Geochemistry of Some Marine Fe–Mn Nodules and Crusts with Respect to Pt Contents     

Alexandre Raphael Cabral  Carl‐Diedrich Sattler  Bernd Lehmann  Harilaos Tsikos 《Resource Geology》2009,59(4):400-406

Bulk chemical analyses for Pt and Pd in marine Fe–Mn nodules and crusts from different provenances are presented, together with a wide range of elements. Platinum contents vary from 70–328 ppb, whereas Pd contents extend from 0.6–4.7 ppb only. Bromine and Pb show strong positive correlations with Pt. Lead is remarkably enriched in Fe–Mn precipitates over seawater, but Br is a conservative‐type element in seawater and shows no enrichment in Fe–Mn precipitates. Hence, the Pt–Br–Pb element association combines two elements, Br and Pb, of extremely contrasting enrichment factors in Fe–Mn precipitates.  相似文献   

When will it end? Long-lived intracontinental reactivation in central Australia     

Raphael Quentin de Gromard  Christopher L.Kirkland  Heather M.Howard  Michael T.D.Wingate  Fred Jourdan  Brent I.A.Mc Innes  Martin Daniík  Noreen J.Evans  Bradley J.McDonald  R.Hugh Smithies 《地学前缘(英文版)》2019,10(1):149-164

The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580 -520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results,from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by40 Ar/39 Ar muscovite and U e Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by Ue Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust,from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende40 Ar/39 Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect,40 Ar/39 Ar muscovite and zircon(Ue Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600-660℃. Subsequent cooling to 150 -220℃ of the core of the orogen occurred between ca. 480 Ma and 400 Ma(zircon [Ue Th]/He data)during reactivation of the Woodroffe Thrust, coincident with the 450 -300 Ma Alice Springs Orogeny.Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016(Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9 -7.0℃/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.  相似文献   

Thermal alteration experiments on organic matter in recent marine sediment—I. Pigments     

Raphael Ikan  Zeev Aizenshtat  Mary Jo Baedecker  Isaac R Kaplan 《Geochimica et cosmochimica acta》1975,39(2):173-185

Sediment from Tanner Basin, located at the outer continental shelf off southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65°, 100°, 150°C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of α-ionene and 2,6-dimethylnaphthalene, thermal-degradation products of β-carotene. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms and geochemical significance of these transformations are presented.  相似文献   

Source, genesis, and timing of giant ignimbrite deposits associated with Ethiopian continental flood basalts     

Dereje AyalewPierre Barbey  Bernard Marty  Laurie ReisbergGezahegn Yirgu  Raphael Pik 《Geochimica et cosmochimica acta》2002,66(8):1429-1448

The Ethiopian continental flood basalt (CFB) province (∼30 Ma, > 3 × 10⁵ km³) was formed as the result of the impingement of the Afar mantle plume beneath the Ethiopian lithosphere. This province includes major sequences of rhyolitic ignimbrites generally found on top of the flood basalt sequence. Their volume is estimated to be at least 6 × 10⁴km³, which represents 20% of that of the trap basalts. Their phenocryst assemblage (alkali feldspar, quartz, aegyrine-augite, ilmenite ± Ti-magnetite, richterite, and eckermanite) suggests temperatures in the range of 740 to 900°C. Four units were recognized in the field (Wegel Tena, Jima, Lima Limo, and Debre Birhan areas), each with its own geochemical specificity. Zr/Nb ratios remain constant between basalt and rhyolite in each area, and rhyolites associated with high-Ti or low-Ti basalts are, respectively, enriched or depleted in titanium. Their trace element and isotope (Sr, Nd, O) signatures (high ¹⁴³Nd/¹⁴⁴Nd and low ⁸⁷Sr/⁸⁶Sr ratios, compared to those of rhyolites from other CFB provinces) are clearly different from those of typical crustal melts and indicate that the Ethiopian rhyolites are among the most isotopically primitive rhyolites. Their major and trace element patterns suggest that they are likely to be derived from fractional crystallization of basaltic magmas similar in composition to the exposed flood basalts with only limited crustal contribution. Since Ethiopian high-Ti basalts have been shown to form from melting of a mantle plume, it is likely that Ethiopian ignimbrites, at least those that are Ti-rich, also incorporated material from the deep mantle.Rb-Sr isochrons on whole rocks and mineral separates (30.1 ± 0.4 Ma for Wegel Tena and 30.5 ± 0.4 Ma for Jima ignimbrites) show that most of the silicic volcanism occurred within < 2 Ma during the Oligocene. Ignimbritic eruptions resumed in the Miocene during two episodes dated at 15.4 ± 0.2 Ma and 8.0 ± 0.2 Ma for the Debre Birhan area. The Rb-Sr isochron ages of ignimbrites (both Oligocene and Miocene rhyolites) are indistinguishable within uncertainties from the ⁴⁰Ar/³⁹Ar ages of the underlying flood basalts. The Oligocene ignimbrites and the underlying trap basalts are synchronous with a shift in the oxygen composition of foraminifera recorded in Indian and Atlantic Ocean cores. The temporal coincidence of Ethiopian Oligocene volcanism, which released immense volumes of S (> 1.4 × 10¹⁵ mol) and Cl (6.4 × 10¹⁵ mol) into the atmosphere over a short time span, with the global cooling event at 30.3 Ma suggests that this volcanism might have accelerated the climate change that was already underway.  相似文献   

Complementary relationships for near-instantaneous evaporation     

Richard Crago  Raphael Crowley 《Journal of Hydrology》2005,300(1-4):199-211

The complementary relationship between actual and potential evaporation provides evaporation (i.e. evapotranspiration) estimates from minimal data. Some versions that require a land surface temperature instead of a humidity measurement could potentially be used with routine remotely sensed surface temperature data. A comparison of alternative complementary approaches, including those that require land surface temperatures, was made at small (10–30 min) time scales with point measurements spatially, using data from the FIFE, CASES, SGP, and Sahel field experiments. The advection-aridity version and a related version based on the Penman and the Priestley–Taylor equations performed the best overall. One of the four versions that incorporated land surface temperature performed fairly well. The complementary approach appears to remain viable, especially in remote sensing applications with sparse data.  相似文献   

Book review     

Raphael G. Kazmann 《Environmental Geology》1990,15(2):159-160

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The short period magnetic variable HD 133029     

Raphael Steinitz  Diane M. Pyper 《Astrophysics and Space Science》1971,11(2):322-329

It is shown that the magnetic measurements of HD 133029 exhibit a correlation of magnetic intensity with exposure length. Due to this effect a re-examination of the star's period was undertaken, resulting in a new period of 0.168 days. The significance of such a short period is discussed. It is argued that this short variation cannot be due to an oblique rotator.  相似文献   

Volcanic red-bed copper mineralisation related to submarine basalt alteration,Mont Alexandre,Quebec Appalachians,Canada   总被引：1，自引：0，他引：1  

Alexandre Raphael Cabral  Georges Beaudoin 《Mineralium Deposita》2007,42(8):901-912

Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000–20,263 ppm) and arsenic (146–6,017 ppm), and a broader range of silver abundances (<65–2,186 ppm Ag) than type 2 (149–1,288 ppm S, <90–146 As, <65–928 ppm Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electron-microprobe scale. Primary igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has Fe/(Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating albite and yarrowite (Cu₉S₈ with up to 0.3 wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm, respectively, and thallium is positively correlated with Fe₂O₃. Such concentrations of thallium and lithium are typical of spilitisation during heated seawater–basalt interaction. Spilitisation is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should be re-examined to account for native copper mineralisation in basalts altered by warm seawater.  相似文献   

Predicting spatial patterns in riverbank erosion for catchment sediment budgets     

Hugh G. Smith  Raphael Spiekermann  John Dymond  Les Basher 《新西兰海洋与淡水研究杂志》2019,53(3):338-362

Riverbank erosion is an important component of catchment sediment budget models but remains one of the least well-understood processes, particularly at large spatial scales. Here, we develop and test a new bank migration model in New Zealand for large catchment applications that (1) better represents spatial variability in factors influencing bank erosion and (2) improves predictive performance. We represent bank migration rates as a function of reach-scale stream power, channel sinuosity, soil texture, valley confinement, riparian woody vegetation and channel protection works. The new model significantly improves prediction compared to the SedNetNZ model. Comparison of measured bank migration rates with individual variables shows percent silt + clay derived from soil maps exhibited the strongest correlation, whereas other variables were non-significant. The model results demonstrate that improved prediction can be achieved by combining spatial representation of multiple factors over large areas, despite low correlation between individual variables and bank migration rates.  相似文献   

Estimated calving interval for the New Zealand southern right whale (Eubalaena australis)     

Anthony Raphael Davidson  William Rayment  Steve M Dawson  Trudi Webster  Elisabeth Slooten 《新西兰海洋与淡水研究杂志》2018,52(3):372-382

Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval?=?3.31 years, 95% CI?=?3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere.  相似文献