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81.
Environmental controls on 10Be‐based catchment‐averaged denudation rates along the western margin of the Peruvian Andes
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Regina Reber Romain Delunel Fritz Schlunegger Camille Litty Andrea Madella Naki Akçar Marcus Christl 《地学学报》2017,29(5):282-293
We present 10Be‐based basin‐averaged denudation rates for the entire western margin of the Peruvian Andes. Denudation rates range from c. 9 mm ka?1 to 190 mm ka?1 and are related neither to the subduction of the Nazca plate nor to the current seismicity along the Pacific coast and the occurrence of raised Quaternary marine terraces. Therefore, we exclude a tectonic control on denudation on a millennial time‐scale. Instead, we explain >60% of the observed denudation rates with a model where erosion rates increase either with mean basin slope angles or with mean annual water discharge. These relationships suggest a strong environmental control on denudation. 相似文献
82.
G. Dreibus H. Palme B. Spettel J. Zipfel H. Wnke 《Meteoritics & planetary science》1995,30(4):439-445
Abstract— We report here new analyses of S and Se in carbonaceous chondrites (2 CIs, 11 CMs, 6 CO3s, 7 CV3s, 2 C4s, 4 CRs, and 1 CH), 2 rumurutiites, ordinary chondrites (2 Hs, 2 Ls, and 1 LL), 3 anomalous chondrites, 3 acapulcoites, 3 lodranites, and in silicate inclusions of the Landes IAB iron meteorite. To avoid problems from inhomogeneous distribution of sulfides, the same samples that had been analysed for Se by INAA were analysed for S using a Leybold Heraeus Carbon and Sulfur Analyser (CSA 2002). With the measured CI contents of 5.41% S and 21.4 ppm Se a CI S/Se ratio of 2540 is obtained. A nearly identical S/Se ratio of 2560 ± 150 is found for carbonaceous chondrites (average of falls). The average ratio of all meteorite falls analysed in this study was 2500 ± 270. These data suggest that the new S content of Orgueil with 5.41% provides a reliable estimate for the average Solar System. The new solar system abundance of S of 4.62 × 105 (atoms/106 Si) is in good agreement with the solar photospheric abundance of 7.21 (log (a(H)) = E12) (Anders and Grevesse, 1989). Among the 50 analysed meteorites, 24 were finds from hot (Australia, Africa) and cold (Antarctica) deserts. Weathering effects in the carbonaceous chondrites and in one lodranite from the hot deserts resulted in losses of S, Se, Na and occasionally Ni. Sulfur is apparently more affected by weathering than Se. No losses were observed in ordinary chondrite finds and in meteorites collected in the Antarctica, except for the obvious loss of Na in the CM-chondrite Y 74662. The low S-content of 0.096% in Gibson, a lodranite, is probably not representative of this group of meteorites. Gibson is a find from the Australian desert and has lost S and also Se by weathering. Two other lodranites, finds from Antarctica, have about 2% S. 相似文献
83.
Abstract— Forsteritic olivine grains in the Allende meteorite are commonly rimmed by FeO-rich olivine. New evidence is presented in this paper that the fayalitic rims formed by condensation from a gas and not by thermal equilibration of forsterite with FeO-rich metal or FeO-rich olivine in the interior of a parent body. A similar origin is inferred for fayalitic veins within forsterite crystals. A good correlation of FeO with MnO was observed along profiles from forsteritic cores to fayalite-rich rims, excluding oxidation of metal as a source of rim FeO. The fayalite content of the rim is generally lower than that of the adjacent matrix olivines excluding formation of FeO-rich rims by equilibration with present matrix. This is also supported by systematic differences in Cr between rim and matrix olivines. Chromites, associated with FeO-rich olivine, were found at the boundary between forsterite and fayalite-rich rim, within the rim itself and in fayalitic veins. Condensation of chromite from a gas phase is likely for the latter two occurrences since no other suitable source of Cr is available. Chromite at the forsterite-fayalite interface was formed by diffusion of Cr from forsterite. Increasingly oxidizing conditions, apparently enabled formation of chromite. The steep compositional gradient between forsterite and fayalite provides severe constraints on the thermal history of forsterite grains. The width of oxidized zones (halos) around metal inclusions in the interior of forsterite grains are not compatible with this steep gradient. Their development requires longer diffusion times than would be allowed by the rims, indicating that these forsterite grains must have had an independent history of oxidation prior to formation of the rim. Condensation calculations indicate that FeO-rich olivine can be formed by condensation from a gas with enhanced oxygen fugacity. Increasing the oxygen fugacity would provide conditions allowing the thermodynamic stability of chromite. High temperatures and oxidizing conditions must have prevailed for some time in that part of the solar nebula where the Allende meteorite formed. 相似文献
84.
Abstract— The origin of the aubrite parent body (APB) and its relation to the enstatite chondrites is still unclear. Therefore we began a detailed chemical study of the aubrite Peña Blanca Spring. Bulk samples and mineral separates (oldhamite, troilite, alabandite, pyroxene) of Peña Blanca Spring were analyzed for major and trace elements by instrumental neutron activation analysis (INAA). In addition, a leaching experiment was performed on a powdered bulk sample to study the distribution of trace elements in aubrite minerals. The elemental abundances in Peña Blanca Spring are compared to abundances in EH-chondrites and EL-chondrites in an attempt to distinguish volatility related fractionations (evaporation, condensation) from planetary differentiation (melting and core formation). Low abundances of siderophile (e.g., Ir) and chalcophile (e.g., V) elements in bulk samples indicate that 25% (by mass) metal and about 6% (by mass) sulfide separated from an enstatite chondrite like-parent body to form a core and a residual mantle with aubrite composition. We argue that the high observed rare earth element (REE) abundances in oldhamite (>100 × EH-chondrite normalized) reflect REE incorporation into oldhamite during nebular condensation. Thus, oldhamite in aubrites is, at least in part, a relict phase as originally proposed by Lodders and Palme (1990). Some re-equilibration of CaS with silicates has, however, occurred, leading to partial redistribution of REE, as exemplified by the uptake of Eu by plagioclase. The distribution of the REE among aubritic minerals cannot be the result of fractional crystallization, which would occur if high degrees of partial melting took place on the APB. Instead, the REE distributions indicate incomplete equilibrium of oldhamite and other phases. Therefore, a short non-equlibrium melting episode led to segregation of metal and sulfides. 相似文献
85.
Xavi Gallach Ludovic Ravanel Markus Egli Dagmar Brandova Michael Schaepman Marcus Christl Stephan Gruber Philip Deline Julien Carcaillet François Pallandre 《Landslides》2018,15(10):1991-2000
Rockfalls and rock avalanches are a recurrent process in high mountain areas like the Mont Blanc massif. These processes are surveyed due to the hazard they present for infrastructure and alpinists. While rockfalls and rock avalanches have been documented for the last 150 years, we know very little about their frequency since the Last Glacial Maximum (LGM). In order to improve our understanding, it is imperative to date them on a longer timescale. A pilot campaign using Terrestrial Cosmogenic Nuclide (TCN) dating of five samples was carried out in 2006 at the Aiguille du Midi (3842 m a.s.l.). In 2011, a larger scale study (20 samples) was carried out in five other test sites in the Mont Blanc massif. This paper presents the exposure ages of the 2011 TCN study as well as the updated exposure ages of the 2006 study using newer TCN dating parameters. Most of these exposure ages lie within the Holocene but three ages are Pleistocene (59.87?±?6.10 ka for the oldest). A comparison of these ages with air temperature and glacier cover proxies explored the possible relationship between the most active rockfall periods and the warmest periods of the Holocene: two clusters of exposure ages have been detected, corresponding to the Middle Holocene (8.2–4.2 ka) and the Roman Warm Period (c. 2 ka) climate periods. Some recent rockfalls have also been dated (<?0.56 ka). 相似文献
86.
Olivia Kronig Susan Ivy-Ochs Irka Hajdas Marcus Christl Christian Wirsig Christian Schlüchter 《Swiss Journal of Geoscience》2018,111(1-2):117-131
To develop a more precise understanding of Alpine glacier fluctuations during the Holocene, the glacier forefields of the Triftjegletscher and the Oberseegletscher east of Zermatt in the Valais Alps, Switzerland, were investigated. A multidisciplinary approach of detailed geological and geomorphological field mapping combined with 10Be exposure and radiocarbon dating was applied. A total of twelve samples of boulders and bedrock were taken from both Little Ice Age (LIA) landforms, as documented by the Dufour map published in 1862, and from landforms outside of the LIA. The resulting 10Be ages range between 12590 ± 350 a and 420 ± 170 a. A piece of wood found embedded in the Little Ice Age moraine gave radiocarbon ages that range between 293 cal years BP up to modern (356–63 cal years before 2013). Based on these results, four tentative steps of the Holocene evolution could be distinguished. An early Holocene stage, which documents the decay of the Egesen stadial glaciers when the first parts of the study area became ice free. This was followed by a phase with no evidence of glacier advance. Then in the late Holocene, the glaciers advanced (at least) twice. An advance around 1200 a, as shown by several moraine ages, coincides with the Göschenen II cold phase. A more extensive readvance occurred during the LIA as shown on the historical maps and underpinned by one 10Be exposure age and the radiocarbon age. This later advance destroyed or overprinted the earlier landforms in most parts of the area. 相似文献