The role of the Antofagasta–Calama Lineament in ore deposit deformation in the Andes of northern Chile

During the Late Jurassic–Early Oligocene interval, widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central Andes, giving rise to four NS-trending metallogenic belts of eastward-decreasing age: Late Jurassic, Early Cretaceous, Late Paleocene–Early Eocene, and Late Eocene–Early Oligocene. The Antofagasta–Calama Lineament (ACL) consists of an important dextral strike-slip NE-trending fault system. Deformation along the ACL system is evidenced by a right-lateral displacement of the Late Paleocene–Early Eocene metallogenic belts. Furthermore, clockwise rotation of the Early Cretaceous Mantos Blancos copper deposit and the Late Paleocene Lomas Bayas porphyry copper occurred. In the Late Eocene–Early Oligocene metallogenic belt, a sigmoidal deflection and a clockwise rotation is observed in the ACL. The ACL is thought to have controlled the emplacement of Early Oligocene porphyry copper deposits (34–37 Ma; Toki, Genoveva, Quetena, and Opache), whereas it deflected the Late Eocene porphyry copper belt (41–44 Ma; Esperanza, Telégrafo, Centinela, and Polo Sur ore deposits). These observations suggest that right-lateral displacement of the ACL was active during the Early Oligocene. We propose that the described structural features need to be considered in future exploration programs within this extensively gravel-covered region of northern Chile.     

Low-latitude “dusty events” vs. high-latitude “icy Heinrich events”

It has been proposed that tropical events could have participated in the triggering of the classic, high-latitude, iceberg-discharge Heinrich events (HE). We explore low-latitude Heinrich events equivalents at high resolution, in a piston core recovered from the tropical north-western African margin. They are characterized by an increase of total dust, lacustrine diatoms and fibrous lacustrine clay minerals. Thus, low-latitude events clearly reflect severe aridity events that occurred over Africa at the Saharan latitudes, probably induced by southward shifts of the Inter Tropical Convergence Zone. At a first approximation, it seems that there is more likely synchronicity between the high-latitude Heinrich Events (HEs) and low-latitude events (LLE), rather than asynchronous behaviours.     

Belowground decomposition of mangrove roots in Florida coastal everglades

Mangrove root decomposition rates were measured by distributing mesh bags containing fine root material across six sites with different soil fertility and hydroperiod to compare ambient differences to substrate quality. Roots from a site with lower soil phosphorus concentration were used as a reference and compared to ambient roots at five other sites with increased phosphorus concentration. Four mesh bags of each root type (ambient versus reference), separated into four 10-cm replicate intervals, were buried up to 42 cm depth at each site and incubated for 250 d (initiation in May 2004). Mass loss of ambient mangrove roots was significant at all study sites and ranged from 17% to 54%; there was no significant difference with depth at any one site. Reference decomposition constants (−k) ranged from 0.0012 to 0.0018 d⁻¹ among Taylor Slough sites compared to 0.0023–0.0028 d⁻¹ among Shark River sites, indicating slower decomposition rates associated with lower soil phosphorous and longer flood duration. Reference roots had similar decomposition rates as ambient roots in four of the six sites, and there were no significant correlations between indices of root substrate quality and decomposition rates. Among these distinct landscape gradients of south Florida mangroves, soil environmental conditions have a greater effect on belowground root decomposition than root substrate quality.     

A regional strategy for geothermal exploration with emphasis on gravity and magnetotellurics

As part of the resource evaluation and exploration program conducted by Los Alamos Scientific Laboratory for the national Hot Dry Rock (HDR) Geothermal Program, a regional magnetotelluric (MT) survey of New Mexico and Arizona is being performed. The MT lines are being located in areas where the results of analysis of residual gravity anomaly maps of Arizona and New Mexico, integrated with other geologic and geophysical studies indicate the greatest potential for HDR resources.The residual gravity anomalies are derived by applying the concept of predicting gravity anomalies from topography. This can be accomplished by employing reductions similar to those used in some isostatic investigations, in which a regional topographic surface is used as the Bouguer reduction datum. The datum is derived by comparison of various harmonics of Bouguer anomalies and elevations of stations. Topography can be used to predict Bouguer anomalies because of isostatic compensation; the resultant anomalies can be considered high frequency residual anomalies or isostatic anomalies corrected for regional compensation. Such maps have been produced for Arizona, New Mexico, west Texas, and Chihuahua, Mexico.The main objective of the MT project is to produce a regional geoelectric contour map of the pervasive deep electrical conductor within the crust and/or upper mantle beneath the Colorado Plateau and the adjacent Basin and Range Province and Rio Grande Rift. The MT survey consists of 200 sites along several long profiles with site spacing of 15–20 km. Pre-existing available MT data are being integrated with the new data. After the data are processed, a one-dimensional inversion is applied to the sounding curve and used as a starting point for 2-D modeling. Such a project and ultimate map will be of major value in studying the regional geophysics and tectonics of the southwest United States as they now apply to HDR resources in particular and geothermal resources in general.Electrical conductivity anomalies of large areal extent are of particular interest in geothermal exploration. Correlation analysis of large conductive anomalies with other geophysical, geological, and geotectonic data is being performed. Preliminary analysis of the data has suggested several major regions of anomalously shallow high electrical conductivity. Among these is the Aquarius area of northwest Arizona which is the site of a longwavelength residual anomaly low, which when modeled and correlated with other geophysical data can be shown to be possibly related to low density and high temperature in the crust at depths of 20 km or less. Preliminary analysis of MT data indicates the possible existence of a mid-crustal high electrical conductivity anomaly in this same region.     

Radial velocities in the open cluster IC 2391

We have determined radial velocities for 31 stars in the field of the open cluster IC 2391, and derived the percentage of probable radial-velocity variables. We improved the orbit of one previously known spectroscopic binary, and confirmed the existence of two double-line binaries. We discussed with such data the membership to the cluster, the average cluster radial velocity and compared the incidence of short-period binaries among the Main-Sequence members of IC 2391 with the incidence for other clusters with similar average axial rotation of its members.Member of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas de la República ArgentinaVisiting Astronomer, Cerro Tololo Inter-American Observatory, operated by AURA, Inc. under contract with the National Science Foundation.