Geochemistry,zircon UPb ages and Hf isotopes of granites and pegmatites from Gubrunde region in the Eastern Nigeria Terrane: Insight into magmatism and tectonic evolution of the late Pan-African orogeny

This study reports a new dataset of whole-rock geochemistry, biotite chemistry, in situ zircon UPb geochronology and Hf isotope for a suite of granite and associated pegmatite samples from the Gubrunde region in the Eastern Nigeria Terrane (ENT), Nigeria. The Gubrunde granitic rocks are weakly ferroan, peraluminous and calc-alkalic to alkali-calcic in composition, and show I-type affinity. The zircon UPb geochronology gives an age of ~580 Ma for the rocks, although the presence of inherited zircons with early Pan-African ages of 696 ± 12, 647 ± 7 and 624–613 Ma are evident indicative of a complex history of their source rocks. The Gubrunde granite and the pegmatite yielded similar average Hf crustal model age T_DM2 of 1.9 ± 0.1 Ga and εHf(t) values ?6.2 ± 1.2, suggesting that they may have sourced from reworked old crustal rocks with minor contributions from the mantle. The granite and the pegmatite were likely to connect by fractional crystallization under low to moderate pressure (~2.2 to 3.0 kbar) and temperature (~717 °C), and low oxygen fugacity (<ΔNNO ?1.14). The ca. 580 Ma magmatism may have been triggered by delamination of the lithospheric mantle as a consequence of crustal thinning during waning stage of the Pan-African orogeny.     

Human genome behaviour: a powerful mechanism for optimizing the use of space technology in surveying networks design

An approach based on the behaviour of human genome is developed to efficiently provide a general framework for optimizing the use of space technology in surveying networks design. The developed approach attempts to apply the successful self-organizing principles based upon the biological evolution to artificial intelligence. It mimics the phenomena of natural selection observed in nature to achieve its goals by continuously adopting a population of candidate solutions and improving its performance over successive generations. The goal of adaptation is to find the best solution that optimizes the design of a surveying network based on the use of satellite observations. This network can be defined as a set of stations, co-ordinated by a series of sessions formed by placing receivers on the stations. The problem is to search for the best order for observing these sessions to give the best observation schedule at minimum cost. The obtained results prove the effectiveness of the developed technique in term of solution quality and computational efforts. The Corresponding Author in formed me that his address is likely to change soon. Please contact me, leick@spatial.maine.edu for the latest on this change.     

Conventional terrestrial system by VLBI a kinematic approach

The paper examines the potential ofVLBI time delay observables for the establishment and maintenance of a Conventional Terrestrial System (CTS). TheCTS is defined in2-D by the standard epoch positions and velocities of a network of control points located on a spherical reference surface. VLBI time delay observables are sensitive to the rotational motion of theCTS control points with respect to a Conventional Inertial System (CIS) which is represented by a network of radio sources. The motion of a control point with respect to theCIS is partitioned into global and regional components. The global components represent the rotational motion of the sphere with respect to theCIS, while the regional components represent the motion of theCTS points with respect to the sphere.     

The effect of carbonaceous fines on the cyclic resistance of poorly graded sands

The potential damage to man-made structures associated with earthquake-induced liquefaction has been demonstrated in catastrophic fashion over the past 40–50 years. The phenomenon of liquefaction of relatively clean, poorly graded, sands is well understood. However, the same cannot be said for cases when fine-grained materials are present within the sand matrix. A resolution of what appears in some reported studies as conflicting observations related to the effect of fines on cyclic resistance is of concern, particularly for land reclamation projects and sea fills where the material source is variable and may contain significant levels of fines. The nature of the fines themselves may have a measurable effect on the matrix behavior. The work presented herein explores the effect of silt and clay-size carbonaceous fines on the liquefaction susceptibility of sand. The choice of fines was guided by the conditions associated with the Lebanon coastal reclamation projects, where limestone/marlstone quarry source materials are dominant. The results obtained confirm the significant effect of fines on the cyclic resistance. They also confirm the existence of a limit fines content and a plasticity index threshold and establish their effect on observed behavior.     

Bacterial community and some physico-chemical characteristics in a subtropical mangrove environment in Bahrain

A study of bacterial communities and some physico-chemical parameters of a subtropical mangrove habitat in the Arabian Gulf (Bahrain) was carried out in 1993-1994. Six stations at different parts of the tidal channel were selected for sampling. The mangrove habitat was found to harbor diverse bacterial communities, included among them anoxygenic phototrophs (AP), oxygenic phototrophs (OP), organotrophs (OT), total coliforms (TC), faecal coliforms (FC) and haloalkaliphiles (HA). Spatial and temporal variations in bacterial communities and environmental parameters were found. Each of the OT, AP, TC, and FC were dominant in the innermost stations (S1&S2) and gradually decreased seaward. The HA community on the other hand, was dominant at the seaward stations (S5&S6) and was most likely to have originated from the sea through the tidal flows. Both AP and OT were considered as part of the mangrove native flora, whereas TC and FC were alien and believed to have been introduced through partially treated sewage released at the upstream of the tidal channel. Closely monitoring of the mangrove water revealed succession pattern in bacterial communities. The AP community was predominant from November 1993 to March 1994, succeeded by dominance of OP from June 1994 to October 1994. Both bacterial blooms gave water a pinkish, purple, or green color, respectively. Although OT prevailed during Transitional period between AP and OP eutrophication, it remained comparatively constant (not less than 2 x 10(5)cfu/ml) through other periods. Frequent eutrophication phenomena of OP, which took place in summer and autumn, coincided with increases in water temperature, chlorophyll a, and nutrients (NO(3)(-) and PO(4)(-)). On the other hand, OT and AP were negatively correlated with temperature, salinity and chlorophyll a, but no specific pattern was observed in relation to NO(3)(-) and PO(4)(-). In comparison with seawater, nutrients such as NO(3)(-) and PO(4)(-) were consistently higher in the mangrove habitat. Partially treated sewage and farm drainage canals are proposed to form additional sources of nutrients. Although, the mangrove habitat has been demonstrated to possess self-cleaning properties, data obtained suggest that anthropogenic pollution has a deleterious effect.     

Robust estimation based on energy minimization principles

 It is argued that the tendency of nature to minimize energy may be used as a unifying basis for all robust estimators. Robustness is defined and discussed based on mechanical rather than empirical and abstract tools. This mechanical view of robustness is then extended to design new and useful robust data editors that suppress the outlying content of the contaminated observations. These editors are applied to edit samples of sea-surface heights, gravity observations and reduced global positioning system baselines. Received: 12 July 1997 / Accepted: 8 June 1999     

Epi- and endobiont faunal communities on an Egyptian Mediterranean rocky shore: species composition and their competition for space

The exposed calcareous rocky area of the Abu Qir Headland,east of Alexandria,Egypt which range from coarse grains,through pebbles,cobbles,and boulders to rocky platforms,was significantly colonized by sclerobionts(epibionts and endobionts).The epibiont species diversity was comparatively higher than that of endobionts.Epibiont communities included bryozoans(the anascan-grade cheilostome Bifiustra savartii),serpulid(Hydroides elegans,Spirobranchus cf.tetraceros,Vermiliopsis striaticeps and Protula or Apomatus) and spirorbid(Spirorbis) wormtubes,and balanoid barnacles(Amphibalanus amphitrite,Balanus trigonus,and Perforatus perforatus).The cheilostome bryozoan colonies,which developed extensive sheets,proliferated on the study rocky shore either encrusting the bioeroded basement directly,or encrusting other epilithic taxa,particularly balanoid barnacles and serpulid worms.Encrusters displayed a remarkable marginal competitive interaction(overgrowth and stand-off) for space on the study rocky shore.On the other hand,endobionts were not well represented on the studied rocky shore exposure.It was possible to identify three ichnotaxa:Gastrochaenolites,Maeandropolydora,and Finichnus.The findings documented represent a significant contribution to our knowledge of sclerobionts composition,sequence of their colonization and/or bioero sion,and their mutual relationships on the intertidal rocky shore of the Abu Qir Headland.     

Applications of cumulative absolute velocity to urban earthquake early warning systems

An early warning system forewarns an urban area of the forthcoming strong shaking, normally with a few seconds to a few tens of seconds of early warning time before the arrival of the destructive S-wave part of the strong ground motion. For urban and industrial areas susceptible to earthquake damage, where the fault rupture system is complex and the fault-site distances are short, there is usually insufficient time to compute the hypocenter, focal parameters and the magnitude of an earthquake. Therefore, simpler and robust early warning algorithm is needed. The direct (engineering) early warning systems are based on algorithms of the exceedance of specified threshold time domain amplitude levels. The continuous stations’ data are processed to compute specific engineering parameters robustly and compared with specified threshold levels. The parameters can be chosen as band-pass filtered peak ground accelerations and/or the bracketed cumulative absolute velocity (BCAV). In this paper, an enhancement to bracket cumulative absolute velocity for the application of online urban early warning systems results in a new parameter called window based bracketed cumulative absolute velocity (BCAV-W). The BCAV-W allows computation of cumulative absolute velocity in a specified window size and to include the vertical component of the motion. The importance of choosing optimum window size for the cumulative absolute velocity BCAV-W is discussed and the correlations between BCAV-W and the macro-seismic intensity are studied for three combinations of horizontal and vertical components of the motion. Empirical relationship is developed to estimate BCAV-W as a function of magnitude, distance, fault mechanism, and site category based on 1,208 recorded ground motion data from 75 earthquakes in active plate-margins.