Regional Variations in the Mineralogy of Metasomatic Assemblages in Mantle Xenoliths from the West Eifel Volcanic Field, Germany

Xenoliths record two distinct events in the mantle below theQuarternary West Eifel Volcanic Field, Germany. The first, duringthe Hercynian Orogeny, led to widespread formation of secondary,Ti-poor amphibole, clinopyroxene and phlogopite. The signatureof the second event, related to Quaternary volcanism, variesacross the field. At Dreiser Weiher and Meerfelder Maar, thisevent is characterized by amphibole–phlogopite–clinopyroxeneveins, hosted in lherzolite and harzburgite xenoliths broughtto the surface by sodic olivine nephelinite–basanite suitelavas. These veins formed from crystallization of sodic magmathat flowed along fractures in the mantle. At Rockeskyller Kopf,Gees and Baarley, the Quaternary event is characterized by wehrlitexenoliths, many of which have phlogopite–clinopyroxeneveins, that were transported by potassic foid suite lavas. Wehrliteformed by reaction of lherzolite–harzburgite, with a largevolume of potassic magma that flowed along grain boundariesrather than in fractures. During reaction, orthopyroxene wasconsumed and secondary clinopyroxene, olivine and phlogopiteprecipitated. Veins formed in wehrlites only during periodicover-pressure events. The composition of the magmas parentalto the veins is similar to the lavas that carried the xenolithsto surface, indicating that the source of foid and olivine nephelinite–basanitesuite magma is domainal, as was the flow regime and magma flux. KEY WORDS: Eifel; mantle xenoliths; metasomatism; trace elements     

Glacial sedimentary processes and environmental reconstruction based on lithofacies

Glacigenic sediments exposed in pits around Villeneuve, near Edmonton, Alberta, are subdivided into facies based on grain size, sedimentary structure, glacially-induced deformation and faulting, and groove marks. Two diamicton facies are recognised, one of which is interpreted as a primary till, deposited directly from glacier ice, and the other as a product of mass-movement. The diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits. The stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities. At any one place the glacier appears to have alternated between being attached to the bed, causing thrusting and sole marking, and being separated from the bed by a cavity in which fluvial and mass-movement sediments accumulated. The net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance. The correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history. In addition, the interpretations presented here have implications regarding the formation of soft zones in ‘till’. They indicate that the soft zones are beds of sorted sediment redeposited by mass-movement.     

The Geochemistry of Scapolite: Part II. Trace Elements, Petrology, and General Geochemistry

Fifty scapolites have been analysed spectrographically for numerouselements. Average concentrations (p.p.m.) were as follows: B25, Be 9–3, Ga 33, Ti 82, Li 56, Cu 4–4, Zr 59,Mn 57, Sr 1,800, Pb 45, Ba 120, Rb 20. The following were seldomor never detected: Cr, Ni, Co, Mo, Sn, V, Sc, Ag, Y, La. Themajor elements Ca, Na, K were also determined. The distributionof the trace elements can be explained by isomorphous substitution,but no detailed correlation of trace elements with each otheror with major elements was found. Refractive indices were determined and the relation betweenaverage index and per cent Me was examined: correlation waspoor, which may in part be attributed to analytical error. Examination of scapolite parageneses shows that scapolite characteristicallyoccurs in the upper amphibolite facies or the pyroxene hornfelsfacies: it is not restricted to these and may occur in any faciesfrom zeolitic to granulitic and in any hornfels facies. Theelements generally concentrated in scapolite include Ca, Na,C, Cl, S, H, B, Be, Li, Sr, Pb. The presence of C, Cl, S, Htestify to genesis in the presence of high partial pressureof CO₂, Cl₂, SO₃, H₂O (or related compounds), that is in pneumatolytic,pegmatitic, or hydrothermal environments. The concentrationof B, Be, Li can also be attributed to these conditions. The source of the elements concentrated in scapolite must inpart be common rocks. In a limited contact zone, the nearbymagma supplied some elements, but where regional scapolitizationhas taken place the presence of magma is less clear. Many commonrocks or rock series contain all the necessary constituents,but some particular conjunction of conditions is necessary forscapolite to form, or it would be more common.     

Rheology of Basalt in the Melting Range

Experimental data have been obtained for viscosities of tholeiitemelts at temperatures from 1300 to 1120 °Cat 1 atm, usinga concentric cylinder viscometer. The apparent viscosity increasesmore than two orders of magnitude between 1200 and 1120 °C(0–25 per cent crystallization) for shear rates of about10 sec^-1 and even more for lower shear rates. Non-Newtonianbehaviour of ‘pseudo-plastic type’ becomes extremelypronounced at temperatures below about 1130 °C. At thesetemperatures, differences of less than 5 °C can producechanges in apparent viscosity amounting to orders of magnitude.These observations have led to the conclusion that the heatof deformation must itself influence rheological behaviour inthe melting range. An equation for thermal energy balances andtheir rates of change is constructed and placed in a non-dimensionalform that has been given published solutions by I. J. Gruntfest(1963) relating the shear stress, rate of strain, and temperaturethrough the temperature dependence of viscosity. The resultsshow that in an adiabatic system the heating rate increaseswith time so that the temperature eventually runs out of bounds,a process termed ‘thermal feedback’ by Gruntfest.A hypothesis of shear melting is derived on the basis of a simplifiedviscosity function extrapolated to the solidus temperature.The hypothesis is applied to magma generation in the earth onthe basis of dimensional arguments. It is also suggested thatthermal instabilities give rise to a sort of viscous failureresponsible for deep-focus earthquakes, and that the two phenomenahave the same cause relating ultimately to a gravitational energysource.     

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (<10 km long) also strike southwest-northeast. The mapped pattern of moraines implies that, shortly after the last maximum glaciation, the tidewater ice sheet began to retreat north from German Bank, forming De Geer moraines at the grounding line with at least one glacial re-advance during the general retreat. The results indicate that the Laurentide Ice Sheet extended onto the continental shelf.     

Till body morphology and structure related to glacier flow

Tills are described which occur in ridges and mounds arranged both parallel and transverse to the flow direction of the depositing glacier. Field localities are drawn from the English Midlands, Western Canada, and South Victoria Land, Antarctica. The tills retain textural and structural properties associated with glacial transport, and have suffered a minimum of redistribution suhsequent to their release from glacier ice. It is shown that ridges and mounds cannot he explained in terms of preferential till accretion. An alternative mechanism is presented in which form and structurc are a result of redistribution of debris in transport by secondary flows in ice.
Flutings are longitudinal forms which are related to helicoidal flow cells. Fabric distributions, patterns of till thickness, and internal structure support the helicoidal flow hypothesis.
Debris entrainment by Antarctic cold-based glaciers is explained by consideration of the morphology and sedimentology of the ice margin and the pattern of glacier flow. Deposition by sublimation and melt-out produces an upwards succession of (1) undisturbed proglacial deposits; (2) a complex of poorly sorted flow deposits intercalated with sorted and stratified water-lain deposits; (3) foliated till with sub-horizantal jointing and isolated clasts. A section shobbing this succession is described from Taylor Valley, Antarctica.
Transverse asymmetric ridges are related to till stacking by over-folding in the marginal compressive zone of cold-based glaciers. Plastic deformation of the debris-laden ice may be enhanced by incorporated salts. The folding process is illustrated by structures within Taylor glacier, and is used to explain Pleistocene landforms and structures in Shropshirc, England and Taylor Valley, Antarctica.     

中国民航客运(国内)空间格局与竞争态势分析

利用统计分析和可视化方法,综合考虑行政、经济、人口和旅游吸引指标,采取抽样方法选择了60个具有代表性的国内大中城市,以近期发布的中国民航班期数据为基础,研究了构成中国民航运输网络的9家民航公司的通航城市和航线网络特征,并分析了各公司相互问的竞争关系。结果表明,三大航空集团和海航的航线呈多中心网状分布,而其他5家航空公司航线呈明显的单中心/双中心放射状分布;在运营中,三大航空集团和海航具有明显的垄断优势。而它们之间也存在明显的竞争关系。其他航空公司在构成中国民航运输网络骨架的大中城市航线运营中处于明显的竞争劣势。研究成果对航空公司航线、航班调整、代码共享和民航政策制订具有参考作用。     

Concentrations of B,Sm, Gd and H in 24 Reference Materials*

Analysis of 24 reference materials for B, Sm, Gd, H, has been carried out over several years, using prompt gamma neutron activation analysis. The results are compared with values obtained by other workers, in order to better calibrate these standards. In most cases our results of repeated analysis of RMs show agreement with results from other laboratories, using various methods. A djustments to working values are proposed in some cases.     

The Petrology of an Adamellite-Porphyrite from the New England Bathylith (New South Wales)

The paper presents an account of the occurrence, petrography,mineralogy, and geochemistry of several intrusions of adamellite-porphyrite,an early member of the New England Bathylith (N.S.W.). The rockis composed of phenocrysts of quartz, andesine, hornblende,biotite, augite (and minor orthopyroxene) which are set in afine-grained quartzofeldspathic groundmass. Compositions ofsilicate phenocrysts (which reveal widespread evidence of cataclasis)accord with coexisting phases of an assemblage appropriate tointermediate rocks. Xenolith mineralogy is similar to equivalentminerals occurring as phenocrysts. The recalculated bulk compositionof a rock represented by the modal andesine, hornblende, biotite,augite, and magnetite of the adamellite-porphyrite is similarto the composition of a biotite–diorite; the compositionof the quartzo-feldspathic groundmass plots in the low-meltingregion of the NaAISi₃O₈-KAISi₃O₈-SiO₂-H₂O system. Evidence ispresented to indicate a hybrid origin for the adamellite-porphyritewhereby disrupted biotite-diorite was invaded and mixed withlow-melting silicic alkalic liquid.     

Understanding the textures and origin of shock melt pockets in Martian meteorites from petrographic studies,comparisons with terrestrial mantle xenoliths,and experimental studies

Abstract— We present a textural comparison of localized shock melt pockets in Martian meteorites and glass pockets in terrestrial, mantle‐derived peridotites. Specific textures such as the development of sieve texture on spinel and pyroxene, and melt migration and reaction with the host rock are identical between these two apparently disparate sample sets. Based on petrographic and compositional observations it is concluded that void collapse/variable shock impedance is able to account for the occurrence of pre‐terrestrial sulfate‐bearing secondary minerals in the melts, high gas emplacement efficiencies, and S, Al, Ca, and Na enrichments and Fe and Mg depletion of shock melt compositions compared to the host rock; previously used as arguments against such a formation mechanism. Recent experimental studies of xenoliths are also reviewed to show how these data further our understanding of texture development and can be used to shed light on the petrogenesis of shock melts in Martian meteorites.