Plio-pleistocene volcanism in the Andean Cordillera of Central Chile (33∘ – 40∘ S. L.)     

Prof. Dr. Mario Vergara 《International Journal of Earth Sciences》1983,72(3):1005-1014

Recent field studies in the Andean Cordillera of Central Chile (33–40 S. L.) have shown a widespread distribution around the Chile-Argentina border of pliopleistocene volcanic and pyroclastic flow (5-1 m. y. K/Ar). The older ages are found in Rio Blanco (Santiago) area and the younger in the Cola de Zorro area. They cover horizontal to sub-horizontally, with strong unconformity their meso-cenozoic basement.In the Rio Blanco area the most silicic rocks are dactic and rhyolitic ignimbrites and lava flows. They are similar to the Rhyolitic Formation (Zeil andPichler, 1967) of northern Chile.South of 36 S. L. most of the rocks are calcalkaline basalts and andesites except for the samples from the Pino Hachado area, which plot nearRittman's alkaline field. Chemical inhomogenety of the plio-pleistocene volcanic rocks is thus present in the Andes of Central Chile.

---

Zusammenfassung Neue Arbeiten über die Geologie der Cordillera de los Andes im zentralen Abschnitt Chiles (33–40 S) haben eine enorme Verbreitung von plio/pleistozänen Vulkaniten (5-1 m. a.) vor allem in der Grenzregion mit Argentinien ergeben. Die höheren Alter fand man im Gebiet von Rio Blanco (Santiago) und die jüngsten im Gebiet von Cola de Zorro.Die Vulkanite bedecken mit einer horizontalen bis subhorizontalen Verbreitung und mit einer scharfen Diskordanz alle Gesteinsserien des Mesozoikums und Känozoikums.Im Gebiet von Rio Blanco handelt es sich um Ignimbrite rhyolitischer und dacitischer Zusammensetzung. Die kieselsäurereichsten Proben sind ähnlich den Gesteinen der Rhyolit-Formation vonZeil &Pichler (1967) in Nordchile.Südlich von 36 S hat die Mehrheit der Proben eine andesitische und basaltische Zusammensetzung. Es sind kalkalkaline Gesteine mit Ausnahme der Proben von Pino Hachado, die einen starken alkalinen Trend nach dem Diagramm vonRittmann haben. Auf diese Weise ergibt sich eine chemische Inhomogenität bei den plio/pleistozänen Vulkaniten von Zentralchile.

---

Resumen Los más recientes trabajos de geología de campo en la Cordillera de los Andes de Chile Central (33–40 L. S.) han evidenciado enormes extensiones de rocas volcánicas pliopleistocénicas (5-1 m. a.) sobre todo en el área limítrofe con Argentina. Las mayores edades fueron encontradas en el area de Rio Blanco (Santiago) y las más jóvenes en el area de Cola de Zorro.Las rocas volcánicas plio-pleistocénicas cubren con disposición horizontal a subhorizontal y con fuerte discordancia a todas las rocas subyacentes del Meso y Cenozoico.En el area de Río Blanco las rocas son ignimbritas de composición riolítica a dacítica y corresponden a las muestras más silícicas similar a rocas de la Formación Riolítica del norte de Chile deZeil yPichler (1967).Al sur del paralelo 36 S la mayoría de las muestras son de composición andesítica y basáltica de naturaleza calcoalcalina excepto las muestras de Pino Hachado que presentan fuerte afînidad alcalina según el diagrama deRittmann. De esta manera se muestra que existe inhomogeneidad química en las rocas volcánicas plios-pleistocénicas de Chile Central.

---

Cordillera de los Andes (33°–40° S) , . - (), --. , , . - . 36° . - , . . . , - .

  相似文献   

Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals   总被引：1，自引：0，他引：1  

Jorge Pousa  Luigi Tosi  Eduardo Kruse  Dardo Guaraglia  Maurizio Bonardi  Andrea Mazzoldi  Federica Rizzetto  Enrique Schnack 《Environmental Geology》2007,51(8):1307-1316

The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors. These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented here.  相似文献   

Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change     

Patrick A. Hesp  Sergio Rebello Dillenburg  Eduardo Guimaraes Barboza  Luiz C. P. Clerot  Luiz J. Tomazelli  Ricardo Norberto Ayup Zouain 《地球表面变化过程与地形》2007,32(3):407-414

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Comment on “Ar/Ar age of plagioclase from Acapulco meteorite and the problem of systematic errors in cosmochronology” by Paul R. Renne     

Mario Trieloff  Elmar K. Jessberger  Christine Fini 《Earth and Planetary Science Letters》2001,190(3-4):267-269

  相似文献   

The meromictic Lake La Cruz (Central Spain). Patterns of stratification     

María A. Rodrigo  María R. Miracle  Eduardo Vicente 《Aquatic Sciences - Research Across Boundaries》2001,63(4):406-416

  相似文献   

Hydrogeological problems of Argentina’s pampas: Editor’s message     

Eduardo J. Usunoff 《Hydrogeology Journal》1996,4(3):2-2

  相似文献   

Sulla turbolenza delle correnti marine nello stretto di messina     

Mario Bossolasco  Ignazio Dagnino 《Pure and Applied Geophysics》1957,37(1):318-324

Riassunto Gli Autori espongono i risultati di un tentativo di valutazione del grado di turbolenza verticale delle correnti marine davanti alle imboccature Nord e Sud dello Stretto di Messina. I valori massimi ottenuti per il coefficiente di diffusione verticale della salinitàK _z sono dell'ordine di 10³–10⁴ cm²/sec.

---

Summary The Authors present the results of some calculations carried out to obtain values of the vertical turbulence (by means of the coefficient of eddy-diffusion of salinityK _z ) of the currents in the Strait of Messina. The maximum values ofK _z are of the order of 10³–10⁴ cm²/sec.

---

---

Comunicazione presentata il 24 Aprile 1957 alla Quinta Assemblea Generale della «Società Italiana di Geofisica e Meteorologia» (Genova: 23–25 Aprile 1957).  相似文献   

Peralkaline acid tendencies in Gran Canaria (Canary Islands)     

Vicente Araña  Eduardo R. Badiola  Dr. Francisco Hernán 《Contributions to Mineralogy and Petrology》1973,40(1):53-62

The study of a volcanic series from the island of Gran Canaria (Canary Islands) in which alkaline and peralkaline, saturated and undersaturated rocks coexist, is reported here. Materials with high volatile content (ignimbritic trachytes) were first emitted and the series ended with the eruption of phonolitic lavas. The average peralkalinity index in these rocks is typically about 1.0 and, therefore, peralkaline rocks coexist with non-peralkaline ones. However, a maximum in peralkalinity is found in the ignimbritic rocks of the lower part of the series. In spite of the evident acid peralkaline tendencies of these rocks, it does not seem appropriate to classify them as pantellerites or comendites. Nor are they consistent with the genetic processes proposed for rocks of similar composition and oceanic environment.The crystallization of the feldspars controls the variation trends among the different magmas but the fractionation alone does not sufficiently explain the genesis of successive fluids. Various factors seem to point to the important role which a gas-transfer process causing a geochemical stratification inside the magmatic chamber may have played.The occurrence of peralkaline silicics at Gran Canaria, which is located for away from the active Mid-Atlantic ridge, is not related to transitional basalts. These rocks are a deviation from the main undersaturated alkalic trend which characterizes the volcanism of the Canary Islands, their genesis being related to the realization of favourable local volcanic conditions.  相似文献   

Relationship between some trace elements and magmatic processes     

Enzo Locardi  Mario Mittempergher 《International Journal of Earth Sciences》1967,57(1):313-334

Relationships between magmatic differentiation, volcanological evolution and occurrence of some trace elements have been pointed out by a petrographic and volcanological study of the Quaternary magmatic products of the Northern Latium alkali-potassic volcanoes (Sabatini, Vico, Vulsini).Several hundred analyses of U, Th, Be, Zr, Rb, Sr have been carried out. The above elements are contained in exceptional quantity in the examined alkaline rocks. The distribution pattern of these elements helps for a better understanding of some types of differentiation and, above all, allows to identify the processes related to the uplift and outflow of magmas which are undetectable with the usual petrochemical methods.In particular, the trace elements considered allow us to distinguish a deepseated magma evolution from superficial differentiations related to the volcanic conditions. Moreover, a loss of alkalies from the upper levels of the magmatic chambers has been ascertained which determines peculiar deformations in the normal petrogenetic trends.-- (: Sabatini, Vico, Vulsini). , . .

---

Zusammenfassung Das petrographische und vulkanologische Studium der quartären Vulkanite der Mediterranen Sippe des nördlichen Latiums (die Vulkane Sabatini, Vico und Vulsini) haben uns die Gelegenheit gegeben, die Verhältnisse zwischen Magmenentwicklung, vulkanologischer Evolution und Verteilung einiger Spurenelemente zu bestätigen.Zu diesem Zweck sind Hunderte von Analysen von U, Th, Be, Zr, Sr, Rb — Elemente welche in ungemein großen Mengen in den untersuchten alkalischen Gesteinen enthalten sind — vorgenommen worden. Das Studium der Verteilung dieser Elemente hat ein gründliches Verstehen einiger Differentiationstypen erlaubt, und vor allem den Ablauf des Prozesses des Magmen-Aufstiegs und Abflusses gezeigt, welcher nicht mittels der normalen petrochemischen Untersuchungen ersichtlich ist.Besonders die in Betracht gezogenen Spurenelemente erlauben die Unterscheidung der magmatischen Evolution in den tiefen Lagen von den oberflächlicheren Differentiationen, welche an das vulkanische Geschehen gebunden sind.In dieser Hinsicht ist ein wichtiges Schlußergebnis die Bestätigung des Alkaliverlustes seitens der oberflächlichen Sektoren der Magmaherde, ein Verlust welcher eigenartige Deformationen von den normalen petrogenetischen Linien gezeigt hat.

---

Résumé L'étude pétrographique et volcanologique des manifestations magmatiques quaternaires de la province alcalin-potassique du Latium septentrional (Volcans Sabatini, Vico et Vulsini) nous a permis de vérifier les rapports entre la différenciation magmatique, l'évolution volcanologique et la distribution de quelques éléments en traces.Dans ce but on a exécuté plusieurs centaines d'analyses de U, Th, Be, Zn, Rb, Sr, éléments qui sont présents en quantité exceptionellement élevé dans les roches alcalines examinées.L'étude de la distribution de ces éléments a permis une compréhension plus approfondie de certains types de differenciation et surtout, elle a indiqué l'existence de processus liés à la remontée et effusion des magmas, qui ne sont pas relevables par les examens pétrochimiques normaux.En particulier les éléments en traces considérés permettent de distinguer l'évolution magmatique de milieu profond des différenciations superficielles liées aux situations volcaniques.A ce propos une conclusion importante a été la constatation de la perte d'alcali par les portions plus superficielles des réservoirs magmatiques; une perte qui a déterminé des déformations particulières qui les éloignent des lignes pétrogénétiques normales.

---

---

Authors are indepded to Dr. S.Smcana and to Dr. G.Falchi for the analyses performance.  相似文献   

Cretaceous stratigraphy and palaeoenvironments of the Southern Petén Basin, Guatemala     

Eric Fourcade  Luis Piccioni  Jos Escrib  Eduardo Rosselo 《Cretaceous Research》1999,20(6):793

The Cretaceous deposits of the Southern Petén Basin, an oil-producing province, are located to the south of the Yucatan Platform and to the east of the Chiapas Carbonate Platform of Mexico. The succession in the southern part of this basin has been studied both in wells and at outcrop by microfacies analysis. It is composed of 5000 m of shallow marine carbonates and evaporites with a few thin layers of pelagic limestones rich in organic carbon and planktic foraminifera deposited during peak transgressions or maximum flooding. The sedimentation of this thick succession was not continuous, and the section is punctuated by subaerial erosional bounding surfaces and a single hardground which marks the final drowning of the carbonate platform during the late Maastrichtian. New age determinations have been obtained on the basis of planktic and benthic foraminifera from the Aptian to Santonian Cobán Formation, D, C, B and A Members. Cobán C (Albian) and B (Cenomanian) Members are the present oil reservoirs. The rudist and alveolinid limestones of late Campanian and Maastrichtian age referred to the Campur Formation in the Southern Petén Basin are here reassigned to the Angostura Formation, as recognized in the Chiapas area. The Actela Formation is defined here to encompass the limestone breccia deposits that occur at the Cretaceous–Tertiary boundary and extend into the Parvularugoglobigerina eugubina Zone of early Danian age. The D, C, B and A Members of the Cobán Formation and the Angostura Formation represent second order transgressive and regressive trends in a passive margin area where the deposits indicate a succession of various environments, including fluviatile, salinas, shallow marine carbonate platform, outer shelf and intrashelf basin. High subsidence rates, sea-level changes and tectonic uplift controlled the sedimentation.

Abstract

Les formations crétacées du sud-est du Bassin du Petén, région pétrolière du nord du Guatemala, sont situées au Sud du Yucatan et à l'Est du Chiapas au Mexique. Ces sédiments ont été étudiés à la fois dans deux puits et à l'affleurement par l'analyse des microfaciès. Cet ensemble sédimentaire est composé de 5000 m de carbonates de plate-forme de faible profondeur et d'évaporites, dans lesquels s'intercalent de minces couches de calcaires pélagiques riches en matière organique et en foraminifères planctoniques. Ces calcaires pélagiques se sont déposés lors des maximums de transgressions. La sédimentation de cette épaisse série n'est pas continue et est ponctuée par quelques surfaces d'érosion sub-aérienne et une surface durcie qui souligne l'ennoyage définitif de la plate-forme carbonatée au Maastrichtien terminal. De nouvelles datations ont été obtenues sur la formation Cobán et ses membres D, C, B et A qui s'étagent de l'Aptien au Santonien. Les membres C (albien) et B (cénomanien) constituent les réservoirs productifs. Les calcaires à rudistes et à alveolinidés du Campanien supérieur–Maastrichtien ont été appelés à tort au Petén formation Campur. Ils doivent, selon nous, être attribués à la formation Angostura comme au Chiapas voisin, où affleurent des faciès comparables et de même âge. Une nouvelle formation est créée (formation Actela) pour les brèches calcaires de la limite Crétacé–Tertiaire et de la Zone à Eugubina du Danien inférieur. Les membres D, C, B, A de la formation Cobán et la formation Angostura représentent des cycles transgressifs–régressifs de deuxième ordre. Sur cette marge passive du Petén, les dépôts correspondent à des environnements variés comme des terres émergées soumises à une altération karstique et à des dépôts fluviatiles, des salinas, des plates-formes carbonatées marines, des shelf externes et des bassins intra plate-forme. La sédimentation a été, ici, contrôlée par une forte vitesse de subsidence, les variations du niveau marin et des soulèvements tectoniques.  相似文献