Dr. Paul Layer, Professor

The laboratory has two mass spectrometer systems that are used for measuring argon gas in rocks and minerals - a Nuclide system installed in 1970, and a VG3600 laser system installed in 1994. The laser system allows for age determinations on single mineral grains and other small samples. Both systems and the data analysis are automated.

The UAF Geochronology Laboratory has been involved in a wide variety of research projects. Some examples are:

The laboratory staff is Dr. Paul Layer, director, and Jeff Drake, Senior Laboratory Technician. Support for the laboratory comes from research grants, internal funding sources, and external contracts.

We are currently collaborating with personnel from the Alaska Division of Geological and Geophysical Surveys, The U.S. Geological Survey, Geological Survey of Canada, Michigan State University, Allegheny College, Purdue University, Yakutsk State University (Yakutsk, Russia), the Northeast Interdisciplinary Scientific Research Institute (Magadan, Russia), Mainz (Germany), Lulea (Sweden), the University of the Witwatersrand (South Africa). We are also engaged in contractual work with a number of mining companies working in Alaska and elsewhere. The laboratory is available for additional contract or collaborative projects. If you are with a university or private company and are interest, please contact Paul Layer for more information and prices

Nuclide system

The older system in the Geochronology Laboratory consists of a resistance-type furnace manufactured by Modifications Ltd. connected "on-line" to a Nuclide 6-60-SGA mass spectrometer. An IBM-AT computer is currently controlling this system. While this system is old, it is very useful for conducting detailed thermochronometric analyses on potassium feldspars.

VG3600 laser system

The newer mass spectrometer system uses a VG3600 mass spectrometer and a Coherent 6-watt argon-ion laser. The spectrometer is equipped with both a Daly multiplier and a Faraday detector. The two detectors with a gain difference of about a factor of 100 allow us to measure a wide variety of samples.

Single mineral grains

Single crystals are heated with the laser and melted. During the heating process, Argon gas is liberated from the sample. The argon gas is purified and measured in the spectrometer. After the heating all that is left is a degassed glass bead. In these pictures, the sample is sitting in a hole 2 mm in diameter drilled into a copper disk. The drill made the concentric circles in the copper. The blue-green laser light heats the sample and melts it.

System Automation

The VG3600 single crystal system has been automated to allow "hands-off" step-heating experiments. The laser, spectrometer, X-Y stage and valves are controlled by a PC running a program developed here at UAF using LabView, a C-based Graphical language. A sample screen is shown here. Data is processed using a program called Argon1 for PC's. Written in Visual Basic, this program allows for interactive data analysis, including plateau calculation and isochron analysis. Contact Paul Layer for more details on these programs or automation of instrumentation.

Interns

The Geophysical Institute is a Research Experience for Undergraduates (REU) site. In this program, undergraduate students from around the country come to Fairbanks to conduct research in a variety of research labs. Intern projects in the geochronology laboratory are listed below. Several of these research projects have led to coauthorship on abstracts presented at meetings and thus far one has led to a published paper.

High school students

The University's proximity to several schools has allowed us to work with teachers and students in getting High School students directly in the lab. These projects are designed to be completed in a school year with work after school or on weekends. Contact us if you want more information. In addition, we are also involved in the Partners in Science Program, designed to bring together University researchers, elementary teachers in a collaborative program to introduce students to science.

Undergraduate Research

Through the department of Geology and Geophysics, students can enroll in GEOS 488, Undergraduate research. Students also work in the geochronology laboratory preparing samples and analyzing data. For the class, students are required to present the results of the study in the form of a written and/or oral presentation.

Past student project areas include:

Patrick Bratton: Geochronology of Augustine Volcano

Dietrie Hanson: Geochronology of the Chulitna Distract, Alaska

Katlin Hanson: Geochronology of the Manley Distract, Alaska

Christian Schrader: Geochronolgy and Geochemistry of the Skholnoe and other gold deposits in Russia.

Graduate student research

Graduate thesis opportunities are available. Recent Geochronology Laboratory graduate students include:

Andrew West: (M.S., 1994) A petrologic and geochronologic study of the McKinley Pluton, Alaska

Tom Douglas (M.S., 1997) Metamorphic histories of the Chatanika eclogite and Fairbanks schist within the Yukon-Tanana terrane, Alaska, as revealed by electron microprobe thermobarometry and 40Ar/39Ar single grain dating

Walt Munley (Ph.D. 2004: Geochronology and mineralogy of illite and its application to the evolution of sedimentary basins in northern Alaska

Other Potential Research Areas

The Dating of Alaska's Gold

In Alaska, there is currently a rebirth in mineral (primarily gold) exploration. This is going on despite the sagging price of gold and the general decline in exploration in other parts of the world. In interior Alaska, in the Fairbanks district, there is an intimate relationship between gold formation (and present occurrence) and late Cretaceous plutonism. Geochronology has played a major role in understanding this relationship and an ongoing research effort in the lab is intended to better constrain the time of gold formation.

Publications

Douglas, T., 1997, Metamorphic histories of the Chatanika eclogite and Fairbanks Schist within the Yukon-Tanana terrane, Alaska, as revealed by electron microprobe and 40Ar/39Ar single grain dating, M.S. thesis

Layer, P. W., D. McCoy, and R. J. Newberry, 1997, Intrusion-hosted and intrusion-related gold deposits of Interior Alaska: another variation on the familiar "porphyry" theme, 1997 Geol. Soc. Am. Abstracts with Programs Annual Meeting

McCoy, D., Newberry, R. J., Layer, P. W. DiMarchi, J. J., Bakke, A., Masterman, J. S., and Minehanne, D. L., 1997, Plutonic-Related Gold deposits of Interior Alaska, in R. J. Goldfarb, and L. D. Miller, eds., Mineral Deposits of Alaska, Economic Geology Monograph 9.

Newberry, R. J., P. W. Layer, R. E. Burleigh, and D. N. Solie, New 40Ar/39Ar dates for intrusion and mineral prospects in the eastern Yukon-Tanana Terrane, Alaska--Regional patterns and significance, USGS special publication

Newberry, R.N. P W Layer, P B Gans, V I Gonchorov, N A Goryachev, and S V Voroshin, 1997, Revised Chronology of Igneous Rocks and Mineral Deposits, Magadan Oblast, NE Russia, EOS Trans. Am. Geophys. U. Fall Meeting Supplement

Werdon, M., B., P.W. Layer, and R. J. Newberry, Dating the undatable using 40Ar/39Ar laser step heating: an application in the northern Brooks Range Zn-Pb-Ag district, Alaska, to be submitted to economic geology.

Dating of young volcanic rocks

Alaska is one of the most volcanologically active regions in the world, however very little is known about the evolutionary history of the Aleutian volcanic arc. The Geochronology Laboratory is currently involved in research in working out the Quaternary history of this region. In addition, we are involved in collaborative efforts elsewhere in the world, looking at young volcanism.

Publications

Begét, J. E., P. Layer and R. Flowers, 1997, Tephrochronology and geochronology of the largest maars on Earth, northern Alaska, IAVCEI General Assembly Abstracts, p. 21.

Layer, P. W., J. Drake, A. K. Gilmer, V. S. McConnell, and B. Martini, 1997, 40Ar/39Ar laser dating of low-K Quaternary volcanic rocks from the Aleutian Arc, Alaska, EOS Trans. Am. Geophys. U. Fall Meeting Supplement

McConnell, V.S., C.K. Shearer, J.C. Eichelberger, M.J. Keskinen, P.W. Layer and J.J. Papike, 1995, Rhyolitic intrusions in the intracaldera Bishop Tuff, Long Valley, California, Journal of Volcanology and Geothermal Research, 67, 41-60.

Schaefer, J. R., P. W. Layer, J. E. Beget, J. Drake, 1997, 40Ar/39Ar dating of Quaternary, low-K hornblende from a fine grained Alaskan tephra, EOS Trans. Am. Geophys. U. Fall Meeting Supplement

Vogel, T. A., Woodburne, T. B., Eichelberger, J. C., and Layer, P. W., 1994, Chemical evolution and periodic eruption of mafic lava flows in the west moat of Long Valley Caldera, California, Journal of Geophysical Research, v. 99, p. 19,829-19,842.

Geochronologic investigations in South Africa

Southern Africa contains some of the oldest rocks in the world, and our investigations of Precambrian rocks from South Africa, Zimbabwe, Malawi and elsewhere have yielded some insights into the development of the early Earth's crust and the nature of plate tectonics at that time. Our studies have involved geochronology, structural geology and paleomagnetism.

Publications

Kroner, A. and Layer, P.W., 1992, Crust formation and plate motion in the Early Archean, Science, v. 256, 1405-1411.

Layer, P. W., A. Kröner and P. Jaeckel, 1996, Cooling history in the Central Zone of the Limpopo belt, South Africa, as revealed by U-Pb, Pb-Pb and 40Ar/39Ar mineral ages, EOS Trans. Am. Geophys. U. Fall Meeting Supplement v77, S820. (view Abstract)

Layer, P. W., Kroner, A., and McWilliams, M., 1996, An Archean geomagnetic reversal in the Kaap Valley Pluton, South Africa, Science, v. 273, p. 943-946.

Layer, P. W., M. Lopez-Martinez, A. Kröner, D. York, and M. McWilliams, Thermochronometry and Paleomagnetism of the Archean Nelshoogte Pluton, South Africa, submitted Geophy. J. Intl. (view Abstract)

Layer, P.W., A. Kroner, M. McWilliams and D. York, 1989, elements of the Archean thermal history and apparent polar wander of the eastern Kaapvaal Craton, Swaziland, from single grain dating and paleomagnetism, Earth and Planetary Science Letters, v. 93, 23-34.

Layer, P.W., Kroner, A. and York, D., 1992, Pre-3000 Ma thermal history of the Archean Kaap Valley pluton, South Africa, Geology, v. 20, 717-720.

Geochronologic investigations in Russia

The geochronologic investigations in Yakutia are part of a multidisciplinary collaborative investigation which includes paleomagnetism, seismology and structural geology which are used to gain an understanding of the tectonic history of the Sakha Republic (Yakutia). These other aspects of the project are discussed under "Paleomagnetism" which outlines the history and directions of our collaborative research.

The geochronologic investigations to date have focused on determining the timing of major events that affected the Chersky Range in eastern Yakutia. We have collected over 300 samples for geochronologic and geochemical analysis. Two areas of focus in 1993 and 1994 were (i) the description and chronology of ophiolites in the region (ii) the timing of granitic intrusion in the region.

Ophiolites in the Chersky Range

Mafic and ultramafic rocks are found in isolated complexes along the Chersky Range, eastern Sakha Republic (Yakutia), Russia. Five of the six exposures are located on the eastern side of a Devonian-Ordovician carbonate platform and appear to be thrust over it; the sixth, the Debin fragment, is located to the west. On the basis of lithology, geochemical composition and structural position, the ultramafic rocks and their associated mafic volcanics and deep-marine sedimentary rocks are interpreted as ophiolites or ophiolite fragments derived from back-arc or oceanic crust that was located to the east of the Chersky Range. Faunal and radiometric dating indicate that the oceanic crust has an age of about 370-430 Ma, Early to Middle Devonian. The ages of metamorphic minerals suggest that the ophiolites were obducted and metamorphosed during the amalgamation of the Kolyma-Omolon superterrane, about 170-174 Ma (Callovian, late Middle Jurassic), at which time olistostromes containing fragments of the ophiolite were formed. This age predates the formation of the Uyandina-Yasachnaya volcanic arc, believed to represent the final closure of the ocean basin between the Kolyma-Omolon superterrane and the North Asian craton. It is possible that the southernmost ophiolite, the Debin fragment, has a different history from the other Chersky Range ophiolites and was emplaced as a result of the accretion of the Kolyma-Omolon superterrane.

Granitic Rocks in the Chersky Range

Our geochronologic investigations of plutonic rocks from the 'Kolymian Structural Loop' (KSL) are intended to investigate whether KSL formed in response to a single tectonic event or to discrete events. Precise ages were obtained from 40Ar/39Ar step-heating of biotite and, in some cases, hornblende, muscovite or feldspar. Plutons from the main northwest-southeast trending axis of the Chersky range show no significant age variations along strike, however, there is a decrease in age across the belt from 142 Ma in the east to 135 Ma in the west. These ages are significantly older than ages from granites of the east-west trending Polousney range north of the Chersky range. These plutons also show a decrease in age across the belt from 127 Ma in the south to 120 Ma along the northern edge of the belt. Thus, our preliminary data suggest discrete tectonic events are responsible for the formation of the Chersky (western KSL) and Polousney (northern KSL) ranges. Linear granitic belts which radiate away from the main KSL tend to be significantly younger than the KSL granites. A 106 Ma north trending transverse belt extending from the Polousney range north to Bolshoi Lyakhov island shows no age progression. A southwest trending belt into the Verkhoyansk foldbelt shows a much clearer age progression. The ages range from 132 Ma near the Adycha-Taryn fault and decrease westward to 124 Ma. These results indicate that various parts of the KSL and other structures in eastern Yakutia formed over a protracted time in the early Cretaceous.

In addition to these Cretaceous intrusions, we have confirmed the presence of at least one Carboniferous intrusive complex in the region, the Tommot Massif which is composed of alkaline-ultrabasic rocks, alkaline and subalkaline gabbroids, and alkaline and quartz syenites. It is located to the east of the Chersky Range. It appears that this complex region has escaped regional Cretaceous thermal overprinting events which seem to have reset the paleomagnetic signature and radiometric ages in volcanics and other rocks.

Scientific personnel: Paul Layer, David Stone; Kazuya Fujita (Michigan State University); Leonid Parfenov and Vladimir Oxman (Yakutsk)

Publications

Izbekov, P., P. W. Layer and J. Drake, 1996, The temporal and compositional relationship between plutonism and volcanism: An example from the Sarichev Range, Yakutia, Russia, EOS Trans. Am. Geophys. U. Fall Meeting Supplement v77, S791-S792.

Layer, P.W., 1997, The Role of High-Precision Geochronology in Deciphering the Tectonic History of Northeastern Russia, EOS Trans. Am. Geophys. U. Fall Meeting Supplement

Layer, P.W., L.M. Parfenov, A.A. Surnin and V.F. Timofeev, 1993, First 40Ar/39Ar age determinations of magmatic and metamorphicrocks of the Verkhoyana-Kolyma Mesozoides (in Russian), Doklady Akademii Nauk Rossiya, v. 329, 621-624.

Leier [Layer], P., L.M. Parfenov, A.A. Surnin and V.F. Timofeev, 1995, First 40Ar/39Ar ages of igneous and metamorphic rocks of the Verkhoyana-Kolyma Mesozoides (translation of 1993 article), Transactions (Doklady) of the Russian Academy of Sciences Earth Science Section, v. 330. (no. 4, 1993), 130-134.

Oxman, V. S., L. M. Parfenov, L. M., Prokop'ev, A. V., Timofeev, V. F., Tretyakov, F. F., Nedosekin, V. D., and Layer, P. W., and Fujita, K., 1995, The Chersky Range ophiolites, northeastern Russia, Journal of Geology 103, 539-556.

Oxman, V. S., L. M. Parfenov, L. M., Prokop'ev, A. V., Timofeev, V. F., Tretyakov, F. F., Nedosekin, V. D., and Layer [Leier], P. W., 1994, The Chersky Range ophiolites (in Russian), Geologiya i Geofizika, v. 36(1), p. 3 - 20.

Parfenov, L. M., Layer [Leier], P., Stone [Stoun], D., and Fujita [Fudzhita], K., 1996, Mesozoic orogenic belts of eastern Yakutia and some problems associated with their study (in Russian: Mezozoiskieorogennye poyasa vostochnoi Yakutii i nekotorye problemy, svyazannye c ikhizucheniem), Nauka i Obrazovanie, v. 1(1), p. 38-43.

Trunilina, V. A., Parfenov, L. M., Leier, P. V., Orlov, Y. S., and Zaitsev, A. I., 1996. Sredenepaleozoiskii Tommottskii massiv shchelochnylkh gabbroidov i sienitov Verkhoyano-Kolymskikh mezozoid i ego tektonicheskaya pozitsiya (severo-vostok Rossii): Geologiya i Geofizika, v. 37(4), p. 71-82 Alaska

Other Geochronologic investgations in Alaska

In addition to the projects discussed elsewhere, the laboratory has been involved in research in a variety of problems of relevance to learning about the geologic history of Alaska. Many of these projects are done in collaboration with the state Geologic Survey, the USGS Alaska branch or personnel at other universities.

Publications

Cole, R. B., K. D. Ridgeway, P. W. Layer and J. Drake, 1996, Volcanic history, geochronology and deformation of the Upper Cantwell formation, Denali National Park, Alaska: Early Eocene transition between terrane accretion and strike-slip tectonics, 1996 Geol. Soc. Am. Abstracts with Programs Annual Meeting, v28, A313.

Layer, P.W., and J. Cook, 1995, Laser 40Ar/39Ar dating of obsidian from Alaskan archeological sites and an aid in the determination of artifact sources, 1995 Geol. Soc. Am. Abstracts with Programs Cordillerian Section, v27, A60.Paegle, J. S. , P. W. Layer, and A. W. West, (in press), Cooling history of the Okpilak batholith, northeastern Brooks Range, as determined from potassium-feldspar thermochronometry, Short notes on Alaskan Geology 1996, Professional report.Peapples, P. R., Wallace, W. K., Hanks, C. L., O'Sullivan, P. B., and Layer, P. W., 1997, Style, controls, and timing of fold-and-thrust deformation of the Jago stock, northeastern Brooks Range, Alaska, Can. J. Earth Sci., v 34, p. 992-1007.Solie, D.N. and Layer, P.W., 1993, The Hayes Glacier fault southern Alaskan Range: Evidence for post-Paleocene movement, Short notes on Alaskan Geology 1993, Professional report 113, 71-80.

West, A., 1994, A petrologic and geochronologic study of the McKinley, Pluton, Alaska, M.S. thesis, University of Alaska, 181p

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Last modified May 4, 2007 by geology@uaf.edu