Preliminary considerations on the potential influence of submarine fans on marine delimitation

The complex issues associated with marine delineation for the outer limit of continental shelf and the boundary delimitation have provoked considerable attention among researchers in a variety of academic circles, particularly in the juristic filed and the geo-science field. In the present contribution, we start from an overview of submarine fans, as one of common types of sediment-deposit bodies in the ocean, and ex- plore the related geological features which may be of relevance to the marine delimitation in accordance with the 1982 United Nations Convention on the Law of the Sea. We carry out a comparative assessment of certain significant geological features of submarine fans, using the Bengal fan as an example, which is the biggest submarine fan in the world and represents an important factor in the maritime boundary dispute between the neighboring states currently. The relationship between the special geological bodies and the international principle in the 1982 United Nations Convention can be established by combining geological and juristic analyses. This preliminary observation on the effect of submarine bodies both on the marine entitlement and boundary delimitation indicates that it is important for the international society to appro- priately deal with this problem so that the marine right of any state can be protected.     

Re-evaluating Nd/Nd in lunar mare basalts with implications for the early evolution and bulk Sm/Nd of the Moon

The Moon likely accreted from melt and vapor ejected during a cataclysmic collision between Proto-Earth and a Mars-sized impactor very early in solar system history. The identical W, O, K, and Cr isotope compositions between materials from the Earth and Moon require that the material from the two bodies were well-homogenized during the collision process. As such, the ancient isotopic signatures preserved in lunar samples provide constraints on the bulk composition of the Earth. Two recent studies to obtain high-precision ¹⁴²Nd/¹⁴⁴Nd ratios of lunar mare basalts yielded contrasting results. In one study, after correction of neutron fluence effects imparted to the Nd isotope compositions of the samples, the coupled ¹⁴²Nd-¹⁴³Nd systematics were interpreted to be consistent with a bulk Moon having a chondritic Sm/Nd ratio [Rankenburg K., Brandon A. D. and Neal C. R. (2006) Neodymium isotope evidence for a chondritic composition of the Moon. Science312, 1369-1372]. The other study found that their data on the same and similar lunar mare basalts were consistent with a bulk Moon having a superchondritic Sm/Nd ratio [Boyet M. and Carlson R. W. (2007) A highly depleted Moon or a non-magma origin for the lunar crust? Earth Planet. Sci. Lett.262, 505-516]. Delineating between these two potential scenarios has key ramifications for a comprehensive understanding of the formation and early evolution of the Moon and for constraining the types of materials available for accretion into large terrestrial planets such as Earth.To further examine this issue, the same six lunar mare basalt samples measured in Rankenburg et al. [Rankenburg K., Brandon A. D. and Neal C. R. (2006) Neodymium isotope evidence for a chondritic composition of the Moon. Science312, 1369-1372] were re-measured for high-precision Nd isotopes using a multidynamic routine with reproducible internal and external precisions to better than ±3 ppm (2σ) for ¹⁴²Nd/¹⁴⁴Nd ratios. The measurements were repeated in a distinct second analytical campaign to further test their reproducibility. Evaluation of accuracy and neutron fluence corrections indicates that the multidynamic Nd isotope measurements in this study and the 3 in Boyet and Carlson [Boyet M. and Carlson R. W. (2007) A highly depleted Moon or a non-magma origin for the lunar crust? Earth Planet. Sci. Lett.262, 505-516] are reproducible, while static measurements in the previous two studies show analytical artifacts and cannot be used at the resolution of 10 ppm to determine a bulk Moon with either chondritic or superchondritic Sm/Nd ratios. The multidynamic data are best explained by a bulk Moon with a superchondritic Sm/Nd ratio that is similar to the present-day average for depleted MORB. Hafnium isotope data were collected on the same aliquots measured for their ¹⁴²Nd/¹⁴⁴Nd isotope ratios in order to assess if the correlation line for ¹⁴²Nd-¹⁴³Nd systematics reflect mixing processes or times at which lunar mantle sources formed. Based on the combined ¹⁴²Nd-¹⁴³Nd-¹⁷⁶Hf obtained we conclude that the ¹⁴²Nd-¹⁴³Nd correlation line measured in this study is best interpreted as an isochron with an age of 229⁺²⁴₋₂₀Ma after the onset of nebular condensation. The uncertainties in the data permit the sources of these samples to have formed over a 44 Ma time interval. These new results for lunar mare basalts are thus consistent with a later Sm-Nd isotope closure time of their source regions than some recent studies have postulated, and a superchondritic bulk Sm/Nd ratio of the Moon and Earth. The superchondritic Sm/Nd signature was inherited from the materials that accreted to make up the Earth-Moon system. Although collisional erosion of crust from planetesimals is favored here to remove subchondritic Sm/Nd portions and drive the bulk of these bodies to superchondritic in composition, removal of explosive basalt material via gravitational escape from such bodies, or chondrule sorting in the inner solar system, may also explain the compositional features that deviate from average chondrites that make up the Earth-Moon system. This inferred superchondritic nature for the Earth similar to the modern convecting mantle means that there is no reason to invoke a missing, subchondritic reservoir to mass balance the Earth back to chondritic for Sm/Nd ratios. However, to account for the subchondritic Sm/Nd ratios of continental crust, a second superchondritic Sm/Nd mantle reservoir is required.     

Variation in si4+-content of phengites through a three stage deformation sequence

Three important phases of deformation (D₁-D₃) affect the Precambrian metamorphic rocks of the Strathgordon region, S.W. Tasmania. Textural analysis has related phengite development to the deformation events in quartz + phengite phyllites. Phengite chemistry suggests a prograde metamorphic history at about 4 kb from 400°C at D₁ to 450°C at D₂. The significant feature of this work is that a sharp break in conditions, shown by a marked change in the composition of the phengites, occurs from D₂ to D₃, the latter taking place at about 250°C and at a pressure <4 kb. A pronounced hiatus in the deformation history is indicated for the D₂/D₃ interval. During D₃ water was introduced.     

An Operational Application of Automatic Feature Extraction: The Measurement of Cracks in Concrete Structures

An understanding of the evolution of cracks in concrete structures due to long term natural deformation is important to civil engineers, but quantitative measurements can be difficult to make. However, digital imaging offers a potential solution. This short paper illustrates the operational application of automated image processing techniques for accurate, multi-temporal crack measurements. The first part of this paper provides an overview of automatic feature extraction, essential for automatic crack detection. The latter part describes the methods developed for detecting and measuring cracks. Due to the long term nature of the application, operational results have yet to be finalised, although sample results are presented     

Controls on supergene enrichment of porphyry copper deposits in the Central Andes: A review and discussion

The Central Andes host some of the world’s largest porphyry copper deposits. The economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket. Published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 Ma due to an increase in aridity. Here we discuss these models using published geochronological, geomorphological and geological data. Geochronological data indicate that supergene oxidation and enrichment has been active between 17 and 27°S across the forearc of northern Chile and southern Peru from 44 to 6 Ma, and on the Bolivian Altiplano and Eastern Cordillera of Argentina from 11 Ma to present. There is evidence for cessation at 20, 14 and 6 Ma. However, a major problem is that as more geochronological data become available the age ranges and periods of enrichment increase. This suggests that the full spectrum of enrichment ages may not have been sampled. The relationship between supergene enrichment and the age of regional pediplain surface development is not well constrained. Only in two areas have surfaces related to enrichment been directly dated (southern Peru and south of 26°S in Chile) and suggest formation post 14 Ma. Sedimentological data indicate that a fluctuating arid/semi-arid climate prevailed across the Atacama Desert until between 4 and 3 Ma, climatic conditions that are thought to be favourable for supergene enrichment. The balance between uplift, erosion, burial and sufficient water supply to promote enrichment is complex. This suggests that a simple model for controlling supergene enrichment is unlikely to be widely applicable in northern Chile. General models that involve climatic desiccation at 14 Ma related to rainshadow development and/or the presence of an ancestral cold-upwelling Humboldt Current are not supported by the available geological evidence. The integration of disparate sedimentological, geomorphological and supergene age data will be required to fully understand the controls on and distribution of supergene oxidation and enrichment in the Central Andes.     

Accuracy assessment of QuickBird stereo imagery

The Geographical Survey Institute of Japan has recently carried out an evaluation of the metric performance of QuickBird stereo satellite imagery. This paper describes the accuracy assessment of the sensor orientation and geopositioning phases of the study, the aim of which was twofold. First, it was desired to confirm the metric potential of QuickBird imagery for 1:25 000 scale topographic mapping. Second, a determination was to be made of the accuracy attainable from the Basic image product. The techniques of rational functions and affine bundle adjustment were employed, the former with bias compensation. The results obtained both reassert the high precision of the rational functions approach and cast doubt upon the applicability of the 3D affine model for accurate geopositioning from QuickBird imagery.     

Visibility Analysis In Vision Metrology Network Design

The aim of this paper is to present a method whereby accuracy enhancement of an existing photogrammetric network is achieved through the automatic selection of additional camera stations. The determination of the positions of these 'accuracy fulfilment' camera stations is based upon what has been termed 'visibility uncertainty prediction modelling' of visibility constraints derived from the existing network geometry. Following a review of vision constraints in network design, the concepts of visibility uncertainty prediction and visibility uncertainty spheres are introduced. These provide a mechanism to predict the visibility of current object target points for the new accuracy fulfilment images. This in turn aids in network design improvement. The visibility uncertainty modelling is then illustrated for two close range photogrammetric network configurations, for which the test results demonstrate that the proposed model can reliably predict target visibility with an overall certainty of 75%.