Timing and Petrogenesis of the Permo-Carboniferous Larvik Plutonic Complex, Oslo Rift, Norway : New Insights from U-Pb, Lu-Hf, and O Isotopes in Zircon

The Permo-Carboniferous Oslo Rift is a narrow, aborted continental rift with comparatively little extension but voluminous magmatism, developed at a Proterozoic lithospheric discontinuity. On the southern flank of the onshore part of the rift, the multiple intrusive phase Larvik plutonic complex (LPC) encompasses almost the width of the rift with a conspicuous over- to undersaturated assemblage of monzonite (larvikite, tonsbergite) and nepheline syenite (lardalite, foyaite). We present new single-crystal U-Pb-, Lu-Hf-, and O-in-zircon isotope data for the intrusive centers of the complex. U-Pb ages of slightly over- to undersaturated monzonites show a shift in igneous activity from 299 Ma on the eastern edge of the complex to 289 Ma in the west. The western part of the complex is built of two consanguineous magmatic systems with a northward shift in the locus of magmatism, from 296 to 289 Ma (undersaturated monzonite) and 296 to similar to 288 Ma (nepheline syenite). Moreover, an early oversaturated monzonite was emplaced in the eastern part of the complex at similar to 302 Ma. The Hf and O isotope composition of the monzonites and nepheline syenites shows little variation with zircon epsilon(Hf) (295 Ma) values of +5.5 to +8 and delta(18)Omicron values of +4.79 parts per thousand to +5.49 parts per thousand. No change in isotope values is observed with varying alkalinity and the Hf and O isotope compositions are interpreted as mantle source values. The source of the precursors of the monzonitic and nepheline syenitic magmas was probably a mildly depleted, sublithospheric peridotite in the lithosphere-asthenosphere boundary zone (at 3-4 GPa). Rhyolite-MELTS modeling implies polybaric fractionation of weakly alkaline basaltic melts from the source having led to an oversaturated/saturated liquid line of descent at similar to 0.5 GPa and an undersaturated one at similar to 1 GPa. Magmatism had an imperative role in the evolution of the rift by localizing strain and weakening the lithosphere along the discontinuity. A fractionating crustal melt column was tapped at varying depths in the course of advancing rupturing with no significant mixing of the over- and undersaturated melts, and magma batches were emplaced as sequential nested plutons in response to differential opening of the rift. Among continental saturated-undersaturated alkaline complexes, the LPC may be unique in the emplacement of successive magma batches across a continental rift in the direction of opening, tapping of increasingly deeper parts of the melt column with advancing rifting, and intrusion of two contemporaneous, contrasting magmatic lineages at the end of igneous activity. The marked lithospheric step at the rift locus in the Precambrian basement of southeastern Norway was probably the driving force for the inception and evolution of the Larvik magmatic system.Peer reviewe

Geochronology and Stable Isotope Analysis of Fracture-Fill and Karst Mineralization Reveal Sub-Surface Paleo-Fluid Flow and Microbial Activity of the COSC-1 Borehole, Scandinavian Caledonides

The deep biosphere hosted in fractured rocks within the upper continental crust is one of the least understood and studied ecological realms on Earth. Scarce knowledge of ancient life and paleo-fluid flow within this realm is owing to the lack of deep drilling into the crust. Here we apply microscale high spatial-resolution analytical techniques to fine-grained secondary minerals in a deep borehole (COSC-1) drilled into the Silurian-Devonian Scandinavian Caledonide mountain range in central Sweden. The aim is to detect and date signs of ancient microbial activity and low-temperature fluid circulation in micro-karsts (foliation-parallel dissolution cavities in the rock) and fractures at depth in the nappe system. Vein carbonates sampled at 684 to 2210 m show a decreased C isotope variability at depths below 1050 m; likely due to decreased influence of organic-C at great depth. Micro-karsts at 122–178 m depth feature at least two generations of secondary calcite and pyrite growth in the voids as shown by secondary ion mass spectrometry analytical transects within individual grains. The younger of these two precipitation phases shows 34S-depleted δ34Spyrite values (−19.8 ± 1.6‰ vs. Vienna-Canyon Diablo Troilite (V-CDT)) suggesting microbial sulfate reduction in situ. The calcite of this late phase can be distinguished from the older calcite by higher δ18Ocalcite values that correspond to precipitation from ambient meteoric water. The late stage calcite gave two separate laser ablation inductively coupled mass spectrometry-derived U-Pb ages (9.6 ± 1.3 Ma and 2.5 ± 0.2 Ma), marking a minimum age for widespread micro-karst formation within the nappe. Several stages of fluid flow and mineral precipitation followed karst formation; with related bacterial activity as late as the Neogene-Quaternary; in structures presently water conducting. The results show that our combined high spatial-resolution stable isotope and geochronology approach is suitable for characterizing paleo-fluid flow in micro-karst; in this case, of the crystalline crust comprising orogenic nappe units

Lunar basalt chronology, mantle differentiation and implications for determining the age of the Moon

Despite more than 40 years of studying Apollo samples, the age and early evolution of the Moon remain contentious. Following the formation of the Moon in the aftermath of a giant impact, the resulting Lunar Magma Ocean (LMO) is predicted to have generated major geochemically distinct silicate reservoirs, including the sources of lunar basalts. Samples of these basalts, therefore, provide a unique opportunity to characterize these reservoirs. However, the precise timing and extent of geochemical fractionation is poorly constrained, not least due to the difficulty in determining accurate ages and initial Pb isotopic compositions of lunar basalts. Application of an in situ ion microprobe approach to Pb isotope analysis has allowed us to obtain precise crystallization ages from six lunar basalts, typically with an uncertainty of about ±10Ma, as well as constrain their initial Pb-isotopic compositions. This has enabled construction of a two-stage model for the Pb-isotopic evolution of lunar silicate reservoirs, which necessitates the prolonged existence of high-μ reservoirs in order to explain the very radiogenic compositions of the samples. Further, once firm constraints on U and Pb partitioning behaviour are established, this model has the potential to help distinguish between conflicting estimates for the age of the Moon. Nonetheless, we are able to constrain the timing of a lunar mantle reservoir differentiation event at 4376±18Ma, which is consistent with that derived from the Sm–Nd and Lu–Hf isotopic systems, and is interpreted as an average estimate of the time at which the high-μ urKREEP reservoir was established and the Ferroan Anorthosite (FAN) suite was formed

The Formation of Highly Positive δ34S Values in Late Devonian Mudstones: Microscale Analysis of Pyrite (δ34S) and Barite (δ34S, δ18O) in the Canol Formation (Selwyn Basin, Canada)

The sulfur isotope composition of pyrite in marine sedimentary rocks is often difficult to interpret due to a lack of precise isotopic constraints for coeval sulfate. This study examines pyrite and barite in the Late Devonian Canol Formation (Selwyn Basin, Canada), which provides an archive of δ34S and δ18O values during diagenesis. Scanning electron microscopy (SEM) has been combined with microscale secondary ion mass spectrometry (SIMS) analysis (n = 1,032) of pyrite (δ34S) and barite (δ34S and δ18O) on samples collected from nine stratigraphic sections of the Canol Formation. Two paragenetic stages of pyrite and barite formation have been distinguished, both replaced by barium carbonate and feldspar. The δ34Sbarite and δ18Obarite values from all sections overlap, between +37.1‰ and +67.9‰ (median = +45.7‰) and +8.8‰ and +23.9‰ (median = +20.0‰), respectively. Barite morphologies and isotopic values are consistent with precipitation from diagenetically modified porewater sulfate (sulfate resupply << sulfate depletion) during early diagenesis. The two pyrite generations (Py-1 and Py-2) preserve distinct textures and end-member isotopic records. There is a large offset from coeval Late Devonian seawater sulfate in the δ34Spyrite values of framboidal pyrite (-29.4‰ to -9.3‰), consistent with dissimilatory microbial sulfate reduction (MSR) during early diagenesis. The Py-2 is in textural equilibrium with barite generation 2 (Brt-2) and records a broad range of more positive δ34SPy-2 values (+9.4‰ to + 44.5‰). The distinctive highly positive δ34Spyrite values developed from sulfate limited conditions around the sulfate methane transition zone (SMTZ). We propose that a combination of factors, including low sulfate concentrations, MSR, and sulfate reduction coupled to anaerobic oxidation of methane (SR-AOM), led to the formation of highly positive δ34Spyrite and δ34Sbarite values in the Canol Formation. The presence of highly positive δ34Spyrite values in other Late Devonian sedimentary units indicate that diagenetic pyrite formation at the SMTZ may be a more general feature of other Lower Paleozoic basins

Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA

Combined U-Pb, O and Hf isotope data in zircon allows discrimination between juvenile and reworked crust, and is therefore a useful tool for understanding formation and evolution of the continental crust. The crustal evolution of basement rocks in central North America (Laurentia) is poorly constrained, as it is almost entirely overlain by Palaeozoic cover. In order to improve our understanding of the evolution of this region we present U-Pb, O and Hf isotope data from zircon in drill-core samples from the subsurface basement of Ohio. The Hf isotope data suggests juvenile crust formation at similar to 1650 Ma followed by continued reworking of a single reservoir. This similar to 1650 Ma reservoir was tapped at similar to 1450 Ma during the formation of the Granite-Rhyolite Province and subsequently reworked again during the Grenvillian orogeny. The similar to 1650 Ma crust formation model age for the suite of samples along with the presence of similar to 1650 Ma magmatic rocks suggests an eastward extension of the Mazatzal Province (or Mazatzal-like crust) and makes it a possible protolith to the subsurface basement of Ohio and surrounding Mesoproterozoic (i.e. Grenville-age) rocks. The eastward extension of this similar to 1650 Ma crustal reservoir into Ohio requires a revision of the crustal boundary defined by Nd isotopic data to be located further east, now overlapping with the Grenville front magnetic lineament in Ohio. In fact, the easternmost sample in this study is derived from a more depleted reservoir. This limits the extent of >1.5 Ga basement in subsurface Ohio and constrains the location of the crustal boundary. Further, syn-orogenic magmatism at similar to 1050 Ma suggests a potential extrapolation of the Interior Magmatic Belt into Ohio. Oxygen isotopic data in zircon suggests that during Grenvillian metamorphism, zircon recrystallisation occurred in the presence of heavy delta O-18 fluids resulting in zircon with elevated delta O-18 values. (C) 2015 Elsevier B.V. All rights reserved

Towards the development of a hybrid-integrated chip interferometer for online surface profile measurements

Non-destructive testing and online measurement of surface features are pressing demands in manufacturing. Thus optical techniques are gaining importance for characterization of complex engineering surfaces. Harnessing integrated optics for miniaturization of interferometry systems onto a silicon wafer and incorporating a compact optical probe would enable the development of a handheld sensor for embedded metrology applications. In this work, we present the progress in the development of a hybrid photonics based metrology sensor device for online surface profile measurements. The measurement principle along with test and measurement results of individual components has been presented. For non-contact measurement, a spectrally encoded lateral scanning probe based on the laser scanning microscopy has been developed to provide fast measurement with lateral resolution limited to the diffraction limit. The probe demonstrates a lateral resolution of ∼3.6 μm while high axial resolution (sub-nanometre) is inherently achieved by interferometry. Further the performance of the hybrid tuneable laser and the scanning probe was evaluated by measuring a standard step height sample of 100 nm

Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet

The Kung Co rift is an approximately NNW striking, WSW dipping normal fault exposed in southern Tibet and is part of an extensive network of active approximately NS striking normal faults exposed across the Tibetan Plateau. Detailed new and published (U-Th)/He zircon and apatite thermochronometric data from the footwall of the early Miocene Kung Co granite provide constraints on the middle Miocene to present-day exhumation history of the footwall to the Kung Co fault. Inverse modeling of thermochronometric data yield age patterns that are interpreted as indicating (1) initiation of normal fault slip at ∼12–13 Ma and rapid exhumation of the footwall between ∼13 and 10 Ma, (2) acceleration of normal fault slip at rates of 21.9–6.9 mm/yr at ∼10 Ma, (3) rapid thermal reequilibration between 10 and 9 Ma, and (4) slow exhumation and/or quiescence from ∼9 Ma to the present day. Hanging glacial valleys in the footwall and fault scarps that cut late Quaternary till and moraine deposits indicate that fault slip continues today. Middle to late Miocene initiation of extension across the Kung Co rift is broadly the same as the documented initiation of EW extension across the south central Tibetan Plateau. Eastward flow of middle or lower crust from beneath Tibet accommodated by northward underthrusting of Indian crust beneath Tibet provides a plausible explanation for the onset of EW extension across the Tibetan Plateau

A cross sectional study of water quality from dental unit water lines in dental practices in the West of Scotland

OBJECTIVE: To determine the microbiological quality of water from dental units in a general practice setting and current practice for disinfection of units. DESIGN: A cross-sectional study of the water quality from 40 dental units in 39 general practices and a questionnaire of the disinfection protocols used in those practices. SETTING: NHS practices in primarydental care. SUBJECTS: Thirty-nine general practices from the West of Scotland. METHODS: Water samples were collected on two separate occasions from dental units and analysed for microbiological quality by the total viable count (TVC) method. Water specimens were collected from the triple syringe, high speed outlet, cup filler and surgery tap. Each participating practitioner was asked to complete a questionnaire. Results Microbial contamination was highest from the high speed outlet followed by the triple syringe and cup filler. On average, the TVC counts from the high speed water lines at 37 degrees C and for the high speed lines, triple syringe and cup filler at 22 degrees C were significantly higher than that from the control tap water specimens. The study included units from 11 different manufacturers with ages ranging from under one year to over eight years. The age of the dental unit analysed did not appear to influence the level of microbial contamination. Five of the practices surveyed used disinfectants to clean the dental units but these had no significant effect on the microbiological quality of the water. The majority of dental units (25 out of 40) were never flushed with water between patients. A number of different non-sterile irrigants were used for surgical procedures. CONCLUSION: The microbiological quality of water from dental units in general dental practice is poor compared with that from drinking water sources. Suitable sterile irrigants should be used for surgical procedures in dental practice. Further work is required for pragmatic decontamination regimens of dental unit water lines in a general dental practice setting