High precision trace element data are reported for representative samples o
f the upper continental crust: 11 loess samples and 22 shale samples (PAAS)
previously used by Taylor and McLennan to define the rare earth element (R
EE) content of the upper crust. Our results confirm the REE concentrations
of Taylor and McLennan's [Taylor, S.R., McLennan, S.M., 1985. The continent
al crust: its composition and evolution. Blackwell, Oxford, 312 pp.] estima
te of the upper continental crust but suggest substantial revisions for Nb
and Ta, in agreement with recent work of Plank and Langmuir [Plank, T., Lan
gmuir, C.H., 1998. The chemical composition of subducting sediment and its
consequences for the crust and mantle. Chem. Geol. 145, 325-394.]. From our
data, the upper continental crust has average Nb = 11.5 +/- 2.6 ppm (inste
ad of 25 ppm) and Ta = 0.93 +/- 0.12 ppm (instead of 2.2 ppm), which transl
ates into a bulk crust Nb = 8 ppm, Ta = 0.7 ppm, La/Nb = 2.2, and Nb/Ta = 1
2-13. These revisions confirm the crustal subchondritic Nb/Ta and superchon
dritic La/Nb ratios and reinforce the observation that the continental crus
t and the Depleted Mantle are not strictly complementary: an additional Nb-
and Ta-rich reservoir having superchondritic Nb/Ta is required to balance
the Silicate Earth. Using the continental crust's La/Nb ratio to estimate t
he proportions of crustal growth in convergent margin and intraplate settin
gs, we suggest a plume contribution of only between 5 and 20% to the contin
ents, even lower than previous estimates. (C) 2000 Elsevier Science B.V. Al
l rights reserved.