Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal

Morphology, trace elements, and geochronology of zircons from monzogranite in the Northeast Xing'an Block, northeastern China: constraints on the genesis of the host magma

The morphology, trace-element composition and geochronology of 43 zircon grains from two monzogranite samples from the Northeast Xing'an Block, northeastern China, were determined using cathodoluminescence imaging and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Three morphological subtypes (S3, S8 and S9) are recognized in the zircon grain samples, and subtype S8 is dominant, reflecting a calc-alkaline, moderately aluminous, high-pressure crystallization medium and a crystallization temperature of 700 +/- 50 degrees C. The zircon grains are characterized by oscillatory zoning, relatively high Th/U ratios (0.3-1.0), steep chondrite-normalized rare-earth element patterns, high Hf contents (>9000 ppm), positive Ce (Ce/Ce* = 4.84 to 2914) and negative Eu (Eu/Eu* = 0.24 to 0.90) anomalies, indicating a magmatic source. The Pb-206/U-238 ages of the two monzogranite samples are 180 +/- 1 and 181 +/- 1 Ma, respectively, implying an Early Jurassic emplacement age for the intrusion. The disparate geochemical behaviors of Hf, Th, and Nb within the zircons, as well as the U/Yb, Nb/Yb, Th/U, Nb/Hf, Th/Nb, and Hf/Th ratios, suggest a continental-crust source in a compressional-magmatic-arc or orogenic-tectonic setting, and a calc-alkaline parent magma. All of the grains show relatively high Ce4+/Ce3+ ratios, suggesting that they were derived from an oxidized magma, which favors enrichment of Cu-Mo elements in the granite porphyry

Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt: A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt (CAOB) are not yet fully understood. In this study, we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean. Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids. Middle Permian adakitic granites have low Na2O and MgO and high K2O contents, indicating a thickened-lower-crust source. Late Permian S-type granites were derived from the partial melting of continental crust. A compilation of the available geochronological data for Permian intrusive rocks (including adakitic and A-, S-, and I-type granites and mafic rocks) from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian, S-type and adakitic granites mostly during the Middle–Late Permian, and I-type granites and mantle-derived mafic rocks throughout the Permian. The A-type granites, which are proposed to have been sourced from thinned continental crust, indicate an extensional setting in the eastern CAOB during the Early Permian. The Middle–Late Permian adakitic granites imply a thickened continental crust, which indicates a compressional setting. Therefore, the eastern CAOB underwent a transition from extension to compression during the Middle Permian, which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust. Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB, we propose that vertical underplating of mantle- and oceanic-slab-derived magmas contributed the materials for continental crust accretion

Volcanism‐Triggered Climatic Control on Late Cretaceous Oceans

Abstract During the Late Cretaceous, Earth's climate oscillated between warm and cool states, and global oceans changed between anoxic and oxic conditions, resulting in black/gray shales and oceanic red beds (ORBs) deposition, respectively. To understand such climate/ocean dynamics, this study investigated bulk Hg and Hg isotopes, as well as Fe3+/Fe2+ in Upper Cretaceous sediments deposited in southern Tibet and the North Atlantic. In both areas, black/gray shales show much higher Hg concentrations than ORBs, indicating enhanced Hg flux to global oceans during time of black/gray shale deposition. Black/gray shales show lower Fe3+/Fe2+ and positive Δ199Hg, suggesting a significant input of Hg into the anoxic/dysoxic ocean via atmospheric deposition. The isotope values are consistent with a volcanic source for this excess Hg. ORBs show high Fe3+/Fe2+ and negative shifts of Δ199Hg, suggesting that the dominant source of Hg into the oxic oceans was via terrestrial runoff. This study suggests that volcanism was an important driver of the climate/ocean dynamics during the Late Cretaceous

Crustal Mercury Addition Into the Giant Jinchuan Ni‐Cu Sulfide Deposit, China, and Its Geological Implications

Abstract Mercury (Hg) isotopes have shown their power of tracing Hg pollution sources in ecosystems, but their potentials for petrogenetic tracing are yet to be explored. Here we conducted Hg isotope analysis for samples collected from major orebodies of the world‐class Jinchuan Ni‐Cu sulfide deposit, China. These samples show large variations of δ202Hg (−2.65 to +0.19‰) and Δ199Hg (−0.16 to +0.19‰). Some of the Δ199Hg values significantly deviate from current estimates on the primitive mantle (Δ199Hg: 0.0 ± 0.1‰, 2SD). The pronounced Hg mass‐independent fractionation (Hg‐MIF) signals, with significant positive (>0.1‰) and negative (<0.1‰) Δ199Hg values similar to marine sediments and terrestrial soils, respectively, suggests the addition of crustal materials into the Jinchuan deposit, via crustal assimilation during mantle‐derived magma ascending to the crust. These samples show δ34S values (−1.09 to +1.38‰) identical to that of the primitive mantle (0.0 ± 2.0‰), which may indicate a major sulfur source from the mantle. However, δ34S provides poor constraints on the sulfur source, and the early reported anomalous Δ33S values (+0.12 to +2.67‰) in the Jinchuan deposit support the involvement of external sulfur from Archean and Proterozoic sedimentary rocks during the formation of this deposit, similar to the case of Hg. This study shows the powerful use of Hg isotopes as a petrogenic tracer and highlights the importance of interaction between mantle‐derived magmas and crustal materials on the formation of the Jinchuan Cu‐Ni sulfide deposit

Alteration mapping with short wavelength infrared (SWIR) spectroscopy on Xiaokelehe porphyry Cu-Mo deposit in the Great Xing'an Range, NE China: Metallogenic and exploration implications

The newly discovered Xiaokelehe porphyry Cu-Mo deposit (PCD) is situated in northern part of the Great Xing'Sn metallogenic belt, northeastern China. The syn-mineralization granodiorite porphyry was intruded by multiple phases of post-ore barren monzonite, diorite porphyry and granite porphyry, leading to complex and over-printing hydrothermal alteration patterns. This paper present new data on the alteration mineralogy, vein paragenesis, sulfide assemblages and SWIR (short wavelength infrared) spectroscopy at Xiaokelehe, and discuss how SWIR spectral data can help to understand hydrothermal fluid evolution and assist PCD exploration. At Xiaokelehe, oligoclase-epidote alteration is distributed at the deeper levels of the granodiorite porphyry but played little role in mineralization. The following potassic alteration (hydrothermal biotite and K-feldspar) was developed in the granodiorite porphyry with the main Cu-Mo mineralization. Drill core logging suggests that the subsequent chlorite-illite alteration affected almost the entire granodiorite porphyry, and is spatially and genetically associated with minor Cu mineralization. The youngest quartz-muscovite-pyrite alteration dominated in the upper level and outer parts of the PCD, and overprints the earlier alteration phases with only very minor mineralization. The short wavelength infrared (SWIR) analysis results indicate that chlorite and white micas (illite and muscovite) are the most abundant alteration minerals at Xiaokelehe. The wavelengths of Fe-OH band (Pos2250) of chlorite show a decreasing trend away from the granodiorite porphyry into the surrounding sedimentary wall rocks, probably reflecting a drop in temperature and Fe contents of the hydrothermal fluids. The Illite crystallinity (IC) values of white micas show a reverse trend, different from many PCDs, which is likely caused by the distribution pattern of illite and muscovite formed in the ore-proximal chlorite-illite and ore-distal quartz muscovite -pyrite alteration, respectively. At Xiaokelehe, Cu and Mo mineralization is mainly distributed in quartz veins or disseminated within the potassic alteration zones, resembling typical PCDs. Meanwhile, chlorite-illite alteration is also associated with minor Cu mineralization. Thus, areas with intensive chlorite-illite alteration overlapping on potassic alteration likely represent the best exploration targets for high grade Cu-Mo mineralization. These target areas coincide spatially with areas of lower IC ( 2245 nm) values, suggesting the latter two are effective vectoring tools for PCD exploration at Xiaokelehe

Mercury isotopic composition of igneous rocks from an accretionary orogen: Implications for lithospheric recycling

International audienceAbstract Mercury (Hg) provides critical information on terrestrial planet formation and evolution due to its unique physicochemical properties and multiform isotopic compositions. Current knowledge of Hg is mainly limited to Earth's surface environments, and the understanding of Hg in the Earth's interior remains unclear. Accretionary orogens are major settings for continental crustal growth and crust-mantle interactions. We studied the Hg concentration and isotopic composition of igneous rocks in the eastern Central Asian orogenic belt, using Hg as a proxy to trace the recycling of surface materials in Earth's lithosphere. Our results show low Hg abundances in mafic through felsic igneous rocks (4.93 ± 4.35 ppb, standard deviation [SD], n = 267). Mafic rocks show slightly lower δ202Hg (−2.9‰ ± 0.5‰, SD, n = 24) than intermediate (−2.4‰ ± 0.8‰, SD, n = 58) and felsic (−1.5‰ ± 0.8‰, SD, n = 185) rocks, indicating a chemical stratification of Hg isotopic composition in the continental crust with isotopically lighter Hg in the lower part and heavier Hg in the upper part. Slightly positive Δ199Hg values are observed in mantle-derived mafic (0.07‰ ± 0.06‰, SD) and intermediate (0.06‰ ± 0.07‰, SD) rocks, which agree well with those reported for marine sediments, indicating the involvement of fluids or melts from the oceanic crust. Larger variations of Δ199Hg values (−0.26‰ to +0.21‰, average: 0.01‰ ± 0.08‰, SD, n = 185) are observed in felsic rocks, further indicating recycling of surface Hg from the marine reservoir via slab subduction (reflected by positive values) plus magmatic assimilation of terrestrial Hg (reflected by negative values). Our study demonstrates that Hg isotopes can be a promising tracer for the chemical dynamics of Earth's lithosphere

Metal recycling tracked by mercury and helium isotopes in platinum–palladium nuggets from Córrego Bom Sucesso, Brazil

The enigmatic botryoidal nuggets of platinum (Pt) and palladium (Pd) from Córrego Bom Sucesso in the southern Serra do Espinhaço, Minas Gerais, Brazil, are considered to have formed during supergene alteration of placer deposits. This requires hitherto unidentified precious-metal enrichment processes and is inconsistent with Pt–Os age of 180 Ma that entails formation at depth, as recently proposed. Here we report the first mercury (Hg) and helium (He) isotopic determinations of Pt–Pd nuggets. Mercury isotopic compositions have a mass-independent fractionation (MIF) signature with an odd-mass deficit (Δ199Hg = − 0.22 ± 0.04; 1SD, n = 15), which requires aqueous photochemical reduction of Hg (II). Extremely low 3He/4He (&lt;0.001 Ra) and extremely high concentrations of He (up to 1.9 × 1017 at/g) are indicative of nugget formation from He-enriched fluids within the quartzite sequence of the Espinhaço basin, not from meteoric surface water. The data are consistent with a nugget-forming setting in the deep biosphere, as a result of groundwater interaction with Pt–Pd–Hg minerals in Pan-African-Brasiliano post-orogenic veins. We propose that the negative Hg-MIF signature was inherited from the vein minerals that originally acquired their Hg from Earth's surface during the intracratonic sedimentation of the Proterozoic Espinhaço basin

Consistent trace element distribution and mercury isotopic signature between a shallow buried volcanic-hosted epithermal gold deposit and its weathered horizon

Trace elements and Hg isotopic composition were investigated in mineralized rocks, barren rocks, and mineral soils in the Xianfeng prospect, a shallow buried epithermal gold deposit in northeastern China, to understand whether this deposit has left a diagnostic geochemical fingerprint to its weathered horizon. All the rocks and soils display congruent patterns for immobile elements (large ion lithophile elements, high field strength elements, and rare earth elements), which reflect the subduction-related tectonic setting. Both mineralized rocks and soils showed common enrichment of elemental suite As -Ag-Sb-Hg, suggesting that the Xianfeng gold deposit has released these elements into its weathered horizon. Similar mercury isotopic composition was observed between mineralized rocks (delta Hg-202: -0.21 +/- 0.70 parts per thousand; Delta Hg-199: -0.02 +/- 0.12 parts per thousand; 2SD) and barren rocks (delta Hg-202: -0.46 +/- 0.48 parts per thousand;Delta Hg-199: 0.00 +/- 0.10 parts per thousand; 2SD), suggesting that mercury in the Xianfeng deposit is mainly derived from the magmatic rocks. Mineralized soils (delta Hg-202: -0.44 +/- 0.60 parts per thousand; -0.03 +/- 0.14 parts per thousand; 2SD) and barren soils (delta Hg-202: -0.54 +/- 0.68 parts per thousand; Delta Hg-199: -0.05 +/- 0.14 parts per thousand; 2SD) displayed congruent Hg isotopic signals to the underlying rocks, suggesting limited Hg isotope fractionation during the release of Hg from ore deposit to soils via weathering. This study reveals evidence of a simple and direct geochemical link between this shallow buried hydrothermal deposit and its weathered horizon, and highlights that the weathering of shallow-buried hydrothermal gold deposits can release a substantial amount of heavy metals (e.g. Hg, As and Sb) to surface soil. (C) 2020 Elsevier Ltd. All rights reserved.11Nsciescopu