Academic literature on the topic 'Intrusions (Geology) Victoria'

At Terra Cotta Mountain, in the Taylor Glacier region of south Victoria Land, a 237 m thick Ferrar Dolerite sill is intruded along the unconformity between basement granitoids and overlying Beacon Supergroup sedimentary rocks. Numerous Ferrar Dolerite dykes intrude the Beacon Supergroup and represent later phases of intrusion. Major and trace element data indicate variation both within and between the separate intrusions. Crystal fractionation accounts for much of the geochemical variation between the intrusive events. However, poor correlations between many trace elements require the additional involvement of open system processes. Chromium is decoupled from highly incompatible elements consistent with behaviour predicted for a periodically replenished, tapped and fractionating magma chamber. Large ion lithophile element-enrichment and depletion in Nb, Sr, P and Ti suggests the addition of a crustal component or an enriched mantle source. The trace element characteristics of the Dolerites from Terra Cotta Mountain are similar to those of other Ferrar Group rocks from the central Transantarctic Mountains and north Victoria Land, as well as with the Tasmanian Dolerites. This supports current ideas that the trace element signature of the Ferrar Group is inherited from a uniformly enriched mantle source region.

AbstractThe Triassic Lashly Formation occurs to the east of Mount Brooke at Coombs Hills. Previously established informal members B, C, and D of the Lashly Formation are now identified at Coombs Hills. Lashly Formation member D passes up into a poorly exposed interval of silicic shard-bearing fine-grained sandstone and tuff, which is correlated with the Jurassic Shafer Peak Formation of north Victoria Land and Hanson Formation of the Beardmore Glacier region. Lashly Formation members C and D are intruded by three phreatic explosion pipes, resulting from emplacement of Ferrar Dolerite intrusions at depth and associated explosive steam generation. These pipes, ranging up to 180 m in horizontal dimension, comprise sedimentary clasts in a sand matrix, most of which was locally derived. Pipe margins are mainly ill defined and adjacent country rock is commonly disaggregated or shattered, although retaining stratigraphic order. Locally, thin basalt intrusions have interacted with coal beds.

In North Victoria Land (Antarctica), the Wilson Terrane is a portion of the palaeomargin of the East Antarctic Craton, deformed during the Late Cambrian–Early Ordovician Ross Orogeny. Crustal deformation, from westward subduction of the palaeo Pacific plate and terrane accretion on this palaeomargin, gave rise to the development of a transpressive fold belt and a wide magmatic arc. In the inner portion of the Wilson Terrane, (Deep Freeze Range–Eisenhower Range) a large portion of this magmatic arc is made up of intrusions and dyke systems. Intrusive rocks range from large unfoliated plutons to well foliated sheet intrusions emplaced in low and medium–high grade metamorphic rocks respectively. Field and structural data on intrusive rocks and metamorphic host rocks, coupled with parameters relative to deformation mechanism and magmatic processes (crystallization and cooling) rates, make it possible to outline an episode of diffuse synkinematic magmatism in the Wilson Terrane. The emplacement of intrusions in both the middle and upper crust was coeval and related to the development of transpressional and transtensional structures along dextral strike-slip shear zones. Furthermore the development of foliated or unfoliated fabrics is related to competition between rates of deformation and magmatic processes, which is a function of the thermal state of the host rocks.

The Annieopsquotch Complex is an ophiolite that forms the Annieopsquotch Mountains of southwest Newfoundland. It contains rocks of the critical zone, gabbro zone (2.3 km thick), sheeted dyke zone (1.5 km thick), and pillow lava zone of a typical ophiolite. The zones trend northeast, face and dip southeast at approximately 50–70°, and are offset by faults.Cumulate rocks of the critical zone preserve graded layers, trough structures, and slump folds and locally are metamorphosed and deformed. The gabbro zone contains many textural varieties of gabbro, pegmatitic pods, layering, trondhjemite pods, and amphibolite near the base. It passes through a transition zone to a sheeted dyke zone that extends the full strike length of the ophiolite. Dykes trend northwest and are aphyric or plagioclase-phyric diabase. The pillow lava zone, besides pillow basalt, contains minor pillow breccia, hyaloclastite, and chert.The Annieopsquotch Complex is faulted against an Ordovician tonalite terrane to the northwest across the Lloyds River Fault and against the Victoria Lake Group to the southeast. It is cut by dykes and sills correlated with both these units. The complex is cut by two Late Ordovician gabbro–diorite intrusions and a granite of presumed Devonian age and is unconformably overlain by Early Silurian terrestrial sedimentary and volcanic rocks.Major-, trace-element, and clinopyroxene chemistry of the complex and other ophiolitic fragments between Buchans and King George IV Lake is typical of N-type MORB. These likely constituted one allochthon of Iapetus Ocean or marginal basin crust emplaced over the Ordovician continental margin of North America during the Taconic Orogeny.

The Darwin Glacier region is located between the Carlyon and Darwin glaciers in southern Victoria Land, Antarctica (Fig. 1). Previous work on Ross Orogeny granitoids of the Darwin Glacier region is mutually conflicting. Haskell et al. (1965) mapped three plutons, the Carlyon Granodiorite, Mount Rich Granite and Hope Granite, Felder & Faure (1990) did not recognise the Hope Granite, and Encarnación & Grunow (1996) interpreted the entire area as underlain by a single intrusion, the Brown Hills pluton. Fieldwork during the 2000 field season and subsequent geochemical and geochronological analysis described here indicates the presence of three distinctive granitic suites, emplaced during Cambrian times. These include the Foggy Dog Granite (FDG) suite, the Darwin calcic suite and the Cooper Granodiorite.

The Tertiary stocks (Meander Intrusives) cropping out along the coasts of the Ross Sea were sampled for a palaeomagnetic study during the sixth Italian expedition to northern Victoria Land. Laboratory investigations concerned magnetic mineralogy and remanent magnetization. Minerals of the magnetiteulvöspinel series occur in the rocks from all stocks, with low-Ti titanomagnetite usually prevalent. Haematite and goethite occur in small amounts as alteration products. Large secondary components commonly screen the characteristic remanent magnetization and were removed by thermal or AF demagnetization at temperatures or peak-fields higher than 360°C and 20 mT respectively. A total of 10 VGPs were obtained from radiometrically dated rocks (42–22 Ma); the averaged position (69°S, 334°E; α95=9.9°) is the first middle Tertiary palaeomagnetic pole for East Antarctica, and gives evidence for a reversal in the course of the APW path. This evidence is not substantially altered by a supposed tilt-correction consistent with geophysical and geological models for the uplift of the Transantarctic Mountains. No definite conclusion about relative movements between East Antarctica and the Antarctic Peninsula can be drawn from the existing palaeomagnetic data.

A magnetic survey was carried out in the area between Lady Newnes Bay and Evans Névé (northern Victoria Land), to ascertain whether the contact between the Wilson and the Bowers terranes could be identified remotely. The survey consisted of three ground and 12 helicopter-borne profiles. The method was calibrated on the southernmost profiles, which cover a well-exposed section of the contact between the Wilson and Bowers terranes. The northern profiles were located in an area where the contact is poorly constrained by outcrops, so that it could be tested whether the junction displays a magnetic signature. The magnetic data and the 2.5-D modeling of three selected profiles indicate that no easily recognizable magnetic signature defines this contact. The main features of the area are magnetic anomalies probably controlled by the “Meander Intrusives” and the McMurdo volcanic rocks, both characterized by high susceptibility values. If an anomaly related to the contact exists, then it is probably masked by these stronger anomalies.

Granitoid gneisses intercalated with Koettlitz Group metasediments in the upper Ferrar, Taylor and Wright valleys of South Victoria Land comprise various hornblende+biotite orthogneisses and biotite orthogneisses, including the km-scale Dun and Calkin plutons. K-feldspar megacryst inclusion textures and discordant cross-cutting relationships with enclosing metasediments are interpreted as firm evidence of an intrusive origin for hornblende+biotite and biotite orthogneiss. The scale of several concordant orthogneiss bodies (including the Dun and Calkin plutons), the presence of mafic enclaves, and relict flow differentiation in hornblende+biotite orthogneiss are also compatible with a plutonic origin. Orthogneisses were emplaced prior to deformation that produced macroscopic upright, tight, folds about NW-trending axes. Petrography and geochemistry indicate I-type affinities for hornblende+biotite orthogneisses and the Dun Pluton. Hornblende+biotite and biotite orthogneisses (with the exception of the Dun Pluton) are part of a single petrogenetic suite, together with younger Bonney, Valhalla, and Hedley plutons. Emplacement of a continuum of I-type intrusives is envisaged which spanned Koettlitz Group deformation, and possibly caused much of the deformation. Hornblende+biotite and biotite orthogneisses are deformed precursors to the younger Bonney, Valhalla, and Hedley plutons. The Dun Pluton contains Fe-rich salitic clinopyroxene relicts and exhibits a unique geochemistry. It is rich in Sr, Al2O3, Na2O, and poor in FeO, K2O, Rb, Y, V. Chemical and petrographic features indicate an evolved body, possibly derived from a primitive source distinct from other orthogneisses and granitoids.

Geóloga
El blanco de exploración Picarón es uno de los proyectos de Cu-Mo (Au) dentro del Proyecto Victoria perteneciente a la minera Hochschild Chile SCM (MHC) en la Región de Antofagasta. El blanco está formado por un grupo de cuerpos intrusivos tabulares porfídicos de composición diorítica del Cretácico Tardío, emplazados en un paquete volcánico-sedimentario, correspondiente a la Formación Pajonales y Formación Candeleros, con alteración hidrotermal asociada. En superficie la alteración coincide con un sistema de pórfido cuprífero. En la zona se realizaron 6 sondajes de diamantina que interceptaron una falla de bajo ángulo a los 200 metros de profundidad en la vertical. Se definieron 8 intrusivos separados en pre mineral, mineral temprano, inter mineral, mineral tardío y post mineral, utilizando las vetillas encontradas como guía, además de 1552 análisis geoquímicos para 36 elementos más Au. Este trabajo consiste en un análisis estadístico univariable y multivariable a estos análisis, así como en la confección de secciones geológicas, utilizando los mapas y logueos hechos por los geólogos de la compañía, para así caracterizar las litologías ya definidas, encontrar diferencias y similitudes entre ellas y estudiar la relación con alteración y mineralización. Los resultados, debido a la naturaleza de los análisis geoquímicos realizados, no son los óptimos para definir una huella geoquímica litológica para cada unidad, sin embargo, fue posible distinguir una diferencia en la composición litológica del intrusivo definido como pre mineral, la microdiorita, que tiene mayor afinidad con la asociación Mg, Sc, V y Cr. Los pórfidos definidos como mineral temprano y pre mineral, tienen las mayores leyes de Cu-Mo y se asocian bastante bien con la alteración potásica, los pórfidos definidos como inter mineral, son estos los que presentan la menor correlación de Cu y otros elementos. Los pórfidos mineral tardío, presentan las mayores leyes y correlaciones de Au, así como una alteración asociada propilítica. Finalmente los pórfidos post mineral, no presenten leyes significativas, ni alteraciones características. Además se reconocieron al menos dos eventos mineralizadores, el primero corresponde a uno de Cu, que está asociado a la alteración potásica, que afecta a los pórfidos pre mineral y mineral temprano, así como a la roca caja, siendo al parecer la más receptiva a este evento el paquete volcanoclástico. El segundo evento mineralizador corresponde a uno de Au que está asociado a los intrusivos mineral tardío, y a las alteraciones registradas como calcita y clorita y fílica, sin embargo las leyes son bajas y están por muy poco sobre el umbral exploratorio recomendado. El resto de los pórfidos no presentan leyes interesantes por lo que deberían ser descartados para objetivos de exploración. Finalmente, la ubicación del prospecto en un modelo de un sistema de pórfido cuprífero, seria en el límite entre las alteraciones potásicas y propilítica, sin embargo, la baja densidad de sondajes dificulto la confección de una zonación más exacta y por lo tanto de una relación entre prospecto y modelo. . Para entender mejor la geometría de este pórfido, se recomienda un análisis estructural en la zona, ya que se desconoce la naturaleza exacta de la falla basal presente en el sistema, y es esta falla la que podría haber desplazado a lo que se conoce hoy del prospecto Picarón del resto del cuerpo mineralizado. Además, este estudio indica una posible vectorización de la mineralización hacia el W y no se descarta que este cuerpo mineralizado desconocido pudiera contener al núcleo de alteración potásica, que alcanzaría mayores leyes de Cu.
Este trabajo ha sido parcialmente financiado por HOCHSCHILD MINING CHILE

After the summer field season of 1989 in the Pakistani Karakoram, I drove to Oxford, the ‘city of dreaming spires’ and arrived in the Department of Earth Sciences. In those days Oxford was probably the best field-geology ‘hard-rock’ department in the country and one of the best in the world. It was a wonderful place for me, buzzing with excitement and full of talented geologists working on projects all over the world. John Platt had post-graduate students working on several projects in the European Alps and the Spanish Betics, Simon Lamb was starting a major new field project in the Andes of Bolivia, and the department had some of the world’s leading igneous petrologists working on volcanic and granitic rocks all over the world. The department was overflowing and I was given an office on the top floor of the ‘annexe’ a wonderful old Victorian building at 62, Banbury Road. My office was up in the attic and I called this grandly the ‘Oxford Centre of Himalayan Research’. Right across the Banbury Road was an excellent public house, the Rose and Crown on North Parade, and we used to congregate there regularly for discussions on geology, and the world in general over a pint or two of traditional real ale. It was an excellent life. In the 1830s the first Professor of Geology in Oxford was the Reverend William Buckland who naturally came with a lot of religious baggage. Buckland was a bit of an eccentric in many ways including living with and eating a whole variety of wild animals and doing his geological fieldwork dressed in full academic gown. Following Buckland the department settled down to a more conventional geological approach, studying the stratigraphy and palaeontology of Oxfordshire. By the 1950s Oxford had become one of the leading departments of geology and mineralogy in the world. The head of department was Lawrence Wager, who had made his name studying the classic Skaergaard igneous intrusion of Greenland. Wager had earlier joined the 1933 Everest expedition climbing to 27,500 feet on the north ridge and collecting an extremely useful set of samples from the north slopes of Everest.