Autochthonous inheritance of zircon through Cretaceous partial melting of Carboniferous plutons: the Arthur River Complex,Fiordland, New Zealand

TIMS and SHRIMP U–Pb analyses of zircons from Milford Orthogneiss metadiorite (P = 1–1.4 GPa; T ≥ 750°C) of the Arthur River Complex of northern Fiordland reveal a bimodal age pattern. Zircons are predominantly either Paleozoic (357.0 ± 4.2 Ma) and prismatic with oscillatory zoning, or Cretaceous (133.9 ± 1.8 Ma) and ovoid with sector or patchy zoning. The younger age component is not observed overgrowing older grains. Most grains of both ages are overgrown by younger Cretaceous (~120 Ma) metamorphic zircon with very low U and Th/U (0.01). We interpret the bimodal ages as indicating initial igneous emplacement and crystallisation of a dioritic protolith pluton at ~357 Ma, followed by Early Cretaceous granulite-facies metamorphism at ~134 Ma, during which a significant fraction (~60%) of the zircon grains dissolved, and subsequently reprecipitated, effectively in situ, in partial melt pockets. The remaining ~40% of original Paleozoic grains were apparently not in contact with the partial melt, remained intact, and show only slight degrees of Pb loss. Sector zoning of the Cretaceous grains discounts their origin by solid state recrystallisation of Paleozoic grains. The alternative explanation—that the Paleozoic component represents a 40% inherited component in an Early Cretaceous transgressive dioritic magma—is considered less likely given the relatively high solubility of zircon in magma of this composition, the absence of 134 Ma overgrowths, the single discrete age of the older component, equivalent time-integrated ¹⁷⁷Hf/¹⁷⁶Hf compositions of both age groups, and the absence of the Cambrian-Proterozoic detrital zircon that dominates regional Cambro-Ordovician metasedimentary populations. Similar bimodal Carboniferous-Early Cretaceous age distributions are characteristic of the wider Arthur River Complex; 8 of 12 previously dated dioritic samples have a Paleozoic component averaging 51%. Furthermore, the age and chemical suite affinity of these and several more felsic rocks can be matched with those of the relatively unmetamorphosed Carboniferous plutonic terrane along the strike of the Mesozoic margin in southern Fiordland, also supporting the in situ derivation of the Carboniferous “inherited” component.     

Seasonal Dynamics of Microbial Processes in Bottom Sediments of the Sevastopol Coastal Area

Oceanology - A seasonal study of microbial methane oxidation (MO) and sulfate reduction (SR) processes in bottom sediments was carried out at five stations in the estuarian Sevastopol coastal area,...     

The distribution of total and electrochemically available copper in the northwestern atlantic ocean

Copper in a series of samples from the northwestern Atlantic has been determined by anodic stripping voltammetry (ASV) and atomic absorption spectrometry after preconcentration by cobalt—APDC coprecipitation. Samples from a transect across the continental shelf directly off the New York Bight showed a linear relationship between total copper and salinity (31–34‰) and less than 5% of the total copper was detectable by ASV. A slope water station showed less than 9% of the total copper to be ASV detectable in the upper 780m, below which the ASV detectable copper increased to 70% at 3000 m. The Sargasso Sea profiles showed less than 7% ASV detectable copper in the upper 150 m; the fraction of the total copper detected by ASV increased to about 80% of the total copper at greater depths. The reduced availability of copper to the ASV measurement in coastal waters and open ocean surface waters appears to be related to recent contact with waters where biological productivity occurs.     

Near-vertical seismic reflection image using a novel acquisition technique across the Vrancea Zone and Foscani Basin, south-eastern Carpathians (Romania)

The DACIA PLAN (Danube and Carpathian Integrated Action on Process in the Lithosphere and Neotectonics) deep seismic sounding survey was performed in August–September 2001 in south-eastern Romania, at the same time as the regional deep refraction seismic survey VRANCEA 2001. The main goal of the experiment was to obtain new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basins developed within and adjacent to the seismically-active Vrancea zone, including the Focsani Basin. The seismic reflection line had a WNW–ESE orientation, running from internal East Carpathians units, across the mountainous south-eastern Carpathians, and the foreland Focsani Basin towards the Danube Delta. There were 131 shot points along the profile, with about 1 km spacing, and data were recorded with stand-alone RefTek-125s (also known as “Texans”), supplied by the University Texas at El Paso and the PASSCAL Institute. The entire line was recorded in three deployments, using about 340 receivers in the first deployment and 640 receivers in each of the other two deployments. The resulting deep seismic reflection stacks, processed to 20 s along the entire profile and to 10 s in the eastern Focsani Basin, are presented here. The regional architecture of the latter, interpreted in the context of abundant independent constraint from exploration seismic and subsurface data, is well imaged. Image quality within and beneath the thrust belt is of much poorer quality. Nevertheless, there is good evidence to suggest that a thick (10 km) sedimentary basin having the structure of a graben and of indeterminate age underlies the westernmost part of the Focsani Basin, in the depth range 10–25 km. Most of the crustal depth seismicity observed in the Vrancea zone (as opposed to the more intense upper mantle seismicity) appears to be associated with this sedimentary basin. The sedimentary successions within this basin and other horizons visible further to the west, beneath the Carpathian nappes, suggest that the geometry of the Neogene and recent uplift observed in the Vrancea zone, likely coupled with contemporaneous rapid subsidence in the foreland, is detached from deeper levels of the crust at about 10 km depth. The Moho lies at a depth of about 40 km along the profile, its poor expression in the reflection stack being strengthened by independent estimates from the refraction data. Given the apparent thickness of the (meta)sedimentary supracrustal units, the crystalline crust beneath this area is quite thin (< 20 km) supporting the hypothesis that there may have been delamination of (lower) continental crust in this area involved in the evolution of the seismic Vrancea zone.     

大山片麻岩地质特征及侵位机制研究

大山片麻岩的原财为奥长化岗石,呈不规则状侵入柳树河子片麻岩中,年龄２７亿年左右,太古代阜平运动晚期侵位的。侵位与当时区域上大规模的韧性剪切作用密切相关。由于剪切带各相关位置的位移量的差异,形成空间,给岩浆被动就位了有利场所,形成大山片麻岩古深成岩体。     

SEM Observation of the Wing Membrane of Beipiaopterus chenianus (Pterosauria)

The cross-section and surface structures of wing membranes from the ctenochasmatid pterosaur Beipiaopterus chenianus were observed through a scanning electron microscope （SEM）. The results show that the wing membrane contains a high density of blood vessels, implying strong thermoregulatory function, similar to that of a bat wing membrane. This is the first comparison of the microstmctures of pterosaur wing membranes with those of the modem bat. It is inferred that a bat-like physiology exists, at least in relatively small pterosaurs suggesting that these pterosaurs were warm-blooded, active fliers.     

Quantitative assessment of gas washing of oils in the Tazhong area of the Tarim Basin,Northwest China

Gas washing has been known in the Tazhong area of the Tarim Basin, but its quantitative assessment has not yet been reported. Here the influence of gas washing fractionation in the area was discussed based on the gas chromatogram data of 68 oils and the results of the mixing experiments of a black oil and a condensate. The results show that the intensity of gas washing fractionation decreased generally from northern to southern part and vertically from deep reservoirs to shallow reservoirs. The gas washing fractionation was mainly controlled by fault systems in this area, with the increase of n-alkane mass depletion positively correlated to the number and scale of faults. Gas washing fractionation appears to have affected the hydrocarbon property, and as a result the diversity of the crude oils is markedly controlled by gas washing. In addition, the occurrence of waxy oil in this area may be resulted from multiple factors including gas washing, mixed filling and migration fractionation. Supported by National Basic Research Program of China (Grant No. 2006CB202303) and the National Natural Science Foundation of China (Grant No. 40672091)     

Algal Dynamics in Relation to Physico-Chemical Factors in a High Altitude Pond of Shillong,India

A one year phycological study of a high altitude pond has been made with a view to studying the algal dynamics as affected by physico-chemical characteristics of the water. This has revealed the presence of 34 genera of algae belonging to Chlorophyta, Bacillariophyta, Cyanophyta, and Euglenophyta. Chlorophytes were the most dominant and diatoms the most frequent representatives of algae. The community diversity along with water chemistry are indicative of the oligotrophic nature of this pond.     

Age and significance of voluminous mafic–ultramafic magmatic events in the Murchison Domain,Yilgarn Craton

Mafic–ultramafic rocks in structurally dismembered layered intrusions comprise approximately 40% by volume of greenstones in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton. Mafic–ultramafic rocks in the Murchison Domain may be divided into five components: (i) the ～2810 Ma Meeline Suite, which includes the large Windimurra Igneous Complex; (ii) the 2800 ± 6 Ma Boodanoo Suite, which includes the Narndee Igneous Complex; (iii) the 2792 ± 5 Ma Little Gap Suite; (iv) the ～2750 Ma Gnanagooragoo Igneous Complex; and (v) the 2735–2710 Ma Yalgowra Suite of layered gabbroic sills. The intrusions are typically layered, tabular bodies of gabbroic rock with ultramafic basal units which, in places, are more than 6 km thick and up to 2500 km² in areal extent. However, these are minimum dimensions as the intrusions have been dismembered by younger deformation. In the Windimurra and Narndee Igneous Complexes, discordant features and geochemical fractionation trends indicate multiple pulses of magma. These pulses produced several megacyclic units, each ～200 m thick. The suites are anhydrous except for the Boodanoo Suite, which contains a large volume of hornblende gabbro. They also host significant vanadium mineralisation, and at least minor Ni–Cu–PGE mineralisation. Collectively, the areal distribution, thickness and volume of mafic–ultramafic magma in these complexes is similar to that in the 2.06 Ga Bushveld Igneous Complex, and represents a major addition of mantle-derived magma to Murchison Domain crust over a 100 Ma period. All suites are demonstrably contemporaneous with packages of high-Mg tholeiitic lavas and/or felsic volcanic rocks in greenstone belts. The distribution, ages and compositions of the earlier mafic–ultramafic rocks are most consistent with genesis in a mantle plume setting.