Evidence for slope instability and current-induced sediment transport,the RMSTitanic wreck search area,Newfoundland rise

The first map of the sea bed morphology and sedimentary features within the RMSTitanic search area is proposed from the interpretation of SAR side-scan sonar images. Downslope sedimentary features such as erosional furrows and crown scarps constitute a 7 km wide instability corridor. A large field (15 km²) of asymmetrical sediment waves indicating a downslope transport is identified. Current-induced features corresponding to associated sand ribbons and barchan dunes resulting from the Western Boundary Undercurrent action are mapped. The morphology of theTitanic Canyon is also precised from the SAR images. Finally, the origin of the sea bed features is discussed in an attempt to link each bed form to a sedimentary process.     

The Proterozoic,albitite-hosted,Valhalla uranium deposit,Queensland, Australia: a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole V39

The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite, (uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the assemblage of Rodinia. The oldest ages of the brannerite overlap with ⁴⁰Ar/³⁹Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr, P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that F⁻ and were important ore-transporting complexes. δ¹⁸O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a fluid having δ¹⁸O_fluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δD_fluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ¹⁸O_fluid and δD_fluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small pegmatite dykes that intruded during the Isan Orogeny.     

Sm−Nd and Pb isotopic study of mafic rocks associated with early Proterozoic continental rifting: the Peröpohja schist belt in northern Finland

The Peräpohja schist belt in northern Finland rests unconformably on Archaean granitoids, and marks the early stages of Proterozoic crustal evolution in the Fennoscandian (Baltic) shield. 2440 Ma old layered mafic intrusions predate the supracrustal , and ca. 2200 Ma old sills of the gabbro-wehrlite association intrude the lowest quartzites and volcanics (Runkaus) of the sequence. The Sm-Nd mineral isochron of the Penikat layered intrusion gives an age of 2410±64 Ma. The initial _Nd-values of the Penikat intrusion (_Nd(2440) = –1.6) and the Runkausvaara sill (_Nd(2200) 0) suggest that these mafic magmas were contaminated by older crustal material. The Sm-Nd and Pb isotopic results on the 2.44–2.2 Ga old Runkaus volcanics indicate mobility of Pb, fractionation of Sm/Nd during late greenschist facies metamorphism, and crustal contamination. The Pb-Pb data provide an age of 1972±80 Ma with a high initial ²⁰⁷Pb/²⁰⁴Pb ratio (₁ = 8.49), while scattered Sm-Nd data result in an imprecise age of 2330±180 Ma, with an initial _Nd-value of about zero. Secondary titanite gives an U-Pb age of ca. 2250 Ma. The Jouttiaapa basalts, in contrast, ascended from the mantle without interaction with older crust. These LREE depleted tholeiites mark a break in continental sedimentation, and yield a Sm-Nd age of 2090±70 Ma. Their initial _Nd = + 4.2 ±0.5 implies that the subcontinental early Proterozoic mantle had been depleted in LREE for a long period of time. The first lava flows are strongly depleted in LREE, suggesting that their source was significantly more depleted than the source of mid-ocean ridge basalts today.     

The origin of reaction textures in mantle peridotite xenoliths from Sal Island, Cape Verde: the case for “metasomatism” by the host lava

Reaction zones around minerals in mantle xenoliths have been reported from many localities worldwide. Interpretations of the origins of these textures fall into two groups: mantle metasomatic reaction or reaction during transport of the xenoliths to the surface. A suite of harzburgitic mantle xenoliths from Sal, Cape Verde show clear evidence of reaction during transport. The reactions resulted in the formation of olivine–clinopyroxene and Si- and alkali-rich glass reaction zones around orthopyroxene and sieve-textured clinopyroxene and sieve textured spinel, both of which are associated with a Si- and alkali-rich glass similar to that in the orthopyroxene reaction zones. Reaction occurred at pressures less than the mantle equilibration pressure and at temperatures close to the liquidus temperature of the host magma. In addition, there is a clear spatial relation of reaction with the host lava: reaction is most intense near the lava/xenolith contact. The residence time of the xenoliths in the host magma, determined from Fe–Mg interdiffusion profiles in olivine, was approximately 4 years. Our results cannot be reconciled with a recent model for the evolution of the mantle below the Cape Verde Archipelago involving mantle metasomatism by kimberlitic melt. We contend that alkali-rich glasses in the Sal xenoliths are not remnants of a kimberlitic melt, but rather they are the result of reaction between the host lava or a similar magma and xenolith minerals, in particular orthopyroxene. The formation of a Si- and alkali-rich glass by host magma–orthopyroxene reaction appears to be a necessary precursor to formation of sieve textured spinel and clinopyroxene.     

Neodymium-strontium isotopic evidence for extreme contamination in a layered basic intrusion

Neodymium and strontium isotopic analyses from the Kalka layered basic intrusion, central Australia, are arrayed parallel to the Sr-axis of a Nd-Sr isotopic correlation diagram and are removed from the normal basaltic field. Initial¹⁴³Nd/¹⁴⁴Nd ratios are almost constant and typical of continental basalts, whereas initial⁸⁷Sr/⁸⁶Sr ratios vary greatly and range to high values (0.7049–0.7088). Acidic granulites from the country rock lie upon the continuation of the Kalka trend at higher⁸⁷Sr/⁸⁶Sr ratios outlining a mixing system between granulite and normal basaltic magma. If average granulite acted as a contaminant, isotope dilution calculations show that amounts assimilated reached as high as 25%. Bulk contamination is confirmed petrologically by the abundance of orthopyroxene, particularly as basal orthopyroxenites and the restriction of olivine to less-contaminated levels. Analogies between Kalka and several other major layered intrusions, such as the Bushveld Complex, suggest that large-scale contamination was a significant aspect of their genesis.     

MANAGING PLANET EARTH TO MAKE FUTURE DEVELOPMENT MORE SUSTAINABLE： CLIMATE CHANGE AND HONG KONG

Selected recent findings related to climate change in Hong Kong include： (1)The Hong Kong seafloor has yielded a ca0.5-million year record of climate and sealevel changes.(2)Greenhouse gases produced naturally from subaerially exposed continental shelves and oceanic islands were a probable forcing mechanism in triggering the abrupt termination of past ice ages. (3)An analysis of annual mean temperature records has revealed that the urban heat island effect has contributed ca75％ of the warming. (4)Past volcanic eruptions are found to lower Hong Kongs temperature and to cause extremely dry and wet years. (5)No evidence can be found for an increase in frequency and intensity of typhoons based on the instrumental record since the end of the Second World War. (6)The observed rate of sealevel rise in the South China Sea is much slower than the predictions of the IPCC Fourth Assessment.
For the Earths management, population growth and the depletion of nonrenewable resources must be recognized as unsustainable. The human impact on the natural hydrological cycle is an important forcing mechanism in climate change. In order to delay the demise of the human race, management must include curbing population growth and much more waste recycling than at present.     

Contemporary Deposition and Long-Term Accumulation of Sediment and Nutrients by Tidal Freshwater Forested Wetlands Impacted by Sea Level Rise

Contemporary deposition (artificial marker horizon, 3.5 years) and long-term accumulation rates (²¹⁰Pb profiles, ~150 years) of sediment and associated carbon (C), nitrogen (N), and phosphorus (P) were measured in wetlands along the tidal Savannah and Waccamaw rivers in the southeastern USA. Four sites along each river spanned an upstream-to-downstream salinification gradient, from upriver tidal freshwater forested wetland (TFFW), through moderately and highly salt-impacted forested wetlands, to oligohaline marsh downriver. Contemporary deposition rates (sediment, C, N, and P) were greatest in oligohaline marsh and lowest in TFFW along both rivers. Greater rates of deposition in oligohaline and salt-stressed forested wetlands were associated with a shift to greater clay and metal content that is likely associated with a change from low availability of watershed-derived sediment to TFFW and to greater availability of a coastal sediment source to oligohaline wetlands. Long-term accumulation rates along the Waccamaw River had the opposite spatial pattern compared to contemporary deposition, with greater rates in TFFW that declined to oligohaline marsh. Long-term sediment and elemental mass accumulation rates also were 3–9× lower than contemporary deposition rates. In comparison to other studies, sediment and associated nutrient accumulation in TFFW are lower than downriver/estuarine freshwater, oligohaline, and salt marshes, suggesting a reduced capacity for surface sedimentation (short-term) as well as shallow soil processes (long-term sedimentation) to offset sea level rise in TFFW. Nonetheless, their potentially large spatial extent suggests that TFFW have a large impact on the transport and fate of sediment and nutrients in tidal rivers and estuaries.     

Uranium-lead isotopic evidence from zircons for lower Palaeozoic tectonic activity in the Austroalpine Nappe,the Eastern Alps

U/Pb isotopic data for two zircon suites are presented:

1. a pre D ₁ tonalite gneiss gives an age of 443 ± ₁₆ ¹³ m.y.
2. a post D ₁ leucogranite gneiss gives 427 ± ₁₁ ¹⁰ m.y.

Both zircon suites contain a minor inherited pre-Cambrian component. The data confirm a lower Palaeozoic age for the major, fabric-forming D ₁ event. Hercynian metamorphism which was sufficient to reset muscovite K/Ar ages to ca. 290 m.y. had little effect on the zircons. The possible importance of lower Palaeozoic orogeny in southern Europe and the uncertainties in regional palaeogeography are emphasised.     

Stratigraphic Correlation of the Malusok Volcanogenic Massive Sulfide Deposits, Southern Mindanao, Philippines

Abstract: Two adjacent volcanogenic massive sulfide (VMS) deposits, the Main Malusok and the Malusok Southeast, are delineated within Barangay Tabayo, Siocon, Zamboanga del Norte, Mindanao, Philippines. These deposits comprise massive to semi-massive sulfide lenses representing the down-dip equivalent of oxidized gossans. The massive sulfides have a primary mineral assemblage of pyrite-chalcopyrite-sphalerite with significant amounts of supergene copper in the form of chal-cocite. Owing to structural and metamorphic overprinting combined with intense alteration, primary textures are generally obliterated. Rock types are classified according to dominant mineral assemblages whereas the main lithologic units comprising the Malusok volcanic package are divided based on the position of each unit relative to the mineralized zone. The main lithologic units are designated as the hanging wall, the host, and the footwall sequences. In correlating the stratigraphy of the Main Malusok zone with that of the Malusok Southeast zone, a chlorite/epidote-rich interval located at the base of the hanging wall sequence serves as a distinct stratigraphic marker from which all lithologies are referred to. Comparisons between the stratigraphy of the two areas show that massive to semi-massive sulfide lenses are confined within a single stratigraphic interval representing the favorable horizon for the entire Malusok area. However, differences exist relative to style of mineralization and configuration of the altered interval between the Main Malusok and the Malusok Southeast VMS deposits. Based on characteristics exhibited by each individual deposit, it is inferred that the Main Malusok VMS deposit overlies a feeder zone whereas the Malusok Southeast sulfide lenses represent satellite deposits and transported blocks.