Metal concentrations in water and sediments from tourist beaches of Acapulco, Mexico

A survey on the metal concentrations (As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) in beach water and sediments is reported from the tourist destination of Acapulco city on the Pacific coast of Mexico. The concentration of dissolved trace metals (DTMs) in beach water and acid leachable trace metals (ALTMs) in sediments indicated that they are anthropogenic in nature due to the increased tourist activities in the crowded beach locations. The statistical analysis indicates Fe and Mn play a major role as metal scavengers in both the medium (water and sediment) and the higher value of other metals is site specific in the study area, indicating that they are transported from the local area. Comparison results suggest that the beach water quality has deteriorated more than the sediments and special care needs to be taken to restore the beach quality.     

Site effect study in central Mexico using H/V and SSR techniques: Independence of seismic site effects on source characteristics

We study the influence of different source characteristics (depth, distance, type and azimuth) on the site effect in Acapulco and the Valley of Mexico. Site amplification was estimated by means of spectral ratios (both horizontal-to-vertical spectral ratio and standard spectral ratio techniques were applied) from earthquake recordings at soft and hard sites. In Acapulco, 125 Mexican earthquakes covering a hypocentral range of 7–290 km and a depth range (H) of 3–61 km were analyzed in three different groups of hypocentral distances. In the Valley of Mexico, we estimate site effect at five locations using recordings from shallow-coastal interplate (200?Δ?570 km; H?35 km) and normal-faulting, intermediate-depth inslab (132?Δ?738 km; 32?H?178 km) earthquakes, as well as from teleseismic events. Our results seem to point to negligible dependence of site effects on the source location and type.     

The thermal history of the Acapulco meteorite and its parent body deduced from U/Pb systematics in mineral separates and bulk rock fragments

U/Pb systematics of the Acapulco meteorite have been determined on phosphate and feldspar separates and on grain size fractions of bulk material. The latter show an enrichment of U and Th with respect to CI chondrites and a low (∼1) Th/U ratio. This is consistent with the model that the majority of U and Th was added early by a low temperature melt to the Acapulco precursor. The feldspar exhibits a Pb isotope composition that is close to the primordial Pb composition. Mineral separates and bulk fractions define a ²⁰⁷Pb/²⁰⁶Pb isochron. The age corresponds to 4555.9 ± 0.6 Ma. This age anchors the thermal evolution of the Acapulco parent body into an absolute time scale. Evaluation of the Hf/W and U/Pb records with the cooling rates deduced from mineralogical investigations confirms the idea that the Acapulco parent body was fragmented during its cooling. The U/Pb system precisely dates this break-up at 4556 ± 1 Ma.