The observation and interpretation of geomagnetic variations in a small area of Hainan Province,China

ＴｈｅｏｂｓｅｒｖａｔｉｏｎａｎｄｉｎｔｅｒｐｒｅｔａｔｉｏｎｏｆｇｅｏｍａｇｎｅｔｉｃｖａｒｉａｔｉｏｎｓｉｎａｓｍａｌａｒｅａｏｆＨａｉｎａｎＰｒｏｖｉｎｃｅ，ＣｈｉｎａＧＵＯＨＵＡＦＡＮ１）（范国华）ＴＯＮＧＱＩＹＡＯ１）（姚同起）ＺＵＯ...     

Attenuation of coda waves and Q_c value beneath the Chengdu telemetered seismic network

ＡｔｅｎｕａｔｉｏｎｏｆｃｏｄａｗａｖｅｓａｎｄＱｃｖａｌｕｅｂｅｎｅａｔｈｔｈｅＣｈｅｎｇｄｕｔｅｌｅｍｅｔｅｒｅｄｓｅｉｓｍｉｃｎｅｔｗｏｒｋＪＩＡＮＺＥＮＧ１）（曾健）ＴＩＡＮＣＨＡＮＧＣＨＥＮ１）（陈天长）ＷＥＩＢＩＮＨＡＮ１）（韩渭宾...     

联合GRACE和气象水文数据研究2010～2016年亚马孙平原水储量异常变化与极端气候和ENSO的关系

利用GRACE时变重力场模型反演2009-07～2017-06期间亚马孙平原的水储量变化,在移除趋势和季节性周期信号后,计算得到其与ENSO指数之间具有较强的相关关系和一定的时延性,并从季节层面进行分析得到ENSO对亚马孙平原旱、雨两季的不同影响,表现为旱季受到ENSO显著影响而雨季受到的影响则较小。最后,结合水文数据分析指出,ENSO会通过影响降雨量进而影响相应区域的水储量变化,且该现象在流域内两次极端旱灾中有较为突出的表现。     

Sensitivity of Snowfall Characteristics to Meteorological Conditions in the Yeongdong Region of Korea

This study investigates the characteristics of cold clouds and snowfall in both the Yeongdong coastal and mountainous regions under different meteorological conditions based on the integration of numerical modeling and three-hourly rawinsonde observations with snow crystal photographs for a snowfall event that occurred on 29?30 January 2016.We found that rimed particles predominantly observed turned into dendrite particles in the latter period of the episode when the 850 hPa temperature decreased at the coastal site,whereas the snow crystal habits at the mountainous site were largely needle or rimed needle.Rawinsonde soundings showed a well-defined,two-layered cloud structure along with distinctive wind-directional shear,and an inversion in the equivalent potential temperature above the low-level cloud layer.The first experiment with a decrease in lower-layer temperature showed that the low-level cloud thickness was reduced to less than 1.5 km,and the accumulated precipitation was decreased by 87%compared with the control experiment.The difference in precipitation amount between the single-layered experiment and control experiment(two-layered)was not so significant to attribute it to the effect of the seeder?feeder mechanism.The precipitation in the last experiment by weakening winddirectional shear was increased by 1.4 times greater than the control experiment specifically at the coastal site,with graupel particles accounting for the highest proportion(~62%).The current results would improve snowfall forecasts in complicated geographical environments such as Yeongdong in terms of snow crystal habit as well as snowfall amount in both time and space domains.     

Oxygen isotope heterogeneity of the mantle beneath the Canary Islands: insights from olivine phenocrysts

A relatively narrow range of oxygen isotopic ratios (?? ¹⁸O?=?5.0?C5.4??) is preserved in olivine of mantle xenoliths, mid-ocean ridge (MORB), and most ocean island basalts (OIB). The values in excess of this range are generally attributed either to the presence of a recycled component in the Earth??s mantle or to shallow level contamination processes. A viable way forward to trace source heterogeneity is to find a link between chemical (elemental and isotopic) composition of the earlier crystallized mineral phases (olivine) and the composition of their parental magmas, then using them to reconstruct the composition of source region. The Canary hotspot is one of a few that contains ~1- to 2-Ga-old recycled ocean crust that can be traced to the core-mantle boundary using seismic tomography and whose origin is attributed to the mixing of at least three main isotopically distinct mantle components i.e. HIMU, DMM, and EM. This work reports ion microprobe and single crystal laser fluorination oxygen isotope data of 148 olivine grains also analyzed for major and minor elements in the same spot. The olivines are from 20 samples resembling the most primitive shield stage picrite through alkali basalt to basanite series erupted on Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro, Canary Islands, for which shallow level contamination processes were not recognized. A broad range of ?? ¹⁸O_olivine values from 4.6 to 6.1?? was obtained and explained by stable, long-term oxygen isotope heterogeneity of crystal cumulates present under different volcanoes. These cumulates are thought to have crystallized from mantle-derived magmas uncontaminated at crustal depth, representing oxygen isotope heterogeneity of source region. A relationship between Ni?×?FeO/MgO and ?? ¹⁸O_olivine values found in one basanitic lava erupted on El Hierro, the westernmost island of the Canary Archipelago, was used to estimate oxygen isotope compositions of partial melts presumably originated from peridotite (HIMU-type component inherited its radiogenic isotope composition from ancient, ~1 to 2?Ga, recycled ocean crust) and pyroxenite (young, <1?Ga, recycled oceanic crust preserved as eclogite with depleted MORB-type isotopic signature) components of the Canary plume. The model calculations yield 5.2 and 5.9?±?0.3?? for peridotite- and pyroxenite-derived melts, respectively, which appeared to correspond closely to the worldwide HIMU-type OIB and upper limit N-MORB ?? ¹⁸O values. This difference together with the broad range of ?? ¹⁸O variations found in the Canarian olivines cannot be explained by thermodynamic effects of oxygen isotopic fractionation and are believed to represent true variations in the mantle, due to oceanic crust and continental lithosphere recycling.     

Zircon from historic eruptions in Iceland: reconstructing storage and evolution of silicic magmas

Zoning patterns, U-Th disequilibria ages, and elemental compositions of zircon from eruptions of Askja (1875 AD), Hekla (1158 AD), ?r?faj?kull (1362 AD) and Torfaj?kull (1477 AD, 871 AD, 3100 BP, 7500 BP) provide insights into the complex, extended, histories of silicic magmatic systems in Iceland. Zircon compositions, which are correlated with proximity to the main axial rift, are distinct from those of mid-ocean ridge environments and fall at the low-Hf edge of the range of continental zircon. Morphology, zoning patterns, compositions, and U-Th ages all indicate growth and storage in subvolcanic silicic mushes or recently solidified rock at temperatures above the solidus but lower than that of the erupting magma. The eruptive products were likely ascending magmas that entrained a zircon ??cargo?? that formed thousands to tens of thousands of years prior to the eruptions.     

Petrology and geochemistry of the 2014–2015 Holuhraun eruption,central Iceland: compositional and mineralogical characteristics,temporal variability and magma storage

The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n?=?62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014–2015 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Bárðarbunga volcanic system, consistent with seismic observations for magma ascent close to the Bárðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8?±?5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with the efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, requires a more complex earlier magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions.     

Using platforms of opportunity to determine the occurrence and group characteristics of orca (Orcinus orca) in the Hauraki Gulf,New Zealand

We present the first fine-scale data relating to the occurrence and group characteristics for killer whales (Orcinus orca) in the Hauraki Gulf, New Zealand, as observed from a platform of opportunity (PoP). Group size and composition were examined in relation to water depth and sea surface temperature (SST). From 2000 to 2010, 119 orca encounters were recorded, involving 1 to 18 animals. The encounter rate varied seasonally, being highest in austral spring and lowest in summer. Water depth in which whales were observed was significantly affected by group composition. Sixty-seven percent of groups contained immature animals. Group size was highly skewed towards smaller groups comprising two animals. While this study illustrates that PoPs can be used to indicate the occurrence and group characteristics of highly mobile social species, biases clearly exist. Through identifying such inaccuracies, we present recommendations on how future data should be collected to minimise error and improve datasets for scientific use.     

Crystal scale anatomy of a dying supervolcano: an isotope and geochronology study of individual phenocrysts from voluminous rhyolites of the Yellowstone caldera

A voluminous (>600 km³) and long-lived (~520–75 ka) phase of rhyolitic eruptions followed collapse of the Yellowstone caldera 640 ka. Whether these eruptions represent a dying cycle, or the growth of a new magma chamber, remains an important question. We use new U–Th zircon ages and δ¹⁸O values determined by ion microprobe, and sanidine Pb isotope ratios determined by laser ablation, to investigate the genesis of voluminous post-caldera rhyolites. The oldest post-caldera rhyolites, erupted between ~520 and 470 ka, exhibit extreme age and oxygen isotopic heterogeneity, requiring derivation from individual parcels of low-δ¹⁸O melts. We find a progressive increase in zircon homogeneity for rhyolite eruptions from ~260 to 75 ka, with homogeneous low-δ¹⁸O zircon values of 2.7–2.8‰ that are in equilibrium with low-δ¹⁸O host melts for the majority of the youngest eruptions. New sanidine Pb isotope data define separate arrays for post-caldera rhyolites and the caldera-forming tuffs that preceded them, indicating that they were not sourced from a mushy Lava Creek Tuff batholith that remained after caldera collapse. Rather, our new age and isotopic data indicate that the post-caldera rhyolites were generated by remelting of a variety of intracaldera source rocks, consisting of pre-Lava Creek Tuff volcanic and plutonic rocks and earlier erupted post-Lava Creek Tuff rhyolites. Batch assembly of low-δ¹⁸O melts starting at ~260 ka resulted in progressive homogenization, followed by differentiation and cooling up until the last rhyolite eruption ~75 ka, a trend that we interpret to be characteristic of a dying magma reservoir beneath the Yellowstone caldera.