Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia

This paper reports geophysical anomalies and intra-crystalline quartz lamellae in drill cores from the Warburton West Basin overlapping the border of South Australia and the Northern Territory. The pre-Upper Carboniferous ~450×300km-large Warburton Basin, north-eastern South Australia, is marked by distinct eastern and western magnetic, gravity and low-velocity seismic tomography anomalies. Quartz grains from arenite core samples contain intra-crystalline lamellae in carbonate-quartz veins and in clastic grains, similar to those reported earlier from arenites, volcanic rocks and granites from the Warburton East Basin. Universal Stage measurements of quartz lamellae in both sub-basins define Miller-Bravais indices of {10-12} and {10-13}. In-situ quartz lamellae occur only in pre-Late Carboniferous rocks whereas lamellae-bearing clastic quartz grains occur in both pre-Late Carboniferous and post-Late Carboniferous rocks - the latter likely redeposited from the pre-Late Carboniferous basement. Quartz lamellae in clastic quartz grains are mostly curved and bent either due to tectonic deformation or to re-deformation of impact-generated planar features during crustal rebound or/and post-impact tectonic deformation. Seismic tomography low-velocity anomalies in both Warburton West Basin and Warburton East Basin suggest fracturing of the crust to depths of more than 20km. Geophysical modelling of the Cooper Basin, which overlies the eastern Warburton East Basin, suggests existence of a body of high-density (~2.9-3.0gr/cm) and high magnetic susceptibility (SI~0.012-0.037) at a depth of ~6-10km at the centre of the anomalies. In the Warburton West Basin a large magnetic body of SI=0.030 is modelled below ~10km, with a large positive gravity anomaly offset to the north of the magnetic anomaly. In both the Warburton East and Warburton West the deep crustal fracturing suggested by the low velocity seismic tomography complicates interpretations of the gravity data. Universal Stage measurements of quartz lamellae suggest presence of both planar deformation features of shock metamorphic derivation and deformed planar lamella. The latter may be attributed either to re-deformation of impact-generated lamella, impact rebound deformation or/and post impact tectonic deformation. The magnetic anomalies in the Warburton East and West sub-basins are interpreted in terms of (1) presence of deep seated central mafic bodies; (2) deep crustal fracturing and (3) removal of Devonian and Carboniferous strata associated with rebound of a central uplift consequent on large asteroid impact. Further tests of the Warburton structures require deep crustal seismic transects

Great Artesian Basin authigenic carbonates as natural analogues for mineralisation trapping

This project is the first to comprehensively investigate the controls on the formation of authigenic carbonates in low salinity, siliciclastic aquifers of the Great Artesian Basin. These processes are\ua0natural analogues for mineralisation trapping of CO2 during geo-sequestration. Calcite is the main carbonate present. Analyses included elemental composition, C and O stable isotopes, fluid inclusion analyses including\ua0gas isotopes, SEM-EDS and QEMSCAN, and X-ray micro-CT scanning.\ua0The samples reflect\ua0a variety of fluid origins, compositions, and temperatures of precipitation.\ua0Differentiating between carbonate formed via different mechanisms, and determining controls on the extent of authigenic carbonate formation, could lead to options for engineered accelerated mineralisation in reservoirs

Quantifying defects in graphene via Raman spectroscopy at different excitation energies.

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities, for a given defect density, strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an interdefect distance ∼3 nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity

Role of fluid and melt inclusion studies in geologic research

Although fluid inclusions were apparently known to early naturalists, actual research on fluid and melt inclusions began only in the mid‐1800s and grew very slowly for the next 100 years. R ussian scientists began systematic studies of inclusions in the 1930s, but it was not until about 1960 that publications mentioning or using fluid inclusions began to increase from a few each year to the present annual level of about 700. Early research focused on ore deposits, first on temperatures and salinities of ore fluids and then on their stable isotopic and major element compositions. Later work extended to fluids in sedimentary and metamorphic environments. Publications using or mentioning melt inclusions only began to increase in number in about 1980 and have grown to today's level of about 200 per year. Early work on melt inclusions focused on igneous rocks with an emphasis on immiscibility and volatile elements and then on rare elements. Recent research on both fluid and melt inclusions has taken advantage of single inclusion analytical methods to investigate speciation and partitioning in both natural and experimental magmatic and aqueous systems. Observations on fluid and melt inclusions began in the mid‐1800s, but research publications were rare until about 1960 for fluid inclusions and 1980 for melt inclusions. Currently, about 700 reports mentioning fluid inclusions and another 200 mentioning melt inclusions are published each year. Research has evolved from measurements on individual inclusions to analysis of bulk inclusions to present efforts to analyze individual natural and experimental inclusions and derive geochemical data and models from them.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100331/1/gfl12055.pd

Extreme isotopologue disequilibrium in molecular SIMS species during SHRIMP geochronology

The current limitation in the accuracy and precision of inter-element analysis in secondary ion mass spectrometry (SIMS) is the ability to find measurable quantities that allow relative differences in ionization and transmission efficiency of secondary ions to be normalized. In uranium-thorium-lead geochronology, the ability to make these corrections, or "calibrate" the data, results in an accuracy limit of approximately 1%. This study looks at the ionization of uranium and thorium oxide species, which are traditionally used in U-Pb calibration, to explore the conditions under which isotopologues, or molecular species whose composition differs only in the isotopic composition of one or more atoms in the molecule, remain in or deviate from equilibrium. Isotopologue deficits of up to 0.2 (200‰) below ideal mixing are observed in UO2+ species during SIMS gechronological analyses using the SHRIMP IIe SIMS instrument. These are identified by bombarding natural U-bearing minerals with an 18O2- primary beam. The large anomalies are associated with repeat analyses down a single SIMS sputtering crater (Compston et al., 1984), analysis of high-uranium, radiation-damaged zircon, and analysis of baddeleyite. Analysis of zircon under routine conditions yield UO2+ isotopologue anomalies generally within a few percent of equilibrium. The conditions under which the isotopologue anomalies are observed are also conditions in which the UOx-based corrections, or calibration, for relative U vs. Pb ionization efficiencies fail. The existence of these isotopologue anomalies suggest that failure of the various UOx species to equilibrate with each other is the rea son that none of them will successfully correct the U/Pb ratio. No simple isotopologue-based correction is apparent. However, isotopologue disequilibrium appears to be a more sensitive tool for detecting high-U calibration breakdowns than Raman spectroscopy, which showed sharper peaks for ~ 37Ma high-uranium zircons than for reference zircons OG1 and Temora. U-Th-Sm/He ages were determined for aliquots of reference zircons OG1 (755±71Ma) and Temora (323±43Ma), suggesting that the broader Raman lines for the Temora reference zircons may be due to something other than accumulated radiation damage. Isotopologue abundances for UO+ and ThO+ and their energy spectra are consistent with most or all molecular species being the product of atomic recombination when the primary beam impact energy is greater than 5.7keV. This, in addition to the large UO2+ instrumentally generated isotopologue disequilibria, suggests that any attempts to use SIMS to detect naturally occurring isotopologue deviations could be tricky

Magmatic Hydrothermal Fluids at the Sedimentary Rock-hosted, Intrusion-related Telfer Gold-Copper Deposit, Paterson Orogen, Western Australia: P-T-X Constraints on the Ore Forming Fluids

The Neoproterozoic Telfer deposit, one of Australia’s largest gold-copper deposits is located in the Paterson Orogen. Several highly differentiated calc-alkaline to alkali-calcic peraluminous granites intruded the metasedimentary rocks near (5-20 km) Telfer contemporaneous with structurally controlled gold-copper mineralization. Fluid inclusion assemblages with different fluid inclusion types were identified in samples from a range of different vein types. These inclusion types range from three phase aqueous Laq+Vaq+Shalite, high salinity (≤ 50 wt % NaCl equiv), high temperature (≤ 460°C) inclusions to two phase aqueous or two phase aqueous carbonic, low to moderate salinity (2 - 22 wt % NaCl equiv.), moderate to high temperature (≤ 480°C) fluid inclusions. Fluid inclusion trapping mechanisms, and interpreted precipitation mechanisms for gold and copper include: (1) adiabatic cooling between 450 and 200°C in all veins, and (2) locally, fluid phase separation at around 300°C. The trapping pressure of fluid inclusion assemblages trapped during phase immiscibility was calculated to be approximately 1.5 kbars. For fluid inclusion assemblages that lack evidence for phase immiscibility a pressure, at the temperature of final homogenization, of up to 3 kbars was calculated. This high pressure value is interpreted to be related to local fluid overpressure, as a consequence of fault zone movement, in faults and fractures that localized gold at Telfer. Phase immiscibility and gold precipitation was induced during sharp pressure decrease accompanying fault zone movement. In situ laser ICP-MS analyses of fluid inclusions revealed high trace element contents in all fluid inclusion assemblages. Manganese/Fe ratios of 0.24 is observed. Given the high temperatures and salinities of up to 480°C and 42 wt % NaCl equiv., Au and Cu were likely transported as chloride complexes. This interpretation is supported by the observation that the highest base metal contents occurs in the highest salinity fluid inclusion. Potassium/Ca ratios of >1 in most assemblages, the high homogenization temperatures (≤ 480°C) in many fluid inclusion assemblages, and the high trace element contents (e.g., Fe, Mg, K, Na) in most of the fluid inclusion assemblages is compatible with involvement of a magmatic hydrothermal fluid during gold-copper mineralization. This fluid was probably derived from the coeval granites in the Telfer area and, thus Telfer is interpreted to be a distal, intrusion-related, metasedimentary rock hosted, gold-copper deposit type. Because of all the arguments mentioned above, Telfer can best be described as an unique intrusion-related, structurally controlled, metasedimentary rock hosted, gold-copper deposit