PAUL B. TOMASCAK

Assistant Research Scientist and
Manager, Isotope Geochemistry Laboratory
Department of Geology
University of Maryland
Building 237, Regents Dr.
College Park, MD 20742  USA
office: 301.405.4054, fax: 301.314.9661

Research 

Lithium isotope studies: 
We are still in our infancy in understanding the scope of stable Li isotope (d⁷Li) variability in nature, and are even earlier in our understanding of the mechanisms of these fractionations. My interest in Li isotopes increased during my time at DTM, where I developed measurement techniques using MC-ICP-MS. The Nu Plasma instrument at Maryland has made measuring Li isotopes possible in even smaller samples and to better precision.
Lithium isotopes hold great potential in mantle studies, particularly for identifying incorporated crustal components, both in modern and paleo- convergent margins (arc lavas and exhumed eclogites) and in the mantle as a whole. My studies in this area have focused on characterizing the MORB reservoir and the processes active in modern subduction zones. Current work is in collaboration with other members of the Isotope Geochemistry Laboratory at Maryland (W.McDonough, R.Rudnick, T.Zack) and with Liz Widom at Miami University.
While at Lamont-Doherty I teamed with Gary and Sidney Hemming to begin a geochemical study of Mono Lake, California. The goal of the study is to determine the modern budget for elements like Li and to use these relations to trace the composition of the lake back through time using carbonate sediments. Although changes in lake level over its long history have been described, it is unknown how water composition has changed. This project has expanded to include other saline lakes of the Great Basin and the Antarcic (with W.B. Lyons at Ohio oState University) in ultimate hopes of understanding the mechanisms of light element fractionation in these hydrological environments.

Granites and tectonics: 
Geochemistry is but one tool by which complex processes like the tectonic assembly of an orogen may be understood. Continuing from my previous work on granitic rocks in Maine, I joined with Gary Solar of SUNY College at Buffalo to explore an area marked by a major crust-scale shear zone system. We seek to couple detailed field and microstructural observations with geochemical and geochronological studies of granites to address the potential interrelatedness of shear zones and melt transfer in the crust: processes that transcend the Appalachians. I continue to study the origin and development of granitic pegmatites in orogenic belts. Radiogenic isotopes afford opportunities to explore links in granite-pegmatite systems, whereas Li isotopes may ultimately allow us to better understand the magmatic-hydrothermal transition as well as the nature of fluid flow during orogensis. 

Education and Fellowships

N.S.F. Postdoctoral Research Fellow (1998-2000) Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY
Carnegie Postdoctoral Research Fellow (1996-1998) Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, DC
Ph.D. (1995) University of Maryland (R.J. Walker, advisor)
M.Sc., geology (1991) University of Manitoba, Winnipeg, Manitoba, Canada (P. Cerny, advisor)
B.S., geology (1988) New Mexico Institute of Mining and Technology, Socorro, NM

Publications (click for abstracts/downloads)

Papers in Peer-Reviewed Literature since 1996:

Tomascak PB, Hemming NG, and Hemming SR (2003) The lithium isotopic composition of waters of the Mono Basin, California. Geochim. Cosmochim. Acta 67 (4), 601-611.

Zack T, Tomascak PB, Rudnick RL, Dalpe C and McDonough WF (2003) Extremely light Li in orogenic eclogites: The role of fractionation during dehydration in subducted oceanic crust. Earth Planetary Sci. Lett. 208, 279-290 .

Tomascak PB, Widom E, Benton LD, Goldstein SL, Ryan JG, and Tera F (2002) The control of lithium budgets in island arcs, Earth Planetary Sci Lett 202, .

Owens BE and Tomascak PB (2002) Mesoproterozoic lamprophyres of the Labrieville Massif, Quebec: clues to the origin of alkalic anorthosites? Can J Earth Sci 39 (6), 983-997. 

Tomascak PB, Ryan JG, and Defant MJ (2000) Lithium isotope evidence for light element decoupling in the Panama subarc mantle. Geology 28(6), 507-510.

Tomascak PB, Tera F, Helz RL, and Walker RJ (1999) The absence of lithium isotope fractionation during basalt differentiation: new measurements by multi-collector sector ICP-MS. Geochim. Cosmochim. Acta 63 (6), 907-910.

Tomascak PB, Carlson RW, and Shirey SB (1999) Accurate and precise determination of Li isotopic compositions by multi-collector sector ICP-MS. Chemical Geology/Isotope Geosciences 158, 145-154.

Tomascak PB, Krogstad EJ and Walker RJ (1999) The significance of the Norumbega Fault Zone in southwestern Maine: clues from the geochemistry of granitic rocks. G.S.A. Special Paper 331: The Norumbega Fault Zone (A. Ludman and D.P. West, Jr., eds), p. 105-119.

Meisel T, Melcher F, Tomascak PB, Dingeldey C, Koller F (1998) Re-Os isotopes in orogenic peridotite massifs from the Eastern Alps, Austria. Chemical Geology 143, 217-229.

Tomascak PB, Krogstad EJ and Walker RJ (1998) Sm-Nd isotope systematics and the derivation of granitic pegmatites in southwestern Maine, USA. Canadian Mineralogist 36 (2), 327-337.

Tomascak PB, Krogstad EJ and Walker RJ (1996) Nature of the crust in Maine, USA: evidence from the Sebago batholith. Contributions to Mineralogy and Petrology 125, 45-59.

Tomascak PB, Krogstad EJ and Walker RJ (1996) U-Pb monazite geochronology in granitic rocks from Maine: Implications for late Paleozoic tectonics in the northern Appalachians. Journal of Geology 104, 185-195.

last updated 6/25/03