MIT's Computer Resource Lab:

Abstract

The paper describes the curriculum on geographic information systems developed in the Department of Planning at the Massachusetts Institute of Technology for those studying for the Master in City Planning degree. Particular emphasis is given to the part played by the Computer Resources Lab in serving the needs of the architecture and planning departments, the interactions between teaching and research, and those between the course and professional practice. The required courses are outlined and the wide range of recommended courses, drawn from a number of departments in the Institute, are listed- The authors emphasize the necessity of their being at the forefront of research if they are lo maintain the flow of hardware and software from contacts and donations on which their research and teaching depend.     

菲律宾Zambales蛇绿岩套的再研究：对其特提斯来源的启示

A number of geological studies have already been conducted on the Zambales Ophiolite Complex (ZOC), a north-south trending complete ophiolite sequence exposed in the western portion of Central Luzon, Philippines. Previous works recognized the ZOC as being made up of two blocks, the Acoje and the Coto, acting as an arc-back arc pair sometime during the Eocene.     

Anorthositic Rocks of the Duluth Complex: Examples of Rocks Formed from Plagioclase Crystal Mush

Anorthositic rocks compose 35–40% of the Middle Proterozoic(Keweenawan; 1?1 Ga) Duluth Complex—a large, compositemafic body in northeastern Minnesota that was intruded beneatha comagmatic volcanic edifice during the formation of the Midcontinentrift system. Anorthositic rocks, of which six general lithologictypes occur in one area of the complex, are common in an earlyseries of intrusions. They are characterized on a local scale(meters to kilometers) by nonstratiform distribution of rocktypes, variably oriented plagioclase lamination, and compositeintrusive relationships. Variably zoned, subhedral plagioclaseof nearly constant average An (60) makes up 82–98% ofthe anorthositic rocks. Other phases include granular to poikiliticolivine (Fo_66–38), poikilitic clinopyrox-ene (En'_73–37),subpoikilitic Fe-Ti oxides, and various late-stage and secondaryminerals. Whole-rock compositions of anorthositic rocks are modelled bymass balance to consist of three components: cumulus plagioclase(70–95 wt.%), minor cumulus olivine (0–5%), anda gabbroic postcumulus assemblage (5–27%) representinga trapped liquid. The postcumulus assemblage has textural andcompositional characteristics which are consistent with crystallizationfrom basaltic magma ranging from moderately evolved olivinetholeiite to highly evolved tholeiite (mg=60–25). Sympatheticvariations of mg in plagioclase and in mafic minerals suggestthat cumulus plagioclase, though constant in An, was in approximateequilibrium with the variety of basaltic magma compositionswhich produced the postcumulus assemblages. Standard models of mafic cumulate formation by fractional crystallizationof basaltic magmas in Duluth Complex chambers, although ableto explain the petrogenesis of younger stratiform troctoliticto gabbroic intrusions, are inadequate to account for the field,petrographic, and geochemical characteristics of the anorthositicrocks. Rather, we suggest an origin by multiple intrusions ofplagioclase crystal mushes—basaltic magmas charged withas much as 60% intratelluric plagioclase. The high concentrationsof cumulus plagioclase (70–95%) estimated to compose theanorthositic rocks may reflect expulsion of some of the transportingmagma during emplacement or early postcumulus crystallizationof only plagioclase from evolved hyperfeldspathic magma. Althoughthe evolved compositions of anorthositic rocks require significantfractionation of mafic minerals, geophysical evidence indicatesthat ultramafic rocks are, as exposure implies, rare in theDuluth Complex and implies that plagioclase crystal mushes werederived from deeper staging chambers. This is consistent withinterpretations of olivine habit and plagioclase zoning. Moreover,plagioclase could have been segregated from coprecipitatingmafic phases in such lower crustal chambers because of the buoyancyof plagioclase in basaltic magmas at high pressure. The geochemicaleffects of plagioclase suspension in basaltic magmas are consistentwith observed compositions of cumulus plagioclase in the anorthositicrocks and with the geochemical characteristics of many comagmaticbasalts. The petrogenesis of the anorthositic rocks and theoverall evolution of Keweenawan magmas can be related to thedynamics of intracontinental rift formation.     

Coexisting Amphiboles

Chemical analyses for the following amphibole pairs are presented:anthophyllite—tremolite (or actinolite, or hornblende),cummingtonite (or grunerite)–actinolite (or hornblende),cummingtonite (or grunerite)–anthophyllite (or gedrite),and manganoan cummingtonitemagnesioriebeckite. Nineteen analyses of such pairs are quoted from the literature,and thirty-seven additional pairs have been newly analyzed byelectron probe techniques. Quantitative microprobe determinationsof Si, Al, Fe, Mn, Mg, Ca, and Na were made on polished thin-sections,using naturally occurring, analyzed, homogeneous amphibolesas standards. The literature analyses and the electron probeanalyses for metamorphic, two-amphibole assemblages are givenfor amphiboles in physical contact, which show no textural evidenceof one amphibole being a reaction or alteration product of theother. The chemical data for some of the volcanic, two—amphiboleassemblages were obtained from occurrences that probably donot represent equilibrium pairs. The chemical data are used to determine the extent of the miscibilitygaps between the various amphibole series and the fractionationof the major elements between the two amphiboles of a pair.Anthophyllite and members of the cummingtonite-grunerite seriesgenerally have a larger Fe(total)/Mg ratio than the coexistingcalcic amphibole. The maximum CaO, Al₂O₃and Na₂O contents ofcummingtonite in metamorphic cummingtonite—hornblendepairs are 19 and 32, 02 weight per cent, respectively. Themaximum CaO, A1₂O₃, and Na₂O contents of cummingtonite in metamorphiccummingtonite-hornblende pairs are 19, 32, and 02 weightper cent, respectively. Larger CaO and Al₂O₃ values reportedin the literature were found to be too high because of admixtureof actinolite or hornblende in the analyzed separates. Smallamounts of MnO tend to concentrate preferentially in anthophylliteor cummingtonite of anthophyllite-hornblende and cummingtonite-hornblendepairs. Anthophyllite-cummingtonite pairs may show very similarFe(total)/Mg ratios and differ slightly in Al₂O₃ content only.     

Chemical Petrology of Grenville Schists near Fernleigh, Ontario

A suite of mica schists from the staurolite zone was studiedin detail. Phase rule considerations and distribution relationsindicate that chemical equilibrium was attained within the samplevolume. Iron-magnesium ratios of the silicates vary greatly,and correlate with rock ferrous-ferric ratio, as does the oxidemineral mode. Rock oxidation state varies locally, and is probablydependent on the composition of the original sediment. Distribution coefficients for Fe, Mg, and Mn among garnet, biotote,and staurolite show no vaiation attributable to temperature.Partition of Fe and Mg between staurolite and biotite is regular,but non-ideal. The staurolite structure permits only limited(15–35 percent) substitution of Mg for Fe.     

Oxygen-isotope record of Late-Glacial climatic change in western Ireland

Oxygen-isotope profiles for the Late-Glacial carbonate sediments from Red Bog and adjacent Lough Gur in County Limerick in western Ireland are readily correlated with the classical hiozones delineated on pollen diagrams for the same cores. The estimated summer temperatures of the Bølling/Allerød were as high as those in the early Holocene and are correlated with increasing Milankovitch summer insolation. This warm phase was abruptly terminated in the Younger Dryas cold episode by a depletion of 4% in δ¹⁸O, suggesting a summer atmospheric temperature decrease of about 12°C, comparable to that inferred from fossil beetle data. The Younger Dryas phase is attributed to a major cooling of the sea-surface temperature by a postulated discharge of icebergs similar to that of the Heinrich events, for the icebergs were much more effective than simple meltwater in cooling the sea surface and thus the climate over Europe. Shorter-term cool phases (Older Dryas. Gerzensee. Preboreal oscillation) are also recognized.     

Multi-technique approach to characterise the effects of cryopreservation on larval development of the Pacific oyster (Crassostrea gigas)

Cryopreservation experiments were conducted on D-stage larvae of the Pacific oyster (Crassostrea gigas) to investigate the effects of two cryoprotectant solutions and three cooling rates on larval development from 1 to 22 days post-fertilisation. Cryoprotectant solutions were made up to final concentrations (after 1:1 dilution with larvae) of 10% ethylene glycol, 1% polyvinylpyrrolidone and either 0.2 or 0.4 M trehalose. Three cooling rates (0.5, 1 and 2 °C min^?1 between ?10 and ?35 °C post-holding) were tested in an orthogonal design with the two cryoprotectants. Results indicate that control larvae out-performed all cryopreservation treatments for survival, feeding consumption and shell length parameters. However, larvae exposed to 0.4 M trehalose did considerably better than those exposed to 0.2 M trehalose, regardless of cooling rate conditions. Scanning electron and light microscopy observations were used to assess larval morphology and organogenesis, indicating that treatments with surviving larvae were morphologically and developmentally similar to control larvae.     

Ordinary (mesostasis) and not‐so‐ordinary (symplectites) late‐stage assemblages in howardites

Abstract– Two categories of symplectites have been observed in howardites: three‐phase, composed of vermicular intergrowths of ferroan augite, fayalitic olivine, and silica, and two‐phase, composed of vermicular intergrowths of orthopyroxene and troilite. Three‐phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene. In howardites, they appear to be genetically related to gabbroic eucrites. In some cases and under yet‐to‐be specified conditions, ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution‐like features. Breakdown phases in those cases are fayalitic olivine, silica, and—depending on the MgO content of the system—orthopyroxene. As opposed to three‐phase symplectites, two‐phase symplectites are most likely of diogenitic origin. They probably formed via impact‐induced localized melting of diogenitic orthopyroxene in the presence of troilite (grain boundary melting). Three‐phase symplectites in howardites occasionally contain accessory amounts of ilmenite, troilite, and/or kamacite and are exclusively associated with medium‐grained FeO‐rich pyroxene, silica, and plagioclase. All minerals involved are late‐stage crystallites or mesostasis phases. In general, highly evolved eucritic lithologies constitute only a minor fraction of howardites. However, considering that three‐phase symplectites are generated in a low‐pressure, i.e., near‐surface, environment, FeO‐ and CaO‐rich eucritic rocks may be exposed locally on Vesta’s surface. This, in turn, is highly relevant to the ongoing DAWN mission.