THE ROTATING CURRENT DIPOLE METHOD - A FIELD TEST*

The outputs and neutral of a three phase generator are converted to six amplitude variable phases in a 3.5 kW 400 Hz transmitter. These outputs are applied to six groundimplanted electrodes, producing a horizontally rotating current dipole in the subsurface. An investigation of the radiation pattern in the vertical magnetic field indicates, in symmetry and closure control, considerable advantages in this form of galvanic energization. These include optimization of inductive anomalies and the ability to interpret phase observations on a spatial basis in depth sounding and orebody location.     

LICHENOMETRY ON ADELAIDE ISLAND, ANTARCTIC PENINSULA: SIZE-FREQUENCY STUDIES, GROWTH RATES AND SNOWPATCHES

This paper presents new lichenometric population data from the Antarctic Peninsula (67°S), and describes a new approach to lichen growth-rate calibration in locations where dated surfaces are extremely rare. We use historical aerial photography and field surveys to identify sites of former perennial snowpatches where lichen populations now exist. As an independent check on lichen mortality by snowkill, and the timing of snow patch disappearance, we use a positive-degree day (PDD) approach based on monthly climate data from Rothera Research Station. We find that maximum growth rates for lichens <40 mm in diameter on Adelaide Island are around 0.8 mm/yr. Furthermore, we propose that our combined methodology may be more widely applicable to the Polar Regions where the construction of lichenometric dating (age-size) curves remains a problem.     

Analysis of Standard Reference Materials for Zr,Nb, Hf and Ta by ICP-MS after Lithium Metaborate Fusion and Cupferron Separation*

Results are presented of the determination of Zr, Nb, Hf and Ta in 74 standard reference materials by inductively coupled plasma mass spectrometry (ICP-MS). Samples are decomposed by fusion with lithium metaborate and the analytes are separated prior to analysis by precipitation of their cupferrates. Calibration is made using synthetic solutions and internal standardization with Ru (for Zr and Nb) and Re (for Hf and Ta). Accuracy is assessed by comparison with recommended values and precision is evaluated by replicate analyses of five SRMs.     

The sedimentological evolution of a Lower Palaeozoic accretionary fore-arc in the Southern Uplands of Scotland

Thick turbidites accumulated along the northern margin of the Iapetus Ocean in Britain from mid-Ordovician to late Silurian times. Recent plate tectonic reconstructions hold that, during subduction, packets of these sediments, together with the underlying pelagic facies and thin portions of the uppermost ocean crust, were stripped from the descending plate and accreted to the inner trench wall on the Laurentian (North American) continental margin. The resulting accretionary prism is represented today by the Ordovician and Silurian rocks of the Southern Uplands of Scotland and the Longford-Down massif of Ireland. In these areas major reverse faults separate tracts of steeply dipping greywackes and mudstones with minor amounts of cherts and basalts. These tracts are up to several kilometres wide; their constituent beds face predominantly to the northwest, away from the site of the ancient ocean, while becoming progressively younger in each major fault slice towards the Iapetus suture in the southeast. From the stratigraphic sequences in these fault slices the sedimentary history of a portion of the Iapetus Ocean, and the British sector of its northern margin, can be reconstructed. In the Southern Uplands the earliest turbidites (mid- and late-Ordovician) are preserved in the northernmost fault slices. Regional facies trends, and vertical facies analysis, suggest that they accumulated in a trench dominated by a series of relatively small lower trench slope-derived fans. Pelagic sediments of the same age are found in the fault slices to the south, suggesting that the Ordovician turbidites were confined to the trench. During the lower and middle Llandovery, volcaniclastic trench turbidites were separated from quartz-rich ocean-floor turbidites (represented in the southern fault slices) by an elongate rise, on which pelagic deposits accumulated. This is interpreted as the outer trench high. In late Llandovery times the rise was overwhelmed, and thick laterally derived quartzose turbidites blanketed both the trench and the ocean floor. Sedimentation was strongly influenced by the evolution of the accretionary prism. By Llandovery times a trench slope break had emerged, supplying sediment both south to the trench and north to an upper slope basin in the Midland Valley of Scotland. In this basin early Silurian turbidites were followed by shallow-water and terrestrial sediments. Most of the sediment was derived from the emergent trench slope break: the volcanic arc and the Grampian orogenic belt to the north provided little or no detritus. Throughout the Ordovician and Silurian, sediment in the trench and on the ocean floor was derived from the volcanic arc, from the lower trench slope/trench slope break, from a degrading plutonic/metamorphic terrain (the Grampian Orogen), and locally by a minor amount of submarine sliding from carbonate-capped volcanic seamounts. Progressive elevation of the trench slope break in Silurian (and perhaps late Ordovician) times indicates that sediment from the arc-orogen hinterland must have bypassed the upper slope in the unexposed section of the margin to the northeast of the Southern Uplands, and travelled into the area axially along the trench floor.     

火山灰的提取及测试技术

同一次火山爆发产生的火山灰 ,能在广阔的区域内形成等时标志层 ,成为地层定年和对比的极有价值的工具。文中介绍了提取肉眼不可见火山灰的 4种方法 :烧失法、稀碱法、重液浮选法和酸化法 ,还介绍了火山玻璃的显微镜下识别技术及电子探针测试技术。     

THE BIOPOLITICAL JUSTIFICATION FOR GEOSURVEILLANCE

ABSTRACT. Biopolitical use of geosurveillance can create and sustain a politics of fear. Although the majority of surveillance literature focuses on individuals, in this article I focus on groups and populations, drawing on Michel Foucault's analysis of biopolitics. After discussing the forms and history of geosurveillance I argue that three particularly important factors contribute to these politics: divisions, geospatial technologies, and the risk‐based society. In order to combat the negative unintended consequences of these factors I suggest that more attention be paid to the mutual relationships between geospatial technology and politics, rather than on assessments of the value of individual surveillant technologies. (09–11–06) 12:01 PDT SAN FRANCISCO—A United Airlines flight that was diverted to Dallas this morning after an unclaimed electronic device was discovered onboard has landed at San Francisco International Airport, an airport spokesman said. The flight crew on United flight 351 from Atlanta to San Francisco elected to stop in Dallas around 7 a.m., said SFO spokesman Mike McCarron, after finding a backpack on board that no one claimed. The unattended backpack contained a PDA device, McCarron said, “like a Blackberry.” Authorities searched the plane in Dallas and found nothing unusual, he said.—Marisa Lagos, 2006.     

Reconstructing the basal thermal regime of an ice stream in a landscape of selective linear erosion: Glen Avon, Cairngorm Mountains, Scotland

The Cairngorm Mountain area of Scotland is a classic example of a landscape of selective linear glacial erosion, with sharp contrasts in the intensity of glacial erosion between the deeply incised troughs and valleys and the undulating high plateau. This article examines the Quaternary development of Glen Avon, a 200 m deep glacial trough set within the high plateau of the mountains. Evidence concerning the aggregate basal thermal regimes of the topographically controlled ice streams that formerly developed in this area is reconstructed from the geomorphological record, including bedforms indicative of wet-based, sliding ice and of dry-based ice frozen to its bed. This mapping indicates that basal sliding was not confined exclusively to the troughs but extended towards valley heads and on to parts of the plateau adjacent to troughs. The extent of basal sliding appears to have been greatest beneath pre-Late Devensian ice sheets. Basal ice temperatures are modelled under steady-state conditions for the last ice sheet at c. 18 ka BP. Basal thermal regimes are predicted using a reconstruction of the preglacial relief and for the current topography of the area. Convergent flow of ice through the preglacial valley system appears to have been sufficient to induce basal melting and therefore to initiate valley deepening. This effect is enhanced when the model is run across the present topography. Comparison of results of the geomorphological mapping and the modelling reveals significant differences between the actual and predicted extent of basal sliding outside the main ice stream. The overall conclusion is that many ice streams in mountainous terrain are inherited from the locations of preglacial valleys, which serve to accelerate ice flow and promote frictional heating beneath ice sheets.     

Fluid inclusion constraints on the uplift history of the metamorphosed massive sulphide deposits at Ducktown, Tennessee

Abstract Standard petrographic, microthermometric and Raman spectroscopic analyses of fluid inclusions from the metamorphosed massive sulphide deposits at Ducktown, Tennessee, indicate that fluids with a wide range of compositions in the C–O–H–N–S–salt system were involved in the syn- to post-metamorphic history of these deposits. Primary fluid inclusions from peak metamorphic clinopyroxene contain low-salinity, H₂O–CH₄ fluids and calcite, quartz and pyrrhotite daughter crystals. Many of these inclusions exhibit morphologies resembling those produced in laboratory experiments in which confining pressures significantly exceed the internal pressures of the inclusions. Secondary inclusions in metamorphic quartz from veins, pods, and host matrix record a complex uplift history involving a variety of fluids in the C–O–H–N–salt system. Early fluids were generated by local devolatilization reactions while later fluids were derived externally. Isochores calculated for secondary inclusions in addition to the chronology of trapping and morphological features of primary and secondary fluid inclusions suggest an uplift path which was concave toward the temperature axis over the P–T range 6–3 kbar and 550–225° C. Immiscible H₂O–CH₄–N₂–NaCl fluids were trapped under lithostatic to hydrostatic pressure conditions at 3–0.5 kbar and 215 ± 20° C. Entrapment occurred during Alleghanian thrusting, and the fluids may have been derived by tectonically driven expulsion of pore fluids and thermal maturation of organic material in lower-plate sedimentary rocks which are thought to underlie the deposits. Episodic fracturing and concomitant pressure decreases in upper-plate rocks, which host the ore bodies, would have allowed these fluids to move upward and become immiscible. Post-Alleghanian uplift appears to have been temperature-convex. Uplift rates of 0.10–0.05 mm year^?1 from middle Ordovician to middle Silurian – late Devonian, and 0.07–0.12 mm year^?1 from middle Silurian – late Devonian to late Permian are suggested by our uplift path and available geochronological data.