VISIBLE LIGHT PHOTOCATALYTIC DEGRADATION OF AQUEOUS METHYLENE BLUE BY Ni/Ti LAYERED DOUBLE HYDROXIDE

Visible light responsive Ni/Ti layered double hydroxide (LDH) was synthesized by a single step hydrothermal route using commercially available Ni(NO3)2.6H2O, TiCl4 and urea which exhibited significant UV-visible absorption with a much narrower band gap (2.69 eV) that contributed significantly to the degradation of methylene blue under visible light. X-ray diffraction, Fourier transformed infrared spectroscopy (FT-IR) and N2 adsorption at 77 K were also carried out to investigate the structure and surface area of the sample. The photocatalytic degradation of aqueous methylene blue (MB) was observed due to the narrow band gap accompanied by comparatively high surface area. The photocatalytic activity improved in alkaline media particularly at pH 11 (catalyst dose 0.075 gL-1, 1 x 10-6 M MB). The catalytic activity was found to be higher than commercial catalysts like ZnO, ZnS, TiO2 and Degussa P25. Thus, this work demonstrated significantly photocatalytic properties of the Ni/Ti LDH in the field of environmental wastewater treatment

Extensive crustal extraction in Earth’s early history inferred from molybdenum isotopes

Estimates of the volume of the earliest crust based on zircon ages and radiogenic isotopes remain equivocal. Stable isotope systems, such as molybdenum, have the potential to provide further constraints but remain underused due to the lack of complementarity between mantle and crustal reservoirs. Here we present molybdenum isotope data for Archaean komatiites and Phanerozoic komatiites and picrites and demonstrate that their mantle sources all possess subchondritic signatures complementary to the superchondritic continental crust. These results confirm that the present-day degree of mantle depletion was achieved by 3.5 billion years ago and that Earth has been in a steady state with respect to molybdenum recycling. Mass balance modelling shows that this early mantle depletion requires the extraction of a far greater volume of mafic-dominated protocrust than previously thought, more than twice the volume of the continental crust today, implying rapid crustal growth and destruction in the first billion years of Earth’s history

Thermal and tectonic style of evolution of Precambrian crust

Nach aktuellem Wissensstand wird oft angenommen, dass die Plattentektonik seit ca. 3 Milliarden Jahren (Ga) aktiv ist. In der vorgelegten Arbeit wurden thermomechanische Modelle genutzt, um die chronologische Entwicklung der Plattentektonik während der Abkühlung der Erde zu untersuchen. Die Ergebnisse zeigen, dass für die heiße, junge Erde (3-2 Ga) "Peeling-off" Prozesse dominierten, welche graduell in die heutigen Mechanismen übergingen. Diese zeitliche Entwicklung hilft Beobachtungen, wie das Auftreten und die Erhaltung von felsischer Kruste oder das große Oxydationsevent, zu erklären. Das Model wurde weiterhin genutzt um petrologische und tektonische Strukturen vorherzusagen, die in Gesteinen geeigneten Alters beobachtet werden könnte. Eine petrologische Fallstudie über das "Southern Granulite Terrain" in Indien belegt, dass die vorausgesagten tektonischen Prozesse in der Natur abgelaufen sind

Time will tell: Secular change in metamorphic timescales and the tectonic implications

The pressure-temperature-time (P-T-t) evolution of metamorphic rocks is directly related to geodynamics as different tectonic settings vary in their thermal architecture. The shapes of P-T paths and thermobaric ratios (T/P) of metamorphic rocks have been extensively used to distinguish different tectonic domains. However, the role of metamorphic timescales in constraining tectonic settings remains underutilized. This is because of the poorly understood relationship between them, and the difficulty in accurately constraining the onset and end of a particular metamorphic event. Here, we show why and how the intrinsic relationship between thermal regime, rheology and rate of motion controlled by the heat, mass and momentum conservation laws translate to differences in heating, cooling, burial, exhumation rates of metamorphic rocks and thereby, to the duration of metamorphism. We compare the P-T-t paths of the orogenic metamorphic rocks of different ages and in particular, analyse their retrograde cooling rates and durations. The results show that cooling rates of the metamorphic rocks are variable but are dominantly 100 °C/Ma) during the late Neoproterozoic to Phanerozoic. To seek what controlled this secular change in metamorphic cooling rates, we use thermomechanical modelling to calculate the P-T-t paths of crustal rocks in different types of continental orogenic settings and compare them with the rock record. The modelled P-T-t paths show that lithospheric peel-back driven orogenic settings, which are postulated as an orogenic mode operating under the hotter mantle conditions of late Archean to early Proterozoic, are characterised by longer durations of metamorphism and slower cooling rates (a few 10s of °C/Ma) as compared to the modern orogenic settings (a few 100s of °C/Ma) operating under relatively colder mantle conditions. This is because peel-back orogens feature: (1) hot lithospheres with very high crustal geotherms being sustained by high mantle heat-flow and profuse magmatism, and (2) distributed deformation patterns that limit vertical extrusion (exhumation) of the metamorphic rocks along localized deformation zones and instead, trap them in the orogenic core for a long time. In contrast, modern orogens mostly involve colder lithospheres and allow rapid exhumation through localized deformation, which facilitates faster cooling of hot, exhumed metamorphic rocks in a colder ambience. Thus, we propose that the secular change in metamorphic cooling rates indicates a changing regime of orogenesis and thereby, of plate tectonics through time. Predominance of the slower metamorphic cooling rates before the Neoproterozoic indicate the occurrences of peel-back orogenesis and truncated hot (collisional) orogenesis during that time, while the appearance of faster cooling rates since the late Neoproterozoic indicates the transition to modern style of orogenesis. A transition between these orogenic styles also accounts for the prolonged longevity (>100 million years) of many Precambrian orogenic belts as compared to the Phanerozoic ones. This study underscores the strength of timescales in combination with P-T paths to distinguish tectonic settings of different styles and ages.ISSN:1342-937XISSN:1878-057

Peel-back controlled lithospheric convergence explains the secular transitions in Archean metamorphism and magmatism

ISSN:0012-821XISSN:1385-013

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north

Detection of Solar Filaments Using Suncharts from Kodaikanal Solar Observatory Archive Employing a Clustering Approach

With over 100 yr of solar observations, the Kodaikanal Solar Observatory (KoSO) is a one-of-a-kind solar data repository in the world. Among its many data catalogs, the “suncharts” at KoSO are of particular interest. These suncharts (1904–2020) are colored drawings of different solar features, such as sunspots, plages, filaments, and prominences, made on papers with a Stonyhurst latitude–longitude grid etched on them. In this paper, we analyze this unique data by first digitizing each sunchart using an industry-standard scanner and saving those digital images in a high-resolution “.tif” format. We then examine cycle 19 and cycle 20 data (two of the strongest cycles of the last century) with the aim of detecting filaments. To this end, we employed the “K-means clustering” method, and obtained different filament parameters such as position, tilt angle, length, and area. Our results show that filament length (and area) increases with latitude and the poleward migration is clearly dominated by a particular tilt sign. Lastly, we cross verified our findings with results from KoSO digitized photographic plate database for the overlapping time period and obtained a good agreement between them. This work, acting as a proof-of-the-concept, will kickstart new efforts to effectively use the entire hand-drawn series of multifeature, full-disk solar data and enable researchers to extract new sciences, such as the generation of pseudomagnetograms for the last 100 yr

The nature and evolution of the Main Central Thrust: Structural and geochronological constraints from the Sikkim Himalaya, NE India

The Main Central Thrust (MCT) is a prominent continental-scale fault within the Himalaya. Its definition has been the topic of some debate in the literature. After a brief consideration of the state of discussion to clarify the definition we use in this work, we report features from the field- to the microstructural- scale of a particularly well-exposed section in Sikkim, NE India. The nature of the protoliths as well as the overlying and underlying rocks is characterized in terms of ε-Nd. The dates of motion on the fault are constrained using U–Pb geochronology of zircon and monazite from pegmatitic dikes that cross-cut the deformation fabric. It is found that the mechanism of deformation recorded in the fault zone rocks is different compared to that found in the overlying Greater Himalayan (GH) or the underlying Lesser Himalayan (LH) rocks. The GH and LH have different protolith characteristics as well. Combined with existing data on P–T history, dates of metamorphism, and cooling- and exhumation-rates of the GH and the LH, our measurements show that major motion on this fault occurred before 20 Ma at 450–700 °C but after peak metamorphism of rocks (750–800 °C) in this zone. Isolated events occurred in this zone as late as 11 Ma, possibly in the brittle domain. This underscores the pulsed nature of movement over an extended period on such major faults, and the related difficulties in dating fault movement, determination of the rates of movement, and designating a fault plane as in- or out-of-sequence within a propagating deformation front