Erik E. Scherer

Bio: Erik E. Scherer is an academic researcher from University of Münster. The author has contributed to research in topics: Eclogite & Zircon. The author has an hindex of 32, co-authored 76 publications receiving 5985 citations. Previous affiliations of Erik E. Scherer include University of California, Santa Cruz & University of Massachusetts Amherst.

Calibration of the lutetium-hafnium clock.

Abstract: Well-defined constants of radioactive decay are the cornerstone of geochronology and the use of radiogenic isotopes to constrain the time scales and mechanisms of planetary differentiation. Four new determinations of the lutetium-176 decay constant (lambda176Lu) made by calibration against the uranium-lead decay schemes yield a mean value of 1.865 +/- 0.015 x 10(-11) year(-1), in agreement with the two most recent decay-counting experiments. Lutetium-hafnium ages that are based on the previously used lambda176Lu of 1.93 x 10(-11) to 1.94 x 10(-11) year(-1) are thus approximately 4% too young, and the initial hafnium isotope compositions of some of Earth's oldest minerals and rocks become less radiogenic relative to bulk undifferentiated Earth when calculated using the new decay constant. The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more. Hence, current models of early terrestrial differentiation need revision.

Separation of high field strength elements (Nb, Ta, Zr, Hf) and Lu from rock samples for MC‐ICPMS measurements

Abstract: [1] The application of multiple collector inductively coupled plasma source mass spectrometry (MC-ICPMS) to 176Lu-176Hf and 92Nb-92Zr chronometry has been hampered by complex Zr-Hf purification procedures that involve multiple ion exchange column steps. This study presents a single-column separation procedure for purification of Hf and Lu by ion exchange using Eichrom® Ln-Spec resin. The sample is loaded in pure HCl, and element yields are not dependent on the sample matrix. For 92Nb-92Zr chronometry, a one-column procedure for purification of Zr using Biorad® AG-1-× 8 resin is described. Titanium and Mo are completely removed from the Zr, thus enabling accurate 92Zr measurements. Zirconium and Nb are quantitatively separated from rock samples using Eichrom Ln-Spec resin, allowing measurements of Zr/Nb with a precision of better than ±5% (2σ). The Ln-Spec and anion resin procedures may be combined into a three-column method for separation of Zr-Nb, Hf, Ta, and Lu from rock samples. For the first time, this procedure permits combined isotope dilution measurements of Nb/Ta, Zr/Hf, and Lu/Hf using a mixed 94Zr-176Lu-180Hf-180Ta tracer. Analytical protocols for Zr and Hf isotope measurements using the Micromass Isoprobe, a second generation, single-focusing MC-ICPMS, are reported. Using the Isoprobe at Munster, 2σ external precisions of ±0.5ɛ units for Hf and Zr isotope measurements are achieved using as little as 5 ng (Hf) to 10 ng (Zr) of the element. The 176Hf/177Hf and Lu/Hf for rock reference materials agree well with other published MC-ICPMS and thermal ionization mass spectrometry (TIMS) data.

Composition of the Continental Crust

Abstract: This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.

Continental and Oceanic Crust Recycling-induced Melt^Peridotite Interactions in the Trans-North China Orogen: U^Pb Dating, Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths

Abstract: We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt^lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2·4^2·5 Ga, 1·6^2·2 Ga and 0·6^1·2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt^peridotite interaction and subsequent high-pressure metamorphism.The 2·5 Ga zircons have positive eHf(t) values (2·9^10·6), whereas the younger Precambrian zircons are dominated by negative eHf(t) values, indicating an ancient continental crustal origin.These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 3 Ma (2 ), 80^170 Ma and 48^64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt^peridotite interactions in the central zone of the NCC. The combination of the positive eHf(t) values (2·91^24·6) of the 315 Ma zircons with the rare occurrence of 302^324 Ma subduction-related diorite^granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt^peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80^170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies.The eHf(t) values of these zircons vary greatly from ^47·6 to 24·6.The 170^110 Ma zircons are generally characterized by negative eHf(t) values, whereas the 110^100 Ma zircons have positive eHf(t) values.These observations suggest that melt^peridotite interactions at 80^170 Ma were induced by partial melting of recycled continental crust. The 48^64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive eHf(t) values.These features imply that the melt^peridotite interactions at 48^64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.