Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx   总被引：1，自引：0，他引：1  

J. W. MORGAN  R. J. WALKER  A. D. BRANDON  M. F. HORAN 《Meteoritics & planetary science》2001,36(9):1257-1275

Abstract— The platinum group elements (PGE; Ru, Rh, Pd, Os, Ir, Pt), Re and Au comprise the highly siderophile elements (HSE). We reexamine selected isotopic and abundance data sets for HSE in upper mantle peridotites to resolve a longstanding dichotomy. Re‐Os and Pt‐Os isotope systematics, and approximately chondritic proportions of PGE in these rocks, suggest the presence in undepleted mantle of a chondrite‐like component, which is parsimoniously explained by late influx of large planetisimals after formation of the Earth's core and the Moon. But some suites of xenolithic and orogenic spinel lherzolites, and abyssal peridotites, have a CI‐normalized PGE pattern with enhanced Pd that is sometimes termed “non‐chondritic”. We find that this observation is consistent with other evidence of a late influx of material more closely resembling enstatite, rather than ordinary or carbonaceous, chondrites. Regional variations in HSE patterns may be a consequence of a late influx of very large objects of variable composition. Studies of many ancient (>3.8 Ga) lunar breccias show regional variations in Au/Ir and suggest that “graininess” existed during the early bombardment of the Earth and Moon. Reliable Pd values are available only for Apollo 17 breccias 73215 and 73255, however. Differences in HSE patterns between the aphanitic and anorthositic lithologies in these breccias show fractionation between a refractory group (Re, Os and Ir) and a normal (Pd, Ni, and Au) group and may reflect the compositions of the impacting bodies. Similar fractionation is apparent between the EH and EL chondrites, whose PGE patterns resemble those of the aphanitic and anorthositic lithologies, respectively. The striking resemblance of HSE and chalcogen (S, Se) patterns in the Apollo aphanites and high‐Pd terrestrial peridotites suggest that the “non‐chondritic” abundance ratios in the latter may be reflected in the composition of planetisimals striking the Moon in the first 700 Ma of Earth–Moon history. Most notably, high Pd may be part of a general enhancement of HSE more volatile than Fe suggesting that the Au abundance in at least parts of the upper mantle may be 1.5 to 2x higher than previously estimated. The early lunar influx may be estimated from observed basin‐sized craters. Comparison of relative influx to Earth and Moon suggests that the enrichment of HSE is limited to the upper mantle above 670 km. To infer enrichment of the whole mantle would require several large lunar impacts not yet identified.  相似文献   

Ultrasonic borehole images of the subsurface crust     

MIKE LOVELL  PHILIPPE PEZARD  PETER HARVEY 《Geology Today》1990,6(6):195-198

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Stone runs in the Falkland Islands   总被引：2，自引：0，他引：2  

MIKE ROSENBAUM 《Geology Today》1996,12(4):151-154

Large parts of the Falkland Islands are covered by conspicuous stone stripes. Their appearance is believed to be the result of partial vegetation cover developing on solifluction-transported rock.  相似文献   

Evaluation of the Glugla method for estimating evapotranspiration and groundwater recharge     

JAMES V. BONTA  MIKE MÜLLER 《水文科学杂志》2013,58(5):743-761

Abstract

Estimates of groundwater recharge are often needed for a variety of groundwater resource evaluation purposes. A method for estimating long-term groundwater recharge and actual evapotranspiration not known in the English literature is presented. The method uses long-term average annual precipitation, runoff, potential evaporation, and crop-yield information, and uses empirical parameter curves that depend on soil and crop types to determine long-term average annual groundwater recharge (GWR). The method is tested using historic lysimeter records from 10 lysimeters at Coshocton, Ohio, USA. Considering the coarse information required, the method provides good estimates of groundwater recharge and actual evapotranspiration, and is sensitive to a range of cropping and land-use conditions. Problems with practical application of the technique are mentioned, including the need for further testing using given parameter curves, and for incorporating parameters that describe current farming practices and other land uses. The method can be used for urban conditions, and can be incorporated into a GIS framework for rapid, large-area, spatially-distributed estimations of GWR. An example application of the method is given.  相似文献   

The local geologist 13: A beginner's guide to the field study of sedimentary rocks     

STEVE KERSHAW  MIKE KEELING 《Geology Today》1993,9(6):230-233

Geology is primarily afield study, and no matter what information is collected from detailed study of hand specimens and thin sections in the laboratory, this must be related to the outcrops in order to develop a geological interpretation of a sequence of rocks. Here we focus on the type of information that should be collected when studying sedimentary rocks in the field, and highlight the main techniques employed.  相似文献   

British Association Annual Science Festival: Loughborough 1994     

PAUL WRIGHT  MIKE BROOKS 《Geology Today》1995,11(1):20-21

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Fragmentation of granitic quartz in water: a reply     

A. J. MOSS  P. H. WALKER  J. HUTKA 《Sedimentology》1974,21(4):637-638

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Ostracod Mg/Sr/Ca and 87Sr/86Sr geochemistry from Tibetan lake sediments: Implications for early to mid‐Pleistocene Indian monsoon and catchment weathering     

ZHANGDONG JIN  MIKE J. BICKLE  HAZEL J. CHAPMAN  JIMIN YU  ZHISHENG AN  SUMIN WANG  MERVYN J. GREAVES 《Boreas: An International Journal of Quaternary Research》2011,40(2):320-331

Jin, Z. D., Bickle, M. J., Chapman, H. J., Yu, J., An, Z., Wang, S. & Greaves, M. J. 2010: Ostracod Mg/Sr/Ca and ⁸⁷Sr/⁸⁶Sr geochemistry from Tibetan lake sediments: Implications for early to mid‐Pleistocene Indian monsoon and catchment weathering. Boreas, 10.1111/j.1502‐3885.2010.00184.x. ISSN 0300‐9483 Lacustrine sediment serves as a valuable archive for tracing catchment weathering processes associated with past climatic and/or tectonic changes. High‐resolution records of fossil ostracod Mg/Ca, Sr/Ca and ⁸⁷Sr/⁸⁶Sr ratios from a lake sediment core from the central Tibetan Plateau reveal a temporal link between lake‐water chemistry and catchment weathering and distinct monsoonal oscillations over the early to mid‐Pleistocene. Between 2.01 and 0.95 Ma, lake‐water chemistry was dominated by a high proportion of carbonate weathering related to variations in the Indian monsoon, resulting in relatively low and constant ostracod ⁸⁷Sr/⁸⁶Sr but obvious fluctuations in Mg/Ca, Sr/Ca and δ¹⁸O. Across the mid‐Pleistocene transition (MPT), a significant increase in ⁸⁷Sr/⁸⁶Sr and frequently fluctuating ratios of ostracod Mg/Ca, Sr/Ca and δ¹⁸O are coincident with increases in both Chinese loess grain size and Arabian Sea lithogenic flux. This correlation indicates an increased glaciation and a strong monsoon seasonal contrast over the plateau. The increase in lake‐water ⁸⁷Sr/⁸⁶Sr across the MPT highlights a change in catchment weathering patterns, rather than one in climate‐enhanced weathering intensity, with an increased weathering of ⁸⁷Sr‐rich minerals potentially induced by marked extensive glaciation and strong seasonality in the central plateau.  相似文献   

100 years of geology teaching in Cheltenham     

C. MIKE BELL 《Geology Today》1998,14(1):31-32

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ADVANTAGES OF SEARCHING FOR ASTEROIDS FROM LOW EARTH ORBIT: THE NEOSSat MISSION     

A. R. HILDEBRAND  K. A. CARROLL  E. F. TEDESCO  D. R. FABER  R. D. CARDINAL  J. M. MATTHEWS  R. KUSCHNIG  G. A. H. WALKER  B. GLADMAN  J. PAZDER  P. G. BROWN  S. M. LARSON  S. P. WORDEN  B. J. WALLACE  P. W. CHODAS  K. MUINONEN  A. CHENG 《Earth, Moon, and Planets》2004,95(1-4):33-40

Space-based observatories have several advantages over ground-based observatories in searching for asteroids and comets. In particular, the Aten and Interior to Earth’s Orbit (IEO) asteroid classes may be efficiently sought at low solar elongations along the ecliptic plane. A telescope in low Earth orbit has a sufficiently long orbital baseline to determine the parallax for all Aten and IEO class asteroids discovered with this observing strategy. The Near Earth Object Space Surveillance Satellite (NEOSSat) mission will launch a microsatellite to exploit this observing strategy complementing ground-based search programmes.  相似文献