New insights on the origin of troctolites from the breakaway area of the Godzilla Megamullion (Parece Vela back‐arc basin): The role of melt‐mantle interaction on the composition of the lower crust

The troctolites and olivine‐gabbros from the Dive 6 K‐1147 represent the most primitive gabbroic rocks collected at the Godzilla Megamullion, a giant oceanic core complex formed at an extinct spreading segment of the Parece Vela back‐arc basin (Philippine Sea). Previous investigations have shown that these rocks have textural and major elements mineral compositions consistent with a formation through multistage interaction between mantle‐derived melts and a pre‐existing ultramafic matrix. New investigations on trace element mineral compositions basically agree with this hypothesis. Clinopyroxenes and plagioclase have incompatible element signatures similar to that of typical‐MORB. However, the clinopyroxenes show very high Cr contents (similar to those of mantle clinopyroxene) and rim having sharply higher Zr/REE ratios with respect to the core. These features are in contrast with an evolution constrained by fractional crystallization processes, and suggest that the clinopyroxene compositions are controlled by melt‐rock interaction processes. The plagioclase anorthite versus clinopyroxene Mg#[Mg/(Mg + Fe^Tot)] correlation of the Dive 6 K‐1147 rocks shows a trend much steeper than those depicted by other oceanic gabbroic sections. Using a thermodynamic model, we show that this trend is reproducible by fractionation of melts assimilating 1 g of mantle peridotite per 1 °C of cooling. This model predicts the early crystallization of high Mg# clinopyroxene, consistent with our petrological observation. The melt‐peridotite interaction process produces Na‐rich melts causing the crystallization of plagioclase with low anorthite component, typically characterizing the evolved gabbros from Godzilla Megamullion.     

The effect of a hydrous phase on P‐wave velocity anisotropy within a detachment shear zone in the slow‐spreading oceanic crust: A case study from the Godzilla Megamullion,Philippine Sea

We studied the contributions of plagioclase, clinopyroxene, and amphibole to the P‐wave velocity properties of gabbroic mylonites of the Godzilla Megamullion (site KH07‐02‐D18) in the Parece Vela Rift of the central Parece Vela Basin, Philippine Sea, based on their crystal‐preferred orientations (CPOs), mineral modes, and elastic constants and densities of single crystals. The gabbroic mylonites have been classified into three types based on their microstructures and temperature conditions: HT1, HT2 and medium‐temperature (MT) mylonites. The P‐wave velocity properties of the HT1 mylonite are dominantly influenced by plagioclase CPOs. Secondary amphibole occurred after deformation in the HT1 mylonite, so that its effect on P‐wave velocity anisotropy is minimal due to weak CPOs. Although the HT2 mylonite developed deformation microstructures in the three minerals, the P‐wave velocity properties of the HT2 mylonite are essentially isotropic, resulting from the destructive interference of different P‐wave velocity anisotropy patterns produced by the distinct CPOs of the three constituent minerals (i.e., plagioclase, clinopyroxene, and amphibole). The P‐wave velocity properties of the MT mylonite are influenced mainly by amphibole CPOs, whereas the effect of plagioclase CPOs on P‐wave velocity anisotropy becomes very small with a decrease in the intensity of plagioclase CPOs. As a result, the gabbroic mylonites tend to have weak P‐wave velocity anisotropy in seismic velocity, although their constituent minerals show distinct CPOs. Such weakness in the whole‐rock P‐wave velocity anisotropy could result from the destructive contributions of the different mineral CPOs with respect to the structural framework (foliation and lineation). These results show that amphibole has a high potential for P‐wave velocity anisotropy by aligning both crystallographically and dimensionally during deformation in the hydrous oceanic crust. The results also suggest that the effect of a hydrous phase on P‐wave velocity anisotropy within the detachment shear zone in a slow‐spreading oceanic crust varies depending on the degree of deformation and on the timing of hydrothermal activity.     

The Godzilla Megamullion,the largest oceanic core complex on the earth: a historical review

The Godzilla Megamullion is the largest known oceanic core complex (OCC) on the Earth, located in the Parece Vela Basin in the Philippine Sea. In this article, the history of Godzilla Megamullion study is reviewed for the first time, dividing it into three major phases: (i) the early studies done before Japan's extended continental shelf survey program; (ii) the studies during Japan's extended continental shelf survey program that discovered the OCC; and (iii) the studies by the post‐discovery cruises. The early studies included an interpretation of US nautical chart of the southwestern Pacific and the site surveys for Deep Sea Drilling Project cruises (DSDP Legs 6, 31 and 59). The early studies recognized the presence of the Parece Vela Rift, the extinct spreading axis of the Parece Vela Basin, and established the currently accepted model that the Philippine Sea evolved with eastward progression of backarc spreading and arc migration. The modern understanding of the Parece Vela Basin comes from Japan's extended continental shelf survey program. The program revealed the ultramafic petrology as well as a two‐stage evolution model of the basin. Following these results, the discovery of the Godzilla Megamullion was made in 2001. The studies by the post‐discovery cruises further revealed important characteristics of the OCC, such as the presence of abundant plagioclase‐bearing peridotite and the systematic temporal changes in both deformation microstructures and composition of plagioclase and amphibole in gabbroic mylonites and ultramylonites. Zircon U–Pb ages of gabboric and leucocratic rocks indicate that the terminal phase of Parece Vela Basin spreading was with a significant decline in spreading rate and asymmetry accompanying formation of the Godzilla Megamullion. The estimated denudation rate of the OCC was approximately 2.5 cm/yr; significantly slower than the previous estimate based on poorly constrained magnetic data.     

Geodynamic evolution of a forearc rift in the southernmost Mariana Arc

The southernmost Mariana forearc stretched to accommodate opening of the Mariana Trough backarc basin in late Neogene time, erupting basalts at 3.7–2.7 Ma that are now exposed in the Southeast Mariana Forearc Rift (SEMFR). Today, SEMFR is a broad zone of extension that formed on hydrated, forearc lithosphere and overlies the shallow subducting slab (slab depth ≤ 30–50 km). It comprises NW–SE trending subparallel deeps, 3–16 km wide, that can be traced ≥ ∼30 km from the trench almost to the backarc spreading center, the Malaguana‐Gadao Ridge (MGR). While forearcs are usually underlain by serpentinized harzburgites too cold to melt, SEMFR crust is mostly composed of Pliocene, low‐K basaltic to basaltic andesite lavas that are compositionally similar to arc lavas and backarc basin (BAB) lavas, and thus defines a forearc region that recently witnessed abundant igneous activity in the form of seafloor spreading. SEMFR igneous rocks have low Na₈, Ti₈, and Fe₈, consistent with extensive melting, at ∼23 ± 6.6 km depth and 1239 ± 40°C, by adiabatic decompression of depleted asthenospheric mantle metasomatized by slab‐derived fluids. Stretching of pre‐existing forearc lithosphere allowed BAB‐like mantle to flow along the SEMFR and melt, forming new oceanic crust. Melts interacted with pre‐existing forearc lithosphere during ascent. The SEMFR is no longer magmatically active and post‐magmatic tectonic activity dominates the rift.     

Evolution of anthropogenic and biomass burning emissions of air pollutants at global and regional scales during the 1980�C2010 period

Several different inventories of global and regional anthropogenic and biomass burning emissions are assessed for the 1980?C2010 period. The species considered in this study are carbon monoxide, nitrogen oxides, sulfur dioxide and black carbon. The inventories considered include the ACCMIP historical emissions developed in support of the simulations for the IPCC AR5 assessment. Emissions for 2005 and 2010 from the Representative Concentration Pathways (RCPs) are also included. Large discrepancies between the global and regional emissions are identified, which shows that there is still no consensus on the best estimates for surface emissions of atmospheric compounds. At the global scale, anthropogenic emissions of CO, NO_x and SO₂ show the best agreement for most years, although agreement does not necessarily mean that uncertainty is low. The agreement is low for BC emissions, particularly in the period prior to 2000. The best consensus is for NO_x emissions for all periods and all regions, except for China, where emissions in 1980 and 1990 need to be better defined. Emissions of CO need better quantification in the USA and India for all periods; in Central Europe, the evolution of emissions during the past two decades needs to be better determined. The agreement between the different SO₂ emissions datasets is rather good for the USA, but better quantification is needed elsewhere, particularly for Central Europe, India and China. The comparisons performed in this study show that the use of RCP8.5 for the extension of the ACCMIP inventory beyond 2000 is reasonable, until more global or regional estimates become available. Concerning biomass burning emissions, most inventories agree within 50?C80%, depending on the year and season. The large differences between biomass burning inventories are due to differences in the estimates of burned areas from the different available products, as well as in the amount of biomass burned.     

Hydrologic impact of regional climate change for the snowfed and glacierfed river basins in the Republic of Tajikistan: hydrological response of flow to climate change

The warming of the Earth's atmosphere system is likely to change temperature and precipitation, which may affect the climate, hydrology and water resources at the river basins over the world. The importance of temperature change becomes even greater in snow or glacier dominated basins where it controls the snowmelt processes during the late‐winter, spring and summer months. In this study hydrologic responses of streamflow in the Pyanj and Vaksh River basins to climate change are analysed with a watershed hydrology model, based on the downscaled atmospheric data as input, in order to assess the regional climate change impact for the snowfed and glacierfed river basins in the Republic of Tajikistan. As a result of this analysis, it was found that the annual mean river discharge is increasing in the future at snow and glacier dominated areas due to the air temperature increase and the consequent increase in snow/ice melt rates until about 2060. Then the annual mean flow discharge starts to decrease from about 2080 onward because the small glaciers start to disappear in the glacier areas. It was also found that there is a gradual change in the hydrologic flow regime throughout a year, with the high flows occuring earlier in the hydrologic year, due to the warmer climate in the future. Furthermore, significant increases in annual maximum daily flows, including the 100‐year return period flows, at the Pyanj and Vaksh River basins toward the end of the 21st century can be inferred from flood frequency analysis results. Copyright © 2012 John Wiley & Sons, Ltd.     

Local deformation‐based design of minimal‐disturbance arm damper for retrofitting steel moment‐resisting frames

This paper presents a design approach for seismic rehabilitation of frames having a beam‐collapse mechanism using a technique termed minimal‐disturbance seismic rehabilitation. This technique pursues enhancing the seismic performance of buildings with the intention of improving the continuity of business. It minimizes obstruction of the visual and physical space of building users and the use of heavy construction equipment and work requiring fire permit (welding/cutting). The developed design approach is simple to use. Yet it leads to designs that limit the beams' plastic rotations to allowable values, while minimizing the number of locations where devices are installed and the devise dimensions. Furthermore, the effectiveness of the design approach and the rehabilitation technique is numerically studied through retrofitting a four‐story steel moment‐resisting frame. Copyright © 2017 John Wiley & Sons, Ltd.     

Seismic study on oceanic core complexes in the Parece Vela back-arc basin

Abstract   In the present study the seismic structure of oceanic core complexes (OCC) in the Parece Vela Basin, Philippine Sea have been imaged. Together with recent work on the Atlantis Massif OCC on the Mid-Atlantic Ridge, including deep drilling, this work provides an unprecedented opportunity to advance our understanding of OCC internal structure. A continuous, strong and relatively smooth reflection that was ca 0.15 s (two way time) below the sea floor of an OCC in the Chaotic Terrain of the Parece Vela Basin was identified. This reflection, termed the D-reflector, is similar to that observed beneath Atlantis Massif. A faster P-wave velocity (>6 km/s) is observed very shallow beneath the Chaotic Terrain OCC, suggesting that the core of these OCC is dominantly gabbroic. The D-reflector might be common beneath OCC, owing to localized alteration along fractured zones within gabbro. We further observed a series of three detachment events in the Chaotic Terrain. The first and second detachments exhumed shallow basaltic crust to deeper gabbroic core, whereas the last one only exhumed shallow basaltic crust.