State Key Laboratory of Lithospheric Evolution

Middle Triassic orogens are widespread around and inside the South China Block (SCB). The southern peripheral belts that develop from northwest to southeast, namely Jinshajiang, Ailaoshan, NW Vietnam, NE Vietnam, Yunkai and Hainan exhibit striking similarities, with Permian–Early Triassic magmatic arc, ophiolitic mélange, northeast- to north-directed synmetamorphic ductile nappes, and fold-and-thrust belt. These collisional belts result from oceanic, then continental subduction of the SCB below Indochina. Eastward of Hainan Island, a Triassic suture is hypothesized offshore of the SCB. Within the SCB, the Xuefengshan is a Middle Triassic intracontinental orogen with northwest-directed folds and thrusts, and an intracrustal ductile décollement . This orogen accommodated the Middle Triassic continental subduction of the western part of the SCB below the eastern part. At variance to the generally accepted models, the inter- and intracontinental Triassic orogens of the SCB are interpreted here as the result of south-directed subductions of the SCB.

Topography effects can be reduced by increasing transfer optics magnification in high precision SIMS isotope analysis.

A straightforward tandem column separation procedure is presented for the separation of Sr, Nd, Pb, and Hf from silicate materials.

In this study, a single-column separation scheme is compared with the traditional three-step separation procedure.

The structure and magnetic properties of nano-sized (1.6 to 4.4 nm) ferrihydrite samples are systematically investigated through a combination of X-ray diffraction (XRD), X-ray pair distribution function (PDF), X-ray absorption spectroscopy (XAS) and magnetic analyses.

. The model is shown not only to be robust and transferable for the AMOEBA model, but also physically meaningful as it universally improves the description of the electrostatic potential around a given molecule.

Abstract More than ten Triassic syenite plutons are revealed to be distributed in North Korea along the boundary to South Korea. The Tokdal Complex is one of these but is unique in its incorporation of early pyroxenite cumulate in the clinopyroxene/amphibole/biotite/nepheline-bearing syenite main body. A SHRIMP U–Pb zircon age of 224 ± 4 Ma was obtained from a biotite syenite sample. Clinopyroxene in pyroxenite is zoned, with either phlogopite and apatite inclusion or ilmenite and magnetite exsolution, and may have resulted from crystallization at high pressure in an active continental margin arc environment followed by ascent and decompression. The pyroxenite and syenite are enriched in light REE and LILE, but strongly depleted in HFSE, with 87 Sr/ 86 Sr t values of ~0.7115 and ϵNd t values of −14 to −20 (t = 224 Ma). The Tokdal Complex could have originated from an enriched lithospheric mantle and undergone assimilation of juvenile materials during differentiation. It indicates an extension of post-collisional magmatism in the Sino-Korean craton. This complex along with many other Triassic plutons in the Sino-Korean craton together constitute three syenite belts along the northern, southern and eastern margins of the craton, possibly resulting in its final configuration in eastern Asia.

Abstract: Major and trace element, including REE, concentrations of the Doushantuo cap carbonate ( c . 635 Ma) in South China show enrichment in Fe, Mn and redox-sensitive elements and slightly negative Ce anomalies, indicating anoxic environments during cap carbonate precipitation. High Fe T /Al ratios but very low concentration of extractable pyrites suggest ferruginous rather than euxinic conditions. The REE + Y patterns of samples show enrichment of heavy REE (HREE), positive Eu anomalies and positive Y anomalies, implying a hydrothermal origin for elevated concentration of Fe, Mn and redox-sensitive elements. The results suggest that ferruginous Ediacaran oceans may have rooted from hydrothermally induced iron accumulation in severely glaciated Cryogenian oceans.

International audience

SIMS Th–Pb dating technique of bastnaesite avoids the excess radiogenic²⁰⁶Pb problem and constrains mineralization time of the Himalayan Mianning–Dechang rare earth element deposits.

We present an analytical protocol for <italic>in situ</italic> U–Pb isotope dating of wolframite series minerals [(Fe,Mn)WO₄], the main ore mineral for tungsten, by LA-SF-ICP-MS.

We report the first U–Pb geochronological investigation of schorlomite garnet from carbonatite and alkaline complexes and demonstrate its applicability for U–Pb age determination using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) due to its relatively high U and Th abundances and negligible common Pb content.

Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ(7)Li in Archean lithospheric mantle. The δ(7)Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from -27 to +21, in marked deviation from the δ(7)Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1-2 ppm). The Li abundances and δ(7)Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ(7)Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ(7)Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.

For the first time, a transitional compound [Ca²⁺ ≡ 2AlSi₃O₈⁻ ≡ <italic>x</italic>OH⁻] was observed for K-feldspar hydrothermal alkaline decomposition, and a model was presented.

Bastnaesite, a common accessory mineral in REE ore deposits, is ideal for U–Pb isotopic dating because of its relatively high U and Th contents.

Abstract The Sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sariçiçek experienced a complex cosmic‐ray exposure history, exposed during ~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid was launched by an impact 22 ± 2 Ma ago to Earth (as did one‐third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages for the basaltic magma clasts. The apatite U‐Pb age of 4525 ± 17 Ma, K‐Ar age of ~3.9 Ga, and the U,Th‐He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic and impact‐related resetting ages, respectively. Petrographic; geochemical; and O‐, Cr‐, and Ti‐isotopic studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 km s −1 from NW ; fragmentations at 37, 33, 31, and 27 km altitude; and provide a pre‐atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Sariçiçek with the Vesta asteroid family (V‐class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the 4 He retention age of Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed ~22 Ma ago.

A new separation method for Sr involving HF coprecipitation combined with AG50 resin from samples with high Rb/Sr ratios.

[1] Following the 2004 Mw9.3 Sumatra earthquake, seismicity rate increased sharply over a wide area of up to ∼2700 km away in Yunnan province, southwestern China. Raised seismicity lasts for ∼14 days. During this period, more than 800 earthquakes with magnitude between 1.5 and 5.1 occurred. This is perhaps the most impressive example of remotely triggered seismicity yet observed. Major events were clustered at several sites that exhibit complex fault geometries, such as step overs and junctures. We use statistic approaches including the β statistics to examine the statistical significance of the seismic rate increases associated with the Sumatra main shock and conclude that there is a reasonable probability that the raised seismicity was remotely triggered by the Sumatra earthquake. Both rapid onset of dynamic triggering (the very first event is a M4.6 earthquake occurred during the passage of the Rayleigh wave from the Sumatra earthquake) and delayed response (activated a few hours to a few days after the Sumatra earthquake) are well established. The triggered activities show more earthquake swarm-like characteristics as indicated by the epidemic-type aftershock sequence modeling results (large percentage of random components and less magnitude dependence in Omori law type self-triggering). Multiple sources of evidence, including intensive hydrothermal activities, and low velocity and high Vp/Vs zones in the lower to middle crust suggests that magma/mantle-generated fluids have a role in the region. High fluid pressure in branched fault zones weakened the faults, making them sensitive to external disturbances and leading to fluid-driven seismicity.

In this study, the laser- and ICP-induced S isotopic fractionation in different S-rich minerals was investigated by using femtosecond (fs) and nanosecond (ns) laser ablation MC-ICP-MS.

One-step separation route based on AG50W-X12 cation-exchange resin and LN Spec extraction chromatographic material for purification of Sr–Nd–Hf from geological samples followed by TIMS and MC-ICP-MS.