Disturbed Spectra Research Articles

Combined lipid-lowering therapy from standpoint of modern guidelines for management of dyslipidaemias

Coronary artery disease (CAD) remains the leading cause of death, and its prevalence is projected to increase in the near future. Dyslipidemia is one of the most important risk factors for CAD, and special attention is currently being paid to improving approaches to its correction. In the new revision of the Russian Guidelines for the Management of Patients with dyslipidemia (2020), priorities are given to high-intensity statin therapy: new more strict target levels of low-density lipoprotein cholesterol (LDL–C) are introduced. Experts also emphasize the important role of the cholesterol fraction of non-high-density lipoproteins (non-HDL–C), primarily triglycerides, and introduce their target levels. The concept of residual risk, which remains despite effective statin therapy and achievement of the target level of LDL–C, is closely related to non-HDL–C. Here, hypertriglyceridemia is of crucial importance, contributing to an increased risk of coronary heart disease and cardiovascular mortality. Therefore, combined lipid-lowering therapy in the form of a combination of high-intensity statin and fenofibrate is an effective approach to significantly improve the prognosis and reduce the residual risk. According to research data, rosuvastatin provides a reduction in LDL–C by ≥ 50 %, has a wide range of pleiotropic effects in combination with an optimal safety profile. Fenofibrate allows you to effectively reduce the level of triglycerides and implements additional protective effects on the cardiovascular system. The logical continuation of the principle of combined lipid-lowering therapy was the appearance of a fixed combination (FC) of rosuvastatin and fenofibrate, which already has its own evidence base of studies indicating a complex and complementary effect on the disturbed blood lipid spectrum, a good safety profile of therapy, and the form of ‘single-pill’ significantly increases patients adherence to treatment. It can be expected that the widespread use of rosuvastatin and fenofibrate in clinical practice will effectively reduce the residual cardiovascular risk and thus provide an improved prognosis for patients.

MO247NOVEL DIAGNOSTIC AND THERAPEUTIC TECHNIQUES REVEAL CHANGED METABOLOMIC PROFILE IN RECURRENT FOCAL SEGMENTAL GLOMERULOSCLEROSIS*

Abstract Background and Aims Idiopathic forms of Focal Segmental Glomerulosclerosis (FSGS) are caused by circulating permeability factors, which can lead early recurrence of FSGS and kidney failure after kidney transplantation. In the past three decades, many research endeavors were undertaken to identify these unknown factors. Even though some potential candidates have been recently discussed in the literature, “the” actual factor remains elusive. Therefore, there is an increased demand in FSGS research for the use of novel technologies that can allow us to study FSGS from a yet unexplored angle. Method We used novel treatment options, a personalized in vitro and in vivo assay as well as Raman spectroscopy and mass spectrometry for recurrent FSGS. Results Here, we report the successful treatment of recurrent FSGS in a patient after living related kidney transplantation by removal of circulating factors with CytoSorb apheresis (Fig. 1). Interestingly, the classical published circulating factors were all in normal range in this patient but early disease recurrence in the transplant kidney and immediate response to CytoSorb apheresis were still suggestive for pathogenic circulating factors. To proof the functional effects of the patient’s serum on podocytes and the glomerular filtration barrier we used a podocyte cell culture model and a proteinuria model in zebrafish to detect pathogenic effects on the podocyte’s actin cytoskeleton inducing a functional phenotype (Fig. 2, Fig. 3). We then performed Raman spectroscopy in the <50 kD serum fraction (Fig. 4), on cultured podocytes treated with the FSGS serum (Fig. 5), and in kidney biopsies of the same patient at the time of transplantation and at the time of disease recurrence (Fig. 6). The analysis revealed metabolomic changes in podocytes induced by the FSGS serum as well as in focal glomerular and parietal epithelial cell regions in the FSGS biopsy. Several disturbed Raman spectra were identified in the fractionated serum and metabolome analysis by mass spectrometry detected lipid profiles in the FSGS serum, which corresponded to disturbances in the Raman spectra. Conclusion Our novel innovative analysis reveals changed lipid metabolome profiles associated with idiopathic FSGS that might reflect a new subtype of the disease.

Mineralization proximal to the final Nuna suture in northeastern Australia

Mineralization along continental suture zones is facilitated through the frequent presence of pathways from fertile mantle source regions to crustal repositories. Due to their inherent rheological weakness, these suture zones are often concealed, which hinders surface-based observations. Here, we use zircon U-Pb and sericite 40Ar/39Ar dating, and whole-rock geochemical data, to investigate the crystallization and mineralization history from a sequence of granites (sensu lato), volcanic rocks and sedimentary rocks from the Au–Ag–Pb–Zn Empress Springs Project in northeast Australia, which are under >50 m of Phanerozoic cover and located near the interpreted ca. 1.6 Ga tectonic boundary between the North Australia Craton (Mount Isa Inlier) and Laurentia (Georgetown Inlier). Zircon U-Pb dating indicates that granite emplacement, volcanic eruptions and dolerite intrusions occurred between 1564 ± 6 and 1546 ± 13 Ma (2σ), corresponding to the 1560–1550 Ma Esmeralda Supersuite and the Croydon Volcanic Group exposed in the western Georgetown Inlier. U-Pb ages from detrital zircon grains in a sedimentary rock revealed a near unimodal ca. 1560 Ma population, likely sourced from the surrounding granitic and volcanic rocks. Sericite 40Ar/39Ar dating yielded disturbed spectra with evidence for incorporation of excess radiogenic Ar, but with a probable Carboniferous to Permian age, potentially dating the timing of gold mineralization. Geochemical similarities point towards an epithermal origin for the Empress Springs Project, consistent with post-orogenic mineralization at either ca. 1560–1550 Ma or 330–250 Ma. It is likely that a series of west-dipping lithospheric-scale faults below the Empress Springs Project, here termed the Empress Suture Zone, demarcate the final suture zone associated with the assembly of Nuna. Reactivation of the Empress Suture Zone ~1.3 b.y. after crystallization with potential contemporaneous gold mineralization attests to its longevity for fluid mobility.

Geologically Meaningful 40Ar/39Ar Ages of Altered Biotite from a Polyphase Deformed Shear Zone Obtained by in Vacuo Step-Heating Method: A Case Study of the Waziyü Detachment Fault, Northeast China

Discordant biotite 40Ar/39Ar age spectra are commonly reported in the literature. These can be caused by a number of processes related to in vacuo heating, homogenization of the argon distribution, and production of misleadingly flat age spectra. Problematic samples are typically derived from metamorphic belts; thermal overprinting and chloritization are two of the main known causes of disturbed age spectra. Biotite and muscovite of the Waziyü detachment fault, Yiwulüshan metamorphic core complex, Jinzhou, China, yield highly variable 40Ar/39Ar data that hinder reconstruction of their deformation history. We combined mineralogical studies with detailed 40Ar/39Ar dating of biotite, phengitic white mica, and K-feldspar augen from this fault. We infer that argon within the biotite was modified by hydrothermal fluids during fault activity and associated epidotization, chloritization, and muscovitization such that bulk sample step-heating, single grain total fusion, and in situ laser ablation of biotite produced mixed 40Ar/39Ar ages. However, detailed step-heating of biotite shows that this mineral records the ages of cooling and later alteration based on data from a coexisting rigid feldspar porphyroblast and neo-crystallized phengite that record two periods of fault activity at ~120–113 and 18–12 Ma. Our data reveal that the discordant biotite 40Ar/39Ar age spectra might represent a mixed age and that only detailed step-heating methods can extract meaningful geological details of the deformation history of a fault. Therefore, the mineral and the method must be carefully considered if metamorphic or deformed samples are dated.

Thermal history of the northern Olympic Domain, Gawler Craton; correlations between thermochronometric data and mineralising systems

Multi-method thermochronology applied to the northern Olympic Domain of South Australia reveals a complex thermal evolution with multiple thermal events. Apatite U/Pb (closure temperature ~550–350 °C) and muscovite 40Ar/39Ar ages (~400–350 °C) record post magmatic cooling from 1850 to 750 Ma for the ~1850 Ma Donington Suite, and from ~1560–1500 Ma for the ~1590 Ma Hiltaba Suite and the Gawler Range Volcanics. Potassium feldspar 40Ar/39Ar ages (~350–150 °C) record disturbed spectra that are likely related to hydrothermal alteration at ~1000–650 Ma in the Neoproterozoic Adelaide Rift Complex. Apatite fission track (~60–120 °C), zircon (U-Th-Sm)/He (~180–200 °C), and apatite (U-Th-Sm)/He (~45–75 °C) ages reveal regional low temperature thermal events at ~1000 Ma, ~430–400 Ma, 350–330 Ma, and ~200 Ma, in addition to localised thermal events during the Cretaceous. The ~1000 Ma apatite fission track ages are amongst the oldest recorded for South Australia and are only preserved near the margins of the Olympic Domain. The ~430–400 Ma and ~350–330 Ma cooling events are interpreted to be driven by the Alice Springs Orogeny. The Mesozoic thermochronometric ages are interpreted to record localised thermal perturbations, possibly related with hydrothermal activity within the northern Olympic Domain. The presence of abundant IOCG deposits near these young thermal anomalies may indicate that these zones record more favourable thermal conditions and/or exposure levels for IOCG discoveries in the study area.

Provenance and paleogeography of the Neruokpuk Formation, northwest Laurentia: An integrated synthesis

The Neruokpuk Formation is a Neoproterozoic and Cambrian turbiditic succession in northwesternmost Yukon (Canada) and northeastern Alaska (USA), part of a latest Proterozoic to Early Devonian slope and basin succession that is correlated in detail with strata in Selwyn Basin of the northern Canadian Cordillera. It includes quartz-lithic sandstone, locally containing altered detrital feldspar and muscovite indicating that a metamorphic source contributed detritus to the unit. The muscovite yields disturbed Ar-Ar spectra suggesting ages of 1800–1900 Ma. Detrital zircon distributions are dominated by 1800–2000 Ma grains with subsidiary populations of 1000–1600 Ma, 2300–2500 Ma and 2600–2800 Ma grains, consistent with a hybrid provenance dominated by a Laurentian cratonic source. Additional populations are derived from recycled Mackenzie Mountains and possibly Wernecke Supergroups. Integrating the geochronology with the regional stratigraphic setting, structural history, and geochemistry leads to the conclusion that the Neruokpuk Formation was deposited near its present location as part of the autochthonous northwest Laurentian continental margin. Therefore, the eastern part of Arctic Alaska, underlain by the Neruokpuk Formation, has a history that is distinct from the allochthonous western part(s) of the Arctic Alaska terrane. However, the rest of Arctic Alaska is structurally and stratigraphically linked to the eastern part by Late Devonian time.

New 40Ar/39Ar dating of the Clearwater Lake impact structures (Québec, Canada) – Not the binary asteroid impact it seems?

The two Clearwater Lake impact structures (Québec, Canada) are generally interpreted as a crater doublet formed by the impact of a binary asteroid. Here, arguments are presented that raise important questions about the proposed double impact scenario. New 40Ar/39Ar dating of two virtually fresh impact melt rock samples from the ⩾36km West Clearwater Lake impact structure yielded two statistically robust Early Permian plateau ages with a weighted mean of 286.2±2.2 (2.6) Ma (2σ; MSWD=0.33; P=0.57). In contrast, 40Ar/39Ar results for two chloritized melt rocks from the ∼26km East Clearwater Lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component. Although individually weakly robust, age spectra corrected for the trapped argon component and inverse isochron plots for the East Clearwater melt rocks consistently yielded apparent ages around ∼460–470Ma. No Permian signal was found in either of these melt aliquots. Our new 40Ar/39Ar results reproduce earlier 40Ar/39Ar plateau ages (∼283Ma and ∼465Ma, respectively) for the two impact structures by Bottomley et al. (1990) and are in conflict with a previous, statistically non-robust Rb–Sr age of 287 [293]±26Ma for East Clearwater. The combined cluster of apparent ages of ∼460–470Ma, derived from four different samples across the impact melt sheet, is very unlikely to represent a ‘false age effect’ due to the incorporation of extraneous argon into the melt; instead, it strongly favors a Middle Ordovician age for the East Clearwater impact and impact-induced hydrothermal chloritization. Moreover, the Clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories, an effect unexpected in the case of a Permian double impact. Whereas the West Clearwater impact affected Ordovician carbonates incorporated into the impact breccia, drill core reports from the 1960s concluded that clasts of Ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the East Clearwater Lake impact structure, which is overlain by >100m of post-impact sandstones, shales and carbonates. No resolvable impactor contamination has so far been detected in the West Clearwater impact melt rocks, whereas East Clearwater carries a distinct ordinary (possibly L-) chondritic impactor signature in its melt rocks. East Clearwater Lake might thus represent one among a long list of Ordovician impact structures in North America and northern Europe that were presumably formed in response to the L-chondrite asteroid breakup event ∼470Ma ago. Paleogeographic reconstructions show that the Ordovician East Clearwater impact probably occurred in a near-coastal to shallow marine setting, while the Permian West Clearwater impact hit continental Pangaea. Along with the new 40Ar/39Ar data, the paleomagnetic, sedimentologic, and geochemical findings suggest that the close spatial arrangement of the two Clearwater Lakes is most likely pure coincidence. The two impact structures seem to represent a ‘false doublet’ struck by impacts separated by ∼180 million years in time. The new results for the Clearwater Lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on Earth and on other planetary bodies in the inner Solar System.

Greenstone belts at the northernmost edge of the Kaapvaal Craton: Timing of tectonic events and a possible crustal fluid source

The Hout River shear zone, a complex thrust system, marks the boundary between the low- to medium grade metamorphic granitoid-greenstone Northern Kaapvaal Craton province and the high grade Southern Marginal Zone of the Limpopo Complex to the north of it. The Giyani greenstone belt, located on the Northern Kaapvaal Craton immediately adjacent to the Hout River shear zone, is in a key position for studying the tectonics of this shear zone. We have mapped two central transects through the greenstone belt, dated metamorphic minerals by 207Pb/206Pb stepwise leaching and 40Ar/36Ar, and compared our results with data from the Pietersburg/Polokwane and Rhenosterkoppies greenstone belts, which are close to the Hout River shear zone further west.The SE domain of the NE–SW striking Giyani greenstone belt appears to constitute a NW-vergent nappe. Movement along the Hout River shear zone is consistently SW-vergent, varying in character between frontal and lateral ramps, and nappe. The NW domain of the Giyani greenstone belt is dominated by ultramafic schists with mafic and banded iron formation (BIF) intercalations; it is considered a separate tectonic unit from the SE domain in which mafic (intrusive and pillow-volcanic) rocks are prevalent, with intercalated clastic sediments. Correlations between this SE domain and the lower mafic unit of the Pietersburg greenstone belt and with the mafic-BIF association of the Rhenosterkoppies greenstone belt are possible.Ages for peak metamorphism in the immediate footwall of the Hout River shear zone from this and previous work yield a weighted mean age of 2717±28Ma (95% confidence), documenting a “hot-iron” metamorphism. A garnet age of 2833±38Ma in the SE domain of the Giyani greenstone belt overlaps with ages from 2854 to 2870Ma for youngest zircons in syntectonic intrusions within the Giyani and the Pietersburg greenstone belts, as well as youngest detrital zircons in the (probably syntectonic) clastic sedimentary Uitkyk Formation of the latter. These ages constrain a tectonometamorphic event in both belts, termed here the PGB-Lwaji orogeny. Amphibole 40Ar/39Ar dates from the Hout River shear zone (from this and previous work) and shear zones within the Giyani greenstone belt yield disturbed age spectra with step ages mainly in the 2550–2670Ma range. The amphiboles are chemically heterogeneous and the ages can be shown to reflect mixtures of older and younger amphibole generations, due to reactivation of the shear zones and fluid activity after the main event in the Hout River shear zone.Thermal modelling shows that, in spite of the very low content of radioactive heat producing elements in the Southern Marginal Zone, its lower crust, after moderate crustal thickening, could be heated to granulite facies conditions in 30–60Ma, a much shorter time than the 120Ma age difference between the PGB-Lwaji orogeny and the Hout River shear event. A causal link between the two tectonic events is thus precluded. On the other hand, previously low-grade supracrustal rocks from the Kaapvaal Craton buried at lower crustal levels during Hout River shear event could provide a source for fluids up to about 80Ma after the event.

Erratum to: Schumann resonance observation in China and anomalous disturbance possibly associated with Tohoku M9.0 earthquake

Schumann resonance (SR) is an electromagnetic resonance phenomenon in the Earth–ionosphere cavity exited by global lightning activities when the wavelength matches the circumference of the Earth, and the lowest four peak frequencies of SR are about 8, 14, 20, and 26 Hz. This article presents the new observational data of SR in China. The observations of two horizontal magnetic components (BNS and BEW) in the frequency band range of 3–29 Hz at Yongsheng observatory (26.7°N, 100.8°E) in southwestern China were mainly analyzed. It is found that the SR amplitudes at peak frequencies in BNS and BEW components all showed diurnal and seasonal variations, and that the SR amplitude in BNS component is always higher than that in BEW component. Diurnal variation of SR amplitude around equinoxes and solstices in BNS component is related to active intervals of three global thunderstorm centers, while SR amplitude in BEW component is the most significant at around 16 LT, corresponding to Asian center. SR amplitudes both in BNS and BEW components increase in the rainy season from May to September. In addition, the SR anomalies in association with the 2011 Japan earthquake are exhibited. The anomalous effect was characterized by an increase in amplitude at the lowest four SR modes beginning at 4 days before this earthquake. Upon analyzing the wave interference between the direct wave and disturbed wave scattered by localized modification of lower ionosphere over the epicenter, Asian and African thunderstorm centers are found to contribute to anomalous effect observed at Yongsheng station. Modeling results of SR regular and disturbed spectra at different local times led to the similar conclusion.

An Ediacaran–Cambrian thermal imprint in Rajasthan, western India: Evidence from 40Ar–39Ar geochronology of the Sindreth volcanics

The Sindreth Group exposed near Sirohi in southern Rajasthan, western India, is a volcanosedimentary sequence. Zircons from Sindreth rhyolite lavas and tuffs have yielded U–Pb crystallization ages of ~768–761 Ma, suggesting that the Sindreth Group is a part of the Malani magmatic event. Earlier 40Ar–39Ar studies of other Malani volcanic and plutonic rocks yielded disturbed argon release spectra, ascribed to a ~550 Ma thermal event possibly related to the Pan-African orogeny. To test and confirm this possibility, we dated two whole-rock and three feldspar separate samples of the Sindreth volcanics by the 40Ar–39Ar method. All samples yield disturbed argon release spectra suggesting radiogenic argon loss and with plateau segments at 550 Ma or 490 Ma. We interpret these as events of argon loss at 550–490 Ma related to an Ediacaran–Cambrian thermal event, possibly related to the Malagasy orogeny. The combined older and new 40Ar–39Ar results are significant in showing that whereas Ediacaran–Cambrian magmatic and metamorphic events are well known from many parts of India, they left thermal imprints in much of Trans-Aravalli Rajasthan as well. The overall evidence is consistent with a model of multiphase assembly of Gondwanaland from separate continental landmasses.

Mafic dykes intrusive into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt (Parnaíba Province), north–northeastern Brazil: Geochemistry, Sr–Nd–Pb–O isotopes, 40Ar/39Ar geochronology, and relationships to CAMP magmatism

Dykes of diabase and microgabbro intruded into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt, which are tectonic and erosive windows of the Parnaíba Basin in north–northeastern Brazil. Ar–Ar ages were determined, and major, trace element, and Nd–Sr–Pb–O isotopic compositions of these dykes were measured to provide insights into their age, and into the nature of their mantle sources and petrogenetic processes. The data have also been used to compare the chemical and isotopic signatures of the dykes with those of the Central Atlantic Magmatic Province (CAMP). Four chemical groups of mafic dykes have been identified. These comprise two subtypes of high-Ti rocks (i) HTi-1 (TiO2<2.3wt.%; SiO2>47 wt.%), (ii) HTi-2 (TiO2>2.7wt.%; SiO2>47wt.%), in addition to (iii) evolved high-Ti (TiO2>4wt.%; SiO2 of ~46wt.%) and (iv) low-Si (TiO2>2.2wt.%; SiO2<45wt.%) rocks. 40Ar/39Ar geochronology of plagioclase returned ages of 201±4 Ma and 193±10 Ma for the HTi-2 subtype, and of 201±2 Ma and 207±9Ma for the evolved high-Ti group. The HTi-1 and low-Si groups presented highly disturbed age spectra, and did not allow the definition of their emplacement ages. The Argon data indicate an age >200Ma for the low-Si group and are dubious with respect to the age of theHTi-1 subtype, if coeval with (i.e., ~200Ma), or older than, the HTi-2 and evolved high-Ti types. All groups present δ18O values of pyroxene that are compatible with uncontaminated mantle-derived magmas. The HTi-1 subtype (average 143Nd/144Nd200=0.512644; 87Sr/86Sr200=0.7035; 206Pb/204Pb of 17.86) shows the less enriched and less fractionated (more primitive) trace element distribution of all groups. The HTi-2 subtype shows enriched trace element pattern and depleted Nd–Sr signature (143Nd/144Nd200=0.512610; 87Sr/86Sr200=0.7037) and average 206Pb/204Pb ratios of 17.23. The evolved high-Ti chemical group shows average ratios of 143Nd/144Nd200=0.512558, 87Sr/86Sr200=0.7035, and 206Pb/204Pb of 16.88, and the more enriched trace-elements signature among the four groups. The chemical and isotopic compositions and trends of the HTi-1/HTi-2/EHTi types are consistent with their derivation from an asthenosphere-derived parental magma further modified by differentiation and minimal crust contamination (higher in the HTi-2 and EHTi types), and by the derivation of one type from another via fractional crystallization. These high- and evolved high-TiO2 types show ages and some chemical and isotopic features that are consistent with those of the CAMP magmatism. Some differences found are ascribed to petrogenetic processes, such as magma differentiation. A combination of warming of the mantle and edge-driven convection beneath the Pangea supercontinent after the closure of the Neoproterozoic (Brasiliano/Pan-African) orogenies in the Ediacaran–Cambrian boundary might have triggered the magmatic event. The low-Si type shows paired Ta–Nb and Zr–Hf depletions, and depleted Sr–Nd (average 143Nd/144Nd200=0.512687; 87Sr/86Sr200=0.703) and enriched Pb (206Pb/204Pb of 18.66) isotopic compositions that may be interpreted to result either from interaction of a subcontinental lithospheric mantle with products of an earlier subduction or by contamination of the mantle-derived magma during ascent and emplacement in the continental crust. It is hypothesized that these dykes were emplaced in the Ediacaran–Cambrian boundary, after the Neoproterozoic orogeny that built up the Gurupi Belt and in the early extensional stages that preceded the formation of the Parnaíba Basin.

Highly Sensitive and Selective Difunctional Ruthenium(II) Complex-Based Chemosensor for Dihydrogen Phosphate Anion and Ferrous Cation

The anion-interaction properties of a Ru(II) complex of [Ru(bpy)2(Htppip)](ClO4)2·H2O·DMF (RuL) {bpy =2,2'-bipyridine and Htppip =2-(4-(2,6-di(pyridin-2-yl)pyridin-4-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} were thoroughly investigated in CH3CN and CH3CN/H2O (50:1, v/v) solutions by UV-visible absorption, emission, and (1)H NMR spectra. These analyses revealed that RuL acts as an efficient "turn on" emission sensor for H2PO4(-), and a "turn off" sensor for F(-) and OAc(-); in addition, RuL exhibited slightly disturbed emission spectra in the presence of the other anions studied (Cl(-), Br(-), I(-), NO3(-), and ClO4(-)). The cation-sensing properties of RuL were also studied in both neat CH3CN and aqueous 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH = 7.2)/CH3CN (71/1, v/v) solutions. RuL was found to exhibit a colorimetric sensing ability that was highly selective for Fe(2+), as evidenced by an obvious color change from pale yellow to light red-purple to the naked eye over the other cations studied (Na(+), Mg(2+), Ba(2+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), and Ag(+)). To obtain insights into the possible binding modes and the sensing mechanisms, (1)H NMR spectral analysis, luminescence lifetime measurements, and density functional theoretical calculations were also performed.

Mineralogy, geochemistry, and 40Ar– 39Ar geochronology of lunar granulitic breccia Northwest Africa 3163 and paired stones: Comparisons with Apollo samples

The lunar meteorites Northwest Africa (NWA) 3163, 4881, and 4483 are paired stones classified as granulitic breccias. At 2.4 kg, these three stones constitute one of the largest known lunar meteorite masses. Here we describe the petrography, mineralogy, and chemistry of NWA 3163, 4881, and 4483, and present 40Ar– 39Ar data for two of the meteorites. Two-pyroxene thermometry indicates that the rocks equilibrated at 1050 ± 50 °C, which represents the high-temperature, low-pressure event that generated their characteristic recrystallization textures and reset their Ar systematics. Stepped-heating, in situ infrared laser microprobe 40Ar– 39Ar geochronology yields a mean age of 3327 ± 29 Ma for NWA 3163, and a more disturbed release spectrum for NWA 4881. NWA 4881 shows an upward-trending pattern, suggesting that it may have had a 40Ar– 39Ar age of >3.0 Ga, but that it was partially reset at ∼2.6 Ga. NWA 3163 et al. exhibit shock effects, including maskelynitized plagioclase, shock veins, and melt pockets, which are absent in the Apollo granulitic breccias. Although the Apollo and meteorite samples are texturally similar and have comparable bulk compositions and equilibration temperatures, their trace and siderophile element contents point to distinct parental lithologies derived from different regions of the Moon. Based on mineralogical and geochemical differences between the Apollo and meteorite samples, we conclude that the parent rock(s) of the paired NWA meteorites came from an area outside the Imbrium region and that they underwent high-temperature (granulite event) metamorphism long after the Late Heavy Bombardment.

Inverted metamorphic field gradient towards a Variscan suture zone (Champtoceaux Complex, Armorican Massif, France)

AbstractWe describe, date and constrain the P–T conditions of a syntectonic inverted metamorphic sequence associated with continental collision and crustal‐scale thrusting in one of the key regions of the late Palaeozoic Variscan belt of Western Europe – the Champtoceaux Complex (Armorican Massif, France), interpreted as a trace of the Variscan suture zone between Laurussia and Gondwana. The Complex consists of several stacked units, some of them eclogite‐bearing, that are sandwiched between two main pieces of continental crust – the Parautochthon and the Upper Allochthon. Moderately to steeply dipping foliation parallels the main lithological boundaries. From the bottom to the top of the metamorphic rock pile, the following sequence testifies to the syntectonic temperature increase: chlorite–biotite‐bearing metagreywackes (Parautochthon); orthogneisses with eclogite lenses; micaschists with chloritoid–chlorite–garnet; orthogneisses; micaschists with staurolite–biotite–garnet with chloritoid inclusions (Lower Allochthon); and migmatites with boudins of eclogite and kyanite–biotite–garnet‐bearing metapelitic lenses (Upper Allochthon). Mylonitic amphibolites with lenses of serpentinized peridotite mark the boundary between the Lower Allochthon and the overlying Upper Allochthon, suggesting the presence of a major thrust. It is inferred that the latter is responsible for the development of the inverted metamorphic zoning. Multiequilibrium thermobarometry and pseudosections calculated with thermocalc indicate that equilibration temperatures of the syntectonic peak metamorphic assemblages increase upwards in the rock pile from &lt;500 °C in the Parautochthon to &gt;650 °C in the Upper Allochthon. All units equilibrated at similar pressures between 7 and 10 kbar. In the Upper Allochthon, chronological results on muscovite suggest initial cooling from c. 343 Ma (muscovite Rb–Sr) to c. 337 Ma (muscovite 40Ar–39Ar). A subsequent very rapid temperature decrease is suggested by the synchronous closure of the muscovite and biotite K–Ar and biotite Rb–Sr isotopic systems (c. 337–335 Ma). This cooling is also recorded in the Upper Micaschists of the Lower Allochthon and in the Parautochthon with muscovite 40Ar–39Ar ages of c. 336–334 and 332 Ma, respectively. Ages of c. 343 Ma inferred from disturbed muscovite spectra from the Parautochthon are possibly linked to a previous higher pressure metamorphic event in this unit. It is suggested that the development of the inverted metamorphic zoning in the Champtoceaux Complex is due to the emplacement of a hot nappe over colder units and is contemporaneous with major crustal thrusting and associated pervasive ductile deformation. The preservation of this inverted field gradient was possible because of fast cooling, tentatively associated with the syn‐compressional denudation of the tectonic pile, expressed by the detachment at the top of the nappe pile. The efficiency of cooling is best shown by the near‐coincidence of Rb–Sr and 40Ar–39Ar ages, obtained on both sides of the major thrust. Finally, we highlight similarities with other regions of the West‐European Variscan belt (Iberian massif, French Massif Central) and suggest that inverted metamorphic zoning is systematically associated with the contact between the Lower and Upper Allochthons.

Multistage boron metasomatism in the Alamo Complex (Central Iberian Zone, Spain): Evidence from field relations, petrography, and 40Ar/39Ar tourmaline dating

The Alamo Complex consists of structural-metamorphic domes surrounded by low-grade metasedimentary rocks of Upper Proterozoic to Lower Cambrian age that form part of the Schist Graywacke Complex (Central Iberian Zone, Spain). Tourmaline is ubiquitous throughout the domes, in which it occurs in tourmalinites, psammo-pelitic schists, quartzites, gneisses, migmatites, leucogranites, aplo-pegmatites, and quartz veins. Overall, tourmaline compositions can be described within the four component system schorl-dravite-foitite-magnesiofoitite, with K 2 O &lt; 0.23%, low Ca contents, Mg/(Mg+Fe) = 0.25-0.71 and X/(X+Na) = 0.18-0.43, where X = vacancies in the X site. Field relations and petrographic observations, combined with tourmaline 40 Ar/ 39 Ar data, provide evidence of intense boron metasomatism affecting this region. Tourmaline 40 Ar/ 39 Ar step-heating spectra for Cambrian-Ordovician orthogneisses are complex, yielding a pseudo-plateau age of ~370 Ma that is interpreted to reflect Variscan rejuvenation of older tourmaline. Tourmaline 40 Ar/ 39 Ar data for mylonitized and folded tourmalinites yield disturbed spectra with pseudo-plateau ages of ~355-342 Ma that are unsuitable for precise age determination. These ages, however, are consistent with published ages (340-350 Ma) for the second Variscan deformation (D 2 ). Tourmaline from fine-layered tourmalinite and metasedimentary rocks yield well-defined plateau ages of 317 and 315 Ma, respectively, recording an additional metasomatic event concomitant with anatexis and evolution of B-bearing granites, pegmatites, and hydrothermal fluids. The different tourmaline-forming stages reflect significant boron cycling within the continental crust of the Central Iberian Zone, driven by deformation, metamorphism, and magmatism during the Variscan orogeny. Boron-rich aqueous fluids related to Cambro-Ordovician magmatism are considered to be the primary source of boron.

40Ar/ 39Ar-ages of phlogopite in mantle xenoliths from South African kimberlites: Evidence for metasomatic mantle impregnation during the Kibaran orogenic cycle

We applied the 40Ar/ 39Ar dating method to an extensive suite of phlogopites from kimberlite-hosted mantle xenoliths (dominantly garnet bearing) from the mines of Bultfontein (South Africa), Letseng-la-Terae and Liqhobong (Lesotho). Argon extraction was performed by conventional high resolution stepwise heating technique, laser incremental heating technique and laser spot analysis. All age spectra obtained by conventional analysis indicate various degrees of 40Ar loss during kimberlite emplacement, but never resulted in a total reset of the argon system. Most intriguingly, the sample-specific maximum apparent ages cluster between 1.0 and 1.22 Ga for the phlogopites with the least disturbed age spectra. A maximum apparent age of 1.02 Ga was observed during laser heating analysis. Individual grains tend to yield older ages in their cores, with successively younger ages at their rims. The range in age obtained via the laser fusion technique and with conventional stepwise heating technique agrees with each other, as well as with literature data. The often inferred presence of excess 40Ar in those phlogopites cannot explain the coherent age pattern in the large suite of samples. Hence, the age constraint of 1.0–1.25 Ga is regarded as geologically meaningful and assigned to metasomatism of the local cratonic mantle during the advent of Kibaran orogenesis (1.00–1.25 Ga). The major consequences of our findings are: (i) The argon system of phlogopite can remain closed for long time scales, even at ambient temperatures of 800–1200 °C within the mantle, most likely because the solid/solid partitioning behaviour of Ar between phlogopite and other major phases in the mantle strongly favours phlogopite, or because conventionally inferred diffusivity of argon in phlogopite is seriously overestimated. Thus, the 40Ar/ 39Ar phlogopite system appears to be a valuable tool for deciphering ancient metasomatic events affecting the lithospheric mantle. (ii) The cratonic lithospheric mantle below southern Africa may have been frequently influenced by different episodes of fluid or melt migration during subduction of oceanic crust at active continental margins.

Permian 40Ar/39Ar ages for post-Variscan minor intrusions in the Iberian Range and Spanish Central System

40Ar/39Ar dating of biotite from a calc-alkaline gabbro stock NW of Loscos in the Iberian Range yielded a slightly disturbed gas release spectrum. It has an early Permian, 288.5 ± 1.4 Ma total gas age, interpreted as the minimum emplacement age. The 40Ar/39Ar apparent age of the gabbro agrees with the Autunian stratigraphic age of related volcanic rocks. 40Ar/39Ar step-heating dating of amphibole phenocrysts from an alkaline camptonite dyke ca. 4 km SE of El Hoyo de Pinares in the Sierra Guadarrama sector of the Spanish Central System yielded a mid-Permian 264 ± 3 Ma plateau age, interpreted as the emplacement age. The age is indistinguishable from published 40Ar/39Ar amphibole ages for N-S trending camptonite dykes from the western, Sierra de Gredos segment of the Central System. This suggests that the camptonite dykes from both sectors belong to the same generation.

Geochronology of the Lower Cretaceous volcanism from the Coastal Range (29°20'-30°S), Chile

Ar/ 39 Ar age data (laser and furnace step heating) on plagioclase from Lower Cretaceous volcanic sequences from the Arqueros Formation in two sections of the Coastal Range at the latitude of La Serena (≈29°S) have been obtained. Due to the partial alteration of plagioclase crystals, disturbed age spectra in the furnace experiments have been observed, whereas laser heating determinations involving a much smaller quantity of grains carefully selected, could display plateau ages corresponding to pure plagioclase, as demonstrated by a constant 37

Datation 40Ar/ 39Ar de la province magmatique de l’Atlantique central dans le Sud-Ouest algérien

40Ar/ 39Ar step-heating analyses performed on plagioclase separates from seven doleritic basalts (four sills, one dyke and two lava flows) from southwestern Algeria display disturbed age spectra, reflecting various contributions of alteration by sericite and/or excess argon. Weighted mean ages corresponding to the less altered plagioclase fractions yielded minimum ages ranging from 192.7 ± 3.0 to 197.9 ± 2.0 Ma and a minimum date of 198.9 ± 1.8 Ma was obtained on a saddle-shaped age spectrum (excess argon). These ages are in accordance with those previously obtained on the CAMP province and partly in agreement with the peak activity of the CAMP at 198 Ma, highlighted in the neighbouring Taoudenni basin (Mali). In Algeria, the eastern boundary of the CAMP seems to coincide with the Pan-African suture zone.

40Ar/ 39Ar thermochronology of the Kampa Dome, southern Tibet: Implications for tectonic evolution of the North Himalayan gneiss domes

Structural and thermochronological studies of the Kampa Dome provide constraints on timing and mechanisms of gneiss dome formation in southern Tibet. The core of Kampa Dome contains the Kampa Granite, a Cambrian orthogneiss that was deformed under high temperature (sub-solidus) conditions during Himalayan orogenesis. The Kampa Granite is intruded by syn-tectonic leucogranite dikes and sills of probable Oligocene to Miocene age. Overlying Paleozoic to Mesozoic metasedimentary rocks decrease in peak metamorphic grade from kyanite + staurolite grade at the base of the sequence to unmetamorphosed at the top. The Kampa Shear Zone traverses the Kampa Granite — metasediment contact and contains evidence for high-temperature to low-temperature ductile deformation and brittle faulting. The shear zone is interpreted to represent an exhumed portion of the South Tibetan Detachment System. Biotite and muscovite 40Ar/ 39Ar thermochronology from the metasedimentary sequence yields disturbed spectra with 14.22 ± 0.18 to 15.54 ± 0.39 Ma cooling ages and concordant spectra with 14.64 ± 0.15 to 14.68 ± 0.07 Ma cooling ages. Petrographic investigations suggest disturbed samples are associated with excess argon, intracrystalline deformation, mineral and fluid inclusions and/or chloritization that led to variations in argon systematics. We conclude that the entire metasedimentary sequence cooled rapidly through mica closure temperatures at ∼ 14.6 Ma. The Kampa Granite yields the youngest biotite 40Ar/ 39Ar ages of ∼ 13.7 Ma immediately below the granite–metasediment contact. We suggest that this age variation reflects either varying mica closure temperatures, re-heating of the Kampa Granite biotites above closure temperatures between 14.6 Ma and 13.7 Ma, or juxtaposition of rocks with different thermal histories. Our data do not corroborate the “inverse” mica cooling gradient observed in adjacent North Himalayan gneiss domes. Instead, we infer that mica cooling occurred in response to exhumation and conduction related to top-to-north normal faulting in the overlying sequence, top-to-south thrusting at depth, and coeval surface denudation.