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"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

Albert Einstein

M.Sc., University of Lausanne (Switzerland) 2003 | Ph.D., University of Bern (Switzerland) 2008

Research interests

• Metamorphic petrology: Evolution of mineral assemblage, state of equilibrium, thermobarometry calculation (TWQ, THERIAK-DOMINO [R. Berman; C. de Capitani] and THERMOCALC [T. Holland & R. Powell]), disequilibrium process.
• Microanalysis, isotope geochemistry: Mineral analysis (major and REE), Ar-Ar geochronology, stable oxygen isotope analysis on silicates, U-Th-Pb dating of monazite.
• Structural geology: Crystallization-deformation-time relations, vein formation, geological maps.

Current research at UMass-Amherst

Julien started his post-doctorate at the department end of July 2009. He is collaborating on two main projects under the supervision of Michael L. Williams:

• Eastern Athabasca Mylonite Triangle (Saskatchewan, Canada): granulite facies mafic and felsic rocks, lower crust
• Grand Canyon (Arizona, USA): amphibolite to granulite facies felsic and pelitic rocks, middle crust

Both projects involve monazite dating. As usual in geochronology, the challenge is to relate an age with a specific geological feature. We investigate here the relation between petrology (thermobarometry), deformation and geochronology in these samples from middle to lower crust. More information will be soon available on Julien's website (geoloweb.ch) or on this page.

Additionally, Julien is partly responsible for the electron microprobe facility (CAMECA SX-50 and UltraChron SX-100), under the supervision of Michael J. Jercinovic. As part of this work, a database for managing microanalysis is currently under development. Access to the database is currently password-protected (here).

Past research

After graduating, Julien did his MSc in structural geology and metamorphic petrology at the University of Lausanne (Institute of Mineralogy and Geochemistry), together with Xavier Maeder, and under the supervision of Prof. Albrecht Steck and PD Dr. Jean-Claude Vannay. This study was conducted in the Swiss Central Alps and included two different topics. First, a detailed petrological and structural study helped us to place the Larecc anticline in the alpine deformation history. Second, the appearance of aluminosilicate-bearing (kyanite and/or andalusite) quartz veins was questioned. This study led to a publication in the Swiss Bulletin of Mineralogy and Petrology (PDF, circa 4.3 Mo). More information available on larecc.geoloweb.ch.

Julien finished in 2008 his PhD about metamorphic petrology and Ar-dating of micas in the northern Central Alps of Switzerland. This study was performed at the University of Bern (Institute of Geological Sciences) under the supervision of Prof. Martin Engi, Prof. Igor M. Villa and PD Dr. Alfons Berger, with collaboration of Dr. Emilie Janots. U-Th-Pb ages on monazite and allanite from Dr. Janots were used to evaluate the significance of Ar-ages, for which we proposed a closure-temperature around 500°C for muscovite and 450°C for biotite. This study demonstrated that good constraints on the pressure and temperature evolution of samples to be dated are necessary, but not sufficient, to yield geologically meaningful metamorphic ages. Related publications are either under review or in preparation. More information available on thesis.geoloweb.ch.

Publications

• Julien Allaz, Martin Engi, Alfons Berger, and Igor M. Villa (submitted): The role of retrograde reactions and of diffusion on ³⁹Ar-⁴⁰Ar ages of micas, Journal of Petrology.
• Julien Allaz (2008): Metamorphic evolution in the northern Central Alps: linking ³⁹Ar-⁴⁰Ar dating with thermobarometry, PhD Thesis, University of Berne, 208 pp (PDF High quality - Low quality).
• Emilie Janots, Martin Engi, Alfons Berger, Julien Allaz and Oliver Schwarz (2008): Metamorphic sequence of REE-minerals in pelitic rocks of the Central Alps: Implications on allanite - monazite - xenotime phase relations, Journal of Metamorphic Geology 26, 509-526. doi:10.1111/j.1525-1314.2008.00774.x
• Julien Allaz, Xavier Maeder, Jean-Claude Vannay and Albrecht Steck (2005): Formation of aluminosilicate-bearing quartz veins in the Simano nappe (Central Alps): structural, thermobarometric and oxygen isotope constraints, Schweizerische Mineralogische und Petrographische Mitteilungen 85 / 2-3, 191-214. (PDF)

Contact Dr. Julien Allaz Department of Geosciences University of Massachusetts 611 North Pleasant Street Amherst, MA 01003-9297 (USA) Email: URL: http://geoloweb.ch

"It was during my enchanted days of travel that the idea came to me, which, through the years, has come into my thoughts again and again and always happily - the idea that geology is the music of the earth."

Hans Cloos