ALBERT

Description: Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50-80 °C, significantly smaller than previously suggested.

Description: Triassic turbidites of the Nanpanjiang basin of south China represent the most expansive and voluminous siliciclastic turbidite accumulation in south China. The Nanpanjiang basin occurs at a critical junction between the southern margin of the south China plate and the Indochina, Siamo and Sibumasu plates to the south and southwest. The Triassic Yangtze carbonate shelf and isolated carbonated platforms in the basin have been extensively studied, but silicilastic turbidites in the basin have received relatively little attention. Deciphering the facies, paleocurrent indicators and provenance of the Triassic turbidites is important for several reasons: it promises to help resolve the timing of plate collisions along suture zones bordering the basin to the south and southwest, it will enable evaluation of which suture zones and Precambrian massifs were source areas, and it will allow an evaluation of the impact of the siliciclastic flux on carbonate platform evolution within the basin. Turbidites in the basin include the Early Triassic Shipao Formation and the Middle-Late Triassic Baifeng, Xinyuan, Lanmu Bianyang and Laishike formations. Each ranges upward of 700 m and the thickest is nearly 3 km. The turbidites contain very-fine sand in the northern part of the basin whereas the central and southern parts of the basin also commonly contain fine and rarely medium sand size. Coarser sand sizes occur where paleocurrents are from the south, and in this area some turbidites exhibit complete bouma sequences with graded A divisions. Successions contain numerous alternations between mud-rich and sand-rich intervals with thickness trends corresponding to proximal/ distal fan components. Spectacularly preserved sedimentary structures enable robust evaluation of turbidite systems and paleocurrent analyses. Analysis of paleocurrent measurements indicates two major directions of sediment fill. The northern part of the basin was sourced primarily by the Jiangnan massif in the northeast, and the central and southern parts of the basin were sourced primarily from suture zones and the Yunkai massif to the south and southeast respectively. Sandstones of the Lower Triassic Shipao Fm. have volcaniclastic composition including embayed quartz and glass shards. Middle Triassic sandstones are moderately mature, matrix-rich, lithic wackes. The average QFL ratio from all point count samples is 54.1/18.1/27.8% and the QmFLt ratio is 37.8/ 18.1/ 44.1%. Lithic fragments are dominantly claystone and siltstone clasts and metasedimentary clasts such as quartz mica tectonite. Volcanic lithics are rare. Most samples fall in the recycled orogen field of QmFLt plots, indicating a relatively quartz and lithic rich composition consistent with derivation from Precambrian massifs such as the Jiangnan, and Yunkai. A few samples from the southwest part of the basin fall into the dissected arc field, indicating a somewhat more lithic and feldspar-rich composition consistent with derivation from a suture zone Analysis of detrial zircon populations from 17 samples collected across the basin indicate: (1) Several samples contain zircons with concordant ages greater than 3000 Ma, (2) there are widespread peaks across the basin at 1800 Ma and 2500, (3) a widespread 900 Ma population, (3) a widespread population of zircons at 440 Ma, and (5) a larger population of younger zircons about 250 Ma in the southwestern part which is replaced to the north and northwest by a somewhat older population around 260-290 Ma. The 900 Ma provenance fits derivation from the Jiangnan Massif, the 2500, 1800, and 440 Ma provenance fits the Yunkai massif, and the 250 Ma is consistent with convergence and arc development in suture zones bordering the basin on the south or southwest. Early siliciclastic turbidite flux, proximal to source areas impacted carbonate platform evolution by infilling the basin, reducing accommodation space, stabilizing carbonate platform margins and promoting margin progradation. Late arrival, in areas far from source areas caused margin aggradation over a starved basin, development of high relief aggradational escarpments and unstable scalloped margins.

Description: The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Serpentinites have low viscosity at geological strain rates. However, compelling geophysical evidence of a serpentinite channel during continental subduction is still lacking. Here we show that anomalously low shear-wave seismic velocities are found beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle. We propose that these seismic velocities indicate the stacked remnants of a weak fossilised serpentinite channel, which includes both slivers of abyssal serpentinite formed at the ocean floor and mantle-wedge serpentinite formed by fluid release from the subducting slab. Our results suggest that this serpentinized plate interface may have favoured the subduction of continental crust into the upper mantle and the formation/exhumation of ultra-high pressure metamorphic rocks, providing new constraints to develop the conceptual and quantitative understanding of continental-subduction dynamics.

Description: This research was supported by NSFC (grant nos. 41888101, 91755000, and 41625016), CAS program (GJHZ1776), Agence Nationale de la Recherche (contract ANR-15-CE31-0015), and Labex OSUG@2020 (Investissement d’Avenir, ANR-10-LABX-56). T.B. is funded by the European Union’s Horizon 2020 research and innovation program (grant no. 716542). This is contribution 1484 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au). This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.

Description: Published

Description: id 2171

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Glutamine synthetase (GS) plays an essential role in metabolism by catalyzing the synthesis of glutamine from glutamate and ammonia. Our recent study showed that CRBN, a direct protein target for the teratogenic and antitumor activities of immunomodulatory drugs such as thalidomide, lenalidomide, and pomalidomide, recognizes an acetyl degron of GS, resulting in ubiquitylation and degradation of GS in response to glutamine. Here, we report that valosin-containing protein (VCP)/p97 promotes the degradation of ubiquitylated GS, resulting in its accumulation in cells with compromised p97 function. Notably, p97 is also required for the degradation of all four known CRBN neo-substrates [Ikaros family zinc finger proteins 1 (IKZF1) and 3 (IKZF3), casein kinase 1α (CK1α), and the translation termination factor GSPT1] whose ubiquitylation is induced by immunomodulatory drugs. Together, these data point to an unexpectedly intimate relationship between the E3 ubiquitin ligase CRL4CRBNand p97 pathways.