This report includes an updated geologic map and cross sections of the upper Santa Cruz River basin, southern Arizona. The map and cross sections describe the geometry, thickness, and structure of the Miocene to Holocene units which form the main aquifers in the basin. The report also includes results of new hydrogeologic studies including (1) mapping and defining depth to bedrock based on geophys
    By
    Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center

    Geologic map of the Poncha Pass area, Chaffee, Fremont, and Saguache Counties, Colorado

    This report presents a 1:24,000-scale geologic map, cross sections, and descriptive and interpretative text for the Poncha Pass area in central Colorado. The map area is irregular in shape, covering all of one 7 ½' quadrangle (Poncha Pass) and parts of five others (Mount Ouray, Maysville, Salida West, Salida East, and Wellsville). The map boundaries were drawn to cover all of the “Poncha mountain
    By
    National Cooperative Geologic Mapping Program, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center

    Geologic map of the San Antonio Mountain area, northern New Mexico and southern Colorado

    The geologic map of the San Antonio Mountain area in northern New Mexico and southern Colorado is located along the west-central part of the San Luis Valley. The San Luis Valley is the geomorphic expression of the San Luis Basin, an extensional basin associated with the northern Rio Grande rift. Deposits within the map area record volcanic, sedimentary, and tectonic processes over the last ~33 mil
    By
    National Cooperative Geologic Mapping Program, Geology, Geophysics, and Geochemistry Science Center, Geosciences and Environmental Change Science Center
  • Publications
    Filter Total Items: 29

    Kesem-Kebena-Dulecha study area, Ethiopia

    In 1988 and 1989, the Paleoanthropological Inventory of Ethiopia (PIE) field expedition discovered numerous localities of prehistoric significance across Ethiopia (WoldeGabriel et al., 1992). One of the regions surveyed by the Inventory team was the Dulecha administrative district (Gabi Rasu), Afar Zone (Fig. 1). The surveyed area (geographic reference: 9.407° N, 40.057° E) includes the watershed
    Authors
    W. Henry Gilbert, V.B. Doronichev, L.V. Golovanova, Leah E. Morgan, Luis Nunez, Laura Rodriguez, Nohemi Sala, D. Cusimano, I. de Gaspar, Paul Mazza, N. Garcia
    By
    Geology, Geophysics, and Geochemistry Science Center

    Potassium-39-derived 36Ar production during fission-neutron irradiation and its effect on 40Ar/39Ar ages

    Various interference reactions producing unwanted Ar isotopes from K, Ca, Cl and Ar require correction to satisfy the 40Ar/39Ar age equation. Using GEANT4, we design and build a model Cadmium Lined In Core Irradiation Tube (CLICIT) irradiation facility, as used in the Oregon State TRIGA Reactor (OSTR). We illustrate the complexity of the irradiation of geologic samples within this framework and de
    Authors
    Jack N. Carter, Paul R. Renne, Leah E. Morgan
    By
    Geology, Geophysics, and Geochemistry Science Center

    Rare 40K decay with implications for fundamental physics and geochronology

    Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts subatomic rare-event searches, nuclear structure theory, and estimated geological ages. A predicted electron-capture decay directly to the ground state of argon-40 has never been observed. The KDK (potassium decay) collaboration reports strong evidence of this rare decay mode. A blinded analysis reveals a nonzero
    Authors
    M. Stukel, L. Hariasz, P.C.F. Di Stefano, B.C. Rasco, K.P. Rykaczewski, N.T. Brewer, D.W. Stracener, Y. Liu, Z. Gai, C. Rouleau, J. B. Carter, J. Kostensalo, J. Suhonen, H. Davis, E.D. Lukosi, K.C. Goetz, R.K. Grzywacz, M. Mancuso, F. Petricca, A. Fijalkowska, M. Wolinska-Cichocka, J. Ninkovic, P. Lechner, R.B. Ickert, Leah E. Morgan, P.R. Renne, I. Yavin
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    First observation of the ground-state electron-capture of 40K

    Potassium-40 is a widespread, naturally occurring isotope whose radioactivity impacts estimated geological ages spanning billions of years, nuclear structure theory, and subatomic rare-event searches—including those for dark matter and neutrinoless double-beta decay. The decays of this long-lived isotope must be precisely known for its use as a geochronometer, and to account for its presence in lo
    Authors
    L. Hariasz, M. Stukel, P.C.F. Di Stefano, B.C. Rasco, K.P. Rykaczewski, N.T. Brewer, D.W. Stracener, Y. Liu, Z. Gai, C. Rouleau, J. B. Carter, J. Kostensalo, J. Suhonen, H. Davis, E.D. Lukosi, K.C. Goetz, R.K. Grzywacz, M. Mancuso, F. Petricca, A. Fijalkowska, M. Wolinska-Cichocka, J. Ninkovic, P. Lechner, R.B. Ickert, Leah E. Morgan, P.R. Renne, I. Yavin
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Constraints on near-ridge magmatism using 40Ar/39Ar geochronology of enriched MORB from the 8°20' N seamount chain

    Our understanding of the spatial-temporal-compositional relationships between off-axis magmatism and mid-ocean ridge spreading centers is limited. Determining the 40Ar/39Ar ages of mid-ocean ridge basalt (MORB) lavas erupting near mid-ocean ridges (MOR) has been a challenge due to the characteristically low K2O contents in incompatible element-depleted normal MORB (NMORB). High-precision 40Ar/39Ar
    Authors
    Molly Anderson, Michael Perfit, Leah E. Morgan, Daniel Fornari, Michael A. Cosca, V. Dorsey Wanless
    By
    Geology, Geophysics, and Geochemistry Science Center

    Community for data integration 2019 project report

    The U.S. Geological Survey Community for Data Integration annually supports small projects focusing on data integration for interdisciplinary research, innovative data management, and demonstration of new technologies. This report provides a summary of the 14 projects supported in fiscal year 2019 and outlines their goals, activities, and accomplishments. Proposals in 2019 were encouraged to addre
    Authors
    Amanda N. Liford, Caitlin M. Andrews, Aparna Bamzai, Joseph A. Bard, David S. Blehert, John B. Bradford, Wesley M. Daniel, Sara L. Caldwell Eldridge, Frank Engel, Jason A. Ferrante, Amy K. Gilmer, Margaret E. Hunter, Jeanne M. Jones, Benjamin Letcher, Frances L. Lightsom, Richard R. McDonald, Leah E. Morgan, Sasha C. Reed, Leslie Hsu
    By
    Ecosystems Mission Area, Water Resources Mission Area, Science Synthesis, Analysis and Research Program, Science Analytics and Synthesis (SAS) Program, Volcano Hazards Program, Community for Data Integration (CDI), Geology, Geophysics, and Geochemistry Science Center, Geosciences and Environmental Change Science Center, National Wildlife Health Center, Oklahoma-Texas Water Science Center, Southwest Biological Science Center, Volcano Science Center, Western Geographic Science Center, Wetland and Aquatic Research Center , Woods Hole Coastal and Marine Science Center, Science Data Management

    First principles calibration of 40Ar abundances in 40Ar/39Ar mineral neutron fluence monitors: Methodology and preliminary results

    The accuracy and traceability of geochronometers are of vital importance to questions asked by many Earth scientists. The widely applied 40Ar/39Ar geochronometer relies on the co-irradiation of samples with neutron fluence monitors (reference materials) of known ages; the ages and uncertainties of these monitors are critical to our ability to apply this chronometer. Previously, first principles, a
    Authors
    Leah E. Morgan, Brett Davidheiser-Kroll, Klaudia F. Kuiper, Darren F. Mark, Noah M. McLean, Jan Wijbrans
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Early Neoproterozoic gold deposits of the Alto Guaporé province, southwestern Amazon craton, western Brazil

    The Alto Guaporé gold province, southwestern Amazon craton, contains gold deposits that have been mined since the beginning of the 18th century and these deposits, together, have modern-day, pre-mining gold resources of at least 1.8 Moz. The ore is associated with quartz vein systems along the southeastern part of the Aguapei belt, a ~35-km-wide and ~500-km-long, NNW-trending shear zone formed due
    Authors
    Rodrigo Prudente de Melo, Marcos Aurélio Farias de Oliveira, Richard J. Goldfarb, Craig A. Johnson, Erin E. Marsh, Roberto Perez Xavier, Leandro Rocha de Oliveira, Leah E. Morgan
    By
    Geology, Geophysics, and Geochemistry Science Center

    Late Jurassic-Early Cretaceous orogenic gold mineralization in the Klamath Mountains, California: Constraints from 40Ar/39Ar dating of hydrothermal muscovite

    The Klamath Mountains gold province is the second most important historical producer in California, having produced more than 7 Moz of gold from both lode and placer sources. Hydrothermal muscovite grains from gold-bearing veins provide the first 40Ar/39Ar age constraints indicative of a protracted period of mineralization in the Klamath Mountains. The data indicate that the window for orogenic go
    Authors
    Ryan D. Taylor, Leah E. Morgan, Fred Jourdan, Thomas Monecke, Erin E. Marsh, Richard J. Goldfarb
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Gondwanic inheritance on the building of the western Central Andes (Domeyko Range, Chile): Structural and thermochronological approach (U-Pb and 40Ar-39Ar)

    Tectonics inheritance controls the evolution of many orogens. To unravel the role of the Gondwanan heritage (late Paleozoic to Triassic) over the building of the Central Andes in northern Chile (Domeyko Range), we performed detrital U‐Pb zircon and 40Ar/39Ar muscovite geochronology along with structural analyses (kinematics and structural balancing). 40Ar/39Ar dating of detrital muscovite reveals
    Authors
    Mauricio Espinoza, Veronica Oliveros, Paulina Vasquez, Laura Giambiagi, Leah E. Morgan, Rodrigo Gonzalez, Luigi Solari, Florencia Bechis
    By
    Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

    Constraining central Himalayan (Nepal) fault geometry through integrated thermochronology and thermokinematic modeling

    Constraining the subsurface structural geometry of the central Himalaya continues to prove difficult, even after the 2015 Gorkha earthquake and the resulting insights into the trajectory of the Main Himalayan thrust (MHT). To this end, we apply a thermokinematic model to evaluate four possible balanced cross section geometries based on three estimates of the MHT in central Nepal. We compare the ef
    Authors
    Surydoy Ghoshal, Nadine McQuarrie, Delores Robinson, D.P. Adhikari, Leah E. Morgan, Todd A. Ehlers
    By
    Natural Hazards Mission Area, Geology, Geophysics, and Geochemistry Science Center

    Conditions and timing of high-grade metamorphism and ductile deformation of the southern segment of the Central Anatolian Ophiolite

    Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern,
    Authors
    Molly S. Radwany, Leah E. Morgan, Donna L. Whitney
    By
    Geology, Geophysics, and Geochemistry Science Center

    Non-USGS Publications**

    Mark, D.F., P.R. Renne, R. Dymock, V.C. Smith, J.I. SImon, L.E. Morgan, R.A. Staff, and B.S. Ellis, 2017. High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary. Quaternary Geochronology 39, 1-23, https://doi.org/10.1016/j.quageo.2017.01.002.
    Morgan, L.E., 2017. 40Ar/39Ar and K-Ar Geochronology, in: A.S. Gilbert (ed.), Encyclopedia of Geoarchaeology. Encyclopedia of Earth Science Series. Springer, Dordrecht, https://doi.org/10.1007/978-1-4020-4409-0.
    Morgan, L.E., 2015. Noble Gas Mass Spectrometry, in: W.J. Rink, and J.W. Thompson (eds.), Encyclopedia of Scientific Dating Methods. Encyclopedia of Earth Science Series. Springer, Dordrecht, https://doi.org/10.1007/978-94-007-6304-3_118.
    Sahle, Y., L.E. Morgan, D.R. Braun, W.K. Hutchings, 2014. Chronological and behavioral contexts of the earliest Middle Stone Age in the Gademotta Formation, Main Ethiopian Rift, Quaternary International, v. 331, p. 6-19, https://doi.org/10.1016/j.quaint.2013.03.010.
    Mark, D.F., M. Petraglia, V.C. Smith, L.E. Morgan, D.N. Barfod, B.S Ellis, N.J. Pearce, J.N. Pal, R. Korisettar, 2014. A high-precision 40Ar/39Ar age for the Young Toba Tuff and dating of ultra- distal tephra: forcing of Quaternary climate and implications for hominin occupation of India, Quaternary Geochronology, v. 21, p. 90-103, https://doi.org/10.1016/j.quageo.2012.12.004.
    Sahle, Y., W.K. Hutchings, D.R. Braun, J.C. Sealy, L.E. Morgan, A. Negash, B. Atnafu, 2013. Earliest stone-tipped projectiles from the Ethiopian Rift date to >279,000 years ago. PLOS ONE, v. 8, no. 11, e78092, https://doi.org/10.1371/journal.pone.0078092.
    Morgan, L.E., D.F. Mark, J. Imlach, D.N. Barfod, 2013. FCs-EK: A new sampling of the Fish Canyon tuff 40Ar/39Ar neutron flux monitor, in: Jourdan, F., Mark, D., and Verati, C. (eds.), Advances in 40Ar/39Ar Dating: from Archaeology to Planetary Sciences. Geological Society, London, Special Publications, 378, https://doi.org/10.1144/SP378.21.
    Renne, P.R., A.L. Deino, F.J. Hilgen, K.F. Kuiper, D.F. Mark, W.S. Mitchell, L.E. Morgan, R. Mundil, J. Smit, 2013. Timescales of critical events around the Cretaceous-Paleogene boundary. Science, v. 339, p. 684-687, https://doi.org/10.1126/science.1230492.
    Schoene, B., D.J. Condon, L.E. Morgan, N. McLean, 2013. Precision and accuracy in geochronology. Elements Magazine, v.9, no.1, p. 23-28, http://elementsmagazine.org/past-issue-archive/2013-volume-9/#February2013.
    Renne, P.R., S.R. Mulcahy, W.S. Cassata,, L.E. Morgan, S.P. Kelley, L. Hlusko, J. Njau, 2012. Retention of inherited Ar by alkali feldspar xenocrysts in a magma: Kinetic constraints from Ba zoning profiles. Geochimica et Cosmochimica Acta, v. 93, p. 129-142, https://doi.org/10.1016/j.gca.2012.06.029.
    Morgan, L.E., P.R. Renne, R. Galotti, G. Kieffer, M. Piperno, J.-P. Raynal, 2012. A chronological framework for a long and persistent archeological record: Melka Kunture, Ethiopia. Journal of Human Evolution, v. 62, no. 1, p. 104-115, https://doi.org/10.1016/j.jhevol.2011.10.007.
    Frost, S.R., H.L. Schwartz, L. Giemsch, L.E. Morgan, P.R. Renne, M. Wildgoose, C. Saanane, F. Schrenk, K. Harvati, 2012. Refined age estimates and paleoanthropological investigation of the Manyara Beds, Tanzania. Journal of Anthropological Sciences, v. 90, p. 151-161, https://doi.org/10.4436/jass.90001.
    Schwartz, H., P.R. Renne, L.E. Morgan, M.M. Wildgoose, P.C. Lippert, S.R. Frost, K. Harvati, F. Schrenk, C. Saanane, 2012. Geochronology of the Manyara Beds, northern Tanzania: stratigraphy and new magnetostratigraphy and 40Ar/39Ar ages. Quaternary Geochronology, v. 7, no. 1, p. 48-66, https://doi.org/10.1016/j.quageo.2011.09.002.
    Morgan, L.E., O. Postma, K.F. Kuiper, D.F. Mark, W. van der Plas, S. Davidson, M. Perkin, I. Villa, J.R. Wijbrans, 2011. A metrological approach to measuring 40Ar* concentrations in K-Ar and 40Ar/39Ar mineral standards, Geochem. Geophys. Geosyst., v. 12, p. A0AA20, https://doi.org/10.1029/2011GC003719.
    Renne, P.R., A.L. Deino, W.E. Hames, M.T. Heizler, S.R. Hemming, K.V. Hodges, A.A.P. Koppers, D.F. Mark, L.E. Morgan, D. Phillips, B.S. Singer, B.D. Turrin, I.M. Villa, M. Villeneuve and J.R. Wijbrans, 2009. Data reporting norms for 40Ar/39Ar geochronology. Quaternary Geochronology, v. 4, no. 5, p. 346-352, https://doi.org/10.1016/j.quageo.2009.06.005.
    Renne, P.R., W.S. Cassata, and L.E. Morgan, 2009. The isotopic composition of atmospheric argon and 40Ar/39Ar geochronology: time for a change? Quaternary Geochronology, v. 4, no. 4, p. 288-298, https://doi.org/10.1016/j.quageo.2009.02.015.
    Renne, P. R., L.E. Morgan, G. WoldeGabriel, W.K. Hart, Y. Haile-Selassie, and T.D. White, 2009. 40Ar/39Ar Ages of the Middle Awash Late Miocene, in: Haile-Selassie, Y., and WoldeGabriel, G. (eds.), Ardipithecus kadabba: Late Miocene evidence from the Middle Awash, Ethiopia. University of California Press, Berkeley, CA.
    Morgan, L.E., P.R. Renne, R.E. Taylor, and G. WoldeGabriel, 2009. Archaeological age constraints from eruption ages of obsidian: Examples from the Middle Awash, Ethiopia. Quaternary Geochronology, v. 4, p. 193-203, https://doi.org/10.1016/j.quageo.2009.01.001.
    Morgan, L.E. and P.R. Renne, 2008. Diachronous Dawn of Africa’s Middle Stone Age: New 40Ar/39Ar ages from the Ethiopian Rift. Geology, v. 36, no. 12, p. 967-970, https://doi.org/10.1130/G25213A.1.
    Gihring, T.M., L.-H. Lin, M. Davidson, T.C. Onstott, L. Morgan, M. Milleson, T.L. Kieft, E. Trimarco, D.L. Balkwill, and M.E. Dollhopf, 2006. The Distribution of Microbial Taxa in the Subsurface Water of the Kalahari Shield, South Africa. Geomicrobiology Journal, v. 23, p. 415-430, https://doi.org/10.1080/01490450600875696.

    **Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

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