High‐grade metamorphism and partial melting in Archean composite grey gneiss complexes

Much of the exposed Archean crust is composed of composite gneiss which includes a large proportion of intermediate to tonalitic material. These gneiss terranes were typically metamorphosed to amphibolite to granulite facies conditions, with evidence for substantial partial melting at higher grade. Recently published activity–composition (a?x) models for partial melting of metabasic to intermediate compositions allows calculation of the stable metamorphic minerals, melt production and melt composition in such rocks for the first time. Calculated P?T pseudosections are presented for six bulk rock compositions taken from the literature, comprising two metabasic compositions, two intermediate/dioritic compositions and two tonalitic compositions. This range of bulk compositions captures much of the diversity of rock types found in Archean banded gneiss terranes, enabling us to present an overview of metamorphism and partial melting in such terranes. If such rocks are fluid saturated at the solidus, they first begin to melt in the upper amphibolite facies. However, at such conditions, very little (< 5%) melt is produced and this melt is granitic in composition for all rocks. The production of greater proportions of melt requires temperatures ～800–850 °C and is associated with the first appearance of orthopyroxene at pressures below 8–9 kbar or with the appearance and growth of garnet at higher pressures. The temperature at which orthopyroxene appears varies little with composition providing a robust estimate of the amphibolite–granulite facies boundary. Across this boundary, melt production is coincident with the breakdown of hornblende and/or biotite. Melts produced at granulite facies range from tonalite–trondhjemite–granodiorite for the metabasic protoliths, granodiorite to granite for the intermediate protoliths and granite for the tonalitic protoliths. Under fluid‐absent conditions the melt fertility of the different protoliths is largely controlled by the relative proportions of hornblende and quartz at high grade, with the intermediate compositions being the most fertile. The least fertile rocks are the most leucocratic tonalites due to their relatively small proportions of hydrous mafic phases such as hornblende or biotite. In the metabasic rocks, melt production becomes limited by the complete consumption of quartz to higher temperatures. The use of phase equilibrium forward‐modelling provides a thermodynamic framework for understanding melt production, melt loss and intracrustal differentiation during the Archean.     

Insights into the complexity of crustal differentiation: K2O‐poor leucosomes within metasedimentary migmatites from the Southern Marginal Zone of the Limpopo Belt,South Africa

Differentiation of the continental crust is the result of complex interactions between a large number of processes, which govern partial melting of the deep crust, magma formation and segregation, and magma ascent to significantly higher crustal levels. The anatectic metasedimentary rocks exposed in the Southern Marginal Zone of the Limpopo Belt represent an unusually well‐exposed natural laboratory where the portion of these processes that operate in the deep crust can be directly investigated in the field. The formation of these migmatites occurred via absent incongruent melting reactions involving biotite, which produced cm‐ to m‐scale, K₂O‐poor garnet‐bearing stromatic leucosomes, with high Ca/Na ratios relative to their source rocks. Field investigation combined with geochemical analyses, and phase equilibrium modelling designed to investigate some aspects of disequilibrium partial melting show that the outcrop features and compositions of the leucosomes suggest several steps in their evolution: (1) Melting of a portion of the source, with restricted plagioclase availability due to kinetic controls, to produce a magma (melt + entrained peritectic minerals in variable proportions relative to melt); (2) Segregation of the magma at near peak metamorphic conditions into melt accumulation sites (MAS), also known as future leucosome; (3a) Re‐equilibration of the magma with a portion of the bounding mafic residuum via chemical diffusion (H₂O, K₂O), which triggers the co‐precipitation of quartz and plagioclase in the MAS; (3b) Extraction of melt‐dominated magma to higher crustal levels, leaving peritectic minerals entrained from the site of the melting reaction, and the minerals precipitated in the MASs to form the leucosome in the source. The key mechanism controlling this behaviour is the kinetically induced restriction of the amount of plagioclase available to the melting reaction. This results in elevated melt H₂O and K₂O and chemical potential gradient for these components across the leucosome/mafic residuum contact. The combination of all of these processes accurately explains the composition of the K₂O‐poor leucosomes. These findings have important implications for our understanding of melt segregation in the lower crust and minimum melt residency time which, according to the chemical modelling, is <5 years. We demonstrate that in some migmatitic granulites, the leucosomes constitute a type of felsic refractory residuum, rather than evidence of failed magma extraction. This provides a new insight into the ways that source heterogeneity may control anatexis.     

New protodiplatyids (Insecta: Dermaptera) from the Lower Cretaceous Yixian Formation of northeastern China

A new genus Barbderma gen. nov. with a new species, Barbderma oblonguata sp. nov., and a new species, Sinoprotodiplatys ellipsoideuata sp. nov., of the family Protodiplatyidae are described from the Lower Cretaceous Yixian Formation at the Huangbanjigou Village, Beipiao City, Liaoning Province, China. Both new species are assigned to Protodiplatyidae mainly based on their diagnostic characters of antenna, pronotum, tegmina, tarsi and the distinct long, slender, multi-segmented cerci. These findings of fossil Protodiplatyidae provide more evidence to confirm the existence of these basal earwigs in the Early Cretaceous. Key diagnostic characters for genera of Protodiplatyidae are compared to highlight the generic variations and similarities. Evolutionary trend of cerci morphology suggests that it is likely that the cerci were evolved from long, slender and segmented to the stout terminal forceps without segmentation.     

New mantises (Insecta: Mantodea) in Cretaceous ambers from Lebanon,Spain, and Myanmar

Diverse new material of mantises found in the Cretaceous amber-bearing deposits from Lebanon (Barremian), Spain (Albian), and Myanmar (Albian–Cenomanian) are described and figured. The Lebanese and Spanish forms are nymphs; while the one from Myanmar is an adult specimen. The Lebanese nymph corresponds to a new specimen of Burmantis lebanensis Grimaldi, 2003 while the adult Burmese (Myanmar) specimen belongs to the new species Burmantis zherikhini. The Spanish specimen represents a new genus and species and is established as Aragonimantis aenigma, but is considered family incertae sedis. The Spanish specimen is the first record of Mesozoic mantises from western-European amber deposits. A revised phylogenetic hypothesis for Cretaceous mantises is proposed.     

Two new glaphyrids (Coleoptera,Scarabaeoidea) from the Jehol Biota,China

Two new species, Cretohypna puncta sp. nov. and Cretohypna robusta sp. nov., of Glaphyridae are described and illustrated. These fossils were collected from the Jehol Biota, Lower Cretaceous Yixian Formation of Liutiaogou Village in Ningcheng, Inner Mongolia, China. Up to date, 18 fossil species in 6 genera of Glaphyridae have been reported, among which ten species are from China. Respective keys to the Mesozoic genera of Glaphyridae and to species of Cretohypna Yan, Nikolajev & Ren, 2012 are provided. This is the first report of spiracles in fossil Glaphyridae leading to a hypothesis that the character of the 7th abdominal spiracles present in pleural membrane is a plesiomorphy for Glaphyridae.     

Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks,Nain, Central Iran

Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO₂ (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO₂, P₂O₅, MnO, Al₂O₃ and Fe₂O₃ define linear trends with negative slopes against SiO₂, whilst Na₂O and K₂O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO₂, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (La_N/Yb_N = 4.5–6.4) with moderate HREE fractionation (Sm_N/Yb_N = 1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the ⁸⁷Sr/⁸⁶Sr initial ratios vary from 0.704432 to 0.705989, and the ¹⁴³Nd/¹⁴⁴Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.     

Modeling the risk of spread and establishment for Asian longhorned beetle (Anoplophora glabripennis) in Massachusetts from 2008-2009

Land managers responsible for invasive species removal in the USA require tools to prevent the Asian longhorned beetle (Anoplophora glabripennis) (ALB) from decimating the maple-dominant hardwood forests of Massachusetts and New England. Species distribution models (SDMs) and spread models have been applied individually to predict the invasion distribution and rate of spread, but the combination of both models can increase the accuracy of predictions of species spread over time when habitat suitability is heterogeneous across landscapes. First, a SDM was fit to 2008 ALB presence-only locations. Then, a stratified spread model was generated to measure the probability of spread due to natural and human causes. Finally, the SDM and spread models were combined to evaluate the risk of ALB spread in Central Massachusetts in 2008–2009. The SDM predicted many urban locations in Central Massachusetts as having suitable environments for species establishment. The combined model shows the greatest risk of spread and establishment in suitable locations immediately surrounding the epicentre of the ALB outbreak in Northern Worcester with lower risk areas in suitable locations only accessible through long-range dispersal from access to human transportation networks. The risk map achieved an accuracy of 67% using 2009 ALB locations for model validation. This model framework can effectively provide risk managers with valuable information concerning the timing and spatial extent of spread/establishment risk of ALB and potential strategies needed for effective future risk management efforts.     

南沙群岛海域长腹剑水蚤(Oithona spp.)的种类组成、数量分布及其与环境因子的关系

中小型桡足类是海洋食物网中重要的中间环节,在碳循环里细菌碳和藻类碳向高营养级转化的过程中扮演重要角色。本文通过分析2013年3—4月、6—7月、9—10月和11—12月南沙群岛海域(111°30′E—112°30′E,4°30′N—11°30′N)的生态环境调查数据,对长腹剑水蚤属(Oithona)的种类组成、数量分布及其与环境因子的关系进行了研究。结果表明:(1)南沙群岛海域共出现长腹剑水蚤15种(包括1个未定种),其中线长腹水蚤(Oithona linearis)、粗长腹剑水蚤(O.robusta)和长刺长腹剑水蚤(O.longispina)为南沙群岛海域首次记录,长腹剑水蚤属种类组成沿水深变化的现象较为明显,该属虽然在南沙群岛海域广泛分布,但单种的出现频率较低,其种类出现的季节性较强;(2)南沙群岛海域的长腹剑水蚤可以划分为常见广布组群Ⅰ和低频组群Ⅱ;(3)长腹剑水蚤年均栖息密度为30ind./m3,季节变化呈单峰型,秋季最高、冬季最低,高数量区主要出现在受南沙西部沿岸流和东部沿岸流影响的近岸海域;(4)在0—750m水深范围内,长腹剑水蚤数量沿水深梯度的垂直变化明显,呈现由浅至深数量明显减少的趋势,长腹剑水蚤主要集中分布在0—75m的水层中,75—500m数量急剧降低至最低后,在500—750m基本维持不变;(5)GAM分析表明,纬度、海水温度、盐度和叶绿素a浓度对长腹剑水蚤数量均有影响,以纬度的影响最为显著,其中长腹剑水蚤属最适温度为28.6—29.2℃,最适盐度为32.6—33.2,最适叶绿素a浓度为5—10μg/L;(6)长腹剑水蚤属更适栖息于低温和低盐,且受沿岸流影响的环境中。因此,其数量分布的季节变化与季风驱动的沿岸流势力强弱密切相关。     

Sexual reproduction and early life‐history traits of the Mediterranean soft coral Alcyonium acaule

Understanding processes that contribute to a better comprehension of the population dynamics of long‐lived species is critical for the maintenance and potential recovery of such species. Despite the abundance of soft corals in Mediterranean rocky reefs, little information exists on their life histories and reproductive patterns. In this study, we assessed the main reproductive characteristics and early life‐history traits of the long‐lived soft coral Alcyonium acaule. The sex ratio was 1:1; the smallest fertile colonies were one finger in size (2.1 ± 0.6 cm in height), and both colony and polyp fertility increased with colony size. Likewise, the number of eggs and spermary sacs per polyp increased significantly with colony size, whereas the diameter of the female and male sexual products did not. Over 6 years of observations (2007–2012), spawning occurred primarily in July, after the seawater reached 20 °C, in a single spawning episode per year. Approximately 80% of female colonies released eggs, which were retained on the surface of the mother colony by mucous strings for up to a few days. High fertilization rates were observed during spawning in 2008 and 2009 (94.9% and 87.0%, respectively). The timing of development was ~24 h for the blastulae, ~48–72 h for the planulae and 8–22 days for metamorphosis into primary polyps. Survivorship of planulae was relatively high (~50% at 45 days after release), but only 24% of larvae metamorphosed into primary polyps, and their survivorship was moderate after 2 months (65% in 2008 and 74% in 2009). Asexual reproduction was negligible, indicating that sexual reproduction is the main mechanism supporting the maintenance and recovery of populations.     

Differentiation in reproductive traits of geminate mangrove crabs of the genus Aratus (Decapoda: Brachyura) across the Central American Isthmus

The mangrove crab Aratus pisonii was considered to have an amphi‐American distribution; however, a recent study revealed that the Eastern Tropical Pacific populations were genetically distinct, thus representing a new species: Aratus pacificus. These species separated by the Isthmus of Panama have diverged under different environmental conditions that may have influenced their reproductive biology. As the available information about this genus concerns almost exclusively the Caribbean species, the aim of the present study was to analyse and compare reproductive aspects of A. pacificus and A. pisonii obtained from both the Pacific and Caribbean coasts of Costa Rica. Females were collected from April 2011 to April 2012, and reproductive features such as breeding season, size distribution of ovigerous females, fecundity, reproductive output, embryo volume and embryo water content were assessed. Both species produced embryos during the entire sampled period. Most females of A. pacificus carrying embryos close to hatching were found during the rainy season. Ovigerous females of A. pisonii were substantially larger and reached sexual maturity at a larger size than females of A. pacificus. Embryo production started in A. pacificus at a smaller female size than in A. pisonii. As fecundity increased with female size, the average fecundity was lower in A. pacificus. Females of A. pisonii produced larger embryos, which might be related to lower food availability: higher energy content in the embryo enhances the chances of larval survival. These data regarding reproductive features of the Pacific and Caribbean species support the conclusion to separate A. pacificus from A. pisonii.