热柱、超级热柱及其成因的研究进展

从20世纪地幔热柱假说问世,经过30多年的发展,在地幔热柱的全球分布、鉴别特征、形态学和成因理论方面都有了长足的进步。特别是通过下地幔不均匀性的研究,发现了下地幔中存在的超级热柱和下地幔底层中的超低速带,为探讨热柱成因提供了重要依据。     

Capture and release zones of permeable reactive barriers under the influence of advective–dispersive transport in the aquifer

The problem of permeable reactive barrier (PRB) capture and release behavior is investigated by means of an approximate analytical approach exploring the invariance of steady-state solutions of the advection–dispersion equation to conformal mapping. PRB configurations considered are doubly-symmetric funnel-and-gate as well as less frequent drain-and-gate systems. The effect of aquifer heterogeneity on contaminant plume spreading is hereby incorporated through an effective transverse macro-dispersion coefficient, which has to be known. Results are normalized and graphically represented in terms of a relative capture efficiency M of contaminant mass or groundwater passing a control plane (transect) at a sufficient distance up-stream of a PRB as to comply with underlying assumptions. Factors of safety FS are given as the ratios of required capture width under advective–dispersive and purely advective transport for achieving equal capture efficiency M. It is found that M also applies to the release behavior down-stream of a PRB, i.e., it describes the spreading and dilution of PRB treated groundwater possibly containing incompletely remediated contamination and/or remediation reaction products. Hypothetical examples are given to demonstrate results.     

Geochemistry of mafic rocks of the Karakaya complex,Turkey: evidence for plume-involvement in the Palaeotethyan extensional regime during the Middle and Late Triassic

The Karakaya Complex within the Early Mesozoic Cimmerian Orogeny in northern Turkey represents the remnants of the Palaeotethys. It includes slivers and/or mega-blocks of slightly metamorphic basic volcanic rocks associated with fossiliferous sediments as well as hypabyssal and intrusive rocks with basaltic-andesitic to ultramafic compositions. They display two distinct compositional groups; namely alkaline and variably tholeiitic. The alkaline basalt samples are more akin to oceanic-island basalts (OIB) with relatively enriched trace element characteristics together with strong partitioning in HREE ([La/Yb]_N = 5.8–16.2), suggesting that garnet is present as a residual phase in the source of those basalts. The variably tholeiitic samples apart from diabases display E-MORB characteristics; being relatively depleted compared to the alkaline counterparts and less fractionated REE patterns ([La/Yb]_N = 2.1–3.6). The diabases, on the other hand, are distinctively different with a significant negative Nb anomaly (Zr/Nb = 28.9–43.4) and flat REE patterns ([La/Yb]_N = 0.8–1.4), suggesting their generation above a supra-subduction zone, probably a back-arc basin. These results may suggest that a mantle plume-related magmatism associated with extensional oceanic system should have been installed within Palaeotethys during Middle-Late Triassic time, which was then incorporated into subduction–accretion prism forming the final picture, that is, “the Karakaya Complex”.     

Metropolitan-scale Transport and Dispersion from the New York World Trade Center Following September 11, 2001. Part I: An Evaluation of the CALMET Meteorological Model

Following the collapse of the New York City World Trade Center towers on September 11, 2001, Local, State and Federal agencies initiated numerous air monitoring activities to better understand the impact of emissions from the disaster. A study of the estimated pathway that a potential plume of emissions would likely track was completed to support the U.S. EPA’s initial exposure assessments. The plume from the World Trade Center was estimated using the CALMET-CALPUFF dispersion modeling system. The following is the first of two reports that compares several meteorological models, including the CALMET diagnostic model, the Advanced Regional Prediction System (ARPS) and 5^th Generation Mesoscale Model (MM5) in the complex marine-influenced urban setting of NYC. Results indicate wind speed, in most cases, is greater in CALMET than the two mesoscale models because the CALMET micrometeorological processor does not properly adjust the wind field for surface roughness variations that exits in a major built-up urban area. Small-scale circulations, which were resolved by the mesoscale models, were not well simulated by CALMET. Independent wind observations in Lower Manhattan suggest that the wind direction estimates of CALMET possess a high degree of error because of the urban influence. Wind speed is on average 1.5 ms⁻¹ stronger in CALMET than what observations indicate. The wind direction downwind of the city is rotated 25–34 clockwise in CALMET, relative to what observations indicate.     

长江河口盐度锋

根据1988－1991年河口锋面现场调查、上海市海岸带调查及历次标准断面调查资料对长江盐度场及盐度锋进行了分析，提出了由口门至外海纵向上存在着三级锋面现象：内侧锋面即长江河口锋为长江河口水与长江冲淡水的界面；羽状锋是长江口羽状流水与口外混合水的界面，它是长江口最主要的盐度锋面，也是长江口一个重要的生物地球化学带，对河口沉积过程及水下三角洲发育具有重要的影响。外侧锋面即海洋锋，是长江冲淡水的最外边缘。     

碳酸岩的地质地球化学特征及其大地构造意义

从已知碳酸岩的地质产状、岩石学特征、Nd-Sr-Pb-O-C同位素及痕量元素地球化学特征数据,结合高温高压实验岩石学资料,论述了其地幔源区的物质成分、交代过程软流圈地幔部分熔融机制和碳酸岩岩浆的演化模型。碳酸岩既可以产生于拉张岩石圈构造背景,也能够产生于挤压而派生的引张岩石圈构造背景。前者以产于裂谷环境、与硅酸不饱和过碱性岩构成环状碳酸岩—碱性杂岩为特征,主要由起源于软流圈地幔的霞石质超基性—基性岩浆经液态不混溶作用而形成;后者产于碰撞造山过程中派生的引张岩石圈断裂带,以单一的透镜状、条带状和似层状碳酸岩体为标志,直接由导源岩石圈富集地幔的低程度部分熔融作用而产生的碳酸岩浆侵入或喷发所形成。     

Modelling of thermochemical plumes and implications for the origin of the Siberian traps

Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t₁ between plume formation and eruption. These relationships are used to determine thermal power and time t₁ for the Tunguska syneclise and the Siberian traps as a whole.

The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts.     

A method for monitoring building construction in urban sprawl areas using object-based analysis of Spot 5 images and existing GIS data

Urban sprawl has been identified as one of the most negative effects of global population growth on the environment and biodiversity. Frequent monitoring of urban sprawl is needed to limit the impact of this ongoing phenomenon. This paper proposes precise monitoring of building construction using an object-based classification methodology applied to Spot 5 images with a 2.5 m resolution. An application at a regional scale on Reunion Island in the Indian Ocean shows that this building extraction methodology has limitations in the production of reference urban maps because of difficulties in defining the shape and the number of buildings compared to classical photo-interpretation of aerial photography. However, these results are of great value for planning in urban sprawl areas where up-to-date information is lacking because of the rapid pace of house construction and residential development.     

Swell impact on reef sedimentary processes: A case study of the La Reunion fringing reef

Two surface‐sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back‐reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain‐size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef‐flat to the back‐reef, but this transport is episodic and occurs principally during high‐tide stages. Sediment transport trends revealed by the grain‐size trend analysis method show onshore and alongshore low‐energy transport processes that are in agreement with the hydrodynamic records. The grain‐size trend analysis method also provides evidence of an offshore high‐energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain‐size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back‐reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones.     

Early Paleozoic tectonics and geodynamics of Central Asia: role of mantle plumes

There were two key stages in the history of Paleozoids that formed in the place of the Paleoasian ocean, one in the Cambrian–Ordovician and the other in the Permian–Triassic. Both time spans were characterized by a combination of similar geodynamic, magmatic, and geomagnetic events: closure and opening of oceanic basins, intense plume magmatism associated with Earth's core cooling, and absence of geomagnetic reversals (superchrons). Three superchrons about 490–460, 260–300, and 124–86 Ma correlate with major events of plume magmatism. Plume reconstructions have to be updated for the period 490–460 Ma, which corresponded to the third superchron and was marked by ocean opening. The previous superplume, about 800–740 Ma, requires further justification but fits the global periodicity with 240 Ma major cycles and smaller ones of 120 (or also 30) Ma.In the Late Cambrian–Ordovician, large-scale accretion and collision events acted, in similar tectonic settings, upon the vast territory that currently extends from the Polar Urals to Lake Baikal (and was times larger in the past). As a result, Gondwanian microcontinents (Kokchetav, Altai–Mongolia, Tuva–Mongolia, etc.) and island arcs joined into the Kazakhstan–Tuva–Mongolia system. The formation of the Late Cambrian–Ordovician orogen in Central Asia was synchronous with opening of the Ural, Ob–Zaisan, Turkestan, and Paleotethys oceans. The plume pulses (520–500 and 490–460 Ma) may have been responsible for opening of new oceans, accelerated amalgamation of terranes, and synchronicity in geodynamic events from the Urals to Transbaikalia.