Academic literature on the topic 'Websteriti'

Abstract: Mantle xenoliths in Neogene-Quaternary alkaline volcanic rocks from the Catalan Volcanic Zone indicate that ≪anhydrous≫ spinel lherzolites, harzburgites and much subordinate olivine websterites form the lithospheric mantle of NE Iberian Peninsula. Olivine crystal preferred orientation, determined by indexation of electron-backscattered diffraction patterns, provides three types of deformation fabric: a dominant [010]-fiber type in peridotites and websterites equilibrated at high temperature, and subordinate orthorhombic and [100]-fiber types, which appear mostly in porphyroclas tic and equigranular lherzolites equilibrated at lower temperature.Keywords: Lithospheric mantle, lherzolites, harzburgites, websterites, olivine, deformation fabric.Resumen: Los xenolitos mantelitos en lavas alcalinas neógeno-cuaternarias de la Zona Volcánica de Cataluña indican que lherzolitas y harzburgitas ≪ anhidras≫ y con espinela son las rocas predominantes en el manto litosférico del NE de la Península Ibérica, con presencia también subordinada de websteritas olivínicas. Las orientaciones cristalográficas preferentes del olivino, determinadas por indexación de los espectros de difracción de electrones retrodispersados, muestran tres tipos de fábrica de deformación: una dominante, tipo axial [010], en peridotitas y websteritas equilibradas a alta temperatura, y otras subordinadas, de tipo ortorrómbico y axial [100], que aparecen en lherzolitas porfidoclásticas y equigranulares equilibradas a menor temperatura.Palabras clave: Manto litosférico, lherzolitas, harzburgitas, websterita, olivino, fábricas de deformación

Abstract —Xenoliths of high-alumina pyroxenites in the Quaternary basalts of the Sigurd Volcano of West Spitsbergen are spinel and spinel–garnet clinopyroxenites, spinel–garnet websterites, and websterites. The granoblastic texture with relics of subhedral magmatic texture, the change of mineral assemblages, and the signs of partial melting in the xenoliths reflect their multistage formation. The goal of our study was to determine the sequence and thermodynamic conditions of the change of mineral assemblages and to establish their age by Re–Os, U–Pb, Sm–Nd, and Rb–Sr isotope dating. It has been established that the primary assemblage in the pyroxenites, which included high-alumina Opx, Cpx, and Spl, was transformed in several stages: (1) Spl→Grt replacement with the formation of garnet-containing websterites and clinopyroxenites, (2) development of kelyphitic Opx–Spl rims over Grt grains, (3) formation of Amph, (4) exsolution with the formation of Cpx and Opx, and (5) partial melting. Comparison of the obtained results with published data shows that the primary assemblage is similar in Al2O3/MgO ratio to Opx + Cpx ± Spl cumulates resulted from the crystallization of basaltic melts at 1.2 GPa and the degree of crystallization of ~15%, i.e., in the lower crust (at 2.0 GPa, Grt and Cpx crystallize from the solution). The equilibrium parameters of the Grt–Opx assemblage in the pyroxenites are 1060–1310 ºC and 2.2–3.3 GPa; in the P–T diagram, their points are localized below the Spl→Grt phase transition curve, in the system CaO–MgO–Al2O3–SiO2, thus corresponding to the model continental geotherm with a surface heat flow density of 60 mV/m2 and somewhat higher. This indicates the Spl→Grt replacement and the formation of garnet-containing pyroxenites in the shallow-depth upper mantle. The formation of kelyphitic Opx–Spl rims over the Grt grains indicates a subsequent temperature and pressure decrease to values above the Grt→Spl phase transition curve. This is confirmed by the presence of exsolution structures in pyroxene, which formed when the temperature decreased by 100–150 ºC. The Re and Os isotope composition in the bulk samples of Spl–Grt websterites that did not undergo partial melting corresponds to an age of 457.0 ± 3.5 Ma, which reflects the time of transformation of the primary Cpx–Opx–Spl assemblage into a garnet-including one. A similar value (488.6 ± 5.9 Ma) was obtained by U–Pb dating of zircon from Spl–Grt websterite, also without signs of melting. Zircon crystals from Spl–Grt clinopyroxenite with clear signs of partial melting have typomorphic features of autochthonous magmatic zircons. They form a single age cluster of 310.7 ± 3.3 Ma, which marks the age of melt crystallization in the pyroxenites. Thus, Spl pyroxenites are, most likely, Opx + Cpx ± Spl cumulates, products of crystallization of basaltic melts in the lower crust. The subsequent Spl→Grt replacement and the formation of garnet-containing websterites and clinopyroxenites in the shallow-depth upper mantle can be regarded as an indicator of the delamination of the continental crust into the mantle, and the Re–Os isochron date of 457.0 ± 3.5 Ma is the most likely upper age bound of the crust delamination into the mantle. The subsequent uplifting of the Spitsbergen lithosphere, which was expressed as the formation of kelyphitic Opx–Spl rims over garnet, exsolution in pyroxene, and partial melting, was not far in time from the delamination stage and lasted ≤ 300 Ma.

Samples of plagioclase olivine websterite included in variously serpentinized harzburgite and lherzolite tectonites were collected by submersible on the northwest flank of the Gettysburg Seamount near 36°N in the northeastern Atlantic. The websterite exhibits a coarse porphyroclastic texture (70% porphyroclasts), and the composition of the pyroxene shows a progressive re-equilibration with decreasing temperature (and probably pressure) under anhydrous conditions from a near-solidus temperature of ~1250 °C (porphyroclasts) down to ~700 °C (granoblasts). In situ observations, as well as textural, mineralogical, and chemical evidence, suggest that the websterite can best be interpreted as a heteradcumulate rock that crystallized on the walls of narrow conduits from a MORB type magma flowing through the residual tectonites.The Mg #'s (= 100 × Mg/(Mg + Fe2+)) of coexisting clinopyroxene, orthopyroxene, and olivine (91.5–90.5, 90.0–89.7, and 89.5–88.5, respectively), the plagioclase composition (An88.7–87.9), and the mineral minor-element distribution are not compatible with the crystallization at low pressure of the websterite from N-MORB type parental magma. Instead, the calculated composition of the liquid in equilibrium with the websterite's most magnesian minerals and the bulk-rock composition are more akin to those of a poorly differentiated T-MORB than of N-MORB parental magma. Phase relations and mineral compositions produced by anhydrous melting experiments for synthetic and natural systems indicate that the pressure of crystallization of the plagioclase olivine websterite is constrained within the narrow range of 7–10 kbar. It is thought that fractionation of websterite is probably a minor but significant petrologic factor of MORB type magma differentiation. It could explain some of the compositional variations observed in magnesian MORB.

The Alpheus websteri Kingsley, 1880 species complex is revised. Alpheus websteri s. str. is redefined and restricted to the western Atlantic, ranging from the type locality in the Florida Keys to northeastern Brazil. The eastern Pacific A. arenensis (Chace, 1937), formerly a synonym of A. websteri, and the eastern Atlantic A. fagei Crosnier and Forest, 1966, are shown to be distinct from A. websteri morphologically, genetically and also by color pattern. Morphology, genetics and color patterns all suggest that A. websteri and A. arenensis are transisthmian sister species, with A. fagei being their closest relative. Complete synonymy, color photographs and GenBank barcodes (COI) are provided for all three species.

The sub-continental mantle beneath North China Craton (NCC) has attracted extensive attention in the past decades because of its dramatic transformation from an old, cold, thick, and refractory mantle to a juvenile, hot, thinner, and fertile mantle. However, the transformation mechanism remains largely controversial. The mantle xenoliths entrapped in basalts, as petrogenetic indicators, can provide an important window to reveal the evolution of the sub-continental lithospheric mantle. In this study, we present a systematical study on the geochemical characteristics of the olivine websterite xenoliths and their minerals in the Cenozoic basalts in the Hannuoba region located at the central orogenic belt of the NCC. The results, compared with the geochemical data of Paleozoic and Meosozic peridotites, the Cenozoic composite pyroxenites as well as the global cumulate pyroxenites, demonstrate that: (1) The source of the websterite is probably the lithospheric mantle, which is mainly newly accreted, but with small amounts of ancient mantle residues. The source may be contaminated by different degrees of crustal materials. The high Nb/Ta ratios (11.36–20.57) of the websterite indicate that the Ti-bearing minerals (such as rutile) are probably involved in the source; (2) The websterite is more likely to be produced as a result of interaction of mantle peridotite with the silica-rich melts that are mainly derived from the asthenospheric mantle and also contributed by the crustal materials; (3) The metasomatic crustal melts might be derived from the subducted Paleo-Pacific plate. These melts interacted with the lithospheric mantle can significantly transform the chemical composition of the lithospheric mantle, and consequently play an important role in the destruction of the NCC. An important implication for the destruction of the NCC is further discussed.

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.

Eclogite, gamet clinopyroxenite, gamet websterite and websterite bodies were discovered within the Skærfjorden gneiss complex during recent mapping in North-East Greenland. These eclogitic pods extend from Danmarkshavn (c. 76° 40'N) to the northern limit of the area mapped (78°N), and attest to widespread high-pressure metamorphism. Eclogites with the assemblage omphacite + garnet ± quartz ± futile are common. The protoliths of some of the eclogites were xenoliths within the precursor batholiths to the gneisses. Field relations, regional correlations and preliminary geochronology indicate that the eclogite facies metamorphism is Caledonian. The eclogites formed at minimum pressures between 10-15 kilobars and temperatures between 600–900°C, and hence are the medium-temperature type typically formed in over-thickened crust during continent collision.

Abstract The Seram-Ambon ophiolitic series comprise peridotites, websterites, gabbros and lavas. Petro-geochemical data show that the peridotites are weakly depleted rocks, except for the rare Cpx-free harzburgites. They underwent a sub-solidus metamorphic re-equilibration in the plagioclase field. The associated websterites and gabbros display various chemical features, allowing to define 3 types of websterites and 2 groups of gabbros. They have mostly BAB characteristics (presence of negative anomalies in Nb, Zr, Ti and Y), except the group 2 gabbros which have N-MORB features and the type 3 websterites which bear adakitic affinities. Lavas also display a variety of compositions, including high-Mg IAT and Mg-rich BABB with sub-alkaline affinities. Both IAT and BABB display high Th/Nb ratios which support an origin close to a continental crust environment. Our 20 to 15 Ma 40K/40Ar ages calculated for the BABB and 15-9 Ma for the IAT show that the basin and arc formed in a very short span of time, before their obduction 9–7 Ma ago [Linthout et al., 1997]. Considering the paleogeographic situation in the Miocene [Haile, 1979 ; Haile, 1981] and our data, we propose that the Seram-Ambon ophiolites formed during the early Miocene in a small, short-lived (10 Ma), transtensive basin bordered on its east by an active margin and on its western part by a passive continental margin over which it was later obducted towards the SW direction.

SUMMARYThe Repulse Bay block (RBb) of the southern Melville Peninsula, Nunavut, lies within the Rae craton and exposes a large (50,000 km2) area of middle to lower crust. The block is composed of ca. 2.86 Ga and 2.73–2.71 Ga tonalite-trondhjemite-granodiorite (TTG) and granitic gneiss that was derived from an older 3.25 and 3.10 Ga crustal substrate. This period of crustal generation was followed by the emplacement of ca. 2.69–2.66 Ga enderbite, charnockite, and granitoid intrusions with entrained websterite xenoliths. These voluminous batholith-scale bodies (dehydrated and hydrated intrusions), and the associated websterite xenoliths, have similar whole rock geochemical properties, including fractionated light rare earth element (LREE)–heavy (H)REE whole rock patterns and negative Nb, Ti, and Ta anomalies. Dehydrated intrusions and websterite xenoliths also contain similar mineralogy (two pyroxene, biotite, interstitial amphibole) and similar pyroxene trace element compositions. Based on geochemical and mineralogical properties, the two lithologies are interpreted to be related by fractional crystallization, and to be the product of a magmatic cumulate processes. Reworking of the crust in a ca. 2.72 Ga subduction zone setting was followed by ca. 2.69 Ga upwelling of the asthenospheric mantle and the intrusion of massif-type granitoid plutons. Based on a dramatic increase in FeO, Zr, Hf, and LREE content of the most evolved granitoid components from the 2.69–2.66 Ga cumulate intrusion, we propose that those granitoid plutons were in part derived from a metasomatized mantle source enriched by fluids from the subducting oceanic slab that underwent further hybridization (via assimilation) with the crust. Large-scale, mantle-derived Neoarchean sanukitoid-type magmatism played a role in the development of a depleted lower crust and residual sub-continental lithospheric mantle, a crucial element in the preservation of the RBb.RÉSUMÉLe bloc de Repulse Bay (RBb) dans le sud de la péninsule de Melville, au Nunavut, est situé dans le craton de Rae et expose une large zone (50 000 km2) de croûte moyenne à inférieur. Ce bloc est composé de tonalite-trondhjémite-granodiorite (TTG) daté à ca. 2,86 Ga et 2,73–2,71 Ga, et de gneiss granitique dérivé d’un substrat crustal plus ancien daté à 3,25 Ga et 3,10 Ga. Cette période de croissance crustale a été suivie par la mise en place entre ca. 2,69 et 2,66 Ga d’intrusions d’enderbite, charnockite et de granitoïde incluant des xénolites d’entraînement de websterite. Ces intrusions de taille batholitique (intrusions déshydratées et hydratées) ainsi que les xénolites d’entraînement de websterite associés, ont des propriétés géochimiques sur roche totale semblables notamment leurs profils de fractionnement des terres rares légers (LREE) et des terres rares lourds (HREE) ainsi que leurs anomalies négatives en Nb, Ti et Ta. Les intrusions déshydratées et les xénolites de websterite ont aussi des minéralogies similaires (deux pyroxènes, biotite, amphibole interstitielle) ainsi que des compositions semblables en éléments traces de leurs pyroxènes. Étant donné leurs propriétés géochimiques et minéralogiques, ces deux lithologies sont interprétées comme provenant d’une cristallisation fractionnée, et comme étant le produit de processus d'accumulations magmatiques. Le remaniement de la croûte dans un contexte de subduction vers ca. 2,72 Ga, a été suivi vers ca. 2,69 Ga d’une remontée du manteau asthénosphérique et de l’intrusion de granitoïdes de type massif. D'après l’importante augmentation en FeO, Zr, Hf et LREE dans les granitoïdes les plus évolués du magmatisme ayant pris place entre ca. 2,69 Ga et 2,66 Ga, nous proposons que ces plutons aient été en partie dérivés d’une source mantélique métasomatisée enrichies par des fluides d’une plaque océanique en subduction et qui a subi une hybridation supplémentaire (par assimilation) avec la croûte. Le magmatisme néo-archéen de type sanukitoïde, dérivé du manteau et de grande échelle, a joué un rôle dans le développement d’une croûte inférieure et d’un manteau lithosphérique continental résiduel appauvri, un élément déterminant pour la préservation du RBb.

L’obiettivo di questo studio è quello di caratterizzare il trasferimento di massa tra crosta e mantello. A questo scopo sono stati considerati due terreni metamorfici di alta pressione (HP) dove peridotiti a granato affiorano all’interno di rocce crostali di alto grado, i.e. l’area del Monte Duria (falda Adula-Cima Lunga, Alpi centrali, N Italia) e la zona d’ Ultimo (falda del Tonale, Alpi orientali, N Italia). Nell’area del Monte Duria, peridotiti a granato affiorano in contatto diretto con eclogiti migmatitiche (Borgo). Sia le peridotiti che le eclogiti registrano condizioni di picco in HP a 2.8 GPa e 750 ° C e un riequilibratura statica a 1.0 GPa e 850 ° C. Le peridotiti mostrano abbondanti anfibolo, dolomite, flogopite e ortopirosseno (su olivina), suggerendo che le peridotiti registrano metasomatismo ad opera di agenti crostali arrichiti in SiO2, K2O, CO2 e H2O. Le peridotiti mostrano anche un frazionamento in LREE (La/Nd = 2.4) legato alla presenza di anfibolo e clinopirosseno. Questi minerali sono equilibrio con il granato, indicando che il metasomatismo è avvenuto in HP. Nelle eclogiti, microstrutture di fusione come aggregati microcristallini a Kfs+Pl+Qz+Cpx e Cpx+Kfs sono allineate lungo la foliazione a Zo+Omp+Grt, indicando che le eclogiti hanno subito un evento di fusione parziale in HP. Il contatto tra le peridotiti e le eclogiti di Borgo è marcato dalla presenza di un livello di tremolitite. Boudins di tremolititi si ritrovano anche trasposti lungo la foliazione a granato della peridotite, indicando che il boudinage delle tremolititi è avvento in alta pressione. Le tremolititi mostrano aggregati a Phl+Tc+Chl+Tr interpretati come psudomorfi su granato. Tali pseudomorfi si sviluppano in condizioni statiche post-datando la formazione dei boudins, suggerendo che le tremolititi derivano da precursori a granato. Le tremolititi mostrano Mg# > 0.90 e Al2O3 = 2.75 wt.% tipici di composizioni ultramafiche ma allo stesso tempo presentano arricchimenti in SiO2, CaO, e LREE, indicando che esse rappresentano il prodotto dell’interazione in alta pressione tra le peridotiti e i fusi derivati dalle eclogiti. Per testare questa ipotesi abbiamo sviluppato un modello termodinamico a P = 3 GPa e T = 750 °C. I nostri risultati indicano che l’interazione fuso-peridotite produce una paragenesi a Opx+Cpx+Grt, suggerendo che le tremolititi rappresentano il prodotto di retrocessione di una westerite a granato. Nella zona d’Ultimo, numerose lenti di peridotite affiorano all’interno di rocce crostali di alto grado. Le peridotiti mostrano una transizione da lherzoliti a spinello protogranulari a peridotiti milonitiche a granato e anfibolo. Le pirosseniti trasposte lungo la foliazione della peridotite mostrano un’evoluzione simile, da pirosseniti a spinello a pirosseniti a granato. Questa evoluzione riflette il passaggio indotto dal corner flow del mantello da condizioni in facies a spinello a a granato. Come consguenza, il granato forma corone intorno allo spinello ed essoluzioni all’interno dei porfiroclasti di pirosseno, e cristallizza lungo la foliazione delle pirosseniti e delle peridotiti Evidenze tessiturali e dati cristallografici indicano che la transizione spinello-granato avviene in un contesto deformativo. I porfiroclasti di pirosseno mostrano evidente CPO, alte frequenze delle misorientazioni a basso angolo, e distribuzione non-random degli assi di misorientazione per misorientazioni a basso angolo, indicando che i pirosseni si deformano per dislocation creep. Il dislocation creep è contemporaneo a processi di ricristallizzazione dinamica e alla transizione spinello-granato. Ciò induce una riduzione della grana e una transizione permanente da disclocation creep nei porfiroclasti a grain-size sensitive creep nei grani ricristallizzati che risulta in un forte indebolimento delle pirosseniti e delle peridotiti quando queste vengono tettonicamente accoppiate alle rocce crostali.
In the Monte Duria area (Adula-Cima Lunga unit, Central Alps, N Italy) garnet peridotites occur in direct contact with migmatised orthogneiss (Mt. Duria) and eclogites (Borgo). Both crustal and ultramafic rocks share a common high pressure (HP) peak at 2.8 GPa and 750 °C and post-peak static equilibration at 0.8-1.0 GPa and 850 °C. Garnet peridotites show abundant amphibole, dolomite, phlogopite and orthopyroxene after olivine, suggesting that they experienced metasomatism by crust-derived agents enriched in SiO2, K2O, CO2 and H2O. Peridotites also display LREE fractionation (La/Nd = 2.4) related to LREE-rich amphibole and clinopyroxene grown in equilibrium with garnet, indicating that metasomatism occurred at HP conditions. Kfs+Pl+Qz+Cpx interstitial pocket aggregates and Cpx+Kfs thin films around symplectites after omphacite parallel to the Zo+Omp+Grt foliation in the eclogites suggest that they underwent partial melting at HP.The contact between garnet peridotites and associated eclogites is marked by a tremolitite layer, which also occurs as layers within the peridotite lens, showing a boudinage parallel to the garnet layering of peridotites, flowing in the boudin necks. This clearly indicates that the tremolitite boudins formed when peridotites were in the garnet stability field. Tremolitites also show Phl+Tc+Chl+Tr pseudomorphs after garnet, both crystallised in a static regime postdating the boudins formation, suggesting that they derive from a garnet-bearing precursor. Tremolitites have Mg# > 0.90 and Al2O3 = 2.75 wt.% pointing to ultramafic compositions but also show enrichments in SiO2, CaO, and LREE suggesting that they formed after the reaction between the eclogite-derived melt and the garnet peridotite at HP. To test this hypothesis, we performed a thermodynamic modelling at fixed P = 3 GPa and T = 750 °C to model the chemical interaction between the garnet peridotite and the eclogite-derived melt. Our results show that this interaction produces a Opx+Cpx+Grt assemblage + Amp+Phl, depending on the water activity in the melt, suggesting that tremolitites likely derive from a previous garnet websterite with amphibole and phlogopite. In the Ulten Zone (Tonale nappe, Eastern Alps, N Italy), peridotite bodies occur within high-grade crustal rocks. Peridotites show a transition from coarse spinel-lherzolites to mylonitic garnet-amphibole peridotites. Pyroxenites veins and dikes, transposed along the peridotite foliation, show a similar evolution from coarse garnet-free websterites to fine-grained garnet + amphibole clinopyroxenites. This coupled evolution has been interpreted to reflect cooling and pressure increase of pyroxenites and host peridotites from spinel- (1200 °C, 1.3-1.6 Gpa) to garnet-facies conditions (850 °C and 2.8 Gpa) likely induced by mantle corner flow. As a consequence, garnet formed coronas around spinel and exsolved from porphyroclastic, high-T pyroxenes, and finally crystallised along the pyroxenite and peridotite foliations. Textural evidences and CPO data indicate that the transition from spinel- to garnet-facies conditions was assisted by intense shearing and deformation. Pyroxene porphyroclasts in garnet clinopyroxenites show well-developed CPOs, high frequencies of low-angle misorientations, and non-random distribution of the low-angle misorientation axes, indicating that pyroxene porphyroclasts primarily deform by dislocation creep. Dislocation creep is accompanied by reaction-induced dynamic recrystallisation during the spinel to garnet phase transition, which promotes a sudden reduction of the grain size and a shift from dislocation creep in the porphyroclast to grain-size sensitive creep (GSS) in the recrystallised grains. This results in a dramatic rheological weakening of pyroxenites at HP peak conditions when pyroxenites and host peridotites were coupled with crustal rocks.

With increasing pressures on sagebrush steppe ecosystems, the sagebrush defoliating Aroga moth, Aroga websteri Clarke (Lepidoptera: Gelechiidae) has become a critical organism of concern. Despite the cyclic nature of A. websteri outbreaks throughout the Great Basin, there is limited information on the moth’s population dynamics. The goal of this dissertation was to develop effective means of assessing and describing population trends of the Aroga moth across space and time, and potentially promoting biological control of the moth to prevent unnaturally large, prolonged and destructive outbreaks. Field studies were conducted to: 1) monitor and quantify activity of the Aroga moth and its damage to sagebrush across a montane landscape, 2) assess the effects of parasitoid and floral diversity on parasitism of the moth, and 3) develop a degree-day (D) model to describe the phenology of the insect, as well as field populations studied previously. North-facing stands of sagebrush, characterized by low values of solar radiation, appear to be especially suitable local habitats for the Aroga moth. High habitat suitability may result from favorable microclimate, both in its direct effects on the Aroga moth and in indirect effects tied to sagebrush plant community productivity and performance. Parasitoid and floral diversity differed strongly and predictably across space and time, with greatest overall parasitism occurring when three major parasitoid species were present. Field experiments revealed individual species of parasitoids differed substantially and complemented one another in their patterns of attack among local populations of the Aroga moth across the montane landscape. Differing responses to provision of floral resources and methyl salicylate (an herbivore- induced plant volatile) support the general hypothesis that over large scales of space and time, species diversity of natural enemies promotes suppression of insect herbivores. Lastly, degree-day models were developed and least variation among years in (D) phenology resulted with the single-sine method with base temperature of 5C. Years of historical Aroga moth outbreaks had characteristic seasonal patterns of D accumulation that were intermediate and characterized by high precipitation in June and July during late stage larval development. Thus, it appears that periodic outbreaks of the defoliator are due to favorable weather conditions.

Une nouvelle approche petrologique pour definir l'evolution des roches ultramafiques des massifs ophiolitiques est etablie, par l'etude petrochimique d'une serie harzburgitique de cherzolitique situe a terre neuve et par l'etude structurale et petrologique des peridotites et websterites du complexe du cap ortegal (espagne). Ce travail sert de support pour definir la methodologie permettant de suivre l'evolution des parametres chimiques lors d'une fusion partielle

Tese de doutoramento em Ciências da Literatura (especialidade de Literatura Inglesa)
As questões de género e o papel da mulher, temas subjacentes a este trabalho, têm mobilizado diferentes artes e áreas de estudo, sendo que a arte literária é uma delas. Inserida no âmbito das Ciências da Literatura, esta tese de doutoramento tem como propósito mais específico estudar o percurso político literário e a obra poética da escritora vitoriana tardia Julia Augusta Webster (1837-1894), no contexto mais alargado da cultura da Inglaterra oitocentista. A pesquisa bibliográfica e a análise textual são os métodos utilizados para o desenvolvimento deste trabalho, cujo propósito é explorar a abordagem crítica da política de género que é feita por Webster e a representação detalhada da mulher e do feminino que ela faz na sua poesia (1860-1890). Os resultados desta investigação sobre Webster revelam, em primeiro lugar, a sua extraordinária capacidade de conciliar família, escrita e ativismo social, e, em segundo lugar, o seu valioso contributo no âmbito literário, cuja obra se distingue pelo uso inovador que faz da ironia e do realismo e pela sua profunda capacidade de análise psicológica das falantes que vai retratando. Como o título deste trabalho sugere (Picture, Performance and Politics), e é depois defendido no corpo do mesmo através dos respetivos conceitos operacionais, os seus muitos ‘retratos’ são sobretudo de carácter pictórico, dramático e político. Esta sua obra original é também confrontada com a dos demais poetas do período, incluindo Tennyson, os Browning, os Rossetti, e ainda Mathilde Blind ou Amy Levy, para evidenciar os aspetos em comum entre os mesmos, mas sobretudo os traços distintivos que a caracterizam. Demonstra-se ainda que através das suas traduções, ensaios, revisões literárias e produção poética, Webster procurou combater a ideologia patriarcal vigente, influenciando, assim, uma mudança de comportamento nas mulheres e inspirando novos escritores. Nos seus poemas mais memoráveis, não só criou personagens contemporâneas como Eulalie e Agnes, as quais representam - de forma pouco convencional - distintos tipos da mulher vitoriana, mas também recriou personagens mitológicas como Medeia e Circe, retirando lhes a conotação negativa tradicional e atribuindo-lhes um papel positivo e atuante, sugerindo ao leitor uma melhor compreensão e valorização do feminino, no âmbito histórico também. A sua obra poética, em particular, expõe um problema de género, onde a própria mulher surge por vezes como a culpada direta pelo seu fracasso, ficando aquém das suas reais potencialidades. Uma realidade que Webster procurou mostrar de forma pedagógica e que, segundo ela, cabia principalmente às mulheres modificar.
The themes underlying this work, gender issues and the role of women, have mobilized different arts and areas of study, with literary art being one of them. Inserted within the scope of the Sciences of Literature, this doctoral thesis has the more specific purpose of studying the political-literary career and the poetic work of the late Victorian writer Julia Augusta Webster (1837-1894), in the broader context of 19th century English culture. Bibliographic research and textual analysis are the methods used for the development of this work, whose purpose is to explore Webster's critical approach to gender politics and the detailed representation of women and the feminine that she makes in her poetry (1860 -1890). The results of this research on Webster reveal, firstly, her extraordinary ability to reconcile family, her writing and social activism, and, secondly, her invaluable contribution in the literary sphere, whose work is distinguished by the innovative use it makes of irony and realism, as well as the deep capacity for psychological analysis of the speakers that it portrays. As the title of this work suggests (Picture, Performance and Politics), and it is later centrally argued through its operational concepts, her many ‘portraits’ are mainly of a pictorial, dramatic and political nature. This original work of hers is also confronted with the work of the other poets of the period, including Tennyson, the Brownings, the Rossettis, and also Mathilde Blind or Amy Levy, in order to highlight the aspects in common and, especially, the distinctive features that characterize it. It is also shown that, through her translations, essays, literary reviews and poetic production, Webster sought to combat the prevailing patriarchal ideology, thus influencing a change in behaviour in women and inspiring new writers. In her memorable poems, she created contemporary characters like Eulalie and Agnes, who represent different types of Victorian women, in an unconventional way. But she also recreated mythological characters like Medea and Circe, removing their traditional negative connotation and assigning them a positive and active role, thus suggesting a better understanding and appreciation of the feminine, in the historical scope as well. Her poetic work, in particular, exposes a gender problem, where the woman herself sometimes appears as the direct culprit for her failure, falling short of her real potential. A reality that Webster tried to show in a pedagogical way, and that she believed was mainly up to women to modify.
A minhas palavras de gratidão são para a Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES e para o Instituto Federal de Educação, Ciência e Tecnologia do Maranhão – IFMA, Campus Monte Castelo, ambos pelo irrestrito apoio financeiro ao meu projeto.

This chapter reassesses the macabre nihilism of The Duchess of Malfi, showing how the distinctive chill of the Websterian universe derives from a relentlessly materialist conception of humanness. Enforcing this definition of the human, the play epitomizes early modern tragedy’s reluctant ecology, which concedes but laments humans’ indistinguishability from the rest of nature. Webster offers a provocative meditation on this theme, so his play anticipates the hypermaterialist hegemony currently governing academic work and pervading the varied domains of popular culture. By negative example, Webster confirms the necessity of harmonizing self and world so that the former is recognizably coterminous with the latter yet capable of periodically claiming some distance from it.