Trace element concentrations and B isotope compositions were determined for lavas from the Eastern Volcanic Front (EVF), the Central Kamchatka Depression (CKD), and the Sredinny Range (SR) in the Kamchatka are. Trace element ratios and delta B-11 values of the EVF lavas show across-arc variations that are consistent with those observed in the adjacent Kurile are: B/Nb, Pb/Nb, and delta B-11 are highest at the volcanic front (14 to 22, 2.0 to 2.4, and +4.9 to +5.6 parts per thousand, respectively) and systematically decrease with increasing slab depth (to similar to3, similar to0.9, and similar to2 parts per thousand, respectively) whereas Rb/Nb, Ba/Nb, K/Nb, Be/Nb, and Li/Zr do not vary significantly across the are. The values for the SR (B/Nb = 1.7 to 2.0, Pb/Nb = 0.9 to 1.2, and delta B-11 = -3.7 to -1.1 parts per thousand) located far behind the EVF are consistent with these across-are trends. However, the CKD lavas exhibit elevated B/Nb (6 to 13) and delta B-11 values (-0.6 to +3.6 parts per thousand) although the slab depths are greater than at the EVF, Despite variations in B/Nb and delta B-11, the values for all these three volcanic zones of Kamchatka can be explained in terms of simple mixing between a depleted mantle wedge and slab-derived aqueous fluids with a relatively homogeneous delta B-11 (+6.2 +/- 0.5 parts per thousand). This mixing trend resembles those observed in Kurile, Izu, and Mariana, suggesting that fluids derived from altered oceanic crust and/or serpentinized peridotite in the subducting slab predominate in the slab-mantle interaction beneath these western Pacific arcs. Given this mixing relationship, the high B/Nb and delta B-11 values observed in the CKD indicate particularly large fluid influx beneath this region, which may partly result from subduction of the altered crust of the Emperor seamount chain in addition to the altered Mid-Ocean Ridge Basalt (MORB) crust. The compositions of the SR lavas in this study are consistent with melting of a weakly fluid-metasomatized mantle. However, the origin of magma in this volcanic zone is complicated, judging from the variable chemical characteristics reported for the SR lavas, Copyright (C) 2001 Elsevier Science Ltd.

Complementary, double- and single-resonance solid-state (H-1 and C-13) nuclear magnetic resonance (NMR) experiments were performed on a solvent extracted and demineralized sample of Murchison meteorite organic macromolecule. These NMR data provide a consistent picture of a complex organic solid composed of a wide range of organic (aromatic and aliphatic) functional groups, including numerous oxygen-containing functional groups. The fraction of aromatic carbon within the Murchison organic residue (constrained by three independent experiments) lies between 0.61 and 0.66. The close similarity in cross-polarized and single-pulse spectra suggests that both methods detect the same distribution of carbon. With the exception of interstellar diamond (readily detected in slow magic angle spinning single-pulse NMR experiments), there is no evidence in the solid-state NMR data for a significant abundance of large laterally condensed aromatic molecules in the Murchison organic insoluble residue. Given the most optimistic estimation, such carbon would not exceed 10%, and more likely is a fraction of this maximum estimate. The fraction of aromatic carbon directly bonded to hydrogen is low (similar to30%), indicating that the aromatic molecules in the Murchison organic residue are highly substituted. The bulk hydrogen content, H/C, derived from NMR data, ranges from a low of 0.53 +/- 0.06 and a high of 0.63 +/- 0.06. The hydrogen content (H/C) determined via elemental analysis is 0.53. The range of oxygen-containing organic functionality in the Murchison is substantial. Depending on whether various oxygen-containing organic functional groups exist as free acids and hydroxyls or are linked as esters and ethers results in a wide range in O/C (0.22 to 0.37). The lowest values are more consistent with elemental analyses, requiring that oxygen-containing functional groups in the Murchison macromolecule are highly linked. The combined H-1 and C-13 NMR data reveal a high proportion of methine carbon, which requires that carbon chains within the Murchison organic macromolecule are highly branched. Copyright (C) 2002 Elsevier Science Ltd.

Lead isotopes are compared in two equivalent diagrams. With a range in U/Pb, a closed system that evolved its radiogenic Pb in a single stage yields data that define a line of exactly the same age in the two presentations. This strict reproducibility (within +/- a few 10(6) yr, at most) is the crux of the concept of Pb-isotope synchronism. In contrast, an open system produces data that disperse variably in the two diagrams, yielding ages which are often different by much greater than 107 yr. However, because an age-calculation reconciles uncertainty in the age with the degree of dispersion in the data, a highly disturbed system yields false ages (from both diagrams), which nevertheless overlap within the calculated errors.