Relict Structure Research Articles

Crystal structure determination of a new LaPO4 phase in a multicomponent glass ceramic via 3D electron diffraction

A glass ceramic from the MgO–Al 2 O 3 –SiO 2 system containing additives of ZrO 2 , TiO 2 , La 2 O 3 and P 2 O 5 was investigated. Via x-ray powder diffraction (XRPD) and Transmission electron microscopy(TEM) the crystalline phases present could be identified as MgAl 2 O 4 (Spinel), orthorhombic ZrTiO 4 and a polymorph of LaPO 4 with a previously unknown crystal structure. The crystal structure of this LaPO 4 phase was solved ab initio via 3D ED Data. The polymorph occurs in a distorted barite structure type in the same space group (P2 1 /n) as the stable monazite type polymorph, however the density is higher and the La has a higher coordination number. Furthermore the LaPO 4 is present in a spinodal relict microstructure. Potential explanations for the presence of this metastable polymorph are pressure due to residual stresses from the crystallization or surface effects due to the high surface area resulting from the spinodal relict structure.

ORPHAN BREAKWATERS: COLLAPSE AND TRANSMISSION REDUCTION

In the past, many coastal towns or villages constructed harbours for trade and/or fishing. These were protected by breakwaters, commonly rubble mounds to low-water, surmounted by vertical walls of dressed stone blocks (later concrete) with rubble core. Now, 100-150 years later, many such harbours have little or no income to maintain or repair their breakwaters, but meantime, the areas protected have been adopted for commercial and residential purposes, at increased risk of flooding if the 'orphan' breakwater were to collapse, Hampshire et al. (2013). Even after collapse, some wave reduction will however still be afforded by the relict structure. Tests by Allsop et al (2017) have modelled the collapse of several simplified breakwaters, and measured levels of wave transmission over the collapsed structures. This paper extends that work with more analysis of collapsed crest levels, and hence of likely wave transmission.

Mode of Slope Failure of Moderately to Completely Weathered Metasedimentary Rock at Bukit Panji, Chendering, Kuala Terengganu

Geology of Bukit Panji, Chendering, Kuala Teregganu consists of interbededmetasedimentary rocks (slate, phyllite and schists with minor quartzite) which haveexperience regional metamorphism. The age of this rock is Carboniferous. A development project which under construction in Bukit Panji, Kuala Terengganu hasenabled a landslide assessment to observe the modes of failure in moderately tocompletely weathered metasedimentary rock. Development on hillsides caused manyslope had to be cut to provide space for the infrastructure construction. From assessment analysis, a total of 21 cases of landslide failure occurred involving 17 cut slopes, and 4 cut-fill slopes. The most common type of failures is gully failures, with 9 cases represent 43% of all the observed slope failure. This was followed by 6 wedge failures, two planar and rock fall failures and one shallow sliding and toppling respectively. Cut slope failure involving moderate weathered rock mass (grade III) to the residual soil (grade VI). Relict structure was identified as the main factors controlling the failure, as well as water, natural slope-forming materials and the use of appropriate slope stabilization.

Structural evolution of the El Salvador Fault Zone: an evolving fault system within a volcanic arc.

The El Salvador Fault Zone, firstly identified after the 13th February 2001 Mw 6.6 El Salvador earthquake, is a 150 km long, 20 km wide right-lateral strike-slip fault system. Ruptures along the ESFZ are thought to be responsible for most of the historical destructive earthquakes along the El Salvador Volcanic Arc, as well as for most of the current seismicity of the area. In this work, we focus on the geological setting of the fault zone by describing its geomorphology and structure, using field-based observations, digital terrain modelling, and aerial photograph interpretation with the aim at contributing to the understanding of the ESFZ slip behaviour. In particular, we address the ESFZ structure, kinematics and evolution with time. The ESFZ is a complex set of traces divided in major rupture segments characterized by different geometry, kinematics and geomorphic expressions. Natural fault exposures and paleoseismic trenches excavated along the fault show that the strike-slip deformation is distributed in several planes. Both geometry and kinematics of the fault zone are consistent with a transtensional strain regime. The estimated geological slip rate for the main fault segments by paleoseismic trenches and displaced geomorphic features implies a deficit in velocity of the fault compared to the available GPS velocities data. The high vertical scarps of some fault segments would require Quaternary slip rates not coherent neither with measured GPS velocities nor with slip rates obtained from paleoseismic analysis. This mismatch suggests a pre-existing graben structure that would be inherited from the previous regional roll back related extensional stage. We consider that the ESFZ is using this relict structure to grow up along it. As a result, we ropose a model for ESFZ development consistent with all these observations.

Intense red photoluminescence from Mn^2+-doped (Na^+; Zn^2+) sulfophosphate glasses and glass ceramics as LED converters

We report on intense red fluorescence from Mn(2+)-doped sulfophosphate glasses and glass ceramics of the type ZnO-Na(2)O-SO(3)-P(2)O(5). As a hypothesis, controlled internal crystallization of as-melted glasses is achieved on the basis of thermally-induced bimodal separation of an SO(3)-rich phase. Crystal formation is then confined to the relict structure of phase separation. The whole synthesis procedure is performed in air at <or= 800 degrees C. Electron spin resonance and Raman spectroscopy indicate that Mn(2+) species are incorporated on Zn(2+) sites with increasingly ionic character for increasing concentration. Correspondingly, in the glasses, increasing MnO content results in decreasing network polymerization. Stable glasses and continuously increasing emission intensity are observed for relatively high dopant concentration of up to 3 mol.%. Recrystallization of the glass results in strongly increasing emission intensity. Dynamic emission spectroscopy reveals only on type of emission centers in the glassy material, whereas three different centers are observed in the glass ceramic. These are attributed to octahedrally coordinated Mn(2+) in the residual glass phase and in crystalline phosphate and sulfate lattices, respectively. Relatively low crystal field strength results in almost ideal red emission, peaking around 625 nm. Excitation bands lie in the blue-to-green spectral range and exhibit strong overlap. The optimum excitation range matches the emission properties of GaN- and InGaN-based light emitting devices.

The use of Brazilian Test as a Quantitative Measure of Rock Weathering

Weathering of igneous rocks under humid tropical conditions produces microstructural changes. These begin with discoloration, microfracturing and loosening of grain boundaries, continue with chemical alteration and leaching of constituent minerals, and end with the collapse of relict (skeletal) structure (Aydin and Duzgoren-Aydin, 2002). Microstructural weakening accompanying this process is expected to be dramatic, especially in terms of tensile strength during the early stages of weathering. The behavior of rocks in tension may therefore be an effective indicator of their microstructure, and hence state of weathering. This study explores the potential of diametral stress-strain behavior of igneous rocks in the Brazilian test to scale and predict their degree of weathering. It is shown that the distinct behavioral patterns exhibited by rocks and their initial response expressed by a tangent modulus (named as Brazilian deformation index) are sensitive enough to detect and interpret even minor variations brought about by weathering.

Microforaminiferal linings from the Early Devonian of eastern Australia, and their generic placement

Microforaminiferal linings assigned to 10 known genera have been recovered from Early Devonian (Lochkovian to Late Emsian) limestones from Victoria, New South Wales, and Queensland. These organic linings have been identified by comparison with normal-sized agglutinated foraminiferan genera known to occur in the associated sediments. Microforaminiferal linings with smooth walls and reticulate sculptured walls were present and the possible implications of these (diagenetic, relict structure, naked homeomorphs, or processing artifact) are discussed. Evidence is presented thatOrdovicinamay have a bilamellar organic wall lining.

Heave and slope failure in an excavation into residual soil

Keywords: Case history ; consolidation ; fabric ; structure of soils ; failure ; residual soils ; slopes ... Show All

The recognition of volcanic clays and the significance of heavy minerals

The explosive ejection of material from a volcanic vent produces pyroclastics. These are stratigraphically important because of their isochronous nature, lateral extent and potential for absolute age determinations. The pyroclastics also provide information on the nature of the volcanic activity, which is possibly the only record because of non-preservation in other areas. The recognition of pyroclastics is therefore important, but often difficult,because the high-temperature igneous material is susceptible to alteration in the diagenetic environment. In Quaternary sediments the composition of glass shards is an important aspect of tephrochronology (Westgate &amp; Briggs, 1980) but in older sediments glass shards are usually altered to clay minerals. Exceptionally, shards are preserved unaltered, as in the case of early carbonate and silica cementation (Francis et al., 1968; Jeans et al., 1977). According to Ross (1928), features that are diagnostic for the recognition of a volcanic clay (bentonite is the term used by Ross) are, in order of apparent reliability: (i) presence of glass relict structure; (ii) presence of minerals and crystal forms characteristic of volcanic rocks, including biotite, feldspar, pyroxenes and hornblende; (iii) absence of minerals that do not have a volcanic origin, including microcline, garnet, muscovite, kyanite and andalusite; (iv) waxy lustre; (v) reaction to water; (vi) optical properties; (vii) chemical properties.

A magnesium oxide defect structure of hexagonal symmetry

When brucite, Mg(OH) 2, is carefully heated in vacuum beyond the dehydration temperature (250–270°C) the (001) x-ray intensity decreases rapidly but does not vanish. The (100) reflection persists up to 480°C. The lattice contracts by 0.2% in c -direction. The thermal expansion in a -direction slows down. This indicates the formation of a nearly anhydrous high defect MgO which retains the brucite structure: Mg(OH) 2−x O x 2 □ x 2 with x→2 (□ unoccupied anion site). This relict structure collapses progressively to the cubic MgO.

Continental Rise off Eastern North America

During mid-1967 two cruises of the Woods Hole Oceanographic Institution's R/V Chain provided nearly continuous seismic, geomagnetic, and gravity measurements along 8,000 km of ship track. These measurements supplement earlier ones from various sources to provide a comprehensive picture of the composition and geologic history of the continental margin off eastern North America, an area that is much larger than all of the United States east of the Mississippi River. The geomagnetic profiles portray a systematic pattern of positive and negative anomalies that are in accord with the concept of sea-floor spreading, whereby North America separated from Europe and Africa at the beginning of the Permian Period, and drifted westward from the site of rifting (the Mid-Atlantic Ridge) at average rates of 0.8-1.4 cm/year. During all this time the continent has been coupled firmly with the adjacent sea floor, as though both continent and sea floor were on the same conveyor belt. Gravity information suggests that a relict structure of the original rift is preserved in the same general area as the geomagnetic slope anomaly, beneath the seaward part of the continental shelf, the continental slope, or the upper continental rise. It has the form of a complex linear ridge of crystalline rocks that rises above the zone of sharpest landward slope of the Mohorovicic discontinuity. Seismic refraction measurements support the presence of such a ridge, bordered on both sides by linear trenches. The continuous seismic reflection profiles measured during the cruises reveal shallow acoustic basement in the form of a ridge complex that is shallower, but in the same general area, and probably is related to the deep ridge. The ridge and associated trenches served as dams and b sin sinks to trap land-derived sediments during the Mesozoic Era, so that only pelagic silts and clays could reach and be deposited on the irregular oceanic basement seaward of the barrier. During Late Cretaceous to middle Eocene time one or more thick deposits of probably chemical origin formed blankets of deep-sea chert throughout broad abyssal plains, which produce the acoustic reflector known as Horizon A. About middle Eocene time the land-derived sediments filled the trap west of the ridge and prograded eastward over the ridge top and built the present continental rise atop the Mesozoic abyssal plain. Continuous seismic reflection profiles show that the rise is a huge prism of generally seaward-dipping, interbedded pelagic sediments and turbidites that contain many masses of sediment displaced from higher on the continental rise and from the continental slope. Such slides continue to occur, a large one having occurred in 1929. The volume of the Cenozoic continental rise in the study region is nearly 3 million km3, about half the volume of all sediments deposited on basement during Mesozoic time. The interbedding of sandy turbidites with organic-rich silts and clays displaced from the continental slope may constitute a thick sequence of oil reservoir and oil source beds, but no exploratory drilling into them has been done.