Transforming the City: People, Property and Identity in Millennial Auckland

Developing on the ‘global’ and ‘postmodern’ cities literatures, this paper sets out a research agenda for exploring the nature of urban transformation in contemporary Auckland. Focusing on the recursive relationship between global and local processes, we examine emerging socio-demographic and cultural processes at work in the city. Our research agenda addresses three themes: emerging ethnoscapes, the creation and reproduction of residential landscapes, and the examination of consumption sites and practices.     

WEIGHTED VERTICAL STACKING IN CRUSTAL SEISMIC REFLECTION STUDIES ON THE CANADIAN SHIELD*

Seismic reflection methods are being developed at the University of Manitoba to aid in determining fine crustal structure in the Precambrian of Manitoba and northwestern Ontario. Present-day environmental concern as well as mineshaft conditions necessitate the detonation of several smaller charges repeated, say, I times and followed by ‘vertical’ stacking. To obtain the familiar √I improvement in signal-to-noise (S:N) amplitude ratio applying the straight-sum (SS) method, one assumes, among other things, that both S:N ratio and signal variance are the same on all traces. Dropping these assumptions, as we must for our data, it becomes necessary to apply weighting coefficients to optimize the S:N ratio of the stacked trace. We still assume the signal shapes to be the same for repeated shots, so for the jth trace on the record of the ith shot we model the time series as: t_ij=a_i (s_j+n_ij); where a_i is a scaling factor. The proper weights w_i are then shown to be proportional to σ_si/σ²_ni where σ² is variance, or to γ_i/a_i where γ_i is S:N power ratio. Applying the weighted-stack (WS) method gives S:N amplitude ratios which are, on average, 55% of the optimal ratios expected from WS theory compared with only 24% for the SS method. The 45% shortfall in WS performance is ascribed mainly to trace-alignment (or time-delay) errors. Varying noise levels on individual traces, slight dissimilarity of signal shape, and correlated noise may also contribute to a lesser extent (in decreasing order of significance). This WS method appears to strike a good practical balance between S:N improvement and processing efficiency.     

Petrology of Submarine Lavas from Kilauea's Puna Ridge, Hawaii

We have studied 30 quenched tholeiitic lava flows recoveredby 20 dredge hauls and one submersible dive along Puna Ridge,the submarine part of the East Rift Zone of Kilauea Volcano,Hawaii Glass grains from numerous additional flows were recoveredin turbidite sands cored in the Hawaiian Trough. These quenchedlavas document variable primary magma compositions; olivineand multiphase crystallization and fractionation; degassing;wall-rock stoping and assimilation; mixing in the crustal reservoirand the rift zone; entrainment of olivine xenocrysts from ahot, ductile, olivine cumulate body; and disruption of gabbrowallrocks in the rift zone. Glass grains in turbidite sands contain up to 15•0wt% MgO,in contrast to < 7•0wt% MgO for the sampled glass rindson lavas. The most forsteritic olivine phenocryst (F0₉₀₇) isin equilibrium with primary Kilauea liquid containing an average16•5 wt% MgO, but ranging from 13•4 to 18•4%.Lavas and glass grains have more restricted P₂O₅/K₂O and TiO₂/K₂Othan glass inclusions in olivine, because more diverse liquidstrapped as glass inclusions are mixed and homogenized beforeeruption. Variable trace element compositions in glass grainsand whole rocks indicate that the primary liquids form by partialmelting of mantle sources retaining clinopyroxene and garnet. Orthopyroxene xenocrysts formed at moderate pressures provideevidence for a sub-crustal staging zone. Chromite and olivinecrystallize in the crustal magma reservoir as the liquid coolsfrom an average 1346C to 1170C. Low viscosities of the primaryliquids (04 Pas) facilitate olivine settling, and the crystallizedolivine forms an olivine cumulate body at the base of the reservoir.Olivine is deformed as the hot ductile dunite body flows downand away from the summit. This flow drives instability of theHilina landslide on Kilauea. Dikes intrude the dunite, and magmaflowing through the dikes disaggregates and entrains olivinexenocrysts in Puna Ridge magmas. Primary liquids pond at or near the base of Kilauea's crustalreservoir because they are denser than more fractionated liquidsthat occupy the upper parts of the reservoir. The sulfur andwater contents of glass rinds indicate that fractionated liquidsnear the top of the reservoir degas at low pressure, a processthat increases their density and causes them to sink to levelswhere they mix with resident undegassed, near-primary liquid.The fractionated liquids near the top of the magma reservoiracquire excess Cl, owing to assimilation of hydrothermally alteredroofrocks. Magma flowing into the rift zone encounters and mixes with low-temperature,multiphase-fractionated melt. The mixed magmas typically containrare orthopyroxene, plagioclase as sodic as andesine, olivineas fayalitic as F0₇₅ and Fe-rich augite derived from the fractionatedmagma. Magma flowing through dikes also dislodged fragmentsof gabbroic wallrocks that occur as xenoliths. The interrelations in the Kilauean submarine lavas between hostglass and glass inclusion compositions, volatile contents andmineral chemistry reveal an extraordinarily complex sequenceof petrogenetic processes and events that are difficult or impossibleto determine in subaerial Kilauea lavas because of crystallization,reequilibration and degassing during or after their eruption. KEY WORDS: submarine lavas; petrology; Kilauea; Hawaii; magma mixing ^*Corresponding authorPresent address: Rosentiel School of Marine and Atmospheric Science, Division of Marine Geology and Geophysics, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA