Leah E Morgan, Ph.D.
Biography
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.
Publications
Morgan, L.E., D.P.S. Ramos, B. Davidheiser-Kroll, J. Faithfull, N.S. Lloyd, R.M. Ellam, and J.A. Higgins, 2018. High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41 K. Journal of Analytical Atomic Spectrometry. https://doi.org/10.1039/C7JA00257B
Shackley M.S., L. Morgan, D. Pyle, 2017. Elemental, isotopic, and geochronological variability in Mogollon-Datil volcanic province archaeological obsidian, southwestern USA: Solving issues of inter-source discrimination. Geoarchaeology.
https://doi.org/10.1002/gea.21672
Morgan, L. E., M. Munk, B. Davidheiser-Kroll, N.H. Warner, S. Gupta, R. Slaybaugh, P. Harkness, and D.F. Mark, 2017. Instrumentation Development for In Situ 40Ar/39Ar Planetary Geochronology. Geostandards and Geoanalytical Research, doi:10.1111/ggr.12170
Kavalieris, I., B.E. Khashgerel, L.E. Morgan, A. Undrakhtamir, and A. Borohul, 2017. Characteristics and 40Ar/39Ar Geochronology of the Erdenet Cu-Mo Deposit, Mongolia. Economic Geology, 112(5), 1033-1053.
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.
Righter, K., M.A. Cosca, and L.E. Morgan, 2016. Preservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende‐bearing R chondrite LAP 04840. Meteoritics & Planetary Science, 51 (9), 1678-1684.
Morgan, L.E., 2016. 40Ar/39Ar and K-Ar Geochronology, in: A.S. Gilbert (ed.), Encyclopedia of Geoarchaeology. Springer.
Morgan, L.E., and B. Davidheiser-Kroll, 2015. Pressure disequilibria induced by rapid valve closure in noble gas extraction lines. Geochemistry, Geophysics, Geosystems, 16, doi:10.1002/2015GC005823.
Morgan, L.E., 2015. Noble Gas Mass Spectrometry, in: W.J., and J.W. Thompson (eds.), Encyclopedia of Scientific Dating Methods. Springer.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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, doi: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.
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.
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.
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.
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.
Science and Products
Petrology of volcanic rocks associated with silver-gold (Ag-Au) epithermal deposits in the Tonopah, Divide, and Goldfield Mining Districts, Nevada
Miocene calc-alkaline volcanic rocks, part of the southern segment of the ancestral Cascades magmatic arc, are spatially, temporally, and likely genetically associated with precious metal epithermal deposits in the Tonopah, Divide, and Goldfield Districts of west-central Nevada. In the Tonopah mining district, volcanic rocks include the Mizpah...
du Bray, Edward A.; John, David A.; Colgan, Joseph P.; Vikre, Peter G.; Cosca, Michael A.; Morgan, Leah E.
Petrographic, geochemical, and geochronologic data for cenozoic volcanic rocks of the Tonopah, Divide, and Goldfield Mining Districts, Nevada
The purpose of this report is to summarize geochemical, petrographic, and geochronologic data for samples, principally those of unmineralized Tertiary volcanic rocks, from the Tonopah, Divide, and Goldfield mining districts of west-central Nevada (fig. 1). Much of the data presented here for the Tonopah and Divide districts are for samples...
du Bray, Edward A.; John, David A.; Vikre, Peter G.; Colgan, Joseph P.; Cosca, Michael A.; Morgan, Leah E.; Fleck, Robert J.; Premo, Wayne R.; Holm-Denoma, Christopher S.
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,...
Turner, Kenzie J.; Thompson, Ren A.; Cosca, Michael A.; Shroba, Ralph R.; Chan, Christine F.; Morgan, Leah E.
Reverse weathering in marine sediments and the geochemical cycle of potassium in seawater: Insights from the K isotopic composition (41K/39K) of deep-sea pore-fluids
In situ Al-silicate formation, also known as “reverse weathering,” is an important sink of many of the major and minor cations in seawater (e.g. Mg, K, and Li). However, the importance of this sink in global geochemical cycles and isotopic budgets of these elements remains poorly constrained. Here, we report on the potassium isotopic...
Santiago Ramos, Danielle P.; Morgan, Leah E.; Lloyd, Nicholas S.; Higgins, John A. 40Ar/39Ar geochronology and petrogenesis of the Table Mountain Shoshonite, Golden, Colorado, U.S.A.
The Upper Cretaceous and Lower Paleogene Table Mountain Shoshonite lava flows and their proposed source, the Ralston Buttes intrusions, provide insight into the volcanic history of the Colorado Front Range. This study affirms the long-held hypothesis linking the extrusive Table Mountain lava flows and their intrusive equivalents at Ralston Buttes...
Millikin, Alexie E. G.; Morgan, Leah E.; Noblett, Jeffery High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K
Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision...
Morgan, Leah E.; Santiago Ramos, Danielle P.; Davidheiser-Kroll, Brett; Faithfull, John; Lloyd, Nicholas S.; Ellam, Rob M.; Higgins, John A. Elemental, isotopic, and geochronological variability in Mogollon-Datil volcanic province archaeological obsidian, southwestern USA: Solving issues of intersource discrimination
Solving issues of intersource discrimination in archaeological obsidian is a recurring problem in geoarchaeological investigation, particularly since the number of known sources of archaeological obsidian worldwide has grown nearly exponentially in the last few decades, and the complexity of archaeological questions asked has grown equally so....
Shackley, M. Steven; Morgan, Leah E.; Pyle, Douglas Characteristics and 40Ar/39Ar geochronology of the Erdenet Cu-Mo deposit, Mongolia
The Early to Middle Triassic Erdenet porphyry Cu-Mo deposit, in northern Mongolia, developed in a continent-continent arc collision zone, within the Central Asian orogenic belt. The porphyry system is related to multiple intrusions of crystal-crowded biotite granodiorite porphyry, which formed a composite stock about 900 m in diameter, with...
Kavalieris, Imants; Khashgerel, Bat-Erdene; Morgan, Leah E.; Undrakhtamir, Alexander; Borohul, Adiya Instrumentation development for In Situ 40Ar/39Ar planetary geochronology
The chronology of the Solar System, particularly the timing of formation of extra-terrestrial bodies and their features, is an outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g., Rb-Sr, K-Ar), and even applied (K-Ar), the reliability, accuracy, and applicability...
Morgan, Leah E.; Munk, Madicken; Davidheiser-Kroll, Brett; Warner, Nicholas H.; Gupta, Sanjeev; Slaybaugh, Rachel; Harkness, Patrick; Mark, Darren Episodic formation of the world-class Waihi epithermal Au-Ag vein system, Hauraki Goldfield, New Zealand
The world-class Waihi vein system in New Zealand has produced more than 248,400 kg Au and 1.43 million kg Ag. New high-precision 40Ar/39Ar dates of adularia from different veins show that some veins formed at different times (6.15 Ma Martha vs. 5.83 and 5.85 Ma Empire and Welcome, respectively), even though they have similar mineralogy. The Martha...
Gasston, Erin; Mauk, Jeffrey L.; Cosca, Michael A.; Morgan, Leah E.; Hall, Chris M. Preservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende-bearing R chondrite LAP 04840
The hornblende- and biotite-bearing R chondrite LAP 04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined 40Ar/39Ar ages on hornblende-rich separates of the meteorite, and obtained...
Righter, Kevin; Cosca, Michael A.; Morgan, Leah E. Pressure disequilibria induced by rapid valve closure in noble gas extraction lines
Pressure disequilibria during rapid valve closures can affect calculated molar quantities for a range of gas abundance measurements (e.g., K-Ar geochronology, (U-Th)/He geochronology, noble gas cosmogenic chronology). Modeling indicates this effect in a system with a 10 L reservoir reaches a bias of 1% before 1000 pipette aliquants have been...
Morgan, Leah E.; Davidheiser-Kroll, Brett