Rare Earth Elements (REE) are essential to modern society but the origins of many large REE deposits remain unclear. The U-Th-Pb ages, chemical compositions and C, O and Mg isotopic compositions of ...Bayan Obo, the world's largest REE deposit, indicate a protracted mineralisation history with unusual chemical and isotopic features. Coexisting calcite and dolomite are in O isotope disequilibrium; some calcitic carbonatite samples show highly varied δ26 Mg which increases with increasing Si and Mg; and ankerite crystals show decreases in Fe and REE from rim to centre, with highly varied REE patterns. These and many other observations are consistent with an unusual mineralisation process not previously considered; protracted fluxing of calcitic carbonatite by subduction-released high-Si fluids during the closure of the Palaeo-Asian Ocean. The fluids leached Fe and Mg from the mantle wedge and scavenged REE, Nb and Th from carbonatite, forming the deposit through metasomatism of overlying sedimentary carbonate.
We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded ...over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 plus or minus 5Ma), at amphibolite-facies grade, at 600 degree C. Abundant monazite yielding similar ages (1557 plus or minus 2 to 1585 plus or minus 3Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 plus or minus 4 and 1587 plus or minus 4Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present ( greater than or equal to 700 degree C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30Ma period of melt crystallisation (1557-1587Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 degree C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 degree C.
The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth's history. Previous temperature estimates of up to ~70°C have spawned controversial ...speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician-Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.
In the aftermath of the Permian-Triassic boundary mass extinction (~252 Ma) ― the most dramatic biotic crisis of the Phanerozoic ― changes in climate, the carbon cycle, and biodiversity patterns ...remained extremely variable for several million years. In particular, the Smithian-Spathian boundary crisis, which occurred ca. 1.5 Ma after the Permian-Triassic boundary, coincided with drastic changes in global climate, a major extinction of nektonic organisms, and major shifts in the carbon and oxygen isotope compositions of marine carbonates and phosphates. However, the timing of these events and their interrelationships remain controversial. Previous studies concluded that the latest Smithian-earliest Spathian interval was a time of extremely high temperatures, which would have precluded marine (macro)-vertebrates from inhabiting the equatorial realm. Conversely, based on oxygen isotope measurements of conodont elements collected at high temporal resolution from the Salt Range record (Pakistan), we report a major cooling event during that time interval. These results suggest that the interplay between climate and biodiversity patterns is more complex than usually portrayed.
Most zircon from Archean (3.8–2.5Ga) trondhjemitic rocks, meta-gabbro, meta-diorite and monzogranite from the Anshan area, North China Craton, has δ18O values in the range of 4.6–7.5‰, but some has ...extreme compositions (0.02–11.0‰, with one value as low as −11.3‰) as a result of pre-, syn- and post-magmatic processes. Nearly all zircon grains with very low δ18O (<4.0‰) are U-rich and show evidence of radiogenic Pb loss, irrespective of their origin (magmatic, metamorphic, recrystallized, inherited or trapped). The low δ18O is not a primary feature of the zircon or the magma from which it crystallized, but is a consequence of high-temperature hydrothermal alteration, probably involving meteoric water. Radiogenic Pb loss is an indicator that the zircon O isotopic composition is likely to have been modified, even if the measured δ18O falls within, or is above, the “normal” igneous range (4.6–7.5‰). Excluding those showing strong Pb loss, most magmatic zircon grains have δ18O values in the “normal” range or only slightly above the previously reported highest δ18O value for Archean igneous zircon (7.5‰), with many, including some analyzed from Eoarchean rocks, being higher than 6.5‰, evidence for crustal reworking in the Anshan area 3.8Ga ago. The 2.5Ga Qidashan syenogranite has the highest zircon δ18O (5.8–11.0‰), consistent with its derivation by melting of sedimentary materials as a result of long-term crustal evolution in the region, as indicated by its chemical and Nd isotopic compositions.
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•Anshan Archean (3.8–2.5Ga) rocks are trondhjemite, gabbro, diorite and monzogranite.•Most zircon has δ18O of 4.6 to 7.5‰ with some having extreme values (−11.3 to 11.0‰).•Low δ18O, with radiogenic Pb loss, from high-U zircon reflects O isotopic alteration.•High δ18O in magmatic zircon is evidence for crustal reworking in Anshan 3.8Ga ago.
Secondary ion mass spectrometry (SIMS) is gaining popularity for molecular imaging in the life sciences because it is label-free and allows imaging in two and three dimensions. The recent ...introduction of the OrbiSIMS has significantly improved the utility for biological imaging through combining subcellular spatial resolution with high-performance Orbitrap mass spectrometry. SIMS instruments operate in high-vacuum, and samples are typically analyzed in a freeze-dried state. Consequently, the molecular and structural information may not be well-preserved. We report a method for molecular imaging of biological materials, preserved in a native state, by using an OrbiSIMS instrument equipped with cryogenic sample handling and a high-pressure freezing protocol compatible with mass spectrometry. The performance is demonstrated by imaging a challenging sample (>90% water) of a mature Pseudomonas aeruginosa biofilm in its native state. The 3D distribution of quorum sensing signaling molecules, nucleobases, and bacterial membrane molecules is revealed with high spatial-resolution and high mass-resolution. We discover that analysis in the frozen-hydrated state yields a 10 000-fold increase in signal intensity for polar molecules such as amino acids, which has important implications for SIMS imaging of metabolites and pharmaceuticals.
The Late Palaeozoic rock associations, in particular A-type igneous rocks, of Iran are rarely exposed, but they are key to reconstructing the evolutionary history of the Tethyan oceans. Zircon U-Pb ...dating of a representative rhyolite sample from Pir-Eshagh, NW Iran, yields an Early Carboniferous (Visean) crystallization age of 340 ± 2.7 Ma. The extrusive rhyolite has the chemical characteristics of the A
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subtype of A-type magmas, providing evidence for a magmatic activity within extensional basin. The composition of rocks is metaluminous to slightly peraluminous and K-rich, with trace element signatures similar to those of OIB. Low Y/Nb and Ce/Nb ratios are consistent with a combination of source enrichment and crustal contamination and ultimately that the studied rhyolites have formed by fractional crystallization from an enriched mantle-derived mafic parental magma, with crustal interactions. Palaeogeographic reconstructions of the Tethyan oceans and their borders imply that the Proto-Tethys Ocean has not spread in Iranian plate, although evidence for Paleo-Tethys and Neo-Tethys in the form of ophiolitic units is well-preserved. The Late Palaeozoic magmatic rocks of Iran define a trend parallel to the ridge separating Neo-Tethys the Iranian plate from Arabia and demonstrate that the separation of the Cimmerian terranes from northern Gondwana by the opening of the Neo-Tethys Ocean, and their drift northwards, began in the Late Devonian to Early Carboniferous.
Migmatites and partial melts are exposed in both the lower and upper package of the Higher Himalayan Crystallines (HHC) thrust sheet within the Sikkim Himalayas. Zircon monazite and quartz oxygen ...isotopic ratios from Yumthang Valley, North Sikkim, and Rathong Chuu, West Sikkim, have been used to identify their sources and equilibrium conditions. Monazites show homogeneous growth, whereas zircons show growth rings. U-Th-Pb data on monazite only indicate the latest metamorphic event. However, zircons show metamorphic rim growth between 36 and 24 Ma over their detrital core with trailing growth from 22 Ma to 15 Ma. Pervasive fluids have been interpreted in coeval development during metamorphism, as shown by monazite and zircon c. 30 Ma. The Th/U ratio of zircon is higher and variable with weak residual zoning in the samples from higher elevations. Quartz–metamorphic zircon oxygen fractionation suggests Teq > 600 °C, while quartz–monazite fractionation shows the same or lower temperatures. Multiple sources of melts in the HHC (even along a single valley) have been observed by δ18O of 7‰ to 10‰ in zircon and 5‰ to 9‰ in monazite. Zircon and monazite generated in the same rock have similar δ18O values. Monazite grown ~20 Ma in the lower elevation sample had a low δ18O, suggesting interaction with an external fluid.
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•Whole body motor unit MRI (MUMRI) offers a sensitive and non-invasive method to image fasciculation in multiple body regions.•Whole body MUMRI fasciculation rates correlated with ...single channel surface EMG fasciculation rates.•MUMRI discriminated well between ALS patients and healthy people for proximal limb and paraspinal muscles, but not the tongue.
Compare fasciculation rates between amyotrophic lateral sclerosis (ALS) patients and healthy controls in body regions relevant for diagnosing ALS using motor unit MRI (MUMRI) at baseline and 6 months follow-up, and relate this to single-channel surface EMG (SEMG).
Tongue, biceps brachii, paraspinals and lower legs were assessed with MUMRI and biceps brachii and soleus with SEMG in 10 healthy controls and 10 patients (9 typical ALS, 1 primary lateral sclerosis PLS).
MUMRI-detected fasciculation rates in typical ALS patients were higher compared to healthy controls for biceps brachii (2.40 ± 1.90 cm-3min−1vs. 0.04 ± 0.10 cm-3min−1, p = 0.004), paraspinals (1.14 ± 1.61 cm-3min−1vs. 0.02 ± 0.02 cm-3min−1, p = 0.016) and lower legs (1.42 ± 1.27 cm-3min−1vs. 0.13 ± 0.10 cm-3min−1, p = 0.004), but not tongue (1.41 ± 1.94 cm-3min−1vs. 0.18 ± 0.18 cm-3min−1, p = 0.556). The PLS patient showed no fasciculation. At baseline, 6/9 ALS patients had increased fasciculation rates compared to healthy controls in at least 2 body regions. At follow-up every patient had increased fasciculation rates in at least 2 body regions. The MUMRI-detected fasciculation rate correlated with SEMG-detected fasciculation rates (τ = 0.475, p = 0.006).
MUMRI can non-invasively image fasciculation in multiple body regions and appears sensitive to disease progression in individual patients.
MUMRI has potential as diagnostic tool for ALS.
The dominant geodynamic processes that underpin the formation and evolution of Earth's early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei. Here, we ...present U–Pb ages and Hf isotopic compositions of detrital zircon grains from ∼2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton, eastern India. The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga. Together with the recently reported Hadean, Eoarchean xenocrystic (up to 4.24 Ga) and modern detritus zircon grains from the Singhbhum craton, our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at ∼4.3–4.2 Ga and ∼3.95 Ga. We observe a prominent shift in Hf isotope compositions at ∼3.6–3.5 Ga towards super-chondritic values, which signify an increased role for depleted mantle and the relevance of plate tectonics. The Paleo-, Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources. We infer a short-lived suprasubduction setting around ∼3.6–3.5 Ga followed by mantle plume activity during the Paleo-, Mesoarchean crust formation in the Singhbhum craton. The Singhbhum craton provides an additional repository for Earth's oldest materials.
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•Detrital zircons with ages of 3.95 to 2.9 Ga from the Singhbhum Craton.•Dacite with age of 3505 ± 5 Ma represents the oldest greenstone sequence in India.•Evidence for both juvenile and recycled crust additions through the Paleoarchean.
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