西藏纳木错地区约120kaBP以来的古植被、古气候与湖面变化

西藏纳木错湖相沉积的U系和^11C测年结果表明，湖泊沿岸的6级湖岸阶地及拔湖约48～139．2m的高位湖相沉积形成于约120ka BP以来的晚第四纪。本文根据该套湖相层的发育和其中的孢粉组合特征对纳木错地区约120ka BP以来的湖面变化与古植被、古气候变迁进行了探讨。结果表明，纳木错地区晚更新世以来经历了频繁的湖面波动、气候的冷暖与干湿变化以及森林—草原与草原植被的交替演化。其总体特征是：约115．9ka BP时，纳木错湖面最高。在116～78ka BP期间，该区气候温和凉爽或温和偏湿，植被以疏林草原与森林草原或森林的交替出现为特征，湖面经历了较大幅度的波动，但基本保持在拔湖140～88m之间。在78～53ka BP期间，该区气候干冷，植被以疏林草原为主，湖面大幅度下降，并在拔湖约36～48m之间波动。约53～32ka BP期间，气候转为温暖偏湿或温暖湿润，湖面波动于拔湖约15～28m之间，波动较为频繁。与阶地的发育相对应，该时期内包含了3次明显的暖期和湖面波动过程，区域植被主要以松、蒿、桦为主，为含一定量的冷杉的森林。其中36ka BP左右气候最温暖湿润，区域内可能出现针叶林或针阔混交林。约32～12ka BP期间，该区气候最为干冷，古植被以草原和疏林草原为主，湖面再次发生较大幅度的下降，最低可至拔湖约8m处，但通常维持在拔湖约12～17m之间。约11．8～4．2ka BP期间，气候整体较为暖湿，其中在约8．4～4．2ka BP期间气候最温暖湿润，该区可能发育针叶林或针阔混交林，湖面波动于拔湖2～9m之间，整体波动幅度较小，但波动最为频繁。区域气候对比发现，纳木错地区的冷、暖气候变化过程与整个青藏高原乃至北半球的气候变化基本是一致的，特别是阶地下切所反映的湖面退缩过程与北大西洋的Henrich冷事件之间具有很好的对应关系。     

青藏高原西北缘晚新生代的隆升特征——来自西昆仑山前盆地的沉积学证据

对西昆仑北缘山前盆地新生代沉积特征的研究结果表明,沿西昆仑山前发育的各沉积序列的垂向特征相似:古新世—中新世早期为石膏层、含瓣腮化石的石灰岩和紫红色较细粒的碎屑岩沉积,指示了海相和海陆过渡相较平静的沉积环境;中新世晚期—上新世初期开始出现陆相磨拉石,指示了陆相非平静的沉积环境,砾石的直径由下至上呈增大趋势,可能反映了西昆仑山体不断隆升,其间相对稳定的层段可能是构造运动间歇期或平稳期的沉积,指示了脉动式的隆升模式;磨拉石底部砾石的成分以沉积岩为主,向上火成岩和变质岩砾石逐渐增多,表明剥蚀程度不断加深。根据磨拉石建造的特征,判断剥蚀量和剥蚀强度自西向东有减小和变弱的趋势,可能暗示了西昆仑山晚新生代隆升有自西向东由强变弱的过渡特征。该结论与本区构造地貌学的研究结果一致。     

A new method to calculate end-member thermodynamic properties of minerals from their constituent polyhedra II: heat capacity, compressibility and thermal expansion

Thermodynamic calculations in petrology are generally performed at pressures and temperatures beyond the standard state conditions. Accurate prediction of mineral equilibria therefore requires knowledge of the heat capacity, thermal expansion and compressibility for the minerals involved. Unfortunately, such data are not always available. In this contribution we present a data set to estimate the heat capacity, thermal expansion and compressibility of mineral end‐members from their constituent polyhedra, based on the premise that the thermodynamic properties of minerals can be described by a linear combination of the fractional properties of their constituents. As such, only the crystallography of the phase of interest needs to be known. This approach is especially powerful for hypothetical mineral end‐members and for minerals, for which the experimental determination of their thermodynamic properties is difficult. The data set consists of the properties for 35 polyhedra in the system K–Na–Ca–Li–Be–Mg–Mn–Fe–Co–Ni–Zn–Al–Ti–Si–H, determined by multiple linear regression analysis on a data set of 111 published end‐member thermodynamic properties. The large number of polyhedra determined allows calculation of a much larger variety of phases than was previously possible, and the choice of constituents together with the large number of thermodynamic input data results in estimates with associated uncertainty of generally <5%. The quality of the data appears to be sufficiently accurate for thermodynamic modelling as demonstrated by modelling the stability of margarite in the CASH system and the position of the talc–staurolite–chloritoid–pyrope absent invariant point in the KMASH system. In both cases, our results overlap within error with published equivalents.     

SURFACE ROUGHNESS EVOLUTION OF SOILS CONTAINING ROCK FRAGMENTS

Soil surface roughness is a dynamic property which determines, to a large extent, erosion and infiltration rates. Although soils containing rock fragments are widespread in the Mediterranean region, the effect of the latter on surface roughness evolution is yet poorly understood. Therefore, laboratory experiments were conducted in order to investigate the effect of rock fragment content, rock fragment size and initial moisture content of the fine earth on the evolution of interrill surface roughness during simulated rainfall. Surface elevations of simulated plough layers along transects of 50 cm length were measured before and after simulated rainfall (totalling 192.5 mm, I = 70 mm h⁻¹) with a laser microreliefmeter. The results were used to investigate whether systematic variations in interrill surface roughness along stony hillslopes in southeastern Spain could be attributed to rock fragment cover and rock fragment size. Soil surface elevations were measured along the contour lines (50 cm long transects) with a contact microreliefmeter. Roughness was expressed by two parameters related to the height and frequency of roughness elements, respectively: standard deviation of de-trended surface elevations (random roughness: RR), and correlation length (L) derived from exponential fits of the autocorrelation functions. The frequently used assumption that surface roughness (RR) of cultivated topsoils decreases exponentially with cumulative rain is not valid for soil surfaces covered by rock fragments. The RR of soils containing small rock fragments (1.7–2.7 cm) increased with cumulative rainfall after an initial decrease during the first 17.5 mm of rainfall. For soils containing large rock fragments (7.7 cm), RR increased with rainfall above a threshold rock fragment content by mass of 52 per cent. For a given rainfall application, RR increased non-linearly with rock fragment content. The correlation length for soils containing small rock fragments decreases with rock fragment content and is significantly lower than for soils with large rock fragments. Soils covered with small rock fragments (large RR and small L) are thus well protected against raindrop impact by a water film in the depressions between the rock fragments. On abandoned agricultural fields along hillslopes in southeastern Spain, rock fragments cover increases non-linearly with slope owing to selective erosion of finer particles on steep slopes. The increase of surface cover by large rock fragments (>25 mm) is even more pronounced. The simultaneous increase of rock fragment cover and rock fragment size with slope explains the non-linear increase of RR with slope. These relationships differ for soils covered by platy misaschists and those covered with cubic andesites. The variations in correlation length along the hillslopes are not clear, probably owing to a simultaneous increase in rock fragment cover and rock fragment size. These findings may provide a better prediction of soil surface roughness of interrill areas covered by rock fragments using slope angle and lithology.     

Mineralogy, Petrology, and Geochemistry of an Ultrapotassic Basaltic Suite, Central Sierra Nevada, California, U.S.A.

Ultrapotassic basaltic lavas erupted 3.4–3.6 m.y. ago(K/Ar) in the central Sierra Nevada and originated by partialmelting of a phlogopite-enriched, garnet-bearing upper mantlesource. Ultrapotassic basanites (K₂O: 5–9 per cent), whichare spatially related to contemporaneous potassic olivine basalts(K₂O: 3–5 per cent) and alkali olivine basalts (K₂O: 1–3per cent), contain the K₂O-bearing minerals phlogopite, sanidine,and leucite as well as olivine, diopside, apatite, magnetite,and pseudobrookite. The presence and modal abundance of theK₂O-bearing minerals closely reflects the east to west increasein K₂O throughout the basaltic suite. Many lines of evidence support the derivation of the ultrapotassicbasanites and the related basalts from an upper mantle source:TiO₂ in phlogopite phenocrysts and groundmass crystals, 2–3and 7–9 per cent respectively, support phlogopite phenocrystcrystallization at high pressure, whole rock Mg values (100Mg/Mg + 0.85 Fe) range from 66–78, phlogopite-rich pyroxeniticand periodotitic nodules are included in some flows, and geobarometriccalculations indicate depths of generation at 100–125km. Also, model calculations show that the major, rare earth,and trace elements, except for Ba, Rb, and Sr, can be accuratelygenerated by 1.0–2.5 per cent melting of a phiogopite-and garnet-bearing clinopyroxene-rich upper mantle source. Partialmelting occurred after a general upper mantle enrichment beneaththe Sierra Nevada, the phlogopite- and clinopyroxene-rich sourceof the ultrapotassic lavas being the extreme result of the enrichmentprocess. Clinopyroxene enrichment of the upper mantle probablyoccurred by introduction of a partial melting fraction intothe upper mantle source areas. Enrichment of the upper mantlein the alkali and alkali-earth elements was not accomplishedby a partial melt, but resulted from influx of a fluid phaserich in Ba, K, Rb, Sr, and, probably, H₂O The continuous rangein K₂O of the erupted lavas implies that the upper mantle enrichmentis a cumulative process. The inverse relationship in the SierraNevada between uplift and the K₂O content of the erupted basaltsimplies that a critical relationship may exist between upliftand upper mantle enrichment.     

Growth, Production, and a Partial Energy Budget for the Amphipod, Talorchestia capensis (Crustacea; Talitridae) in the Eastern Cape, South Africa

Abstract. .A population of Talorchestia capensis was sampled in dune slacks over the period of one year. Two hatching periods, one in March and one in September, were observed. Growth was rapid, the amphipods reaching a size of 8.4 mm standard length in 18 months. Maximum growth occurred in spring and minimum growth in winter. Annual mortality rates for summer- and winter-hatched individuals were low, 0.22-y“¹ and 0.16-y”¹. Average production for the summer classes was 7.2g-y?‘ (dry mass) and for the winter classes 2.9-y“¹, with a P/B ratio of 2.25-y”’. Production values peaked during autumn and summer. Abundance and biomass estimates showed maxima during summer and minima in early spring. Reproductive output was low, 0.1 kJ ? m^-2 y“¹, indicating that 7 % of the total production is used for reproduction and 93 % for somatic production. The assimilated energy flow through the population was estimated to be 16.3 kJ m?² y?‘ and consumption about 81.6 kJ m^-2 y^_’.     

Source and Differentiation of Deccan Trap Lavas: Implications of Geochemical and Mineral Chemical Variations

The basalt stratigraphy of the Deccan Trap between MahabaleshwarGhat and Belgaum over-steps the basement from north to south.Sr-isotope and Zr/Nb ratios, and Sr, Rb, and Ba concentrationscorrelate portions of the post-Poladpur stratigraphy over 250km along the Western Ghats, thereby confirming a southerly componentof dip of 0?06?. At the southwestern margin, the stratigraphyextends upwards from the compositionally uniform Ambenali Formation(Cox & Hawkesworth, 1984) into a sequence of grossly heterogeneousflow units which have been allocated to the Mahabaleshwar andPanhala Formations (Lightfoot & Hawkesworth, 1988). TheMahabaleshwar Formation is represented only by a sequence ofhighly fractionated flows (termed the Kolhapur unit) with similar⁸⁷Sr/⁸⁶Sr₀ to the Mahabaleshwar (0?7045), but with Sr<240ppm and TiO₂>2?25%. Succeeding the Kolhapur unit are a seriesof flows with high ⁸⁷Sr/⁸⁶Sr₀ (0?7045-0?705), Zr/Nb > 13,and low Sr (< 200 ppm), which have been allocated to thePanhala Formation, and a group of flows with high ⁸⁷Sr/⁸⁶Sr₀(0?707–0?708) and Sr (>230), but trace element concentrationssimilar to the Mahabaleshwar Formation; these have been allocatedto the Desur unit of the Panhala. Geochemical variations in flows overlying the Ambenali definetwo distinct trends: one is attributed to gabbro fractionation,and the other to variations in the compositions of the parentalmagmas, and arguably their source regions. There is little evidencefor significant crustal contamination in these flows, and thedegree of fractionation and the composition of the phase extractare shown to vary along strike within the Mahabaleshwar Formation.The high TiO₂ content of Kolhapur unit flows is shown to bethe result of shallow-level gabbro fractionation, rather thanthe presence of a primitive high-Ti magma. Mahabaleshwar Formationbasalts exhibit a broad negative correlation between the degreeof fractionation and Sr-isotopic composition. The endmemberwith lower ⁸⁷Sr/⁸⁶Sr₀ has different Zr/Y from the Ambenali basalts,and would appear to have been generated by lower degrees ofmelting of a similar source. The other endmember has more radiogenicSr, lower Zr/Nb, similar Zr/Y, but higher mg-number. The simplestinterpretation is that these magmas were more primitive andhence hotter and more able to interact with the lithosphereen route to the surface, and that they then mixed to producethe Mahabaleshwar array. The Panhala Formation basalts ploton the Sr-Nd array defined by the Mahabaleshwar Formation, andthe Desur unit basalts plot on an extension of this array; thissuggests that the source characteristics are also lithospheric.The absolute elemental abundances may then be a function ofmelting and fractionation. We are impressed by the apparentswitch from crustal lithospheric contributions to mantle lithosphericcontributions through the stratigraphy, and suggest that this,together with the more protracted fractionation of the magma,reflects a change in the availability of the lithospheric componentsaccompanying the southerly migration of the volcanic edifice. ^* Present address: Geoscience Laboratories, Ontario Geological Survey, 11th Floor, 77, Grenville Street, Toronto, Ontario, M7A 1W4, Canada     

An Archean(?) to Paleozoic Evolution for a Garnet Peridotite Lens with Sub-Baltic Shield Affinity within the Seve Nappe Complex of Jamtland, Sweden, Central Scandinavian Caledonides

Mineralogical, isotopic, geochemical and geochronological evidencedemonstrates that the Friningen body, a garnet peridotite bodycontaining garnet pyroxenite layers in the Seve Nappe Complex(SNC) of Northern Jämtland, Sweden, represents old, certainlyProterozoic and possibly Archean, lithosphere that became incorporatedinto the Caledonian tectonic edifice during crustal subductioninto the mantle at c. 450 Ma. Both garnet peridotite and pyroxenitecontain two (M₁ and M₂) generations of garnet-bearing assemblagesseparated by the formation of two-pyroxene, spinel symplectitearound the M₁ garnet and the crystallization of low-Cr spinel_1Cin the matrix. These textures suggest initial high-pressure(HP) crystallization of garnet peridotite and pyroxenite succeededby decompression into the spinel stability field, followed byrecompression into the garnet peridotite facies. Some pyroxenitelayers appear to be characterized solely by M₂ assemblages withstretched garnet as large as several centimeters. Laser ablationmicroprobe–inductively coupled plasma mass spectrometryRe–Os analyses of single sulfide grains generally definemeaningless model ages suggesting more than one episode of Reand/or Os addition and/or loss to the body. Pentlandite grainsfrom a single polished slab of one garnet peridotite, however,define a linear array on an Re–Os isochron diagram that,if interpreted as an errorchron, suggests an Archean melt extractionevent that left behind the depleted dunite and harzburgite bodiesthat characterize the SNC. Refertilization of this mantle bymelts associated with the development of the pyroxenite layersis indicated by enriched clinopyroxene Sr–Nd isotope ratios,and by parallel large ion lithophile-enriched trace elementpatterns in clinopyroxene from pyroxenite and the immediatelyadjacent peridotite. Clinopyroxene and whole-rock model Sm–Ndages (T_DM = 1·1–2·2 Ga) indicate that fertilizationtook place in Proterozoic times. Sm–Nd garnet₂–clinopyroxene₂–wholerock ± orthopyroxene₂ mineral isochrons from three pyroxenitelayers define overlapping ages of 452·1 ± 7·5and 448 ± 13 Ma and 451 ± 43 Ma (2     

SOME RESULTS OF THE GEO-ELECTRICAL RESISTIVITY METHOD IN GROUND WATER INVESTIGATIONS IN THE NETHERLANDS*

In the year 1958 the Service for Water Management of the ?Rijkswaterstaat” started its program of geo-electrical resistivity prospecting in the western part of the Netherlands. The aim of this program was to obtain data on the salinity distribution of the ground water. The ground water regime in this part of the Netherlands is most intricate. This is due to the geological and geo-hydrological conditions and to the low elevation of the land. Many reclaimed areas are up to several metres below mean sea level. The resistivity data obtained are closely related to the salinity of the ground water. On the basis of bore hole data it was even possible to arrive at calibration curves for the salinity of the ground water in sand deposits. Under special conditions it was also possible to draw conclusions with respect to the presence of less permeable formations as e.g. clay layers. Some remarks are given on the practical performance and the interpretation of the measurements. A review is given of the work done until now. Some results are shown by means of maps of the salinity distribution of the ground water in the western and northern parts of the Netherlands. Two examples are described of the use of the data obtained during the survey in the province of Zuid-Holland. Another two examples are presented of detailed investigations for special purposes in relatively small areas.