Academic literature on the topic 'Facies (Geology) Victoria Leura'

ABSTRACT The study on a unique set of outstandingly preserved sedimentary surface textures (SSTs) found in the late Tremadocian Áspero Formation of northwestern Argentina, coupled with the sedimentological and ichnological analysis, indicate that they were formed in the intertidal to supratidal setting of a mixed-energy estuary recording storm and tide sedimentation. We recognize seven types of SSTs: probably biotic microbial mat-related SSTs (Kinneyia, elephant skin, exfoliating sandy laminae), abiotic SSTs (elliptical scours and convex parallel ridges type I “wrinkle marks” sensuAllen 1985), and problematic (convex parallel ridges type II and dot matrix texture). Elliptical scours and convex parallel ridges type I show features which indicate reworking of a cohesive sandy substrate in an intertidal or supratidal setting. Abundance of biotic SSTs with specific associated trace fossils reflect matground development and mat-grazing ichnofaunas, indicating the suppression of intense, penetrative bioturbation due to intense physicochemical stress. The “dot matrix” texture, described here for the first time, consists of a regular horizontal network of millimeter-scale pits; it appears associated with exfoliating sandy laminae, probably reflecting a mat-related origin. Three facies associations are defined through paleoenvironmental analysis. Facies association 1 is dominated by high-energy sandy and bioclastic storm deposits with tidal flat facies, and corresponds to the outer bay of a mixed-energy estuary; highly impoverished Cruziana assemblages and distal expressions of the Skolithos Ichnofacies reflect high energy and sedimentation rate. Facies association 2 shows tidal-channel and tidal-flat facies with subordinated storm deposits, representing the middle bay; impoverished Cruziana assemblages dominated by simple facies-crossing structures, with high-density monogeneric opportunistic suites, evidence physicochemical stress associated with subaerial exposure, frequent episodic deposition, high water turbidity, and/or brackish water conditions in these relatively sheltered tidal flats. Facies association 3 is formed by interdistributary-bay deposits with intercalation of channel-fill deposits in the upper part, and represents the river-dominated bay-head delta; low degrees of bioturbation in fine-grained facies indicate brackish- to fresh-water conditions. SSTs are found in tidal flat facies of facies association 2; they indicate an intertidal to supratidal environment subject to localized conditions of intense physicochemical stress. The paleoenvironmental interpretation of SSTs converges with the one performed through sedimentological and ichnological analysis, producing a robust and more detailed paleoenvironmental model for the Áspero Formation. Our study highlights the use of SSTs as a tool for supporting and refining paleoenvironmental analysis.

The poly-deformed Priestley schist (Wilson Terrane) of north Victoria Land, Antarctica ranges in metamorphic grade from lower greenschist facies to upper amphibolite facies. All grades of schist have been affected by structurally controlled retrogressive H2O-CO2 fluids with 45–70 mole % CO2. The fluids have deposited quartz-carbonate veins with pyrite and chlorite or biotite in late stage structures. Veins typically constitute < 1% of the rock mass, but in one greenschist facies area > 10% of the rock is vein. Veins in higher grade schists have been boudinaged after formation, and many have been annealed. Primary fluid inclusions are preserved in veins in biotite zone schists in two localities. At one locality, entrapment of immiscible fluids (water with c. 8 and 45 mole % CO2) occurred during vein formation, at about 280–300°C and 700 ± 200 bars fluid pressure. The aqueous fluid is slightly saline (4 wt % NaCl equivalent). At the other primary fluid inclusion locality, veins were formed from a single phase fluid (c. 70 mole % CO2) at 200–350°C and 1600 ± 500 bars fluid pressure. Both these vein systems are inferred to have formed between 2 and 8 km depth, near the brittle-ductile transition. Retrogressive fluid mobility and vein formation occurred throughout schist in the Priestly metamorphic complex during uplift in the latter part of the Ross Orogeny (c. 490 Ma), following near-isobaric cooling at metamorphic depths.

AbstractThe Lower Palaeozoic Bonney Pluton is a regionally extensive coarse-grained, variably megacrystic, monzodioritic to granitic body that crops out over 1000 km2 in South Victoria Land. It intruded upper amphibolite facies Koettlitz Group metasediments and interlayered orthogneisses. Magmatic fabrics are developed in the centre of the pluton by flow alignment of K-feldspars before the majority of phases had crystallized, whereas solid-state fabrics developed in the pluton margins by ductile–plastic deformation. Structures developed in the host-rocks vary around this elongate northwest–southeast-trending pluton. Upright, tight northwest–southeast-trending macroscopic folds are developed at the sides of the pluton, with axis-parallel stretching lineations and boudinage indicating strong northwest–southeast extension. Broad warps of tight macroscopic folds, and mesoscopic refolded folds, sheath folds and complicated interference patterns characterize areas at the ends of the pluton. Emplacement of the pluton involved radial expansion in a regional northeast–southwest compression, and growth predominantly in the northwest–southeast direction. Superposition of the radial expansion and regional compression resulted in an inhomogeneous strain field at a regional scale, with coaxial strain at the sides of the pluton and non-coaxial strain at the ends. Upright folds developed at the pluton's sides, and became tighter with continued coaxial deformation. Non-coaxial structures developed at the ends of the pluton and were pushed aside by the growing pluton into areas of coaxial deformation, resulting in complex folding, re-folding and sheath folds. Metamorphism of the host-rocks and migmatite development was more intense at the sides of the pluton than near the ends, possibly due to different P-T-t paths of host-rocks around syntectonic plutons.

AbstractPrecambrian continental extension is described in detail for the first time in the Victoria Land segment of the Transantarctic Mountains and is comparable with plume related intercontinental rifting of the Afar area, Africa. The Baronick Formation comprises igneous-derived conglomerate, marble and volcanic to sub-volcanic igneous layers. Volcanic and carbonate horizons were eroded in a fluvial or marine environment and provided debris for mass flow and slump deposits which formed in a marginal marine basin in the Precambrian. Clasts in these deposits include basalt, trachyte and comendite, and along with the interbedded volcanic layers of basalt, trachyte and quartz syenite, indicate proximity and contemporaneity of volcanic activity. Igneous layers and source rocks for clasts of the Baronick Formation have an enriched MORB chemistry and underwent albitization of calcic feldspar before erosion and conglomerate deposition. The Highway Suite forms a kilometre-scale body of gabbro and dolerite plugs and is interpreted as a slice of transitional continental oceanic crust. The chemistry of all igneous rocks suggests a continental rift environment and the associated sediments are consistent with such a setting. The Baronick Formation was locally intruded by sills of the Highway Suite; however, the main body of the Highway Suite was juxtaposed against the Baronick Formation during greenschist facies shearing before c. 551 Ma.

Well-preserved eclogites were found for the first time in Antarctica, at the Lanterman Range, northern Victoria Land. They are part of a mafic–ultramafic belt that lies between the Wilson Terrane, representing part of the palaeo-Pacific margin of Gondwana, and the Bowers Terrane, a Cambro-Ordovician volcanic are and related sediments, accreted to the margin during the Ross Orogeny. The eclogites formed at temperatures in the range 750–850°C and pressures above 15 kbar and subsequently experienced a decompressional path to low pressure amphibolite facies conditions. The formation and exhumation of eclogites and the attainment of the metamorphic peak in adjacent rock units is consistent with a plate convergent setting model at the palaeo-Pacific margin of Gondwana.

Highly deformed metaconglomerates, mafic to felsic in composition, characterize the eastern Lanterman Range (northern Victoria Land, Antarctica). In the literature the mafic and felsic metaconglomerates are known as Husky Conglomerate and Lanterman Conglomerate respectively. They occur in a 25 km long strip along the Lanterman Fault, which is a major tectonic boundary between the Wilson and the Bowers terranes. New field observations show that there is a gradual transition from mafic to felsic metaconglomerates: this supports a stratigraphical continuum from Husky to Lanterman Conglomerate, and indicates that they belong to the same sedimentary succession. Structural analysis indicates that Husky and Lanterman conglomerates suffered the same structural evolution. From all these evidences, there is no reason to distinguish two types of metaconglomerates, apart from the diversity in the lithological features. However the two terms “Husky Conglomerate” and “Lanterman Conglomerate” can be still used to refer to the mafic and felsic facies of the same sedimentary succession. On the basis of their lithology the Husky Conglomerate can be derived from the Glasgow volcanic arc, whereas the felsic clasts of the Lanterman Conglomerate may be derived from a continental basement below the Glasgow arc or from a continental block bounding the Bowers trough.

AbstractThe Lake Ambrose volcanic belt (LAVB) outcrops as a 45 km long northeast-trending belt of mafic and felsic volcanic rocks along the eastern side of the Victoria Lake Group in south-central Newfoundland. It comprises roughly equal proportions of mafic pillow basalt and high silica rhyolite, locally interbedded with epiclastic turbidites. Volcanic rocks have been metamorphosed in the greenschist facies and are extensively carbonatized.U-Pb (zircon) dates from rhyolite at two, widely separated localities give identical ages of 513 ± 2 Ma (Upper Cambrian), and this is interpreted as the eruptive age of the volcanic sequence. Primitive arc and low-K tholeiites can be recognized on the basis of major and trace element geochemistry, ranging from LREE-depleted to LREE-enriched. Geochemical variation between mafic volcanic types is interpreted predominantly to reflect contrasts in source characteristics and degree of partial melting; some variation within each geochemical type attributable to fractional crystallization can be recognized. Detailed examination of some samples indicates that the heavy REE and related elements have locally been mobile, probably as a result of carbonate complexing.The LAVB is the oldest well-dated island arc sequence in Newfoundland, and perhaps in the Appalachian–Caledonian Orogen. Its age requires modification of widely held models for the tectonic history of central Newfoundland. It is older than the oldest known ophiolite, demonstrating that arc volcanism was extant before the generation of the oldest known oceanic crust in this part of Iapetus. It further demonstrates that there was a maximum of approximately 30 Ma between the rift-drift transition which initiated Iapetus, and the initiation of subduction. This suggests that the oceanic sequences preserved in Newfoundland represent a series of arcs and back arc basins marginal to the main Iapetus Ocean, and brings into question whether the Appalachian accreted terranes contain any remnants of normal mid-ocean ridge type Iapetan crust.