Climatic control of the assemblages of secondary clay minerals in the A-horizon of United States soils

The concentrations (per cent) of secondary clay minerals (mica, vermiculite, montmorillonite, chlorite and kaolinite) in the A-horizon of 99 soil sample sites were entered into a cluster program to determine the common clay mineral assemblages found in U.S. soils. Five major assemblages were identified with the most common assemblage consisting of mica, montmorillonite and kaolinite. A suite of climatic variables was determined for each of the 99 sites, including the water balance variables and Arkley's leaching index. A discriminant analysis was then used to predict the occurrence of a clay assemblage from the climate data. Sixty per cent of the sites could be correctly predicted, although not all assemblages could be predicted equally well; two assemblages could be predicted with 88 and 82 per cent accuracy. The precipitation of the wettest month and Arkley's leaching index accounted for most of the predictive power. Thus this study supports theoretical models which suggest that seasonal moisture supply is an important control of clay genesis and persistence. A residuals analysis indicated that many of the palaeosols in the data set and many of the soils from glacial parent materials possessed clay mineral assemblages not expected on the basis of modern climate.     

The impact of moral conditions associated with culture on the traditional adoption-diffusion Model: The case of the Qassim Region of Saudi Arabia

The main objective of this paper is to develop a conceptual framework that views cooperative membership in Saudi Arabia as a function of both utilitarian and deontological (moral) perspectives. The research was conducted in the Qassim, an agricultural area located in the Central Region of Saudi Arabia. The sample includes 83 cooperative members, besides 136 non-members. Discriminant analysis is used to test the hypothesis derived in this research. Two models are examined, the first model is based on the traditional adoption-diffusion framework. Thus, discriminating variables included in the first model are related to the socioeconomic characteristics of respondents, information content, sources of information, and advantages of membership in agricultural cooperatives. In the second model, discriminating variables pertaining to moral conditions were used in addition to the original discriminating variables. Results of the discriminant analysis fit the theoretical framework of the study, meaning that farmers become members because of economic (utilitarian) expectations and also because of their desire to cooperate with other farmers. Deontology therefore plays an important role in distinguishing members from non-members.     

The first electric field pulse of cloud and cloud-to-ground lightning discharges

In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as ‘small’, ‘medium’ and ‘large’, depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.     

Inclusion trail patterns in porphyroblasts from the Foothills Terrane,California: a record of orogenesis or local strain heterogeneity?

A major problem with the current use of porphyroblast–matrix microstructural relationships to infer orogenic histories, such as multiple orthogonal orogenic events, is that other evidence for these events is typically lacking. For example, a comparison of regional relationships and local structures formed in and adjacent to porphyroblasts present in contact aureoles in the Foothills Terrane, Sierra Nevada, California, shows that: (1) except in shear zones, contact aureoles and local zones along lithological contacts, the Foothills Terrane has a single regional cleavage, although locally formed by multiple processes; (2) the regional cleavage and locally developed porphyroblast inclusion trails have variable orientations, and neither dataset supports the formation of dominantly subhorizontal and subvertical cleavages in this orogen; (3) structural and metamorphic heterogeneities occur at all scales and can markedly affect inclusion trail patterns in porphyroblasts; (4) complex porphyroblast growth features and internal inclusion trail patterns can form in porphyroblasts that grow during short time intervals in contact aureoles, indicating that local complexity in porphyroblasts does not imply regional complexity. Because of these conclusions, multiple datasets, rather than data acquired only from porphyroblasts, should be considered when attempting to understand the evolution of orogens. Furthermore, using microstructural information preserved only in porphyroblasts to infer orogenic processes and plate motions is generally unjustified.     

Effects of buoyancy and mechanical layering on collisional deformation of continental lithosphere: Results from physical modeling

We use two suites of lithospheric-scale physical experiments to investigate the manner in which deformation of the continental lithosphere is affected by both (1) variations of lithospheric density (quantified by the net buoyant mass per area in the lithospheric mantle layer, M_B), and (2) the degree of coupling between the crust and lithospheric mantle (characterized by a modified Ampferer ratio, Am). The dynamics of the experiments can be characterized with a Rayleigh–Taylor type ratio, _CLM. Models with a positively buoyant lithospheric mantle layer (M_B > 0 and _CLM > 0) result in distributed root formation and a wide deformation belt. In contrast, models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust (M_B < 0, 0 > _CLM > ≈ − 0.2, and Am > ≈ 10^{− 3}) exhibit localized roots and narrow deformation belts. Syncollisional delamination of the model lithospheric mantle layer and a wide deformation belt is exhibited in models with negatively buoyant lithospheric mantle layers weakly coupled to the crust (M_B < 0, _CLM < 0, and Am < ≈ 10^{− 3}). Syncollisional delamination of the continental lithosphere may initiate due to buoyancy contrasts within the continental plate, instead of resulting from wedging by the opposing plate. Rayleigh–Taylor instabilities dominate the style of deformation in models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust and a slow convergence rate (M_B < 0 and _CLM > ≈ − 0.2). The degree of coupling (Am) between the model crust and lithospheric mantle plays a lesser role in both the style of lower-lithospheric deformation and the width of the crustal deformed zone with increasing density of the lithospheric mantle layer.     

Reactions involving hydration of cordierite and hypersthene

Petrographic evidence for the hydration reactions: cordierite + water = gedrite + kyanite + quartz, and aluminous hypersthene + water = aluminous anthophyllite, is shown by some granulite facies rocks in the Arunta Complex, near Alice Springs, central Australia. Electron microprobe analyses enable the reactions to be written in some detail. Preliminary thermodynamic and experimental information suggests that the reactions took place at relatively high confining pressures. The reactions may have proceeded more in response to addition of water to the system, rather than a major change in P-T conditions.     

Igneous origin of K-feldspar megacrysts in deformed granite of the Papoose Flat Pluton, California, USA

Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts. Evidence of an igneous origin includes features such as crystal shapes, simple twinning, zonally arranged euhedral plagioclase inclusions, oscillatory compositional zoning, and local occurrence in microgranitoid enclaves. Evidence of solid-state deformation of the megacrysts (which is consistent with their existence prior to the mylonitic deformation) includes marginal recrystallization and neocrystallization, microcline twinning, marginal replacement by myrmekite, and recrystallized/neocrystallized “tails”. Evidence of porphyroblastic growth, such as overgrown inclusion trails, is absent. This appears to be the situation in most felsic augen gneisses and mylonites.