Managing the transition to climate stabilization

It is becoming increasingly clear that economically efficient climate policies are unlikely to be implemented in the near term. Therefore an analysis is warranted that considers the implications of certain suboptimal transition policies. This analysis constructs a transition scenario based on realistic assumptions about the current trends in policy-making. The transition is examined in the context of varying assumptions about the stringency of the target and the availability of low- or no-carbon energy technologies in the future. In addition to evaluating the effects of suboptimal policies, the transitional analysis offers new insights about the intrinsic uncertainty regarding both the appropriate stabilization target and technology.     

A sequence of partial melting reactions at Mt Stafford, central Australia

Metasedimentary gneisses show a rapid change in grade in a 10  km wide low- P /high- T  regional aureole at Mt Stafford in the Arunta Block, central Australia. Migmatite occurs in all but the lowermost of five metamorphic zones, which grade from greenschist (Zone 1) through amphibolite (Zones 2–3) to granulite facies (Zones 4–5). The sequence of partial melting reactions inferred for metapelitic rocks is dependant upon protolith, temperature and fluid conditions. The metapelite solidus in Zone 2 reflects vapour-present melting at P ≈3  kbar and T  ≈640  °C, melting having initially been controlled by the congruent breakdown of the assemblage Crd–Kfs–Bt–Qtz. At slightly higher temperature, andalusite in leucosome formed via the reaction Kfs+Qtz+Bt+H₂O→And+melt; And+melt having been stabilized by the presence of boron. Sillimanite coaxially replaces andalusite in the high-grade portion of Zone 2. In Zone 3, large aluminosilicate aggregates in leucosome are armoured by Spl–Crd±Grt symplectites. Garnet partially pseudomorphs biotite, cordierite or spinel in high-grade portions of Zone 3. Zone 4 Grt–Crd–Opx-bearing metapsammite assemblages and garnet-bearing leucosome reflect T  ≈800  °C and P =2.2±0.9  kbar. In the model KFMASH system the principal vapour-absent melting step reflected significant modal changes related to the breakdown of the As–Bt tie-line and the establishment of the Spl–Crd tie-line; the bulk rock geochemistry of migmatite samples straddle the Spl–Crd tie-line. The aluminous bulk-rock composition of the common bedded migmatite restricted its potential to witness garnet-forming and orthopyroxene-forming reactions, minor textural and modal changes in and above Zone 3 reflecting biotite destablization in biotite-poor assemblages.     

Contradictory socio-economic consequences of structural adjustment in Kingston, Jamaica

Since the early 1980s, the introduction of International Monetary Fund-directed structural adjustment packages to stabilize the Jamaican economy has reduced the scope of the government, cut back its capacity to intervene in the housing market, opened the economy to foreign goods (but limited capital), and re-produced the colonial version of a non-dynamic, labour-surplus urban economy in Kingston. This paper traces the impact of structural adjustment on unemployment and class formation in Kingston, and the relationship of these issues to housing problems. Rented, poor-quality housing, underpinned by low socio-economic status and historically high rates of unemployment, has created an overt spatial concentration of poverty, located in West and East Kingston. Nevertheless, overall unemployment is currently lower than at independence in 1962, and virtually all housing indicators have recorded improvements over the same time period. These improvements have been due to a deceleration in the growth of Kingston's population since the mid-1960s; government commitment, despite structural adjustment, to improve the quality of collective consumption; and the determination of Kingston's citizens to build better homes for themselves, often aided by loans from local building societies and remittances from family members resident overseas. However, at least a quarter of Kingston's population remains both unemployed and concentrated into areas of poor quality housing. These circumstances in Kingston are compared with those in adjacent Latin American cites under structural adjustment.     

Inter-Regional Comparisons on the Quaternary Large Mammalian Faunas between China and Sub-Saharan Africa

The current and dominant theory about the origin of modern humans is the out-of-Africa hypothesis, which asserts that populations of Homo sapiens left Africa 100,000 years ago and replaced indigenous populations of humans in Eurasia. Many scholars equated the out-of-Africa dispersal of humans with paleoenvironmental changes. However, until now, few have paid special attention to the faunal data and whether or not faunal patterns are supportive of the popular theory. Recent comparative study of the Chinese fauna shows that the communication of faunas between Africa and East Asia could have occurred during the Neogene, but it was very limited during the Pleistocene. In the Chinese Quaternary fauna, only 16% of the genera are also present in the sub-Saharan African fauna. There is also no element among the dominant taxa of the Chinese Quaternary fauna which can be related to the African fauna. There is no reliable proof for the existence of Hippopotamus and Giraffa, as well as Panthera leo, during the Quaternary in China. Two controversial taxa are Acinonyx and Crocuta, about which there is still argument concerning their species identification in Eurasia. It is possible that both of the genera have co-specific taxa in Africa and Eurasia. Although the two genera are confined to Africa today, they did have a long evolutionary history in China. For the Out of Africa hypothesis for Homo sapiens, the implications of the limited faunal interchanges between China and Africa are not completely clear yet.     

Proterozoic granulite facies metamorphism in the southeastern Reynolds Range, central Australia: geological context, P–T path and overprinting relationships

In the southeastern Reynolds Range, central Australia, a low- P granulite facies metamorphism affected two sedimentary sequences: the Lander Rock Beds and the Reynolds Range Group. In the context of the whole of the Reynolds Range and the adjacent Anmatjira Range, this metamorphism is M3 in a sequence M1–4 that occurred over a period of 250 Ma. In particular, M1 affected the Lander Rock Beds prior to the deposition of the Reynolds Group. M3 has an areally restricted, high-grade area in the southeastern Reynolds Range, affecting both the Reynolds Range Group and the underlying Lander Rock Beds. The effects of M3 are characterized by spinel + quartz-bearing peak metamorphic assemblages in metapelites, which imply peak conditions of ≥750°C and 4.5 ± 1 kbar, and involved isobaric cooling or compression with cooling. It is concluded that one of a series of thermal perturbations caused by thinning of mantle lithosphere contemporaneous with crustal thickening was responsible for M3. In the southeastern Reynolds Range, evidence of both the unconformity between the two rock groups and previous metamorphism/deformation has been completely erased by recrystallization during M3–D3.     

Reaction relationships during retrograde metamorphism at Olary, South Australia

Abstract In metapelitic schists of the north-eastern Weekeroo Inliers, Olary Block, Willyama Supergroup, South Australia, syn-S1 and syn-S2 assemblages involving staurolite, garnet, biotite and another mineral, most probably cordierite, were overgrown by large syn-S3 andalusite porphyroblasts, owing to isobaric heating from metamorphic conditions that existed during the development of S2. Conditions during the development of S3 probably just reached the andalusite—sillimanite transition. During the development of S4, at somewhat lower temperatures than those that accompanied the development of S3, the following reaction occurred:
staurolite + chlorite + muscovite ± biotite + andalusite + quartz + H₂O.
The amount of retrogression is controlled primarily by the amount of H₂O added by infiltration. As the syn-S3 matrix assemblage was stable during the development of S4, but the andalusite porphyroblasts were no longer stable with the matrix when H₂O was added, the retrogression is focused in and around the porphyroblasts. With enough H₂O available, and if quartz was consumed before biotite in a porphyroblast, then the following reaction occurred:
staurolite + chlorite + muscovite + corundum ± biotite + andalusite + H₂O.
This reaction allowed corundum inclusions in the andalusite to grow, regardless of the presence of quartz in the matrix assemblage.     

Contrasting behaviour of rare earth and major elements during partial melting in granulite facies migmatites, Wuluma Hills, Arunta Block, central Australia

Low‐P granulite facies metapelitic migmatites in the Wuluma Hills, Strangways Metamorphic Complex, Arunta Block, preserve evidence of polyphase deformation and migmatite formation which is of the same age of the c. 1730 Ma Wuluma granite. Mineral equilibria modelling of garnet‐orthoproxene‐cordierite‐bearing assemblages using thermocalc is consistent with peak S3 conditions of 6.0–6.5 kbar and 850–900 °C. The growth of orthopyroxene and garnet was primarily controlled by biotite breakdown during partial melting reactions. Whereas orthopyroxene in the cordierite‐biotite mesosome shows enrichment of heavy‐REE (HREE) relative to medium‐REE (MREE), orthopyroxene in adjacent garnet‐bearing leucosome shows depletion of HREE relative to MREE. There is no appreciable difference in major element contents of minerals common to both the mesosome and leucosome. The REE variations can be satisfactorily explained by decoupling of major element and REE partitioning, in the context of appropriate phase‐equilibria modelling of a prograde path at ～6 kbar. Sparse garnet nucleii formed at ～760 °C, along with concentrated leucosome development and preferentially partitioned HREE. Further heating to ～800 °C at constant or subtly increasing pressure conditions additionally stabilized orthopyroxene and decreased the garnet mode. Orthopyroxene in the leucosome inherited an REE pattern consequent to the partial consumption of garnet, it being distinct from the REE pattern in mesosome orthoproxene that was mostly controlled by biotite breakdown. Such within‐sample variability in the enrichment of heavy REE indicates that caution needs to be exercised in the application of common elemental partitioning coefficients in spatially complex metamorphic rocks.     

In-situ migmatite and hybrid diatexite at Mt Stafford, central Australia

Metasedimentary gneisses show a rapid change in grade within a 10-km-wide low- P /high- T  regional aureole at Mt Stafford, Arunta Block, central Australia. Migmatites occur in all but the lowermost of five metamorphic zones, which are characterized by: (1) muscovite–quartz schist; (2) andalusite–cordierite–K-feldspar granofels with small melt segregations; (3) spinel–sillimanite–cordierite–K-feldspar migmatite; (4) garnet–orthopyroxene–cordierite migmatite and minor diatexite; and (5) biotite–cordierite–plagioclase diatexite that shows a transition to granite. A subsolidus unit comprising interbedded sandstone and siltstone is equivalent to bedded migmatite , the main rock type in Zones 2–4. Mesoscopic textures and migmatite classification of this unit vary with grade. In Zone 2, metatexite is developed in siltstone layers that are separated by quartz-rich, unmelted metapsammite layers. Melt segregation was less efficient in Zones 3 and 4, where the dominant migmatite layering is a modified bedding. High proportions of melt were present in Zone 4, in which schlieren migmatite is transitional between bedded migmatite and metapelite-sourced diatexite. The preservation of sedimentary structures and coexistence of melt reactants and products in Zone 4 metapelite imply that melting proceeded in situ without substantial migration of melt. Zone 5 biotite–cordierite–plagioclase diatexite carries rafts of bedded migmatite with strongly resorbed edges, as well as large K-feldspar and quartz augen. This unit of comparatively Ca-rich migmatites is inferred to have been formed by the mixing of locally derived and injected granitic melt.     

Prograde Metamorphic Assemblage Evolution during Partial Melting of Metasedimentary Rocks at Low Pressures: Migmatites from Mt Stafford, Central Australia

The Mt Stafford area in central Australia preserves a low-pressuregreenschist- to granulite-facies regional aureole. The metasedimentarysequence has been divided into five zones from greenschist (Zone1) to granulite facies (Zone 4) and a zone of hybrid diatexiteformed from the introduction of granitic magma into the high-grademigmatites (Zone 5). Melt production was dominated by a seriesof multivariant biotite breakdown reactions, not the univariantreactions suggested by previous studies. Although the threemain metasedimentary rock types produced similar amounts ofmelt at the highest grades, their melt production historiesdiffered markedly as a function of temperature. Aluminous metapelitesproduced more melt at lower temperatures (Zones 2 and 3), whereasmetapsammite and cordierite granofels experienced an additionalmajor melt-producing step at higher temperatures (upper Zone3 and Zone 4). This melting step involved the breakdown of biotiteto produce garnet, K-feldspar and melt, and in some rocks theproduction of orthopyroxene. Melt production in Zone 4 exceeded25 mol %, resulting in the formation of in situ diatexites.Complex relationships involving aluminosilicate porphyroblastsresulted in the breakdown of biotite and aluminosilicate beingdrawn out over a wide temperature range, from subsolidus conditionsto temperatures close to 750°C. Initially, much of the meltingdeveloped around the aluminosilicate porphyroblasts during thebreakdown of coexisting biotite, aluminosilicate and quartz.However, much of the rock was chemically isolated from the porphyroblastsand could not react to produce melt. As temperatures rose, thepresence of the large isolated aluminosilicate porphyroblastscontrolled the spatial development of quartz-absent, spinel-presentcompositional domains, the formation of spinel being governedby the silica-undersaturated breakdown of coexisting biotiteand aluminosilicate. KEY WORDS: NCKFMASHTO; metapelite; granulite facies; petrogenetic grid; partial melting; THERMOCALC     

REMOTE-REFERENCE MAGNETOTELLURICS: EQUIPMENT AND PROCEDURES*

During the past 3 years, major advances in the magnetotelluric technique have improved the quality of magnetotelluric data to the point where random errors in the impedance tensor and tipper are generally smaller than the uncertainty in their interpretation. The major factor in this improvement has been the introduction of the remote-reference technique, although the use of ultrasensitive magnetometers and minicomputers for in-field data processing has also been important. After a review of the remote-reference technique, this paper describes the equipment and procedures used for remote-reference magnetotellurics by the authors. Magnetometers using d.c. Superconducting Quantum Interference Devices typically have a sensitivity of 10^?14 T Hz^?1/2, a dynamic range of 10⁷ in a 1 Hz bandwidth, and a slewing rate of 3 × 10^?5.T s^?1 at 10 kHz. The electric field measurements use conventional Cu-CuSO⁴ electrodes. The remote magnetic reference signals are transmitted to the base station using FM analog telemetry. The data are collected and processed by a minicomputer based on an LSI-11 microprocessor; the essential results—for example, the apparent resistivities and the tipper components, with their probable errors—are available in the field. Practical details are given of the handling of superconducting devices, low temperature cryostats and liquid helium in the field. Various spurious noise sources are mentioned, and techniques for minimizing their effects are described.