Isotopic studies of the Guerrero composite terrane, west-central Mexico: Implications for provenance of crustal rocks and genesis of ore metals

A variety of world-class mineral deposits occur in Mesozoic and Tertiary rocks of the Guerrero terrane. New Pb isotope analyses of various crustal units and ores from distinct subterranes of the Guerrero terrane are presented to trace metal sources in these deposits and infer source reservoirs. New Sr and Nd isotope results are provided to gain insight into the provenance of the crustal rocks from the Guerrero terrane. Triassic schist samples from the Arteaga Complex and Triassic-Jurassic phyllite and slate samples from the Tejupilco metamorphic suite contain radiogenic Pb (206Pb/204Pb = 18.701–19.256) relative to bulk earth models. Cretaceous sedimentary rocks of the Zihuatanejo Sequence are more radiogenic (206Pb/204Pb = 18.763–19.437) than samples from the Huetamo Sequence (206Pb/204Pb = 18.630–18.998). Tertiary intrusive rocks from La Verde, Inguaran, La Esmeralda, and El Malacate plot to the right of the average Pb crust evolution curve of Stacey and Kramers (206Pb/204Pb = 18.705–19.033). Ores from the La Verde and La Esmeralda porphyry copper deposits yield isotopic ratios (206Pb/204Pb = 18.678–18.723) that are generally less radiogenic than the host igneous rocks, but plot within the field defined by the sedimentary rocks from the Huetamo Sequence. Tertiary intrusive rocks from the Zimapan and La Negra districts in the Sierra Madre terrane plot above and to the right of the Stacey-Kramers reference line (206Pb/204Pb = 18.804–18.972). Lead isotope ratios of ore minerals from the Zimapan and La Negra skarn mines ( 206Pb/204Pb = 18.775–18.975) resemble those of the associated igneous rocks, implying a magmatic Pb input in the skarn deposits. New Sr and Nd isotope data on metamorphic rocks (87Sr/ 86Sr = 0.707757–0.726494 and 143Nd/144 Nd = 0.512109–0.512653) suggest that the basement of the Guerrero terrane originated from sources that had been derived from an old cratonic area. The narrow ranges and generally low 87Sr/86Sr ratios (0.704860–0.705755) and 143Nd/144Nd values (0.512765–0.512772) above that of bulk earth for igneous rocks from Inguaran, El Malacate, and La Esmeralda suggest a relatively low degree of crustal contamination. However, the isotopic values for the La Verde site (87Sr/86Sr = 0.708784 and 143Nd/144Nd = 0.512640) may indicate the involvement of a more evolved crustal component.

Depth-related variations of trace metal abundances in south Florida sediments

Variations in trace element abundances with depth in soils and sediments may be due to natural processes or reflect anthropogenic influences. The depth related variations of five major elements (Fe, Si, Al, Ca and Mg), seventeen trace elements (Mn, Cr, Ti, P, Ni, Ba, Sc, Sr, Sb, Zn, Pb, Cd, Co, V, Be, Cu and Y) and volatile loss patterns were examined for sediment cores from five sites in South Florida (Lake Okeechobee, SFWMD Water Conservation area 3B, F.I.U., the Everglades and Chekika State Recreation Area). Principal component analysis of the chemical data combined with microscopic examination of the soils reveal that depth-related variations can be explained by varying proportions of three natural soil constituents and one anthropogenic component. The results can be used as a geochemical baseline for human influence on South Florida soils.

Study of the physical properties of metals and oxides at extreme pressure and temperature conditions

The high-pressure and temperature investigations on transition metals, metal doped-oxide system, nanocrystalline materials are presented in this dissertation. The metal-doped oxide systems are technologically important because of their applications, e.g. LSC, opto electronic applications, luminescence from lasers, etc., and from the earth sciences point of view, e.g. the study of trace elements in the MgO-SiO2 system, which accounts for 50% of the Earth's chondritic model. We have carried out thorough investigations on Cr2O3 and on chromium bearing oxides at high PT-conditions using in situ X-ray diffractometry and florescence spectroscopy techniques. Having obtained exciting results, an attempt to focus on the mechanism of the coordination of transition metals in oxides has been made. Additionally, the florescence from the metals in host oxides was found to be helpful to obtain information on structural variations like changes in the coordination of the doped element, formation of new phases, the diffusion processes. The possible reactions taking place at extreme conditions in the MgO-SiO2 system has been observed using florescence as markers. A new heating assemblage has been designed and fabricated for a precise determination of temperature at high pressures. An equation combining pressure shifts of ruby wavelength and temperature has been proposed. We observed that the compressibility of nanocrystalline material (MgO and Ni) is independent of crystallite size. A reduction in the transition pressure of nanocrystalline ceria at high-pressure has been observed as compare to the corresponding bulk material. ^

Trace elemental analysis of glass by inductively coupled plasma-mass spectrometry (ICP-MS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)

This work evaluated the capabilities of inductively coupled plasma mass spectrometry (ICP-MS) for elemental analysis of trace evidence. A method was developed and validated for the analysis of glass by ICP-MS. A database of ∼700 glass samples was analyzed for elemental composition by external calibration with internal standardization (EC) ICP-MS and refractive index (RI). Additional methods were developed during the course of this work using two well-known techniques, isotope dilution (ID) and laser ablation (LA). These methods were then applied to analyze subsets of this database. ICP-MS data from 161 containers, 45 headlamps, and 458 float glasses (among them at least 143 vehicle windows) are presented and summarized. Data from the analysis of ∼190 glass samples collected from a single glass manufacturing facility over a period of 53 months at different intervals, including 97 samples collected in a 24 hour period are presented. Data from the analysis of 125 glass samples representing 36 manufacturing plants in the U.S. are also presented. ^ The three methods used, ICP-MS, ID-ICP-MS and LA-ICP-MS, were shown to be excellent methods for distinguishing between different glass samples. The database provided information about the variability of refractive index and elemental composition in glasses from diverse population types. Using the proposed methods, the database supports the hypothesis that different glass samples have different elemental profiles and a comparison between fragments from the same source results in indistinguishable profiles. ^

Determining Spatial and Temporal Inputs of Freshwater, Including Submarine Groundwater Discharge, to a Subtropical Estuary Using Geochemical Tracers, Biscayne Bay, South Florida

Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ 18O = −2.66‰, δD −7.60‰) similar to rainfall (δ 18O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ 18O = −0.46‰, δD  = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.

Effects of increased urban and agricultural land use on the anthropogenic loading to southwest Florida estuaries

South Florida has been subject to considerable changes during the last 100 years. This study provides a detailed survey of the presence, concentration levels, and spatial distribution of organic and inorganic contaminants in sediment samples collected within the coastal environments of southwest Florida. It evaluates the potential contributions and effects of the urban and agricultural development to the pollution loading of the estuarine sediments. And it also provides information regarding chronology of contamination at impacted sites. Copper was found to be the most critical contaminant among the trace metals. 12% of the samples exceeded the Threshold Effects Level (TEL). None of organic contaminants measured exceeded the Probable Effects Level (PEL) criteria. Total PAHs concentrations exceeded the TEL criteria in 6% of the samples. The evaluation for the chronology of contamination showed a significant increase with time of every contaminant analyzed. Fluorescence spectroscopy proves to be a good method for fast screening PAHs.