Neodymium and strontium isotopic characteristics of New Zealand granitoids and related rocks

Initial ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of Phanerozoic granitoids and related intrusions of the New Zealand block display a mixing-type array indicative of the involvement in their sources of old continental crustal material, most likely of Proterozoic age. _Sr(T) values range from –4 to +273 (⁸⁷Sr/⁸⁶Sr=0.7041–0.7233), while _Nd(T) ranges from +2.7 to –11.0. Preexisting metasedimentary rocks have generally higher _Sr and lower _Nd (ranging to present-day values of +646 and –15.0, respectively), and, particularly for the Mesozoic intrusives, are isotopically appropriate mixing end-members. The widespread, early Paleozoic Greenland Group graywackes, which are derived from Proterozoic sources, are modeled as the source of the crustal end-member mixing with mantle-derived mafic magmas to produce the intrusive rocks. Four different types of models are applied to the isotopic and trace-element (Rb, Sr, Ba, REE) data: simple mixing; mixing with a partial melt of the metasedimentary rock, with or without isotopic equilibrium; and assimilation-fractional crystallization. Based on these models, some constraints may be applied on petrogenesis (e.g., the lack of high Rb concentrations points to the presence of biotite, and HREE depletion points to the presence of garnet); however, the models fail to adequately explain all the data. The New Zealand granitoids show similarities in isotopic character not only to rocks from offshore islands on the New Zealand block, but also to similar-aged granitoids in adjacent regions of Antarctica and Australia. This points to similarities in crustal character between continental blocks formerly proximal in Gondwanaland. We note an overall increase in _Nd and decrease in _Sr in felsic magmas from the Paleozoic to the Mesozoic to the Cenozoic in New Zealand, indicative of a decrease over time in the level of influence of recycled continental crust in subduction-related magmatism.Division Contribution No. 4538 (582)     

The race is not to the swift

Megan K Pickett and Andrew J Lim examine the role of spirals in protoplanetary disks and the formation of gas giant planets, and find that slower may be better than faster, if planets are to endure.     

Estimating site-specific strong earthquake motions

The Campus Earthquake Program (CEP) of the University of California (UC) started in March 1996, and involved a partnership among seven campuses of the UC—Berkeley, Davis, Los Angeles, Riverside, San Diego, Santa Barbara, Santa Cruz—and the Lawrence Livermore National Laboratory (LLNL). The aim of the CEP was to provide University campuses with site-specific assessments of their earthquake strong motion exposure, to complement estimates they obtain from consultants according to the state-of-the-practice (SOP), i.e. Building Codes (UBC 97, IBC 2000), and Probabilistic Seismic Hazard Analysis (PSHA). The Building Codes are highly simplified tools, while the more sophisticated PSHA is still somewhat generic in its approach because it usually draws from many earthquakes not necessarily related to the faults threatening the site under study.Between 1996 and 2001, the site-specific studies focused on three campuses: Riverside, San Diego, and Santa Barbara. Each campus selected 1–3 sites to demonstrate the methods and procedures used by the CEP: Rivera Library and Parking Lots (PL) 13 and 16 at UCR, Thornton Hospital, the Cancer Center, and PL 601 at UCSD, and Engineering I building at UCSB. The project provided an estimate of strong ground motions at each selected site, for selected earthquake scenarios. These estimates were obtained by using an integrated geological, seismological, geophysical, and geotechnical approach, that brings together the capabilities of campus and laboratory personnel. Most of the site-specific results are also applicable to risk evaluation of other sites on the respective campuses.The CEP studies have provided a critical assessment of whether existing campus seismic design bases are appropriate. Generally speaking, the current assumptions are not acknowledging the severity of the majority of expected motions. Eventually, both the results from the SOP and from the CEP should be analyzed, to arrive at decisions concerning the design-basis for buildings on UC campuses.     

Statistical Insights Regarding Fully Softened Shear Strength

The fully softened shear strength (FSS) concept is a practical approximation of the mobilized drained shear strength of first-time slides in stiff-fissured clays. There has been a recent increase in interest in measurement and estimation of FSS secant friction angle (FSS-ϕ′sec) to develop correlations for preliminary design and cost approximation. However, such correlations do not help in understanding the cause and effect relationship between soil properties and FSS-ϕ′sec. In this study, a laboratory database containing FSS-ϕ′sec values (output) and soil properties (inputs) of several overconsolidated clays is used to develop a predictive model for FSS-ϕ′sec (output or response). The goal is to detect which inputs from the whole parameter space dominate the response while creating an accurate prediction tool to provide statistical insights regarding the FSS-ϕ′sec. The proposed methodology is used to assess and quantify the relationships among variables, estimate testing device effects on FSS-ϕ′sec, and analyze the danger of extrapolation due to model constraints. The applicability of the predicted FSS-ϕ′sec is also evaluated and compared. Recommendations regarding the studied prediction tools for slope stability design in stiff-fissured clays are provided.

     

Review of Microstructural Evidence of Magmatic and Solid-State Flow

Evidence of magmatic flow includes: (a) parallel to sub-parallel alignment of elongate euhedral crystals (e.g., of feldspar or hornblende) that are not internally deformed, (b) imbrication (‘tiling’) of elongate euhedral crystals that are not internally deformed, (c) insufficient solid-state strain in regions between aligned or imbricated crystals to accommodate phenocryst rotation, (d) elongation of microgranitoid enclaves without plastic deformation of the minerals, (e) magmatic flow foliations and elongate microgranitoid enclaves deflected around xenoliths, and (f) schlieren layering (if due to flow sorting) in the absence of plastic deformation of the minerals involved. These features are consistent with rotation of crystals in a much weaker medium, namely a melt phase, at a stage when the magma has become viscous enough to preserve the alignment.Evidence of solid-state flow includes: (a) internal deformation and recrystallization of grains, (b) recrystallized “tails,” (c) elongation of recrystallized aggregates (e.g. of quartz and mica), (d) grainsize reduction, (e) fine-grained folia anastomosing around less deformed relics, (f) microcline twinning, (g) myrmekite, (h) flame perthite, (i) boudinage of strong minerals, typically with recrystallized aggregates of weaker minerals (e.g. quartz and mica) between the boudins, (j) foliation passing through, rather than around enclaves, and (k) heterogeneous strain with local mylonitic zones.Several criteria suggest “submagmatic flow,” including recrystallized feldspar, inferred transitions from magmatic imbrication to solid-state S/C arrangements, evidence of c-slip in quartz, and especially evidence of migration of residual melt into lower-pressure sites.Recent experimental studies indicate that a change from grain-supported flow to suspension flow typically occurs in deforming magmas at melt contents of between 20% to 40%, and that large amounts of strain may accumulate in magmas without being recorded by the final fabric. At lower melt percentages, perhaps as low as a few percent, depending on the minerals and their shapes, strain may be accommodated by: (a) melt-assisted grain-boundary sliding, (b) contact-melting assisted grain-boundary migration, (c) strain partitioning into melt-rich zones, (d) intracrystalline plastic deformation (c-slip in quartz indicating plastic deformation at temperatures near the granite solidus), and (f) transfer of melt to sites of low mean stress. The only indication of strain in the absence of crystal plasticity may be an alignment of crystals. Moreover, magmatic flow microstructures may be destroyed by fracturing, crystal plasticity and recrystallization before the magma reaches its solidus.Many rocks show evidence of solid-state flow superimposed on magmatic flow. Evidence of magmatic flow is commonly preserved in deformed felsic metamorphic rocks: for example the alignment of rectangular K-feldspar megacrysts and of microgranitoid enclaves. However, absence of alignment does not preclude a magmatic origin for K-feldspar megacrysts in felsic gneisses, as magmatic flow may cease before the magma becomes viscous enough to preserve an alignment.     

On the electric field at the tip of dart leaders in lightning flashes

The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to values larger than the critical electric field necessary for the initiation of cold electron runaway in low-density air comprising the channel. These results are in support of the hypothesis that cold runaway electron breakdown may play a role in the emission of X-ray bursts by dart leaders. The calculations also show that the peak power dissipated by a typical dart leader is about 300–500 MW/m and the energy dissipated within the first 10 μs or so is about 500–600 J/m. Furthermore, the minimum resistance and the maximum radius of the core of a typical dart leader are estimated to be about 3 Ω/m and 0.003 m, respectively.     

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.