Actively rising surficial gneiss domes in Papua New Guinea

Surficial gneiss domes are previously undescribed landforms two to three thousand metres high and tens of kilometres across, consisting of gneiss; they have the form of a dissected dome. On geomorphic grounds it is unlikely that the domes could be formed by differential erosion, so it is proposed that they emerged at the ground surface by shouldering the bounding rocks aside. Foliation in the gneiss is parallel to the dome surface, and therefore concentric in plan. Any small part of the dome surface looks like a fault scarp, but the ‘fault’ can be traced around the entire dome on Goodenough Island and around considerable arcs on other domes in southeast Papua New Guinea. We postulate that each dome originated by the pushing of a granite pluton and the foliation was created during the rise, whereas Davies (1978) has proposed that the domes are re‐folded thrust faults (which had earlier created the foliation) and that the granodiorite intrusions are later events only accidentally associated with the domes. In Davies’ hypothesis the topographic domes are created by differential erosion exposing orginally sub‐surface features, and some of the dome boundaries are fault‐line scarps. We consider that the topographic domes actually emerged at the ground surface, like a horst, and they are bounded by fault scarps. A review of the structural setting suggests that the domes may have been originally aligned as culminations on top of an elongated batholith rising beneath an axis of uplift along the Owen Stanley‐D'Entrecasteaux line. The domes are formed in an area of thick crust in a tensional environment.     

Natural realgar and amorphous AsS oxidation kinetics

The oxidation rates of natural realgar and amorphous synthetic AsS by dissolved oxygen were evaluated using mixed flow reactors at pH 7.2 to 8.8 and dissolved oxygen contents of 5.9 to 16.5 ppm over a temperature range of 25 to 40°C. The ratios of As/S are stoichiometric for all amorphous AsS oxidation experiments except for two experiments conducted at pH ∼8.8. In these experiments, stoichiometric ratios of As/S were only observed in the early stages of AsS (am) oxidation whereas lower As/S ratios were observed during steady state. For realgar oxidation experiments, the As/S ratio is less than the stoichiometric ratio of realgar, ranging between 0.61 and 0.71. This nonstoichiometric release of As and S to solution indicates that realgar oxidation is more selective for S after the rates of oxidation become constant. All measured oxidation rates at 25°C can be described within experimental uncertainties as follows: Table 1

Rate Expression	Activation Energy (kJ/mol)
R(Realgar/As) = 10−9.63(±0.41)[DO]0.51(±0.08)[H+]−0.28(±0.05)	64.2 ± 9.8
R(Realgar/S) = 10−9.74(±0.35)[DO]0.54(±0.05)[H+]−0.31(±0.04)	62.2 ± 9.0
R(AsS(am)) = 10−13.65(±0.82)[DO]0.92(±0.08)[H+]−1.09(±0.10)	124 ± 18.8

Full-size table

     

Thermal impact of waste emplacement and surface cooling associated with geologic disposal of high-level nuclear waste

This article is a study of the thermal effects associated with the emplacement of aged radioactive high-level wastes in a geologic repository, with emphasis on the following subjects: waste characteristics, repository structure, and rock properties controlling the thermally induced effects; thermal, thermomechanical, and thermohydrologic impacts, determined mainly on the basis of previous studies that assume 10-yr-old wastes; thermal criteria used to determine the repository waste loading densities; and technical advantages and disadvantages of surface cooling of the wastes prior to disposal as a means of mitigating the thermal impacts. Waste loading densities determined by repository designs for 10-yr-old wastes are extended to older wastes using the near-field thermomechanical criteria based on room stability considerations. Also discussed are the effects of long surface cooling periods determined on the basis of far-field thermomechanical and thermohydrologic considerations. Extension of the surface cooling period from 10 yr to longer periods can lower the near-field thermal impact but have only modest long-term effects for spent fuel. More significant long-term effects can be achieved by surface cooling of reprocessed high-level waste.     

The role of shoshonitic and calc-alkaline suites in the tectonic evolution of the Carajás District, Brazil

In the Carajás District, the Bahia Prospect and Grão Pará volcanosedimentary sequences, both of Archean age, have been the object of extensive petrochemical studies for major, trace, and rare earth elements. In spite of the widespread spilitization that affected the volcanic mafic rocks, the petrochemical nature of the mafic volcanism may still be assessed on the basis of the less mobile elements like P, Cr, Zr, Nb, Ti, and REE. The Bahia Prospect basalts have a petrochemical affinity with Phanerozoic island-arc calc-alkaline basalts. The Grão Pará basalts and basaltic andesites, on the other hand, have a petrochemical affinity with Phanerozoic basalts of a mature island arc environment. The petrochemical data presented here lead to a new geotectonic interpretation of the area, where the volcanic sequences are genetically linked to Archean subduction processes.     

A structural synthesis of the Proterozoic Arabian-Nubian Shield in Egypt

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 – 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime.     

Archaeoseismic record at the ancient Roman City of Baelo Claudia (Cádiz, south Spain)

This study represents the first paleoseismic approach in Spain in which archaeological remains are considered. The ancient Roman city of Baelo Claudia (1st–4th centuries AD), located at the axial zone of the Gibraltar Strait (Cadiz, south Spain), contains abundant disrupted architectural relics and ground collapses (i.e. landsliding, liquefacion) probably related to historic earthquake damage of intensity IX–X MSK. The archaeological stratigraphy of the city evidence two major episodes of abrupt city destruction bracketed in AD 40–60 and AD 350–395 separated by an intervening horizon of demolition for city rebuilding, otherwise characteristic for many earthquake-damaged archaeological sites in the Mediterranean. The second episode led the eventual city abandonment, and it is evidenced by good examples of column collapse, distortion, failure and breakdown of house and city walls, and pavement warping and disruptions documented during different archaeological excavations, which can be catalogued as secondary coseismic effects. Main damaged relicts observable today are the set of pop-up like arrays and warping developed in the ancient Roman pavement. Their analysis indicate an anomalous westwards ground displacement oblique to the main gentle southward slope of the topography, as also evidence failures, collapses and breakdown of walls and columns, suggesting that stress acted in a broad SW–NE/WSW–ENE orientation consistent whit the expectable motion along the largest NE–SW strike-slip faults of the zone, which in turn can be catalogued as seismic sources of moderate events (ca. 5 mb). Major disruptions and city abandonment were hesitantly related to relatively far strong earthquakes occurred during the late 4th century AD in the Mediterranean or western coast of Iberia by Menanteau et al. [Menanteau, L., Vanney, J.R., Zazo, C., 1983. Belo II : Belo et son environment (Detroit de Gibraltar), Etude physique d'un site antique. Pub. Casa de Velazquez, Serie Archeologie 4., Ed. Broccard, París.]. However, this study indicates that the occurrence of close moderate earthquakes jointly with the unstable character of the ground at the zone (site effect) is a more reliable hypothesis to explain the observed deformations.     

Clay mineralogy as a tool for integrated sequence stratigraphic and palaeogeographic reconstructions: Late Oligocene–Early Aquitanian western internal South Iberian Margin,Spain

The different hydrodynamic behaviour of detrital clay minerals in the marine depositional environment allows assessment of relative sea‐level variations in the sedimentary record. Comparison of smectite and kaolinite:illite (S+K:I) changes with the global sea‐level curves and with the third‐order cycles of the eustatic curve for European basins allows assessment of the influence of global eustasy and local tectonics on sequence stratigraphy. In the South Iberian Margin, sedimentation took place both on open‐marine platforms and in deeper water areas. On this margin during the Late Oligocene to Early Aquitanian, the variations in sedimentation were caused not only by global eustasy but also by compressive tectonics. Correlations were made between the S+K:I cycles and the third‐order cycles for European basins, enabling the definition of four third‐order sedimentary sequences (here called C1, C2, C3, and A1) and two lower‐order sequences within C3 and A1 (here called C3a, C3b, A1a, and A1b) related to tectonic movements. High S+K:I values were observed during episodes of maximum flooding in each sequence and lower‐order sequence and in each succession, enabling changes in palaeocoastal morphology to be considered. Copyright © 2012 John Wiley & Sons, Ltd.     

Formation of Carbon and Hydrogen Species in Magmas at Low Oxygen Fugacity

Studies of iron-bearing silicate melt (ferrobasalt) + iron metallicphase + graphite + hydrogen equilibria show that carbon andhydrogen solubilities in melts are important for the evolutionof the upper mantle. In a series of experiments conducted at3·7 GPa and 1520–1600°C, we have characterizedthe nature (oxidized vs reduced) and quantified the abundancesof C- and H-compounds dissolved in iron-bearing silicate melts.Experiments were carried out in an anvil-with-hole apparatuspermitting the achievement of equal chemical potentials of H₂in the inner Pt capsule and outer furnace assembly. The fO₂for silicate melt–iron equilibrium was 2·32 ±0·04 log units below iron–wüstite (IW). Theferrobasalt used as starting material experienced a reductionof its iron oxides and silicate network. The counterpart wasa liberation of oxygen reacting with the hydrogen entering thecapsule. The amount of H₂O dissolved in the glasses was measuredby ion microprobe and by step-heating and was found to be between1 and 2 wt %. The dissolved carbon content was found to be 1600ppm C by step-heating. The speciation of C and H componentswas determined by IR and Raman spectroscopy. It was establishedthat the main part of the liberated oxygen was used to formOH^– and to a much lesser extent H₂O, and only traces ofH₂, CO₂ and     

The palaeoenvironmental and palaeohydrological evolution of Padul Peat Bog (Granada, Spain) over one million years, from elemental, isotopic and molecular organic geochemical proxies

The elemental (concentration of organic carbon, atomic H/C and C/N ratios), isotopic (δ¹³C values of organic matter) and molecular (predominant n-alkane chain length and carbon preference index (CPI)) organic components were measured for 600 samples taken from a 107-m long core from the Padul Basin (Andalusia, Spain). The record runs from the Lower Pleistocene (ca. 1 Ma B.P.) to the mid-Holocene (ca. 4.5 ka B.P.) with, in general, little diagenesis (removal of components). Two markedly different hydrogeological scenarios were interpreted: (1) From ca. 1 Ma to ca. 400 ka B.P. run-off recharge was significant and water depths were greater (lacustrine scenario). From ca. 400 to 4.5 ka B.P., the Padul Basin became a peat bog s.s. with the major water input coming from groundwater inflow. From ca. 400 to ca. 180 ka B.P. alternating episodes with either predominant grasses, trees or aquatic macrophytes which were linked to wet/dry phases, took place. An important deglaciation episode has been interpreted to occur between ca. 180 and 170 ka B.P. The global climatic changes occurring from ca. 170 to 25 ka B.P. were not recorded in the proxies, though they do show important variations linked to the Last Glacial Maximum and the beginning of the Holocene (ca. 25–10 ka B.P.): (2) Cold phases coexisting with dry periods produced the recession of forests and the development of grasses. After these periods, as both temperature and precipitation increased, forests expanded and the water level, linked to thaw, rose, especially at ca. 20 ka B.P. Few changes occurred during the Holocene, although there were short alternations between wet and dry episodes. Overall, the techniques applied proved to be excellent palaeoenvironmental proxies for studying the basin’s palaeoclimatological and palaeohydrological evolution.