西藏雅鲁藏布缝合带甲查拉组:晚白垩世新特提斯洋海沟沉积?

雅鲁藏布缝合带记录了印度与亚洲板块汇聚、碰撞及碰撞后造山的信息.甲查拉组位于雅鲁藏布缝合带南侧,自建组以来一直被认为是印度-亚洲大陆碰撞后前陆盆地的深水沉积,物源来自其北侧亚洲大陆南缘的冈底斯弧.然而,一个长期令人不解的问题是:甲查拉组砂岩最年轻的碎屑锆石年龄为88Ma,考虑冈底斯弧晚白垩世-古近纪持续的岩浆活动,如果地层时代是前人基于孢粉、沟鞭藻化石提出的古新世-早始新世(65~50Ma),为何砂岩中缺乏白垩纪晚期-始新世早期(88~50Ma)的碎屑锆石?针对这个问题,本次研究对江孜-萨迦地区的甲查拉组开展了孢粉、沟鞭藻化石分析、岩石地层学、沉积学与物源分析等工作.两个不同实验室的分析处理都未获得保存良好的孢粉、沟鞭藻化石;甲查拉组与宗卓组呈断层接触,岩石组合与沉积结构、构造指示海底扇沉积环境;碎屑组分、碎屑锆石U-Pb年龄和Hf同位素指示甲查拉组的物源来自冈底斯弧和中拉萨地体,最年轻的碎屑锆石年龄为84Ma.综合考虑沉积环境、物源与大地构造位置,在区域对比研究基础上,本文认为甲查拉组的时代很可能是晚白垩世(88~84Ma),代表了新特提斯洋向北俯冲阶段亚洲南缘的海沟沉积.     

Butterfly-plant interactions and body size patterns along an elevational gradient in the Manang region of central Nepal

Butterflies are widely studied due to their key ecosystem functions.For this reason,they are used in ecosystem assessment,formulating conservation plans and in raising the environmental awareness.Quantification of different factors affecting diversity of butterflies is important for their effective conservation.In this study,we investigated abiotic and biotic factors affecting species richness and community composition of butterflies along an elevational gradient in Manang region,central Nepal.We also tested if butterfly species follow the Bergmann’s rule.A total of 57 butterfly species belonging to 39 genera and 8 families were recorded in the study area.Out of a total of 127 plant species identified in the study region,only 67 plant species were visited by butterflies as nectar sources.Species richness of butterflies increased with increasing elevation.Species richness was significantly higher in places with shrubs compared to other places and also in autumn than in summer.Species richness of butterflies also depended on composition of plant species occurring at the localities.Butterfly species composition varied among sampling localities.It was also determined by habitat type,elevation,sampling time,plant species and interactions of elevation×time.The relationship between butterfly size and elevation was in the opposite direction than expected according to the Bergmann’s rule.In conclusion,protection of butterfly diversity can only be achieved by protecting different habitats across the diverse physiography of the region and different plant species,in particular herbs and shrubs.Our results do not support the Bergmann’s rule for butterflies along an elevational gradient in our region.     

The impact of northern Indian Ocean rivers on the Bay of Bengal using NEMO global ocean model

The effect of river runoff over the northern Indian Ocean(NIO) especially over the Bay of Bengal(Bo B) has been studied using global Nucleus for European Modelling of the Ocean(NEMO). Two sensitivity experiments, with and without river runoff are conducted and the influence of river runoff on the Indian Ocean hydrography,stratification and circulation features are studied. It is found that due to river runoff surface salinity over the northern Bo B decreases by more than 5 and the East India Coastal Current strengthens by 2 cm/s during post monsoon season. The fresh river water reaches up to 15°N in the Bo B and is the main cause for low salinity there.Sea surface temperature in the northwestern Bo B increases by more than 0.2℃ due to the river runoff in summer monsoon while surface cooling upto 0.2℃ is seen in north-west part of Bo B in winter season. The seasonal mixed layer depth in the region is found to be dependent on river runoff. The effect of vertical shear and Brunt Vaisala frequency on stratification is also examined. The ocean water becomes highly stratified up to 3 035 m due to the river runoff. It is found that the energy required for mixing is high in the northern and coastal Bo B.     

Geochemistry and Petrogenesis of Intracontinental Basaltic Volcanism on the Northwest Arabian Plate,Gaziantep Basin,Southeast Anatolia,Turkey

Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.