P. Thy

Structure and petrology of Tauride ophiolites and mafic dike intrusions (Turkey): Implications for the Neotethyan ocean

Cretaceous Neotethyan ophiolites occur in four east-west–trending subparallel zones within the Tauride tectonic belt in southern Turkey. The ophiolites of the Inner, Intermediate, and Outer zones tectonically overlie the Mesozoic platform carbonates of the Tauride belt and are commonly underlain by a Cenomanian ophiolitic melange. These ophiolites consist mainly of tectonized mantle rocks, mafic-ultramafic cumulates, and gabbros, and commonly lack sheeted dike complexes and extrusive rocks of a complete ophiolite sequence. Metamorphic soles that are several hundred meters thick occur as thrust-faulted slices beneath these ophiolites and show well-developed metamorphic field gradients. Ophiolitic units and the metamorphic soles are intruded by mafic dike swarms that are truncated at the contact with the underlying melange unit. Dike rocks are made of subalkalic basalt to andesite typical of evolved island-arc tholeiites; they display large compositional variations, with SiO 2 content between 50 and 60 wt% and MgO between 8 and 4 wt%, and contain higher Ti augite phenocrysts and significantly less calcic plagioclase than their host cumulates. The majority of the analyzed dike rocks show a slight depletion in light rare earth elements (REE) with low La/SmN ratios and are depleted in both high-field strength (HFS) and heavy REEs, while enriched in large-ion-lithophile elements (LILE) relative to normal mid-ocean ridge basalt (MORB). These characteristics suggest a mantle source that underwent previous melt extractions and subsequent metasomatism by LILE- and light REE-enriched fluids. Geochemical modeling of trace elements shows that melting occurred at relatively low pressures under hydrous conditions and that it may have required the existence of an asthenospheric window, in which the dike magmas developed through tapping and mixing of melts generated within a rising melting column starting slightly within the garnet stability field, or in a transitional zone between the garnet and spinel stability fields at about 60 km depth. This asthenospheric window was probably created during subduction of a Neotethyan ridge system; magmas ascending from the melt column within this window generated dikes that crosscut the metamorphic soles and were injected into the overlying mantle wedge and oceanic lithosphere. The new 40 Ar/ 39 Ar hornblende dates of 92–90 Ma and 90–91 Ma from the metamorphic soles and dike swarms, respectively, show that evolution of these two geologic units was closely related in time and space and that they formed at the same intraoceanic subduction zone within the Inner Tauride seaway. These data suggest that the Tauride ophiolites within the three zones to the north originated from the same root zone situated north of the Tauride carbonate platform, and that they constitute remnants of a single ophiolitic nappe sheet derived from the Inner Tauride seaway within the Neotethyan ocean.

Experimental determination of high-temperature elemental losses from biomass slag

Abstract The loss of alkali metal elements from high-temperature molten biomass slag (wood and rice straw) can be related to the extent of polymerization of the melt. If the alkali metals occur as network-modifying and charge-balancing cations in highly depolymerized melts, such as wood slag, they are easily evaporated during prolonged heating and subsequently deposited on heat exchangers. If the melt is highly polymerized, such as rice straw slag, where the alkali metals occur as network-modifying cations, they are strongly retained in the polymerized network. These differences can be related to the availability of large-sized and low-density charged melt positions. Rice straw ash melt is dominated by a relatively open polymerized network that will easily accommodate the large Na + and K + ions. Wood ash melt is highly depolymerized and does not easily accommodate the large K + ion and only to a certain extent the Na + ion, but will accommodate the smaller and more highly charged Ca 2+ ion. Therefore, the alkali metals in wood slag melt are strongly partitioned into the vapor phase, with K preferentially lost relative to Na from the liquid phase. It is a consequence of this study that the use of straw fuels, compared to wood fuels, may significantly reduce the alkali loss from high temperature molten slag. It is tentatively estimated that about 70% of potassium in rice ash may be retained in the slag. This is in contrast to wood ash where all potassium is lost to the combustion gas with prolonged heating. However, the highly polymerized nature of rice and wheat straw melts and their low melting points render these straws less attractive as fuels for many biomass-fueled power plants.

Structure, petrology, and seafloor spreading tectonics of the Kizildag Ophiolite, Turkey

Abstract The Kizildag ophiolite in southern Turkey is a remnant of the Neo-Tethyan oceanic crust and displays well-preserved magmatic and tectonic structures of seafloor spreading origin. The ophiolite consists of two structurally distinct massifs that are separated by the NW-striking high-angle Tahtaköprü fault. The main massif to the west contains a serpentinized peridotite core adjoined on the southeast by the normal fault-bounded plutonic sequence and sheeted dyke complex in a structural graben. The dyke-gabbro boundary within this graben is in places faulted along a low-angle detachment surface and is locally marked by a transition zone with mutual intrusive relations between the dykes and isotropic gabbros and plagiogranites. This igneous boundary contains numerous proto-dyke intrusions marking a well-preserved root zone of the sheeted dyke complex and may represent the roof of a fossil magma chamber. Mineralized oceanic faults within the dyke complex form two major subsets. Dyke-parallel normal faults form horst and graben structures and locally flatten with depth acquiring a listric geometry. Dyke-perpendicular faults display steep dips and subhorizontal slickenside lineations, suggesting their oblique- to strike-slip nature. The graben structure containing the plutonic sequence and the sheeted dyke complex is analogous to those documented in the Troodos ophiolite and may similarly represent a fossil spreading axis. The second massif east of the Tahtaköprü fault consists mainly of serpentinized peridotites directly overlain by lava flows, rotated dyke blocks, and gabbros. Sulfide mineralization along some fault planes in the extrusive rocks indicates that hydrothermal systems were associated and operated synchronously with magmatic and tectonic extensional processes. Stratigraphic relations and the structural architecture in this massif suggest that the Kizildag oceanic crust underwent crustal denudation and unroofing of the upper mantle as a result of tectonic extension at a spreading centre. The Tahtaköprü fault separating the two massifs is an accommodation zone that permitted differential movements between the adjacent ridge segments during generation of the Neo-Tethyan oceanic lithosphere. The general structure of the ophiolite suggests its evolution via seafloor spreading and an asymmetric simple shear extension along a slow-spreading centre. The sheeted dykes and pillow lavas have relatively high SiO2 and Al2O3 and low FeO and TiO2 concentrations and show limited FeO and TiO2 enrichments with decreasing MgO contents. These compositional properties differ markedly from typical tholeiitic suites from the ocean floor and arc settings, but correspond closely to those documented from the sheeted dyke complex and the lower volcanic suite of the Troodos ophiolite. The major element compositions suggest low pressure and high degree of melting from a depleted mantle source. The trace element concentrations are markedly depleted in both high-field strength and rare-earth elements and relatively enriched in largeion-lithophile elements compared to normal MORB. It is inferred that the Kizildag ophiolite formed in a tectonic setting where melting occurred at relatively low pressures within the stability field of spinel and proceeded to high melt fractions possibly by progressive depletion and melt removal. A limited positive correlation between the extent of melting and light rare-earth enrichment can be related to infiltration by fluids or melts derived from a more fertile source or possibly a subducting slab fragment. Comparison of the structure and petrology of the Troodos and Kizildag ophiolites and the regional geology suggest their evolution along a seafloor spreading system within the Southern Neo-Tethys. Spreading probably occurred in short segments and resulted in development of the Cretaceous Neo-Tethyan seaway as a marginal basin between the Tauride platform in the north and Afro-Arabia in the south.

Episodic dike intrusions in the northwestern Sierra Nevada, California: Implications for multistage evolution of a Jurassic arc terrane

In the northwestern Sierra Nevada, California, volcanic and plutonic rocks of the Smartville and Slate Creek complexes, both fragments of a Jurassic arc terrane, are tectonically juxtaposed against ophiolitic and marine rocks that represent late Paleozoic-early Mesozoic oceanic basement. This oceanic basement is intruded by Early Jurassic dikes that are coeval with hypabyssal and plutonic rocks within the Smartville and Slate Creek complexes. These dikes have geochemical characteristics reflecting a depleted and metasomatized source, as commonly observed in modern fore-arc settings and incipient volcanic arcs, and are interpreted to be the conduits for the Early Jurassic arc volcanism, which was built on and across the disrupted oceanic basement. Late Jurassic sheeted dikes intruding the Smartville complex have basaltic compositions compatible with an intra-arc or back-arc origin and indicate that a spreading event occurred within the arc in early Late Jurassic time. These interpretations support models for a complex multistage evolution via episodic magmatism and deformation within a singly ensimatic Jurassic arc terrane west of the North American continent.

Mineral chemistry and crystallization sequences in kimberlite and lamproite dikes from the Sisimiut area, central West Greenland

Precambrian and Eocambrian ultramafic and ultrapotassic dike rocks from the Sisimiut (Holsteinsborg) area of West Greenland can be grouped into three main types each showing characteristic mineral parageneses. Micaceous kimberlites contain macrocrysts and phenocrysts of olivine and phlogopite set in a groundmass of olivine, phlogopite, diopside, perovskite, and spinels. Leucite lamproites contain olivine, leucite (pseudomorphed), and phlogopite macrocrysts and phenocrysts in a matrix of phlogopite, leucite, diopside, and rutile. Amphibole lamproites contain phenocrysts of diopside in a fine-grained matrix of phlogopite, diopside, sanidine, richterite, ilmenite, rutile, and quartz. Olivine in the leucite lamproites have compositions Fo93 to Fo89, while olivine in the kimberlites have compositions Fo90 to Fo80. Diopside in the kimberlites are calcic and contain relatively high Al when compared to the diopside in the lamproites. Phlogopite in the kimberlites contain relatively high Al and low ti and are deficient or low in calculated Fe3+. Phlogopite in the lamproites contain relatively high Ti and significant amounts of Fe3+. Ilmenite xenocrysts from the kimberlites are magnesian with relatively high hematite contents, whereas the groundmass ilmenites from the amphibole lamproites are manganoan ilmenites with low hematite and magnesium. The spinels range compositionally from titaniferous magnesiochromite to titanomagnetite. Amphiboles are mainly potassium-titanian richterites. Leucite is mostly pseudomorphed to K-feldspar. Other phases present in variable amounts in the groundmass of the dikes are carbonate minerals, chlorite, serpentine, apatite, amphiboles (actinolite, arfvedsonite, and a riebeckite-like phase), priderite, sulphides, and zircon. Mg-ilmenites and pyrope garnets are considered xenocrystic while most olivine, phlogopite, and leucite macrocrysts are believed to be cognate. The primary kimberlite and lamproite magmas originated in the mantle and were emplaced at a low level in the upper crust where they consolidated at contrasting levels of T, ϱH2O, ϱCO2, ƒO2, aAl2O3, and aSiO2. The kimberlites crystallized olivine, phlogopite, spinels, and perovskite as early phases. The two lamproite types are related to different levels of volatile pressure. A low ϱH2O type crystallized leucite, phlogopite, and olivine at a pressure below 0.5 kbar and liquidus temperatures ranging from 1260° to 900°C. A relatively high ϱH2O type crystallized diopside, phlogopite, richterite, rutile, and ilmenite at a pressure above 1 kbar and liquidus temperatures most likely from 1150° to 950°C. The crystallization of perovskite and Al-rich phlogopite points to a relatively low aSiO2 in the kimberlite magmas. Higher aSiO2 appears to have prevailed in the leucite lamproites, constrained by the leucite-orthoclase and perovskite-rutile silica buffers. The sanidine-bearing amphibole lamproites record a relatively high aSiO2 with zircon and quartz crystallization in the groundmass. The oxygen fugacities in the kimberlites are suggested, from the appearance of olivine and magnetite in the groundmass, to have been controlled by a FMQ oxygen buffer. The compositions of the richterites, ilmenites, and rutiles in the lamproites point to a relatively low Fe3+ and ƒO2 in the melts.

Liquidus temperatures of the Skaergaard magma

Abstract The liquidus temperatures of the Skaergaard intrusion can be estimated for the layered series from plagioclase compositions. Plagioclase saturation in one-atmosphere melting experiments on evolved North Atlantic basalts is a function of An content (mol%) and can be described by an empirical linear relationship [T (°C) = 899 + 3.6 An; 1σ = 20 °C]. This relationship predicts a total crystallization interval for the intrusion of ~150 °C. Plagioclase crystallized in the Hidden Zone (An71) at 1155 °C, at the base of the Lower Zone (An66) at 1137 °C, and finally in the Sandwich Horizon (An30) at 1007 °C. These temperatures are in good agreement with previous estimates based on melting studies of suitable chilled margin rocks and gabbros from the Skaergaard intrusion and liquid line of descent modeling. Our temperature estimates, however, are markedly lower (by up to 60 °C) than recent temperature estimates based on an extrapolation of high-pressure experimental data for the Kiglapait intrusion to Skaergaard emplacement conditions. Proposed variations in magmatic pressure during Skaergaard evolution and reasonable estimates of magmatic water contents do not alter these conclusions.

Seafloor spreading and the ophiolitic sequences of the Troodos Complex: A principal component analysis of lava and dike compositions

The Troodos complex of Cyprus has been interpreted as a slice of oceanic crust formed from ultramafic magma in a back-arc basin. Recent investigations, however, have suggested that only the upper gabbros, the sheeted dike complex, and the lower lava sequence formed as a direct consequence of seafloor spreading and that the primary magma was of basaltic composition. According to this model, the upper lava suite and related ultramafic cumulates are not represented in the sheeted dike complex. A multivariate statistical analysis of major element compositions of 480 dikes and 130 volcanic glasses supports this suggestion. Statistically (98%), the dikes are similar to the glasses of the lower lava suite. This supports the model that the seafloor spreading related sequence of the Troodos ophiolite is relatively thin and of basaltic composition. The magma chambers represented by the ultramafic cumulates and associated gabbros and the upper lavas appear to have been emplaced after, or during, the termination of the major spreading events.

Experimental constraints on the evolution of transitional and mildly alkalic basalts: crystallization of spinel

Abstract Melting experiments on a mildly alkalic basaltic rock show that the spinel field penetrates slightly into the transitional volume of the natural basalt phase diagram at one-atmosphere pressure and the fayalite-magnetite-quartz oxygen buffer. The examined sample contains 22.5 wt.% Al2O3 and crystallized spinel as the liquidus phase at 1290 ±11 °C, followed by plagioclase at 1261 ± 10 °C, olivine at 1175 ± 5 °C, and magnetite at 1145 ± 5 °C. The amount of crystallizing spinel is about 4 wt.% and relatively constant throughout the melting interval. Compositionally, the spinel is dominatly pleonaste with minor components of magnetite and ulvospinel in the solid solution, and shows a marked rise in Ti, Fe2+ and Fe3+ with falling temperature, reflecting the coexisting liquid. The distribution of Fe2+ and Mg between olivine and liquid defines a KDFe-Mg (ol/liq) of 0.30 ± 0.02. Similarly calculated distribution of Fe2+ and Mg between spinel and liquid, gives KDFe-Mg (p/liq) of 0.52 ± 0.03. In pseudoternary projections of the basalt system, the liquids reach pseudounivariant spinel, plagioclase, and olivine crystallization near the thermal divide, with about 64% liquid remaining and slightly hypersthene normative compositions. The position of the spinel saturated cotectic confirms that low pressure spinel crystallization is unlikely in most oceanic basalts. A survey of high pressure mantle assemblage equilibria shows that oceanic mildly alkalic and transitional basaltic glasses plot significantly away from the low variance multiply saturated cotectics representing likely mantle melting. Therefore, these types of oceanic basalts must reflect extensive olivine and plagioclase fractionation, subsequently to separation from their mantle sources and prior to augite saturation at relatively low pressures.

Salt separation and purification concepts in integrated farm drainage management systems

Agriculture on the west side of the San Joaquin Valley of California, like many irrigated arid land agricultures, suffers from increasing soil salinity and water logging and faces large scale land retirement in the near future if salts and subsurface drainage cannot be removed. Following discovery of avian deformities and mortalities at Kesterson reservoir due to high selenium levels, closure of drains originally intended to convey subsurface drainage out of the Valley left farmers with few alternatives. Integrated farm drainage management (IFDM) systems employing sequential water reuse have emerged in recent years as potential phytoremediation techniques to improve salinity management. Development of acceptable final salt removal approaches is critical to the overall success of such systems. Solubility characteristics of sodium sulfate offer the potential to recover purified sulfate for commercial markets. Salt separation and purification using solar concentration and ambient cooling processes are currently being analyzed and tested. Sodium sulfate recoveries depend on the composition of the drainage feed to the concentrator along with local meteorological conditions and may range from as low as 28% to more than 85% of total salt.