No description available.

No description available.

The aims of this work were to make a statistical study of variations in chemical composition within and between two major pelitic units in the Moine Series of Morar, western Inverness-shire, and to assess the metamorphic grade across the area by means of the calc-silicate bands found. Two of the major pelitic units, the Lochailort Pelitic Group and the Garnetiferous Pelite, were sampled to a rigid sampling plan which allowed analysis of variance techniques to be applied to the results, in a study of chemical variation within each of the units. Stepwise linear discriminant function analysis of the data was also undertaken, to provide functions which could be used to separate the two units on the basis of their chemical compositions. These derived functions could also be used to classify unknown samples and assign them to their correct stratigraphic position. Calc-silicate bands found as a minor rock type within the area may be used as precise indicators of metamorphic grade, since their chemistry determines their mineralogical response to metamorphism in a predictable fashion. Evidence from the less responsive pelites indicates that metamorphic grade rises generally eastwards across Morar, and a study of the calc-silicates, while confirming this, also provided evidence of a later, retrogressive event in the east of the area. In order to obtain large numbers of chemical analyses, rapid X-ray fluorescence analytical techniques were employed. For major element analysis a fusion method of sample preparation was adopted, and a new method of calibration was devised which allows a large range of rock compositions to be analysed using a single set of linear calibration regression equations.

The 500,000 km2 of Deccan basalts are situated in Maharastra, India. The basalt flows are predominantly tholeiitic and were penetrated by post-depositional fluids from which zeolites, and associated secondary minerals, crystallised. The frequency of occurrence and distribution of the zeolite species in an area 15,000 km2 has been determined and does not support the zonal scheme proposed by earlier workers. The zeolites occur in vesicles and veins which are often lined by celadonite. Heulandite, stilbite, mordenite and apophyllite are the most common secondary minerals with other species occurring at a frequency of less than one identification per locality studied. Evidence is discussed which shows that the observed zeolite distribution was produced by temperatures of 70°C at the top and 110°C at the base of the basalt pile. This temperature range is low in comparison with other zeolitised basalt domains and zeolite zones which are characteristic of similar regions elsewhere have not developed. Chemical analysis of the secondary minerals for major and trace elements indicates considerable variation in the principle cations within a species, and a marked absence of trace constituents, especially the rare earth elements. The trace element compositions of the secondary minerals cannot be used as petrogenetic indicators. The sequences of zeolite crystallisation have been determined and these together with the stability relationships are examined by thermodynamic analysis. Chemical and oxygen isotopic compositions of the basalt indicate that interaction occurred between the zeolitising fluid and the basalt and that this interaction was more intensive along fluid pathways e.g. at flow boundaries. Major elements, Ba, Rb and Sr were leached from the basalt in contrast to other trace elements including the rare earth elements. The leached elements were incorporated by the secondary minerals to varying degrees. Zeolitisation may therefore have considerable implications in petrogenetic studies of basaltic rocks.

The Troodos Massif exposes an intact section of harzburgitic mantle from its contact with crustal lithologies to a depth of approximately 3 km, where it is faulted out against a mass of heavily fractured and serpentinised peridotites: the serpentinite diapir. The harzburgites are host to several generations of pyroxenitic and dunitic intrusives, many of which have features suggestive of a reaction relationship with the enclosing harzburgites such as resorbed harzburgite xenoliths and marginal dunites. Mineral chemistry and whole-rock data suggest that the harzburgites in the Troodos sequence are residues from up to 30% fractional partial melting in the spinel stability field. The serpentinite diapir exposes iherzolitic lithologies which can be modelled by 10 to 15% fractional partial melting in the spinel stability field. In both cases, the starting composition for the melt modelling was a fertile MORB mantle source. Deviations from the compositions expected to result from simple fractional partial melting are found in several situations in the mantle section and suggest that melts/fluids interacted with the mantle during and after the partial melting event. Three main situations are identified: i) enrichments in mineral chemistry and whole-rock parameters in specific parts of the background harzburgite section; ii) mineral chemistry enrichments around pyroxenites and iii) the clinopyroxene crystals in the Troodos harzburgites which have LREE/HREE ratios higher than those that could be produced by simple fractional melting models. In the background harzburgites, mineral chemistries were enriched at the top of the sequence (Anomaly 1) and in a layer towards the base of the sequence (Anomaly 2). Pyroxenites also enriched their wallrocks and two trends were identified on the basis of spinel compositions. The Type I trend is of Cr-Fe-Ti enrichment and is similar to the mineral chemistry variations in the Anomaly 1 harzburgites. The melt involved is inferred to be tholeiitic. The Type II trend is of Mg-Al enrichment and is similar to the mineral chemistry variations in the Anomaly 2 harzburgites. The melt involved is inferred to be boninitic. The fact that the lower pillow lavas (LPL) have tholeiitic chemistries and the upper pillow lavas (UPL) boninitic chemistries suggests a link between the melt which crystallised the pyroxenites and the pillow lava sequence. The clinopyroxene trace element patterns from the background harzburgites suggest that the LREE, Nd, Sr and Zr are enriched in these minerals compared to the expected values for fractional melting. The enriched component was modelled from the clinopyroxene data and is similar in trace element pattern to the enriched component in the UPL. This suggests that the addition of the subduction component that has been proposed to explain the UPL chemistries was probably added to the mantle both during and after the melting event which produced the UPL.

No description available.

The Panamanian Isthmus presents an ideal opportunity to study arc magmatism, arc-hotspot interaction, and the effects of the South America-Panama collision. These effects include changing mantle wedge compositions and localized tectonic activities in western Panama. The Bocas del Toro sedimentary basin contains interbedded Miocene volcanic lava flows that range in age from 12 Ma to 8 Ma and sit behind the main body of the arc. The volcanic rocks of Bocas del Toro consist of trachy-basalt to trachy-andesite with SiO₂ content ranging from 45 wt. % to 64 wt. %. The MgO content is relatively low ranging from 0.35 wt. % to 3.43 wt. %, and with moderate depletion in FeOt (3.9 wt. %-8.0 wt. %) and CaO (2.8 wt. %-10 wt. %). However, K₂O content is extremely high (2.0 wt. %-5.2 wt. %), and these rocks are among the most alkaline in Panama. In terms of trace element geochemistry, the Bocas del Toro rocks exhibit a distinct, but decreased slab dehydration signature with a low Nb-Ta anomaly, enriched fluid-mobile LILEs and low Ti content. We have grouped Miocene and younger western Panama and eastern Costa Rica volcanic rocks into five groups: main arc tholeiite (~17-11 Ma) and calc-alkaline (~12-8 Ma), Bocas del Toro (~12-8 Ma), backarc alkaline (~8-2 Ma), and adakite ([less than]2 Ma) groups. In terms of trace element ratios, the Bocas del Toro rocks have relative low Ba/La, and have values that are higher, but approach the Cocos Ridge, that tracks of the Galapagos hot spot. The La/Yb and Th/Yb vs. Ta/Yb also show values that plot between the tholeiite and general calc-alkaline groups. Overall, trace element geochemistry indicates that an enriched OIB-like component mixed into the melts of the mantle wedge. With constraints from referenced Pb-Nd-Sr isotopes and the pattern of trace element geochemistry, the data range of the Bocas del Toro samples should be distributed close to the general calc-alkaline and backarc alkaline groups. According to the trace element geochemistry and isotope modeling, the percentage of enriched (OIB / Cocos track) geochemical component mixed into the melts of the mantle wedge, was quantified at 1-3%. Moreover, the pattern indicates that, as arc evolution continued, a progressively greater enriched geochemical components mixed into the wedge melts. Geochemical modeling allows estimates of the pressure, temperature etc., conditions under which magma formed. The MELTS software was used for major element modeling and show that the Bocas del Toro rocks underwent low-pressure (0.5-1.0 kbars) fractional crystallization, from 1200° C to 900° C with 50%-55% fractionation from a starting magma with ~11 wt. % MgO. In addition, trace element models and the ARC BASALT SIMULATOR 3.0 were used to simulate partial melting in the mantle wedge. These models indicate a component of enriched OIB-like mantle. The simulator also shows that the mantle wedge underwent 3.5%-6.0% of melting fraction under dry conditions at pressures of 1.8 Gpa to 1.9 Gpa (~60km) with temperatures of 1150-1350°C. In conclusion, we suggest that the geochemical variations of Bocas del Toro were caused by an influx of an OIB-like component into the mantle wedge by 12 Ma, and that possible effects from crustal extension reduced the overall subduction signature. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the Master of Science. / Fall Semester 2015. / November 10, 2015. / Bocas del Toro, Geochemical Modeling, Mantle Wedge, Panama, Subduction Zone / Includes bibliographical references. / David Farris, Professor Directing Thesis; Stephen Kish, Committee Member; Leroy Odom, Committee Member; William Parker, Committee Member.

The Dadeville Complex is a large klippe located in the Alabama Inner Piedmont of the southern Appalachian orogen lying immediately above rocks of the eastern Blue Ridge and Brevard Zone, in the core of the Tallassee synform. Structural field data outline the overall nature of the Tallassee synform in the Dadeville Complex. The Camp Hill 7.5' quadrangle contains the two major Dadeville Complex lithostratigraphic sequences, from southeast to northwest: the Ropes Creek Amphibolite, a bimodal metabasalt/metatuff, metadacite at the base, overlain by the Agricola Schist, a metaturbidite consisting of metapelitic, metagreywacke, and minor metabasalt. These sequences are intruded by felsic plutonic rocks, with the Chattasofka Creek Gneiss (granite) intrusive into the Agricola Schist, and the Camp Hill Granite (tonalite) intrusive into the Ropes Creek Amphibolite. Also intrusive into the Agricola Schist is a mafic complex consisting of the Doss Mountain suite and the Slaughters Gabbro suite. The Doss Mountain suite is characterized by having an abundance of interlayered metaorthopyroxenite and metanorite, and their metamorphosed equivalents. The Slaughters Gabbro suite consists of both olivine and non-olivine bearing gabbro. Within the mafic complex, there are various felsic dikes cutting through metagabbro and amphibolite, which suggest that intrusions of felsic and mafic rocks could have overlapped temporarily. Distinctive major and trace element geochemical signatures of the Chattasofka Creek Gneiss, Camp Hill Granite, Ropes Creek Amphibolite, Doss Mountain suite, and Slaughters Gabbro suite on tectonic discrimination diagrams all suggest formation within a volcanic arc environment. Preliminary U/Pb dating of detrital zircons in the Agricola Schist and igneous zircons in the Chattasofka Creek Gneiss yield Middle Ordovician ages, with the Agricola Schist also containing a subordinate fraction of Grenville ages. These relationships suggest that the Dadeville Complex arc resulted from subduction of Iapetus lithosphere beneath the distended Laurentian plate, and that the Dadeville Complex could potentially be a key fragment of the missing Taconic arc in the southern Appalachians. A supplementary file of a detailed geologic map of the Camp Hill 7.5' quadrangle is included with this document. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / October 19, 2015. / Appalachian Inner Piedmont, Dadeville Complex, Structure, Taconic Arc, Tectonics / Includes bibliographical references. / James F. Tull, Professor Directing Thesis; David W. Farris, Committee Member; Stephen A. Kish, Committee Member.

New and existing geochemical and Sr-isotopic data are used to characterize the composition and time-space distribution of Laramide and younger calc-alkaline to alkaline igneous rocks in central Colorado. The study is focussed on the $\sim$36.7-31 Ma Thirtynine Mile volcanic field, a suite of shoshonitic rocks that forms the bulk of the Central Colorado alkaline province. Various petrochemical characteristics suggest generation of Thirtynine Mile mafic rocks involved melting of LIL- and HFSE-enriched lithospheric mantle, perhaps phlogopite-bearing lherzolite. Subsequent crystal fractionation appears capable of explaining diversification of the suite. The Thirtynine Mile suite is LIL- and HFSE-enriched relative to time-contemporaneous high-K calc-alkaline rocks of the San Juan volcanic field, but shares some geochemical similarities with Laramide shoshonitic rocks of the northeastern Colorado mineral belt. General petrochemistry and spatial distribution of calc-alkaline and shoshonitic volcanic rocks in the region may be consistent with a subduction origin, but no unambiguous evidence is available to confirm this. / Geochemical and Sr-isotopic evidence confirms tuff occurrences in the southern Denver basin are Wall Mountain Tuff ($\sim$36.7 Ma). Previous suggestions that the Wall Mountain Tuff is closely related to the Mount Princeton batholith are not supported by new data, and the origin of the tuff remains unknown. Combined petrologic, geochemical, and Sr-isotopic data confirm that the $\sim$33.7 Ma Badger Creek Tuff is closely related to intracauldron tuff and a resurgent(?) pluton at the Mount Aetna volcanic center. Tuff at Buffalo Peaks is probably not related to Badger Creek Tuff. Geochemical and Sr-isotopic data suggest that andesitic tuff, lahar debris, and andesite flows at Buffalo Peaks are closely related, but the source of the volcanic suite remains unknown. Tuff in the Howard paleovalley and in the southeastern Thirtynine Mile volcanic field is probably Fish Canyon Tuff derived from the San Juan volcanic field. Sparse late-Tertiary rocks within the study area include shoshonite, trachyte, latite, and siliceous rhyolite and granite. / Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3211. / Major Professors: Stephen A. Kish; Paul C. Ragland. / Thesis (Ph.D.)--The Florida State University, 1994.

To better understand the hydrochemical interaction between groundwater and lakewater in a mantled karst setting, a comprehensive study was conducted to determine the processes that control the patterns and rates of chemical evolution of groundwater near Lake Barco, a sinkhole lake in northern Florida. Environmental isotopes, chlorofluorocarbons (CFCs), solute tracers, and geochemical modeling techniques were used to determine flow patterns, origin and age of waters, and to quantify the net sources and sinks of major ions, dissolved silica, and dissolved carbon species. The stable isotopic composition $(\delta\sp2$H and $\delta\sp{18}$O) of rainfall and groundwater upgradient from the lake (sampled near the water table and at several depths below the water table) plot together along the global meteoric water line. In contrast, the $\delta\sp2$H and $\delta\sp{18}$O composition of lakewater and groundwater downgradient from the lake were enriched relative to meteoric water as a result of evaporation and mixing. The relation between $\delta\sp2$H and $\delta\sp{18}$O in groundwater downgradient from the lake can be described by the expression $\delta\sp2$H(per mil) = 4.76$\delta\sp{18}$O(per mil) $-$ 0.41 (r$\sp2$ = 0.992). A two end-member mixing model, developed to account for the enriched isotopic composition of groundwater, indicated that the amount of lakewater leakage that mixed with infiltrating meteoric water ranged from 11 to 67%, with a limit of detection of lakewater in groundwater of 4.3%. / Groundwater downgradient of Lake Barco was anoxic, with elevated concentrations of hydrogen sulfide, ferrous iron, and methane, resulting from leakage of lakewater through reducing, organic-rich sediments at the bottom of the lake. Based on the $\delta\sp2$H and $\delta\sp{13}$C content of methane, the dominant process for methane generation was by the carbon dioxide reduction pathway. Dissolved inorganic carbon species are being produced by reactions involving microbially mediated oxidation of organic matter along with three possible terminal electron accepting processes: ferric iron reduction, sulfate reduction, and methanogenesis. Rates of carbon dioxide production, determined from computed mass transfer for microbially mediated oxidation of organic matter and ages based on CFC-12 modeled recharge dates, were consistent with rates of microbial activity in other deeper aquifer systems. / This research study has provided a framework for a better understanding of recharge processes and the importance of both abiotic (mineral dissolution and precipitation) and biotic (microbially mediated degradation of organic matter) processes in controlling the cycling of solutes in a dilute groundwater-lakewater system. These results indicate that in areas where leakage of lakewater recharges shallow aquifer systems, flow patterns can be understood using changes in the concentration of major and minor chemical species as well as stable isotopes. / Source: Dissertation Abstracts International, Volume: 55-01, Section: B, page: 0063. / Major Professor: James B. Cowart. / Thesis (Ph.D.)--The Florida State University, 1993.