319 Heroy Geology Laboratory
Scott D. Samson
Professor of Earth Sciences
Research and Teaching Interests
My primary research interests are related to the evolution of the Earth's continental crust, the tectonic/magmatic evolution of Neoproterozoic orogenic belts, tephrochronology of ancient tephra, and new geochemical approaches to sedimentary provenance. Research projects involve the use of the Nd, Sr, Pb and Hf isotopes, major and trace element chemistry, and U-Pb geochronology, to solve a wide variety of geological problems. A few of the current projects my students are involved in are described below.
• LARGE SCALE CORRELATION OF ORDOVICIAN ASH BEDS – North America and Scandinavia: Numerous Ordovician K-bentonites occur throughout the mid-continent and eastern USA as well as in Denmark, Norway and Sweden. The ash beds have essentially identical physical features, making correlation of individual bentonites by traditional methods impossible. However, we have developed new geochemical techniques, including the trace element chemistry and isotopic composition of apatite phenocrysts, that can be used to identify individual beds. Correlations can now be made for certain key beds that we have traced from Kentucky through to Pennsylvania, New York, Minnesota, Wisconsin, Iowa, and Ohio – distances exceeding 1,000 km! Correlating these ash beds is important because the correlations allow us, for the first time, to ‘stitch’ together strata that are conodont-bearing with those that are graptolite-bearing. The ash beds are thus a bridge between two separate but powerful biostratigraphic indicators. We are continuing this research to ash beds of similar age in Scandinavia, with a major goal being testing the provocative hypothesis that the same, unusually thick, ash bed occurs on both continents.
• NEW APPROACHES TO SEDIMENTARY PROVENANCE – In the last decade there has been a huge increase in the number of studies that rely on the age of detrital zircon to help distinguish the provenance of clastic sedimentary rocks. That information is used in a variety of ways, one of the most important being to unravel the history past major tectonic events in an area. However, our recent work has demonstrated that the detrital zircon record is actually one of low ‘tectonic fidelity’. For example, by relying on the ages of detrital zircon from Pennsylvanian – Recent sediments one would miss the occurrence of the Alleghanian Orogeny. It is as if the Himalayan-scale collision between Laurentia and the supercontinent Gondwana newver occurred! We are thus in the process of testing the idea that the age of detrital monazite (a rare-earth phosphate mineral common in metamorphic rocks) may be a more accurate recorder of past tectonic events. Furthermore, in addition to deteriming U-Th-Pb ages of detrital monazite we are testing the ability to ‘fingerprint’ the origin of individual crystals using both their chemical and Nd isotopic composition. This full interrogation of accessory minerals may provide great advances in our understanding of the origins of sedimentary units, and thus provide a much more accurate view of past tectonic events.
• THE ORIGINS OF OROGENS – There are a number of intriguing similarities between late Neoproterozoic rocks in the southern Appalachians, Canadian Appalachians, coastal France, and the Anti-Atlas mountains of Morocco. These circum-Atlantic regions all contain large, lithologically similar Neoproterozoic terranes. Because of a lack of geochemical and isotopic data for these terranes, as well as a poor geochronological record, the relationship of each of these orogens is not yet understood. My graduate students have been working in each of these regions to better understand the tectonic evolution of the region, its magmatic history, the nature of the orogen basement, and their timing of accretion. In addition to field work, students are involved in high precision U-Pb geochronology, and Nd-Sr-Pb isotopic research.
• MAGMATIC COMPLEXITY AND ISOTOPIC ZONATION IN APATITE – The notion that all minerals crystallizing from a magmatic body have the same initial isotopic composition is one often repeated in undergraduate courses. However, the reality is that magma generation, evolution and emplacement is a very complex process and the idea of complete mineral isotopic homogeneity is only a generalization. Recent studies of Cenozoic volcanic rocks have shown that initial Sr isotopic variation is not uncommon in plagioclase and sanidine phenocrysts, with both increases and decreases in 87Sr/86Sr from core to rim being observed. Comparable variations in initial isotopic ratios in plutonic feldspar are much rarer, but have been reported. In addition, there have been interesting reports of both oxygen and hafnium isotopic variation within single zircon crystals in granitoids, suggesting that isotopic zonation is more common than thought, even in slowly cooled magmatic systems.
Ce zonation in apatite Given the importance of these previous results we are investigating the isotopic composition of apatite in a series of ~ 300 Ma granitoids from southeastern USA. Our approach has been to compare whole apatite crystals with cores, rims, and whole-rock values. To analyze the cores of crystals we have followed two methods – physical abrasion to remove ~ 50% of the outer portion of the crystals, and acid leaching of the apatite to provide us with rim material and residual, core material. Because leaching may not simply attack rims, but could dissolve inner portions of the apatite following microcracks or fission-tracks, we first annealed the apatite at 300ºC. This is hot enough to anneal the crystals but substantially below temperature-driven Sr or Nd diffusion. Our preliminary results are comparable to those found in the volcanic studies – in some cases 87Sr/86Sr increases from core to rim, in other granites the opposite is observed. Variations in 143Nd/144Nd also occur between core and rim.
It thus appears that some Alleghanian granitic magmas were isotopically juvenile and after a period of crystallization interacted with isotopically evolved material, whereas in other bodies evolved magmas were apparently injected by more juvenile, perhaps mafic, magmas. Thus it appears that apatite could be an incredible recorder of the complex events that occur in magmatic systems. To test further the ‘magmatic memory’ of apatite we will examine suites of granitoids that formed in very different environments than those in the Appalachians, such as mantle-dominated environments and in regions where granites had significant interaction with ancient basement material.
Dynamic Earth (EAR 101)
Geochemistry (EAR 417/617)
Geochemical record of major events in Earth’s history (EAR 400/600)
Isotope Geology (EAR 478/678)
Bonich, Mariana (Ph.D. Student)
Satkoski, Aaron (Ph.D. Student)
Salerno, Ross (Freshman)
Syracuse University Radiogenic Isotope Laboratory
The main components of the Scott Samson’s radiogenic isotope laboratory include a VG Sector 54 thermal ionization mass spectrometer TIMS equipped with seven Faraday detectors and an ion-counting Daly photomultiplier detector system, a custom-modified degas bench, a large class 100 clean laboratory, full mineral separation facilities, and most recently, a high pressure microwave digestion system, the Milestone Ethos plus. Avariety of different studies are pursued in the radiogenic isotope laboratory, but the current emphasis is on studies combining high precision U-Pb dating of accessory minerals (zircon, monazite, titanite, and xenotime) with Sm-Nd, Rb-Sr, and common Pb isotopic measurements. Lu-Hf isotopic studies are also being pursued now that chemical techniques to isolate Hf have been developed as standard part of our traditional U and Pb separation procedures of dissolved zircon. Each of the major components of the laboratory are described below.
The originally purchased VG degas bench, employing a Balzers turbo pump and Edwards roughing pumps, new Degas Bench has undergone a series of dramatic modifications. The system now incorporates a custom fabricated all stainless housing (replacing the older bell jar system) equipped with a liquid nitrogen cold finger and with a combined ceramic and stainless steel filament black design that can be completely dismantled and cleaned with nitric acid. As a result ultra-low Pb loading blanks can be consistently obtained (~ 0.1 picograms). This bench will continue to be used with the new TIMS.
The clean lab, originally constructed in 1990, has also undergone a series of significant upgrades. The primary upgrades include he installation of series of large class 10 laminar flow benches where all chemical separations occur. In addition, specially designed ‘clean boxes’ were constructed allowing samples to be dried down under continuous flow of HEPA-filtered air with Teflon beakers exposed to only Plexiglas and Teflon material (i.e. all metal components are shielded). Clean LabThis simple, but elegant, design has been copied by a number of research s who have visited the SU radiogenic isotope laboratory.
The most recent upgrades include a new large, custom-made HEPA-filtered exhaust hood allowing for both class 10 chemistry and the exhausting of acid fumes, a new Millipore water purification system (replacing the previous aging Millipore system), and an overhaul of the electrical system feeding the clean laboratory. It is partly thanks to this excellently designed clean laboratory that we are able to obtained full Pb procedural blanks of < 1 picogram.
Scott Samson has been working with microwave digestion companies for the past decade to help develop a microwave system capable of reaching and maintaining very high (~ 280 °C) temperatures for several hours. Ethos Microwave OvenRecently, the Milestone company developed a proto-type instrument designed to hold vessels at 270 – 280 °C for a minimum of two hours with the goal of being able to completely dissolve zircon. Scott Samson worked with Milestone engineers and finally they were able to produce an instrument capable of digesting typical zircon within two hours. The normal current dissolution times for zircon at the SU laboratory (using a conventional oven and Parr metal jacket system) is between 48-60 hours. As a result of the successful demonstration a system was purchased. This is the only such ultra high-pressure microwave system in the USA. Its substantial advantage is a dramatic increase in sample throughput for digestion, the lowering of blanks due to the reduced time of solutions in contact with vessels, and the ability to rapidly clean beakers at very high temperatures.
Syracuse University Radiogenic Isotope Laboratory
Samson, S.D., and Moecher, D., in review, High resolution zircon-based provenance studies: Integrating sampling, imaging, and in situ microanalytical methodologies: Earth and Planetary Science Letters.
* Hietpas, J., Samson, S.D., Moecher, D., and Schmitt, A., in review, Detrital monazite: A higher fidelity provenance proxy than detrital zircon?: Nature Geoscience.
*Carey, A., Samson, S.D., and Sell, B., in press, Utility and limitations of apatite phenocryst chemistry for continent-scale correlation of Ordovician K-bentonites: Journal of Geology.
* D’Lemos, Samson, S.D. and Strachan, R. (2008), The geological evolution of North Armorica: in, The Geology of Central Europe (U. Linneman, ed.), The Geological Society of London.
* Azzolina,N.A., Siegel, D.I. ,Brower, J.C., Samson, S.D., Otz, M.H. and Otz. I. (2007), Can the HGM Classification of Small Non-Peat Forming Wetlands Distinguish Wetlands From Surface Water Geochemistry: Wetlands, 27, 884-893.
* Moecher, D.P. and Samson, S.D. (2006) Differential zircon fertility of source terranes and natural bias in the detrital zircon record: Implications for sedimentary provenance analysis: Earth and Planetary Science Letters, 247, 252-266.
* Ivany, L., Simaeys, S.V., Domack, E.W., and Samson, S.D. (2006), Evidence for an earliest Oligocene ice sheet on the Antarctic Peninsula: Geology, 34, 377-380.
* D’Lemos, R.S., Samson, S.D., and Inglis, J.D. (2006), A newly discovered orogenic event in Morocco: Neoproterozoic ages for supposed ‘Eburnian’ basement of the Bou Azzer inlier, Anti-Atlas Mountains: Precambrian Research, 147, 75-78.
* Samson, S.D., D'Lemos, R.S., Miller, B.V. & Hamilton, M.A. (2005) Neoproterozoic palaeogeography of the Cadomia and Avalon terranes: constraints from detrital zircon U–Pb ages, J. Geol. Soc., Lond. 162 , 65-71.
* Inglis, J.D., D’Lemos, R.S., Samson, S.D. & Admou, H. (2005) Geochronological Constraints on Late Precambrian intrusion, metamorphism, and tectonism in the Anti-Atlas Mountains, J. Geol. 113, 439 - 450.
* Becker, T.P., Thomas, W.A., Samson, S.D. and Gehrels, G.E. (2005), Detrital zircon evidence of Laurentian crustal dominance in the Lower Pennsylvania deposits of the Alleghanian clastic wedge in eastern North America: J. of Sedimentology, 182, 59-86.
* Owens, B.E. and Samson, S.D. (2004) Nd isotopic constraints on the magmatic history of the Goochland terrane, easternmost Grenville crust in the southern Appalachians, GSA Special Paper 197 , 601-608.
* Samson, S.D., Inglis, J.D., D'Lemos, R.S., Admou, H., Blichert-Toft, J. & Hefferan, K. (2004) Geochronological, geochemical, and Nd–Hf isotopic constraints on the origin of Neoproterozoic plagiogranites in the Tasriwine ophiolite, Anti-Atlas orogen, Morocco, Precambrian Research 135 , 133–147.
* Inglis, J.D., Maclean, J.S., Samson, S.D., D'Lemos, R.S., Admou, H. & Hefferan, K. (2004) A precise U-Pb zircon age for the Bleïda granodiorite, Anti-Atlas, Morocco: implications for the timing of deformation and terrane assembly in the eastern Anti-Atlas, J. Afr. Earth Sci. 39 , 277-283.
* Thomas, W.A., Becker, T.P., Samson, S.D. & Hamilton, M.A. (2004) Detrital zircon evidence of a recycled orogenic foreland provenance for Alleghanian clastic-wedge sandstones, J. Geol. 112 , 23-37.
* Inglis, J.D., D’Lemos, R.S., Samson, S.D. & Miller, B.V. (2004) Timing of Cadomian deformation and magmatism within La Hague, NW France, J. Geol. Soc., Lond. 161, 1-12.
* Patchett, P.J. & Samson, S.D. (2003) Isotopic evolution and crustal growth history, In: Rudnick (ed.) Treatise of Geochemistry 3 , The Crust, Elsevier-Pergamon, Oxford, 321-348.
* Moecher, D.P., Samson, S.D. & Miller, C.F. (2004) Precise time and conditions of peak Taconian granulite facies metamorphism in the southern Appalachian orogen, U.S.A., with Implications for zircon behavior during crustal melting events, J. Geol. 112 , 289-304.
* Inglis, J.D., Samson, S.D., D'Lemos, R.S. & Hamilton, M. (2004) Evidence for Neoproterozoic crustal thickening within the Paleoproterozoic basement of Cadomia, La Hague, NW France, Precambrian Research , 134 (3-4) 293-315.
* Samson, S.D., D'Lemos, R.S., Blichert-Toft, J. & Vervoort, J. (2003) U-Pb geochronology and Hf-Nd isotope compositions of the oldest Neoproterozoic crust within the Cadomian Orogen: new evidence for a unique juvenile terrane, Earth Planet. Sci. Lett. 208 , 165-180.
* Hefferan, K., Admou, H., Hilal, R., Karson, J., Saquaque, A., Samson , S., & Kornprobst, J. (2002) Proterozoic blueschist-bearing mélange in the Anti-Atlas Mountains, Morocco, Precambrian Research 118 , 179-184.
* Miller, B.V., Samson, S.D. & D'Lemos, R.S. (2001) U-Pb geochronological constraints on the timing of plutonism, volcanism, and sedimentation, Jersey, Channel Islands, UK, J. Geol. Soc., Lond. 158 , 243-252.
* Barr, S.M., Hamilton, M.A., White, C.E. & Samson, S.D. (2001) A late Neoproterozoic age for the Caledonia Mountain Pluton, a high Ti-V layered gabbro in the Caledonia (Avalon) terrane, southern New Brunswick, Atlantic Geology 36 , 157-166.
* D'Lemos, R.S., Miller, B.V.M. & Samson, S.D. (2001) Precise U-Pb zircon ages from Alderney, Channel Islands: growing evidence for discrete Neoproterozoic magmatic episodes in northern Cadomia, Geol. Mag. 138 , 719-726. * Nagy, E.A., Samson, S.D. & D'Lemos, R.S. (2001) U-Pb geochronologic constraints on the timing of Brioverian sedimentation and regional deformation within the St. Brieuc region of the Neoproterozoic Cadomian orogen, northern France, Precambrian Research 116 (1-2), 1-17.
* Wortman, G.L., Samson, S.D. & Hibbard, J.P. (2000) Precise U-Pb zircon constraints on the earliest magmatic history of the Carolina terrane, J. Geol. 108 , 321-338.
* Samson, S.D., Barr, S.M & White, C.E. (2000) Nd isotopic characteristics of terranes within the Avalon Zone, southern New Brunswick, Canad. J. Earth Sci. 37 , 1039-1052.
* Coler, D.G., Wortman, G.L., Samson, S.D., Hibbard, J.P. & Stern, R. (2000) U-Pb geochronologic, Nd isotopic and geochemical evidence for the correlation of the Chopawamsic and Milton terranes, Piedmont Zone, southern Appalachian Orogen, J. Geol. 108 , 363-380.
* Samson, S.D. & D'Lemos, R.S. (1999) Precise late Neoproterozoic U-Pb zircon age of the syn-tectonic Perelle quartz diorite, Guernsey, Channel Islands, UK, J. Geol. Soc., Lond. 156 , 47-54.
* Miller, B.V., Samson, S.D. & D'Lemos, R.S. (1999) Time span of plutonism, fabric development, and cooling in a Neoproterozoic magmatic arc segment: U-Pb age constraints from syn-tectonic plutons, Sark, Channel Islands, U.K., Tectonophysics 312 , 79-95.
* Wortman, G.L., Samson, S.D. & Hibbard, J.P. (1998) Precise timing constraints on the kinematic development of the Hyco Shear Zone, southern Appalachians, Am. J. Sci. 298 , 108-130.
* Hibbard, J.P., Shell, G.S., Bradley, P.J., Samson, S.D. & Wortman, G.L. (1998) The Hyco Shear Zone: the northern extension of the central piedmont suture in North Carolina and southern Virginia: American, J. Sci. 298 , 85-107.
* Changde, W., Nelson, K.D., Wortman, G.L., Samson, S.D., Yonjun, Y., Jixiang, Li, Kidd, W.S.F. & Edwards, M. (1998) Yadong cross-structure and south Tibet detachment in the East-Central Himalaya (89°-90°E), Tectonics 17 , 28-45.
* Samson, S.D. & D'Lemos, R.S. (1998) U-Pb geochronology and Sm-Nd isotopic composition of Proterozoic gneisses, Channel Islands, U.K, J. Geol. Soc., Lond. 155 , 609-618.
* Karabinos, P., Samson, S.D., Hepburn, J.C. & Stoll, H. (1998) Taconian orogeny in the New England Appalachians: Collision between Laurentia and the Shelburne Falls arc, Geology 26 , 215-218.
* Coler, D.G., Samson, S.D. & Speer, J.A. (1997) Nd and Sr isotopic constraints on the source of Alleghanian granites in the Raleigh Metamorphic belt and Eastern slate belt, southern Appalachians, Chem. Geol. 134 , 257-275.
* Wortman, G., Samson, S.D. & Hibbard, J.P. (1996) Discrimination of the Milton and Carolina slate belts, southern Appalachians: A Nd isotopic approach, J. Geol. 104 , 239-247.
* Andersen, B. & Samson, S.D. (1996) Temporal changes in the Nd isotopic composition of sedimentary rocks in the Sevier and Taconic foreland basins: Increasing influence of juvenile sources, Geology 23 , 983-986.
* Samson, S.D. (1996) 40Ar-39Ar and Nd-Sr isotopic characteristics of mid-Ordovician North American K- bentonites: A test of early Paleozoic Laurentia-Gondwana interactions, Tectonics 15 , 1084-1092.
* Samson, S.D., Coler, D.G. & Speer, J.A. (1995) Geochemical and Nd-Sr-Pb isotopic composition of Alleghanian granites in the southern Appalachians: Origin, tectonic setting, and source characterization, Earth Planet. Sci. Lett. 134 , 359-376.
* Hibbard, J.P. and Samson, S.D. (1995), Orogenesis exotic to the Iapetan cycle in the southern Appalachians, in Hibbard, J., van Staal, C.R., and Cawood, P., eds., New Perspectives in the Appalachian-Caledonian Orogen, Geological Association of Canada Special Paper 41, 191-205.
* Samson, S.D. (1995), Is the Carolina terrane part of Avalon? in Hibbard, J.P., van Staal, C.R., and Cawood, P., eds., New Perspectives in the Appalachian-Caledonian Orogen , Geological Association of Canada Special Paper 41, 253-264.
* Samson, S.D., Hibbard, J.P. and Wortman, G.L. (1995), Nd isotopic evidence for juvenile crust in the Carolina terrane, southern Appalachians: Contributions to Mineralogy and Petrology, 121, 171-184.
* Samson, S.D., Matthews, S.V.L., Mitchell, C.E., Goldman, D. (1995), Tephrochronology of highly altered ash beds: The use of trace element and strontium isotope geochemistry of apatite phenocrysts to correlate K-bentonites: Geochimica et Cosmochimica Acta, 59, 2527-2536.