Magmatic And Tectonic Evolution Of Southern Tibet And The Himalaya

The Himalaya-Tibetan orogen has become the paradigm for continental collision and is central to deciphering continental tectonics. Neogene extension in the orogen is not predicted by plate tectonic theory, and its significance is widely debated.In the Himalaya, north-south extension is restricted to the Southern Tibetan Detachment System (STDS), which juxtaposes the High Himalayan Crystalline Series (HHCS) against the Tibetan Sedimentary Series (TSS). 40Ar-39Ar ages from HHCS and TSS of the Garhwal Himalaya indicate that STDS movement initiated between 17.3 ± 0.4 to 24.3 ± 1.6 Ma (2σ), synchronous with Main Central Thrust (MCT) movement. One-dimensional thermal modelling suggests that the STDS is a reactivated thrust, implying a fundamental change in Himalayan tectonics in the early Miocene.The onset of east-west extension in southern Tibet is constrained by north-south trending shoshonitic dykes to be 13.3 ± 0.8-18.3 ± 2.7 Ma. Trace-element modelling indicates that the shoshonitic dykes and associated lavas in southern and northern Tibet were derived by ≤2% melting of enriched sub-continental lithospheric mantle (SCLM) at 65-85km. The northern and southern shoshonites have distinctive isotopic (εNd(i), north, -5.5 to-10.3; south -8.8 to - 18.1) and major element signatures that relate to distinct SCLM sources corresponding to the tectonically accreted terranes of the plateau. The trace-element compositions of these sources, determined by inverse modelling, suggest subduction-related metasomatism. 40Ar- 39Ar dating of xenocrystic phlogopites indicates metasomatism of the southern SCLM occurred at 62±2 Ma, synchronous with collision.These data link Neogene extension to a thermally perturbed lithosphere. SCLM thinning following slab detachment explains magmatism, extension and uplift in southern Tibet. Episodic convective removal of the SCLM is proposed for northern Tibet. In view of these models, initiation of extension at 18.3±1.6 Ma in southern Tibet places a minimum constraint on plateau uplift. This overlaps with STDS and MCT movement, implying that changes in Himalayan tectonics are controlled by plateau uplift

Service user and carer feedback: simply pass/fail or a genuine learning tool?

Social Work Students in Britain are required to submit feedback from Service Users and Carers as part of their Practice Learning portfolios. The purpose of this is twofold—to demonstrate evidence of the student’s ability and to provide information for the student to reflect on and learn from. Members of the Service User and Carer Advisory group attached to a Social Work degree course believe this represents an opportunity for users and carers to influence future social work practice. In reality however, does this feedback actually make a difference? Group members reviewed user and carer feedback contained within student portfolios submitted during one academic year. They found that whilst there were some excellent examples of constructive criticism, the feedback was overwhelmingly positive towards students. The findings raised questions about how gathering Service User and Carer feedback is viewed and undertaken. Is the feedback seen more as a pass/fail issue or as an opportunity to learn from? Could there be better ways to gain constructive feedback for students? What conditions enable students to learn from the feedback that is gathered? This paper starts to explore these questions and suggests ideas for further research and training

High-pressure synthesis and storage of solid organic compounds in active subduction zones.

Recent thermodynamic and experimental studies have suggested that volatile organic compounds (e.g., methane, formate, and acetate) can be produced and stabilized in subduction zones, potentially playing an important role in the deep carbon cycle. However, field evidence for the high-pressure production and storage of solid organic compounds is missing. Here, we examine forearc serpentinite clasts recovered by drilling mud volcanoes above the Mariana subduction zone. Notable correlations between carbon and iron stable-isotope signatures and fluid-mobile element (B, As and Sb) concentrations provide evidence for the percolation of slab-derived CO2-rich aqueous fluids through the forearc mantle. The presence of carbonaceous matter rich in aliphatic moieties within high-temperature clasts (>350°C) demonstrates that molecular hydrogen production associated with forearc serpentinization is an efficient mechanism for the reduction and conversion of slab-derived CO2-rich fluids into solid organic compounds. These findings emphasize the need to consider the forearc mantle as an important reservoir of organic carbon on Earth