Initial accretion of the North Qinling Terrane to the North China Craton before the Grenville orogeny: constraints from detrital zircons

Whether the North Qinling Terrane (NQT) was accreted to the North China Craton (NCC) in the Proterozoic is still a matter of debate. We report the first detrital zircon study from the Baishugou Formation, which forms the uppermost part of the Mesoproterozoic Guandaokou Group, at the southernmost NCC margin. Detrital zircons from carbonaceous silty phyllite in the lower part of the Baishugou Formation yield U–Pb ages peaking at ca. 2500 Ma, with minor peaks at ca. 2300–2000, 1800, and 1600 Ma, and εHf(t) values ranging from ?10.8 to +9.1. These zircons are considered to have been sourced from the NCC. In contrast, the middle-to-upper part of the formation contains detrital zircons which yield an age group ranging from 1800 to 1000 Ma, with peaks at 1800, 1500, 1300, and 1100 Ma; the zircons with ages of 1500–1300 Ma dominantly have εHf(t) values greater than +5 and the majority plot along the depleted mantle evolution curve. The striking difference between the U–Pb ages of the detrital zircons from the upper and lower parts of the formation suggests a shift in provenance. Magmatism at 1500–1300 Ma has not been reported from the southern margin of the NCC but has been discovered in the NQT. Hence, we deduce that the zircons from the upper part of the formation were primarily derived from the NQT, where an episode of crustal growth and magmatism is recorded between 1500 and 1100 million years. The variable sediment provenances imply that the NCC and NQT could be connected during the late Mesoproterozoic to early Neoproterozoic. The pattern of detrital zircon ages in the new sediments from the Baishugou Formation is distinct from those in the Kuanping Group and the Palaeozoic Erlangping Complex, which are at present sandwiched between the NCC and the NQT. The detrital zircons from these two groups are dominated by an age peak at ca. 1000 Ma, which is formed as the result of amalgamation of the NQT and the Rodinia Supercontinent during the Grenville orogeny. It is possible that the new sediments of the Baishugou Formation were deposited before Grenville orogeny.     

An irregular triangle mesh buffer analysis method for boundary representation geological object in three-dimension

Three-dimensional (3D) buffer analysis is a basic function of spatial analysis used widely in 3D Geographic Information Systems (3DGIS). Current buffer analysis methods for spatial points and curves generally function well. One exception is buffer zone of surface. Previous researchers in this field have used voxel models to overcome this limitation; however, defects with voxel model buffer analysis include redundancies, approximations, and poor visualization characteristics. In this contribution, a surface buffer analysis method is presented for the boundary representation of geological objects. Exact geometric representation is achieved via the construction of irregular triangle meshes in 3D. The results can be used for 3D structural modeling and then form the basis for spatial analysis or model-based quantitative assessment in mineral potential mapping and resource evaluation. Three comparisons between existing voxel methods and our new method, evaluating visualization, precision and redundancy, are conducted. The comparisons show that our proposed method is robust and provides a higher quality output than voxel modeling. Finally, uncertainty analysis of buffer distance in different geological objects was discussed.     

Copper and sewage inputs from recreational vessels at popular anchor sites in a semi-enclosed Bay (Qld, Australia): estimates of potential annual loads

Environmental impacts of vessels are well documented; Cu pollution as result of Cu based antifouling paints and nutrient pollution (such as N) from marine sewage are two examples of such disturbances. Understanding environmental impacts as well as the use of coastal waterways by recreational vessels is of concern to regulatory authorities, waterway users and local residents. In this study more than 55 aerial surveys were conducted of selected popular anchorages in eastern Moreton Bay, Queensland, Australia. Numbers of recreational vessels at certain times during the year were used in multiple linear regression analyses to develop predictive models for recreational vessel numbers. Over one year approximately 10,000 locally registered recreational craft (>6m length overall) generated an estimated 59,000 vessel nights. With Cu leaching rates from the literature, and estimates of sewage inputs (assuming little or no use of pump-out facilities), load estimates associated with overnight use of 20 popular anchor sites were calculated as 141+/-46 kg of Cu and 1.17+/-0.38 t of nitrogen (N) annually. More importantly, the models showed vessel activity to be highly variable, and focused at peak holiday times, with 14% of vessel activity and associated pollutant loads entering the environment during Christmas and Easter. This study highlighted the inherent difficulties in managing a popular maritime amenity and Marine Parks such as the Moreton Bay Marine Protected Area, Queensland, Australia with its variety of stakeholders and types and intensities of uses.     

Long-lived Coronal Loop Profiles from TRACE

An initial study of long-lived loops observed with TRACE (Lenz et al., 1999) shows that they have no significant temperature stratification and that they are denser than the classic loop model predicts. Models that agree better with the observations include a loop consisting of a bundle of filaments at different temperatures and a loop with momentum input by MHD waves. Some implications for coronal heating models and mechanisms are discussed.     

The radiative influence of aerosol effects on liquid-phase cumulus and stratiform clouds based on sensitivity studies with two climate models

Aerosol effects on warm (liquid-phase) cumulus cloud systems may have a strong radiative influence via suppression of precipitation in convective systems. A consequence of this suppression of precipitation is increased liquid water available for large-scale stratiform clouds, through detrainment, that in turn affect their precipitation efficiency. The nature of this influence on radiation, however, is dependent on both the treatment of convective condensate and the aerosol distribution. Here, we examine these issues with two climate models—CSIRO and GISS, which treat detrained condensate differently. Aerosol–cloud interactions in warm stratiform and cumulus clouds (via cloud droplet formation and autoconversion) are treated similarly in both models. The influence of aerosol–cumulus cloud interactions on precipitation and radiation are examined via simulations with present-day and pre-industrial aerosol emissions. Sensitivity tests are also conducted to examine changes to climate due to changes in cumulus cloud droplet number (N _c); the main connection between aerosols and cumulus cloud microphysics. Results indicate that the CSIRO GCM is quite sensitive to changes in aerosol concentrations such that an increase in aerosols increases N _c, cloud cover, total liquid water path (LWP) and reduces total precipitation and net cloud radiative forcings. On the other hand, the radiative fluxes in the GISS GCM appear to have minimal changes despite an increase in aerosols and N _c. These differences between the two models—reduced total LWP in the GISS GCM for increased aerosols, opposite to that seen in CSIRO—appear to be more sensitive to the detrainment of convective condensate, rather than to changes in N _c. If aerosols suppress convective precipitation as noted in some observationally based studies (but not currently treated in most climate models), the consequence of this change in LWP suggests that: (1) the aerosol indirect effect (calculated as changes to net cloud radiative forcing from anthropogenic aerosols) may be higher than previously calculated or (2) lower than previously calculated. Observational constrains on these results are difficult to obtain and hence, until realistic cumulus-scale updrafts are implemented in models, the logic of detraining non-precipitating condensate at appropriate levels based on updrafts and its effects on radiation, will remain an uncertainty.     

Petrogenesis of picrite and associated basalts from the southern Mid-Atlantic Ridge

Basalts dredged from the south wall of a fracture zone transecting the southern Mid-Atlantic Ridge (SMAR) at 54° S are unusual in that they include a suite of highly olivine phyric basalts, sampled along with more normal sparsely plagioclase phyric basalts, and a highly plagioclase phyric basalt. Four basalt types (olivine phyric, sparsely plagioclase phyric, evolved sparsely plagioclase phyric and highly plagioclase phyric) are readily distinguished on the basis of petrography, mineralogy and bulk composition. They range from primitive to evolved, with the olivine phyric basalts having elevated MgO (up to 15.5%) and the plagioclase phyric basalt having elevated Al₂O₃ (19.3%) and CaO (13.1%) contents. Compositional variations are extremely consistant, with the olivine phyric basalts and the sparsely plagioclase phyric basalts defining coherent linear trends. On the basis of the ratios and covariation of the incompatible trace elements Zr, Nb, Y and Ba, distinct parental magmas for each basalt type are required. An investigation of Fe-Mg and Mg-Ni distribution coefficients between olivine and magma indicates that olivines from the olivine phyric basalts are on average too forsteritic and too Ni poor to have crystallized in a magma corresponding to the host bulk rock composition. This implies that these basalts are enriched in xenocrystic olivine. Olivines from the other basalt types are mostly of equilibrium composition, although there are some exceptions. Petrogenetic models for the formation of the different basalt types are quantitatively evaluated in terms of fractional crystallization/crystal accumulation processes. These indicate that (1) the olivine phyric basalts are the products of olivine and minor Cr-spinel accumulation and do not represent analogues of primary magma, or a liquid fractionation trend; (2) that the sparsely plagioclase phyric basalts were formed by polybaric fractional crystallization of olivine, plagioclase and clinopyroxene; and (3) that the evolved sparsely plagioclase phyric basalts are not readily related to one another. The single highly plagioclase phyric basalt is unrelated to the other basalt types and is cumulus enriched in plagioclase.The different basalt types are unrelated to one another and document the presence of at least four distinct magma types erupted in close proximity at this ridge/transform intersection on the southern end of the Mid-Atlantic Ridge.     

Solar Scintillometry: Calibration of Signals and its Use for Seeing Measurements

Since 1993 it is known that there is a good correlation between the scintillation in the solar irradiance and solar image quality (Seykora, 1993). This effect is now being used in a number of experiments to evaluate solar image quality and to measure site seeing. In this paper we explore further the calibration of this scintillation (_I) in terms of the Fried parameter (_r0) taking into account variations in the refractive index structure constant C _N ² with height (h), zenith distance () dependence and the effects of wind velocities. A variant in the scintillometer setup is proposed which decreases sharply the dependance on C _N ² , , and the wind velocities. It uses an array of scintillometers. The same array can be used to measure theC _N ² profile with height. Some preliminary results of the calibration of current NSO site survey measurements are presented.