Mineral reactions in a calc-mica schist from Gassetts,Vermont, U.S.A.

A petrographic and electron microprobe study of an interbedded calc-mica schist from Gassetts, Vermont reveals the complexities of Fe-Mg crystalline solution and gradients in X _H2O/X _CO2 during regional metamorphism. The common association of microcline+diopside ± zoisite formed from biotite +calcite+quartz may be produced by continuous (Fe-Mg) exchange reactions, despite the implied metastability in the CaO-K₂O-MgO-Al₂O₃-SiO₂-H₂O-CO₂ system. Different assemblages are produced in a reaction zone between carbonate and pelite beds of varying thickness. This illustrates the importance of exhaustion of fluid buffering assemblages due to mineral reactions proceeding on a local scale. Siliceous dolomites at the same metamorphic grade have produced significantly different assemblages to the interlayered carbonatepelite sequence.     

Primary basalts and magma genesis

The Pliocene-Holocene lavas of the Snake River Plain, Idaho, U.S.A., have a bimodal composition range, consisting predominantly of basalts (olivine-tholeiites), with subordinate intercalated tholeiitic andesites but with very few analyses falling between these groups. The more-magnesian of the tholeiitic andesites contain more total Fe, alkalis, TiO₂ and P₂O₅ but less SiO₂ than the less-magnesian basalts. Derivation of the tholeiitic andesites from the basalts by low-pressure fractional crystallization or by major-element crustal contamination does not seem possible, although some minor-element exchange with ancient crust apparently has occurred. Two lavas, representative of the least-magnesian basalts and the most-magnesian tholeiitic andesites, respectively, have been subjected to anhydrous experimental studies within their melting ranges at pressures up to 35kb. Both appear to show four-phase points on their liquidi at about 8kb and these are thought to have genetic significance. Microprobe analyses of the interstitial glasses in partially-crystalline runs on the basalt between 8 and 12kb show that these reproduce all the characteristic features of the Snake River Plain most-magnesian tholeiitic andesites, notably their reduced Si-saturation. The compositions of the most Mg-rich Snake River Plain basalts are such that they may perhaps be primary magmas, produced by partial fusion of a relatively Fe-rich spinel-lherzolite upper mantle at 50 to 60km depth; a proposal which accords well with the geophysics of this currently-active region. Partial crystallization of batches of this magma, delayed during ascent within the crust at depths of about 30 km, is thought to have given rise to the tholeiitic andesites.     

U234U238 Ratios in limestone cave seepage waters and speleothem from West Virginia

Speleothem from West Virginia, ranging in age from 2000 to 200,000 yr B.P. contains uranium with $\text{U}{}^{234}\text{U}{}^{238}$ ratios significantly greater than unity. This ratio varies from one speleothem to another, as does average U content. Initial ratios, corrected for age, are remarkably constant for a given speleothem. By contrast, $\text{U}{}^{234}\text{U}{}^{238}$ ratios in seepage waters vary significantly from month to month at a given drip site, and their average values differ from that of the speleothem which they are depositing. This discrepancy is attributed either to long-term averaging-out of fluctuations, or fractional precipitation on the speleothem of a chemical species of uranium with a more constant ratio. Constancy of initial $\text{U}{}^{234}\text{U}{}^{238}$ ratios from $\text{Th}{}^{230}\text{U}{}^{234}$. datable portions of speleothems should permit $\text{U}{}^{234}\text{U}{}^{238}$-dating of older portions of the same speleothem, back to about 10⁶ yr B.P., with estimated precision of ±5 per cent.     

Evidence for heterogenes primary MORB and mantle sources,NW Indian Ocean

Basalts from 5 Deep Sea Drilling Project (DSDP) sites in the northwest Indian Ocean (Somali Basin and Arabian Sea) have general geochemical features consistent with a spreading origin at the ancient Carlsberg Ridge. However, compared to most MORBS from other oceans they have low normative olivine, TiO₂, and Zr contents. There is no evidence that the mantle source of these northwest Indian Ocean basalts was enriched in incompatible elements relative to the Atlantic and Pacific ocean mantles. In detail, incompatible element abundances in these DSDP basalts establish that they evolved from several compositionally distinct parental magmas. In particular, basalts from site 236 in the Somali Basin have relatively high SiO₂ and low Na, P, Ti, and Zr contents. These compositional features along with low normative olivine contents are similar to those proposed for melts derived by two-stage (or dynamic) melting. Published data also indicate there is no enrichment in incompatible elements at the southwest Indian Ocean triple junction, although southwest Indian Ocean basalts have slightly higher ⁸⁷Sr/⁸⁶Sr than normal Atlantic MORB. The data suggest that there are significant subtle geochemical variations in the Indian Ocean mantle sources, but are insufficient to show whether these variations have a systematic temporal or geographic distribution.     

Coke/carbon reactions in the study of factors affecting coke quality

Pilot-scale and plant cokes with initially different properties were subjected to weight loss by reaction with carbon dioxide, and the resulting products were characterized both microscopically and by ASTM Tumbler tests. The cokes were found to lose strength progressively as weight loss occured, and the examination of carbon forms and microstructures showed the strength changes to be related to the initial properties of the cokes and ultimately to particular compositional characteristics of the coals used to make the cokes. The results have been providing coal-selection guidelines to assist in the manufacture of higher-quality coke. Our coke reactivity test is also being used to signal changes in the coal supply and to monitor certain other coking parameters.     

A design study for an advanced ocean color scanner system

The spaceborne ocean color scanners currently being planned for flights on Nimbus-G satellite or space shuttle craft are, in every aspect, only a modest beginning towards what is to be expected of ocean color scanners in the eighties. Improvements are necessary in the following areas: present systems provide a spatial resolution on the order of 1 km at nadir, which would not satisfy most of the coastal zone study requirements. Also the present design of radiomers is less than optimum for the removal of the atmospheric effects on ocean colorimetry.Along with a colorimetric data analysis scheme, the instrumental parameters which need to be optimized in future systems are outlined. One technique for meeting these requirements entails use of large linear array detector technology.     

Geometric adjustment of pools to changes in slope and discharge: a flume experiment

To characterize the factors controlling pool shape, 30 different forced pools were created utilizing a 50% triangular constriction in a 0.5-m wide, 6-m long recirculating flume. Pools were scoured from an initial plane bed of sand with a d₅₀ of 0.25 mm. Pool depth and length were measured and used as dependent variables in least-squares, multiple-regression analyses. Discharge, channel-bed gradient and energy slope were the independent variables. Additional linear-regression analyses were conducted with either pool depth or length and stream power. Results indicate that both pool depth and length are primarily a function of discharge. Channel-bed and energy slopes are also significantly related to pool length but are not significantly related to pool depth. Stream power is significantly related to both pool depth and length, but R² values for pool depth versus discharge indicate stronger relations than those between pool depth and stream power. Observations on the type of geometric adjustment indicate that pools may minimize their rate of energy expenditure primarily through elongation. In contrast, pool depth appears to be more sensitive to the characteristics of the constrictions that create the forced pools. The results suggest that many field studies may suffer from cross-correlation problems. In particular, channel erodibility may exert a more dominant influence on pool geometry than hydraulic controls in many constriction-influenced channels.     

A technique for predicting the amplitude of the solar cycle

Predictions of the amplitude of the last three solar cycles have demonstrated the value and accuracy of the group of prediction methods known as the precursor techniques. These are based on a correlation between cycle amplitude and phenomena observed on the Sun, or originating from the Sun, during the declining phase of the cycle or at solar minimum. In many cases, precursor predictions make use of the long record of geomagnetic disturbance indices, assuming that these indices are indicative of solar phenomena such as the occurrence of coronal holes.This paper describes a precursor technique for predicting the amplitude of the solar cycle using geomagnetic indices. The technique is accurate — it would have predicted each of the last 11 cycles with a typical error of less than 20 in sunspot number. It has also advantage that a prediction of the lower limit of the amplitude can be made throughout the declining phase, this limit building to a final value at the onset of the new cycle.     

Correlation of He II lyman alpha with He I 10830 Å, and with chromospheric and EUV coronal emission

This paper describes the results of comparing SERTS-3 images obtained in the transition region line of Heii 304 with chromospheric Hei 10830 absorption, with strong coronal lines of Mgix 368 , Fexv 284 and 417 , and Fexvi 335 and 31 , with H, with Caii 8542 , and with magnetograms in Fei 8688H. All of the images are illustrated, and the image reconstruction techniques used are described and evaluated. The high correlation of the Heii 304 and Hei 10830 images, originally found by Harvey and Sheeley (1977), is confirmed and is put on a quantitative basis. We find that the supergranulation network has greater contrast, and that filaments appear darker, in 10830 than in 304 . In active regions, the 304 line follows more closely the behavior of H and Caii 8542 than the 10830 line.