Kimberlite from Rajmahal magmatic province: Sr-Nd-Pb isotopic evidence for Kerguelen plume derived magmas

Previous studies showed that the Rajmahal-Sylhet-Bengal (RSB) flood basalt province (117 ± 2 Ma) in eastern India was spatially close to the active Kerguelen hotspot about 118 Ma ago. Yet, it could not be unequivocally correlated to this hotspot due to wide variation in isotopic compositions of both the RSB and Kerguelen plateau basalts. However, we report Sr-Nd-Pb isotopic compositions (87Sr/86Sri: 0.70535 to 0.70561; εNd(T): -2.6 to -3.2; 206Pb/204Pbi: 17.88 to 18.07) of a co-eval (116 ± 2 Ma) Group II kimberlite from this flood basalt province that is identical to recently identified pristine Kerguelen plume basalts from the Kerguelen Plateau/Archipelago and Broken Ridge. This suggests that the Kerguelen hotspot could indeed be responsible for the ˜117 Ma magmatic activity in Eastern India

Is strontium isotope record a strict proxy for chemical weathering rates during the late Miocene (Ocean Drilling Program Site 758A)?

The strontium isotope ratios are examined in the shells of planktic foraminifer Orbulina universa in 20 samples from the late Miocene (8.03-6.36 Ma) sequence of Ocean Drilling Program (ODP) Site 758A, northeastern Indian Ocean. The Sr isotope ratios increased between 7.91 and 7.36 Ma and in the latest Miocene (6.48-6.36 Ma) reflecting high riverine flux from increased chemical weathering and high precipitation in the Himalayan region. The 87Sr/86Sr values decreased during 7.36 to 6.48 Ma coincident with the main phase of Chron-6 negative carbon shift. The carbon shift reflects high delivery of nutrients to the oceans. This contradicts the use of Sr isotope record as a strict proxy for global chemical weathering rates. The Sr isotope ratio should be used with great care in understanding the climatic- tectonic connections

Trace element and isotopic studies of Permo-Carboniferous carbonate nodules from Talchir sediments of peninsular India: environmental and provenance implications

Syngenetic carbonate nodules constitute an interesting feature of the glaciogene sediments of various Talchir basins in peninsular India. Petrographic, cathodoluminescence and sedimentary results suggest that many of these nodules contain primary carbonate precipitates whose geochemical signatures can be used for determining environment of deposition and provenance of the sediments and drainage source. Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean δ18O and δ13C values of the calcites in the nodules are - 19.5% and-9.7% (w.r.t. PDB) respectively suggesting a freshwater environment (probably lacustrine) for formation of these objects. Trace element ratios (Eu/Eu* and La/Yb) of the nodule samples show that the source of the sediments in the Damodar valley basin was the granites, gneisses and intrusives in the Chotanagpur region. The sediments in the Mahanadi valley were derived from granulites, charnockites and granites of the eastern ghat region. The Sr concentration of the carbonate phase of the nodules is low, ranging from 10-60 ng/g. The87Sr/86Sr ratios of the samples from the west Bokaro basin and Ramgarh basin vary from 0.735 to 0.748 (mean: 0.739) and from 0.726 to 0.733 (mean: 0.730) respectively. These values are consistent with our proposition that water of these basins drained through the granitic rocks of the Chotanagpur region. In contrast, the87Sr/86Sr ratios of the samples from the Talchir basin (Type area) of Mahanadi valley vary from 0.718 to 0.723 (mean: 0.719). These87Sr/86Sr ratios are close to those of the granulites in the adjoining eastern ghat belt suggesting that area as the drainage source

The ALPS project: open source software for strongly correlated systems

We present the ALPS (Algorithms and Libraries for Physics Simulations) project, an international open source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. Development is centered on common XML and binary data formats, on libraries to simplify and speed up code development, and on full-featured simulation programs. The programs enable non-experts to start carrying out numerical simulations by providing basic implementations of the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended ensemble simulations, exact and full diagonalization (ED), as well as the density matrix renormalization group (DMRG). The software is available from our web server at http://alps.comp-phys.org.Comment: For full software and introductory turorials see http://alps.comp-phys.or

Performance Limitations of Flat Histogram Methods and Optimality of Wang-Landau Sampling

We determine the optimal scaling of local-update flat-histogram methods with system size by using a perfect flat-histogram scheme based on the exact density of states of 2D Ising models.The typical tunneling time needed to sample the entire bandwidth does not scale with the number of spins N as the minimal N^2 of an unbiased random walk in energy space. While the scaling is power law for the ferromagnetic and fully frustrated Ising model, for the +/- J nearest-neighbor spin glass the distribution of tunneling times is governed by a fat-tailed Frechet extremal value distribution that obeys exponential scaling. We find that the Wang-Landau algorithm shows the same scaling as the perfect scheme and is thus optimal.Comment: 5 pages, 6 figure

Reionization with galaxies and active galactic nuclei

In this work we investigate the properties of the sources that reionized the intergalactic medium (IGM) in the high-redshift Universe. Using a semi-Analytical model aimed at reproducing galaxies and black holes in the first ∼1.5 Gyr of the Universe, we revisit the relative role of star formation and black hole accretion in producing ionizing photons that can escape into the IGM. Both star formation and black hole accretion are regulated by supernova feedback, resulting in black hole accretion being stunted in low-mass haloes. We explore a wide range of combinations for the escape fraction of ionizing photons (redshift-dependent, constant, and scaling with stellar mass) from both star formation ($langle f_{ m esc}^{ m sf} angle$) and AGN ($f_{ m esc}^{ m bh}$) to find: (i) the ionizing budget is dominated by stellar radiation from low stellar mass ($M_∗lt 10^9 , { m m M_odot }$) galaxies at z > 6 with the AGN contribution (driven by $M_{bh}gt 10^6 , { m m M_odot }$ black holes in $M_∗ gtrsim 10^9, { m m M_odot }$ galaxies) dominating at lower redshifts; (ii) AGN only contribute $10-25{{ m per cent}}$ to the cumulative ionizing emissivity by z = 4 for the models that match the observed reionization constraints; (iii) if the stellar mass dependence of $langle f_{ m esc}^{ m sf} angle$ is shallower than $f_{ m esc}^{ m bh}$, at z < 7 a transition stellar mass exists above which AGN dominate the escaping ionizing photon production rate; (iv) the transition stellar mass decreases with decreasing redshift. While AGN dominate the escaping emissivity above the knee of the stellar mass function at z ∼6.8, they take-over at stellar masses that are a tenth of the knee mass by z = 4

Seasonal snowpack microbial ecology and biogeochemistry on a High Arctic ice cap reveals negligible autotrophic activity during spring and summer melt

Snowpack ecosystem studies are primarily derived from research on snow-on-soil ecosystems. Greater research attention needs to be directed to the study of glacial snow covers as most snow cover lies on glaciers and ice sheets. With rising temperatures, snowpacks are getting wetter, which can potentially give rise to biologically productive snowpacks. The present study set out to determine the linkage between the thermal evolution of a snowpack and the seasonal microbial ecology of snow. We present the first comprehensive study of the seasonal microbial activity and biogeochemistry within a melting glacial snowpack on a High Arctic ice cap, Foxfonna, in Svalbard. Nutrients from winter atmospheric bulk deposition were supplemented by dust fertilization and weathering processes. NH4+ and PO43− resources in the snow therefore reached their highest values during late June and early July, at 22 and 13.9 mg m−2, respectively. However, primary production did not respond to this nutrient resource due to an absence of autotrophs in the snowpack. The average autotrophic abundance on the ice cap throughout the melt season was 0.5 ± 2.7 cells mL−1. Instead, the microbial cell abundance was dominated by bacterial cells that increased from an average of (39 ± 19 cells mL−1) in June to (363 ± 595 cells mL−1) in early July. Thus, the total seasonal biological production on Foxfonna was estimated at 153 mg C m−2, and the glacial snowpack microbial ecosystem was identified as net-heterotrophic. This work presents a seasonal “album” documenting the bacterial ecology of glacial snowpacks