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Ferri-taramite (IMA CNMNC 2021-046), ideally ANaB(CaNa)C(Mg3Fe23+)(Si6Al2)O22W(OH)2, occurs in skarn from the Jakobsberg manganese mine, Värmland, Sweden. Associated minerals are celsian, phlogopite, aegirine-augite, andradite, hancockite, melanotekite, microcline (var. hyalophane), calcite, baryte, prehnite, macedonite and oxyplumboroméite. Conditions of formation, close to peak metamorphism (at circa 650 ∘C and 0.4 GPa), include silica undersaturation, a slightly peralkaline character and relatively high oxygen fugacities. Ferri-taramite forms poikiloblastic crystals up to 5 mm and is dark brownish black with a yellowish grey streak. The amphibole is brittle with an uneven to splintery fracture. Cleavage parallel to {110} is good. Hardness (Mohs) is ∼ 6, and Dcalc=3.227(5) g cm−3. Holotype ferri-taramite has the experimental unit formula A(Na0.79K0.16Pb0.01)Σ0.96B(Ca1.26Na0.72Mn0.022+)Σ2C(Mg2.66Mn0.582+Fe0.162+Zn0.02Fe1.263+ Al0.26Ti0.06)Σ5.00T(Al1.86Si6.14)Σ8O22W(OH)2, based on chemical analyses (EDS, laser-ablation ICP-MS) and spectroscopic (Mössbauer, infrared) and single-crystal X-ray diffraction data. The mineral is optically biaxial (–), with α=1.670(5), β=1.680(5) and γ=1.685(5) in white light and 2Vmeas=70(10)∘ and 2Vcalc=70.2∘. Ferri-taramite is distinctly pleochroic in transmitted light, with X pale yellow, Y dark brown, Z yellowish brown and absorption Y>Z>X. The eight strongest reflections in the X-ray powder pattern (d values (in Å), Irel, hkl) are 8.44, 60, 110; 3.392, 25, 131; 3.281, 39, 240; 3.140, 100, 310; 2.816, 45, 330; 2.7104, 38, 151; 1.3654, 26, 461; and 1.4451, 33, 6‾61. Refined unit-cell parameters from single-crystal diffraction data are a=9.89596(13), b=18.015(2), c=5.32164(7) Å, β=105.003(13)∘ and V=916.38(2) Å3 for Z=2. Refinement of the crystal structure yielded R=2.26 % for 2722 reflections with Io>2σ(I). The Mn2+ and Fe2+ ions show preference for the M1 and M3 octahedrally coordinated sites, whereas Fe3+ is strongly ordered at M2. The A-group cations, K and Na, are split over two subsites, A(m) and A(2), respectively.

Mica, especially white mica, is a common detrital mineral in siliciclastic sediments and sedimentary rocks. It is used in provenance studies to constrain the thermal history and exhumation processes in the source region. It thus records valuable complementary provenance information to e.g. U-Pb geochronology of detrital zircon that date magmatic and high-grade metamorphic events in the provenance area.However, in contrast to U-Pb geochronology of detrital zircon, there was a major disadvantage of using mica geochronology in provenance investigations until now: the conventional Argon-Argon (Ar-Ar) or Rubidium-Strontium (Rb-Sr) dating techniques are rather time-consuming due to complex sample preparation. Thus, of major interest for mica-based provenance studies is a recent improvement in in-situ Rb-Sr dating by laser ablation (LA) – inductively coupled plasma (ICP) - mass spectrometer (MS/MS) analyses. This analytical setup uses a reaction cell between two mass spectrometers. Induced gases allow the reaction of targeted masses and thus to chemically separating 87Rb and its daughter isotope 87Sr. This avoids the isobaric overlap during mass-spectrometric analysis. In combination with the novel approach of Rösel and Zack (2022) (GGR 46, 143-168), single-spot Rb-Sr ages can be calculated from individual detrital mica grains. Trace and major elements can be determined contamporaneously from the same laser spots. Consequently, LA-ICP-MS/MS analyses of detrital mica enables collecting of time and cost efficient multi-proxy datasets – a prerequisite for provenance studies.In this contribution, we focus on (1) the analytical routine, (2) data reduction and age calculation strategy and (3) interpretation of in-situ Rb-Sr age and geochemical data from detral mica for provenance investigations. In-situ Rb-Sr LA-ICP-MS/MS dating was tested on detrital white mica from the Late Miocene Loxton Sand Formation, Murray Bain, South Australia. U-Pb dating from detrital zircon extracted from the same formation was performed for comparison.

The emerging field of “in-situ beta decay dating” has enormous potential for Earth Sciences. Here, the Rb-Sr system is the most advanced, although other systems (e.g., K-Ca, Lu-Hf, Re-Os) promise exciting opportunities as well. In this contribution, I want to first highlight several analytical and conceptual advances made with regard to in-situ Rb-Sr geochronology, and in particular utilizing the mica group (mostly biotite, muscovite and glauconite): (1) the community (e.g., Redaa et al, 2022) has made important progress characterizing the reference material Mica-Mg (from CRPG) for Rb-Sr ratios and Sr isotope composition, used as a nanopowder pellet, it currently serves in most laboratories as a primary reference material; (2) several new natural mica samples have been distributed to several laboratories to serve as secondary reference materials (Rösel & Zack, 2022). Both these activities serve not only to improve precision and accuracy of this technique, but in general allows better comparison of results of different studies. Furthermore, (3) many micas are almost devoid of Sr when forming, which allows treating them similar to zircon in the U-Pb system, meaning that the common Sr can simply be estimated, making the isochron approach obsolete (Rösel & Zack, 2022). This has important practical implication; so-called single spot ages can be utilized to map out age distribution within single crystals, target crystals of different textural context or even used in provenance studies of detrital mica (Rösel et al., this conference). Finally, (4) as most analytical facilities where in-situ beta decay dating is possible employ a quadrupole ICP-MS, selecting isotopes for spot analysis are not limited to Rb and Sr isotopes, but can set to cover all elements of interest from Li to U. With sufficient care in the choice of calibration material, it is possible to not only couple age information with trace element signatures, but even calculate mica mineral formula with surprising accuracy. In my presentation I want to illustrate how in-situ Rb-Sr mica geochronology can be utilized in the field of metamorphic petrology. For further applications in metamorphic settings, please also see Barnes et al. (this session).

Authigenic components in marine sediments are important archives for past environment reconstructions. However, defining reliable age constraints and assessing the effects of post depositional overprints in Precambrian sequences are challenging. We demonstrate a new laserbased analytical approach that has the potential to rapidly and accurately evaluate the depositional and alteration histories of Proterozoic shales. Our study employs a novel application of in situ Rb-Sr dating coupled with simultaneous trace-element analysis using reaction-cell laser ablation– inductively coupled plasma–tandem mass spectrometry (LA-ICPMS/MS). We present results from shales sourced from two wells in the Proterozoic McArthur Basin, northern Australia. These rocks have been widely used by previous studies as a key section for ancient biogeochemical and paleoredox reconstructions. Shales from well UR5 yielded initial ⁸⁷Sr/⁸⁶Sr ratios, Rb-Sr ages, and rare earth element plus yttrium (REEY) patterns similar to those of a dolerite sampled from the same core. We propose that the UR5 samples chronicle hydrothermal alteration instigated by the dolerite intrusion. In contrast, a correlative shale from well UR6 yielded an age consistent with the expected depositional age (1577 ± 56 Ma) with REEY and initial ⁸⁷Sr/⁸⁶Sr ratios similar to ca. 1.5 Ga seawater. We suggest that this sample records the minimum depositional age and early marine diagenetic history for this unit. This new technique can date Proterozoic shales quickly, cheaply, and with minimum sample preparation. Importantly, ages are triaged to differentiate between those recording primary marine versus secondary processes. This novel approach provides a potentially powerful tool for dating and fingerprinting the vast array of ancient marine shales for further studies of Earth systems through deep time.

Authigenic components in marine sediments are important archives for past environment reconstructions. However, defining reliable age constraints and assessing the effects of post-depositional overprints in Precambrian sequences are challenging. We demonstrate a new laser-based analytical approach that has the potential to rapidly and accurately evaluate the depositional and alteration histories of Proterozoic shales. Our study employs a novel application of in situ Rb-Sr dating coupled with simultaneous trace-element analysis using reaction-cell laser ablation–inductively coupled plasma–tandem mass spectrometry (LA-ICP-MS/MS). We present results from shales sourced from two wells in the Proterozoic McArthur Basin, northern Australia. These rocks have been widely used by previous studies as a key section for ancient biogeochemical and paleo-redox reconstructions. Shales from well UR5 yielded initial 87Sr/86Sr ratios, Rb-Sr ages, and rare earth element plus yttrium (REEY) patterns similar to those of a dolerite sampled from the same core. We propose that the UR5 samples chronicle hydrothermal alteration instigated by the dolerite intrusion. In contrast, a correlative shale from well UR6 yielded an age consistent with the expected depositional age (1577 ±56 Ma) with REEY and initial 87Sr/86Sr ratios similar to ca. 1.5 Ga seawater. We suggest that this sample records the minimum depositional age and early marine diagenetic history for this unit. This new technique can date Proterozoic shales quickly, cheaply, and with minimum sample preparation. Importantly, ages are triaged to differentiate between those recording primary marine versus secondary processes. This novel approach provides a potentially powerful tool for dating and fingerprinting the vast array of ancient marine shales for further studies of Earth systems through deep time.

The Seve Nappe Complex is a subduction-related high-grade metamorphic unit that was emplaced onto the margin of Baltica during Caledonian orogenesis. In this paper, the tectonometamorphic evolution of the Lower Seve Nappe in the Scandinavian Caledonides was characterized with the help of the continuous Collisional Orogeny in the Scandinavian Caledonides (COSC-1) drill core, using a combination of various P–T estimation techniques based on garnet–quartz mineral pairs (quartz-in-garnet and Ti-in-quartz [QuiG–TiQ]), conventional thermobarometry and thermodynamic modelling of phase equilibria. This multi-method approach yields complementary results and delivers critical data to constrain a comprehensive pressure–temperature–deformation–time (P–T–D–t) evolutionary path for the metasedimentary rocks of the Lower Seve Nappe. In the garnetiferous metasedimentary rocks, quartz inclusions in garnet preserve the P–T conditions of three distinct garnet growth stages corresponding to three metamorphic stages Ms1 to Ms3, including prograde and peak metamorphic conditions. Ms1 and Ms2 stages were constrained via quartz inclusions in garnet core and mantle. They are relatively close in the P–T space and could be considered as one single continuous prograde event occurring at epidote–amphibolite facies conditions of 460–520°C and 0.6–0.85 GPa. The growth of the garnet outermost rim defines the Ms3 stage at amphibolite facies conditions of 590–610°C and 1.13–1.18 GPa and corresponds to the peak metamorphic conditions. The microstructural analysis shows that the finite ductile strain pattern of the Lower Seve Nappe results from the superposition of four deformation phases. The initial phase D1 is defined by the S1 foliation that is still preserved as a curved inclusion trail in the garnet core. The D2 phase initiated contemporaneously with garnet core growth and the development of muscovite–biotite–plagioclase S2 foliation. Garnet outermost rim growth marks the end of the prograde path and peak metamorphic conditions. This stage is overprinted by the D3 phase and Ms4 stage associated with the development of the main regional metamorphic and mylonitic fabric S3 associated with C′-type shear bands along the retrograde path. Ms4 stage, which was constrained using traditional thermobarometric techniques, corresponds to the chemical re-equilibration of the metasedimentary minerals and occurred under amphibolite facies conditions at ~570–610°C and 0.78–1.00 GPa. The D3 phase is then generally weakly to strongly overprinted by later lower grade deformation D4 phase at greenschist facies conditions (Ms5). 40Ar/39Ar ages of syn-kinematic white mica and biotite indicate that the final stage of the thrusting of the Lower Seve Nappe and thus the timing of its emplacement onto the Offerdal Nappe occurred at c. 423 Ma. Collectively, these results are consistent with previous estimates of the timing and conditions of metamorphism derived from the Lower Seve Nappe especially in west-central Jämtland. However, application of QuiG–TiQ thermobarometry demonstrated that quartz inclusions in garnet can preserve different aspects of garnet growth, which are not accessible by traditional methods especially in complex terranes, and therefore provided new significant insights into the Lower Seve prograde evolution.

© 2022 Elsevier B.V.This study deals with the age and petrogenesis of mafic-ultramafic intrusions ranging in size from a few meters to 10 km within the Early Carboniferous high-grade gneisses of the Pulur Complex in the Eastern Pontides. The intrusions comprise dunite, wehrlite, gabbronorite, leucogabbro, anorthosite and ilmenite-bearing gabbronorite of cumulus origin, and are crosscut by dikes of ilmenite-bearing gabbronorite, leucogranite and microdiorite. U–Pb dating on zircons from gabbronorite, anorthosite and leucogranite yielded igneous crystallization ages of 322–326 Ma, indicating that the intrusions were emplaced ca. 5–7 Ma after the peak of high-grade metamorphism, and form part of the Late Carboniferous high-volume magmatism in the region. In most cumulate rocks, Cr–Al spinel, olivine and plagioclase were early crystallizing phases, followed by orthopyroxene, clinopyroxene and hornblende. Whole rock geochemical data suggest that wehrlite, gabbronorite, leucogabbro and anorthosite stem from a common magma, and ilmenite-bearing gabbronorite and dikes of leucogranite and microdiorite from different magmas. Application of mineral/melt partition coefficients to trace element compositions of clinopyroxene and hornblende in cumulate rocks suggests that the main cumulate body was derived from middle- to high-K calc-alkaline basic melts, and relatively late ilmenite-bearing gabbronorites from hypersthene-normative Ca-rich melts. All the rock types display radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios, which are indistinguishable from those of the coeval voluminous high-K calc-alkaline I-type granites in the region; the isotopic ratios are probably related to the metasomatism of the lithospheric mantle by sediment-derived melts. We suggest that the parental melts of the mafic-ultramafic intrusions and those of the high-K calc-alkaline granites were genetically related, and melts of the high-K calc-alkaline granites were probably derived from the melting of newly underplated calc-alkaline basic material at lower crustal depths, that were compositionally comparable to the parental magmas of the mafic-ultramafic intrusions.

The formation and evolution of Palaeoarchaean De Kraalen and Witrivier Greenstone Belts (DKGB and WGB) of the Kaapvaal Craton are poorly known. Here we report zircon and rutile in situ U-Pb ages and zircon Hf isotopic data from a variety of supracrustal rocks. The zircon cores from a metamafic amphibole-bearing gneiss from the DKGB give a protolith age of 3 441 ± 5 Ma, whereas the zircon mantle domains give a metamorphic age of 3 211 ± 16 Ma. The 176Hf/177Hft values for all zircon domains give a tight cluster around 0.280596 ± 0.00006 (2 SD). U-Pb analyses of zircon for an amphibolite intercalated with thin calc-silicate layers from the WGB give a single crystallisation age of 3 230 ± 3 Ma, but the Hf isotope ratios of these zircon grains define two different populations. The first population yields 176Hf/177Hf~3.23 Ga = 0.28064 ± 0.00004, corresponding to εHf~3.23 Ga = 2.4 ± 1.9 (2SD) and Hf model ages between ca. 3.51 to 3.30 Ga. These are Hf isotope characteristics for zircons from a relatively juvenile source extracted from a depleted mantle source ca. 0.28 to 0.07 Ga prior zircon crystallisation. The second population yields 176Hf/177Hf~3.23 Ga = 0.28093 ± 0.00004 with εHf~3.23 Ga = 8.1 ± 1.3 (2SD). These Hf data combined with the 206Pb/207Pb ages lead to isotope ratios that lie above those of Depleted Mantle. The unusually high Hf isotope signature for the cores of the zircons from the WGB amphibolite most likely represent a contribution from an early highly depleted mantle source. A rutile in situ U-Pb age of 3.085 Ga from a recrystallised quartzite indicate that the rocks from the DKGB experienced slow cooling following the 3.21 Ga metamorphic event or (partial) resetting due to elevated geothermal gradient caused by the ca. 3.1 Ga intrusions of the Vrede Granitiod Suite. The latter interpretation is preferred because ~145 Ma of slow cooling from the amphibolite facies conditions of peak metamorphism to the blocking temperature for mass diffusion of Pb in rutile is unlikely. While the Zr-in-rutile temperature of ca. 710°C at 7 kbar for DKGB most likely records the peak temperature of the ~3.23 to 3.21 Ga event. The trace element concentrations of the metamorphic rutile grains within the quartzite of the DKGB indicate that the source rock was enriched in Cr. Either due to silification during hydrothermal alteration of the (ultra)mafic country rock or during deposition in an atmosphere that allowed for chromite grains to be part of the sediment.

Laser-ablation inductively-coupled plasma tandem mass-spectrometry (LA-ICP-MS/MS) allows for rapid and interference free analyses of Rb and Sr isotopes, permitting in situ Rb–Sr dating of minerals. However, the general lack of matrix matched reference materials remains one of its main obstacles, affecting both precision and accuracy. This study systematically investigates the impact of matrix effects and down-hole fractionation (DHF) on the in situ Rb–Sr ages of an igneous phlogopite mineral (MDC) analysed by an ICP-MS/MS using two different LA systems: (i) a RESOlution ArF (193 nm) excimer and (ii) a NWR (213 nm) Nd-YAG laser system. A phlogopite reference material (Mica-Mg), originating from the same location as the MDC, was prepared as a pressed nano-powder pellet (NP) and used in this study as a primary reference material. The results revealed that the accuracy of the Rb–Sr ages is typically within about 3% (for 70% of analysed samples), but occasionally higher ranging between 4 to 8% (ca. 30% of cases). We hypothesize that the above bias and uncertainty in the Rb–Sr ages are related to matrix effects between Mica-Mg-NP and MDC, due to their specific ablation characteristics and different physical properties. In addition, the elemental fractionation effects observed in this study for 87Rb/86Sr are also dependent on laser wavelength (i.e., 193 nm vs. 213 nm). Hence, developing an improved nano-powder reference material, or a mineral or glass with better matrix matching to natural phlogopite minerals would be desirable to further improve the accuracy of in situ Rb–Sr dating. Currently, regular monitoring of secondary and matrix-matched reference minerals such as the MDC phlogopite can be used to assess and evaluate the accuracy of in situ Rb–Sr dating of phlogopite, yielding ages within accuracy of ca. 3% or better.

Made available in DSpace on 2022-05-01T09:47:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-04-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) We use a combination of several in situ techniques to assess the P-T-t path of high-pressure granulites from the Passos Nappe in the Southern Brasília Orogen (SE Brazil). Quantitative element mapping and single-element thermometers (Zr-in-rutile and Ti-in-quartz) are coupled with P-T pseudosections and monazite and rutile dating. Compositional and temperature maps, based on cathodoluminescence mapping and in situ analyses of Ti-in-quartz, are presented as a novel approach to evaluate crystallization temperature. The studied rocks have a pelitic protolith and record a peak pressure assemblage of garnet + kyanite + rutile + K-feldspar + quartz + melt ± plagioclase that formed at ~830°C and 1.2 GPa. Retrograde conditions of ~560°C and 0.6 GPa are determined based on the grossular content of garnet and the crystallization of biotite and ilmenite. Metamorphic peak conditions occurred ca. 635 Ma, according to monazite dating, with a younger date of ca. 615 Ma associated with later kyanite crystallization. Rutile ages of ca. 590 Ma are linked to the late retrograde stage (at ~600°C). Results show that the distribution of Ti-in-quartz is heterogeneous, decreasing in abundance towards the rim of crystals, though the higher temperatures constrained with Ti-in-quartz thermometry are broadly consistent with peak conditions. The peak pressure conditions are consistent with continental collision setting in the Southern Brasília Orogen and were followed by an early cooling/decompression stage and then by a slow cooling during exhumation and transport to shallower crustal levels. Department of Geology São Paulo State University Department of Mineralogy and Geotectonics University of São Paulo Institute of Geological Sciences University of Bern TEKTOS Research Group Faculdade de Geologia Universidade do Estado Rio de Janeiro (UERJ) Department of Earth Sciences University of Gothenburg Department of Geosciences Virginia Tech Department of Geology São Paulo State University CNPq: 141604/2018-2 FAPESP: 2015/05230-0 FAPESP: 2016/22627-3 CNPq: 305720/2001-1 CNPq: 311606/2019-9 CNPq: 486328/2013-9

Establishing temporal constraints of faulting is of importance for tectonic and seismicity reconstructions and predictions. Conventional fault dating techniques commonly use bulk samples of syn-kinematic illite and other K-bearing minerals in fault gouges, which results in mixed ages of repeatedly reactivated faults as well as grain-size dependent age variations. Here we present a new approach to resolve fault reactivation histories by applying high-spatial resolution Rb-Sr dating to fine-grained mineral slickenfibres in faults occurring in Paleoproterozoic crystalline rocks. Slickenfibre illite and/or K-feldspar together with co-genetic calcite and/or albite were targeted with 50 µm laser ablation triple quadrupole inductively coupled plasma mass spectrometry analyses (LA-ICP-MS/MS). The ages obtained disclose slickenfibre growth at several occasions spanning over 1 billion years, from at least 1527 Ma to 349 ± 9 Ma. The timing of these growth phases and the associated structural orientation information of the kinematic indicators on the fracture surfaces are linked to far-field tectonic events, including the Caledonian orogeny. Our approach links faulting to individual regional deformation events by minimizing age mixing through micro-scale analysis of individual grains and narrow crystal zones in common fault mineral assemblages.

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ18O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT is also an important tool for forecasting effects of anthropogenic climate change.Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (K-feldspar only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), the combination with in-situ Sr-isotope fingerprinting and 87Rb/87Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, recovered from the Weddell Sea, ca. 750 km from the continental rise in 4671 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14.09 to 14.26 Ma.Our findings are consistent with predictions made by recent palaeo-ice sheet models (eg., Gasson et al. 2016), which predict the development of sizeable and discrete embayments around the continent, including the Weddell Sea. We argue that the IRD derived from the unstable sector associated with this embayment formation at the time.Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.Gasson, E, et al., 2016, Proceedings of the National Academy of Sciences, v. 113, (13), p. 3459-3464, doi: www.pnas.org/cgi/doi/10.1073/pnas.1516130113.Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

The scarcity of well-preserved and directly dateable sedimentary sequences is a major impediment to inferring the Earth’s paleo-environmental evolution. The authigenic mineral glauconite can potentially provide absolute stratigraphic ages for sedimentary sequences and constraints on paleo-depositional conditions. This requires improved approaches for measuring and interpreting glauconite formation ages. Here, glauconite from a Cretaceous shelfal sequence (Langenstein, northern Germany) was characterized using petrographical, geochemical (EMP), andmineralogical (XRD) screening methods before in situ Rb-Sr dating via LA-ICP-MS/MS. The obtained glauconite ages (~101 to 97 Ma) partly overlap with the depositional age of the Langenstein sequence (±3 Ma), but without the expected stratigraphic age progression, which we attribute to detrital and diagenetic illitic phase impurities inside the glauconites. Using a novel age deconvolution approach, which combines the new Rb-Sr dataset with published K-Ar ages, we recalculate the glauconite bulk ages to obtain stratigraphically significant ‘pure’ glauconite ages (~100 to 96 Ma). Thus, our results show that pristine ages can be preserved in mineralogically complex glauconite grains even under burial diagenetic conditions (T < 65 °C

Retrograde clay mineral reactions (i.e., reverse weathering), including glauconite formation, are first-order controls on element (re)cycling vs sequestration in modern and ancient marine sediments. Here, we report substantial K–Mg–Fe sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 4 ± 3 mmol K·cm−²·kyr− 1, 4 ± 2 mmol Mg·cm−²·kyr− 1 and 10 ± 6 mmol Fe·cm−²·kyr− 1, which is ~ 2 orders of magnitude higher compared to deep-sea settings. Upscaling of glauconite abundances in shallow-water (− 1, ~ 0.04–0.06 Tmol Mg·yr− 1 and ~ 0.11–0.14 Tmol Fe·yr− 1. We conclude that authigenic clay elemental uptake had a large impact on the global marine K, Mg and Fe cycles throughout Earth`s history, in particular during ‘greenhouse’ periods with sea level highstand. Quantifying authigenic clay formation is key for better understanding past and present geochemical cycling in marine sediments.

Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm−²·kyr−1 for K, Mg and Al, 16 ± 9 mmol·cm−²·kyr−1 for Si and 6 ± 3 mmol·cm−²·kyr−1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0–200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr−1 of K, Mg and Al, and ~0.1–0.4 Tmol·yr−1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth’s history, in particular during ‘greenhouse’ periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.

Rheology of the continental lower crust plays an integral role in governing the style of continental extension. Temperature-dependent creep deformation in the lower crust decreases lithospheric strength and promotes coupling of deformation in the brittle crust and upper mantle; however, few constraints exist concerning the thermal evolution of extending lower crust. Here, we present a high-temperature thermochronological investigation of the Ivrea-Verbano Zone—archetypal continental lower crust that was attenuated during opening of the Alpine Tethys oceanic basin. Rutile U–Pb dates collected from three samples spanning the bottom ∼2-km of the crustal section are between ∼160 and ∼180 Ma, and exhibit near-rim zonations in Zr, Hf, Nb and Ta. Thermal-kinematic modeling of these data, combined with existing rutile U–Pb dates, show that the base of the Ivrea-Verbano Zone experienced heating on two timescales: conductive heating over ∼10 Myr, associated with thinning of the lithospheric mantle, and advective heating over

rom ca. 50 Ma to present, the western Pacific plate has been subducting under the Philippine Sea plate, forming the oceanic Izu-Bonin-Mariana (IBM) subduction system. It is the only known location where subduction zone products are presently being transported to the surface by serpentinite-mud volcanoes. A large serpentine mud “volcano” forms the South Chamorro Seamount and was successfully drilled by ODP during Leg 195. This returned mostly partially serpentinized harzburgites enclosed in serpentinite muds. In addition, limited numbers of small (1 mm–1 cm) fragments of rare blueschists were also discovered. U–Pb dating of zircon and rutile from one of these blueschist clasts give ages of 51.1 ± 1.2 Ma and 47.5 ± 2.0 Ma, respectively. These are interpreted to date prograde high-pressure metamorphism. Mineral equilibria modelling of the blueschist clast suggests the mineral assemblage formed at conditions of ∼1.6 GPa and ∼590 °C. We interpret that this high-pressure assemblage formed at a depth of ∼50 km within the subduction channel and was subsequently exhumed and entrained into the South Chamorro serpentinite volcano system at depths of ∼27 km. Consequently, we propose that the material erupted from the South Chamarro Seamount may be sampling far greater depths within the Mariana subduction system than previously thought. The apparent thermal gradient implied by the pressure–temperature modelling (∼370 °C/GPa) is slightly warmer than that predicted by typical subduction channel numerical models and other blueschists worldwide. The age of the blueschist suggests it formed during the arc initiation stages of the proto-Izu-Bonin-Mariana arc, with the P–T conditions recording thermally elevated conditions during initial stages of western Pacific plate subduction. This indicates the blueschist had prolonged residence time in the stable forearc as the system underwent east-directed rollback. The Mariana blueschist shows that subduction products can remain entrained in subduction channels for many millions of years prior to exhumation. Refereed/Peer-reviewed

Conventional dating of molybdenite (187Re-187Os) provides one of few options for direct dating of sulfide mineralization. Unfortunately, in situ dating of molybdenite is considered unreliable due to intra-granular decoupling of 187Re-187Os. In this study, we developed a new analytical protocol for studies of micron- to grain scale 187Re-187Os systematics in molybdenite. Online chemical separation using ICP-MS/MS technology enables in situ dating by β-decay systems (e.g., Rb-Sr and K-Ca in micas) using laser ablation. Here, the methodology is extended to the 187Re-187Os system, another β-decay system that cannot be resolved by mass spectrometry. Several reaction gases were evaluated, and production of OsCH2 by reaction with CH4 was found to produce strong separation of Os from Re. However, in contrast to the e.g., 87Rb-87Sr system, 1–2% of the parent isotope Re also reacted to ReCH2, leaving a significant interference. A mathematical correction of this remaining interference is possible, and 187Re-187Os (mass-shifted) can be measured accurately even for fairly extreme ratios. For laser ablation, standards were developed by pressing particulate pellets of conventionally dated molybdenite (Moly Hill and Merlin), because there are no appropriate reference materials available. Six natural molybdenite samples from a range of geological settings, containing > 10 ppm Re, were analyzed by 70 μm laser ablation spots, and ages were calibrated by analysis of molybdenite pellets. Contrary to our expectation, weighted average ages obtained were in agreement (within 1%) with conventional age determinations, with fairly good precision (from ~ 1 to 5% 2σ depending on Re concentration), suggesting limited or essentially nonexistent decoupling within crystals. Two important implications of this result are that decoupling Re-Os is not universal, and that our new analytical protocol is useful both for dating and for studies of decoupling. The benefit of in situ dating compared to conventional dating is, apart from lower cost and time consumption, the possibility of targeting smaller molybdenite crystals (≥ 100 μm) in thin sections and epoxy mounts. The youngest sample in the study is 920 Ma, but we see potential of dating significantly younger Re-rich molybdenite.

Here we present major element, trace element, and oxygen isotope data for garnet from an amphibolitized eclogite block from Ring Mountain, Franciscan Complex, California, USA. Garnetite veins 1–5 cm thick are laterally continuous up to 10 m within an Mg-rich blackwall zone of the eclogite block. Complex major and trace element zoning patterns reveal multiple stages of garnet growth in both the matrix and garnetite veins. Similarities in major and trace element zoning between matrix and vein garnet suggest that crystallization of the garnetite veins began toward the end of matrix garnet core growth, and continued throughout the garnet growth history of the rock. Oscillatory zoning in rare-earth elements suggests garnet growth in pulses, with matrix-diffusion-limited growth in between pulses. Oxygen isotope analyses of matrix and vein garnet have a range in δ18O values of 5.3–11.1 ‰. Differences in δ18O values of up to ~ 4 ‰ between garnet core and rim are observed in both the matrix and vein; garnet cores range from 9.8 to 11.1 ‰ (median 10.4‰), garnet mantles range from 8.3 to 10.0 ‰ (median 9.7 ‰), and garnet rims range from 5.8 to 7.8 ‰ (median 6.7 ‰). Late-stage vein crystallization appears as a garnet “cement” that fills in a network of small (typically 5–50 µm) garnet cores, and likely crystallized from an amorphous phase. The low δ18O values of this latest stage of garnet growth are consistent with interaction with serpentinites, and likely represent the physical incorporation of the eclogite block into the serpentinite matrix melange.

Antarctic ice-sheet instability is recorded by ice-rafted debris (IRD) in mid- to high-latitude marine sediment, especially throughout climate transitions. The middle Miocene climatic transition (MMCT), 14.2 to 13.8 Ma, which marks the end of a significant warm period during the mid-Miocene, saw a rapid cooling of ca. 6-7 °C in the high-latitude Southern Ocean. This climatic shift was also accompanied by a global δ18O excursion of ca. 1‰, indicating a time of global cooling and significant Antarctic ice expansion (Shevenell et al., 2004). The MMCT is recorded by numerous IRD-rich sediment horizons in deep-sea sediment cores around the Antarctic margin, reflecting iceberg calving during times of ice-sheet instability. Resolving the locations of iceberg calving sites by detrital provenance analysis during the MMCT will be an important tool for forecasting effects of anthropogenic climate change.Here we present results of a multi-proxy provenance study by using K- and plagioclase feldspar, selected due to their relative abundance in clastic sediment, and tendency to incorporate Rb (Kfs only), Pb, and Sr at analytically useful concentrations, thus enabling source-terrane fingerprinting. While Pb-isotope fingerprinting is an established method for provenance analysis of glaciogenic sediment (Flowerdew et al., 2012), combining in-situ Sr-isotope fingerprinting with 87Rb/87Sr dating is a novel approach. These techniques are applied to deep-sea core ODP113-694, which was recovered from the Weddell Sea; as this is located ca. 750 km from the continental rise, in 4671.3 m of water. This location is ideal, as it acts as a major iceberg graveyard making it a key IRD depocenter (Barker, Kennett et al., 1988). Within the core, several IRD layers were identified and analysed with preliminary depositional ages of 14 to 14.4 Ma.We discuss the implications of our results in terms of location of active iceberg calving sites and further consider the viability of our multi-proxy provenance approach to the Antarctic offshore.Barker, P.F., Kennett, J.P., et al., 1988, Proc. Init. Repts. (Pt. A): ODP, 113, College Station, TX (Ocean Drilling Program).Flowerdew, M.J., et al., 2012, Chemical Geology, v. 292–293, p. 88–102, doi: 10.1016/j.chemgeo.2011.11.006.Shevenell, A.E., et al., 2004, Science, v. 305, p. 1766-1770, doi: 10.1126/science.1100061.

This study encompasses the ore mineralogy, textures and sulphide trace element chemistry of the Palaeoproterozoic Lovisa stratiform Zn-Pb deposit and the stratigraphically underlying Lovisa Fe Formation in the Bergslagen ore province (Sweden). We investigate the relative timing of formation and subsequent modifications of its ores in relation to the c. 1.87–1.80 Ga Svecokarelian orogeny. The Lovisa Zn-Pb deposit consists of several different ore types. The massive sphalerite-galena ore is distinctly deformed, exhibiting a multiple-scale “ball ore” texture with rounded silicate clasts within a deformed, fine-grained sulphide matrix. Underlying the massive ore is a locally folded, sphalerite-rich laminated ore, interpreted to represent a metamorphosed relict primary lamination. Several generations of sphalerite-galena fracture fillings and veins occur adjacent to the main ore zones and they cross-cut early ductile structures and metamorphic features. The trace element signatures of the sphalerite-galena infillings generally mimic those of the two main ore zones, thus supporting an origin by localised remobilisation of the primary sulphide ore and demonstrating limited trace element redistribution during this process. In contrast, discrete sulphosalt-rich fracture fillings cross-cutting earlier galena-chalcopyrite-rich fracture fillings and veinlets in the Lovisa Fe Formation suggest a significant but still relatively localised redistribution of metals. Trace element mapping of sulphides from the Lovisa Zn-Pb deposit reveals that inclusion-free overgrowths on pyrite crystals are locally Co-enriched compared to the cores, which resulted from the redistribution of Co during late metamorphic processes. Combined textural and geochemical evidence suggest that the originally syngenetic exhalative sulphide ore at Lovisa was locally strongly affected by polyphase deformation and remobilisation. This was initiated during the first stage of amphibolite facies grade regional metamorphism and deformation (D1, c. 1.87–1.85 Ga) but is mostly evident from the later stages (D2) and the evolution to retrograde and brittle conditions (c. 1.83–1.80 Ga and later).

Made available in DSpace on 2022-04-29T08:36:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) High-pressure metamafic rocks from the Passos Nappe, Southern Brasília Orogen, have been traditionally interpreted as highly retrogressed eclogites, even though no reliable P-T conditions were available thus far. In this work, samples from the least retrogressed sample were studied using petrography, mineral and whole-rock chemical analysis, thermodynamic modelling, and rutile U–Pb geochronology, with the objective of unravelling its metamorphic history. The studied rocks are, descriptively, hornblende-garnet-clinopyroxene schists. Garnet and hornblende occur in a matrix composed of clinopyroxene-plagioclase symplectite, with garnet being surrounded by plagioclase-hornblende coronas. A combination of thermodynamic modelling, Zr-in-rutile and Ti-in-quartz thermobarometry suggests peak temperature to be 725 ± 30 °C, attained at a minimum pressure of ≈16 kbar, and data from rutile and quartz crystals included in garnet qualitatively indicate an earlier stage at higher P and lower T, constraining a clockwise P-T path. No evidences of UHP metamorphism were found thus far. A lower intercept age of 579 ± 23 Ma was calculated from rutile data, which is identical, within uncertainty, to rutile ages obtained previously in units immediately above the rocks studied here. The data suggests that these rocks were submitted to a different P-T path compared to the adjacent units, and that they were subducted to depths of at least ≈60 km and tectonically emplaced amid the surrounding metapelitic rocks before 579 Ma, which is compatible with current models for the evolution of the Southern Brasilia Orogen. Department of Mineralogy and Geotectonics Institute of Geosciences University of São Paulo, Rua do Lago, 562 Department of Petrology and Metallogeny São Paulo State University, Av. 24A, 1515 Department of Earth Sciences University of Gothenburg, PO Box 460 Department of Petrology and Metallogeny São Paulo State University, Av. 24A, 1515 FAPESP: 13/04007-0 FAPESP: 15/05230-0 FAPESP: 16/22627-3 CNPq: 305720/2020-1 CNPq: 311606/2019-9 CNPq: 486328/2013-9

Translating burial and exhumation histories from the petrological and geochronological record of high-pressure assemblages in subduction channels is key to understanding subduction channel processes. Convective return flow, either serpentinite or sediment hosted, has been suggested as a potential mechanism to retrieve rocks from significant depths and exhume them. Numerical modelling predicts that during convective flow, subducted material can be cycled within a serpentinite-filled subduction channel. Geochronological and petrological evidences for such cycling during subduction are preserved in lawsonite eclogite from serpentinite melange in the Southern New England Orogen, eastern Australia. Ar–Ar, Rb–Sr phengite and U–Pb titanite geochronology, supported by phase equilibrium forward modelling and mineral zoning, suggest Cambro–Ordovician eclogite underwent two stages of burial separated by a stage of partial exhumation. The initial subduction of the eclogite at ca. 490 Ma formed porphyroblastic prograde-zoned garnet and lawsonite at approximate P–T conditions of at least 2.9 GPa and 600 °C. Partial exhumation to at least 2.0 GPa and 500 °C is recorded by garnet dissolution. Reburial of the eclogite resulted in growth of new Mg-rich garnet rims, growth of new prograde-zoned phengite and recrystallization of titanite at P–T conditions of approximately 2.7 GPa and 590 °C. U–Pb titanite, and Ar–Ar and Rb–Sr phengite ages constrain the timing of reburial to ca. 450 Ma. This was followed by a second exhumation event at approximately 1.9 GPa and 520 °C. These conditions fall along a cold approximate geotherm of 230 °C/GPa. The inferred changes in pressure suggest the lawsonite eclogite underwent depth cycling within the subduction channel. Geochronological data indicate that partial exhumation and reburial occurred over ca. 50 M y., providing some estimation on the timescales of material convective cycling in the subduction channel Refereed/Peer-reviewed

The Pontiac subprovince consists of metaturbidites, plutons and thin ultramafic rock layers of Archean age and lies south of the Cadillac-Larder Lake (C-LL) fault zone which is the boundary between the Pontiac and the extensively mineralized Abitibi Greenstone Belt. The sediments show a Barrovian metamorphic gradient which increases southwards, away from the C-LL fault. The most likely tectonic provenance for the Pontiac sedimentary rocks is that they represent a relic accretionary prism with material derived from both the Abitibi and an older terrane. Zircon U-Pb dating shows that deposition occurred not later than 2685±3 Ma ago and recent, robust Lu-Hf dating of garnets bracketed Pontiac's peak metamorphic conditions at 2658±4 Ma. For this study we used a recently developed LA-ICP-MS/MS method for in-situ Rb-Sr dating of biotite and plagioclase in samples ranging in metamorphic grade (biotite to sillimanite zones) from the Pontiac subprovince. Calibration of the instrument was achieved by repeated ablations on several reference materials (see Hogmalm et al. 2017) which also provided the monitoring of accuracy and precision throughout the analyses. Results show a range in dates between 2550 Ma and 2200 Ma with an average of 2440±50 Ma (2σ). Samples from the staurolite and kyanite zones have a larger range with respect to the other zones, but no significant differences are observed in the data with any method of data handing. These dates are ≈300Ma younger than the peak metamorphism in the area and this is attributed to either overgrowth and re-setting of the Rb-Sr system by a second metamorphic/hydrothermal event, or diffusional resetting with core-rim age variations. Possible influence from the adjacent late syntectonic to post-tectonic monzodiorite-monzonite-granodiorite-syenite (MMGS) plutons dated 2671±4 Ma and the garnet-muscovite-granite series (GMG) dated ≈2650 Ma cannot be ruled out. This study provides insights about the metamorphic history of the sequence and supports previous findings regarding resetting of some isotopic systems with relatively low closure temperatures (≈350-400°C) by later thermal events.

The Barberton Greenstone Belt (BGB) is a well-preserved remnant of Paleo- to Mesoarchean crust. The oldest supracrustal rocks of the BGB consist of the 3.5-3.3 Ga Onverwacht Group. These rocks form a NE-SW trending belt deformed and metamorphosed largely under lower greenschist-facies conditions. In the southern BGB, the Komati Fault separates the structurally uppermost, lower greenschist-facies Onverwacht Group from its stratigraphically lowest components – the Sandspruit and Theespruit Formations (hereafter referred to as Lower Onverwacht Group), which occur south of the Komati Fault and have been metamorphosed under high-pressure amphibolite-facies conditions. The Lower Onverwacht Group rocks occur as a band along the southern edge of the greenstone belt and as septa between several ca. 3.55, 3.45 and 3.23 Ga Tonalite-Trondhjemite-Granodiorite plutons. The Lower Onverwacht Group rocks record a complex history of metamorphism and retrogression. An early phase of amphibolite-facies metamorphism is recorded at ca. 3.44 Ga by monazite in metasediments, whilst the main phase of the regional metamorphism occurred at ca. 3.23 Ga (e.g. Cutts et al., 2014).The rocks targeted in this study have felsic metavolcanic protoliths and occur as a greenstone remnant within deformed and undeformed phases of 3.45 Ga Trondhjemites. They contain cm-sized garnets and the mineralogy of the samples indicate amphibolite-facies peak metamorphism. The garnets show major element growth zonation from core to rim (Alm0.63-0.80 Grs0.15-0.08Pyr0.0.05-0.09Sps0.17-0.0.03). U-Pb rutile geochronology gives an age at 3.15 Ga and Zr-in-rutile thermometry yields a temperature of ca. 640 °C (at 5 kbar). The rutile grains contain small, pristine zircon inclusions and the rutile is assumed to have grown in equilibrium with both zircon and quartz as buffer phases. The amphibolite-facies assemblage and the Zr-in-rutile temperature indicate that the rutile dates are cooling ages, which are difficult to interpret without information on the age of peak metamorphism of the samples. The objective of this study is to attempt to elucidate the early metamorphic record of these samples by directly dating the large garnet grains using in situ U-Pb laser-ablation inductively-coupled-plasma mass-spectrometry geochronology. Ongoing research shows that low-U garnet is datable by this method (Albert Roper et al., 2018). Preliminary results have been obtained from a different Lower Onverwacht Group sample, yielding a 3.45 Ga age for the garnet core and a 3.22 Ga age for the garnet rim (Cutts et al, unpublished data). The results indicate that U-Pb in rutile and in garnet from Archaean greenstones can be used in order to date metamorphic events. This is especially relevant when other potential datable accessory minerals, such as zircon or monazite, are not present. ReferencesCutts et al., 2014. Geological Society of America Bulletin 126, 251–270.Albert Roper et al., 2018. Goldschmidt Abstracts, 2018, 32.

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sancakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sancakaya Massif over an area of ca. 12 km by 15 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 +/- 6 to 434 +/- 7 Ma (2 sigma), and on those from a felsic vein an age of 319 +/- 5 Ma (2 sigma) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial cHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of -16 to -9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the PaleoTethyan accretionary complexes, and (ii) the resemblance of the U-Pb age spectra of detrital zircons in the metadastic sequence of the Sancakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the AnatolideTauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sancakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions. (C) 2019 Elsevier B.V. All rights reserved.

Kesebolite-(Ce), ideal formula CeCa2Mn(AsO4)[SiO3]3, is a new mineral (IMA No. 2019-097) recovered from mine dumps at the Kesebol Mn-(Fe-Cu) deposit in V&auml, stra G&ouml, taland, Sweden. It occurs with rhodonite, baryte, quartz, calcite, talc, andradite, rhodochrosite, K-feldspar, hematite, gasparite-(Ce), chernovite-(Y) and ferriakasakaite-(Ce). It forms mostly euhedral crystals, with lengthwise striation. The mineral is dark grayish-brown to brown, translucent, with light brown streak. It is optically biaxial (+), with weak pleochroism, and ncalc = 1.74. H = 5&ndash, 6 and VHN100 = 825. Fair cleavage is observed on {100}. The calculated density is 3.998(5) g&middot, cm&minus, 3. Kesebolite-(Ce) is monoclinic, P21/c, with unit-cell parameters from X-ray single-crystal diffraction data: a = 6.7382(3), b = 13.0368(6), c = 12.0958(6) &Aring, &beta, = 98.578(2)&deg, and V = 1050.66(9) &Aring, 3, with Z = 4. Strongest Bragg peaks in the X-ray powder pattern are: [I(%), d(&Aring, ) (hkl)] 100, 3.114 (20-2), 92, 2.924 (140), 84, 3.138 (041), 72, 2.908 (014), 57, 3.228 (210), 48, 2.856 (042), 48, 3.002 (132). The unique crystal structure was solved and refined to R1 = 4.6%. It consists of 6-periodic single silicate chains along (001), these are interconnected to infinite (010) strings of alternating, corner-sharing MnO6 and AsO4 polyhedra, altogether forming a trellis-like framework parallel to (100).

The U–Pb age and trace element composition of detrital rutile provide information about the metamorphic history of the source region that cannot be constrained by traditional U–Pb dating of detrital zircon. Previous provenance investigations focussed on only one of these methods. Based on a large LA-ICP-MS trace element and U–Pb isotopic dataset of detrital rutile and U–Pb isotopic data of detrital zircon from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany, this paper discusses the application and significance of combining these methods in provenance investigations. U–Pb age spectra from the detrital zircons analysed show multiple age components (multimodal age spectra) in all samples. This is in contrast with the detrital rutile data, as only one sample yielded a multimodal U–Pb age distribution. Multimodal age spectra of detrital rutile are most likely preserved in sediments from (large) catchment areas with complex geological histories. They may also be related to specific sedimentation events, such as glacial washout during the retreat of large ice shields (e.g. the Hirnantian glaciation of Gondwana). Unimodal age spectra are however not restricted to small catchment areas, if the provenance region is characterized by a pervasive thermal overprint such as the Pan-African orogeny throughout Gondwana. Unimodal age distributions may further consist of overlapping age cluster detectable by different trace element composition of the detrital rutile grains. The combined U–Pb age and trace element data from detrital rutile grains demonstrate that rutile sourced from metapelitic rocks yield reliable and precise U–Pb ages. In contrast, detrital rutile classified to be of metamafic origin generally has too low uranium concentrations to be dated reliably by LA-ICP-MS. Detrital rutile records low- to medium-grade metamorphic events in the source region and therefore has the potential to better constrain the maximum depositional age of sedimentary rocks in comparison to U–Pb dating of detrital zircon.

Coralline algae have been used for sclerochronological studies throughout the last decade. These studies have focused on two different growth morphologies of the photosynthetic coralline algae: massive crusts forming small buildups on hard substrate, and free-living branching algal nodules, known as rhodoliths. The latter are generally found on soft-substrate, where they are frequently overturned by water movement and bottom feeding organisms, leaving one side of the rhodolith partially buried in the sediment at any given time. Here we test whether either of these growth morphologies is more suitable for proxy reconstructions by comparing Mg/Ca ratios – a temperature proxy – in multiple replicates of rhodoliths of Lithothamnion glaciale and in rhodoliths as well as encrusting specimens of Clathromorphum compactum. With both species being widespread throughout the Temperate and Arctic regions, we have chosen two North Atlantic localities at Nuuk Fjord, Greenland (Subarctic), and off the southeastern coast of Newfoundland, Canada (Temperate), for this study. Two to three Mg/Ca ratio transects spanning 18 years of growth were analysed on multiple specimens with encrusting morphologies and along different sides of rhodoliths using laser ablation inductively coupled mass spectrometry and compared to remotely sensed sea surface temperature (SST) data. The length of the common time span used for comparison was limited by growth interruptions in rhodoliths. Furthermore, our comparison is based on the assumption that rhodolith growth increments are annual – an assumption that has recently been challenged by mesocosm studies. Monthly Mg/Ca values from multiple transects within each individual were compared and in samples from Nuuk fjord significant correlations were found in 4 of 4 encrusting C. compactum, 4 of 4 C. compactum rhodoliths, and 2 of 3 L. glaciale rhodoliths. In Newfoundland significant correlations were found in 6 of 6 encrusting C. compactum comparisons (average: r = 0.61, p