Plagioclase in the Skaergaard intrusion. Part 1: Core and rim compositions in the layered series

The anorthite content of plagioclase grains (X_An) in 12 rocks from the layered series of the Skaergaard intrusion has been studied by electron microprobe (typically ∼30 core and ∼70 rim analyses per thin section). Mean core compositions vary continuously from An₆₆ at the base of the layered series (LZa) to An_32–30 at the top. On the other hand, crystal rims are of approximately constant composition (An_{50 ± 1}) from the LZa to the lower Middle Zone (MZ). Above the MZ, core and rim compositions generally overlap. Profiles across individual plagioclase grains from the lower zone show that most crystals have an external zone buffered at X_An ∼50 ± 1. The simplest explanation for these features is that during postcumulus crystallization in the lower zone, interstitial liquids passed through a density maximum. This interpretation is consistent with proposed liquid lines of descent that predict silica enrichment of the liquid associated with the appearance of cumulus magnetite.     

Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between< 0.5 to  1% in Albian rocks, and between  1 and 2% in succeeding Cenomanian to Campanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al₂O₃ (average < 16%), low Mg-number (molar Mg/Mg + Fe < 0.5), TiO₂ (< 1.0%), and Sr/Y (< 10), oceanic or arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (< 20%) of silicic lavas were erupted. The systematic variation of both sediment flux and abundance of crustally derived silicic lavas are consistent with current tectonic models of Caribbean evolution involving approximately perpendicular subduction of the Caribbean spur of the mid-Atlantic Ridge, which was located approximately midway between North and South America until Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment flux was limited. Conversely, toward the west in central Puerto Rico, which was consistently more remote from the subducting ridge, heat flow was relatively low and produced limited crustal melting, while the sediment flux was comparatively elevated.     

Basin- and Mountain-Building Dynamic Model of “Ramping-Detachment-Compression” in the West Kunlun-Southern Tarim Basin Margin

Analysis of the deformation structures in the West Kunlun-Tarim basin-range junction belt indicates that sediments in the southwestern Tarim depression were mainly derived from the West Kunlun Mountains and that with time the region of sedimentation extended progressivdy toward the north. Three north-underthrusting （subducting）, steep-dipping, high-velocity zones （bodies） are recognized at depths, which correspond to the central West Kunlun junction belt （bounded by the Kiida-Kaxtax fault on the north and Bulungkol-Kangxiwar fault on the south）, Quanshuigou fault belt （whose eastward extension is the Jinshajiang fault belt） and Bangong Co-Nujiang fault belt. The geodynamic process of the basin-range junction belt generally proceeded as follows： centering around the magma source region （which largely corresponds with the Karatag terrane at the surface）, the deep-seated material flowed and extended from below upward and to all sides, resulting in strong deformation （mainly extension） in the overlying lithosphere and even the upper mantle, appearance of extensional stress perpendicular to the strike of the orogenic belt in the thermal uplift region or at the top of the mantle diapir and localized thickening of the sedimentary cover （thermal subsidence in the upper crust）. Three stages of the basin- and mountain-forming processes in the West Kunlun-southern Tarim basin margin may be summarized： （1） the stage of Late Jurassic-Early Cretaceous rampingrapid uplift and rapid subsidence, when north-directed thrust propagation and south-directed intracontinental subduction, was the dominant mechanism for basin- and mountain-building processes; （2） the stage of Late Cretaceous-Paleogene deep-level detachment-slow uplift and homogeneous subsidence, when the dominant mechanism for the basin- and mountain-forming processes was detachment （subhorizontal north-directed deep-level ductile shear） and its resulting lateral propagation of deep material; and （3） the stage of Neogene-pre     

1979年以来南黄海辐射沙洲潮滩脊线时空变化研究

基于遥感和GIS技术,提取了南黄海辐射沙洲1979年、1990年、2002年和2014年4个时期的潮滩脊线,并对时空变化特征进行系统分析。研究显示：① 辐射沙洲潮滩脊线可分为主线和支线2级,滩脊主线为条子泥-高泥-东沙潮滩脊线,支线为滩脊主线两侧分支;② 辐射沙洲潮滩脊线空间组合形态总体稳定,条子泥段滩脊主线总体呈东西向,东沙段滩脊主线总体呈南北向,高泥段滩脊主线连接条子泥和东沙;③ 滩脊线演变呈显著空间分异,条子泥段滩脊主线南向迁移显著,东沙段和高泥段滩脊主线总体向东迁移,迁移距离条子泥段滩脊主线>高泥段、东沙段,条子泥段滩脊主线中部>两侧、东沙段滩脊主线北段>南段,条子泥滩脊支线形态和位置变化均较东沙滩脊支线显著。     

Effects of Topographic Slopes on Hydrological Proecsses and Climate

Based on previous research results on river re-distribution models, a modification on the effects of topographic slopes for a runoff parameterization was proposed and implemented to the NCAR＇s land sur face model (LSM). This modification has two aspects: firstly, the topographic slopes cause outflows from higher topography and inflows into the lower topography points; secondly, topographic slopes also cause decrease of infiltration at higher topography and increases of infiltration at lower topography. Then changes in infiltration result in changes in soil moisture, surface fluxes and then in surface temperature, and eventual ly in the upper atmosphere and the climate. This mechanism is very clearly demonstrated in the point bud gets analysis at the Andes Mountains vicinities. Analysis from a regional scale perspective in the Mackenzie GEWEX Study (MAGS) area, the focus of the ongoing Canadian GEWEX program, shows that the modi fied runoff parameterization does bring significant changes in the regional surface climate. More important ly, detailed analysis from a global perspective shows many encouraging improvements introduced by the modified LSM over the original model in simulating basic atmospheric climate properties such as thermodynamic features (temperature and humidity). All of these improvements in the atmospheric climate simulation illustrate that the inclusion of topographic effects in the LSM can force the AGCM to produce a more realistic model climate.     

Selection of Multifractal Scaling Breaks andSeparation of Geochemical andGeophysical Anomaly

1Multifractalities have been observed and estimated formany quantities in physics, chemistry, as well as earth andspace sciences (see a review in Agterberg, 20011 Cheng,1999al Agterberg et al., 1993 1 Schertzer and Love joy, 1991).The multifractal theory has provided a superior distributiontype for describing the complex measures in comparison withthe ordinary statistical distributions. The former usually involves the multiple moments and parameters (Cheng, 1999alAgterberg et al., 1993 1 Sc…     

河口沉积物—水界面重金属生物地球化学研究进展

河口区既是人类排污物的主要汇集地，又是单向流体和双向流体相互作用的场所，三者构成一个复杂而多变的地球化学物理场。在这里因一定的物理，化学和生物化学作用使来自陆地的重金属污染物从水体中沉降下来，进入底部沉积物即积累过程，又会因类似的作用使这些金属从沉积物中活化而再次进入水体即释放过程，产生所谓的“二次污染”，河口沉积物水界面过程调控着这一体系的方向与限度。     

MODELING SEDIMENT PROCESSES ON SMALL WATERSHEDS:A CONCEPTUAL FRAMEWORK Ⅰ. BROAD SHALLOW FLOW PROCESSE

A conceptual modeling framework for developing process-based mathematical models of sediment generation, transport, and deposition on broad shallow flow areas is presented. The governing equations relevant to process-based modeling of broad shallow flow sediment processes on small watersheds are presented and the effects of space and time averaging on the predictive equations are described. Starting from the most general one-dimensional, unsteady model of sediment processes, simpler model structures are obtained and the successive simplifications made on the governing equations in order to obtain simpler and less detailed formulations are described. Specific model formulations are given for illustrative purposes and applications of these models to erosion and sediment yield prediction from broad shallow flow areas are shown using sediment data from rainfall simulator plots. In spite of some progress made in the development of process-based erosion and sediment yield models from broad shallow flow areas, further developmental modeling efforts must be based on a clear separation between hydrologic and hydraulic processes, and the soil properties which are significant for each.     

Chemical reactions and transport of alkanes and their products in the troposphere

The product distributions have been calculated for more abundant alkanes contributing most of the carbon atoms in the alkane fraction of an ambient air hydrocarbon mixture reasonably representative of U.S. emissions. The effects of ambient temperatures on product yields has been calculated for a range of temperatures from 250 to 330 K. The sensitivity of product yields to uncertainties in alkoxy radical process rate constants has been examined with emphasis on uncertainties in decomposition reactions. Chemical lifetimes are estimated at 300 K under summertime conditions for hydrocarbons and for products of alkane photooxidation in the atmosphere. The atmospheric distribution of alkanes and products is evaluated in terms of the extent to which reaction processes are likely to occur in the planetary boundary layer compared to the free troposphere.The calculations predict a substantial effect of temperature on product yields. A large decrease in alkyl nitrate yields and a smaller decrease in ketone yields occur with increasing temperature. The yields of the short-lived, more reactive aldehydes undergo substantial increases with increasing temperature. Lower yields of ketones and higher yields of aldehydes are associated with the use of higher compared to lower decomposition process rate constants. For the type of U.S. hydrocarbon mixture available from measurements, 16 oxygenated products account for more than 60% of the total alkane carbon atoms converted to products, with most of these carbon atoms accounted for by four products. The effects of increased temperature on product reactivity and radical production may also influence O₃ production.     

耗散结构理论及其在火成岩岩石学中的意义

本文简要介绍了耗散结构理论及其研究方法,以及它在火成岩中的应用,其中包括以下几个方面:(1)基性杂岩体的层状构造;)2)花岗岩中的球状构造;(3)斜长石的环带;(4)花岗岩体的成分分带。并讨论了这四种耗散结构的形成机理。这些耗散结构都是在远离平衡的条件下,通过内部不可逆的非线性过程,由于外界的扰动和内部的涨落造成定态的失稳而形成的。其形成的根本原因是其内部反馈机制作用的结果。斜长石的环带是时间耗散结构——极限环。利用耗散结构理论简要地解释了辽宁二道沟花岗闪长岩的成因。