(Table 1) K-Ar age and inert-gas-isotopes at DSDP Holes 68-501, 69-504B and 69-505B

Conventional K-Ar ages have been determined and inert-gas abundances have been measured on representative samples of altered rocks from Deep Sea Drilling Project Holes 501, 504B, and 505B in an attempt to correlate their degree of alteration with inert-gas and K-Ar data. Samples taken from the first 60 meters below the sediment/basalt interface give significantly higher ages than would be expected from the magnetic stratigraphy, though at greater depths the calculated ages are in broad agreement with the expected age. The inert gas ratios 20Ne/36Ar, 36Ar/84Kr, and 84Kr/130Xe also show a marked discontinuity at the 60-meter depth, and all these effects are interpreted as being a consequence of low-temperature alteration produced by burial metamorphism and by interaction with sea water (halmyrolysis).

(Table 1) Sedimentary thicknesses, lithologies, ages, and interpreted paleowater depths for ODP Sites 135-840 and 135-841

The sedimentary succession drilled at Sites 840 and 841 on the Tonga forearc allows the sedimentary evolution of the active margin to be reconstructed since shortly after the initiation of subduction during the mid Eocene. Sedimentation has been dominated by submarine fan deposits, principally volcaniclastic turbidites and mass-flows derived from the volcanic arc. Volcaniclastic sedimentation occurred against a background of pelagic nannofossil sedimentation. A number of upward-fining cycles are recognized and are correlated to regional tectonic events, such as the rifting of the Lau Basin at 5.6 Ma. Episodes of sedimentation dating from 16.0 and 10.0 Ma also correlate well with major falls in eustatic sea level and may be at least partially caused by the resulting enhanced erosion of the arc edifice. The early stages of rifting of the Lau Basin are marked by the formation of a brief hiatus at Site 840 (Horizon A), probably a result of the uplift of the Tonga Platform. Controversy exists as to the degree and timing of the uplift of Site 840 before Lau Basin rifting, with estimates ranging from 2500 to 300 m. Structural information favors a lower value. Breakup of the Tonga Arc during rifting resulted in deposition of dacite-dominated, volcaniclastic mass flows, probably reflecting a maximum in arc volcanism at this time. A pelagic interval at Site 840 suggests that no volcanic arc was present adjacent to the Tonga Platform from 5.0 to 3.0 Ma. This represents the time between separation of the Lau Ridge from the Tonga Platform and the start of activity on the Tofua Arc at 3.0 Ma. The sedimentary successions at both sites provide a record of the arc volcanism despite the reworked nature of the deposits. Probe analyses of volcanic glass grains from Site 840 indicate a consistent low-K tholeiite chemistry from 7.0 Ma to the present, possibly reflecting sediment sourcing from a single volcanic center over long periods of time. Trace and rare-earth-element (REE) analyses of basaltic glass grains indicate that thinning of the arc lithosphere had begun by 7.0 Ma and was the principle cause of a progressive depletion of the high-field-strength (HFSE), REE, and large-ion-lithophile (LILE) elements within the arc magmas before rifting. Magmatic underplating of the Tofua Arc has reversed this trend since that time. Increasing fluid flux from the subducting slab since basin rifting has caused a progressive enrichment in LILEs. Subduction erosion of the underside of the forearc lithosphere has caused continuous subsidence and tilting toward the trench since 37.0 Ma. Enhanced subsidence occurred during rifting of the South Fiji and Lau basins. Collision of the Louisville Ridge with the trench has caused no change in the nature of the sedimentation, but it may have been responsible for up to 300 m of uplift at Site 840.

Beryllium-10, mineralogy and grain size distribution of DSDP Hole 68-502B (Table 1)

We present a high-resolution 10Be profile from deep sea sediments (sampled from Hole 502B in the Caribbean sea) that strongly resembles the 10Be record in ice core profiles, particularly the Vostok core from Antarctica. This high-resolution profile revealed occurrences of enhanced 10Be concentrations at about 23-24, 37-39 and 60-65 ka. The excellent match between these peaks appearing in a georeservoir profile other than in polar ice, strengthens the implications that can be inferred from 10Be and provide global markers for chronological correlation of climatic events. The position at low latitude of the studied sediment section is, unlike the case with the high latitude polar regions, excellent for exposing causes of modulation in 10Be production. We interpret the source of the pattern and enhancements, particularly the 37-39 ka peak, of 10Be to be global and do not strictly relate to climatic conditions and/or production rates specific to the polar regions.

"The Pickwick club," a humoreske in two parts. String quartet [no. 3] (Op. 68)

"Synopsis" ([4] p.) inserted.

Les trois graces. op. 68 /

Mode of access: Internet.

Quintette, pour piano, deux violons, alto et violoncelle, op. 68 /

Mode of access: Internet.