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During continental collision, crustal rocks are buried, deformed, transformed and exhumed. The rates, timescales and tectonic implications of these processes are constrained through the sequence and conditions of metamorphic reactions in major and accessory phases. Petrographic, isotopic and elemental data from metabasite samples in NW Bhutan, eastern Himalaya, suggest initial equilibration under high‐pressure (plagioclase‐absent and rutile‐present) conditions, followed by decompression to lower pressure conditions at high‐temperatures that stabilized plagioclase, orthopyroxene and ilmenite. Field observations and chemical indicators suggest equilibration under the lower pressure conditions is likely linked to the infiltration of melt from the host metasedimentary rocks. The metabasites preserve two metamorphic growth stages of chemically‐and petrographically distinct allanite that temporally overlap two stages of zircon growth. Allanite cores and zircon mantles grew at c. 19 ± 2 and 17–15.5 Ma respectively, linked texturally and chemically to the high‐pressure evolution. Symplectitic rims on embayed allanite cores, wholly symplectized Aln–Ilm and Aln–Cpx grains, and high U zircon rims grew at c. 15.5–14.5 Ma, linked chemically to the presence of melt and lower pressure, high‐temperature conditions. A single garnet Lu–Hf date is interpreted as geologically meaningless, with the bulk rock composition modified by melt infiltration after garnet formation. The open system evolution of these rocks precludes precise determination of the reactive bulk composition during metamorphic evolution and thus absolute conditions, especially during the early high‐pressure evolution. Despite these limitations, we show that combined geochemical and petrographic datasets are still able to provide insights into the rates and timescales of deep orogenic processes. The data suggest a younger and shallower evolution for the NW Bhutan metabasites compared to similar rocks in the central and eastern Himalayas. [ABSTRACT FROM AUTHOR]

Strong demand for GIS and burgeoning cohorts have encouraged the delivery of GIS teaching via online distance education models. This contribution reviews a brief foray (2012-2014) into this field by the Open University, deploying open source GIS software to enable students to perform practical science investigations online. The "Remote observation" topic spanned four science disciplines in 6 weeks--an ambitious remit within an innovative overarching module. Documenting the challenges and strategies involved, this paper uses forum usage and student feedback data to derive insights into the student experience and the pitfalls and pleasures of teaching GIS at a distance.

There is lively debate on whether Asian plate material was involved in southward flow of mid-lower crust in a ductile channel beneath southern Tibet. One argument against such involvement is the apparent absence of material derived from Asian lithosphere within the High Himalayan Series (Indian plate) that could represent the putative channel. A north-south--trending mid-Miocene dike swarm that intrudes the Tethyan sedimentary cover of the Sakya gneiss dome (Indian plate) yields new Sr-Nd isotopic data ([sup.87]Sr/[sup.86]Sr = 0.7071-0.7079;[[epsilon].sub.Nd]-4 to-6) indicating that these melts share the same source as Miocene dacitic dikes from north of the Indus-Tsangpo suture. Moreover, dikes on both sides of this suture represent crustal melts derived largely from mid-lower crust of the Asian plate, exposed today as the Nyainqentanglha gneisses that underlie the Gangdese batholith. We infer that melting of the Asian lithosphere extended south of the surface trace of the suture, requiring southward propagation of anatectic Asian middle crustal material during the Miocene. The emplacement ages of the southern dike swarm (12-9 Ma) thus delimit the timing of active southward ductile flow of Asian material. Keywords: Himalaya, isotope geochemistry, tectonics, channel flow.

Clastic sediments deposited in foreland basins and offshore fans allow the evolution of an orogen to be reconstructed--provided their source regions are properly characterized. Isotopic data from the lithotectonic units of the eastern Himalaya (Bhutan) indicate clear isotopic differences directly comparable with the equivalent units from the central Himalaya. Zircons from metaquartzites of the High Himalayan Series that range in age from 980 to 1820 Ma and an orthogneiss intruded at 825 [+ or -] 9 Ma bracket deposition to between 816 and 980 Ma. Model ages derived from Nd isotopes of associated metapelites range from 1700 to 2200 Ma. In contrast, zircons from a metaquartzite from the Lesser Himalayan Series range from 1850 to 2550 Ma. A Paleoproterozoic deposition age (ca. 1750 Ma) is inferred from the age of a metarhyolite associated with the sediments. Model Nd ages of metapelites from the Lesser Himalayan Series range from 2500 to 2600 Ma. The Bhutanese Himalayan units can be correlated more than 1000 km westward along strike from catchments of the Brahmaputra to the headwaters of the Sutlej on the basis of their structural position, provenance, and isotopes. Because current discharge from the Brahmaputra carries the dominant sedimentary flux into the Bengal Fan, results from this work validate the interpretation of isotopic variations observed in offshore deposits, in terms of the unroofing history of the component lithologies of the Himalaya. Keywords: Himalaya, U-Pb ages, zircon, isotope geochemistry.

Many models of orogenesis invoke simple anatomies for mountain belts, comprising a small number of major tectonic provinces separated by major faults. In the Himalayan arc, three main tectonic provinces (the Lesser Himalayan, High Himalayan and Tethyan Series) have been recognized over 2500 km along strike from Bhutan to Kashmir. However, their extension westward to the Nanga Parbat syntaxis remains equivocal. We have supplemented detailed field work in the area with isotopic analysis aimed at revealing distinct signatures for each of the three main provinces. Using Sr isotopic data to refine previous Nd-based discrimination, we demonstrate that the three main tectonic provinces of the central Himalaya also occur in the western syntaxis of northern Pakistan. These three units are thus continuous along the entire orogenic arc. However, their metamorphic grade is generally higher in the syntaxis than in the central Himalaya, challenging the validity of distinctions commonly drawn on this basis elsewhere in the mountain belt. The corollary is that these high-grade units probably continue beyond the syntaxis into northwestern Pakistan, which suggests that, although the precollisional materials may be identical, the western syntaxis marks a change in tectonic style from the main orogen. This conclusion in turn requires that the burial and exhumation history in the western Himalaya be radically different from that in the central Himalaya and thus necessitates a reexamination of models for India-Asia collision. Keywords: Himalaya, Sr/Nd, isotopes, correlations, lithostratigraphic unit.

Debris flows are fast‐moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris‐flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris‐flow release styles by integrating high‐resolution multi‐temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris‐flow triggering processes were previously hypothesised for this site: (i) slope failure, characterised by landslides evolving into debris flows; and (ii) the fire‐hose effect, in which debris accumulated in pre‐existing, steep‐sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris‐flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire‐hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source‐area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire‐hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris‐flow initiation in the absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. We compare two airborne datasets (LiDAR topography and aerial images) to study debris flows in Ísafjörður (Iceland). We assess and distinguish the role of two release mechanisms in debris‐flow generation: slope failure and fire‐hose effect. We find that slope failure is the dominant debris‐flow release process on the slope of Ísafjörður. Two new debris‐flow tracks were created by slope failures, which also created the preparatory conditions for the fire‐hose effect to mobilise existing debris in two other recently active tracks. [ABSTRACT FROM AUTHOR]

The OpenScience Laboratory (OSL) is a virtual laboratory. It's an app store for the application of science. It's an attractive online platform that delivers practical science engagements. It offers experiences of experiments; opportunities to make observations; techniques and tools and teleports into citizen science. It deploys real data via authentic interfaces. It's available globally: on tap 24 hours a day, seven days a week. It's a Times Higher Education award winner. It's fun. And it's still growing. [ABSTRACT FROM AUTHOR]

This article is based on a presentation and demonstration of new virtual field trip software, Virtual Skiddaw, given on 28th September at the 2013 ESTA annual course and conference at Plymouth University. The software was developed by the Open University for online delivery to its distance learning undergraduate students (in 2014/5). The particular innovation of this virtual application is that it uses a gaming engine (Unity 3D). This carries with it several benefits: immersion within a simulated, three-dimensional landscape, deepened by ambient sounds; interactivity through an avatar; integrated access to a variety of resources such as map overlays, virtual microscope slides, and geological information; different perspectives, from walking to flying over the landscape; the ability to interact with several other users within the environment; and a choice of following a guided, linear excursion to 6 detailed sites or roaming the area in a more exploratory manner. This article describes how this software application developed in the context of pedagogical, technical and logistical constraints, reflecting on the tensions that arose during this process and the fundamental purpose of virtual field trips. [ABSTRACT FROM AUTHOR]

Aluminosilicate minerals are commonly used to constrain P-T conditions in a wide range of metamorphic rocks and peraluminous granites. In granites, however, these minerals could be xenocrysts, peritectic phases or have directly crystallised from melt: each of these occurrences provides different implications for the formation of their host. The presence of kyanite in Himalayan leucogranites is commonly interpreted as a sign of early (Oligocene) melting during prograde burial; by contrast, sillimanite-bearing leucogranites are interpreted as forming during later (Miocene) decompression melting. The petrogenesis of these aluminosilicate-bearing melts therefore carries implications for the timing of mid-crustal weakening and overall Himalayan tectonics.The provenance of kyanite in small-scale (cm-dm), in situ leucogranites from eastern Bhutan and their host schists was investigated using cathodoluminescence imaging (CL), LA-ICP-MS trace element spot analysis and LA-ICP-MS trace element (V, Cr, Ge) mapping. Kyanite grains vary in morphology, internal CL zonation and geochemistry. Kyanite in the schist is commonly tabular with complex internal CL zonation. Kyanite in the leucosome immediately adjacent to the schist shows similarly complex internal textures, but is corroded, skeletal and rimmed by coarse muscovite. Both the complexly-zoned kyanite in the schist and in the leucosome show similar V, Cr, Ge and Fe concentrations. Within the leucosome, but further from the schist margin, kyanite crystals are distinctly different: thin and bladed, with little to no internal CL zonation and higher Ge content (>7.5 ppm). We interpret the corroded kyanite crystals in the leucosome to be xenocrysts from the schist that retained the complex CL patterns and chemical composition of metamorphic kyanite. The thin, bladed kyanite crystals are thought to represent "igneous" kyanite that formed either peritectically or by crystallisation from the melt. Inter-sample differences in kyanite Cr and Fe content appear to represent differences in protolith composition. Both types of kyanite, and evidence for both prograde and retrograde mineral reactions, can be found in close proximity on the thin-section scale, demonstrating very localised control of composition over mineralogy. LA-ICP-MS trace element mapping is able to resolve the features visible in greyscale CL images, with the best resolution apparent in V and Cr concentrations. High V/Cr ratios correspond to dark CL areas and low V/Cr ratios correspond to brighter CL areas. Understanding the significance of these variations in terms of reaction history and the genesis of kyanite is important for constraining future P-T-t modelling of the leucogranites, and is crucial for the tectonic interpretation of these melts as drivers for the exhumation of the orogenic mid-crust. [ABSTRACT FROM AUTHOR]