<p> The knowledge of transport properties such as atomic diffusion, viscosity and electrical conductivity in the lower mantle is critical for our understanding of the evolution and dynamics of the entire Earth. Those transport properties are largely controlled by point defects, but the relative importance of various species of point defect was poorly constrained in the lower mantle. Laboratory experiments on point defect concentrations in ferropericlase ((Mg,Fe)O) demonstrate that Fe³⁺ and metal vacancies are the dominant defect pairs in ferropericlase at the top of the lower mantle even at water-saturated conditions. Experiments on Fe-Mg interdiffusion in ferropericlase indicate that the influence of Fe³⁺ in cation diffusion likely dominates at temperatures expected for the lower mantle, while the influence of both Fe³⁺ and I¹⁺ is important at lower temperature environments such as near the subduction zone.</p><p> Ferropericlase inclusions encapsulated in diamonds derived from the lower mantle are unique proxies for the chemical environment in the lower mantle. Redox conditions inferred from Fe³⁺ concentration in ferropericlase inclusions indicate that host diamonds were precipitated from carbonatite melts near the top of the lower mantle at significantly oxidized conditions compared with the metal-saturated lower mantle.</p><p> A new method was presented to control water fugacity as an independent variable in solid-state high pressure apparatus. Results indicate that water is predominantly incorporated in olivine via two hydrogen atoms substituted into a Mg-site vacancy under the condition we explored.</p><p> Iron-rich metallic liquid interacts with silicate/oxides at the core-mantle boundary, but mechanisms of interaction between the core and the mantle have been poorly known. Experiments show that the bulk disequilibrium between solid ferropericlase and the metallic liquid causes migration of metallic liquid in ferropericlase crystals, which provides an efficient mechanism of chemical transport compared with conventional Fe-Mg interdiffusion. Iron entrainment from the core by trans-crystalline melt migration gives a plausible explanation of several geophysical and geochemical observations including the presence of low-velocity and high-density regions near the bottom of the mantle, the observed length of the day variation in the decadal time scale and isotope signatures of the core observed in some of the hot spot volcanisms.</p>

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Raman spectroscopy has recently become a common laboratory analytical technique due to the introduction of technology such as lasers, charge-coupled devices, and holographic filters. The information given by Raman spectroscopy is complimentary to infrared absorption spectroscopy, but sample preparation is often much easier, if any is needed at all. Because of this, the field of Raman spectroscopy has expanded in many areas, including mineralogy. The ongoing development of a database of Raman spectra of minerals enables facile identification of many minerals. Pyroxenes are a class of minerals that make up approximately 25% of the Earth's upper mantle, to a depth of 400 km. A recently discovered phase change in pyroxenes, accompanied by a volume change, is now accepted as the origin of some deep-focus earthquakes, which are clustered at a depth of approximately 225 km. However, the bonding change that accompanies this phase change is not completely understood. Raman spectroscopy was utilized to follow the phase change of spodumene. Polarized spectra of an oriented single crystal of spodumene were utilized to assign Raman modes that were previously ambiguously assigned in the pyroxenes. The pressure-induced phase transition was also followed in LiFeSi2O6 utilizing both Raman spectroscopy and single crystal x-ray diffraction. Similarities were noted between the Raman spectra of spodumene and LiFeSi2O6, enabling the assignment of Raman bands in the second material studied. Finally, a third pyroxene, LiCrSi2O6, was studied with Raman spectroscopy while the sample was subjected to pressure. This material changed color with application of pressure and the color change was quantified with visible absorption spectroscopy. Though no phase change occurred in this material, changes in the spectra did occur at high pressures. These high-pressure changes in the Raman spectra were observed in all three crystals studied and could provide a better understanding of the pyroxenes at high pressures. Additionally, none of the three pyroxenes in P21/c phase displayed a doublet of peaks in the spectroscopic region that had been previously utilized as a benchmark for the identification of the P21/c phase of the pyroxenes until higher pressures. Spodumene did not display a doublet at any pressure studied.

The Concepcion del Oro, Providencia, Noche Buena and Santa Rosa igneous centers are located in the central sector of the Sierra Madre Oriental, to the southwest from the city of Saltillo, in the state of Zacatecas, Mexico. Their associated mineral deposits constitute a coherent igneous and metallogenic area. It is characterized by a sequence of magmatic bodies intruding a predominantly carbonate sedimentary sequence of Mesozoic age. Field reconnaissance, whole rock major, trace and isotope geochemistry, and mineral chemistry define three magmatic pulses. The first pulse is characterized by a intermediate to mafic, relatively oxidized magma with low contents in halogens that becomes more contaminated with crustal material, enriched in fluorine relative to chlorine, and reduced as it evolves. The second pulse is at first more oxidized than the previous, but, like its later phases, it shows also significant crustal contamination and relatively high halogen contents. It becomes significantly more reduced, its overall halogen contents decreases and becomes strongly dominated by fluorine towards the late stages. A late magmatic pulse consisting of mafic dikes with major and trace element characteristics suggestive of a crustal, rather than mantle source, does not appear to be related to significant alteration and mineralization in the area. Trace element and radiogenic isotope geochemical data suggest similar sources for the different intrusive phases in the area with a significant component from either a mafic crust and/or the mantle. Amphibole geobarometry suggests final emplacement of the different intrusives at less than or around 1 kbar pressure, in agreement with the regionalGeology. Values obtained from relict inclusions, show a cluster of values between 3 and 4 kbars that suggest possible mid-crustal residence for the magmas in the area. Halogen contents and oxidation state of the different intrusives appear to describe similar evolutionary trends. Available field evidence, geochemical data and documented metal suites associated with the intrusives, indicate that mineralization is dominated by copper in the early phases, and lead-zinc-silver in the later. While the lead-zinc-silver mineralization has many parallels to other mineralized systems in the Sierra Madre Oriental, the significant copper mineralization is uncommon for the region.

The Acatlan Complex of southern Mexico is one of two high-pressure metamorphic belts reported in Mexico. This complex contains an extensive sequence of metabasic, pelitic, granitic, mafic, ultramafic and carbonate rocks affected by an eclogite-facies metamorphic event of apparently Devonian age and subsequent overprinting of amphibolite and greenschist metamorphism. The purpose of this study was to characterize the metabasic eclogites from the Paleozoic Acatlan Complex, southern Mexico in terms of their thermobarometric conditions of formation as well as to identify the nature of the magmatic precursors. The approach was to place constraints on the petrogenetic history of the eclogites. Microtextures indicate that equilibrium existed among mineral phases of garnet, sodic pyroxene and sodic-calcic amphibole in the eclogites. This indicates that a complete equilibration to a sensu-stricto named eclogite did not occur and eclogitic assemblages were only locally developed. According to electron microprobe analyses conducted in high-pressure mineral assemblages from two-type areas, the petrogenetic evolution of these rocks is bracketed between a maximum P-T conditions of 565 ± 37°C and 11-15 kbar for basic metaeclogites from the areas of Izucar de Matamoros and Piaxtla-Tecomatlan. Minimum P-T conditions of 343°C, 3.5 kbar were constrained for greenschist metamorphism. The obtained P-T path for the polymetamorphic rocks from the Acatlan Complex has similarities with those of metamorphic rocks from New Caledonia which has a less complicated retrogressional history than alpine eclogites. Analyses of major, trace and REE abundances were determined for representative samples. The whole-rock REE-patterns suggest that there was no significant REE mobility of the protolith system. Consistent geochemistry allows identification of the protoliths as Mid Ocean Ridge Basalts (MORB), Oceanic Island Basalts (OIB) and Island Arc Volcanism (IAV). Geochemical evidence also indicates that the Acatlan Complex eclogites are tectonically emplaced slices of oceanic material suggesting a more complex tectonic regime. The data from this work suggest that the basic metaeclogites could be the product of two different convergent tectonic scenarios: (a) a collision of a small block(s) such as an island arc or a microcontinent or (b) lateral or non-frontal collision of a continent.

The effects of various application rates of gypsum (Aqua-cal = finely ground gypsum), langbeinite (K₂SO₄.2MgSO₄), and CaCl₂ (anhydrous) on exchangeable Na removal and saturated hydraulic conductivity of a sodic soil were investigated under laboratory batch studies and laboratory column leaching studies. The research involved four phases of studies. Characterization of the soil and irrigation water indicated that the soil sample is sodic (ESP=35.3), ECₑ = 3.36 dS/m), and the irrigation water is moderately saline (EC = 2.2 dS/m). The laboratory batch studies showed that CaCl₂ and langbeinite treatments were more efficient in the displacement of Na than gypsum which increased with increasing application rate. In contrast, with gypsum, Na displacement increased to a maximum at an application rate of 7 tons/ha; then, no further increase in displacement was observed above that level. In the column leaching studies, applied amendments at equivalent rates of 7 tons/ha each and leaching with 5 pore volumes of irrigation water resulted in a total Na displacement of 60%, 80%, and 84% for gypsum, langbeinite, and CaCl₂, respectively. Moreover, the SAR of the soil was reduced significantly in the above treatments from 34.5 in the beginning of leaching to 6.80 for gypsum (G7), from 41.8 to 5.60 for langbeinite (L₇), and from 32.6 to 2.5 for CaCl₂(7). When amendments were applied at higher rates (G7 tons/ha gypsum and 13 tons/ha of each of CaCl₂ and langbeinite), the % total Na displaced was 60%, 100%, and 94% for gypsum, langbeinite, and CaCl₂, respectively. The corresponding SAR values at the end of reclamation were 6.80, 4.50, and 5.50 for gypsum, langbeinite, and CaCl₂, respectively. The combination treatments significantly improved the reclamation at 0.05 level as compared to the G7 treatment alone and saved more leaching water and displaced higher exchangeable Na as compared to the gypsum treatment (G7) alone. Saturated hydraulic conductivity (Ks) studies indicated that Ks was increased significantly when the amendments were applied at equivalent weights (7 tons/ha) and at higher application rates as compared to the control. The Ks of the gypsum treated soil (G7) was significantly higher than Ks of langbeinite and CaCl₂ treated soil at both equivalent rates and when applied at higher rates L13 and CaCl₂(13).

The Santa Rosalia basin is a NW-SE elongated and fault limited basin, which evolved from Upper Miocene to Pleistocene time. The transtensional Upper Miocene Santa Rosalia basin located in central Baja California, consists of almost 500 m of nonmarine to marine sedimentary rocks, with tuffaceous beds interbedded in its lower part. The sedimentary rocks consist of the Boleo Formation, which is 200 to 300 m thick and is dominated in its lower part by marine transgressive sediments and evaporite bodies followed by 170 to 300 m of clastic coarsening upward fan-delta marine-nonmarine sequence. The clastic sequence presents at least three well organized upward coarsing cycles (90-100 m thick each one). Each cycle represents a prograding fan-delta formed probably as a consequence of large and repeated vertical movements of the basin floor with respect to source areas, during the early stage of the opening of Gulf of California. Coeval with the deposition of the clastic sequence of the Boleo Formation there was extensive ash volcanism which originated from a volcanic center north of the basin. Copper-cobalt-zinc stratiform ore bodies (mantos) are hosted within the tuffaceous fine facies in the bottom of each sedimentary cycle. At least five mantos were recognized named as 4, 3, 3(1), 2 and 1. Ore minerals and their textures, the geometry of the mantos and elemental zonation, suggest a diagenetic origin for the different ore bodies. The lowest manto, 4, in the district seems to have a geological correspondence with the Lucifer manganese deposit north of the district associated with hot spring mineralization. Manto 3, 3(1), 2 and others all of which occur at a higher stratigraphic level than manto 4, are associated with mineralized fluids sourced from NW-SE faults. Fluids moving through the conduits crossed an oxidation-reduction boundary with the consequent precipitation of sulfide under reducing conditions. Sulfur and carbon-oxygen isotopes studies support anoxic conditions and a bacteriological origin for the sulfur and a mixture of seawater and freshwater during the formation of the mantos. Cu/Co, Cu/Zn and Co/Zn ratios and Cu-Co and Zn absolute values in the mantos support a horizontal and vertical zoning produced by low temperature up-ward moving solutions. The spatial and temporal correlation of the Boleo deposit with the opening of the Gulf of California indicate that the rifting setting might be the source of the metals and the same time might have induced the migration of the ore fluids.

Pyrrhotite and pyrite commonly contain minor quantities of cobalt, nickel, arsenic and other trace elements, which reflect major effects of source lithology and fluid chemistry, and subordinate effects relating to local processes. Electron probe micro-analyses (EPMA) of silicates from a suite of fifteen metasomatic Fe-oxide and affiliated ore samples show enrichments of chlorine in biopyriboles associated with Co-bearing iron sulfides and arsenides. Biotite from several localities contains from 1.5 to over 5.5 wt.% Cl. Amphiboles from several localities are also Cl-enriched, with up to 2.7 wt.% Cl. Amphibole from the Osborne Au-Cu deposit in Queensland also contains up to 1.5 wt.% scandium. Otherwise, mild enrichments of both scandium and vanadium are widespread in the silicates from many of these samples, particularly in epidote (up to 550 ppm Sc and up to 1860 ppm V), amphibole (to 260 ppm Sc) and diopside (to 0.57 wt.% V from one locality). A more extensive study was undertaken to determine the trace element distribution in iron sulfides. Over 1100 EPMA and 150 SIMS analyses of pyrite, pyrrhotite, and other sulfides were collected, representing over 100 localities and a dozen major ore-forming environments. These results were combined with data from the literature to assess overall Co, Ni, As, Se, Pd and Au distributions in iron sulfides across a range of geologic processes and lithologies. Iron sulfides from mafic-hosted magmatic oxide and sulfide systems are enriched in Co and Ni. In contrast to magmatic systems, iron sulfides from hydrothermal systems dominated by magmatic-derived aqueous fluids tend to be low in overall trace elements, regardless of the host lithology. Iron sulfides from hydrothermal systems dominated by external fluids show a wide variation in trace element content. In deposit types formed by dilute fluids (e.g. epithermal Au), Co and Ni tend to be low in pyrite whereas As may be quite high. Where high salinity fluids are implicated (as in metasomatic Fe-oxide systems), As and Ni contents in pyrite are variable but Co is typically enriched. Iron sulfide compositions also reflect source lithologies. Among diverse volcanogenic massive sulfide (VMS) deposits, pyrite from the more mafic Cyprus and Besshi types show notable enrichments of Co whereas Kuroko deposits rarely show any enrichment. Hence, source lithology and fluid chemistry play major roles in the minor element make-up of the iron sulfides across a range of deposit types. A parallel investigation was undertaken to assess the role of thermodynamics on the trace elements contents of iron sulfides. From a synthesis and evaluation of published experimental results, phase relationships in the Co-S-O-(Si) system were calculated and contrasted to the equivalent Fe system. The boundaries between the sulfides and oxides in the Co-S-O system are shifted to higher oxygen fugacities relative to the phase boundaries in the Fe-S-O system. In addition to the Fe-Co-S-O-(Si) system, phase relations in the Fe-(Ni,Co)-As-S system have been evaluated. Arsenic is implicated in a coupled substitution mechanism [CoAs]₁[FeS]₋₁ observed in some pyrite. The observed substitution behavior may be a reflection of the limiting assemblages present.