Search

We report composition and age data from a restricted <370 km2, volcano-sedimentary basin beneath Mesozoic cover to the northwest of the Flinders Ranges, South Australia. This volcano-sedimentary basin comprises two components: a sedimentary sequence that includes shales, siltstones and sandstones, and a basalt–sedimentary member. Together, these components are defined as the Ooloo Hill Formation. Whole-rock K–Ar geochronology for five basalt samples yields a preferred mean K–Ar age of 392 ± 8 Ma. Two samples of detrital zircons from the sedimentary rock yield SHRIMP U–Pb maximum depositional ages of ca 527 and 510 Ma. These ages are significant, as they rule out a Neoproterozoic age for the sedimentary basin and demonstrate that this basin is not part of the Adelaide Superbasin. Lower eruptive sequences are calc-alkaline and mafic in composition (SiO2 = 46.1–47.8 wt%, Na2O + K2O = 3.7–6.1 wt%, MgO = 6.85–8.37 wt%, Mg# = 57–65 and εNd(390 Ma) = 3.4–4.0) and may represent two small-scale melting events from compositionally distinct mantle reservoirs. The uppermost eruptive sequence is tholeiitic andesite (SiO2 = 51.6 wt%, Na2O + K2O = 8.1 wt%, MgO = 2.2 wt%, Mg# = 27 and εNd(390 Ma) = 3.0) and displays geochemical affinity to the first two eruptive sequences, possibly representing a differentiated magma from a similar source region. Incompatible trace-element ratios and isotopic compositions suggest the source was a heterogeneous oceanic island basalt-like parent magma derived from partial melting of the asthenospheric mantle. We envisage decompressional melting was linked to large-scale tectonic processes inboard of the Tasman Orogen, with magma ascent facilitated by crustal faulting. First record of a mid-Devonian intracontinental volcano-sedimentary basin in South Australia. Basalts have an oceanic island basalt-like mantle source that represents at least two small-scale melting events from compositionally distinct mantle reservoirs. A localised mid-Devonian backarc basin or transpressional/transtensional basin linked to intracontinental faulting formed inboard of the Tasman Orogen. [ABSTRACT FROM AUTHOR]

This study investigates the age and composition of a suite of mafic dykes in the southeastern Gawler Craton. Mafic dykes intrude the gneissic fabric of the ca 1850 Ma Donington Suite and were previously interpreted to have been emplaced at ca 1845 Ma. However, sensitive high-resolution ion microprobe U–Pb dating of zircon within one of these mafic dykes shows it was emplaced at 1564 ± 4 Ma. The sampled dyke also contains a population of inherited zircon cores with an age of 1770 ± 6 Ma, and one grain with an age of ca 1860 Ma, likely derived from country rock. Whole-rock geochemistry from this dyke and nearby dykes with similar structural and mineralogical features show that there is a suite of dykes in the region with gabbroic, low SiO2 and TiO2 contents and tholeiitic characteristics. The dykes are enriched in Ba, K and Rb, with low to moderate MgO, Ni and Cr contents, and moderate light rare earth element enrichment. Negative Nb and Ta anomalies with subtle negative Ti anomalies suggest some interaction with continental crust. Sm–Nd isotopic data have εNd(1560 Ma) between −6.8 and −2.9, and depleted mantle model ages >2.5 Ga. Th/Nb ratios are 0.21–0.73 consistent with a metasomatised, subduction modified lithospheric mantle source. The relatively primitive nature of the tholeiites suggests the crustal-like signatures are inherited from the source region, which likely represents an enriched continental lithospheric mantle in the eastern Gawler Craton. This ca 1564 Ma mafic magmatism is newly named the Daly Head Metadolerite. In addition, narrow high-strain zones overprint the dated mafic dyke and locally the Donington Suite wall rocks. A syn-kinematic granitic dyke intrusion within one high-strain zone has been dated via laser ablation-inductively coupled plasma mass spectrometry U–Pb zircon methods and was emplaced at ca 1555 Ma. This localised ca 1555 Ma deformation is a previously unrecognised tectonic event in the southern Gawler Craton. This study adds to the growing database showing magmatism and deformation in the Gawler Craton continued after the voluminous Gawler Range Volcanics and Hiltaba Suite magmatism (ca 1596–1575 Ma). These younger tectono-magmatic events typically occur around the margins of the Gawler Craton, suggesting the internal 'core' of the craton may have been substantially less fertile for melting during these younger thermal/structural events, likely because of the high-temperature nature of the early Mesoproterozoic Gawler Range Volcanics and Hiltaba Suite magmatism. Geochronology shows mafic dykes in southeastern Gawler Craton emplaced at 1564 ± 4 Ma. Mafic dykes are tholeiitic, derived from a metasomatised, subduction modified lithospheric mantle source. Narrow high-strain zones overprint the dated mafic dyke and contain syn-kinematic granitic dyke dated at ca 1555 Ma. Localisation of post-ca 1575 Ma tectono-magmatic events occur around margins of the craton, reflecting reduced melt fertility in the centre owing to previous high-temperature events. [ABSTRACT FROM AUTHOR]

Reconstructing ancient tectonic environments is inherently difficult and requires the integration of many datasets. Here we attempt to reconstruct the tectonic setting of a Proterozoic magmatic rock suite from the Archean to Mesoproterozoic Gawler Craton, South Australia. We evaluate previous models of subduction or non-subduction tectonics for the St Peter Suite through field observations coupled with geochemical and isotopic data. Field observations indicate the presence of mafic magma chambers, felsic plutons and zones of mixing represented by multiphase plutons and zones of magma transfer. Syn-magmatic and solid-state deformation fabrics suggest magmatism was associated with a compressional tectonic regime, at least during some stages of magmatism. Zircon U–Pb geochronology suggests magmatism occurred between ca 1633 and ca 1608 Ma, an interval of ca 25 Myr. Mafic rocks are tholeiitic and enrichment in high field strength and light rare earth elements supports a modified mantle source region. Mafic rocks have εNd1620 Ma values around 0, and zircon εHf(t) values around 4, supporting minor crustal contamination. Felsic plutons have a geochemical signature similar to average continental crust, εNd1620 Ma between –3.7 and 0.4, and zircon Lu–Hf isotopic compositions that yield to εHf(t) values between –1.8 and 7.7, suggesting they were derived from fractionation of enriched tholeiitic parent magmas. A model for the formation of the St Peter Suite that is most consistent with the available data is one that places the magmatism in a broadly continental magmatic arc setting, albeit one in which little or no Archean crust was involved. Potentially this magmatic arc could have been built on a thinned, or hyper-extended continental margin. The integration of structural, geochemical and isotopic constraints has provided a more holistic view of the St Peter Suite petrogenesis than previously available. Evaluation of models of subduction vs non-subduction tectonics for formation of Paleoproterozoic magmatic suite Evidence for syn-magmatic compression and mafic–felsic magma mingling Isotopically juvenile (Nd--Sr--Hf) with mantle-like zircon δ18O values Continental arc setting proposed, possibly on hyper-extended continental margin [ABSTRACT FROM AUTHOR]

The Olympic Cu–Au Province, Gawler Craton, is host to the Olympic Dam and Prominent Hill iron oxide–copper–gold (IOCG) deposits. Both of these deposits and the region between the two are covered by Neoproterozoic to Cenozoic sediment, making inferences about prospectivity in this portion of the Olympic Domain reliant on geophysical interpretation and sparse drill hole information. We present new U–Pb zircon sensitive high resolution ion microprobe (SHRIMP) dates from two basement intersecting drill holes in the region between Olympic Dam and Prominent Hill that show bimodal volcanism occurred at 2555 ± 5 Ma, and was followed by intrusion of tonalite at 2529 ± 6 Ma. Laser40Ar/39Ar dating of biotite and muscovite from the tonalite yields ages aroundca2000 Ma, consistent with slow cooling trends observed in Archean rocks elsewhere in the northern Gawler Craton. Step heating experiments on K-feldspar from the same tonalite yields an age spectrum with older ages around 1740 Ma from the highest temperature steps becoming progressively younger to a minimum of 1565 Ma in the lowest temperature heating steps; this is consistent with either Paleoproterozic cooling to final closure of K-feldspar by 1565 Ma or a reheating event atca1565 Ma, with the latter more likely, given the evidence for sub-solidus alteration of the K-feldspar. Sericite within hematite–sericite–chlorite altered portions of the tonalite yield a poorly defined age ofca1.6 Ga. Taken together the40Ar/39Ar data providing evidence for a fluid event affecting this region between Olympic Dam and Prominent Hill during the early Mesoproterozoic. Low temperature quartz–carbonate–adularia veins occur in <10 cm wide fractures within basalt in one drill hole in this region. Adularia from these veins yields40Ar/39Ar ages that span fromca1.3–1.1 Ga. This age range is interpreted to approximate either the timing of adularia formation during a hydrothermal event or the timing of resetting of the40Ar/39Ar systematics within the adularia as a result of fluid flow in this sample. This is evidence for a mid-Mesoproterozoic fluid event in the Gawler Craton and necessitates a reconsideration of the long-term stability of the craton, as it appears to have been affected, at least locally, by fluid flow related to a much larger event within the Australian continent, the Musgrave Orogeny. [ABSTRACT FROM AUTHOR]

SHRIMP U–Pb zircon data obtained from a magnetite gneiss deposit in the southeast Gawler Craton indicate that the protoliths were deposited between 1750 and 1735 Ma. Previously, these iron-rich gneisses were thought to have been a metamorphosed banded iron formation and part of the Neoarchean to early Paleoproterozoic Sleaford Complex. Detrital zircon data provide maximum depositional ages between 1765 Ma and 1740 Ma, with ϵNd(1750)values between –4.6 and –3.3. Metamorphic zircon ages are 1735–1725 Ma, indicating that the magnetite gneiss was formed during the 1730–1690 Ma Kimban Orogeny. The pelitic mineralogy of the magnetite gneiss and presence of detrital zircon demonstrate that the protoliths were not a pure chemical sediment. Correlation with the greenschist facies Price Metasediments in the southern Gawler Craton suggests a series of iron-bearing basins were developed prior to the onset of the Kimban Orogeny and suggest that metamorphism played a role in ore formation. [ABSTRACT FROM AUTHOR]

Integrated structural, metamorphic and geochronological data demonstrate the existence of a contractional orogen preserved in the ca 1850 Ma Donington Suite batholith along the eastern margin of the Gawler Craton, South Australia. The earliest structures are a pervasive gneissic foliation developed in the Donington Suite and interleaved metasedimentary rocks. This has been overprinted by isoclinal and non-cylindrical folding, and zones of pervasive non-coaxial shear with north-directed transport, suggesting that deformation was the result of orogenic contraction. SHRIMP U - Pb zircon data indicate that a syn-contractional granitic dyke was emplaced at 1846 ± 4 Ma. Overprinting the contractional structures are a series of discrete, migmatitic high-strain zones that show a normal geometry with a component of oblique dextral shear. U - Pb zircon data from a weakly foliated microgranite in one such shear zone give an emplacement age of 1843 ± 5 Ma. Rare aluminous metasedimentary rocks in the belt preserve a granulite-grade assemblage of garnet + biotite + plagioclase + K-feldspar + silicate melt that formed at ∼600 MPa and ∼750°C. Peak metamorphic garnets are partially replaced by biotite + sillimanite+ cordierite assemblages suggesting post-thermal peak cooling and decompression, and are indicative of a clockwise P - T evolution. Chemical U - Th - Pb electron microprobe ages from monazites in retrograde biotite yield a minimum estimate for the timing of retrogression of ca 1830 Ma, indicating that decompression may be linked to the development of the broadly extensional shear zones and that the clockwise P - T path occurred during a single tectonothermal cycle. We define this ca 1850 Ma phase of crustal evolution in the eastern Gawler Craton as the Cornian Orogeny. [ABSTRACT FROM AUTHOR]

The Hill End Trough of central-western New South Wales was an elongate deep marine basin that existed in the Lachlan Fold Belt from the early Late Silurian to late Early Devonian. It is represented by a regionally extensive, unfossiliferous sequence of interbedded turbidites and hemipelagites of substantially silicic volcanic derivation, which passes laterally into contemporaneous shallow-water sedimentary rocks. The Turondale and Merrions Formations of the Lower Devonian Crudine Group are two prominent volcanogenic formations in the predominantly sedimentary trough sequence. They contain a range of primary and resedimented volcanic facies suitable for U–Pb dating. These include widespread subaqueous silicic lavas and/or lava cryptodomes, and thick sequences of crystal-rich volcaniclastic sandstone emplaced by a succession of mass-flows that were generated by interaction between contemporaneous subaerial pyroclastic flows and the sea. Ion microprobe dating of the two volcanogenic formations by means of the commonly used SL 13 zircon standard yields ages ranging between 411.3 ± 5.1 and 404.8 ± 4.8 Ma. Normalising the data against a different zircon standard (QGNG) yields preferred slightly older mean ages that range between 413.4 ± 6.6 and 407.1 ± 6.9 Ma. These ages broadly approximate the Early Devonian age that has been historically associated with the Crudine Group. However, the biostratigraphically inferred late Lochkovian – early Emsian (mid-Early Devonian) age for the Merrions Formation is inconsistent with the current Australian Phanerozoic Timescale, which assigns an age of 410 Ma to the Silurian–Devonian boundary, and ages of 404.5 Ma and 395.5 Ma to the base and top of the Pragian, respectively. There is, however, good agreement if the new ages are compared with the most recently published revision of the Devonian time-scale. This suggests that the Early Devonian stage boundaries of the Australian Phanerozoic... [ABSTRACT FROM AUTHOR]

Development and use of on-farm assays to detect antimicrobial residues in milk is important to reduce the risk of violative residues in marketed milk. The objective of this study was to evaluate the effectiveness of a lateral-flow immunodiagnostic assay (BetaStar Plus, Neogen Corp., Lansing, MI) in detecting ceftiofur residues in milk from individual cows treated for mastitis. This assay is currently approved by the US Federal Drug Administration (FDA) for detecting β-lactam residues in commingled milk. Forty-five dairy cows with clinical mastitis from 4 dairy farms were enrolled and treated intramammary with 125 mg of ceftiofur hydrochloride (Spectramast LC, Zoetis, Madison, NJ) according to the manufacturer's label recommendation. Composite milk samples were collected (A) before first intramammary antimicrobial treatment, (B) before the last intramammary antimicrobial treatment, (C) the last milking of the product-labeled milk withhold, (D) the first milking after the product-labeled milk withhold had been met, and (E) 72 h after the product-labeled milk withhold had been met. Samples were tested using the BetaStar Plus assay within 48 h of collection. Parallel samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and for somatic cell count and milk components. The BetaStar Plus assay identified 6.7, 60.0, 46.7, 22.2, and 6.7% positive samples at each of the respective time points. The assay had sensitivity and specificity of 100 and 84.7%, respectively, compared with liquid chromatography-tandem mass spectrometry analysis using FDA published residue tolerance levels for ceftiofur (or ceftiofur metabolites) as a threshold. The BetaStar Plus assay could be useful for detecting ceftiofur residues in milk from individual cows following intramammary treatment for mastitis before the milk is shipped for processing. [ABSTRACT FROM AUTHOR]

Background: A meta-analysis of randomized trials has shown a significant reduction of mortality rate in patients receiving aspirin for secondary prevention after acute myocardial infarction (AMI). However, a significant number of patients do not receive aspirin after AMI. Little is known about why aspirin is withheld or the long-term outcome of these patients today., Methods: The Maximal Individual Therapy in Acute Myocardial Infarction (MITRA) registry is a multicenter registry of patients with AMI in Germany., Results: Of 4902 patients, 509 (10%) did not receive aspirin at the time of discharge from the hospital. The mean follow-up period for these patients was 17 months. Relative contraindications to aspirin were significantly associated with the withholding of aspirin (in-hospital bleeding: odds ratio [OR], 3.56; 95% CI, 1.86-6.80; history of peptic ulcer: OR, 2.49; 95% CI, 1.62-3.83). Absolute contraindications to aspirin were rare (2.2%). Other medications of proven benefit were also given less often in these patients (beta-blockers: 49.0% vs 61.9%, P <.001; angiotensin-converting enzyme inhibitors: 65.6% vs 70.2%, P =.06; statins: 12.2% vs 15.1%, P =.10). Patients who were not given aspirin were at high risk for vascular events. They were more likely to have a history of prior AMI (OR, 1.34; 95% CI, 1.02-1.79), were in critical clinical condition at admission more often (cardiogenic shock: OR, 1.98; 95% CI, 1.09-3.56; overt heart failure: OR, 1.6; 95% CI, 1.05-2.3), and received acute revascularization less often (OR, 1.32; 95% CI, 1.05-1.67). The 1-year mortality was 2-times higher in patients who did not receive aspirin than in patients who did receive aspirin (16.5% vs 8.3%, P <.001). A significant association of withheld aspirin at discharge with a higher long-term mortality rate was confirmed with multivariate analysis (OR, 1.62; 95% CI, 1.15-2.29)., Conclusions: Ten percent of patients who sustained an AMI did not receive aspirin at the time of hospital discharge. Most of these patients were at high risk for cardiovascular events. Withheld aspirin was significantly associated with higher mortality rate during follow up.

Objectives: We describe the baseline characteristics and clinical course of patients who had an acute myocardial infarction (AMI) during their hospital stay., Background: In comparison with patients who had an AMI outside of the hospital (prehospital AMI), the data on patients who had an AMI in the hospital are poorly described., Methods: Patients with an in-hospital AMI were prospectively registered in the Southwest German Maximal Individual TheRapy in Acute myocardial infarction (MITRA) study and compared with patients with prehospital AMI., Results: Of 5,888 patients with AMI, 403 patients (6.8%) had an in-hospital AMI. These patients were older, more often male and sicker as compared with the patients with a prehospital AMI. They also showed a higher prevalence of concomitant diseases, such as arterial hypertension, diabetes mellitus, renal insufficiency and contraindications for thrombolysis. There was no significant difference regarding the use of reperfusion therapy, either thrombolysis (in-hospital AMI 44.2% vs. prehospital AMI 49.1%; odds ratio [OR] 0.86, 95% confidence interval [CI] 0.70 to 1.05) or primary angioplasty (9.9% vs. 8.2%; OR 1.23, 95% CI 0.88 to 1.73), or a combination of both, between the two groups. The interval from symptom onset to the start of treatment in patients receiving reperfusion therapy was 55 min for patients with an in-hospital AMI versus 180 min for patients with a prehospital AMI (p = 0.001). In-hospital death occurred in 110 (27.3%) of 403 patients with an in-hospital versus 762 (13.9%) of 5,485 patients with a prehospital AMI (OR 2.33, 95% CI 1.85 to 2.94). This was confirmed by logistic regression analysis after adjusting for other confounding variables (OR 1.67, 95% CI 1.23 to 2.24)., Conclusions: In-hospital AMI occurred in 6.8% of patients. Time to intervention was shorter; however, the use of reperfusion therapy for in-hospital AMI was not different from that for prehospital AMI. In particular, primary angioplasty seems to be underused in these patients. This, as well as the selection of patients, may result in the high hospital mortality rate of 27.3%.