Serpentinite: clasts and muds erupted from Conical Seamount, Mariana forearc, show substantial enrichment in boron (B) and B-11 (delta B-11 up to +15 parts per thousand) relative to mantle values. These elevated B isotope signatures result from chemical exchange with B-rich pore fluids that are upwelling through the seamount. If the trends of decreasing delta B-11 with slab depth shown by cross-are magmatic suites in the Izu and Kurile arcs of the western Pacific are extended to shallow depths (similar to 25 km), they intersect the inferred delta B-11 of the slab-derived fluids (+13 parts per thousand) at Conical Seamount. Simple mixtures of a B-rich fluid with a high delta B-11 and B-poor mantle with a low delta B-11 are insufficient to explain the combined forearc and are data sets. The B isotope systematics of subduction-related rocks thus indicate that the fluids evolved from downgoing slabs are more enriched in B-11 than the slab materials from which they originate. Progressively lower delta B-11 in are lavas erupted above deep slabs reflects both the progressive depletion of B-11 from the slab and progressively greater inputs of mantle-derived B. This suggests that the slab releases B-11-enriched fluids from the shallowest levels to depths greater than 200 km. (C) 2001 Elsevier Science B.V. All rights reserved.

A method for determining the initial Pb of a terrain, on the basis of the measured isotopic compositions of its rocks, is put forward in this report. The method was inspired by the premise that the initial Pb inherited by the rocks from a reservoir from which they were extracted, is immutable and inerasable, irrespective ofthe multitude of disturbances that may have subsequently been superimposed on the terrain. This is because while these disturbances may have altered the isotopic composition of some or all the rocks, they lacked the vehemence to re-melt the entire terrain or at least a very large portion of it, which is a pre-requisite for altering the isotopic composition of initial Pb. If this rational is valid, then a large Pb isotope database (including data on mineral separates with low affinities for U and Th) that is representative of a terrain, when plotted on any Pb isotope correlation diagram (e.g., the conventional Pb/Pb plot), may define a dispersion field that tapers toward a single spot. That single spot (once unambiguously determined) is the initial Pb isotopic composition.

The recently developed TULIP methodology for determining Initial lead, based on the measured Pb isotopic compositions of rocks, was applied to four terrestrial terrains, and the results are shown and discussed in this report. Particular emphasis was given to the determination of initial Pb of the South Of Isua (SOI) terrain, because of the availability of a large high-quality database on its rocks and feldspar separates. The initial Pb results for SOI, are: Pb-206/Pb-204 = 11.088 +/- 0.024, Pb-207/Pb-204 = 12.983 +/- 0.002, and Pb-208/Pb-204 = 31.196 +/- 0.014. Initial Pb was also precisely determined for the Beartooth Mountains, and the results are: 206/204 = 13.571 +/- 0.071, 207/204 = 14.891 +/- 0.003, and 208/204 = 32.41 +/- 0.08. These results demonstrate the feasibility of routine determination of initial Pb by the developed methodology, once large databases for the terrains are established. Extending the methodology to terrains of other planets should be possible.

Results of multiple sulfur isotope analyses from five Archean paleosols show the widespread presence of mass-independently fractionated sulfur in the regolith developed on the pre-2.5 Ga Earth. Analysis of sulfur from a small set of diamictite samples gave similar results. All values of Delta S-33 are negative, indicating that the Archean surface environments preferentially retained atmospheric S from the SO42- pathway, which carried a negative Delta S-33 signal, whereas a portion of the S from the S-8 pathway, with a positive Delta S-33, was transferred to the oceans. The soil SO42- was then converted to sulfide by bacterial sulfate reduction with terrestrial organic matter in the weathering horizon acting as a reductant. Some S from the S-8 pathway also included, which resulted in a net soil Delta S-33 anomaly from atmospheric S in the range-0.3 to-0.6%, similar to values for pyrites from floodplain sediments. Excess S-8-derived S was carried to the oceans, resulting in the negative/positive dichotomy between terrestrial and marine systems. Pyrite that formed in paleosols and pyrite grains that formed in flood-plain deposits, both carrying the terrestrial Delta S-33 signal, were then recycled into detrital pyrite grains nowfound in sand-stones and conglomerates deposited before the rise of atmospheric oxygen. Therefore the Earth's early regolith constituted a reservoir of S with negative Delta S-33 values that could be important for balancing the predominantly positive Delta S-33 signature found in marine sediments. (C) 2013 Elsevier B. V. All rights reserved.

Trojan and Shangani mines are low-grade (< 0.8 % Ni), komatiite-hosted nickel sulfide deposits associated with ca. 2.7 Ga volcano-sedimentary sequences of the Zimbabwe craton. At both mines, nickel sulfide mineralization is present in strongly deformed serpentinite bodies that are enveloped by a complex network of highly sheared, silicified, and sulfide-bearing metasedimentary rocks. Strong, polyphase structural-metamorphic-metasomatic overprints in both the Trojan and Shangani deposits make it difficult to ascertain if sulfide mineralization was derived from orthomagmatic or hydrothermal processes, or by a combination of both. Multiple S, Fe, and Ni isotope analyses were applied to test these competing models. Massive ores at Shangani Mine show mass-dependent fractionation of sulfur isotopes consistent with a mantle sulfur source, whereas S-isotope systematics of net-textured ore and disseminated ore in talcose serpentinite indicates mixing of magmatic and sedimentary sulfur sources, potentially via post-magmatic hydrothermal processes. A restricted range of strongly mass-independent Delta S-33 values in ore samples from Trojan Mine likely reflects high-temperature assimilation of sulfur from supracrustal rocks and later superimposed low-temperature hydrothermal remobilization. Iron isotope values for most Ni-bearing sulfides show a narrow range suggesting that, in contrast to sulfur, nearly all of iron was derived from an igneous source. Negative Ni isotope values also agree with derivation of Ni from ultramafic melt and a significant high-temperature fractionation of Ni isotopes. Fe isotope values of some samples from Shangani Mine are more fractionated than expected to occur in high-temperature magmatic systems, further suggesting that hydrothermal processes were involved in either low-grade ore formation (liberation of Ni from olivine by sulfur-bearing hydrothermal fluids) or remobilization of existing sulfides potentially inducing secondary Ni-sulfide mineralization.

Graphitic carbon, with its diverse structures and unique properties, is everywhere at Earth's surface. Strategically located at the interface between the lithosphere, biosphere, hydrosphere, and atmosphere, graphitic carbon constitutes a major terrestrial carbon reservoir. Natural and synthetic graphitic carbon is also used in a broad range of applications, and graphitic carbon, so widely varied in its physical properties, has proven to be adaptable to many uses in society. Graphitic carbon has played an important role in human history (for example, coal mining) and is now a building block of nanotechnology, but this remarkable material is also an active player in geological processes.