The Nevados de Payachata volcanic region (18°S/69°W,N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism     

Jon P. Davidson  Nancy J. McMillan  Stephen Moorbath  Gerhard Wörner  Russell S. Harmon  Leopoldo Lopez-Escobar 《Contributions to Mineralogy and Petrology》1990,105(4):412-432

Volcanism extending over 11 Ma is represented in the rocks of the Nevados de Payachata region, culminating in the formation of two large composite stratocones within the last 500 000 years. Chemically distinct mafic magmas are erupted at a number of parasitic centers. These cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones. Two distinct trends are defined by the intermediate and evolved rocks; a high LILE (large ion lithophile element), TiO₂ and Ce/Yb lineage among the youngest rocks (including the two major stratocones), and a more typical calc-alkaline trend among the older (>1 Ma) rock types. Within individual volcanic centers, differentiation involves fractionation of plagioclase, pyroxene and hornblende, with biotite and K-feldspar in the more-evolved rock types. Isotopic compositions (Sr, Pb, Nd, O) vary little with differentiation from basaltic andesite to rhyolite, or with age. Contamination during differentiation from basalt to rhyolite may occur, but the most mafic rocks erupted in the region are already enriched in incompatible trace elements and therefore may be insensitive to the effects of interaction with the crust. The majority of data are similar to baseline compositions (Cenozoic parental magmas) from other parts of the central Andes and may reflect a relatively homogeneous magma source (or source mixture) throughout this central volcanic zone (CVZ), which is distinct from the southern and northern Andes, and from island-arc volcanic rocks.The detailed study of Nevados de Payachata serves as a useful reference against which to assess magmatism in general in the CVZ. The possibility that central Andean magmas are generated from an enriched subcontinental-lithosphere mantle wedge is rejected on the basis of: (1) thermal considerations (subcontinental mantle lithosphere is probably cold and refractory); (2) lack of consistency between the tectonic history of the region and geochemical variations through time. Instead, parental magmas in the CVZ are thought to be generated by mixing between normal arc magmas originating in the depleted mantle wedge followed by contamination and homogenization with lower crustal melts. In the central Andes, the extent of contamination increased greatly as the crust thickened due to crustal shortening within the last 20 Ma, the thicker crust providing an effective filter to trap and differentiate magma batches repeatedly during ascent.  相似文献   

Ancient Mediterranean harbours: a heritage to preserve     

Leopoldo Franco 《Ocean & Coastal Management》1996,30(2-3)

Management and protection in coastal areas mainly addresses the natural environment and rarely addresses cultural and technical resources. This paper represents a plea for diverting more attention to some valuable historical features which exist, abandoned, along the Mediterranean shores.Along these shores a UN inventory identified some 1255 submerged archaeological coastal sites, many of which showed no signs of any protection from the attack of the sea and of growing coastal tourism. Many of them are remnants of harbour structures which are over 2000 years old.A condensed overview is given of the historical evolution of ancient harbour engineering, particularly related to the Roman age, describing the most interesting and innovative technological aspects, which could still add a valuable insight to the design of modern coastal structures. This knowledge was initially derived from literary and pictorial evidence and is now greatly expanded by the recent discoveries of underwater archaeology and by the developments of remote sensing technology.Co-operation between coastal engineers and archaeologists is encouraged, both for the preliminary surveys before the execution of new coastal works and for the interpretation, defence and revaluation of discovered maritime remains.Finally, recommendations for the restoration and creation of major ancient port sites as museums, possibly within innovative ‘coastal submarine archaeological parks’, are given.  相似文献   

Discussion on &quot;Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism&quot; by Oyarzun et al. (<Emphasis Type="Italic">Mineralium Deposita</Emphasis> 36:794–798, 2001)     

Osvaldo?M.?RabbiaEmail author  Laura?B.?Hernández  Robert?W.?King  Leopoldo?López-Escobar 《Mineralium Deposita》2002,37(8):791-794

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Search for contact systems among EB-type binaries     

F. Barone  L. Di Fiore  L. Milano  L. Pirozzi  G. Russo 《Astrophysics and Space Science》1992,198(2):321-340

We present the analysis of the data of four EB-type eclipsing binaries, continuing our search for contact or almost contact systems. The Price algorithm has been used in conjunction to the Wilson-Devinney model to try to obtain, where possible, unambiguous solutions for all the systems.  相似文献   

Search for contact systems among EB-type binaries     

L. Milano  F. Barone  S. Mancuso  G. Russo 《Astrophysics and Space Science》1989,153(2):273-288

In a search of contact systems among EB-type binaries, the existing photometric observations of ES Lib and AR Boo have been analysed. We find that ES Lib is a semi-detached system, with the primary filling the Roche lobe. AR Boo is instead found to be a contact system, with no lobe overfilling, and with a large temperature difference between the components, but this solution has to be considered as temptative, because of the poor quality of the data and the lack of any spectroscopic information.Associated with the Istituto Nazionale Fisica Nucleare, Italy.  相似文献