http://www.sciencedirect.com/science/article/pii/S1674987114001601

Data from a migmatised metapelite raft enclosed within charnockite provide quantitative constraints on the pressure-temperature-time[P-T-t) evolution of the Nagercoil Block at the southernmost tip of peninsular India.An inferred peak metamorphic assemblage of garnet,K-feldspar.sillimanite,plagioclase,magnetite,ilmenite,spinel and melt is consistent with peak metamorphic pressures of 6-8 kbar and temperatures in excess of 900℃.Subsequent growth of cordierite and biotite record high-temperature retrograde decompression to around 5 kbar and 800 C.SHRIMP U-Pb dating of magmatic zircon cores suggests that the sedimentary protoliths were in part derived from felsic igneous rocks with Palaeoproterozoic crystallisation ages.New growth of metamorphic zircon on the rims of detrital grains constrains the onset of melt crystallisation,and the minimum age of the metamorphic peak,to around560 Ma.The data suggest two stages of monazite growth.The first generation of REE-enriched monazite grew during partial melting along the prograde path at around 570 Ma via the incongruent breakdown of apatite.Relatively REE-depleted rims,which have a pronounced negative europium anomaly,grew during melt crystallisation along the retrograde path at around 535 Ma.Our data show the rocks remained at suprasolidus temperatures for at least 35 million years and probably much longer,supporting a long-lived high-grade metamorphic history.The metamorphic conditions,timing and duration of the implied clockwise P-T-t path are similar to that previously established for other regions in peninsular India during the Ediacaran to Cambrian assembly of that part of the Gondwanan supercontinent.     

Wind and freshwater influence over hydrocarbon dispersal on Patos Lagoon, Brazil

The two-dimensional barotropic, hydrodynamic and transport model MOHID is applied to the Patos Lagoon system using a nested modelling approach to reproduce both the lagoon and estuary hydrodynamics. A new Lagrangian oil spill model is presented and used to simulate a hypothetical oil spill in the estuary. Hydrodynamic fields are validated and used to force the oil model. Results show that the hydrodynamics of this system is mainly controlled by the wind and freshwater discharge. The dispersion, concentration and thickness evolution of the oil in the first day after the spill is determined by the equilibrium between these two factors. The freshwater discharge is the major factor controlling the oil dispersion for discharges greater than 5000 m3 while the wind assumes control for lower discharge amounts. The results presented are a first step toward a coastal management tool for the Patos Lagoon.     

The last 40 ka tephrostratigraphic record of Lake Ohrid,Albania and Macedonia: a very distal archive for ash dispersal from Italian volcanoes

A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896–897 cm and 1070–1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310–315 cm. Major element analyses on glass shards of the tephra layers at 896–897 cm and 1070–1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310–315 cm has a mugearitic–benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five ¹⁴C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core.     

Source depletion and extent of melting in the Tongan sub-arc mantle

The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab.     

Modeling fluvial response to in‐stream woody vegetation: implications for stream corridor restoration

River restoration and bank stabilization programs often use vegetation for improving stream corridor habitat, aesthetic and function. Yet no study has examined the use of managed vegetation plantings to transform a straight, degraded stream corridor into an ecologically functional meandering channel. Experimental data collected using a distorted Froude‐scaled flume analysis show that channel expansion and widening, thalweg meandering and riffle and pool development are possible using discrete plantings of rigid, emergent vegetation, and the magnitudes of these adjustments depend on the shape of the vegetation zone and the density of the vegetation. These experimental results were verified and validated using a recently developed numerical model, and model output was then used to discuss mechanistically how rivers respond to the introduction of in‐stream woody vegetation. Finally, a hybrid method of meander design is proposed herein where managed vegetation plantings are used to trigger or force the desired morphologic response, transforming a straight, degraded reach into a more functional meandering corridor. It is envisioned that such numerical models could become the primary tool for designing future stream restoration programs involving vegetation and assessing the long‐term stability of such activities. Copyright © 2007 John Wiley & Sons, Ltd.     

Controls on the morphological evolution of embayed beaches: Morphometry versus external forcing

The morphological evolution of embayed beaches on a microtidal coast is assumed to largely respond to the degree of exposure to wave conditions, decreasing the mobility with increasing beach indentation (and vice versa). However, the number of sediment arrivals at the beach or the impact of extreme storms can modify this relationship. Here, we present an analysis of 10 embayed beaches along the Catalan coast with different morphometric and sedimentary characteristics to identify the most relevant parameters controlling the morphological evolution of these embayed beaches at the inter-annual and decadal scales. The study was mostly based on LiDAR topographic data collected from 2012 to 2017, aerial photographs from 1945 to 2021, sediment sampling and a long-term series analysis of the forcing parameters (waves, sea level, precipitation and land-use changes). The results show a net loss of volume on all the studied beaches at an inter-annual scale and a general shoreline retreat during the last few decades, suggesting the influence of common processes on the evolution of the studied beaches. Smaller pocket beaches with medium-to-high indentations are more sensitive to changes induced by local factors and show higher variability in the volume of the emerged beach and shoreline position than larger beaches. The most relevant factors influencing the evolution of the studied beaches on a decadal scale were identified as changes in sea level and the reduction in sediment inputs provided by streams due to land-use changes in the drainage basin. At the inter-annual scale, the impact of extreme events is the main factor controlling beach behaviour. These general trends can be opposite locally for beaches that receive large amounts of sediment via longshore transport from adjacent beaches.     

The prospects for modernizing very broadband seismometers

This paper considers the possibilities for modernizing the KSESh broadband seismic station developed earlier at the IPE AS USSR. The goal of the modernization was to extend the frequency and dynamic ranges and to decrease nonlinear distortions. The ways and concrete methods for improving the mechanical construction and electronic components of the station are shown and the intermediate results are described. As preliminary estimates show, there is an opportunity to build devices with the velocimeter response up to 520–540 s periods on the basis of this pendulum.     

Earthquake distribution and volcanism in Kamchatka,Kurile Islands,and Hokkaido Part 3: Southern Kuriles and Hokkaido

Summary The morphology of the Wadati-Benioff zone in the region of Southern Kuriles and Hokkaido, based on the distribution of 4015 earthquake foci, verified the existence of an intermediate depth aseismic gap and its relation to active andesitic volcanism. A paleosubduction zone activated by an intermediate depth collision with the active subduction zone was found and described.

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New average global P and PcP travel times

This paper deals with the construction procedure for regional travel-time curves and the new average global curve for P times. This paper also presents new average global values for PcP times constructed from observed travel times.