Basalt generation at the Apollo 12 site,Part 1: New data,classification, and re-evaluation     

Clive R. Neal  Matthew D. Hacker  Gregory A. Snyder  Lawrence A. Taylor  Yun-Gang Liu  Roman A. Schmitt 《Meteoritics & planetary science》1994,29(3):334-348

Abstract— New data are reported from five previously unanalyzed Apollo 12 mare basalts that are incorporated into an evaluation of previous petrogenetic models and classification schemes for these basalts. This paper proposes a classification for Apollo 12 mare basalts on the basis of whole-rock Mg# [molar 100*(Mg/(Mg+Fe))] and Rb/Sr ratio (analyzed by isotope dilution), whereby the ilmenite, olivine, and pigeonite basalt groups are readily distinguished from each other. Scrutiny of the Apollo 12 feldspathic “suite” demonstrates that two of the three basalts previously assigned to this group (12031, 12038, 12072) can be reclassified: 12031 is a plagioclase-rich pigeonite basalt (Nyquist et al, 1979); and 12072 is an olivine basalt Only basalt 12038 stands out as a unique sample (Nyquist et al., 1981) to the Apollo 12 she, but whether this represents a single sample from another flow at the Apollo 12 site or is exotic to this site is equivocal. The question of whether the olivine and pigeonite basalt suites are co-magmatic is addressed by incompatible trace-element chemistry: the trends defined by these two suites when Co/Sm and Sm/Eu ratios are plotted against Rb/Sr ratio demonstrate that these two basaltic types cannot be co-magmatic. Crystal fractionation/accumulation paths have been calculated and show that neither the pigeonite, olivine, or ilmenite basalts are related by this process. Each suite requires a distinct and separate source region. This study also examines sample heterogeneity and the degree to which whole-rock analyses are representative, which is critical when petrogenetic interpretation is undertaken. Sample heterogeneity has been investigated petrographically (inhomogeneous mineral distribution) with consideration of duplicate analyses, and whether a specific sample (using average data) plots consistently upon a fractionation trend when a number of different compositional parameters are considered. Using these criteria, four basalts have been identified where reported analyses are not representative of the whole-rock composition: 12005, an ilmenite basalt; 12006 and 12036, olivine basalts; and 12031 previously classified as a feldspathic basalt, but reclassified as part of the pigeonite suite (Nyquist et al., 1979).  相似文献   

Man's impact on shorelines and nearshore environments: a geomorphological perspective     

H.Jesse Walker 《Geoforum》1984,15(3):395-417

Man evolved late in terms of geologic history, yet he has become a major geomorphologic agent despite his short tenure on Earth. His ability to alter the materials, processes and forms along the world's shorelines are manifested in a variety of ways. Beginning with the indirect changes that resulted from early agriculture and animal husbandry, he progressed to direct modification through reclamation and harbor construction. Today, in the name of shoreline stabilization, thousands of kilometers of natural shoreline have been modified by the addition of artificial structures.  相似文献   

A ground reaction curve based upon block theory     

Jesse L. Yow Jr.  Richard E. Goodman 《Rock Mechanics and Rock Engineering》1987,20(3):167-190

Summary Discontinuities in a rock mass can intersect an excavation surface to form discrete blocks (keyblocks) which can be unstable. Once a potentially unstable block is identified, initial normal and shear stresses on each block face are calculated using elastic theory, and are then modified by discontinuity deformations as the keyblock displaces. The modified stresses are summed into resultant forces to evaluate block stability. Since the resultant forces change with displacement, successive increments of block movement are examined to see whether the block ultimately becomes stable or fails. Calculated keyblock stability increases with larger in situ stress magnitudes, larger lateral stress ratios, and larger shear strengths. Discontinuity stiffness controls block displacement more strongly than it does stability itself. Large keyblocks are less stable than small ones, and stability increases as blocks become more slender.  相似文献   

Psychrometric apparatus for Bowen-ratio determination over forests     

T. A. Black  K. G. McNaughton 《Boundary-Layer Meteorology》1971,2(2):246-254

The psychrometric apparatus design for Bowen ratio determination reported previously by Sargeant and Tanner was modified and a new apparatus built. Modification of the intake design improved the symmetry and rigidity of the sensor mounting. Wet- and dry-bulb differences were measured with an error less than 0.01 °C over a vertical distance of 1 m. Continuous measurements of the Bowen ratio over a 7.8-m Douglas fir forest were made for 6 weeks. An example of the energy balance for the forest for one day using this equipment is reported.  相似文献   

Inequality of eddy transfer coefficients for vertical transport of sensible and latent heats during advective inversions   总被引：1，自引：0，他引：1  

A. R. G. Lang  K. G. McNaughton  Chen Fazu  E. F. Bradley  Eiji Ohtaki 《Boundary-Layer Meteorology》1983,25(1):25-41

Similarity of transport of water vapour and sensible heat was investigated within an advective inversion layer by measuring eddy fluxes together with gradients of temperature and humidity. The experimental site was a field of rice, grown under flood irrigation, which was situated in a semi-arid region. The fetch was about 300 m and local stabilities (z/L) over the rice ranged from 0 to 0.1. Results were expressed as the ratio of eddy transfer coefficients for sensible heat (K _H) and water vapour (K _w). Near neutral stability, K _H/K_W approached 1, but the ratio decreased to about 0.65 with increasing stability. Existing theory predicts the result qualitatively but accounts for only about one fifth of the decrease in K _H/K_W with stability.  相似文献   

On modelling the effects of afforestation on acidification in heterogeneous catchments at different spatial and temporal scales     

A. J. Wade  C. Neal  C. Soulsby  S. J. Langan  R. P. Smart 《Journal of Hydrology》2001,250(1-4):149-169

A modelling approach is presented for simulating and predicting future changes in streamwater Gran alkalinity throughout a large, heterogeneous river system. The methodology is based on integrating End Member Mixing Analysis (EMMA), the Model of Acidification of Groundwater in Catchments (MAGIC) and spatial data describing the catchment characteristics stored on a Geographical Information System (GIS). These are integrated within a Functional Unit Network (FUN) to predict the changes in Gran alkalinity resulting from possible future changes in atmospheric deposition and land use (low intensity afforestation) in the River Dee catchment, NE Scotland. Model results indicate that declining sulphate and constant nitrogen deposition, combined with low intensity Scots pine (Pinus sylvestris) afforestation are unlikely to contribute significantly to streamwater acidification.  相似文献   

Single zircon U-Pb dating of the Kongling high-grade metamorphic terrain: Evidence for >3.2 Ga old continental crust in the Yangtze craton   总被引：4，自引：0，他引：4  

Shan Gao  Yumin Qiu  Wenli Ling  McNaughton Neal J.  Groves David I. 《中国科学D辑(英文版)》2001,44(4):326-335

Single zircons from two trondhjemitic gneisses and two clastic metasedimentary rocks without Eu anomaly of the Kongling high-grade metamorphic terrain are dated by thein situSHRIMP U-Pb method. The results show that the trondhjemitic magma emplaced at 2947-2903 Ma. Concordant age of as old as 3.3 Ga is present in the detrital zircons from the clastic metasedimentary rocks. Together with the depleted mantle Nd model age (T_DM =3.2-3.3 Ga) of the clastic metasedimentary rocks, this documents the presence of Paleoarchean continental crust in the Yangtze craton.  相似文献   

澳大利亚纳沃日金矿流体混合与金的成矿作用   总被引：9，自引：0，他引：9  

范宏瑞  D I Groves  E J Mikuckj  N J McNaughton 《矿床地质》2001,20(1):37-43

流体包裹体研究表明，纳沃日金矿成矿脉体中流体包裹体类型有三种，富CH4、CH4－CO2－H2O和富H2O包裹体。初始成矿流体是富CH4热液，在主矿化阶段，另一来源的CO2－H2O流体与CH4流体发生了不均匀混合，并且在石英－磁黄铁矿阶段最为强烈，造成不同矿化部位的xCH4变化极大，早期近于纯CH4流体被充分“稀释”后，石英－黄铁矿阶段的xCH4显著减小，到成矿晚期只剩CO2－H2O流体。正是由于不同性质流体的混合，造成热液的pH及fo2的升高，流体中的金－硫络合物分解，金沉淀成矿。  相似文献   

In situ target-strength estimation of Pacific whiting (Merluccius productus) using a dual-beam transducer     

Williamson  Neal J.; Traynor  Jimmie J. 《ICES Journal of Marine Science》1984,41(3):285-292

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The role of frontal currents in larval fish transport on Georges Bank     

David W. Townsend  Neal R. Pettigrew 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)

The hydrography and distributions of cod larvae on Georges Bank were surveyed during two research cruises in April and May 1993 in order to relate larval drift between cruises to the vernal intensification of the frontal component of the residual circulation. We observed the transport of two patches of cod larvae. One patch, which had maximum larval cod densities of 45 larvae 100 m⁻³ in April, appeared to have been advected south about 75 km between surveys, while the other, which had maximum larval cod densities of 20 larvae 100 m⁻³ in April, appeared to have been advected north-northeast about 25 km. Maximum larval densities in each patch sampled during the second cruise in May were 15 and 18 larvae 100 m⁻³, respectively, and mean growth in total length for larvae in the two patches was approximately 5.5 mm and 4.5 mm, respectively, between the two cruises. During the April cruise there was a large volume of anomalous cold, fresh water, of Scotian Shelf origin, which occupied much of the eastern third of Georges Bank. During May, relatively cold, fresh water appeared in a band from the Northeast Peak along the Southern Flank, between Georges Bank water on the top of the Bank, and upper Slope Water offshore. The distribution of cold, fresh water suggests its participation in the general clockwise circulation around the Bank. The transport of cod larvae comprising the first patch appeared to become organized within, and move along, the frontal boundary established by the Scotian Shelf-like water mass, while larvae in the second patch, which we assumed to have moved to the north, may have been transported northward in an on-Bank flow of warmer and saltier upper Slope Water, which may have originated from a Gulf Stream Ring. Based upon observed transport of the first patch of larvae in relation to the frontal boundary, we present a conceptual model of frontal mixing currents on Georges Bank, where current velocities may reach 5 cm s⁻¹ at the depth of the pycnocline. We suggest that this frontal component of the residual circulation, which is in addition to that resulting from tidal rectification, may be important in the transport of fish larvae, and that interannual variability in the degree of intrusion of extrinsic water masses may contribute to variable larval cod drift patterns, to variable larval cod retention on the Bank, and ultimately, to variable larval fish recruitment to the early juvenile stage.  相似文献