Average compositions and analyses range for clinopyroxene, olivines, orthopyroxene, and spinel from the MARK area at DSDP Site 45-395A, and ODP Site 153-920

Mineral compositions of residual peridotites collected at various locations in the Mid-Atlantic Ridge south of the Kane transform (MARK area) are consistent with generally smaller degrees of melting in the mantle near the large offset Kane transform than near the other, small offset, axial discontinuities in the area. We propose that this transform fault effect is due to along-axis variations in the final depth of melting in the subaxial mantle, reflecting the colder thermal regime of the ridge near the Kane transform. Calculations made with a passive mantle flow regime suggest that these along-axis variations in the final depth of melting would not produce the full range of crustal thickness variations observed in the MARK area seismic record. It is therefore likely that the transform fault effect in the MARK area is combined with other mechanisms capable of producing crustal thickness variations, such as along-axis melt migration, the trapping of part of the magma in a cold mantle root beneath the ridge, or active mantle upwelling.

Petrographic properties of tephras of DSDP Leg 56 Holes

Examining volcanic materials in deep sea sediments may be one of the most important tasks of the Deep Sea Drilling Project. The investigation of volcanic ash near young source volcanoes is particularly helpful in enabling us to infer the history of volcanism in and around the island arcs. In the area of the Japanese islands volcanic deposits are usually distributed east of the source by prevailing westerly winds. It is also possible that some deep sea tephra has its source in a large, already known land volcanism.

Composition of sedimemts from the Transpacific profile

The book is devoted to comprehensive study of composition of sediments from the North Pacific Ocean. The sediments have been divided characterized by their lithologic and facial types, grain size composition and mineralogy. Influence of volcanism on formation of mineral and chemical composition of these sediments has been shown. Regularities of distribution of sediment accumulation rates and of a number of chemical elements on the Transpacific profile have been found. Determining role of mechanical fractionation in their localization has been shown.

Geochemistry, lithology, and bulk density of Cricket Flat paleosol samples

The high-resolution marine isotope climate record indicates pronounced global cooling during the Langhian (16-13.8 Ma), beginning with the warm middle Miocene climatic optimum and ending with significant Antarctic ice sheet expansion and the transition to "icehouse" conditions. Terrestrial paleoclimate data from this interval is sparse and sometimes conflicting. In particular, there are gaps in the terrestrial record in the Pacific Northwest during the late Langhian and early Serravallian between about 14.5 and 12.5 Ma. New terrestrial paleoclimate data from this time and region could reconcile these conflicting records. Paleosols are particularly useful for reconstructing paleoenvironment because the rate and style of pedogenesis is primarily a function of surface environmental conditions; however, complete and well-preserved paleosols are uncommon. Most soils form in erosive environments that are not preserved, or in environments such as floodplains that accumulate in small increments; the resulting cumulic soils are usually thin, weakly developed, and subject to diagenetic overprinting from subsequent soils. The paleosol at Cricket Flat in northeastern Oregon is an unusually complete and well-preserved paleosol from a middle Miocene volcanic sequence in the Powder River Volcanic Field. An olivine basalt flow buried the paleosol at approximately 13.8 ± 0.6 Ma, based on three 40Ar/39Ar dates on the basalt. We described the Cricket Flat paleosol and used its physical and chemical profile and micromorphology to assess pedogenesis. The Cricket Flat paleosol is an Ultisol-like paleosol, chemically consistent with a high degree of weathering. Temperature and rainfall proxies suggest that Cricket Flat received 1120 ± 180 mm precipitation y-1 and experienced a mean annual temperature of 14.5 ± 2.1 °C during the formation of the paleosol, significantly warmer and wetter than today. This suggests slower cooling after the middle Miocene climatic optimum than is seen in the existing paleosol record.

Geochemistry of DSDP Hole 86-577B samples

THE chemical, mineralogical and isotopic characteristics of deposits at the Cretaceous/Tertiary (K/T) boundary are suggestive of a large impact event, the prime candidate (Sharpton et al., 1992, doi:10.1038/359819a0) being the Chicxulub crater in Yucatan, Mexico. Spinel-bearing spherules, which may be associated with such impacts, have been reported (Smit and Romein, 1985, doi:10.1016/0012-821X(85)90019-6) at several K/T boundary sites worldwide, but their origin is still uncertain. We have examined the spinel-bearing material recovered from K/T boundary deposits at site 577 in the Pacific Ocean (Heath et al., 1985, doi:10.2973/dsdp.proc.86.104.1985) and find two distinct populations of particles: spherules with dendritic spinel textures dispersed throughout the grains and irregularly shaped fragments with spinels essentially confined to the rim. The morphology and composition of the particles are characteristic of melted and partially melted meteoritic ablation debris, but their location is difficult to reconcile with an impact on the Yucatan peninsula, some 10,000 km away. We suggest instead that the spinel-bearing particles at site 577 are derived from the impact of a 2-km asteroid in the Pacific Ocean, and that several accretionary events of this type are required to explain the global distribution of spinel-bearing spherules at the K/T boundary.

Compositions of paleosols from the Salarevo Formation, Sukhona River valley (Severnaya Dvina basin)

Paleosols crop out in the Sukhona River valley as several members up to 10 m thick embedded into the Salarevo Formation sediments. Principal characteristics of the paleosols include a dense network of root channels, indications of eluvial gley alteration, redistribution and formation of secondary carbonates represented by several generations, and formation of block-prismatic soil structure with specific clayey films at structural jointing faces. The paleosols are divided into a number of genetically interrelated horizons (from top to bottom): presumably organogenic accumulation (AElg), eluvial gley horizon (Elg), illuvial horizons (B1 and B2), illuvial gley horizon (Bg), and transitional horizons (ElBg and BElg). The paleosols formed under conditions of a semiarid climate with sharp seasonal or secular and multisecular oscillations of atmospheric precipitation. Such soils point to specific ecological environments existed in the northern semiarid belt of the Earth before the greatest (in Phanerozoic) biospheric crisis at the Permian-Triassic boundary.

Petrology and geochemistry of altered ocenaic crust of ODP Hole 140-504B

Altered basalt dikes from Hole 504B were partially melted at 1150°C and 1180°C to determine the composition of the first melts as oceanic Layer 2C is assimilated by a magma chamber. The partial melts are chemically similar to actinolite, the most abundant secondary mineral, but the melts are not simply melted actinolite. High TiO2, P2O5, and K2O abundances of the melts indicate that minor secondary minerals that are enriched in these elements also contribute to the melt. The incorporation of partial melts into a ridge-crest magma chamber may explain the local variability that is sometimes found in ocean ridge basalts that are not readily explained fractional crystallization or partial melting.

Chemistry of fluid inclusions in rock samples from Dronning Maud Land

Dense, CO2-rich fluid inclusions hosted by plagioclases, An45 to An54, of the O.-v.-Gruber- Anorthosite body, central Dronning Maud Land, East Antarctica, contain varying amounts of small calcite, paragonite and pyrophyllite crystals detected by Raman microspectroscopy. These crystals are reaction products that have formed during cooling of the host and the original CO2-rich H2O-bearing enclosed fluid. Variable amounts of these reaction products illustrates that the reaction did not take place uniformly in all fluid inclusions, possibly due to differences in kinetics as caused by differences in shape and size, or due to compositional variation in the originally trapped fluid. The reaction albite + 2anorthite + 2H2O + 2CO2 = pyrophyllite + paragonite + 2calcite was thermodynamically modelled with consideration of different original fluid compositions. Although free H2O is not detectable in most fluid inclusions, the occurrence of OH-bearing sheet silicates indicates that the original fluid was not pure CO2, but contained significant amounts of H2O. Compared to an actual fluid inclusion it is obvious, that volume estimations of solid phases can be used as a starting point to reverse the retrograde reaction and recalculate the compositional and volumetrical properties of the original fluid. Isochores for an unmodified inclusion can thus be reconstructed, leading to a more realistic estimation of P-T conditions during earlier metamorphic stages or fluid capturing.

Composition of bottom sediments and serpentinites from Core PS-846

A core of foraminiferal-coccolithic oozes filling a valley of the transform fault located at 29°40'S on the South Atlantic Ridge contains layers composed of angular fragments of igneous and metamorphic rocks. They include many serpentinites deriving from serpentinized ultrabasic rocks, probably exposed on the lower section of the southern slope of the fault valley. A mineral and chemical description of these serpentinites is given.

Chemical composition and description of a ferromanganese crust, sample 89D, obtained during R/V Capricorne cruise ARCANTE 1

A manganese oxide encrustation (2.5 kg) was dredged, in an island arc setting, downslope of Bertrand bank, a seamount culminating at 70-m depth and located NNE of Grande-Terre, Guadeloupe, and SE of Antigua, West Indies. A thorough texturai analysis indicated a rhythmic precipitation and growth polarity as well as mineralogical ( 10 A tektomanganate) and geochemical (low concentrations of Ni, Cu, Co, Zn, Pb and REE) criteria, point to a submarine hydrothermal origin for most of the sample. The crust was coated with a fine ferromanganese oxide cortex deposited iii a "normal" oceanic environment; it also included micritic fillings, a main pyroclastic zone near the top of the crust, and a Mg-Al sulphate deposit. Planktonic foraminifera coeval with the precipitation of the manganese oxide indicate an age of ca. 3 m. y. (upper Pliocene); i.e., more than 20 m. y. after the cessation of the volcanic activity of the Lesser Antilles outer arc that was responsible for the buildup of the Bertrand seamount. Furthermore, the genesis of the crust is not linked to the activity of the contemporaneous inner arc (Miocene to Present), particularly of its nearmost segment (Basse Terre, Guadeloupe-Montserrat) located about 50 km to the West. The authors suggest that the manganese oxide is the result of convective circulation of sea water through a faulted system occurring in an area of intense seismic activity. The remobilization of chemical elements (Mn, S, etc.) within the seamount volcanic core bas probably affected a substratum that was still hydrothermally altered during the previous volcanic activity of the outer arc. The authors insist on the interest in using texturai analysis for Fe/Mn oxide investigations.

Utility of thallium and geochemical analysis of Mariana arc sediments from ODP Hole 129-801A and 129-801B

We provide the first exploration of thallium (Tl) abundances and stable isotope compositions as potential tracers during arc lava genesis. We present a case study of lavas from the Central Island Province (CIP) of the Mariana arc, supplemented by representative sedimentary and altered oceanic crust (AOC) inputs from ODP Leg 129 Hole 801 outboard of the Mariana trench. Given the large Tl concentration contrast between the mantle and subduction inputs coupled with previously published distinctive Tl isotope signatures of sediment and AOC, the Tl isotope system has great potential to distinguish different inputs to arc lavas. Furthermore, CIP lavas have well-established inter island variability, providing excellent context for the examination of Tl as a new stable isotope tracer. In contrast to previous work (Nielsen et al., 2006b), we do not observe Tl enrichment or light epsilon 205Tl (where epsilon 205Tl is the deviation in parts per 10,000 of a sample 205Tl/203Tl ratio compared to NIST SRM 997 Tl standard) in the Jurassic-aged altered mafic ocean crust subducting outboard of the Marianas (epsilon 205Tl = - 4.4 to 0). The lack of a distinctive epsilon 205Tl signature may be related to secular changes in ocean chemistry. Sediments representative of the major lithologies from ODP Hole Leg 129 801 have 1-2 orders of magnitude of Tl enrichment compared to the CIP lavas, but do not record heavy signatures (epsilon 205Tl = - 3.0 to + 0.4), as previously found in similar sediment types (epsilon 205Tl > + 2.5; Rehkämper et al., 2004). We find a restricted range of epsilon 205Tl = - 1.8 to - 0.4 in CIP lavas, which overlaps with MORB. One lava from Guguan falls outside this range with epsilon 205Tl = + 1.2. Coupled Cs, Tl and Pb systematics of Guguan lavas suggests that this heavy Tl isotope composition may be due to preferential degassing of isotopically light Tl. In general, the low Tl concentrations and limited isotopic range in the CIP lavas is likely due to the unexpectedly narrow range of epsilon 205Tl found in Mariana subduction inputs, coupled with volcaniclastic, rather than pelagic sediment as the dominant source of Tl. Much work remains to better understand the controls on Tl processing through a subduction zone. For example, Tl could be retained in residual phengite, offering the potential exploration of Cs/Tl ratios as a slab thermometer. However, data for Tl partitioning in phengite (and other micas) is required before developing this application further. Establishing a database of Tl concentrations and stable isotopes in subduction zone lavas with different thermal parameters and sedimentary inputs is required for the future use of Tl as a subduction zone tracer.

Toba Tephra across India

A controversy currently exists regarding the number of Toba eruptive events represented in the tephra occurrences across peninsular India. Some claim the presence of a single bed, the 75,000-yr-old Toba tephra; others argue that dating and archaeological evidence suggest the presence of earlier Toba tephra. Resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples, allowing comparison of the Indian samples to those from the Toba caldera in northern Sumatra, Malaysia, and, importantly, the sedimentary core at ODP Site 758 in the Indian Ocean - a core that contains several of the earlier Toba tephra beds. In addition, two samples of Toba tephra from western India were dated by the fission-track method. The results unequivocally demonstrate that all the presently known Toba tephra occurrences in peninsular India belong to the 75,000 yr B.P. Toba eruption. Hence, this tephra bed can be used as an effective tool in the correlation and dating of late Quaternary sedimentary sequences across India and it can no longer be used in support of a middle Pleistocene age for associated Acheulian artifacts.

Composition of post-Jurassic deposits from the Northwest Pacific and the Galapagos Rift, data of DSDP Legs 62, 65, and 70

The monogragh contains results of mineralogicai and geochemical studies of Mesozoic and Cenozoic deposits from the Pacific Ocean collected during Deep Sea Drilling Project. Special attention is paid on the aspects of geochemical history of post-Jurassic sedimentation in the central part of the Northwest Pacific, detailed characteristics of the main stages of sedimentary evolution are given: Early Cretaceons (protooceanic), Late Cretaceons (transitional) and Cenozoic (oceanic). Results of mineralogical and geochemical studies of hydrothermal deposits from the Galapagos Rift are given as well.

Geochemistry at DSDP Leg 92 Holes

The major-element and most of the trace-element data from the different laboratories that contributed to the study of samples recovered during Leg 82 are presented in the following tables. The different basalt groups, identified on the basis of their chemical properties (major and trace elements), were defined from the data available on board the Glomar Challenger as the cruise progressed (see site chapters, all sites, this volume). Most of the data obtained since the end of the cruise and presented in these tables confirm the classification that was proposed by the shipboard party (see site chapters, all sites, this volume). Nevertheless, special mention should be made about Site 564. The shipboard party proposed a single chemical group at this site but noticed significant variations down the hole, mainly in trace-element data. However, the range of variation was small compared to the precision of the measurements. These variations were confirmed by the onshore studies (see papers in Part IV of this volume, especially Brannon's paper, partly devoted to this topic).