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Luigi Marini Valeria Chiappini Roberto Cioni G. Cortecci E. Dinelli Claudia Principe Giorgio Ferrara 《Bulletin of Volcanology》1998,60(3):187-194
Sulfur contents and δ34S values of Somma-Vesuvius magmas are consistent with syneruptive, open-system degassing at temperatures of 800–850°C for
Plinian pumices and 1100–1200°C for lavas. The extent of degassing appears to be greater in lavas than in pumices. The key
parameter controlling the 34S/32S ratio of Somma-Vesuvius volcanics is the average magma oxidation state, which generally varies from 0.85 to 1.20 Δ NNO units
for lavas and from 1.20 to 1.40 Δ NNO units for pumices. Consequently, S contents and δ34S values of magmas constitute a potentially valuable tool in estimating their average redox conditions. The results of this
study may help in risk mitigation when the Vesuvius magmatic system evolves toward eruptive conditions.
Received: 20 January 1998 / Accepted: 5 May 1998 相似文献
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The aim of this study is to establish if the San Luis Potosi Plateau (SLPP), which is part of the southern edge of the Chihuahuan Desert, is generating desertification processes, indicating a progression of the desert toward the central part of Mexico. Therefore, we analyzed the temporal evolution of four environmental indicators of desertification: Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Iron Oxides Index (IO) and Surface Temperature (ST). Landsat TM images are used to cover a period from 1990 to 2011. A new equation of total balance is proposed to generate an image of the overall evolution of each factor which is applied to get a probability map of desertification. The evolution of NDVI, NDWI and IO shows a behavior almost stable over the time. In contrast, the ST shows a slight increase. The outcomes of this study confirm periods of vegetation re-greening and 8.80% of the SLPP has the highest probability to develop desertification. The most affected area is the portion west of the region, and the east and south are the least affected areas. The results suggest a slight advance of the desert, although most of the area doesn’t have the necessary conditions to develop desertification. 相似文献
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Valeria Murgulov William L. Griffin Suzanne Y. O’Reilly 《International Journal of Earth Sciences》2012,101(5):1091-1109
Hf model ages yielded by rutiles in a garnet-rich lower-crustal granulite xenolith from the McBride Province and whole-rock Nd and Hf model ages for the plagioclase- and garnet-rich Chudleigh and McBride granulites overlap with the well-defined U–Pb ages for detrital zircons and zircons in granitoids (Murgulov et al. Chem Geol 245:198–218, 2007; Mineral Petrol 95:17–45, 2009), suggesting temporal correlation of magmatic-tectonic events in the lower and upper crust in the north-east Australian craton. Intrusion of basaltic magmas into and below the lower crust beneath the Chudleigh Province around 1.4, 1.7 and 2.3?Ga and beneath the McBride Province around 1.5, 1.7, 2.3 and 2.5?Ga provided heat for remelting and supplied magmas with juvenile mantle isotope signatures to the upper crust. Similar magmas provided enough heat to cause melting in the lower crust beneath the Chudleigh Province around 0.12 and 0.8–0.9?Ga and beneath the McBride Province around 0.42, 0.8–0.9?Ga, 1.1 and 1.3?Ga but were not sufficient to cause significant melting in the upper crust. A wide range in initial 176Hf/177Hf values and a ~1.55?Ga Hf model age yielded by rutiles in the McBride granulite provide a link to the genesis of ~420?Ma granitoids. The data for a plagioclase-rich granulite from the Atherton Province are similar to those for the Chudleigh and McBride granulites. However, additional samples are required to test whether the lower crust of the Tasman orogenic belt is lithologically and isotopically similar to the lower crust of the craton. 相似文献