Las Matras Block, Central Argentina (37°S-67°W): the Southernmost Cuyania Terrane and its Relationship with the Famatinian Orogeny

The Las Matras Block in Central Argentina constitutes the southernmost part of the Cuyania terrane, which was accreted to the southwestern margin of Gondwana during the Early to Mid Ordovician Famatinian orogeny. The Grenville-aged rocks of the Las Matras Block are represented by the tonalitic to trondhjemitic Las Matras pluton. A new U-Pb conventional zircon age of 1244±42 Ma confirms previous Sm-Nd and Rb-Sr isochron ages of this pluton. Mineral composition data are consistent with the tonalitic-trondhjemitic character of the pluton, and constrain its emplacement level to 1.9 to 2.6 kb. This shallow level of emplacement and the undeformed character of the pluton are distinctive features of this southernmost basement. A regional comparison indicates that the igneous-metamorphic evolution of the Grenville-aged basement rocks of the Cuyania terrane occurred over a period of more than 200 million years, with ages older than 1200 Ma up to those close to 1000 Ma. The shallowest crustal level is found in Las Matras, suggesting a southward shallowing of the exposed level of basement. The deformation and metamorphism associated with the collisional Famatinian orogeny affect both the Cuyania terrane and the adjacent western margin of Gondwana, and the Gondwana margin was also the locus of the related arc magmatism, but the compressive effects of the collision decrease in intensity toward the south. The Famatinian metamorphism and magmatism continue even further south into the Patagonia region, but the southern continuity of the Cuyania terrane into this region remains uncertain.     

The Local Tsunami Alert System [``SLAT']: A Computational Tool for the Integral Management of a Tsunami Emergency

During a tsunami emergency numerous local authorities responsible for the security oflocal persons and businesses which function in the coastal zone are required to makecritical decisions within a very short time frame. It is known that the consequencesof the situation will depend on the quality and quantity of decisions which they makeor allow to occur at the critical time. Based on this concept, the Local System of Tsunami Alert (SLAT; Spanish) was developed. This is a computational tool designed for the automatic implementation of integral management for an emergency of this type.The System is able to immediately evaluate possible risks and determine thetype of alert represented (Red, Yellow, Green, Blue, and Celeste) if relevantdata such as coordinates of the epicenter, magnitude, date, and origin of theearthquake (>6.5° on the Richter scale) threatening the Pacific areknown. Other relevant data include location of the coastal or marine epicentreand the superficial hypocenter. The relevant data may now be obtained fromthe internet from international seismological services, and fed into the programto give the most probable time for arrival of the first wave train at a given pointof interest, whether this be a port, bathing area, generating plant, or coastal city.The program also gives the time required for the first wave train to arrive at agiven coast, and displays a menu of previously planned actions to be taken accordingto the type of alert. It also permits dissemination of a bulletin with critical data and action plans by fax or e-mail to scattered users as well as for storage on the computer disc. The system is designed in a way that the user always confirms with authorities that anevent has in fact been generated. On a local scale, the user is required to prepare an operative emergency plan of action to be followed by his company, community, or municipality, to be followed for each type of alert.The System permits carrying out test exercises with the users, as well as simulationof past events. Knowledge concerning past events permits understanding correctdesign of emergency action plans for mitigation of potential present and future events.This software is specifically designed for the Pacific Coast of South America, and isprepared in Spanish, with the intention of improving responses of inhabitants of coastalareas to the potential threat from tsunamis.     

Porphyry copper and tin-bearing porphyries a discussion of genetic models

The paper briefly describes the characteristics of the Chilean porphyry copper deposits, emphasizing the volcanic characteristics observed in the youngest ore bodies. Mention is made of the polymetallic ore bodies that are associated with rhyolitic porphyries intruding Jurassic sedimentary formations in the north of Chile, and the similarities and differences between the Chilean porphyry coppers and the Bolivian tin-bearing porphyries are pointed out.The models proposed by Sillitoe (1972), Brousse and Oyarzún (1971), and Mitchell and Garson (1972), are discussed and a new model is proposed agreeing with that of Mitchell and Garson for the genesis of the tin-bearing porphyries (the transportation of Sn as volatile halogenide by F liberated in the Benioff zone), but suggesting different generating mechanism for the porphyry coppers and polymetallic deposits related with porphyries. This mechanism, as a part of the global tectonic model, is based on the separation at depth of hydrogen sulphide from pyrite and water introduced with the upper layers of the lithospheric plate. The ascending migration of H₂S to high levels in the crust would be responsible for the porphyry copper mineralization by segregating sulphides of Fe, Cu, Mo and other sulphophile metals contained in the calc-alkaline magmas, brines, or sedimentary-volcanic formations intruded by the porphyries. The excess of H₂S would give rise to the formation of sulphur deposits normally present in the volcanic belt situated along the same line but at a higher level than those of the emplacement of porphyry coppers.The generation of copper and tin-bearing porphyries would be a consequence of the upward migration of volatile substances from different depths in the subduction zone, which explain its different emplacement with regards to the continental margins.     

Sulphidizing reactions in the flotation of oxidized copper minerals,I. Chemical factors in the sulphidization of copper oxide

The rate and extent of the heterogeneous reaction that takes place between dissolved sodium sulphide and synthetic tenorite is studied for a wide range of sodium sulphide to copper oxide ratios. Besides the sulphidization with the formation of a copper-sulphide layer, a substantial oxidation of sulphide ions takes place at the surface of the solid. The extent of both types of reactions is quantitized by combining specific analytical methods.The results are discussed in terms of possible mechanisms and of their implications in the sulphidization process applied in the flotation of oxidized copper ores.     

Sulphidizing reactions in the flotation of oxidized copper minerals,II. Role of the adsorption and oxidation of sodium sulphide in the flotation of chrysocolla and malachite

The rate of consumption of sulphide in the sulphidizing reactions of malachite and chrysocolla has been measured. The oxidation of sulphide ions at the surface of sulphidized chrysocolla was shown to take place. The influence of thiosulphate anions on the xanthate flotation of sulphidized malachite and chrysocolla was investigated and it was shown to depress the flotation of chrysocolla strongly.The result suggest, that the presence of thiosulphate as a product of simultaneous oxidation can be one of the reasons for the more difficult flotation of sulphidized chrysocolla.     

Stiff-matter solitons in cosmology

We study exact solutions of the Einstein field equations of the cylindrical-symmetric Einstein-Rosen type with stiff matter (p=) as a source with development and collisions of solitons associated with the metric and the fluid.Supported by a CONICET fellowship.     

Estimation or simulation? That is the question

The issue of smoothing in kriging has been addressed either by estimation or simulation. The solution via estimation calls for postprocessing kriging estimates in order to correct the smoothing effect. Stochastic simulation provides equiprobable images presenting no smoothing and reproducing the covariance model. Consequently, these images reproduce both the sample histogram and the sample semivariogram. However, there is still a problem, which is the lack of local accuracy of simulated images. In this paper, a postprocessing algorithm for correcting the smoothing effect of ordinary kriging estimates is compared with sequential Gaussian simulation realizations. Based on samples drawn from exhaustive data sets, the postprocessing algorithm is shown to be superior to any individual simulation realization yet, at the expense of providing one deterministic estimate of the random function.     

Continuation of normal doubly symmetric orbits in conservative reversible systems

In this paper we introduce the concept of a quasi-submersive mapping between two finite-dimensional spaces, we obtain the main properties of such mappings, and we introduce “normality conditions” under which a particular class of so-called “constrained mappings” are quasi-submersive at their zeros. Our main application is concerned with the continuation properties of normal doubly symmetric orbits in time-reversible systems with one or more first integrals. As examples we study the continuation of the figure-eight and the supereight choreographies in the N-body problem.